Winter 2010-11 for the Southern Plains

[SouthernMet]

The 12z ECMWF looks interesting. If it is correct, then Oklahoma City would receive freezing rain turning to sleet next Thursday/Friday followed by snow on Saturday.

Model Output + Climatology = Possible Winter Weather or Ice Storm. Stay tuned..

[TwisterFanatic]

GFS showing a nice little path of snow across much of Oklahoma 108-120 hour timeframe.

[Extremeweatherguy]

A look at today's 12z model runs concerning the winter weather potential later this week...

GFS
The GFS, while becoming more aggressive with each run, is still only showing a minor event as of this afternoon. In Oklahoma City it shows light rain Thursday morning changing to a very brief wintry mix (frz rain/sleet) and then ultimately becoming light snow. The total QPF for OKC is only 0.13" during the entire event, which means there would only be very light accumulations if this scenario actually played out. The GFS does show slightly higher snow totals across northern Oklahoma though, with Twisterdata.com maps indicating a large swath of 1-4" totals.

http://www.meteo.psu.edu/~gadomski/AVN_12z/f90.gif
http://www.meteo.psu.edu/~gadomski/AVN_12z/f96.gif
http://www.meteo.psu.edu/~gadomski/AVN_12z/f102.gif
http://www.meteo.psu.edu/~gadomski/AVN_12z/f108.gif

OKC Skew-T:
http://www.twisterdata.com/data/tmp/scr ... .5000W.png
http://www.twisterdata.com/data/tmp/scr ... .5000W.png
http://www.twisterdata.com/data/tmp/scr ... .5000W.png

Accumulated snow at hour 114:
http://www.twisterdata.com/data/models/ ... URFACE.png

CMC
The latest Canadian is showing a good potential for snow across most of Oklahoma (but favoring the northern half) during the day on Thursday. It does not look like a huge event in terms of duration or magnitude, but widespread light to moderate snow accumulations would still be possible.

http://www.meteo.psu.edu/~gadomski/CMC_12z/f90.gif
http://www.meteo.psu.edu/~gadomski/CMC_12z/f96.gif
http://www.meteo.psu.edu/~gadomski/CMC_12z/f102.gif
http://www.meteo.psu.edu/~gadomski/CMC_12z/f108.gif

ECMWF
The ECMWF is also showing a fairly minor event, with the total QPF for OKC being 0.12" (very similar to the GFS). It does show very cold air though, with surface temperatures Thursday afternoon running only in the middle 20s. 1000-500mb Thicknesses are a little high (mid 540s to start the day; upper 530s to end the day), and without skew-t data it is hard to know the precipitation type for sure. Given the very cold surface temperature though and 850mb temperatures below 0C, freezing rain seems unlikely except at the very beginning of the event. Sleet or snow would probably be the main p-type across Oklahoma City during the day if the ECMWF is correct, with only light accumulations (1" or less) given the low QPF. As with the other models, slightly higher precipitation amounts are shown across northern Oklahoma, with a QPF of 0.26" in Ponca City. This would equate to a snow total of 2-3" in that region using a ~10:1 ratio.

http://raleighwx.americanwx.com/models/ ... PUS096.gif


Things to take note of...
- We are still 3 to 4+ days out, and changes are still very possible (especially with the recent model uncertainty).
- The trend in some of the models has been towards higher/more widespread QPF values as the trough axis is lingering further behind the front with each new run (GFS especially). If this trend continues, then the potential for higher winter-type accumulations would exist.
- The precipitation type is not yet set in stone. This looks like it might be a tricky one, especially from 1-40 southward, and snow, sleet, freezing rain and rain are all still possibilities. Some places might even manage to see all four over the course of the event, depending on how things actually evolve.

[Extremeweatherguy]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
301 PM CST SUN JAN 16 2011

.DISCUSSION...
CLOUDS WILL LIKELY CONTINUE A SLOW EROSION THIS AFTERNOON AND
EARLY EVENING OVER SW OK AND OUR NORTH TEXAS COUNTIES...BUT HANG
TOUGH OVER FAR SOUTHEAST OKLAHOMA. HOWEVER...WITH VEERING LOWER
LEVEL FLOW...CLOUDS AND SOME FOG EXPECTED TO REDEVELOP ACROSS THE
SOUTHWEST AND SPREAD NORTH AND EAST. HRRR PICKING UP ON THIS
SCENARIO AND WILL GIVE US ENOUGH CONFIDENCE TO INCREASE OVERNIGHT
LOWS A BIT AND ADD FOG WORDING THROUGH EARLY TOMORROW MORNING.
MOST OF THE PRECIP WITH INCOMING S/WV SHOULD STAY NORTH OF OUR CWA
TOMORROW AFTERNOON AND MONDAY NIGHT...BUT WILL LEAVE LOW POPS
ACROSS FAR NORTH/EAST PARTS OF CWA.

SHALLOW BUT FAIRLY COLD AIRMASS WILL MAKE ITS WAY INTO REGION
LATE MONDAY NIGHT AND TUESDAY. THERE IS DEBATE BETWEEN MODELS ON
HOW FAST THIS COLDER AIR CAN BE DISPLACED ON WEDNESDAY. THE ECMWF
AND LESSER EXTENT NAM/WRF ARE SLOWER TO ERODE THE COLD AIR...WHILE
THE GFS IS VERY AGGRESSIVE WITH LOWER-LEVEL CYCLOGENESIS AND
EROSION OF SAID AIRMASS. WE WILL CONTINUE TO SIDE WITH THE COOLER
ECMWF THIS FORECAST CYCLE WHICH MATCHES BETTER WITH HPC AND NEIGHBORS.
THIS ALSO HAS IMPLICATIONS ON PRECIP TYPE WEDNESDAY NIGHT AND
EARLY THURSDAY AS RESPECTABLE TROUGH PROGRESSES OVER THE SOUTHERN
PLAINS. GFS MORE AGGRESSIVE WITH ELEVATED WAA RESULTING IN THE
POTENTIAL FOR MORE IN THE WAY OF FREEZING RAIN AND SLEET EARLY
THURSDAY. THIS WILL BE MENTIONED IN WEATHER GRIDS BUT IF ECMWF IS
CLOSER TO VERIFICATION...WHICH WE CURRENTLY BELIEVE IT WILL
BE...THIS TRANSITION WILL BE QUICKER AND MOST OF THE PRECIPITATION
WOULD CHANGE FROM RAIN TO SNOW RATHER QUICKLY. THE WEDNESDAY
NIGHT-THURSDAY TIME FRAME NEEDS TO BE WATCHED CLOSELY.

[TwisterFanatic]

Looks like this has the potential to be a decent storm. We'll See!

[Extremeweatherguy]

18z GFS for OKC...

**I have highlighted subfreezing temperatures and sub-540 thicknesses in blue**
**I have highlighted all QPF values >0.00" in green**

6pm Wed --> 48.0F (surface); 44.4F (850mb); 556 (1000-500mb thickness); 0.00" (6 hr QPF)
12am Thur --> 44.4F (surface); 46.6F (850mb); 553 (1000-500mb thickness); 0.00" (6 hr QPF)
6am Thur --> 25.5F (surface); 34.9F (850mb); 544 (1000-500mb thickness); 0.06" (6 hr QPF)
12pm Thur --> 22.1F (surface); 25.7F (850mb); 538 (1000-500mb thickness); 0.07" (6 hr QPF)
6pm Thur --> 24.1F (surface); 21.5F (850mb); 534 (1000-500mb thickness); 0.04" (6 hr QPF)
12am Fri --> 16.7F (surface); 23.7F (850mb); 534 (1000-500mb thickness); 0.00" (6 hr QPF)
6am Fri --> 12.6F (surface); 24.5F (850mb); 537 (1000-500mb thickness); 0.00" (6 hr QPF)
12pm Fri --> 29.1F (surface); 27.1F (850mb); 542 (1000-500mb thickness); 0.00" (6 hr QPF)

Definitely an interesting scenario. The rapid cooling during early Thursday would likely lead to a very quick progression from rain to freezing rain to sleet and then eventually snow sometime between 6am and noon. The total QPF for the event is still on the light side (0.17"), but it has come up slightly from the 12z run (0.13").

[wx247]

I am liking the 00z GFS for us here in SW MO. Not as huge of a friend to our Oklahoma folk.

[Extremeweatherguy]

Yeah, the 00z GFS is definitely looking good for you guys in SW MO. Not as promising overall for central Oklahoma, but not really a bad run either. It is very similar to the 18z run, showing between 0.15-0.20" total QPF for OKC.

Not a major storm for us if this scenario plays out, but still noteworthy considering we have yet to see an accumulating snowfall so far this winter.

[Extremeweatherguy]

A look at the 00z Canadian..

http://www.meteo.psu.edu/~gadomski/CMC_0zA/f72.gif
http://www.meteo.psu.edu/~gadomski/CMC_0zA/f78.gif
http://www.meteo.psu.edu/~gadomski/CMC_0zA/f84.gif
http://www.meteo.psu.edu/~gadomski/CMC_0zA/f90.gif
http://www.meteo.psu.edu/~gadomski/CMC_0zA/f96.gif


Also, for central Oklahoma folks, it is worth noting that the 00z ECMWF has come in wetter across the area. The latest run is showing a storm total QPF of 0.21" for OKC, which is up significantly from 0.12" in the 12z run. While 0.21" would still only equate to a minor/moderate winter event, it is definitely starting to inch toward the more respectable category. Looking at the text output, it appears as though the precipitation would likely start as sleet and then quickly transition to snow for OKC. Assuming a ~10:1 liquid to snow ratio, Oklahoma City would receive roughly 1.5-2.0" of snowfall (on top of a thin layer of sleet) if tonight's 00z ECMWF run played out exactly.

[Extremeweatherguy]

The 12z GFS is not a very good run. Only 0.05" total QPF for Oklahoma City, which would mean a fairly insignificant event; rain turning to a few flurries with little to no accumulation. Hopefully this is just a brief "kink" in the trend that had previously been toward wetter.

On the flip side, the NAM, which had previously been showing 0.00" for OKC is now showing 0.04" total QPF. This is still a very low and almost insignificant amount, but it is noteworthy considering previous runs were showing nothing at all. It will be interesting to see if this continues in future runs.

Both models may not be handling the arrival speed/erosion of the cold air very well though, and this could lead to big changes as the event draws closer (as discussed in the Texas thread). This possibility will need to be monitored closely.

Now let's wait and see what the 12z CMC and ECMWF have to offer..

[Extremeweatherguy]

The 12z CMC has come in pretty impressive, definitely more so than the GFS and NAM.

If it is correct, then most of Oklahoma and parts of far north Texas would receive accumulating winter precipitation on Thursday.

60 HR


66HR


72HR


78HR


84HR

[wx247]

18z NAM should be more to your liking Extremeweatherguy!!!

[Extremeweatherguy]

Yeah, definitely trending more and more in the right direction for those wanting some wintry precipitation. Not an amazing setup by any means, and the quick nature of the system would argue against any major accumulations, but overall the NAM definitely looks better now than it did last evening.

Last evening's 00z NAM valid 6am THURS: http://i43.photobucket.com/albums/e371/ ... 084l-2.gif
Today's 18z NAM valid 6am THURS: http://i43.photobucket.com/albums/e371/ ... p_066l.gif

[TwisterFanatic]

Looks like the NAM may be coming in line with the CMC, QPF wise.

[Extremeweatherguy]

Not much good news from the 00z models so far. The NAM and GFS continue to show a fairly mediocre storm, enough to perhaps generate 1-3" of snow across northern Oklahoma and a trace-1" across central Oklahoma. There might also be a little bit of frz rain or sleet mixed in towards the beginning of the event, especially the further south you go, but the amounts would not be all that significant. Overall, if these two runs proved correct, then this would simply be your run-of-the-mill winter system; probably only deserving of winter weather advisories and not full-fledged winter storm warnings for the southern plains region.

[Extremeweatherguy]

Nothing new from the 12z models really.

Based on everything I'm seeing, the most likely scenario for the Oklahoma city area on Thursday would probably go something like this...

The first showers should enter the area between midnight and 6am. Initially precipitation could start as rain, but expect a quick transition to freezing rain/sleet and then eventually snow. By sunrise, parts of the area are likely to have a glaze of ice and a dusting of sleet or snow. One or two places that get heavier bands might have slightly higher accumulations, and a couple of other spots might have nothing at all. Roads are likely to become slick in areas by the morning commute hours. Scattered snow showers should continue until about noon and then gradually taper off. Most areas around OKC will likely only see between a dusting and an inch of total snow accumulation (on top of a light glaze of ice), but a few locations could see slightly more/less. Gusty north winds could cause periods of blowing snow in the zones that managed to recieve appreciable accumulations during the morning hours. Low wind chills will also be present as actual air temperatures are likely to remain below freezing during the afternoon.

This scenario is currently the most probable based the latest model trends. However, an even faster arrival of the cold air/precipitation or more moisture to work with would certainly change things a bit. Sometimes these things can be a bit unpredictable until the last minute, so stay tuned!

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

[TwisterFanatic]

Winter Weather Advisory issued for all of Eastern Oklahoma pretty much

* UP TO 4 INCHES OF SNOW AND SLEET ACCUMULATION AND LESS THAN A
TENTH OF AN INCH OF ICE ACCUMULATION IS EXPECTED FROM 3 PM
WEDNESDAY TO 6 PM CST THURSDAY.

[Ntxw]

NAM and GFS snow maps. Pretty good consensus that the best chances for significant accumulations would be northern Oklahoma. But as EWG mentioned, any shifts in precip or cold would cause more significant impacts.

[Extremeweatherguy]

18z GFS and NAM precipitation totals for OKC, OUN, and PNC...

(found at: http://www.meteor.iastate.edu/~ckarsten ... index.html)

Oklahoma City:

18z NAM
Rain - 0.03"
Snow - 0.20"
Sleet - 0.01"
Frz rain - 0.01"

18z GFS
Rain - 0.02-0.03"
Snow - 0.90"
Sleet - 0.00"
Frz rain - 0.05"

Norman:

18z NAM
Rain - 0.02"
Snow - 0.10"
Sleet - 0.00"
Frz rain - 0.02"

18z GFS
Rain - 0.00"
Snow - 0.40"
Sleet - 0.00"
Frz rain - 0.03"

Ponca City:

18z NAM
Rain - 0.00"
Snow - 2.50"
Sleet - 0.12"
Frz rain - 0.03"

18z GFS
Rain - 0.00"
Snow - 3.60"
Sleet - 0.00"
Frz rain - 0.00"

[TwisterFanatic]

Woah, 0z NAM with a pretty significant snowstorm for NW Arkansas and Eastern Oklahoma! This is also the 1st run with the system on land.