Southern Plains winter wx thread (2009-2010)

[Extremeweatherguy]

The NWS is still not forecasting winter precipitation for my part of OKC, but they are definitely getting more and more bullish each day. Yesterday they were calling for a low of 40F on Tuesday night with a 50% chance of rain, and this morning they are now calling for a low of 34F on Tuesday night with a 60% chance of rain. Basically we are about as close as you can get right now to having a forecast of snow/sleet thrown in. If the models continue to look as cold or colder than they have been, I fully expect the NWS to upgrade the forecast to include some sort of wintry mix in the days to come.

Here is the morning discussion from Norman...

.DISCUSSION...
SUNNY AND MILD CONDITIONS EXPECTED TODAY BEFORE NEXT STORM SYSTEM
IMPACTS THE REGION. OVERALL THINKING HAS NOT CHANGED MUCH SINCE
LAST ISSUANCE. GFS HAS TRENDED FARTHER NORTH WITH UPPER LOW
TUESDAY NIGHT AND WEDNESDAY...AND ITS TIMING/POSITION IS PRETTY
MUCH RIGHT-ON WITH THE ECM...SO POPS WERE ADJUSTED BY SPREADING
NORTH AND INCREASING CENTRAL AND SOUTHERN OKLAHOMA AND NORTH
TEXAS. BIG QUESTION IS IF A CHANGE-OVER TO SNOW WILL OCCUR LATE
TUESDAY NIGHT AND WEDNESDAY. WITH DEEP COLD AIR NOT IN PLACE UNTIL
SYSTEM BEGINS TO PULL OUT...WE WILL BE LEAVING MENTION OF SNOW TO
FAR WESTERN OKLAHOMA PRIMARILY DUE TO COLD AIR TIMING AND
ELEVATION...AND TO WESTERN NORTH TEXAS AND SOUTHERN OKLAHOMA DUE
TO PROXIMITY OF GREATER LIFT/COOLING NEAR UPPER LOW. LIGHT
ACCUMULATIONS ON GRASSY/ELEVATED SURFACES CANNOT BE RULED OUT
ACROSS SOUTHERN PARTS OF FORECAST AREA. GFS HAS BEEN CONSISTENT IN
PRODUCING A BAND OF ENHANCED LIFT ASSOCIATED WITH DEFORMATION ZONE
NORTH OF STORM SYSTEM...WHICH ALSO COINCIDES WITH EDGE OF WEAK
TROWAL POKING IN FROM ARKLATEX. THIS REGION EXTENDS ALONG/NEAR THE
I-44 CORRIDOR. IF MORE COLD AIR WERE EXPECTED...WE WOULD BE
THINKING OF ACCUMULATING SNOWS. HOWEVER...UNLESS FORECAST TRENDS
SPEED UP COLD AIR ARRIVAL...THIS WILL BE ALL LIQUID AS IS
CURRENTLY FORECAST.

MUCH COOLER AND DRY WEATHER EXPECTED FROM LATE WEDNESDAY THROUGH
NEXT WEEKEND. MEDIUM RANGE MODELS AT ODDS WITH EVOLUTION WITH
SECONDARY TROUGH THAT MOVES INTO PACIFIC NORTHWEST THIS WEEKEND.
MAJORITY OF GFS ENSEMBLES CLOSER TO ECM SOLUTION SO WILL CONTINUE
A FORECAST CLOSER TO ECM AND ERODE COLD AIR AT A SLOWER PACE.

[Extremeweatherguy]

The 12z NAM is showing over an inch of liquid equivalent precipitation falling on OKC on Wednesday! If even just a small fraction of that were to fall as snow, then we could be talking about several inches of accumulation. I am not getting my hopes up too much though. While the upper levels should be becoming cold enough for wintery precipitation, there is still some question as to the immediate surface conditions. Considering the models usually error too warm at the surface though, I think the potential is definitely there for snow to fall...and possibly even accumulate. This is definitely going to be a fun system to watch! I have the feeling there will be lots of teeth grinding and headaches going on in NWS offices up until the very last moment.

[iorange55]

The 12z NAM is showing over an inch of liquid equivalent precipitation falling on OKC on Wednesday! If even just a small fraction of that were to fall as snow, then we could be talking about several inches of accumulation. I am not getting my hopes up too much though. While the upper levels should be becoming cold enough for wintery precipitation, there is still some question as to the immediate surface conditions. Considering the models usually error too warm at the surface though, I think the potential is definitely there for snow to fall...and possibly even accumulate. This is definitely going to be a fun system to watch. I have the feeling there will be lots of teeth grinding up until the very last moment.

I hope we at least get teeth grinding in Dallas. It's going to suck if we get no drama, and just plain cold rain. While lubbock enjoys a foot of snow.

[srainhoutx]

Just remember the NAM tends to have a drier and warmer bias with wintry type systems IMHO.

[Extremeweatherguy]

The 12z GFS is less impressive than the NAM overall (especially with regards to precipitation amounts), but still looks to show the possibility of a mixing with or changeover to some sleet or snow before the system pulls out. The 12z run is also now hinting at another chance of wintry precipitation closer to the weekend which could be interesting.

[Extremeweatherguy]

The NWS has now officially added the wording of "rain and snow" to the forecast for Wednesday in and around OKC...

Tuesday Night...Cloudy. Rain likely in the evening...then rain showers likely after midnight. Lows in the lower 30s. Southwest winds up to 10 mph shifting to the north after midnight. Chance of precipitation 60 percent.

Wednesday...Partly cloudy with chance of rain and snow. Colder. Highs in the lower 40s. North winds 15 to 25 mph. Chance of precipitation 40 percent.

[iorange55]

The NWS has now officially added the wording of "rain and snow" to the forecast for Wednesday in and around OKC...

Tuesday Night...Cloudy. Rain likely in the evening...then rain showers likely after midnight. Lows in the lower 30s. Southwest winds up to 10 mph shifting to the north after midnight. Chance of precipitation 60 percent.

Wednesday...Partly cloudy with chance of rain and snow. Colder. Highs in the lower 40s. North winds 15 to 25 mph. Chance of precipitation 40 percent.

They still have it in there, and bumped the percentage up a little. I hope you see some snow! I'm pretty much convinced it won't snow here with this storm.

[Extremeweatherguy]

The NWS has now officially added the wording of "rain and snow" to the forecast for Wednesday in and around OKC...

Tuesday Night...Cloudy. Rain likely in the evening...then rain showers likely after midnight. Lows in the lower 30s. Southwest winds up to 10 mph shifting to the north after midnight. Chance of precipitation 60 percent.

Wednesday...Partly cloudy with chance of rain and snow. Colder. Highs in the lower 40s. North winds 15 to 25 mph. Chance of precipitation 40 percent.

They still have it in there, and bumped the percentage up a little. I hope you see some snow! I'm pretty much convinced it won't snow here with this storm.

Yeah I am still not really convinced that we'll see much up here either. May be a few flakes if we're lucky and and actual changeover/light accumulation if we're REALLY lucky, but i doubt it. Either way though, this colder and stormier pattern does promise several more threats of wintery precipitation over the next few weeks, so I won't be too disappointed if we miss out on this one.

[Extremeweatherguy]

I am starting to think that Thursday into Friday could wind up being more interesting for the southern plains than tomorrow will be. The 12z NAM MOS is showing OKC starting the day in the 20s and then barely breaking 40F during the afternoon. By the evening it has temperatures dropping rapidly, reaching a low of 23F overnight. At the same time, the models are also pumping up our cloud cover into the mostly cloudy or overcast category and small precipitation chances are being introduced. The 12z NAM MOS is showing a 31% chance of precipitation for OKC by Friday morning, which given the subfreezing temperatures and low thicknesses, would all be in the form of snow. The low temperatures would also strongly favor accumulations of any snow that fell. The only negative factor would be the fact that the snow showers would probably be isolated/scattered in nature, thus not favoring more than a light dusting around the region.

The Dallas area could also get in on the fun if the 12z NAM MOS proves correct. It is showing temperatures falling into the low/mid 30s for the city by Friday AM with precipitation chances at 33%. Thicknesses would support everything falling being in the form of snow.

[Extremeweatherguy]

The 12z GFS MOS is less impressive for Oklahoma City in terms of late week snow, only showing a 17% chance of light precipitation on Thursday. It still looks to get very cold though, with a projected low on Friday morning of just 19F.

It's also worth noting that the actual 12z run of the GFS looks pretty interesting for next week. It seems to be having lots of problems handling the building arctic airmass, and seems to be holding the cold air too far north and west. I expect to see lots of back and forth with the model in the extended, probably eventually coming around to a cold and wintery look across the southern plains. I think ice and snow threats are very possible for Oklahoma and north Texas next week, with the arctic air creeping much further south than the current 12z run indicates.

[Weatherfreak14]

Looks like tomorrow morning i will be waking up here on campus in Norman to see snow falling when I walk to classes. The way the NAM and GFS are looking, it maybe cold enough to have snow accumulate on cars and cold surfaces. Gonna be very interesting indeed!

[Extremeweatherguy]

Getting a nice sleet shower right now in south OKC!

...and now 5 minutes later it is over.

This is officially one of the warmest temperature sleets I have ever seen.

[srainhoutx]

Very potent Upper Low. This is the game changer we've been looking at via guidance for some time. Pattern is changing. Storm track looks encouraging for future events. Lay some snow cover down for us further S.

[cheezyWXguy]

Getting a nice sleet shower right now in south OKC!

...and now 5 minutes later it is over.

This is officially one of the warmest temperature sleets I have ever seen.

yeah had the same thing today around 1215. It sleeted for about 2 or 3 minutes at like 46 degrees here in Plano..same thing happened in Denton from what I heard.

[Extremeweatherguy]

It looks like a larger area of rain/sleet mix could be on the way. The latest radar trends are showing an area of increasing reflectivities in southern Oklahoma lifting toward the north. Once this precipitation arrives I expect that it will probably be in the form of moderate rain mixed with periods of sleet pellets.

http://www.wunderground.com/radar/radbl ... rainsnow=0

[Extremeweatherguy]

Getting more sleet now. It's coming down pretty steadily, but unfortunately it is too warm for any kind of accumulations. Still interesting to watch though.

edit: Starting to mix with rain now. Probably a 75% rain/25% sleet mix.

[Extremeweatherguy]

Finally managing to see a few snowflakes on the back edge of the precipitation here in south OKC, but it doesn't look to last long. Seems like it's too little too late this time. Just as it's getting cold enough, the precip. is ending.

[Tireman4]

EWG,

You will miss our ( maybe..who knows) snow event again ( Houston). LOL.

[Extremeweatherguy]

EWG,

You will miss our ( maybe..who knows) snow event again ( Houston). LOL.

Yeah, I know. It seems like mother nature hasn't been liking me lately. It never really ever snowed the entire time I lived in Houston (other than a handful of flurries in March '08), but then right after I moved away everything changed. It snowed last December and now it looks like it will try to do so again this December too. That's just crazy!

[Extremeweatherguy]

Very interesting AFD from Wichita this afternoon concerning early next week and all the problems the models seem to be having handling the evolving pattern...

SUN-WED:

THIS PERIOD CONTINUE TO DEVOLVE INTO A BIG MESS WITH THE WAY THE
EUROPEAN CENTRE FOR MEDIUM RANGE WEATHER FORECASTS MODEL HAS BEEN
FLIP-FLOPPING ON THE SURFACE PATTERN AND AM SUSPCIOUS OF GLOBAL
FORECAST SYSTEM MODEL TOO. AM CONCERNED WITH THE WAY BOTH GLOBAL
FORECAST SYSTEM MODEL/EUROPEAN CENTRE FOR MEDIUM RANGE WEATHER
FORECASTS MODEL/CANADIAN ALL CUT OFF/DEEPEN 500MB LOW ON WEST COAST
OVER WEEKEND. GIVEN HIGH AMPLITUDE FLOW GOING INTO WEEKEND...
WONDER WHY IT WOULD STOP/RETROGRADE THERE...RATHER THAN KEEP
MOVING UNTIL THE SHORTWAVE APPROACHES THE CLOUD BASE OF THE LONG
WAVE TROUGH. THE ORIENTATION OF UPPER JET DOES NOT SEEM TO FAVOR
AN EARLY CUT OFF SOLUTION EITHER. THE SHORTWAVE IN QUESTION IS
STILL IN GULF OF AK SO SAMPLING IS POOR. THIS WAVE WILL BE THE
DRIVING FACTOR IN TEMPERATURES/PRECIPITATION FOR THE FIRST OF THE
WEEK. THE GLOBAL FORECAST SYSTEM MODEL HAS SHOWN A LOT MORE RUN TO
RUN CONSISTENCY...BUT AM NOT CONVINCED THAT IT IS CORRECT GIVEN
THE HIGHLY UNUSUAL PATTERN OVER THE WEEKEND. CURRENT PLAN IS TO
KEEP COOL AIR IN PLACE THROUGHOUT THE PERIOD UNTIL LAST PERIOD
WHEN INSOLATION SHOULD ALLOW A BIT OF A REBOUND/MODERATION OF THE
SECOND SURGE OF COLD AIR. THIS IS AN EXTREMELY LOW CONFIDENCE
FORECAST WITH VERY HIGH ERROR POTENTIAL FOR BOTH TEMPERATURES AND
PRECIPITATION. -HOWERTON