Texas Winter 2014-2015

[ronyan]

Excellent discussion for the Dallas area by Cavanaugh. I just got the chance to read it.

TAKING A STEP BACK FROM LOCAL AREA WEATHER...ELSEWHERE ON
SUNDAY...A STRONG UPPER TROUGH IS EXPECTED TO DIG SOUTH ACROSS
WESTERN CANADA AND MOVE OVER THE NORTHERN CONUS ROCKIES. THIS IS
IN RESPONSE TO A VERY STRONG UPPER LEVEL RIDGE THAT ALL MODEL
GUIDANCE INDICATES WILL AMPLIFY OVER THE YUKON AND OVER THE
ALASKA/CANADIAN BORDER. CONFIDENCE IN THIS PATTERN VERIFYING IS
HIGH AT THIS TIME AS THE NAEFS AND ECMWF ENSEMBLE MEANS ALL
STRONGLY POINT TO THIS SOLUTION. THE UPPER TROUGH APPEARS TO BE
STRONG...AND WAS LOCATED SOUTH OF DUTCH HARBOR ALASKA EARLY THIS
AFTERNOON PER WATER VAPOR SATELLITE IMAGERY.

ASSUMING THIS STRONG UPPER TROUGH MOVES OVER THE YUKON...AND THEN
DIVES SOUTH AS UPPER RIDGING AMPLIFIES THIS WEEKEND...THIS APPEARS
TO BE A VERY FAVORABLE LARGE SCALE UPPER AIR PATTERN THAT WILL
RESULT IN AN ARCTIC OUTBREAK FOR THE SOUTHERN PLAINS NEXT WEEK.
THE CONSENSUS OF 12Z MODEL GUIDANCE CERTAINLY SEEMS TO SUPPORT
THIS SOLUTION...SO THINK THAT THE POTENTIAL FOR ARCTIC AIR TO
BUILD ACROSS THE SOUTHERN PLAINS ON TUESDAY IS VERY HIGH AT THIS
TIME. THE STRENGTH OF THIS ARCTIC AIRMASS...ONCE IN PLACE...WILL
HAVE A LARGE IMPACT ON THE FORECAST FOR NEW YEAR`S EVE AND DAY AS
PRECIPITATION IS EXPECTED TO BEGIN TO BUILD OVER THE REGION ABOUT
24 HOURS AFTER THIS ARCTIC AIR IS IN PLACE.

MODELS SEND A SHALLOW ARCTIC AIRMASS SOUTH ALONG THE HIGH PLAINS
RAPIDLY MONDAY NIGHT INTO TUESDAY MORNING. THIS AIRMASS IS THEN
EXPECTED TO BUILD A BIT SLOWER TO THE EAST...ALMOST SPREADING
ITSELF FROM WEST TO EAST ACROSS THE CWA INSTEAD OF RUSHING IN
BEHIND A WELL DEFINED FRONTAL BOUNDARY. MODELS INDICATE THAT THIS
AIRMASS WILL SEND TEMPERATURES BELOW FREEZING FOR MOST LOCATIONS
BY WEDNESDAY MORNING...HOWEVER THIS COULD OCCUR MUCH FASTER IF
MODELS ARE UNDER DOING THE STRENGTH OF THE SHALLOW ARCTIC AIRMASS.
THIS IN SHORT IS THE PRIMARY FORECAST CHALLENGE MOVING FORWARD...
HOW STRONG AND EXPANSIVE WILL THE ARCTIC AIR BE WHEN IT MOVES INTO
THE REGION ON TUESDAY?

THE LOW-LEVEL AIRMASS THAT MOVES OUR WAY APPEARS TO BE IN NORTHERN
CANADA RIGHT NOW. MODELS ARE CURRENTLY DOING A DECENT JOB HANDLING
LOW-LEVEL TEMPERATURES THERE FOR NOW...BUT THAT DOES NOT MEAN
MODELS ARE NOT UNDER-FORECASTING THE STRENGTH OF THE COLD AIR
ONCE IT ARRIVES IN TEXAS. THE LOW-LEVEL CANADIAN AIRMASS WILL
MODIFY AS IT MOVES SOUTH ACROSS THE PLAINS EARLY NEXT WEEK...BUT
BY HOW MUCH? ONE OF THE KEY INGREDIENTS TO LOOK FOR IN TERMS OF
ARCTIC AIRMASS MODIFICATION POTENTIAL IS MODEL MID-LEVEL WIND
FIELDS. STRONG WESTERLY MID-LEVEL FLOW OVER THE ROCKIES BEHIND AN
ARCTIC AIRMASS WILL TEND TO ADIABATICALLY WARM THE ARCTIC AIR AS
IT MOVES SOUTH. THIS IS SIMPLY DUE TO WARMING AIR ASSOCIATED WITH
DOWNSLOPE WINDS IN THE LEE OF THE ROCKIES. AT THIS TIME...WHILE
THE ARCTIC AIRMASS IS MOVING SOUTH MONDAY AND TUESDAY...MOST
MODELS SHOW WEAK 700 MB FLOW...BUT MAYBE MORE
IMPORTANTLY...SUGGEST EASTERLY WINDS AS OPPOSED TO WESTERLY WINDS.
EASTERLY MID-LEVEL WINDS WILL TEND TO HELP KEEP THE ARCTIC AIRMASS
COLD BY PROVIDING CLOUD COVER AND COLD AIR DAMMING AGAINST THE
HIGH TERRAIN WHICH MAY ACTUALLY SPEED THE ARCTIC AIR UP. THE 12Z
ECMWF SOLUTION SEEMED TO HANDLE THIS PROCESS THE BEST...SO WENT
AHEAD AND NUDGED THE FORECAST TOWARDS THIS SOLUTION FOR TUESDAY
THROUGH THURSDAY.

IN GENERAL THE ECMWF SOLUTION IS A BIT FASTER WITH THE ARRIVAL OF
THE ARCTIC AIR ON TUESDAY...AND IS COLDER IN GENERAL WITH THE
FORECAST ONCE THE ARCTIC AIR IS IN PLACE. BOTH THE ECMWF AND GFS
INDICATE THAT THE DUTCH HARBOR UPPER TROUGH WILL CLOSE OFF INTO AN
UPPER LEVEL LOW OVER SOUTHERN CALIFORNIA BY TUESDAY NIGHT.
ASSUMING THIS OCCURS...THIS WOULD RESULT IN SOUTHWEST FLOW ALOFT
OVER THE SOUTHERN PLAINS...WHICH WOULD INDUCE A LONG PERIOD OF
WARM AIR ADVECTION OVER THIS SHALLOW ARCTIC AIRMASS BY THE EARLY
MORNING HOURS OF NEW YEAR`S EVE...ALL THE WAY THROUGH JANUARY 2ND.
WITH HIGHER CONFIDENCE IN SHALLOW ARCTIC AIR IN PLACE...BUT LOW
CONFIDENCE ON THE EXACT DETAILS OF THE VERTICAL TEMPERATURE
PROFILE 6-7 DAYS OUT...WENT AHEAD AND MENTIONED A 20 TO 30 PERCENT
CHANCE OF FREEZING RAIN OR LIGHT RAIN IN THE FORECAST OVER MUCH OF
NORTH AND CENTRAL TEXAS.

CONFIDENCE IN THE AMOUNT OF LIFT AVAILABLE FOR PRECIPITATION OVER
THE ARCTIC AIRMASS...AS WELL AS AVAILABLE MOISTURE FOR
PRECIPITATION REMAIN LOW AT THIS TIME FOR NEW YEAR`S EVE AND
NEW YEAR`S DAY. CONFIDENCE IN LIFT AND AVAILABLE MOISTURE
INCREASES QUITE A BIT ON JANUARY 2ND WHEN MODELS SUGGEST THE DUTCH
HARBOR UPPER LOW WILL MOVE OVER NEW MEXICO AND SPREAD STRONG LARGE
SCALE FORCING FOR ASCENT OVER THE ENTIRE CWA. UNFORTUNATELY AS
CONFIDENCE IN PRECIPITATION RISES...CONFIDENCE IN THE SHALLOW
ARCTIC AIRMASS REMAINING IN PLACE DECREASES. GFS AND ECMWF DYNAMIC
TROPOPAUSE MAPS INDICATE THAT THE CUT OFF UPPER LOW IS ISOLATED
FROM THE POLAR JET STREAM BY THE TIME IT MOVES EAST OVER THE
SOUTHWEST CONUS AND TOWARDS TEXAS ON NEW YEAR`S DAY AND JANUARY
2ND. ONCE THIS OCCURS...DOWNSTREAM AIRMASS MODIFICATION BECOMES
INCREASINGLY LIKELY...WHICH REALLY JUST MEANS THE ARCTIC AIR IS
MORE LIKELY TO WARM UP BECAUSE IT WILL NOT BE REINFORCED BY ANY
MORE COLD AIR FROM THE NORTH.

AT ANY RATE THE BASIC THREAT TO THE REGION FOR WINTRY WEATHER
LOOKS LIKE THIS:

ARCTIC AIR WILL BUILD IN TUESDAY/TUESDAY NIGHT WHILE VERY LIGHT
RAIN/DRIZZLE CHANCES INCREASE INTO THE MORNING HOURS ON NEW YEAR`S
EVE. WHEREVER LIGHT RAIN/DRIZZLE SETS UP...IT HAS A GOOD CHANCE AT
FREEZING UPON CONTACT WITH ELEVATED SURFACES.

CONFIDENCE IN PRECIPITATION AND PRECIPITATION AMOUNTS INCREASES
THROUGH JANUARY 2ND WHILE THE SHALLOW ARCTIC AIRMASS WILL SLOWLY
WARM UP. RAINFALL CHANCES LOOK TO BE HIGHEST WHILE ARCTIC AIR IS
STILL PROBABLY COLD ENOUGH TO FREEZE THINGS ON NEW YEAR`S DAY. BY
JANUARY 2ND...WIDESPREAD PRECIPITATION IS LIKELY...BUT IT MAY TEND
TO ALL FALL IN LIQUID FORM BY THAT TIME.

IN GENERAL...CONFIDENCE REMAINS TOO LOW TO EXPECT ANY MAJOR WINTER
WEATHER EVENT ACROSS NORTH OR CENTRAL TEXAS AT THIS TIME.
HOWEVER...WE WILL CONTINUE TO WATCH THIS PERIOD CLOSELY MOVING
FORWARD AS THE POTENTIAL FOR WINTRY IMPACTS ARE CERTAINLY THERE
FOR THE REGION DURING NEW YEAR`S EVE/NEW YEAR`S DAY FESTIVITIES.

CAVANAUGH

[Rgv20]

0zNAM has a 1064mb High in NW Canada on the end of the run!



500mb Anomalies valid for Monday Morning..

[dhweather]

In 2834 hours:

GFS: Cat 5 in the Gulf
GFSP: Cat 5 over Lake Michigan
ECMWF: Polar Vortex over Yucatan Peninsula
CMC: Build an Arc





My sincere advice: It is going to get really cold, that we are very confident of. Use the next 2-3 days to get pipes, pets, plants ready for it, so you are not out in it trying to do this.

[Ralph's Weather]

In 2834 hours:

GFS: Cat 5 in the Gulf
GFSP: Cat 5 over Lake Michigan
ECMWF: Polar Vortex over Yucatan Peninsula
CMC: Build an Arc





My sincere advice: It is going to get really cold, that we are very confident of. Use the next 2-3 days to get pipes, pets, plants ready for it, so you are not out in it trying to do this.

Very good advice, tomorrow may be about the last day that the weather will be nice for a while.

[ravyrn]

A belated Merry Christmas from East Texas. Stayed at my mom's in Maydelle last night. We got down to 27.9F this morning. It was cold! And we had a pretty significant amount of frost on everything as we were below freezing for about 8 hours. Fortunately, it didn't seem to have any impact on the 60 bluebonnets that I've found sprouting up of the 2,000 I secretly placed around her fenced in yard and a few other suitable spots on their moderate acreage property! I can't wait until Spring comes to see how many come up!

Glad Santa didn't have anyone to stop by for or he may have taken a fall as the porch was quite slippery this morning! Went for a walk once it warmed up to about 40F and it almost seemed like a light rain in the woods with all the frost on the trees melting.

Haven't seen many birds at her place this Fall/Winter. Though a flock of blue birds and waxwings stopped by last week and finished off the holly and dogwood berries. One of the blue birds was rather ill-mannered, however, and I hope she doesn't return. She didn't even have the courtesy to eat with her mouth closed during her visit! How rude!

[ronyan]

Not a lot of change from the 0z GFS models. GFS has 1055mb high in Montana, PGFS has 1059mb. The 0z GFS is colder at the surface than the 12z for TX on Dec 31, but not what you would expect from that caliber HP. Para-GFS is also colder on the 2m temp anomalies than the 12z run. Perhaps we will see a gradual shift towards a more reasonable solution over a few more runs. I await the Euro.

[Rgv20]

The following are tonight's 0z High Pressure forecast on Tuesday Morning for Montana...Going to be interesting just how much cold air the actual Arctic High comes with!

CMC--1059hp
GFS--1055hp
GFSPA--1059hp
NAVGEM--1052hp

[CYCLONE MIKE]

In 2834 hours:

GFS: Cat 5 in the Gulf
GFSP: Cat 5 over Lake Michigan
ECMWF: Polar Vortex over Yucatan Peninsula
CMC: Build an Arc





My sincere advice: It is going to get really cold, that we are very confident of. Use the next 2-3 days to get pipes, pets, plants ready for it, so you are not out in it trying to do this.

Don't forget about the new years day blizzard for parts of us along the gulf coast as well

Also it might get very cold for y'all up in north Texas but the se ridge is gonna make sure its for there and points west. Nothing showing a freeze for the SE for the next two weeks. Enjoy it though.

[ronyan]

Alright but this is a TX thread, hence we talk about cold in TX.

I wouldn't count all of the SE out yet, things can still change, and the GFS already has significant negative anomalies predicted for practically all of the SE on New Year's.

[CYCLONE MIKE]

Yeah I know there's another thread for us folks further east but its been dead for days. Guess everyine sees what is looming and not worth talking about. Will kick back and wait for our rains to begin tomorrow and let y'all enjoy whatever cold you might get. Enjoy

[somethingfunny]

Get hype!

I got hype

I think an ice storm is very likely with this upcoming pattern.

[somethingfunny]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
402 AM CST FRI DEC 26 2014

.DISCUSSION...

/NOTE: DUE TO TIME CONSTRAINTS AS A RESULT OF A BUSY AND
CHALLENGING FORECAST...THE EXTENDED PORTION OF THE FORECAST
DISCUSSION HAS BEEN ABBREVIATED AND A FULL DISCUSSION IS EXPECTED
TO BE ISSUED BY 430 AM/

THERE ARE SEVERAL DIFFERENT WEATHER ELEMENTS AFFECTING THE
FORECAST IN THE NEXT 7-8 DAYS BUT NO SIGNIFICANT IMPACTS ARE
EXPECTED ACROSS NORTH AND/OR CENTRAL TEXAS. OF NOTE...ALL MENTION
OF WINTER PRECIPITATION NEXT WEEK HAS BEEN REMOVED AND THE
REASONING FOR THIS WILL BE DISCUSSED BELOW.


...


ABBREVIATED EXTENDED DISCUSSION...THE NEXT UPPER LEVEL LOW/TROUGH
THAT WE HAVE BEEN MONITORING CONTINUES TO SLOW ITS ARRIVAL TIME
ACROSS THE SOUTHERN PLAINS. AN ARCTIC FRONT IS STILL EXPECTED TO
ARRIVE ON TUESDAY BRINGING SIGNIFICANTLY COLDER AIR TO THE REGION
AND PREVIOUSLY WE WERE MONITORING A CHANCE FOR WINTER
PRECIPITATION NEXT WEEK. HOWEVER...DUE TO THE SLOWER TIMING OF THE
UPPER LEVEL LOW AND THUS A LACK OF LARGE SCALE LIFT AS THE ARCTIC
AIR ARRIVES WE REMOVED THE POPS AND THE MENTION FOR WINTER PRECIP
ON TUESDAY AND WEDNESDAY. BETTER RAIN CHANCES ARE EXPECTED ON
THURSDAY AND FRIDAY AS THE UPPER LEVEL LOW FINALLY STARTS MOVING
EAST...BUT BY THEN SOUTHERLY WINDS AT THE SURFACE WILL HAVE
ALREADY STARTED TO MODIFY AND WARM THE ARCTIC AIRMASS AND JUST A
COLD RAIN /ALL LIQUID/ IS EXPECTED THURSDAY THROUGH FRIDAY.


...........

(Continuation now)

ON THE HEELS OF SUNDAYS UPPER LEVEL TROUGH WILL BE ANOTHER
DEVELOPING UPPER LEVEL TROUGH ALONG THE WEST COAST. THIS SECOND
TROUGH ACTUALLY ORIGINATES SOUTH OF ALASKA WHERE IT IS CURRENTLY
LOCATED. AS IT DIVES SOUTH...IT WILL FACILITATE COLD ARCTIC AIR
MOVING OUT OF CANADA AND DOWN THE PLAINS TO TEXAS. THE ARCTIC
FRONT IS STILL EXPECTED TO ARRIVE ON TUESDAY WITH DRASTICALLY
COLDER TEMPERATURES TUESDAY THROUGH THURSDAY.

PREVIOUS FORECASTS MENTIONED LOW CHANCES FOR WINTER PRECIPITATION
SOMETIME DURING THE TUESDAY THROUGH THURSDAY/FRIDAY TIME FRAME.
THIS WAS DUE TO THE INTERACTION OF THE ARCTIC AIR WITH THE UPPER
LEVEL TROUGH IN DEVELOPING PRECIPITATION ACROSS THE REGION. THE
MODELS HAVE CONTINUED TO TREND TOWARDS A SLOWER TIMING AND TRACK
OF THE UPPER LEVEL LOW AND THEY DO NOT BRING THE UPPER LEVEL LOW
INTO THE SOUTHERN PLAINS UNTIL FRIDAY NOW. WITH A LACK OF LARGE
SCALE LIFT ACROSS THE REGION AND WEAK RIDGING AHEAD OF THE UPPER
LEVEL LOW...HAVE REMOVED THE MENTION OF PRECIPITATION AND WINTER
PRECIPITATION FROM THE FORECAST TUESDAY THROUGH WEDNESDAY. SOME OF
THE MODELS ARE STILL DEVELOPING LIGHT QPF ACROSS OUR WESTERN
COUNTIES ON TUESDAY ALONG AN ELEVATED FRONT...AND WILL CONTINUE
TO MONITOR THIS SITUATION...BUT A LACK OF LARGER SCALE LIFT TENDS
TO RESULT IN A DRIER FORECAST.

PRECIPITATION CHANCES INCREASE ON THURSDAY AND FRIDAY AS THE UPPER
LEVEL LOW MOVES INTO THE SOUTHERN PLAINS...BUT BY THEN THE SURFACE
HIGH WILL HAVE ALREADY MOVED EAST AND SOUTH WINDS WILL ACT TO
MODIFY AND WARM THE SURFACE TEMPERATURES. THUS...ALL LIQUID
PRECIPITATION IS EXPECTED TO FALL THURSDAY AND FRIDAY AND REMOVED
THE MENTION OF WINTER PRECIPITATION FROM THESE DAYS AS WELL.



I personally would not throw in the towel on this one yet. This pattern certainly looks ripe for wintry precipitation, and the recent models I've seen have not looked particularly dry. On the other hand, these surface precipitation output maps produced by computers are notorious for overestimating precip sometimes, and there isn't much snow cover to our north.

[TexasF6]

Not so fast, Fort Worth...

AFDEWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
404 AM CST FRI DEC 26 2014

.SHORT TERM (TODAY THROUGH SATURDAY)...
EXPECT WARMER TEMPERATURES WITH HIGHS IN THE MID TO UPPER 60S
ACROSS THE HILL COUNTRY AND LOWER 70S ALONG AND SOUTH OF HIGHWAY 90.
THE RETURN OF SOUTHERLY FLOW AND INCREASED MOISTURE ACROSS THE
AREA WILL RESULT IN PARTLY CLOUDY SKIES. THERE IS A SLIGHT CHANCE
FOR RAIN ACROSS THE FAR EAST COUNTIES THIS AFTERNOON WHERE DEEPER
MOISTURE RESIDES. A COLD FRONT WILL PUSH ACROSS LATE TONIGHT INTO
SATURDAY. LIGHT TO MODERATE RAIN-SHOWERS ARE EXPECTED AHEAD OF THE
COLD FRONT OVERNIGHT WITH RAIN CHANCES INCREASING SATURDAY.
ALSO...THERE ARE GOOD CHANCES FOR PATCHY TO AREAS OF FOG ALONG AND
EAST OF INTERSTATE 35 OVERNIGHT/EARLY SATURDAY MORNING. OVERNIGHT
LOWS WILL DROP TO THE UPPER 40S ACROSS THE HILL COUNTRY WITH MID
TO LOWER 60S ALONG AND EAST OF THE I-35 CORRIDOR. RAINFALL AMOUNTS
WILL GENERALLY RANGE FROM FEW HUNDREDTHS TO ONE TENTH OF AN INCH
WITH ISOLATED ONE QUARTER INCH.

&&

.LONG TERM (SATURDAY NIGHT THROUGH THURSDAY)...
AN UPPER LEVEL TROUGH ACROSS THE FOUR CORNERS REGION WILL PUSH
ACROSS THE SOUTHERN/CENTRAL PLAINS SATURDAY WITH A SECONDARY
SHORTWAVE TROUGH MOVING ACROSS SOUTH CENTRAL TEXAS ON SUNDAY. THIS
WILL KEEP RAIN CHANCES ACROSS THE EASTERN HALF OF SOUTH CENTRAL
TEXAS AT LEAST THROUGH SUNDAY AFTERNOON. DRY WEATHER CONDITIONS
ARE EXPECTED FROM SUNDAY EVENING THROUGH LATE MONDAY. AN UPPER
LEVEL TROUGH WITH POLAR CHARACTERISTIC WILL SPLIT EARLY NEXT WEEK
WITH ONE AREA PUSHING ACROSS THE GREAT LAKES AND THE OTHER ALONG
THE WEST COAST AND THEN OVER THE FOUR CORNERS REGION. MEDIUM-RANGE
MODELS ARE HAVING SOME DIFFICULTIES WITH THESE FEATURES. SO FAR...
LATEST PARALLEL GFS KEEPS OUR ARE RELATIVELY DRY WHILE GFS40 AND
ECM GUIDANCE SHOW PRECIP. NOW...TEMPS HAVE BEEN TURNING COLDER
FOR THE PAST 3 TO 4 RUNS ACROSS MOST AREAS WITH UPPER 20S AND
LOWER 30S ACROSS THE EDWARDS PLATEAU/HILL COUNTRY. AT THIS
TIME...ONLY SHOWING SLIGHT CHANCE OF RAIN TUESDAY NIGHT INTO
WEDNESDAY ALONG HIGHWAY 90 AND WEST OF A SAN ANTONIO TO ROCKSPRINGS
TO JUNO LINE. TEMPS WILL INCREASE TO THE 40S ON WEDNESDAY WITH
POPS ACROSS THE SOUTHEAST COUNTIES. WILL KEEP MONITORING CLOSELY
THE EVOLUTION OF THIS SYSTEM AND THE POTENTIAL FOR WINTRY
PRECIPITATION.

[Ralph's Weather]

Not sure why FWD is so quick to pull the plug especially for their western areas. The models have been far from consistent and we still are 5 days out. Once added I would think they would have left at least low end chances for mid week and I would not be so sure of a quick warm-up either by the end of the week especially for eastern areas. This is a very powerful Arctic air mass with good southwest flow over the top.

[Tammie]

Not sure why FWD is so quick to pull the plug especially for their western areas. The models have been far from consistent and we still are 5 days out. Once added I would think they would have left at least low end chances for mid week and I would not be so sure of a quick warm-up either by the end of the week especially for eastern areas. This is a very powerful Arctic air mass with good southwest flow over the top.

I have to agree. I don't know who wrote that discussion, but Cavanaugh's previous discussion is where my faith will lie. Mr. C's history of AFD's have ALWAYS been more accurate than the other mets. I'll sit back and relax until we hear from him. This event is still 5-7 days away, and nobody has a crystal ball.

[Ralph's Weather]

After a quick glance through the models I see why we may not get the expected sustained blast. The jet stream is just moving too fast and it just leaves the upper trough behind. Maybe it will slow down, but it is what we have been fighting all year. With this setup it will be hard to get much sustained winter here, but the Southwestern US sure will continue getting it.

[Dallasaggie01]

After a quick glance through the models I see why we may not get the expected sustained blast. The jet stream is just moving too fast and it just leaves the upper trough behind. Maybe it will slow down, but it is what we have been fighting all year. With this setup it will be hard to get much sustained winter here, but the Southwestern US sure will continue getting it.

So in other words, the fact that Cavenaugh previously discussed the low as being cut off from the polar flow means that the polar air will be here and gone too quickly for any meaningful precipitation to make its way in time? DFW has highs back in the 40's by 1/1. Trying to understand the timing discrepancies here.

[Ralph's Weather]

After a quick glance through the models I see why we may not get the expected sustained blast. The jet stream is just moving too fast and it just leaves the upper trough behind. Maybe it will slow down, but it is what we have been fighting all year. With this setup it will be hard to get much sustained winter here, but the Southwestern US sure will continue getting it.

So in other words, the fact that Cavenaugh previously discussed the low as being cut off from the polar flow means that the polar air will be here and gone too quickly for any meaningful precipitation to make its way in time? DFW has highs back in the 40's by 1/1. Trying to understand the timing discrepancies here.

It is looking that way. Something moving very fast will tend to want to go straight and that is what we are fighting with the jet right now. Anyone know what could get it to slow down?

[wxman57]

I'm seeing a classic case of the models not handling shallow Arctic air well. I've seen it many times over the past 35 years here in Texas. Of course, back in 1980 the models didn't go out beyond 48 hrs. I have print-outs of model runs from the early 1990s demonstrating how the models handled the Arctic air. Here's the way I've seen it happen in the more recent past.

From around 10 days out (10-15 with the current GFS), the models pick up on the Arctic air and forecast it to blast south through Texas, despite a not-so-favorable upper-level wind pattern (upper trof/low moving in from the west). Freezing/frozen precip will be indicated well to the south across Texas. The models actually handle it well in the extended range.

Then, they lose the Arctic air to a degree. Maybe they shunt it off to the east, but generally, in the medium range (7-10 days), they try to drive the cold air northward as a warm front as the upper trof/low approaches. Models are programmed to see upper trof approaching and they think this will dislodge the shallow Arctic air and move it northward. That just does not happen. I have a model run saved from November of 1993 where the American model drove the Arctic front back into central Oklahoma about 4-5 days before the event. Turned out the front was off the Texas coast and not budging. Then the ice storm began as the upper trof approached and spun up a low in the Gulf along the front. We called that event the "Leon Lett Bowl ice storm".

What I see happen very often is that after the models see the event in the extended range then lose it in the mid range they eventually catch back on 3-5 days before it happens, though they tend to play catch-up until it happens. The cold air arrives faster (and colder) than the models are forecasting and the front stays offshore as the upper low/trof approaches. Ice storm ensues, but farther south than the models were forecasting.

As of this morning, the models are in that "lost" phase in the mid range. The GFS is forecasting lowest temps of 38 in Houston. The Euro barely indicates a freeze in Dallas on New Year's. Both are unlikely given the 1060+mb high dropping southward. Look for the models to trend colder by Sunday/Monday.

[Ralph's Weather]

Thanks for that explanation wxman57. The cold is coming and it will be very cold (Dallas could see highs in the 20s for the middle of next week). It would not surprise me if the models are digging the Southwestern trough too much so overrunning precip is still a concern. I really an doubting the models retreating the child's for the end pig the week. It may well stay pretty chilly until the next blasts comes around the 6th.