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Texas/New Mexico/Louisiana/Mexico Obs And Discussion Thread Part 5

wxmx

By wxmx,
in Central/Western States

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bubba hotep

bubba hotep

Posted
Posted

FWD issuing an update to expand the Watch area to cover most of DFW:

 

image1.gif

 

Great discussion with the update:

 

000
FXUS64 KFWD 040315
AFDFWD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
915 PM CST TUE DEC 3 2013

.UPDATE...
THE MAIN UPDATE ISSUE OF INTEREST IS THAT WE HAVE EXPANDED THE
WINTER STORM WATCH TO COVER THE NW HALF OF NORTH TEXAS. BUT FOR
TONIGHTS FORECAST HAVE LOWERED TEMPERATURES IN A FEW AREAS WHERE
DRY AIR AND GOOD RADIATIONAL COOLING ARE EXPECTED. HAVE ALSO ADDED
A MENTION OF FOG TO THE EAST AND SOUTHEAST ZONES WHERE
TEMPERATURES WILL COOL TO REACH THE DEWPOINTS.

WITHOUT EVEN LOOKING AT THE MODEL DATA THE 0Z UPPER AIR ANALYSIS
FOREBODES AN OMINOUS SETUP FOR WINTER WEATHER FOR NORTH TEXAS. THE
UPPER PATTERN SUGGESTS THAT AT SOME POINT IN THE NEXT FEW
DAYS...EITHER THURSDAY NIGHT/FRIDAY AND/OR THIS WEEKEND THE
COMBINATION OF COLD AIR AND MOISTURE/LIFT ARE GOING TO COME INTO
PLAY TO CREATE A WINTRY MIX OVER MUCH OF THE AREA.

WHILE SURFACE TEMPS ARE THE GO-TO FOR SEEING HOW COLD AN AIR MASS
IS...IT IS ACTUALLY BETTER TO ANALYZE THE LOW-MID LEVEL TEMPS
UPSTREAM TO SEE HOW COLD THE AIR IS THERE. THIS IS BECAUSE AIR
BEHIND A COLD FRONT UNDERGOES SLOW SUBSIDENCE AS IT MAKES ITS WAY
SOUTH FROM THE ARCTIC. BACKWARD TRAJECTORIES OF PAST COLD FRONTS
SHOW US TO CHECK 500-700MB TEMPS IN THE ARCTIC REGION SEVERAL DAYS
OUT...AND 700-850MB TEMPS ACROSS SOUTHERN CANADA 2 TO 3 DAYS OUT
TO GET A ROUGH IDEA ON HOW COLD IT IS GOING TO GET. THUS IT IS
CONCERNING THAT THE UPPER AIR ANALYSIS FROM 00Z REVEALS
EXCEPTIONALLY COLD AIR AT 700MB-850MB ACROSS MONTANA AND INTO
ALBERTA. GREAT FALLS MONTANA HAD A 700MB TEMP OF -24C AND -20C AT
850MB. THESE TEMPS ARE RUNNING 2 TO 3 STANDARD DEVIATIONS BELOW
NORMAL...WHICH IS AKIN TO SAYING THIS WOULD BE NEAR RECORD COLD
IF WE KEPT RECORDS AT THIS POINT IN SPACE. MODEL GUIDANCE HAS BEEN
2-4 DEG C TOO WARM WITH 6-12 HOUR FORECAST TEMPS AT THIS LEVEL AS
WELL...BUT IS BEGINNING TO CATCH ON.

MEANWHILE THE SURFACE ANALYSIS IS SHOWING THE COLD FRONT
BARRELING SOUTH THROUGH THE PLAINS...AND AHEAD OF SCHEDULE...NOW
CROSSING THROUGH MOST OF WESTERN KANSAS. ALL MODELS EXCEPT FOR THE
RAP/NAM ARE MUCH TOO SLOW IN THEIR 3-6 HOUR FORECASTS. THIS IS A
COMMON ISSUE WITH ARCTIC FRONTS WHEN THE 500MB PATTERN IS SITUATED
IN THIS FASHION. LEE SIDE COLD AIR DAMMING IN THE FRONT RANGE OF
THE ROCKIES CAUSES THE SURFACE HIGH TO BUILD FARTHER SOUTH AND
ALLOWS FOR STRONGER EQUATOR-WARD TRANSPORT OF ARCTIC AIR THAN
FORECAST. HIGH RESOLUTION MODELS DO A BETTER JOB AT FORECASTING
THIS...AND THE NAM/WRF MODELS ARE ABOUT THE BEST WE HAVE IN THE
SHORT-MEDIUM TIME RANGE. THE RAP IS EXCELLENT IN THIS SITUATION AS
WELL...BUT ONLY GOES OUT 18 HOURS. THE NAM AND RAP MODELS ARE
INDICATING THE FRONT WILL REACH THE NORTHWEST ZONES AFTER
SUNRISE...AND WILL LIKELY STALL ALONG OR JUST NORTH OF THE I-20
CORRIDOR WEDNESDAY AFTERNOON. THE AIR BEHIND THIS FRONT WILL BE
VERY SHALLOW...AND SUNSHINE WILL MODERATE THE LEADING EDGE OF THIS
AIR GREATLY. THUS HAVE BUMPED UP THE TIMING OF THE FRONT SEVERAL
HOURS AND LOWERED HIGHS INTO THE 60S IN THE NORTHERN ZONES.
WOULD NOT BE SURPRISED TO SEE THE FRONT MOVE THROUGH THE METROPLEX
IN THE AFTERNOON HOURS BUT AGAIN...THE CHANGE IN TEMPS AND WINDS
WILL NOT BE ALL THAT DRASTIC AT FIRST. THE REAL COLD AIR WILL
GRADUALLY INVADE THE REGION THROUGH THE OVERNIGHT HOURS.

THE NEW 00Z NAM HAS COME IN COLDER THURSDAY...AND ESSENTIALLY ALL
GUIDANCE BUT THE SREF IS INDICATING TEMPERATURES NEAR FREEZING
ACROSS THE NORTHWEST ZONES THURSDAY AFTERNOON AS PRECIPITATION
BEGINS TO DEVELOP. SINCE THE AIR IS SO COLD UPSTREAM IN THE SOURCE
REGION...AND THESE FRONTS TEND TO RUN A LITTLE COLDER THAN
MODEL FORECASTS...HAVE BUMPED UP THE TIMING OF THE FREEZING RAIN
AND WINTER STORM WATCH TO THURSDAY AFTERNOON OVER THE NORTHWEST
ZONES. IT IS TOO TOUGH TO SAY WHETHER IMPACTS WILL BEGIN
IMMEDIATELY THURSDAY AFTERNOON...BUT FELT THAT THE WATCH STARTING
AT 0Z WAS CUTTING IT TOO CLOSE.

AGAIN THERE IS GOOD MODEL AGREEMENT REGARDING THE FORECAST FOR
THURSDAY NIGHT AND FRIDAY. HAVE NOT CHANGED ANY OF THE FORECASTED
SENSIBLE WEATHER FROM THE PREVIOUS FORECAST AS IT ALL LOOKS
GOOD. HOWEVER...THERE MAY END UP BEING MORE SLEET THAN FREEZING
RAIN OVER THE NORTHWEST ZONES BUT IT IS TOO EARLY TO TELL FOR
SURE. HOWEVER PLACING A PERCENT LIKELIHOOD OF WINTER STORM WARNING
CRITERIA BEING MET IS TOUGH AT THIS POINT. WPC NOW INDICATES THE
DFW METROPLEX AND NORTHEAST INTO PARIS HAVE A 50-60 PERCENT CHANCE
OF A QUARTER INCH OF ICE ACCUMULATION THURSDAY NIGHT AND FRIDAY
MORNING. WATCH CRITERIA THRESHOLD IS A 50 PERCENT CONFIDENCE LEVEL
WHILE WARNING IS 80 PERCENT. SO GOING BY THIS PIECE OF GUIDANCE WE
SHOULD ISSUE A WATCH NOW. HOWEVER IT IS CONCERNING THE SREF IS
STILL FORECASTING A MARGINAL FREEZING RAIN EVENT FOR THIS REGION
WHICH LOWERS OUR CONFIDENCE. IT IS ALSO CONCERNING THAT THE WARM
NOSE WILL BE VERY WARM...AND RAIN DROPS WILL LIKELY TRANSPORT WARM
AIR TO THE SURFACE...WHICH WOULD INHIBIT ICE ACCUMULATION AND
IMPACTS. ON THE FLIP SIDE IT IS VERY CONCERNING THAT THE AIR
TEMPERATURES MAY STAY BELOW FREEZING FOR MUCH OF THE CWA FRIDAY
AND SATURDAY WITH CLOUDY SKIES. THIS MEANS IF ICE AND/OR SLEET IS
SIGNIFICANT THURSDAY NIGHT AND FRIDAY MORNING...ICE ON ROADS MAY
LINGER INTO SATURDAY OR SUNDAY WHEN COINCIDENTALLY ANOTHER SHOT AT
WINTER PRECIP ARRIVES. THE ISSUE IS THAT THIS EVENT UNLIKE THE
LAST MARGINAL/NON-EVENT DOES HAVE THE POTENTIAL FOR PROLONGED
WINTRY IMPACTS WHICH IS MORE REASON TO RAISE PUBLIC AWARENESS NOW
AND GO AHEAD AND EXPAND THE WATCH SOUTHEASTWARD TO INCLUDE MORE
AREA.

NOTE THIS DOES NOT MEAN THE ENTIRE WATCH AREA WILL BE UPGRADED TO
A WARNING...BUT AT THIS POINT WE BELIEVE THE ENTIRE WATCH AREA
WILL BE IN AT LEAST A WINTER WEATHER ADVISORY THURSDAY NIGHT AND
FRIDAY MORNING. IT IS TOO EARLY TO FINE TUNE ACCUMULATION AMOUNTS
OR ENTERTAIN WHO WILL SEE WHAT IMPACTS...AND THOSE WILL COME LATER
AS CONFIDENCE INCREASES FURTHER.

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DFWWeather

DFWWeather

Posted
Posted

Much of Texas to take a direct discharge of Arctic air Monday. Full blown McFarland signature to 500mb pattern. Perhaps the coldest air in nearly 20 years at DFW. Lows next Wednesday morning could be in the single digits. Both ECWMF and GFS are showing just that. GFS had 15 below zero in parts of central Oklahoma.

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Ed Lizard

Ed Lizard

Posted
Posted

Dallas area (my Mom lives in Bedford) New 6Z GFS much wetter, and when it is really starting to pour down midnight Friday morning/Thursday night, that is a stout warm nose, that is a liquid sounding, not a sleet sounding.  Verbatim, still liquid rain at this point, surface just reaching freezing.  But there'll probably be a healthy amount of the 3/4" liquid equivalent falling in the following six hours that will coat trees, power lines and overpasses before possibly changing to sleet.

 

The warm ground and all, I'd bet even below freezing at 2 meters, it'll stay water for a while on the ground and streets, some will run off or absorb into the ground, but the trees and power lines wouldn't take too long to cool to freezing, then the rural overpasses, then the untreated surface streets, again, almost certainly in time to cancel school Friday.

 

post-138-0-38462800-1386164722_thumb.gif

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msp

msp

Posted
Posted

That doesn't help.

Now, 6Z GFS holds out some hope for class cancellations (final exam week seemed to be about this time, IIRC) mid week CLL and AUS.

Final exams here at A&M are from this Fri through next Wed (I've got a killer Data Methods final on Wed I'd love to get out of). Unfortunately, I've also got to fly up to MN next Thurs through DFW.

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wxmx

wxmx

Posted
  • Author
Posted

Second wave will be colder than modeled, I suspect (and it's modeled as very cold as of now). 500mb pattern, snow cover and dense arctic cold air all suggest that models are still in catchup mode, which is usual with most severe arctic shots.

 

The 500mb pattern goes from a severe -EPO pattern to strongish west coast ridging, the best pattern to shepherd arctic cold air south. There's a modeled short wave coming south from the backside of the trough at the time, elongating and giving the trough a more positive tilt, which would strengthen the STJ and moisten the atmosphere. The modeled air is very dry, so it would need a strong s/w to direct enough moisture for wintry precipitation. A NW MX ULL slowly ejecting ENE wouldn't hurt :P

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1900hurricane

1900hurricane

Posted
Posted

Yeah, next week's shot looks like it could be very cold to me. FWD mentioned that models seemed to be having a somewhat difficult time grasping the intensity of the cold air for this go around, and I imagine it'll be the same for next week.

 

Interestingly enough, mid-range guidance is hinting at a bit of shortwave energy being left behind from the full-latitude trough. I'm not really expecting much of it at the moment, but with the very cold air in place, it could be something to watch for.

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Srain

Srain

Posted
Posted

Second wave will be colder than modeled, I suspect (and it's modeled as very cold as of now). 500mb pattern, snow cover and dense arctic cold air all suggest that models are still in catchup mode, which is usual with most severe arctic shots.

 

The 500mb pattern goes from a severe -EPO pattern to strongish west coast ridging, the best pattern to shepherd arctic cold air south. There's a modeled short wave coming south from the backside of the trough at the time, elongating and giving the trough a more positive tilt, which would strengthen the STJ and moisten the atmosphere. The modeled air is very dry, so it would need a strong s/w to direct enough moisture for wintry precipitation. A NW MX ULL slowly ejecting ENE wouldn't hurt :P

Heh...

 

 

 

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DFWWeather

DFWWeather

Posted
Posted

 

Well, if the models are underestimating the above. There is no hope! ECMWF is down to 3°F for DFW for next Wednesday morning which is only 5 degrees shy of the all time record for the month of -1°F. If single digits verify, it would be the earliest date ever recorded of single digit temperatures for DFW. Not to mention finally breaking the 18 year long stretch of no single digit temps.

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DFWWeather

DFWWeather

Posted
Posted

I don't know how the web site wxmaps.org generates p-types on its meteograms, but almost an inch of freezing rain in DFW is a *big story*.

 

That would mean several days of going nowhere. Looks like temps may not even climb above freezing on Monday, if so, just barely, not enough to melt something like that.

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bubba hotep

bubba hotep

Posted
Posted

Don't trust 18z gfs - no ensemble support. Will wait for 0z nam before beginning to worry. This cold airmass has been busting numbers, so dont think it will be like last time. Also noticed warm nose may be too high up for heat transfer to surface and perhaps more sleet may be involved than we think.

 

 

FWD sounds like they are going to go "all in" on this after being pretty conservative in their discussions the last couple of days.  Evening update sounds pretty ominous for us up here in the northern burbs:

 

000

FXUS64 KFWD 050328

AFDFWD

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE FORT WORTH TX

928 PM CST WED DEC 4 2013

.UPDATE...

THE EVENING BALLOON DATA HAS BEEN ANALYZED AND AT 850MB IT

INDICATES VERY COLD AIR ACROSS THE PLAINS IS NOW POURING SOUTH.

DODGE CITY REPORTED -10C AT 850MB AND NORTH PLATTE HAD -17C WITH

NORTH WINDS AT 25 TO 30 KNOTS. SURFACE WINDS AND PRESSURES WERE

NOW RISING TO OUR NORTHWEST...IN RESPONSE TO THE VERY STRONG COLD

ADVECTION OCCURRING ABOVE THE SURFACE. TEMPERATURES AT 850MB

ACROSS THE PLAINS GIVE A BETTER INDICATION OF WHAT OUR SURFACE

TEMPERATURES WILL BE THAN THE CURRENT SURFACE TEMPERATURES THERE

DO. THIS IS BECAUSE THE AIR BEHIND A COLD FRONT UNDERGOES GRADUAL

SUBSIDENCE BEFORE IT REACHES THE SURFACE AT A GIVEN LOCATION.

850MB IS A GREAT LEVEL TO ANALYZE ACROSS KANSAS AND NEBRASKA FOR

AN APPROXIMATION OF WHAT OUR SURFACE TEMPS WILL BE HERE. ASSUMING

ONLY ADIABATIC COMPRESSIONAL WARMING TAKES PLACE .../I.E. NO

SUNSHINE/RADIATIVE/LATENT HEAT CHANGES OCCUR/... THE -10C

EXTRAPOLATES TO SURFACE TEMPS IN THE MID 30S F AND THE -17C TO MID

20S F. THIS AIR WILL ARRIVE INTO OUR AREA THURSDAY AND THURSDAY

NIGHT. ALSO OF NOTE...THE 6-12 HOUR OLD FORECASTS FROM THE

GFS/SREF/NAM WERE 2-4 DEG C TOO WARM AT 850MB ACROSS THE PLAINS.

ALL OF THIS RAISES OUR CONFIDENCE THAT MOST OF THE MODELS CONTINUE

TO UNDERESTIMATE THE SPEED OF THIS COLD AIR AND THAT THE COLDER

TEMPS ARE LIKELY TO ARRIVE EARLIER.

THE RAP HAS SO FAR DONE AN EXCELLENT JOB WITH THIS FRONT AND IT IS

FORECASTING THE FRONT TO CLEAR THE SOUTHERN CWA BY SUNRISE. AS A

RESULT HAVE LOWERED TEMPERATURES SIGNIFICANTLY ACROSS THE SOUTHERN

ZONES FOR LOWS TONIGHT AND HIGHS TOMORROW. THE RAP IS ALSO

FORECASTING THE FREEZING LINE TO REACH THE I-20 CORRIDOR BY MIDDAY

TOMORROW. MEANWHILE A BAND OF PRECIPITATION WILL DEVELOP AND

STREAM ACROSS THE NORTHWESTERN AND NORTHERN ZONES. MOST OF THIS

PRECIP WILL ORIGINATE ABOVE 700MB OR ABOUT 10000 FEET WHICH WILL

LIMIT ITS INTENSITY. FURTHERMORE THE AIR BELOW IT WILL BE VERY DRY

AND SOME OF THIS PRECIP WILL BE LOST TO EVAPORATION BEFORE IT CAN

REACH THE SURFACE. NONETHELESS IT IS LIKELY THAT PRECIP WILL REACH

THE GROUND ACROSS THE NORTHWEST AND NORTHERN ZONES AND EVAPORATIVE

COOLING WILL PUSH SURFACE TEMPS INTO THE 20S. WHILE GROUND

SURFACES ARE STILL VERY WARM...TEMPS IN THE 20S AND WINDS OF 15

MPH WILL BE ENOUGH TO COOL ELEVATED SURFACES/BRIDGES BELOW

FREEZING TO START ACCUMULATING ICE BY THE AFTERNOON HOURS. THE

WINTER STORM WARNING BEGINS AT NOON IN THE AREA ALONG AND NORTH OF

A CISCO TO WEATHERFORD TO SHERMAN LINE AND THIS REGION MAY BEGIN

TO SEE IMPACTS BY AFTERNOON.

FARTHER SOUTH ACROSS THE I-20 CORRIDOR...FREEZING TEMPERATURES ARE

POSSIBLE BY AFTERNOON...BUT PRECIPITATION COVERAGE AND INTENSITY

BECOMES A LITTLE MORE QUESTIONABLE. EITHER WAY FEEL THAT IT IS TOO

LOW OF A RISK FOR IMPACTS TO BRING THE WARNING INTO THE AFTERNOON

HOURS...EVEN THOUGH LIGHT FREEZING RAIN MAY BEGIN TO SHOW UP ON

CARS AND TREES BY THE AFTERNOON RUSH.

THE ONLY CHANGES TO THE PREVIOUS FORECAST FOR THURSDAY NIGHT AND

FRIDAY WERE TO INCREASE ICE ACCUMULATION AMOUNTS NORTH OF I-20.

CONFIDENCE CONTINUES TO INCREASE THAT SIGNIFICANT ICE ACCUMULATION

FROM FREEZING RAIN WILL OCCUR AS TEMPERATURES SHOULD DROP INTO THE

MID TO UPPER 20S AS A LARGE AREA OF MODERATE PRECIPITATION MOVES

INTO THE REGION. EVEN DESPITE THE VERY WARM TEMPERATURES ALOFT AND

RAIN DROPS THAT WILL LIKELY BE A FEW DEGREES ABOVE FREEZING WHEN

THEY REACH THE GROUND...STRONG COLD/DRY ADVECTION WILL BE ONGOING

DURING THIS EVENT WHICH SHOULD KEEP TEMPERATURES BELOW FREEZING

AND LIKELY IN 20S ACROSS THE WARNING AREA. WE ARE PARTICULARLY

CONCERNED ABOUT DENTON...COLLIN...COOKE...GRAYSON...AND FANNIN

COUNTIES WHERE THE JUXTAPOSITION OF HIGH AMOUNTS OF FREEZING RAIN

AND TEMPERATURES IN THE MID TO UPPER 20S WILL OCCUR. SIGNIFICANT

ICING OF TREES IN THIS AREA WOULD LEAD TO LIMB BREAKAGE AND POWER

OUTAGES THAT MAY LAST FOR DAYS IN SOME COMMUNITIES. FURTHERMORE

NOT ALL TREES HAVE LOST THEIR LEAVES YET WHICH WILL ADD TO TREE

LIMB STRESS DUE TO THE WEIGHT OF MORE ICE. MORE SLEET IS POSSIBLE

FOR THE NORTHWESTERN ZONES WHICH SHOULD LIMIT ICE ACCUMULATION ON

TREES AND HOPEFULLY MITIGATE DAMAGE TO THE POWER GRID BUT IT IS A

TOUGH CALL. ACROSS THE REMAINDER OF THE WARNING AREA...AND

ESPECIALLY ALONG AND NORTH OF I-20...SIGNIFICANT TRAVEL

DISRUPTIONS WILL OCCUR FROM ICE ON ROADS. ICE MAY LINGER FOR DAYS

AS SKIES STAY CLOUDY AND TEMPERATURES REMAIN BELOW FREEZING.

ANOTHER SHOT AT SLEET AND FREEZING RAIN WILL OCCUR ON SATURDAY

AFTERNOON AND NIGHT.

WILL BE UPDATING THE WINTER STORM WARNING TO INCREASE THE

SEVERITY OF THE WORDING AND IMPACTS ACROSS THE NORTHERN AND

NORTHWESTERN ZONES.

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DoctorMu

DoctorMu

Posted
Posted

The usual models are only beginning to catch up with the ferocity and reinforcements of this arctic blast.  We had a wind shift from the SW to WSW about 11:10 pm without a perceptible drop in temp or dewpoint...yet.   Our 06Z OT model had the fastest run I've ever seen...


 


...in through the front door at an unprecedented speed.  Logging a regression of speed vs. drop in temperature over the course of the week, the predicted low next Tuesday night is 18°F in CLL


 


 


 


 


OT = orange tabby  


 


 


 


Seriously, that's the fastest I've ever seen a 13 year old cat as fat and generally lazy as Garfield run


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bubba hotep

bubba hotep

Posted
Posted

Is your "bust" sensor going off, hotep? Mine isn't. When they're talking about thunder in the mid twenties. it feels like the real deal.

Just to be safe I bought groceries and firewood.

Down to 34, IMBY, it looks like temp drops are still ahead of schedule. I'm wondering if we can possibly squeeze out some sleet and cut down on ice accumulation tonight.

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