Winter 2010-11 for the Southern Plains

[Extremeweatherguy]

Wow, the 12z ECMWF is once again coming in very cold, showing quite the frigid airmass working into the northern USA by Tuesday and Wednesday. A large area of -20C or colder 850mb temperatures are shown working in to the Dakotas, Wyoming and Montana by 12z Wednesday with a low setting up over the Oklahoma panhandle region. As the low swings east, the gates to the north open up, and by Thanksgiving morning, the ECMWF drives a powerful blue norther-style front deep into the heart of Texas!

I will be in central Missouri for Thanksgiving day, and if this scenario proves correct then 850mb temperatures over my location will reach -14 to -16C or colder! I will definitely be bringing the heavy coat.. lol

[fogbreath]

Never had to worry much about really cold air being in the SF Bay Area, but now I've got some regularly scheduled travel going into typically colder regions of the US going now, so I've been following this thread with interest lately.

Is there a standard guideline how the 850 mb plot temps translate in terms of what the temperature would be closer to sea level?

[Ntxw]

Wow 12z euro is coldddd (Dropping into the 30s on TG for Okla and Northern Texas). Either it is on crack or latching onto something.

Anyone check out the weekend after Thanksgiving?

You're talking about 30s for highs in Southeast Texas all the way down to the coast!

[TwisterFanatic]

Holy Cow, that is cold.

[srainhoutx]

HPC:

...AFTERNOON UPDATE...
LASTEST CMC REMAINS SIMILAR HOLDING THE MAIN FULL LATITUDE TROF
WELL WEST OF OTHER MODEL SOLUTIONS WHILE THE 12Z GFS IS MORE
PROGRESSIVE THAN ITS 06Z RUN. A MINOR COMPROMISE IN TIMING USED
FOR DAYS 6 AND 7 WED/THU WITH ERN CONUS FRONTAL TIMING BETWEEN
PRIOR HPC PRELIM PROGS AND LASTEST 12Z GFS AS 12Z GFS ENS MEANS
REMAIN CLOSER TO THE SLOWER FRONTAL TIMING AND MID LEVEL TROF
PROGRESSION OF THE 06Z GFS RUN. LATEST 12Z ECMWF MUCH SLOWER THAN
ITS PRIOR RUN AND HAS CONSIDERABLE MORE DIGGING OF THE TROF TO THE
LEE OF THE ROCKIES. THIS WAS ACCOUNTED FOR BY USING A LAGGED
AVERAGE FORECAST AND THE 06Z GFS FOR MORNING PRELIMS AND THIS
AFTERNOONS FINALS....HOWEVER WE COULD STILL BE FAST CONSIDERING
THE SLOWER CMC AND NOW MUCH SLOWER ECMWF. CERTAINLY DOES NOT
INCREASE CONFIDENCE. THE 06Z GFS USED EARLIER REMAINS A REASONABLE
COMPROMISE AT THIS TIME.

[Extremeweatherguy]

00z ECMWF:


TUESDAY EVENING:


WEDNESDAY EVENING:


THURSDAY EVENING:

[Extremeweatherguy]

Never had to worry much about really cold air being in the SF Bay Area, but now I've got some regularly scheduled travel going into typically colder regions of the US going now, so I've been following this thread with interest lately.

Is there a standard guideline how the 850 mb plot temps translate in terms of what the temperature would be closer to sea level?

In general, 850mb temperatures will be colder than the surface during the daylight hours and warmer than the surface during the nighttime hours. This is based on an idealized situation though; which features a run-of-the-mill sunny, not too windy day followed by a clear, light wind night. During the daylight hours, incoming solar radiation heats the surface much more quickly than the upper levels causing warmer temperatures, and during the nighttime hours, outgoing long wave radiation has the opposite effect; cooling the surface much more quickly.

Most of the time our days are not so idealized though, and several factors can cause the "typical" setup to change. The surface, for instance, can be much colder than the 850mb levels during the daytime immediately following a cold frontal passage, and also while under the influence of a shallow arctic airmass (the type known for their role in ice storms). Conversely, during the nighttime, the surface can be similar to, or warmer than the 850mb levels when it is very windy and well-mixed. These are just a few examples though, and there are other scenarios that can have similar results.

In the end, the key is looking at the entire setup. If the 850mb temperatures are very cold (a.k.a. the ECMWF), then it will certainly be cold at the surface; but looking at components such as the upper level and surface winds (noting CAA and WAA), cloud cover, precipitation, etc, etc will help you to determine how the relationship will actually behave if you desire a more detailed surface temperature forecast.

[wall_cloud]

These are my thoughts on what I'm looking at this morning. If its "common knowledge" to you, please disregard. Its mainly meant for the novice forecasters that want to know what goes on inside the head of a met on a midnight shift! Keep in mind that these thoughts are my own and do not necessarily reflect those of NOAA/NWS (or the individual responsible for that portion of the forecast).

The medium range models are coming into better agreement on the timing of this system although the 00z ECMWF is again the cooler of the two. This ECMWF run shows a much stronger (and well timed) vort lobe rounding the base of the trof is it swings into the Plains. The GFS shows a similar wave but it is delayed by about 24 hrs. The 00z GEM appears to be very much in line with the ECMWF. The GFS ensemble suite still offers a wide range of solutions and is toward the bottom of my trust ladder at this time so I'm going to focus more on the ECMWF/GEM solutions.

The strong southwest flow aloft ahead of the main trof will support strong lee cyclogenesis. This should bump the southwest winds up across west TX early in the week with highs around 80 in my neck of the woods. However, it looks like a wave train of shortwaves will move out of the southwest almost daily beginning Monday. This will eject the lee cyclone off to the east, keeping the primary baroclinic zone waffling over the central plains. By Tuesday, the cold air dislodges and begins its trek south, aided by another surface low moving out into the plains.

*Now for what I was waiting to see (hoping the ECMWF pans out)* The main trof slowly moves east with the surface low preceding. As the strong vort lobe rotates around the southwest periphery of the main trof, surface cyclogenesis is induced over the southern plains. I think this low (in addition to the mass aspect) will be the main factor in whether or not this cold air blasts all the way through TX. The GFS being out of phases does not have time to reinforce the initial push and really slows the front as it approaches the gulf coast while the ECMWF brings north winds to our friends on the Yucatan by Friday. Look for this shortwave/vort lobe rounding the main trof in the coming days. It will be key.

I wouldn't trust any MOS out this far even if the model solution looked good. Take the GFS MOS. We are looking at days 6-7 for west central TX (SJT area). At these stages, there is way too much climatology built into the model to account for a strong fropa. It is spouting off a max of 53 for Thursday and we could easily be 10 degrees cooler.

[Ntxw]

Thanks wall_cloud! Very easy to understand for the typical reader and I'm sure many will take that into account (including myself) planning TG week!

Here's a snippet from FW which I think is very much in line with your thinking.

SUB-ZERO ARCTIC AIR HAS ALREADY SLIPPED SOUTH OF THE CANADIAN
BORDER...BUT THE AIR MASS OF INTEREST REMAINS IN NORTHERN CANADA.
SITE ON ELLESMERE ISLAND IS CURRENTLY AT -35F. THIS BITTER COLD
WILL SPILL SOUTH INTO THE PRAIRIE PROVINCES EARLY NEXT WEEK.
LITTLE CHANGE TO FROPA TIMING IN NORTH TEXAS WEDNESDAY. RATHER
UNCHARACTERISTICALLY...GFS REMAINS AMONG THE FASTEST SOLUTIONS.
SHALLOW ARCTIC FRONTS TYPICALLY ARRIVE MORE QUICKLY THAN THE
VERTICAL RESOLUTION OF THE GFS CAN PREDICT...BUT LOOKING AT THE
LIKELY EVOLUTION OF THE SURFACE FRONT EARLY NEXT WEEK...ARCTIC
AIR WOULD BE HARD PRESSED TO ARRIVE MUCH SOONER THAN CURRENT
FORECAST. PATTERN SHOULD ASSURE THAT COLDEST AIR IMPACTS GREAT
LAKES AND NORTHEAST STATES...BUT THANKSGIVING WILL BE A CHILLY ONE
FOR NORTH TEXAS.

[srainhoutx]

A bit chilly to our N...

[wxman57]

I don't think there's much question the front will blast right through Texas all the way to the Bay of Campeche by Friday. Doesn't look nearly as cold as the Thanksgiving 1993 event which produced sleet/freezing rain all across TX, but cold enough to knock daytime temps into the lower 40s or near 40 in Dallas on Thanksgiving and the mid to upper 40s in Houston.

[natlib]

These are my thoughts on what I'm looking at this morning. If its "common knowledge" to you, please disregard. Its mainly meant for the novice forecasters that want to know what goes on inside the head of a met on a midnight shift! Keep in mind that these thoughts are my own and do not necessarily reflect those of NOAA/NWS (or the individual responsible for that portion of the forecast).

The medium range models are coming into better agreement on the timing of this system although the 00z ECMWF is again the cooler of the two. This ECMWF run shows a much stronger (and well timed) vort lobe rounding the base of the trof is it swings into the Plains. The GFS shows a similar wave but it is delayed by about 24 hrs. The 00z GEM appears to be very much in line with the ECMWF. The GFS ensemble suite still offers a wide range of solutions and is toward the bottom of my trust ladder at this time so I'm going to focus more on the ECMWF/GEM solutions.

The strong southwest flow aloft ahead of the main trof will support strong lee cyclogenesis. This should bump the southwest winds up across west TX early in the week with highs around 80 in my neck of the woods. However, it looks like a wave train of shortwaves will move out of the southwest almost daily beginning Monday. This will eject the lee cyclone off to the east, keeping the primary baroclinic zone waffling over the central plains. By Tuesday, the cold air dislodges and begins its trek south, aided by another surface low moving out into the plains.

*Now for what I was waiting to see (hoping the ECMWF pans out)* The main trof slowly moves east with the surface low preceding. As the strong vort lobe rotates around the southwest periphery of the main trof, surface cyclogenesis is induced over the southern plains. I think this low (in addition to the mass aspect) will be the main factor in whether or not this cold air blasts all the way through TX. The GFS being out of phases does not have time to reinforce the initial push and really slows the front as it approaches the gulf coast while the ECMWF brings north winds to our friends on the Yucatan by Friday. Look for this shortwave/vort lobe rounding the main trof in the coming days. It will be key.

I wouldn't trust any MOS out this far even if the model solution looked good. Take the GFS MOS. We are looking at days 6-7 for west central TX (SJT area). At these stages, there is way too much climatology built into the model to account for a strong fropa. It is spouting off a max of 53 for Thursday and we could easily be 10 degrees cooler.

Thanks wall cloud. Glad to have a fellow San Angeloan on here.

[Ntxw]

I think we should keep an eye on the disturbance depicted by the 500mb flow after frontal passage lagging a bit (expected to keep it cloudy in our vicinity). There won't be much moisture left but it's worth noting for now...timing will be everything.

[kb75007]

When is this cold air expected to arrive? I've noticed some of you on here are saying maybe highs in the 30's for Dallas on thursday or friday but weather.com is saying high 50 and sunny on Thanksgiving. Also, the news is saying high 47. No one really seems to have a grip on what is going to happen. Is this front going to have moisture coming in behind it at all? Or does it look like just sunny or cloudy skies? Whats the latest on this front?! Im hoping for

[Ntxw]

When is this cold air expected to arrive? I've noticed some of you on here are saying maybe highs in the 30's for Dallas on thursday or friday but weather.com is saying high 50 and sunny on Thanksgiving. Also, the news is saying high 47. No one really seems to have a grip on what is going to happen. Is this front going to have moisture coming in behind it at all? Or does it look like just sunny or cloudy skies? Whats the latest on this front?! Im hoping for

I never use the weather channel anymore. Their data is simply straight out of the models without much human input and in depth analysis. The NWS is the best choice to go a few days out.

It will get cold in Dallas Weds-Friday. Can't pinpoint the exact timing (looks like Weds currently but will it be morning, midday or evening is yet to be seen) because dense air masses can travel faster than what models depict typically. 30s-40s for highs on Thurs is a real possibility with cloudy skies with some light rain as the cold front moves through with lots of wind.

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For official information, please refer to NWS products.

[kb75007]

When is this cold air expected to arrive? I've noticed some of you on here are saying maybe highs in the 30's for Dallas on thursday or friday but weather.com is saying high 50 and sunny on Thanksgiving. Also, the news is saying high 47. No one really seems to have a grip on what is going to happen. Is this front going to have moisture coming in behind it at all? Or does it look like just sunny or cloudy skies? Whats the latest on this front?! Im hoping for

I never use the weather channel anymore. Their data is simply straight out of the models without much human input and in depth analysis. The NWS is the best choice to go a few days out.

It will get cold in Dallas Weds-Friday. Can't pinpoint the exact timing (looks like Weds currently but will it be morning, midday or evening is yet to be seen) because dense air masses can travel faster than what models depict typically. 30s-40s for highs on Thurs is a real possibility.

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For official information, please refer to NWS products.

Thanks for the information! I'll be on here keeping an eye out and am interested in this front, keep me updated!

[Ntxw]

FW discussion today mentions the possibility of energy held back to swing across. If this does occur to any extent, with such dry air in place I wonder if wet bulbing might enter the picture?

THERE WERE HINTS IN THE MODELS YESTERDAY THAT THE MAIN UPPER
TROUGH AXIS WOULD HANG BACK AND NOT CLEAR THE AREA UNTIL THURSDAY
EVENING. ALL OF THE GUIDANCE CONTINUES TO SEEMINGLY TREND IN THIS
DIRECTION TODAY...WITH THE UPPER TROUGH AXIS LOOKING SHARPER AND
MORE POTENT. SOME OF THE GEM AND GFS MODEL ENSEMBLES ACTUALLY
CLOSE OFF A LOW AT THE BASE OF THE TROUGH OVER THE DESERT SW. THE
INTENSIFICATION OF THE TROUGH AXIS APPEARS TO BE RELATED TO A
TROPOPAUSE FOLDING EVENT AS A STRONG RIDGE OVER THE WESTERN
PACIFIC PUSHES ONSHORE. STRATOSPHERIC AIR IS HIGH IN POTENTIAL
VORTICITY...AND DETERMINING JUST HOW MUCH OF THIS AIR DESCENDS IS
IMPOSSIBLE AT THIS POINT. HOWEVER THE POSSIBILITY EXISTS THAT THE
LAGGING DISTURBANCE WILL INDUCE ENOUGH OF A DYNAMIC RESPONSE TO
RESULT IN ISENTROPIC LIFT OVER THE AREA THURSDAY. THE LOW LEVEL
AIR MASS WILL BE FAIRLY DRY...BUT SATURATION ALOFT AND SOME
ELEVATED INSTABILITY ARE INDICATED IN THE VARIOUS SOLUTIONS. WILL
SHOW A LOW CHANCE OF A VERY COLD RAIN THURSDAY OVER THE CENTRAL
AND SOUTHEAST HALF OF THE AREA.

[srainhoutx]

It certainly can not be ruled out, IMO. The 'wrinkle' started showing itself with the 00Z yesterday runs and with todays output, you can almost sense a move toward biting on a stronger/slower progression of the Upper Air feature coming through Thanksgiving Day/night. I suspect there will be some model watching in the days ahead.

[Portastorm]

:uarrow:

It certainly can not be ruled out, IMO. The 'wrinkle' started showing itself with the 00Z yesterday runs and with todays output, you can almost sense a move toward biting on a stronger/slower progression of the Upper Air feature coming through Thanksgiving Day/night. I suspect there will be some model watching in the days ahead.

Hey, didn't I point this out this 'wrinkle' last weekend based on one of the Euro model runs?! In fact, a certain unnamed S2K mod who has a username referencing a certain large city in southeast Texas saw this before any of us did ... guess who?

[srainhoutx]

One run didn't count. But you are right Portastorm, you called it buddy.