Southern Plains winter wx thread (2008-2009)

[Ed Mahmoud]

GFS numbers suggests nothing more than drizzle. Light enough that it might sublimate before accumulating enough to ice even the most susceptible bridges and overpasses. Until maybe Saturday.

[Extremeweatherguy]

GFS numbers suggests nothing more than drizzle. Light enough that it might sublimate before accumulating enough to ice even the most susceptible bridges and overpasses. Until maybe Saturday.

The GFS squeezes out about 0.20 to 0.25 inches of liquid over OKC during the course of next week (based on text output). Not a major accumulation, but definitely more than drizzle would provide.

[jasons2k]

FWIW I found in my years spent up in the Metroplex that freezing drizzle can be the worst possible form of precipitation for traffic/roadways, sometimes even worse than full-blown freezing rain.

[Ed Mahmoud]

GFS numbers suggests nothing more than drizzle. Light enough that it might sublimate before accumulating enough to ice even the most susceptible bridges and overpasses. Until maybe Saturday.

The GFS squeezes out about 0.20 to 0.25 inches of liquid over OKC during the course of next week (based on text output). Not a major accumulation, but definitely more than drizzle would provide.

I'd call a quarter inch over several days not much more than drizzle. Its subjective.

If the perfect prog is before us, the quarter inch Friday evening into Saturday would be enough for trouble.

[Ed Mahmoud]

FWIW I found in my years spent up in the Metroplex that freezing drizzle can be the worst possible form of precipitation for traffic/roadways, sometimes even worse than full-blown freezing rain.

Because people know enough to be careful in a full blown freezing rain, I'd suspect.


The sand they put down during ice episodes isn't great when the weather dries either, I've had some skids braking on sand long after the event was over.

[Extremeweatherguy]

GFS numbers suggests nothing more than drizzle. Light enough that it might sublimate before accumulating enough to ice even the most susceptible bridges and overpasses. Until maybe Saturday.

The GFS squeezes out about 0.20 to 0.25 inches of liquid over OKC during the course of next week (based on text output). Not a major accumulation, but definitely more than drizzle would provide.

I'd call a quarter inch over several days not much more than drizzle. Its subjective.

If the perfect prog is before us, the quarter inch Friday evening into Saturday would be enough for trouble.

That's one thing I hope doesn't happen. I am flying out of OKC on Saturday and ice+airports = bad news.

[jasons2k]

Because people know enough to be careful in a full blown freezing rain, I'd suspect.

Actually, because freezing drizzle tends to stick to road surfaces like glue, whereas freezing rain often will just stay liquid on the roadways, at least during the daytime.

A lot of times it needs to be below 30F for the roads to ice-up if it's raining liquid, while freezing drizzle will ice-up as soon as the temp. hits 32F.

Another example would be this - run a faucet over a freezing slab of granite and most of the water will just runoff as liquid, but if you use a medicine dropper and slowly drop water on it, it will turn to ice almost immediately.

[gboudx]

Because people know enough to be careful in a full blown freezing rain, I'd suspect.

Actually, because freezing drizzle tends to stick to road surfaces like glue, whereas freezing rain often will just stay liquid on the roadways, at least during the daytime.

A lot of times it needs to be below 30F for the roads to ice-up if it's raining liquid, while freezing drizzle will ice-up as soon as the temp. hits 32F.

Another example would be this - run a faucet over a freezing slab of granite and most of the water will just runoff as liquid, but if you use a medicine dropper and slowly drop water on it, it will turn to ice almost immediately.

Yep. That nastiness can stay away as far as I'm concerned.

[Extremeweatherguy]

Here is the latest from the very confused Norman, OK forecast office...

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORMAN OK
310 PM CST FRI DEC 12 2008

.DISCUSSION...
IN THE SHORT TERM...A VIGOROUS SHORTWAVE NOW MOVING ONTO THE COAST
OF WA/OR WILL DIG SOUTHWARD OVER THE NEXT 24-36 HOURS...WITH LEE
TROUGHING OCCURRING AHEAD OF THIS SHORTWAVE AND ANOTHER WAVE NOW
OVER THE GREAT BASIN. LEE TROUGHING HAS ALREADY
COMMENCED...EVIDENCED BY SOUTHERLY WINDS NOW HAVING BEGUN ACROSS THE
CWA WIND SPEEDS WILL INCREASE IN SPEED FRI NIGHT INTO SAT...WITH
SUSTAINED SPEEDS OF 30 MPH AND GUSTS OVER 40 MPH EXPECTED ACROSS
PORTIONS OF THE AREA. A WIND ADVISORY WILL LIKELY BE NECESSARY AS A
RESULT. WE HAVE DECIDED TO LET FUTURE SHIFTS CONFIGURE THE
GEOGRAPHIC LAYOUT AND THE SPECIFIC TIME WINDOW FOR THE ADVISORY.
STRONG WINDS COMBINED WITH TEMPERATURES IN THE 70S ACROSS PORTIONS
OF WESTERN OK AND WESTERN NORTH TX WILL ELEVATE FIRE WX CONCERNS ON
SAT AFTERNOON. HOWEVER...MOISTURE WILL LIKELY BE GREAT ENOUGH TO
PRECLUDE ISSUANCE OF A RED FLAG WARNING.

WARM AND WINDY CONDITIONS WILL CONTINUE SUN AFTERNOON ACROSS MUCH OF
THE CWA. BIG CHANGE IN STORE SUN AFTERNOON AS A SHALLOW COLD AIRMASS
OF ARCTIC ORIGIN TAKES AIM AT OK/N TX. THE COLD FRONT SHOULD ENTER
NW OK BY MIDDAY SUNDAY...CLEARING THE CWA BY MIDNIGHT MONDAY. SOME
LIGHT PRECIP IS POSSIBLE ON SUN NIGHT INTO MON MORNING...WITH A
WINTRY MIX OF RAIN...FREEZING RAIN OR DRIZZLE...SLEET...AND SOME
SNOW EXPECTED. THE COLD AIR IS EXPECTED TO HANG ON FOR MUCH OF NEXT
WEEK. A SPECIAL WEATHER STATEMENT HAS BEEN CONTINUED TO COVER THIS
SITUATION IN MORE DETAIL.

WE HAVE LOW CONFIDENCE IN THE FORECAST BEYOND EARLY NEXT WEEK. MED
RANGE MODELS CONTINUE TO SHOW DIVERGENT SOLUTIONS...WITH 12Z GFS
INDICATING THE COLD AIR REMAINING IN PLACE THROUGHOUT MUCH OF NEXT
WEEK...WHILE THE 12Z ECMWF FAVORING THE ARCTIC HIGH MOVING MORE
QUICKLY TO THE EAST AND A WARM UP BY MID WEEK. THE PROBLEM
IS...THE MODELS HAD OPPOSITE SOLUTIONS YESTERDAY. THEREFORE...VERY
FEW CHANGES WERE MADE TO THE EXTENDED AND WE WILL CONTINUE TO
FAVOR THE COLD AIR BEING IN PLACE FOR A LONGER PERIOD OF TIME. THE
ONLY CHANGE WAS TO EDIT TEMPERATURE GRIDS NEAR THE END OF THE
EXTENDED TO ALIGN THEM A LITTLE CLOSER TO CLIMATOLOGY.

[iorange55]

After reading all this basically we still know nothing......lol.

[amawea]

Man! What a mess. Niether the mets or the modles have a clue yet for next week.

[Extremeweatherguy]

After reviewing the 18z GFS skew-t diagrams for next week, it looks as though Oklahoma City might be getting more than just freezing rain out of this mess...

At 12z Monday morning (~7am), the skew-t looks favorable for freezing drizzle and perhaps some sleet (or snow with great enough evap. cooling). The freezing drizzle is a given due to the nearly saturated 900mb layer above a <32F surface. Sleet is less certain though, but a sure possibility. There is a dry layer between 850mb and 500mb, but up near 450-500mb it becomes nearly saturated again. If the precipitation falling out of this layer can moisten the dry layer, then some of the snowflakes may make it down, partially melt around 800mb, and then re-freeze before reaching the surface (and if evap. cooling becomes great enough from this process, then the sleet could eventually become snow as the wetbulb temperature [below 32F] could be reached between the 500-850mb layer):


By 06z Tuesday morning (~1am), the skew-t starts looking more favorable for snow. The entire upper profile drops below freezing with saturation occurring up near 250-300mb and then again near 600-650mb. There are some small dry layers on this skew-t, but any precipitation that does manage to make it to the surface during this time will likely be in the form of snowflakes:


All in all, based on what I am seeing so far, this looks to be a very interesting setup. We could certainly wind up seeing a true "wintry mix" around these parts next week, with snow, sleet and freezing rain all possible.

[iorange55]

I really hope the cold is a little further south so here in Dallas we get something besides the ever so exciting.....rain.

[Johnny]

Like I said before EWG, you will see more than just some freezing drizzle/rain. Wanna make a bet?

[Extremeweatherguy]

The new 00z GFS is back to its old ways of trying to pull the cold air back north too quickly next week. It still looks cold for Monday, then moderates by Tuesday, cools back down again on Wednesday, and then modifies once more for Thursday. It's all over the place!

When will this constant flip-flopping ever end!

[iorange55]

Lol that seems like a MUCH warmer run compared to the last one. The models have no idea what's going on....no one does.

[vbhoutex]

Lol that seems like a MUCH warmer run compared to the last one. The models have no idea what's going on....no one does.

This is a common denominator with the models and these Arctic air masses when they come down the plains. We've seen this several times before and the cold did come on down all the way to the coast as advertised. Temps may moderate or be colder than forecast depending on the set up and snow pack, but normally with cold air that dense it makes it's way south no matter what the models say. JMHO from many observations over the years.

[Ed Mahmoud]

Getting out into model fantasy land (beyond 180 hours), the threat for some wintry fun in North Texas and Oklahoma on Christmas Eve.

[iorange55]

Dallas Noaa discussion.

BROAD POSITIVELY TILTED UPPER LEVEL TROUGH WILL REMAIN IN PLACE
OVER NORTH AMERICA AND NORTH TX WILL BE UNDER STRONG SOUTHWESTERLY
MID-UPPER LEVEL FLOW. THUS ONLY A SHALLOW...3000 FT DEEP...LAYER
OF COLD AIR WILL MAKE IT TO NORTH TEXAS. THIS SHALLOW LAYER OF
COLD AIR IS PLAYING HAVOC WITH THE MEDIUM RANGE MODEL GUIDANCE.
MODELS CONTINUE TO DISPLAY POOR RUN TO RUN CONTINUITY ON WHETHER
TO HOLD THE COLD AIR IN ALL WEEK OR ERODE IT AS EARLY AS TUESDAY.
IN FACT MOST OF THE 0Z GUIDANCE IS SHOWING US NEAR OR ABOVE NORMAL
BY WEDNESDAY. HOWEVER...MODELS NEVER FORECAST THESE SITUATIONS
WELL AND THEY ARE ALMOST ALWAYS TOO WARM. THE NAM IS PROBABLY THE
ONE MODEL TO TRUST...BUT IT ONLY FORECASTS OUT THROUGH NOON TUES.
THEREFORE...FORECAST CONFIDENCE BEYOND TUESDAY IS EXTREMELY
LOW...AND THE FORECAST IS SIGNIFICANTLY COLDER THAN MEX MOS.

SHORTWAVE IN FAST UPPER FLOW COMES ACROSS TUESDAY AND SOUTHERLY
FLOW STRENGTHENS IN THE LOW LEVELS. ISENTROPIC LIFT IS FORECAST TO
OCCUR BY THE NAM/GFS WITH LIGHT RAIN OVER NORTH TEXAS. WHERE EVER
THE FREEZE LINE ENDS UP WILL BE THE LOCATION OF CONCERN FOR
FREEZING RAIN TUESDAY MORNING. RIGHT NOW WE WILL CONTINUE TO
FORECAST A CHANCE OF FZRA NORTH OF COMANCHE...TO DENTON...TO PARIS
LINE. TEMPS WILL SLOWLY MODERATE INTO WEDNESDAY...AND HAVE JUST
COLD RAIN CHANCES TUESDAY NIGHT ONWARD. HOWEVER...THIS IS STILL
HIGHLY UNCERTAIN AS THERE IS THE POTENTIAL THAT TEMPS MAY BE A FEW
DEGREES COLDER WITH THE INITIAL SURGE...AS WELL AS THE POTENTIAL
THAT THE ARCTIC FRONT WILL MAINTAIN MORE DEFINITION AND STALL
ACROSS THE NORTHERN COUNTIES AS SECONDARY HIGH PRESSURE SURGE
MOVES INTO THE PLAINS WEDNESDAY. STAY TUNED.

OTHERWISE...OUT OF RESPECT FOR THE MUCH WARMER NUMERICAL GUIDANCE
DID SHOW A SOUTH TO NORTH WARMING TREND WEDNESDAY AND THURSDAY...
WITH TEMPS NEAR OR ABOVE CLIMO BY FRIDAY. LOW CHANCES OF RAIN
WILL CONTINUE TO LINGER MAINLY OVER THE NORTHEAST LATE NEXT WEEK.

Very interesting stuff. Cold and wet for sure next week and maybe icy.

[Extremeweatherguy]

The NWS in Norman is still not buying the models that want to erode the cold air too fast. They continue to forecast us to be below freezing through Thursday morning with wintry weather threats each and every day next week.

As for the actual models, the only thing they really agree on is that Monday will be cold. The GFS, the NAM, the ECMWF, the NAM MOS, and the GFS MOS all show temperatures below freezing in OKC during the day on Monday. The big differences come in the longer range, where the handling of the shallow cold air becomes difficult. Tuesday afternoon and beyond is still pretty much a guessing game at this point, with multiple scenarios possible. Hopefully by Monday we will finally be able to get a handle on that portion of the forecast.