2011-12-01-KCVH-SC Mtn and Gabilan Wave-1CH - Matt Gillis–Low Level NE Jet High Wind Event

Photos: 2011-12-01-KCVH-SC Mtn and Gabilan Wave-1CH - Matt Gillis - Picasa Web Albums
To: <hgcgroup@yahoogroups.com>
From: "Matt Gillis" <mattman@ix.netcom.com>
Subject: RE: [hgcgroup] Re: Serious winds -- low level jet
With regards to primary, secondary wave etc., with this event and looking at the forecast wave being propagated off the sierra crest (‘backward Sierra Wave’), the period was likely initiated well upwind of the SC mtns with the SC Mtns simply augmenting the wave.  This couple with high winds tended to produce a long period wave.  This might be a case of appropriate model scale estimates, on the influence of larger versus smaller scale.  Usually it is lack of resolution at microscale that creates uncertainty.  I wonder if this is a case of the RASP not taking into account the breadth of the event on influencing local triggers.
-Matt
From: hgcgroup@yahoogroups.com [mailto:hgcgroup@yahoogroups.com] On Behalf Of Matt Gillis
Sent: Friday, December 02, 2011 3:26 PM
To: hgcgroup@yahoogroups.com
Subject: RE: [hgcgroup] Re: Serious winds
The wave was much further downwind than ‘normal’, probably due to the long period from the higher winds, particularly at low level.  I was using the RASP VV and referenced them for initially finding the wave.  The lee of the SC Mtns was indicating the best entry spot between Aptos and Loma Prieta.  Nada, the RASP was not accurate in the wave position and possibly period there, other areas such as the Salinas Valley later were further downwind also.  The period in the RASP was showing about 10 nm when it appear to me that it was probably more like ~15 nm. Because of very strong conditions, I considered this comparable to towsurfing into big waves but not being able to see where the wave is.  Subsequently, [which is the source of Quests comment] I stayed on tow to search it out when it wasn’t where advertised.  My intuition said it was downwind, but my standard approach is to exhaust upwind advantages first.  When that proved unfruitful we went downwind and found it right, ironically, over First Peak" at Pleasure Point.  I was being somewhat convservative, since we were otherwise committed to Watsonville.  This was further augmented by the fact that it was a “two hands on the stick” tow down lower, the sink and strong winds down in the mix could leave little margin if in the wrong spot…or major pucker for a sucker.    Nevertheless, when I found it, it was good, elevator to 17.9K.  The line was close to the coast near Santa Cruz but went out over the ocean.  ER tried to push up and find a bar closer to the crest of the SC Mtns, but found sink.  When I turned near Pescadero, I was going to try and push upwind and find an upwind bar, but progress was so slow and with Class B in front, decided to explore the options south.   Soaring in conditions this strong made even slight errors costly time wise to get back into position.  That is to say, the wave can giveth and taketh away not just quickly, but can put one in a stationary hard spot with limited options, until it giveth again.  Although the sweet spots were 6-8 knots at best glider, this usually meant going backwards at a noticeable clip.  Needless to say, it took 2.5 hours out of the afternoon exploring the SC Mtn Wave, which didn’t leave much daylight left for exploration south.   I had downloaded the RASP VVs onto my Droid to compare relative position of the wave and used this to compare target spots.    ER and us in 1CH headed south toward Salinas, ER following a track further east.  Right over Salinas there was really good bounce and a nice bar running down the valley.   Above 17K I was able to covert lift to speed and fly at 90-100 knots in a more productive manner.  I turned near Soledad since we needed to get back before dark.  We topped out at 17.9K near Salinas and burned off 13K getting back to just north of the airport at 5K; I maintained a notch above the required glide of about 6:1 with emphasis on speed.  Had a nice smooth x-wind landing in spite of the wind shear.
From that position, it would have been easy to have tested the forecast Arroyo Seco bounce and if that was happening, the Big Sur bounce would have been easily reached.  The Big Sur/Santa Lucia Range had the hottest forecast VV of all and it was even marked by a ’haze bar.   Strategy would have been to push quartering downwind (perp. thru strong sink) from 17.9 and then dogleg if it was elusive, using San Simeon as an alternate.   Launching earlier with electric socks and some hot tea would have made it doable and bearable.  And yes, with the winds yesterday I probably would have been having dinner in SLO with Morgan    Although Carmel Valley or Arroyo Seco may have had a short enough frequency bounce to get back upwind into the Gabilan Wave.
Got a few pics of ER that are˜keepers I will post later.  Flight trace is now on OLC.
-Matt
From: hgcgroup@yahoogroups.com [mailto:hgcgroup@yahoogroups.com] On Behalf Of Ramy Yanetz
Sent: Friday, December 02, 2011 2:16 PM
To: hgcgroup@yahoogroups.com
Subject: Re: [hgcgroup] Re: Serious winds
Eric, you saying the wave was mostly in the familiar places, but your traces showing way further downwind than usual. Was it hard to get in? I am curious if you were flying the secondary or was it the primary? reason I am curious about it is that today I could not find wave in the usual spot downwind of Mt Diablo although it was blowing 37 knots, and I suspect the wave was much further downwind in class bravo, so couldn't confirm it. A double blow for me so far. One more chance tomorrow but not sure where to look for the wave. Glider is setup and ready at Byron.
Ramy

From: Eric Rupp <ericrupp@got.net>
To: hgcgroup@yahoogroups.com
Sent: Thursday, December 1, 2011 11:09 PM
Subject: [hgcgroup] Re: Serious winds
Sorry to make it hard to work today...
Very cool sight seeing with wave mostly in the familiar places. Got further northwest than before (up to 6nm off shore) and south to Salinas. Matt went down the Salinas Valley and found strong wave lift - next time. Harry flew with friend Jeremy and they tried to stay low to stay warmer. My feet were blocks of ice after a few hours. Electric socks?
Getting back from Salinas from near 18,000 feet wasn't a gimme with head winds (up to 100 knots earlier). After getting shot down on my first attempt I retreated downwind, climbed over Salinas, then flew north to avoid charging directly into the wind. Still lost 11k' in 14 nm as I approached Hollister! Exciting landing with 20/G28 knots out of the north.
All in a days work
Eric
--- In hgcgroup@yahoogroups.com, Ramy Yanetz <ryanetz@...> wrote:
>
> Spot shows Matt and Eric way out over the ocean between Santa Cruz and Half Moon Bay. Another first from Hollister.
> Wish I joined them...
> Â
> Ramy
>
> From: Quest <questiam@...>
> >To: "hgcgroup@yahoogroups.com" <hgcgroup@yahoogroups.com>
> >Sent: Thursday, December 1, 2011 9:32 AM
> >Subject: Re: [hgcgroup] Re: Serious winds
> >
> >
> > 
> >Hi everybody,
> >
> >
> >For those who hadn't seen my post on Monday regarding tows today, this is just a confirmation of Harry's posting that HSC will in fact be providing tows all day Thursday, and then of course on Friday as well.
> >
> >
> >
> >Happy wave flying,
> >Quest
> >
> >
> >
> >From: Harry Fox <harryfox@...>
> >To: hgcgroup@yahoogroups.com
> >Sent: Thursday, December 1, 2011 8:56 AM
> >Subject: RE: [hgcgroup] Re: Serious winds
> >
> >
> > 
> >There are tows available at Hollister this morning, starting around 10AM.  Matt is flying with Haven, I'm coming over with a friend around 10:30.
> >Â
> >From:hgcgroup@yahoogroups.com [mailto:hgcgroup@yahoogroups.com] On Behalf Of Eric Rupp
> >Sent: Thursday, December 01, 2011 8:16 AM
> >To: hgcgroup@yahoogroups.com
> >Subject: [hgcgroup] Re: Serious winds
> >
> > 
> >Giving the wave a try seems like a reasonable proposition - starting around the Aromas quarry or Watsonville. Winds are relatively calm at Hollister and Salinas (<10 knots, but it's blowing like stink at my house at 500' in Santa Cruz).
> >
> >What time can we tow?
> >
> >Eric
> >
> >--- In hgcgroup@yahoogroups.com, "cah1ch" <charlie@> wrote:
> >>
> >>
> >>
> >> Any thoughts about penetrating upwind to the (reverse) Sierra wave over the foothills. Take a look at the Byron RASP and the VV 850,700,500 for 1000 and 1300. It looks like jumps along the harmonics are possible from the Pacheco Pass area. I'm in the Phoenix area but wish I was there!
> >>
> >> Charlie
> >>
> >> --- In hgcgroup@yahoogroups.com, Morgan Hall <morhall@> wrote:
> >> >
> >> > Noticed a weather station with barbs and flags I'd never seen before.
> >> > Gusts to nearly 100mph tonight.
> >> >
> >> > Mt Umunhum, San Jose, CA
> >> > http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCASANJO78&day=30&year=2011&month=11&graphspan=day
> >> >
> >>

To: <hgcgroup@yahoogroups.com>
From: "Matt Gillis" <mattman@ix.netcom.com>
Subject: RE: [hgcgroup] North wind wave on Thursday-sounding for SC Mtns--looking good
Quest,
It looks like Thursday will be better than Wednesday with a more easterly component.   It could be a very good offshore wave day.  Maybe Buzz and Ramy will come out and run the Santa Lucia’s south, top out over Santa Barbara and final glide to Catalina [a little weaker further south closer to the low, but velocities still look good with the jet shift in that direction]? I imagine they take glider trailers on the ferry. 
Sounding is for Thursday in the lee of SC Mtns.  The GFS 700 mb charts below show the streak coming through the Bay Area and decreasing toward sunset.  As Doug commented out of Reno, the jet appears to be moving fast.   Sounding shows ~10-15 knot decrease in wind speed by 0z.  Max winds about 80 knots at 18K dropping to ~70 knots at 0z.   Definitely strong, winds ramp quick so penetration could be an issue even down low; but, the conditions look pretty good for systemic wave along the coastal ranges.  Worth a higher tow to get into a sweet spot.  When the RASP 3.0 km comes out later it may light up even better than Wednesday.
Since Quest is going to be there anyway, I gotta try.  Anybody else game?
-Matt
To: <hgcgroup@yahoogroups.com>
From: "Matt Gillis" <mattman@ix.netcom.com>
Subject: RE: [hgcgroup] North wind wave on Thursday-sounding for Aromas Quarry
Thanks once again to Kurt Thames for his fine Google map FSL sounding popper upper.
Snapping a sounding for Aromas Quarry we have 24 knots with BL top/inversion just above ridgetop. Strong surface inversion early.  Although the wind profile steadies at ~70 knots from 10-18K there is good progression to that.  We have seen good conditions with less favorable profiles.  Slight burble in the profile during mid-day but then it looks like it smooth gradient toward sunset.  Need to check soundings for spots in other good trigger zones on the local ranges.  The high res RASP, when it comes out, resolves wave position well.  Because of the position of the low/jet, looks like conditions will be best from ~Hollister north to…. The North Bay; but, that could change with this  ‘spinning top’ in the mix.
If Quest is towing, I’ll probably check it

image0018.png


image0024.png
out.
-Matt
To: hgcgroup@yahoogroups.com
From: "Matt Gillis" <mattman@ix.netcom.com>
Subject: RE: [hgcgroup] North wind wave on Thursday
Yes, it has improved in the 850 mb from yesterday.  The jet wrapping around the high and spinning the inside slider is better lined up, broader, and more sustained with the low not progressing east as quickly, in fact retrograding.  Wednesday is looking good too but with a more northerly component.    Seasonable timing.  Have to tune into the soundings, but ~35 knots at 5K is a good clue. 
http://wxweb.meteostar.com/models/ipsm_looper.php?PROD 11112812_WST_GFS_850_HGT_WINDS   The dynamics are pretty cool the way the low spins around the high from the ~meridional jet; very dynamic, like the jet is spinning a top.
-Matt
From: hgcgroup@yahoogroups.com [mailto:hgcgroup@yahoogroups.com] On Behalf Of Harry Fox
Sent: Monday, November 28, 2011 1:54 PM
To: hgcgroup@yahoogroups.com
Subject: [hgcgroup] North wind wave on Thursday
Looks like strong northeast winds on Thursday -- should set up good wave.
-- Harry

December 1, 2011 Northeast Wind Wave

Serious winds -- low level jet


With regards to primary, secondary wave etc., with this event and looking at the forecast wave being propagated off the sierra crest (‘backward Sierra Wave’), the period was likely initiated well upwind of the SC mtns with the SC Mtns simply augmenting the wave. This couple with high winds tended to produce a long period wave. This might be a case of appropriate model scale estimates, on the influence of larger versus smaller scale. Usually it is lack of resolution at microscale that creates uncertainty. I wonder if this is a case of the RASP not taking into account the breadth of the event on influencing local triggers.



-Matt



From: hgcgroup@yahoogroups.com [mailto:hgcgroup@yahoogroups.com] On Behalf Of Matt Gillis

Sent: Friday, December 02, 2011 3:26 PM

To: hgcgroup@yahoogroups.com

Subject: RE: [hgcgroup] Re: Serious winds

The wave was much further downwind than ‘normal’, probably due to the long period from the higher winds, particularly at low level. I was using the RASP VV and referenced them for initially finding the wave. The lee of the SC Mtns was indicating the best entry spot between Aptos and Loma Prieta. Nada, the RASP was not accurate in the wave position and possibly period there, other areas such as the Salinas Valley later were further downwind also. The period in the RASP was showing about 10 nm when it appear to me that it was probably more like ~15 nm. Because of very strong conditions, I considered this comparable to towsurfing into big waves but not being able to see where the wave is. Subsequently, [which is the source of Quests comment] I stayed on tow to search it out when it wasn’t where advertised. My intuition said it was downwind, but my standard approach is to exhaust upwind advantages first. When that proved unfruitful we went downwind and found it right, ironically, over First Peak" at Pleasure Point. I was being somewhat convservative, since we were otherwise committed to Watsonville. This was further augmented by the fact that it was a “two hands on the stick” tow down lower, the sink and strong winds down in the mix could leave little margin if in the wrong spot…or major pucker for a sucker. Nevertheless, when I found it, it was good, elevator to 17.9K. The line was close to the coast near Santa Cruz but went out over the ocean. ER tried to push up and find a bar closer to the crest of the SC Mtns, but found sink. When I turned near Pescadero, I was going to try and push upwind and find an upwind bar, but progress was so slow and with Class B in front, decided to explore the options south. Soaring in conditions this strong made even slight errors costly time wise to get back into position. That is to say, the wave can giveth and taketh away not just quickly, but can put one in a stationary hard spot with limited options, until it giveth again. Although the sweet spots were 6-8 knots at best glide, this usually meant going backwards at a noticeable clip. Needless to say, it took 2.5 hours out of the afternoon exploring the SC Mtn Wave, which didn’t leave much daylight left for exploration south. I had downloaded the RASP VVs onto my Droid to compare relative position of the wave and used this to compare target spots. ER and us in 1CH headed south toward Salinas, ER following a track further east. Right ov

er Salinas there was really good bounce and a nice bar running down the valley. Above 17K I was able to covert lift to speed and fly at 90-100 knots in a more productive manner. I turned near Soledad since we needed to get back before dark. We topped out at 17.9K near Salinas and burned off 13K getting back to just north of the airport at 5K; I maintained a notch above the required glide of about 6:1 with emphasis on speed. Had a nice smooth x-wind landing in spite of the wind shear.



From that position, it would have been easy to have tested the forecast Arroyo Seco bounce and if that was happening, the Big Sur bounce would have been easily reached. The Big Sur/Santa Lucia Range had the hottest forecast VV of all and it was even marked by a ’haze bar. Strategy would have been to push quartering downwind (perp. thru strong sink) from 17.9 and then dogleg if it was elusive, using San Simeon as an alternate. Launching earlier with electric socks and some hot tea would have made it doable and bearable. And yes, with the winds yesterday I probably would have been having dinner in SLO with Morgan Although Carmel Valley or Arroyo Seco may have had a short enough frequency bounce to get back upwind into the Gabilan Wave.



https://picasaweb.google.com/111461517128275850244/20111201KCVHSCMtnAndGabilanWave1CH?authuser=0&feat=directlink

December 2011-Exceptional Season of Ice Skating in the Sierras

The month of December resulted in no significant precipitation to cover the ice that had been formed. Conditions remained cold with polar air streaming around the stationary ridge that was blocking the storm systems. The high pressure was promoting subsidence inversions that was capping the cold air in the valleys. Some low lying areas were much colder than higher elevations. Temperatures dropped into the single digits and even subzero temperatures the week before the winter solstice. Without any snow, ice skating became prevalent in the Lake Tahoe area and all along the Eastern Sierras. With it this good, it even made the main stream news.

Bridgeport Reservoir December 10th

Virginia Lake December 10th (old but clean sections-good for the Alpenglow)

Tioga Lake December 11th (next 4 pics) - old thick but glassy between crack lines

Prosser Reservoir

Temperatures in the basin around Truckee were getting into the single digits and this provided solid 6-8" ice on Prosser Reservoir. Most of the lake was frozen with the west arm having the most consistent smooth ice and easy access. Several other lakes and ponds in the Tahoe area had excellent ice skating conditions.

More Pictures December 23rd:
https://picasaweb.google.com/111461517128275850244/20111223IceSkateProsserReservoir?authuser=0&feat=directlink

Conditions at Tenaya Lake

This a beautiful lake in Yosemite accessible by Highway 120.  This is quintessential treat for anyone that loves skating on natural ice.  Tenaya was marginal in early December, but consistent drops into the teens thickened the ice.  This inspired skaters from all over to come enjoy it.

..Gotta do another road trip
Some videos on YouTube inspired me to head back up, since being able to drive to Tenaya and have good ice this time of year are both rare.   It looked like the night/morning of 12/27-28 was going to be the last of the cold period AND it was holiday season.  Gotta try.....
We got to Tenaya and skated at sunrise (of course the ~East/West orientation keeps the lake in shade for quite a while this time of year-which is good).   The ice was a foot thick with the thinnest spots in isolated areas around 4-5" thick and only a few melt spots near the outlet and a spot in the middle that was sheeted but thin.  The ~north side of the lake had the ice buckled up onto the shore form expansion; the expansion actually having moved boulders.  The south side which appeared to remain in the shade, was clear black ice.  Although cracked, there were stretches of very glassy smooth ice that provided incredible glides with a view of the lake bottom.  Being able to see through ice while skating is a treat.  It feels as though I'm simultaneously observing a transcendence of dimensions and physical phases while in motion. 
We arrived and skated in solitude for a couple hours.  Soon skates and travellers showed up.  By the time we left around 1:30pm, there were well over a hundred people enjoying the ice.  Temperatures in warm spots were close to 60°F and people began sunbathing.  The ice surface began to form a skim layer that was getting close to the high spots by the time we left.  The south side in the shade remained good quality with no apparent melt.  If no snow falls over the next couple weeks, the melted skim layer could form a natural Zamboni effect.  With the slab of ice that is already there, clear nights with lows in the low 20s or teens should keep the ice in good shape, with the skim layer even improving the surface. 

Temperature trend shows warming on the afternoon of the 28th which formed skim layer:

Tenaya Lake Morning of December 28th

 

It was so good I went back twice......

Worth the Choreography.....

It is mid-January and still no snow.  Temps have been cold enough that morning skates are probably still good although ice is getting old and blemished with surface aberations even with some skim layers forming.

Link to more pictures: https://picasaweb.google.com/111461517128275850244/20111228TenayaLakeIceSkate?authuser=0&feat=directlink


Below is a link to a video someone posted online in mid-December.  Made me want to head back up for one more skate.

Synoptic Weather Pattern in Early December Setting up a persistent pattern

Recent strong NE winds may have blown the small amount of snow off any previous ice if the snow did not fall wet or cause snow ice. The following plot is from the CDEC Water resources site: http://cdec.water.ca.gov/cgi-progs/queryF?TNY

http://www.youtube.com/watch?v=b7XSFh5rYhI&feature=player_embedded

http://cdec.water.ca.gov/cgi-progs/queryF?VRG

Sources of Temperature Data for Estimating Ice Formation

Other locations for California can be found here: http://cdec.water.ca.gov/cgi-progs/mapper

These data go back some time so that that trends over the entire fall can be looked at.

Another good source of surface data to see temperature trends is the Mesowest site which provides data and plots of temperature for the past 7 days for various regions:

http://www.wrh.noaa.gov/mesowest/

Temperatures provided by surface stations are representative and can actually vary significantly from microscale conditions at the water body(s) of interest. Overall trends with regional weather stations should be considered along with observations. It is obviously easiest to watch the ice form and make physical measurements of thickness along with observing temperatures; however, this is often not practical. With remote sensing data available on the internet, the likelihood of ice formation can determined adequately enough to pursue further investigation.

Early December 2011 Temperature Forecasts

Forecast for the week is single digits and teens for lows in the Eastern Sierra cold air basins. Some inversions indicated at upper levels moderating temperatures, but generally colder higher up. Daytime highs in the 30s and 40s. A week worth of single digit lows and only 8 hours of daylight for ramping

Ice Skating on Natural Ice in California

With changes in temperature and weather patterns bring changes in recreational opportunities. Every late fall on the approaching winter solstice there is the potential for good natural ice for ice skating.  The winter solstice with low sun angles and long nights often brings cold temperatures to high elevations. This can be augmented with favorable weather conditions. When snow does not prevail for snow sports, ice can be great if a persistent polar jet sets up with only early fall snows to chill down the water.

Skating Bridgeport Lake

Ice Safety

 Testing the ice is curucial for safety.  A drill is usful for verifying thickness.  In good water ice, cracks can give an estimate of thickness from the thickness of the shearplane.  Also, small bubbles can indicate depth.  Over 3" of good water ice is adequate for supporting a skater; 5-6" provides good margins.  A portable electric drill with a 1/2-3/4" diam. 6" long bit works well for determining thickness (keep battery from cold soaking prior to use). 

The Kiwis have been making good use of ice on the South Island of New Zealand have an excellent site with good eneral information (I'm going to have to go skate there sometime; the east side is much like the Eastern Sierra).  http://iceblock.org.nz/safety/

Here are additional sites with useful information on ice formation and safety:

http://www.blueiceonline.com/howsite/lakeice_about.html
http://lakeice.squarespace.com/thickness/
http://www2.gi.alaska.edu/alison/ALISON_SCIENCE_BConcepts.html

It is important to recognize ice variabiilty inherent with water bodies.based upon subsuface flow, artesians, springs, inlets/outlets. Surveying ice from aircraft can help identifying good ice areas.

Weather and Ice

 The weather is of course crucial for not just forming thick enough ice but also the quality.  Late November 2011 has provided a string of dry cold days due to a stationary high pressure and a low to the south with the polar jet providing the chilldown.  The condition is somewhat characteristic of a Rex Block which is the reverse "S" pattern of the high pressure which prevents eastward migration of the high pressure from the the complimentary cyclonic and anti-cyclonic flow around the low and high.  A key is a persistent high pressure over the west coast blocking storm systems with the anti-cyclonic cold northerly flow around the high providing the low temperatures needed.  These persistent cold dry condition can be favorable for good ice formation.  Monitoring the weather conditions can help identify periods favorable to ice formation.

Weather is particularily important in the Sierras for determining good safe ice due to the relatively mild conditions that can prevail in fall.  It is the trends and duration of cold that provide good sheeting.  Although ice can thicken into January and February at higher elevations where freezing condiotns are more persistent, the best quality ice often occurs early season before much snow has fallen and ruined surface conditions.  The short days of late fall provide the advantage of duration or cold nights and low sun angles to provide net freezing. 

The following graph illustrates typical trends ice sheet formation thickness versus time for various temperatures:

December 2011-Exceptional Season of Ice Skating in the Sierras

The month of December resulted in no significant precipitation to cover the ice that had been formed.  Conditions remained cold with polar air streaming around the stationary ridge that was blocking the storm systems.   The high pressure was promoting subsidence inversions that was capping the cold air in the valleys.  Some low lying areas were much colder than higher elevations.  Temperatures dropped into the single digits and even subzero temperatures the week before the winter solstice.   Without any snow, ice skating became prevalent in the Lake Tahoe area and all along the Eastern Sierras.  With it this good, it even made the main stream news.

Bridgeport Reservoir

 Virginia Lake

 Tioga Lake

Ice Skating on Natural Ice in California: Development of an Index for Remotely Estimating Probable Ice Formation

Availability of real-time weather data has revolutionized the ability to monitor remote locations for conditions suitable for ice formation. Since ice formation requires sustained cold temperatures one can surmise that if one were to quantify the amount of freezing versus thawing, one could come up with a reasonable estimate of forecasting ice. There are other variables that go into good quality skating ice, but paramount is temperature trends.  This is particurily helpful if one does not reside near the water bodies in question.

The short days and long nights in late fall provide a skewing of cooling/freezing hours. When temperatures fall below freezing at sunset and stay freezing after sunrise for several days during late fall-winter solstice times, ice formation becomes more favorable. Since temperature can spike during the day, temperatures typically need to fall well below freezing to insure adequate cooling to overcome heat flux form absorbed solar heat and latent heat exchange.  Otherwise, thawing occurs.  Optimum conditions often occur on new water ice that sheets clean rapidly in very cold calm conditions. Rapid cooling can produce ice with fewer air bubbles making the ice clear and transparent. Once ice has formed, latent heat of fusion works to the advantage of maintaining state through short warming periods allowing water ice to form in subsequent cold snaps; however, it is the new ice that is often the best and also the thinnest.  Ice for ice skating is often good early season before snow has had a chance to cover the ice and ruin the ice. Ice that has under gone excessive freeze-thaw, strong winds or accumulated debris can ruin the quality also.    Old ice tends to crack and form ridges which ruins quality. Early season/late fall ice is often best; often this ice is on the thin side which requires careful monitoring of conditions during formation.

Ice Formation Index

For lack of a better term, I am using this term to describe the integrated temperature conditions over time that favor ice formation for ice skating. The index utilizes the a concept of integrated temperature accumulation above or below a reference value to indicate an accumulative effect.   Although one could use an average, that can be misleading, since spiked low minimum temperatures can skew the average. In this case, temperature is often logged in hourly increments by various weather reporting stations such as the CDEC and Mesowest. These data can the summed (integrated) for periods above and below freezing [#hours X temperature for <=32F and >32F] and then the ratio [ratio of degree-hours below freezing to that above freezing = FDH/HDH]  or the net freezing [FDH-HDH] provides a quantitative way to compare observations with ice formation.  The Index Ratio should be >1 or thawing is likely, degrading the ice and making the ice structure unsafe.   Ratios of  >5 indicated skatable or thick ice this season.  The Net Freezing Degree Hours were 1400-2000 for 7 days for observed skatable lakes.  Below is an example of processing a weeks worth of data from near Bridgeport, California.  Data was copied into a spreadsheet and the values computed: This resulted in 3-4" of ice on Bridgeport Reservoir.  Observation of the temperature plot shows the long duration of cold temperatures with only short spikes above 32°F.  A week of single digit lows around early December (after water has chilled during November) is an indication ice is potentially thick enough to skate on. The following chart is an estimation gleaned from one the websites below and is a representation of ice formation trends.  It shows an inital rapid phase and then a slowing of thickening. The graph is somewhat idealized since actual temperatures and diurnal/nocturnal heat flux could add significant variabilty from mean daily temperatures.    Nevertheless, five days of net freezing shows sheet ice thick enough to skate.   This is consistent with several years of observations in the Sierras.  http://lakeice.squarespace.com/thickness/ An example of Index where the ratio was <1 is for Silver Lake near Kit Carson Pass.  The ratio 0.48 and there was a negative Net Freezing Degree Hours.   Observations on the evening of 12/8 indicated that ice was marginal <2" and melted at the edges.   The water had been chilled by early snowfall but was being warmed by warm air subsidence inversions on the west slopes of Sierras during preceeding days limiting nocturnal cooling. Prosser Reservoir Near Truckee The following temperature plot from CDEC data (Martis Creek Res.) is near Prosser Reservoir and shows the temperature dipping in early December 2011.  The lake was skatable by 12/10 with marginal thicknesses (reported).   There werew 5 nights of teens and single digits. Another 10 days resulted in thicknesses of 6-8" around the solstice.  During that time there was light snowfall on one occasion with minor effect on the ice quality.  When there is any question of thickness, the ice should be measured in several representative locations. Ideally, ice thickness can be measure with an auger or spike. It should at least estimated for a given location. Cracks or bubbles in clear ice can give and indication of thickness by simple visual parallax. Nevertheless, water does not freeze if the temperature is not cold enough. So this approach is a way to 'quantify the cold'. The data becomes a tool in predicting when good ice skating conditions can be had. There are many other variables which influence ice formation on a water body/feature, such as, size, depth, flows/currents, springs, topography and weather are important for specific locations. All of this should be taken into account. Air temperature is one of the most useful parameters readily available as an indication of the likelihood of ice formation. Additional data such as solar radiation, wind and snow-pack are also useful indicators for understanding the melt freeze cycle and probable characteristics of any ice present, particularly the presence of water ice or snow ice. Occasionally, when ice freezes before snow falls, the ice can still be skatable. If the conditions remain cold and the snow does not bond with the ice, up to 2 inches can still allow for adequate glide over the ice. Since the ice is obscured, it is even more imperative the thickness should be verified. Often early fall snow falls can form snow ice which will result in a lot of air bubbles in the ice which can make the ice weaker requiring extra thickness to account for that weakness. The most significant quality issue with snow ice is that is often creates a rougher surface even if the surface remelts. Ironically, early fall snows followed by a slight warming trend to melt any snow ice will chill the water and make it more conducive to freezing during a cold snap in late fall. Sources of Temperature Data for Estimating Ice Formation Other locations for California can be found here: http://cdec.water.ca.gov/cgi-progs/mapper These data go back some time so that that trends over the entire fall can be looked at. Another good source of surface data to see temperature trends is the Mesowest site which provides data and plots of temperature for the past 7 days for various regions: http://www.wrh.noaa.gov/mesowest/ Temperatures provided by surface stations are representative and can actually vary significantly from microscale conditions at the water body(s) of interest. Overall trends with regional weather stations should be considered along with observations. It is obviously easiest to watch the ice form and make physical measurements of thickness along with observing temperatures; however, this is often not practical. With remote sensing data available on the internet, the likelyhood of ice formation can deterimined adequately enough to pursue further investigation. Early December 2011 Temperature Forecasts Forecast for the week is single digits and teens for lows in the Eastern Sierra cold air basins. Some inversions indicated at upper levels moderating temperatures, but generally colder higher up. Daytime highs in the 30s and 40s. A week worth of single digit lows and only 8 hours of daylight for ramping with maxes in the 40s usually means a net gain in thickness. The slight warming in the day can help glaze the ice, a natural zamboni effect. Links: http://www.blueiceonline.com/howsite/lakeice_about.html http://lakeice.squarespace.com/thickness/ http://www2.gi.alaska.edu/alison/ALISON_SCIENCE_BConcepts.html