Texas Fall-2014

[BigB0882]

That looks too much like last year where my area, Baton Rouge, was always just on the edge of the really cold. Hopefully that comes down a little further south and east.

Also, thanks so much for the comments on analogs. You guys are so good at explaining this really confusing information.

[gpsnowman]

Larry Cosgrove seems to think another shot of cold shoots down just after Thanksgiving, according to the last couple tweets he posted. The nasty ice storm last December occurred in the first week if I recall. We are getting close. Man, I need to see some snow!!!

[BrokenGlassRepublicn]

I hate to be "that guy", and realize we are 48 hours out, but is there any sense of timing with the Saturday storms? My boys are flying out of Dallas Love to NYC on Saturday, and I may try to adjust their flight times to give them a better shot at getting out of town.

[gboudx]

I hate to be "that guy", and realize we are 48 hours out, but is there any sense of timing with the Saturday storms? My boys are flying out of Dallas Love to NYC on Saturday, and I may try to adjust their flight times to give them a better shot at getting out of town.

Try to get to the DFW NWS page soon before they change the graphics. They show the timing.

http://www.srh.noaa.gov/fwd/

To summarize, they show the heaviest rain over the Metroplex between 12-6pm. The HRRR will be a good model to use, but not close enough yet. Based on the graphic, it appears morning may be best to try and avoid delays.

[gboudx]

Morning email from jeff:

***Severe thunderstorms including tornadoes increasingly likely this Saturday.***

Powerful upper level storm system off the NW US coast currently will move rapidly SE and into W TX by early Saturday and sweep across the state late Saturday.

Moisture return clearly underway this morning with scattered showers developing in the corridor from Matagorda Bay to near I-10 west of Houston. Expect this activity to increase in coverage today and spread inland as a warm front moves toward the upper TX coast. Warm front will move inland tonight and progress across SE TX on Friday with additional scattered showers and a few thunderstorms especially along and north of the boundary. Warm sector air mass south of the boundary will support mid to upper 60 degree dewpoint maritime tropical air mass moving onshore. A few showers will be possible in the increasing onshore flow south of the warm front. Temperatures will be running about 20-30 degrees warmer than the first part of this week tomorrow and Saturday.

Saturday:
Powerful storm system sweeps across TX with impressively deep short wave rotating far south across S TX Saturday afternoon in the base of the upper level trough. Trough axis takes on a slight negative tilt pattern (SE to NW) which supports an overall increase in directional wind shear along the eastern flank of the trough axis (or in the region over the coastal bend and SE TX). Forecast models have shown a slight tendency to slow to eastward progression of the storm system slightly over the last 24 hours which places the greatest weather threat/impacts in the afternoon and evening hours of Saturday. A 35-45kt low level jet develops off the western Gulf of Mexico late Friday evening and continues into Saturday with a 100kt mid level jet streak carving into the region from the SW Saturday afternoon. The result is significant low level wind shear and wind energy in the lowest several thousand feet of the atmosphere. Latest guidance suggests breaks in the cloud cover are possible Saturday morning and early afternoon over SC/SE TX helping to boast surface based energy values (CAPE) and resulting in an increasingly unstable warm sector air mass.

Usually in this part of the state the warm sector is capped off and we await the actual strong forcing from the upper level trough or the cold front to develop a line of strong to severe thunderstorms. Saturday appears to be a possible exception where the warm sector air mass is only weakly capped and this could allow for the development of discrete supercell thunderstorms prior to the arrival of the main forcing toward early evening. This is important due to the fact that warm sector discrete supercells tend to produce a majority of the tornadoes in such severe weather outbreaks.

Model guidance is trending to point toward some development of discrete cells by early Saturday afternoon with an enhanced tornado threat which would be certainly supported by the sheared low level air mass resulting in updraft rotation. An example of the potential wind shear in the lowest part of the atmosphere being forecasted at noon on Saturday for IAH is a helicity value of around 260 m^2/s^2 on the GFS forecast sounding. Additionally the GFS shows a significant increase in PWS values between 06Z Saturday and 18Z Saturday from around 1.1 inches to nearly 1.70 inches.

The greatest severe weather threat currently appears across the southern 2/3rds of the area into the coastal bend and SC TX where the air mass becomes the most unstable Saturday afternoon and the favorable wind profiles and dynamics aloft align. (See SPC graphic outlines below).

The following threat analysis discusses the severe potential for Saturday:

Wind Damage:
Strong wind energy will be present both in the form of the low level jet overhead and mid level winds. Strong to severe thunderstorms will be capable of transporting some of this wind energy to the surface in the form of damaging winds of 60-70mph. This would be especially true in the event of an ESE or E moving squall line/MCS which guidance does develop out of C TX during the afternoon hours and sweeps across SE TX during the late afternoon and evening hours. The pattern supports bowing segments with the potential for larger than average corridors of wind damage.

Tornado:
The concern is in the potential for discrete warm sector development of supercells early Saturday afternoon in a favorable 850mb convergent zone over SC/SE TX. If supercells do in fact initiate in such a highly sheared and unstable air mass tornado formation is certainly possible. Such tornadoes would tend to be stronger than what we would normally see in this area and could track for a longer period of time on the ground. Cell motions would likely be quick toward the NE and ENE reducing warning lead times. This enhanced tornado threat is strongly conditional on the development of supercells in the warm sector air mass which as stated above is a bit unusual for this area. A lack of warm sector discrete cell development would reduce the tornado threat across the area.

In addition there would also be a tornado risk along the main squall line/MCS toward the early evening hours with what we more commonly see in this area which is weaker rain wrapped tornadoes along the leading edge of squall lines where localized vorticity values are increased.

Large Hail:
Colder mid level temperatures will arrive with the cold pocket of the upper level system. This would support a large hail threat with both warm sector supercells and with the squall line. This threat is secondary to the wind and tornado threat at the moment.

Heavy Rainfall:
A significant increase in moisture will occur tonight-early Saturday with scattered showers for the next 24-36 hours. Heavy rains will certainly occur with the strong to severe thunderstorms on Saturday, but fast storm motions should help negate a serious flood threat. Of some concern is the model tendency to slow the system some which could result in a slightly longer duration of the heavy rainfall threat and the potential for high precipitation supercells to train in the warm sector. The heavy rainfall threat is secondary to the wind and tornado threat at the moment.

[aggiecutter]

[cigtyme]

Crap I hate when I am in these kind of maps

[Tireman4]

This is getting more serious by the hour. Hummm....I am not liking this setup one bit...

[weatherguy425]

Re: Holiday Weekend Cold Blast

To me, signals (teleconnections) are not quite as obvious for any sustained cold, particularly across the Southern Plains over the next week to week and a half. Stormy? Possibly. But, ensemble outlooks have EPO continuing to rise to a positive state along with the AO. Granted, we've seen these ensemble outlooks bust many-a-time.

Will be interesting to watch nonetheless...

[Ntxw]

Re: Holiday Weekend Cold Blast

To me, signals (teleconnections) are not quite as obvious for any sustained cold, particularly across the Southern Plains over the next week to week and a half. Stormy? Possibly. But, ensemble outlooks have EPO continuing to rise to a positive state along with the AO. Granted, we've seen these ensemble outlooks bust many-a-time.

Will be interesting to watch nonetheless...

I agree at this time nothing sustained prolonged type blocking. But don't be surprised if the Pacific (EPO/PNA) sneaks in a more typical transitional type cold blast right after TG. Canada is going to get very cold next week, cold source region.

[srainhoutx]

Re: Holiday Weekend Cold Blast

To me, signals (teleconnections) are not quite as obvious for any sustained cold, particularly across the Southern Plains over the next week to week and a half. Stormy? Possibly. But, ensemble outlooks have EPO continuing to rise to a positive state along with the AO. Granted, we've seen these ensemble outlooks bust many-a-time.

Will be interesting to watch nonetheless...

I agree at this time nothing sustained prolonged type blocking. But don't be surprised if the Pacific (EPO/PNA) sneaks in a more typical transitional type cold blast right after TG. Canada is going to get very cold next week, cold source region.

The Euro and its ensembles are trending to a -AO/-EPO/+PDO regime around the 24th. There is a significant sudden stratospheric warming event unfolding across Eurasia and Siberia. Look for a wind reversal as well as a polar vortex split coming near the early December timeframe.

[TeamPlayersBlue]

Woah Srain. Thats a very big deal if so. I dont think you would say something like this unless you truly believed in it. I, in a post a few pages back, also thought something would happen early Dec time frame.

Also i find it crazy that we are having two SSW events in 2 months. Dont they happen like once a year maybe?

Im excited. I guess now is a good time to reveal that i made a bet with a friend in early October that we will see snowfall in Houston this winter. Just once, even though i told him i think it may happen multiple times.My friends know me as the meteorologist of the group so i have a lot of pride on the line with this bet.

Bring on the cold!

[gatorcane]

12Z ECMWF persistent with the next Arctic surge into the Central and Eastern US just after Thanksgiving. Looks like another potent one:

[TheProfessor]

Right now this weekend seems like a good situation for North and Northwest North Texas, 2-3 inches of rain is being predicted and the severe storm threat is not as high here, correct me if I'm wrong but it seems like the further north the low goes the further north the severe threat goes, so I'm hoping the track doesn't shift north. Hopefully this event will also help the lakes out up here too.

[srainhoutx]

The Updated Model Diagnostic Discussion indicated a slower, deeper (stronger) and further south tracking storm system is likely this Saturday...


MODEL DIAGNOSTIC DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
226 PM EST THU NOV 20 2014

VALID NOV 20/1200 UTC THRU NOV 24/0000 UTC

...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR
INGEST...

==============================================
12Z MODEL EVALUATION AND PREFERENCES
==============================================
NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO
SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT.
==============================================

...STRONG SOUTHERN STREAM TROUGH LEADING TO WIDESPREAD RAIN FROM
THE PLAINS EASTWARD...

PREFERENCE: BLEND OF 12Z GFS/ECMWF
CONFIDENCE: AVERAGE

A DYNAMIC TROUGH OF SHORT TO MEDIUM WAVELENGTH WILL DIVE FROM
CALIFORNIA TOWARD THE RIO GRANDE BASIN. THE SYSTEM WILL CONTINUE
TO BE URGED ALONG TO THE EAST BY STRONG UPSTREAM FLOW...BUT THE
12Z MODELS TRENDED TOWARD A SLOWER PROGRESSION FROM LATE SATURDAY
INTO SUNDAY. THE MODELS THAT TRENDED SLOWER ARE ALSO A LITTLE
DEEPER AND FORECAST A TRACK THAT IS SUPPRESSED SOUTHWARD COMPARED
TO THE 00Z ECMWF. THESE TRENDS APPEAR REASONABLE FOR A STRONG AND
STILL DEEPENING WAVE...AND THE 12Z ECMWF SUPPORTED THE TREND. THE
NAM AND CANADIAN ARE GENERALLY CONSISTENT WITH THE GFS/ECMWF IN
THE MASS FIELDS...BUT THE NAM/CANADIAN PRECIPITATION OUTPUT IS
LESS PREFERRED. THE UKMET STRAYS FROM CONSENSUS ON DAY 3 WHEN IT
DRIVES THE CORE OF THE MID LEVEL WAVE STRONGLY EASTWARD INTO THE
DEEP SOUTH RATHER THAN LIFTING IT THROUGH THE MID MISSISSIPPI
VALLEY.

[BigB0882]

Those anomaly maps seem interesting. There seems to be the coldest anomalies situated over North Tx, Oklahoma and Kansas on the 28th, then those really cold anomalies disappear on the 29th (although it is still plenty cold, just not AS cold) and then the coldest anomalies reappear on the 30th along the Eastern seaboard. I find that interesting. Why would the cold air moderate and then seem to be back in force the next day? Do you think that is just the Euro not able to handle the cold airmass so far out or could there be a reason for cold air to behave that way? Am I even making sense? lol

[BigB0882]

It sure has been quiet in here since this afternoon. Are the models showing a blow torch or something? lol

[KatDaddy]

Its the calm before the storm. An active weather day across a large portion of Texas Saturday.

[KatDaddy]

Our potent storm system which is likely to become negatively tilted across Central and S Central TX can be seen on IR satellite over SoCal this morning. Temps in the low to mid 60s currently as GOM moisture continues to stream inland. A few areas of light to moderate rain moving across SE TX this morning. A significant severe weather event on target to unfold across a large portion of TX tomorrow afternoon. The SPC continues the Enhanced Risk across Central, S Central and SE TX. The environment will support supercell development to the SW of Houston across the Middle TX Coast including the Victoria area leading to a tornado threat. These storms will likely consolidate into MCS later in the afternoon and evening resulting in possible widespread damaging winds across SE TX and the Upper TX Coast.

[cycloneye]

MODEL FORECASTS SUGGEST THE GREATEST CHANCE FOR ORGANIZED CONVECTION
WILL BE JUST AHEAD OF THE UPPER-LEVEL TROUGH EARLY SATURDAY EVENING
FROM THE TX COASTAL PLAINS SEWD TO THE TX GULF COAST. FORECAST
SOUNDINGS AT SAN ANTONIO AND HOUSTON AT 00Z/SUN SHOW MLCAPE NEAR
1000 J/KG WITH 0-6 KM SHEAR OF 50 TO 60 KT. THIS ENVIRONMENT SHOULD
SUPPORT SUPERCELL DEVELOPMENT WITH STORMS THAT HAVE ACCESS TO
MAXIMIZED INSTABILITY. THE POTENTIAL FOR SUPERCELLS AND POSSIBLY A
TORNADO OR TWO MAY BE GREATEST ALONG THE MIDDLE TX COAST JUST AHEAD
OF A 60 TO 70 KT MID-LEVEL JET ROUNDING THE BASE OF THE TROUGH.
SUPERCELLS MAY ALSO PRODUCE ISOLATED LARGE HAIL. SOME MODELS SUGGEST
THAT A LINE OF STRONG TO SEVERE STORMS WILL DEVELOP IN CNTRL TX JUST
AHEAD OF THE APPROACHING UPPER-LEVEL TROUGH. IF THIS SCENARIO PANS
OUT...THEN A WIND DAMAGE THREAT WOULD DEVELOP LATE SATURDAY
AFTERNOON MOVING EWD FROM THE TX HILL COUNTRY TO THE VICTORIA AND
HOUSTON AREA WHERE A 30 PERCENT SEVERE PROBABILITY HAS BEEN
MAINTAINED.