Texas Fall 2013

[joshskeety]

But wait a sec.. Didnt we just get done discussing the fact that the NAM has a much better handle on these situations than the GFS does? 3rd run in a row of this on the NAM and we will call it the outlier?

Look, Im not sitting here and telling you the Metroplex is about to have a historic blizzard snowstorm of all time in mid november.. What I am suggesting though is after 3 runs in a row, it has to be looked into and not discounted.. The ECMWF last night although warmer showed the upper low merging also, maybe not as quick, but it did have it..[/quote]

Just because the NAM is forecasting one aspect of this better than the others (cold coming down), does not mean it has a better handle on another aspect (low ejecting across). It may very well end up being right on all of it, but you can't assume that right now.[/quote]

Then why the assumption that the GFS is correct when it just went belly up on the last run? If one is to assume one way, you would expect at least a meeting of the middle..

[CaptinCrunch]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
402 PM CST THU NOV 21 2013

.DISCUSSION...

ARCTIC FRONT CONTINUES TO MOVE QUICKLY TOWARD THE CWA AND WILL NOW
BE ARRIVING IN THE FAR NORTHWEST CORNER WITHIN THE NEXT HOUR. IN
THE SHORT TERM FORECAST...SPED UP THE FRONT ANOTHER HOUR THROUGH
THE OVERNIGHT PERIOD. OTHERWISE...NO SIGNIFICANT CHANGES WERE MADE
TO THE FORECAST FOR TONIGHT OR TOMORROW FROM THE UPDATE ISSUED
AROUND MIDDAY. WE WILL BE ISSUING A FREEZING RAIN ADVISORY
STARTING LATE TONIGHT AND CONTINUING THROUGH SATURDAY MORNING FOR
OUR WEST AND NORTHWEST COUNTIES. ACCUMULATIONS ARE EXPECTED TO BE
RELATIVELY LIGHT DESPITE THE DURATION OF THE EVENT. THE
RAIN/FREEZING RAIN WILL NOT BE CONTINUOUS THROUGHOUT THE PERIOD
BUT IMPACTS ON ELEVATED SURFACES SUCH AS BRIDGES AND OVERPASSES
CAN BE EXPECTED IN THE ADVISORY AREA. ALSO DRIVING THE DECISION TO
ISSUE THE ADVISORY IS THE FACT THAT IT IS A WEEKEND WITH MANY
PEOPLE STARTING THEIR HOLIDAY TRAVELS.

FRIDAY WILL BE A BITTERLY COLD DAY WITH STRONG NORTH WINDS KEEPING
WIND CHILLS IN THE TEENS TO LOWER 30S THROUGHOUT THE DAY. THE
STRONG WINDS AND LOW WIND CHILLS WILL CONTINUE INTO FRIDAY NIGHT.
WHERE FREEZING RAIN IS NOT OCCURRING...SCATTERED LIGHT RAIN AND
SHOWERS WILL CONTINUE THROUGH THE WEEKEND.

WE WILL SEE A BREAK IN THE FREEZING RAIN ON SATURDAY BEFORE THE
NEXT WINTER WEATHER EVENT BEGINS SATURDAY NIGHT. AS AN UPPER LEVEL
LOW APPROACHES FROM THE WEST...WARM AIR WILL LIFT OVER THE COLD
LAYER AT THE SURFACE PRODUCING MORE RAIN AND FROZEN PRECIPITATION.
IT STILL APPEARS SLEET WILL BE LIKELY OVER A GOOD PART OF THE
REGION WITH SIGNIFICANT ACCUMULATIONS POSSIBLE OVER OUR WESTERN
AND NORTHWESTERN COUNTIES. HOWEVER...BOTH THE LATEST RUNS OF THE
GFS AND NAM SUGGEST SURFACE TEMPERATURES DURING THE DAY ON SUNDAY
COULD BE CLOSER TO FREEZING OVER A GOOD PORTION OF THE REGION
WHICH COULD RESULT IN MORE WIDESPREAD IMPACTS. THE MODELS ALSO
APPEAR TO BE CREATING MORE QPF ON SUNDAY...INCREASING THE
CONCERN THAT AMOUNTS AND IMPACTS COULD BE MORE SIGNIFICANT AS
WELL. IF THE GFS AND NAM VERIFY...WE COULD BE LOOKING AT A MORE
SIGNIFICANT ICE STORM OVER A LARGE PART OF THE CWA. HOWEVER...WITH
THIS BEING THE FIRST MODEL RUNS THAT SHOW THE COLDER TEMPERATURES
AND HIGHER QPFS...WILL KEEP THE AREA AND AMOUNTS OF SLEET THE SAME
FOR NOW AND CONTINUE TO MONITOR THE SITUATION. HAVE UPDATED THE
SPS OUTLOOK FOR SATURDAY NIGHT THROUGH MONDAY MORNING AND WILL
LIKELY ISSUE A WATCH TOMORROW. TEMPERATURES WILL START TO WARM ON
MONDAY DESPITE THE EXTENDED RAIN...AND THE FROZEN PRECIPITATION
WILL END MONDAY MORNING. THE UPPER LEVEL LOW IS MUCH SLOWER TO
PASS THE REGION AND EXTENDED POPS INTO TUESDAY.

[joshskeety]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
402 PM CST THU NOV 21 2013

.DISCUSSION...

ARCTIC FRONT CONTINUES TO MOVE QUICKLY TOWARD THE CWA AND WILL NOW
BE ARRIVING IN THE FAR NORTHWEST CORNER WITHIN THE NEXT HOUR. IN
THE SHORT TERM FORECAST...SPED UP THE FRONT ANOTHER HOUR THROUGH
THE OVERNIGHT PERIOD. OTHERWISE...NO SIGNIFICANT CHANGES WERE MADE
TO THE FORECAST FOR TONIGHT OR TOMORROW FROM THE UPDATE ISSUED
AROUND MIDDAY. WE WILL BE ISSUING A FREEZING RAIN ADVISORY
STARTING LATE TONIGHT AND CONTINUING THROUGH SATURDAY MORNING FOR
OUR WEST AND NORTHWEST COUNTIES. ACCUMULATIONS ARE EXPECTED TO BE
RELATIVELY LIGHT DESPITE THE DURATION OF THE EVENT. THE
RAIN/FREEZING RAIN WILL NOT BE CONTINUOUS THROUGHOUT THE PERIOD
BUT IMPACTS ON ELEVATED SURFACES SUCH AS BRIDGES AND OVERPASSES
CAN BE EXPECTED IN THE ADVISORY AREA. ALSO DRIVING THE DECISION TO
ISSUE THE ADVISORY IS THE FACT THAT IT IS A WEEKEND WITH MANY
PEOPLE STARTING THEIR HOLIDAY TRAVELS.

FRIDAY WILL BE A BITTERLY COLD DAY WITH STRONG NORTH WINDS KEEPING
WIND CHILLS IN THE TEENS TO LOWER 30S THROUGHOUT THE DAY. THE
STRONG WINDS AND LOW WIND CHILLS WILL CONTINUE INTO FRIDAY NIGHT.
WHERE FREEZING RAIN IS NOT OCCURRING...SCATTERED LIGHT RAIN AND
SHOWERS WILL CONTINUE THROUGH THE WEEKEND.

WE WILL SEE A BREAK IN THE FREEZING RAIN ON SATURDAY BEFORE THE
NEXT WINTER WEATHER EVENT BEGINS SATURDAY NIGHT. AS AN UPPER LEVEL
LOW APPROACHES FROM THE WEST...WARM AIR WILL LIFT OVER THE COLD
LAYER AT THE SURFACE PRODUCING MORE RAIN AND FROZEN PRECIPITATION.
IT STILL APPEARS SLEET WILL BE LIKELY OVER A GOOD PART OF THE
REGION WITH SIGNIFICANT ACCUMULATIONS POSSIBLE OVER OUR WESTERN
AND NORTHWESTERN COUNTIES. HOWEVER...BOTH THE LATEST RUNS OF THE
GFS AND NAM SUGGEST SURFACE TEMPERATURES DURING THE DAY ON SUNDAY
COULD BE CLOSER TO FREEZING OVER A GOOD PORTION OF THE REGION
WHICH COULD RESULT IN MORE WIDESPREAD IMPACTS. THE MODELS ALSO
APPEAR TO BE CREATING MORE QPF ON SUNDAY...INCREASING THE
CONCERN THAT AMOUNTS AND IMPACTS COULD BE MORE SIGNIFICANT AS
WELL. IF THE GFS AND NAM VERIFY...WE COULD BE LOOKING AT A MORE
SIGNIFICANT ICE STORM OVER A LARGE PART OF THE CWA. HOWEVER...WITH
THIS BEING THE FIRST MODEL RUNS THAT SHOW THE COLDER TEMPERATURES
AND HIGHER QPFS...WILL KEEP THE AREA AND AMOUNTS OF SLEET THE SAME
FOR NOW AND CONTINUE TO MONITOR THE SITUATION. HAVE UPDATED THE
SPS OUTLOOK FOR SATURDAY NIGHT THROUGH MONDAY MORNING AND WILL
LIKELY ISSUE A WATCH TOMORROW. TEMPERATURES WILL START TO WARM ON
MONDAY DESPITE THE EXTENDED RAIN...AND THE FROZEN PRECIPITATION
WILL END MONDAY MORNING. THE UPPER LEVEL LOW IS MUCH SLOWER TO
PASS THE REGION AND EXTENDED POPS INTO TUESDAY.

Yet at this time sounding for Ft. Worth westward show the warm nose at 875mb GONE... 0c at KFTW and -1 at KWEA.. That is the 18z NAM anyway.. Not sure how they can say sleet still unless they are talking about the other 2/3rd of the Metroplex..

[Longhornmaniac8]

So I'm looking at the 18Z GFS 850 mb output on the Wundermap, and I'm noticing there is a very steep temperature gradient between Austin and San Antonio (for example, at +75 hrs). Would it be an accurate interpretation to say that if the actual conditions deviated a slightly from this forecast one way or the other (that is, if the temperatures were off by 50 miles or so), that it would have profound impacts on the precipitation that fell?

If the 850 level is below freezing, and the surface temperatures are slightly above freezing, that's a candidate for sleet, yes? I'm still trying to wrap my head around all of the different atmospheric layers and their temperature profiles and what that means as far as falling precip.

Thanks,
Cameron

[Jarodm12]

00z guidance will be really important tonight i cant wait

[TeamPlayersBlue]

Oh man, that NAM run is incredible hahaha wow. Thats ALOT of precip. This could be the most epic snow event for you guys.

[orangeblood]

Still a warm layer on the latest NAM and GFS Skew T's for FTW and DFW, 2-3 deg C in the 700-825 mb levels.....heck of a sleet storm if that were to verify

[joshskeety]

So I'm looking at the 18Z GFS 850 mb output on the Wundermap, and I'm noticing there is a very steep temperature gradient between Austin and San Antonio (for example, at +75 hrs). Would it be an accurate interpretation to say that if the actual conditions deviated a slightly from this forecast one way or the other (that is, if the temperatures were off by 50 miles or so), that it would have profound impacts on the precipitation that fell?

If the 850 level is below freezing, and the surface temperatures are slightly above freezing, that's a candidate for sleet, yes? I'm still trying to wrap my head around all of the different atmospheric layers and their temperature profiles and what that means as far as falling precip.

Thanks,
Cameron

Depends on how deep the warm layer is.. If it is really shallow say from 825-830mb then yes that would be sleet, but if its a deep warm layer say 800mb-875mb that would suggest freezing rain..

[aggiecutter]

Afternoon AFD from the NWS office in Shreveport:

"HOWEVER...COMPLEXITIES ABOUND FOR OUR FCST FOR SUNDAY/MONDAY...AS
MOISTURE SURGES BACK INTO THE REGION AHEAD OF A CUT OFF LOW THAT
WILL BEGIN TO EJECT EWD SUNDAY. WARM/MOIST MID AND UPPER LEVEL SW
FLOW IS EXPECTED TO OVERRUN COLD AIR AT THE SFC...SETTING UP THE
POSSIBILITY FOR FROZEN PRECIP. MODEL SOUNDINGS FROM BOTH THE GFS
AND NAM SUPPORT THIS SCENARIO...MAINLY FOR AREAS IN THE I-30
CORRIDOR AND NWD FOR SUNDAY AFTERNOON THROUGH EARLY MONDAY
MORNING"

[joshskeety]

Still a warm layer on the latest NAM and GFS Skew T's for FTW and DFW, 2-3 deg C in the 700-825 mb levels.....heck of a sleet storm if that were to verify

Though NAM at KWEA (Weatherford) shows only +.1 at 825mb on the latest NAM.. Of course, 1.0 from 750mb and above, but thats pretty high up there..

That is just to the west and is getting colder on every run.. Wouldn't surprise me at all that somewhere northwest of Jacksboro someone gets a heck of a SNOW storm...

[srainhoutx]

Folks there is a lot of severe weather breaking out across SE Texas into the Dallas/Ft Worth area. Reports of a wall could spotted just N of the Texas A & M Campus, so don't forget the severe side of this incoming storm system.

[Portastorm]

So I'm looking at the 18Z GFS 850 mb output on the Wundermap, and I'm noticing there is a very steep temperature gradient between Austin and San Antonio (for example, at +75 hrs). Would it be an accurate interpretation to say that if the actual conditions deviated a slightly from this forecast one way or the other (that is, if the temperatures were off by 50 miles or so), that it would have profound impacts on the precipitation that fell?

If the 850 level is below freezing, and the surface temperatures are slightly above freezing, that's a candidate for sleet, yes? I'm still trying to wrap my head around all of the different atmospheric layers and their temperature profiles and what that means as far as falling precip.

Thanks,
Cameron

Sleet, I think, depends on more than just the 850mb level being below freezing but 700mb level as well. And you've got to have a warm layer aloft sandwiched by below freezing layers. Freezing rain requires nothing more than surface temps below 32 degrees Farenheit.

Here's a fairly good resource, albeit a bit technical:

http://www.theweatherprediction.com/winterwx/thicknesscriteria/

[Jarodm12]

is the front slowing down?

[joshskeety]

So I'm looking at the 18Z GFS 850 mb output on the Wundermap, and I'm noticing there is a very steep temperature gradient between Austin and San Antonio (for example, at +75 hrs). Would it be an accurate interpretation to say that if the actual conditions deviated a slightly from this forecast one way or the other (that is, if the temperatures were off by 50 miles or so), that it would have profound impacts on the precipitation that fell?

If the 850 level is below freezing, and the surface temperatures are slightly above freezing, that's a candidate for sleet, yes? I'm still trying to wrap my head around all of the different atmospheric layers and their temperature profiles and what that means as far as falling precip.

Thanks,
Cameron

Sleet, I think, depends on more than just the 850mb level being below freezing but 700mb level as well. And you've got to have a warm layer aloft sandwiched by below freezing layers. Freezing rain requires nothing more than surface temps below 32 degrees Farenheit.

Here's a fairly good resource, albeit a bit technical:

http://www.theweatherprediction.com/winterwx/thicknesscriteria/

Yea, but lets be honest.. 32 degrees when Ground temps are in the 50's and 60's isn't much to worry about minus overpasses and bridges.. But you are correct, it is technically freezing rain.. However, the fact that it will be in the 30's from Tomorrow onward in much of Central or North Texas for nearly 3 days before this big event starts could spell ground temps much lower than that..

Just something to think about...

[dhweather]

The fine folks at FWD have a graphic up on their web page that will help explain the layers for you.

[gboudx]

Update from Jeff. I don't know what areas he's referring to when he says NTX. I assume mostly from west of Ft. Worth to Abilene to Lubbock but not sure.

Arctic boundary is blasting southward this afternoon and has cleared the panhandle and is pushing toward NC TX. Temperatures behind the boundary are falling rapidly into the 40’s with upstream air mass near Amarillo now in the upper 20’s winds NW winds of 30-45mph.

Will speed up frontal timing to reach our NW counties prior to sunrise and push off the coast by midday. Temperatures will quickly fall into the 40’s during the afternoon hours under strong cold air advection regime and then fall into the upper 30’s Friday night.

Surface temperatures should remain above freezing across all of SE TX precluding freezing rain Friday night into Saturday, but freezing rain is becoming increasing likely with potential for glazing of bridges and overpasses NW of our area from roughly Fort Worth to W of Waco to NW of Austin.

Models continue to come in slightly faster and a touch colder with the winter storm to affect the state late in the weekend into early next week. Latest guidance is suggesting the potential for a prolonged ice/sleet storm across much of N TX into the Hill Country starting Sunday morning and continuing into midday Monday with significant impacts. Our northern counties are getting very close to being on the edge of the potential rain/sleet line and would not be surprised if models come in a degree or two colder that sleet would be possible Sunday night into Monday morning N of a line from Livingston to College Station. Still expect surface temperatures to remain above freezing in this region, but that could be a close call also with current forecasted lows in the 34-36 range only a slight bit of additional cooling could result in some icing.

Metro Houston area will be cold but all liquid and in fact depending on the track of the coastal surface low…a few strong/severe storms could be possible near the coast as this very dynamic weather system pushes across on Monday into Tuesday.

Best to go ahead and lower temperatures through the entire period. Suspect from Friday night-Tuesday night temperatures will range from the mid 30’s to mid 40’s. Some locations may very well stay in the 30’s the entire time from early Saturday through early Tuesday.

Note: Numerous winter weather and winter storm advisories/watches will be issued over the next 12-24 hours to cover the upcoming winter storm impacts across the state for this weekend into early next week. Persons with travel plans to areas west of I-35 this weekend should be fully aware of the potential for impacts to both surface and aviation travel due to ice.

[Jarodm12]

rap isnt even initializing the first hour correctly as our temps in the south pan handle all the way to Oklahoma city are at or below freezing? am i missing something?

[Ntxw]

The NAM is overdoing it I believe especially when you are looking at snowfall. What the models are likely portraying is heavy sleet, we're not going to get 2 feet of snow. Best snow areas is under the low for a period Monday or Tuesday if the low is deep enough but I agree it will be a heck of a sleet storm with the heaviest precip riding up I-35 and where it meets the freeze line, plot soundings support sleet and ice pellets From Northeast Texas, Waco, to Dallas, to the Hill country on west. This heavier precip probably is misleading so models like the NAM is revealing it as snow.

If it were up to me I would definitely consider winter storm watches for everyone in the list mentioned above.

Edit: Looking at the categorical type of precip falling from the NAM most of it is sleet with snow confined to NW Texas and Oklahoma

[Jarodm12]

Ntxw, im in Waco visiting where do we sit in your opinion?

[Ntxw]

Ntxw, im in Waco visiting where do we sit in your opinion?

Waco is on the edge most likely if you were to believe the NAM and extent Euro. I wouldn't be surprised if sleet fell there but just to your west and NW would probably see some hefty accumulating sleet and/or snow.

There will be very heavy precip falling with perhaps thunderstorms involved overrunning the cold dome which is something I'm not familiar with and may play some kind of role.