November 2014: Nice Seanonal Thanksgiving Ahead

[Ptarmigan]

Travis Herzog posted this on his Facebook today. I found it really interesting. (Mods, I hope it's okay to post since it's from channel 13. If not, please let me know)

https://m.facebook.com/story.php?story_ ... 0656887594

Heads up! Our weather will radically shift from record-breaking arctic cold to a potential severe weather outbreak this Saturday.

One way to forecast the weather is to compare weather patterns predicted by computer models with similar weather patterns from the past. We call these past weather patterns "analogs." If you look at all the severe weather reports from the top 15 "analogs" for Saturday's predicted weather pattern, you get the following maps. One map I saved from yesterday's output, the other is from today's output. Both show a large number of tornadoes stretching from Texas into the Deep South.

Does this mean we're going to have a tornado outbreak on Saturday? No. Several of the analogs show NO severe weather at all.

But does this mean we *could* have a tornado outbreak on Saturday? Yes, it is possible, but only IF the current computer projections verify. The key here is the track and strength of an upper level low that is currently over the north Pacific Ocean where observations are sparse. As it gets closer to our observation network, I would expect the computer forecasts to shift a bit in the days ahead. We will see.

One interesting "analog" I see on both maps is October of 2006. On October 12-13, a major lake effect snow event took place over Buffalo, NY. Four days later, a major tornado outbreak occurred right here over Southeast Texas and Louisiana.

Fast forward to today. A major lake effect snow event just took place near Buffalo, NY. Four days later would be Saturday...will history repeat itself? Time will tell. The final map attached to this post shows the current "Day 4" severe weather outlook for the US, with a risk area drawn right over our part of the state.

https://fbcdn-photos-g-a.akamaihd.net/h ... 6a5c1f5827

https://fbcdn-photos-e-a.akamaihd.net/h ... b2afaf8fd6

Deja vu? Interesting, there was a huge snow event in October 2006 in Buffalo area.

[jeff]

Think the tornado threat will be enhanced along NE moving maritime boundary clearly noted from Matagorda Bay ESE into the Gulf of Mexico. Winds NE of the boundary are backed to the E and ESE while winds SW of this boundary are out of the SE to SSE. This backed low level flow near this boundary will support enhanced low level shear for the first round of activity late morning to early/mid afternoon on Saturday.

[Ptarmigan]

I'm not seeing anything that raises a big flag that changes the overall thinking regarding tomorrow. The warm front has moved well to the N of Central and SE Texas and as the upper low over Southern California begins its trek ESE across N Mexico and nears W Texas, rapid cyclogenesis should commence and a potent surface low will likely develop. If I recall correctly back in November 1992, we had a few early day storms and cloudiness before all heck broke loose and low topped rain wrapped tornado reports began coming in. The severe analogs for our cool season severe weather episodes are still showing up, so I encourage folks to not let their guard down tomorrow and into Sunday for our neighbors in Louisiana and Mississippi. After an extended cold snap, the last thing on many folks mind is a severe weather episode.

http://www.ssd.noaa.gov/goes/comp/ceus/wv-animated.gif

I have noticed before the day of tornado outbreaks, there are storms.

Here is weather record between 11/19/1992 to 11/22/1992 from Intercontinental Airport.
11/19 62/77 2.05
11/20 59/62 0.51
11/21 50/72 0.51
11/22 42/60 0

[srainhoutx]

The latest sounding analysis suggest the cold core upper low has cooled substantially (-12C to -17C) increasing lapse rates across West Central Texas. This would tend to favor increasing chances of super cell development across the Edwards Plateau into Central/S Central Texas. It is also noteworthy that some very impressive wind energy from the Eastern Pacific is moving across Mexico in association with a disturbance at the mid/upper levels. I would not be surprised to see the severe modes increase later this afternoon into tonight across our Region.

[Katdaddy]

A few showers and thunderstorms developing across N, Central and S TX this morning. The SPC continues the Slight Risk over the southern half of TX including SE TX. The severe weather threat will be a conditional event. Drier dew points filtered into the NE portions of SE TX overnight and we have partly cloudy skies. The clouds may be our friend today lessing the severe weather threat by not allowing much surface heating to occur. If heating occurs and storms can become surface based; the parameters (low level jet - LLJ, shear values, and helicities) will be there for all modes of severe weather (damaging straight line winds, hail, and possible tornadoes). During the late evening and night the storms will likely to congeal into an MCS over SE TX. Primary threat time remains during the afternoon from 3PM into the night time hours for the Houston-Galveston areas. By 2AM the MCS should E of SE TX plowing into SW LA. Sunday will feel like the first Spring 2015 day with sunny skies and highs in the upper 70s to low 80s. Turkey week also looks great with mostly sunny skies and highs in the 60s and low in the 40s. For now its time to wait, watch, and see how this conditional threat plays out.

[srainhoutx]

Morning briefing from Jeff:

Powerful upper level storm system heading for TX with widespread thunderstorms likely.

Associated lift and cold pocket with approaching upper level system is currently starting to cross the Rio Grande out of NE MX where recent Del Rio sounding has shown a significant decrease in mid level temperatures from 17C to 12C in the last 12 hours and very steep lapse rates on the order of 9C/KM. Sounding shows the capping inversion lifting and eroding and should be gone in the next few hours. Of somewhat great interest has been what has transpired overnight over SE TX with low level easterly winds backing dry dewpoints into the area from the east. Dewpoints have fallen into the low 50’s at Beaumont versus the mid 60’s at Victoria. SPC 850mb moisture analysis also shows a dry pocket from the ENE over SE TX and this was shown a couple of days ago by the GFS model. The area between the “moist” and “dry” surface air appears to be along a line from offshore of Galveston to near Port O Connor to Austin. Increasing large scale ascent from the approaching upper storm system is resulting in development of thunderstorms along this boundary, but thus far they have not gone severe. Expect this boundary to lift northeastward this morning allowing better moisture to surge into the area. Backed low level winds near this feature could enhance the tornado threat, but with such marginal instability in place currently it is likely to keep the tornado threat at least through early afternoon low.

Shear values and instability really increase this afternoon as powerful 100kt mid level jet streak carves across S TX into the coastal bend overtopping a 40kt low level jet. 0-6km shear values increase to nearly 50-60kts supporting low level storm rotation. Instability peaks in the 1000-2000 J/kg range over the coastal bend and then gradually weakens northward over SE TX. With lift at this point maximized over the warm sector numerous severe thunderstorms are likely with some producing tornadoes. Will focus the highest threat bounded by a line from Columbus to Wharton to Angleton and southwest where instability will be greatest. Meso models show the initial line of storms to move SW to NE across the region by mid afternoon and then a gradual slowing and even stalling of this line north of I-10 for a period of time this evening as the area awaits the actual push from the incoming upper level system. This greatly increases the flash flood threat for the evening hours as a period of cell training is looking fairly likely over some portion of SE TX from about 300pm until 900pm. A very close look at the TX TECH 3km WRF model even suggests a meso scale outflow boundary may be generated across our central counties (I-10) by late afternoon with numerous storms feeding northward into a slow moving or stationary line….this has some support from the HRRR (Rapid Refresh model).

Secondary episode of adverse weather will move across the region between 600pm and 200am…in fact there may not really be a break. The second event will be more of a squall line that develops along I-35 and spreads eastward across SE TX this evening. Damaging winds will be the main threat with this line where bowing segments help transport wind energy aloft down to the surface. Best threat for wind damage appears to focus in the defined warm sector along and southwest of a line from College Station to Katy to Galveston. Corridors of wind damage will be possible with winds up to 60-70mph.

Flash flood threat continues to increase with more expected development over a longer duration. Main concern is cell training along any boundaries that will be developed by storm generated cold pools. Fairly concerned on the meso scale models attempting to show meso scale outflow boundary development for about a 6 hour period this afternoon/evening which anchors storms across our central and northern counties. Given the expected increase in moisture today across the area, storms will be capable of a quick 1-2 inches and where this extends over a couple of hours rapid flash flooding may result. Will just have to watch radar trends and see when/if storms begin to slow and train as that is where the flooding risk will be maximized. Both of the TX TECH and HRRR models give support for this scenario, but that does not mean they will be correct nor have the correct location.

The next 6 hours will likely begin to transition into watch and warning mode with defined threats becoming realized across the region.

[srainhoutx]

A weak frontal wave is developing near Matagorda Bay prompting Special Marine Warnings. These storms are moving NE and are associated with a maritime warm front which will moisten up our atmosphere rather quickly and push out the direr air that filtered in overnight.

[srainhoutx]

From Nesdis:

SATELLITE PRECIPITATION ESTIMATES..DATE/TIME 11/22/14 1601Z
SATELLITE ANALYSIS BRANCH/NESDIS---NPPU---TEL.301-683-1404
LATEST DATA USED: GOES-13 1545Z KUSSELSON
NOAA AMSU:1147Z 1328Z DMSP SSMIS:1126Z 1320Z 1308Z
.
LOCATION...TEXAS...OKLAHOMA...
.
ATTN WFOS...HGX...FWD...OUN...EWX...SJT...
ATTN RFCS...ABRFC...WGRFC...
.
EVENT...BEST MOISTURE AND ADVECTION FROM WESTERN GULF/S TEXAS...POOR
EAST PACIFIC MOISTURE WHICH WILL LIMIT WIDESPREAD HVY RAIN EVEN WITH
ANOMALOUS LOW COMING OUT...
.
SATELLITE ANALYSIS AND TRENDS...PACIFIC MOISTURE AND ADVECTION OVER THE
MEXICAN MOUNTAINS INTO WESTERN AND CENTRAL TEXAS NOT VERY GOOD TILL YOU
GET TO 20N/105W AND SE AND THEN THE ADVECTION IS MORE TOWARD S TX AND
INCREASING MOISTURE ON TOP OF BETTER WESTERN GU;F/S TX LOW LEVEL MOISTURE.
THOUGH RAIN HAS BEEN WIDESPREAD SW/S CENTRAL
INTO C OKLAHOMA...LIMITING OF MOSTLY WEST GULF MOISTURE PREVENTING REALLY
BIG AMOUNTS THERE. THIS IDEA OF THE MAJORITY OF THE MOISTURE AT THE
LOW LEVELS AND FROM S TX/WESTERN GULF CAN KEEP RAIN ACCUMULATIONS FROM
GETTING TOO HEAVY DESPITE VIGOROUS ANOMALOUS LOW NOW BOTTOMING OUT OVER N
CENTRAL MEXICO AND SHORTLY BEGIN ITS NORTH OF EAST TRACK INTO THE BIG BEND
AREA THIS AFTERNOON. EASTERN PACIFIC JET INTO S OREGON/FAR NORTHERN
CA NOSING SE THROUGH NEVADA INTO NW ARIZONA AND WILL HELP CONTINUE TO
PUSH UPPER LOW EAST AND MAKE THIS A MODERATE PROGRESSIVE SYSTEM...WHICH
SHOULD BE ANOTHER NEGATING FACTOR TO PROLONGED AND EXPANSIVE HEAVY RAIN
CENTRAL TEXAS.

.
AN ANNOTATED SATELLITE GRAPHIC SHOWING THE HEAVY PRECIPITATION
THREAT AREA SHOULD BE AVAILABLE ON THE INTERNET ADDRESS LISTED
BELOW IN APPROXIMATELY 10-15 MINUTES.
.
SHORT TERM OUTLOOK VALID 1600-2100Z...MEDIUM CONFIDENCE FACTOR
IN SHORT TERM OUTLOOK...PWAT MOISTURE FLOW CONTINUING NORTH AND NW INTO
CENTRAL AND
INTEROR EASTERN TX AND SE OKLAHOMA. UPPER LEVEL LOW JUST SOUTH/SE OF KELP
WILL BEGIN IT ENE TRACK INTO THE BIG BEND AREA OF TEXAS AND INCREASING
ACT ON FIRST WESTERN EDGE OF DEEP MOSTLY WESTERN GULF OF MEXICO/S TEXAS
MOISTURE ADVECTION INTO C TEXAS...THEN EAST ACROSS SE OKLAHOMA THIS PERIOD
AND EASTERN TEXAS MOSTLY AFTER THIS PERIOD. SUBTROPICAL JET AS PER
WATER VAPOR INCREASING ACROSS FAR SOUTHERN TEXAS...NO POLAR JET TO SPEAK
OF...SO UNLESS THERE IS INCREASED DIFFLUENCE AND INCREASED ORGANIZATION
OF SLOWER MOVING CELLS...JUST WON'T BE ENOUGH TIME TO PRODUCE WIDESPREAD
HVY RAIN FROM JUST THE WEST GULF/S TEXAS DEEP MOISTURE THAT WAS MOSTLY
LESS THAN 2 STANDARD DEVIATIONS ABOVE CLIMO. SEE CURRENT WPC EXCESSIVE
DISCUSSION ISSUED 1411Z AND METWATCH 1-2 PLANET CHAT MESSAGE FROM 1431Z.

[Ptarmigan]

This could get rough.

[srainhoutx]

Update from Jeff:


Radars out of Houston, Corpus Christi, and Austin show significant increase in thunderstorm development over the last 2 hours from north of Corpus Christi to Austin in region of enhanced lift in broad warm air advection regime southwest of northeast moving maritime warm front.

 

Recent storms north of Corpus Christi have begun to show some modest low level rotation, yet to this point activity has remained below severe criteria. Expect a rapid increase in coverage over thunderstorms over SE TX over the next few hours.

 

Threat matrix is starting to shift slightly away from severe weather and more toward heavy rainfall with widespread low cloud cover in place preventing surface heating and keeping instability low. With that said visible satellite images show thinning and clearing over cloud cover from roughly College Station to Wharton and this may allow instability to increase in this corridor as SC TX activity approaches in the next 2-3 hours. Heavy rainfall factor is clearly noted with training convection along I-35 corridor currently and this threat will be watched very closely this afternoon especially along and north of the I-10 corridor.

 

A slightly more enhanced severe risk will likely begin to take place along the Rio Grande over the next 6 hours as strong forcing moves into an increasingly unstable air mass over that area. The development of an eastward moving squall line/MCS appears likely with a damaging wind threat on its leading edge which will sweep across SC, coastal bend, and parts of SE TX overnight.

[Portastorm]

Getting some heavy thundershowers in SW Austin at the moment with training on radar, could be a soggy afternoon.

[Andrew]

Kcll sounding earlier this morning.

[Katdaddy]

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
235 PM CST SAT NOV 22 2014

THE NATIONAL WEATHER SERVICE IN AUSTIN SAN ANTONIO HAS ISSUED A

* TORNADO WARNING FOR...
EXTREME SOUTH CENTRAL FAYETTE COUNTY IN SOUTH CENTRAL TEXAS...
LAVACA COUNTY IN SOUTH CENTRAL TEXAS...
THIS INCLUDES THE CITY OF HALLETTSVILLE...

* UNTIL 315 PM CST

* AT 233 PM CST...NWS METEOROLOGISTS HAVE DETECTED A SEVERE
THUNDERSTORM CAPABLE OF PRODUCING A TORNADO NEAR EZZELL...OR 8
MILES SOUTH OF HALLETTSVILLE...MOVING NORTHEAST AT 30 MPH.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
SUBLIME

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IN ADDITION TO THE TORNADO...THIS STORM IS CAPABLE OF PRODUCING
DESTRUCTIVE STRAIGHT LINE WINDS AND VERY HEAVY RAINS.

THE SAFEST PLACE TO BE DURING A TORNADO IS IN A BASEMENT. GET UNDER A
WORKBENCH OR OTHER PIECE OF STURDY FURNITURE. IF NO BASEMENT IS
AVAILABLE...SEEK SHELTER ON THE LOWEST FLOOR OF THE BUILDING IN AN
INTERIOR HALLWAY OR ROOM SUCH AS A CLOSET. USE BLANKETS OR PILLOWS TO
COVER YOUR BODY AND ALWAYS STAY AWAY FROM WINDOWS.

IF IN MOBILE HOMES OR VEHICLES...EVACUATE THEM AND GET INSIDE A
SUBSTANTIAL SHELTER. IF NO SHELTER IS AVAILABLE...LIE FLAT IN THE
NEAREST DITCH OR OTHER LOW SPOT AND COVER YOUR HEAD WITH YOUR HANDS.

[singlemom]

Am I missing something? It appears that this system is moving to the northeast, and we're going to get a glancing blow from this? I'm in Spring and it looks like the system to the southwest is moving far north of us? What am I missing?

[srainhoutx]

Am I missing something? It appears that this system is moving to the northeast, and we're going to get a glancing blow from this? I'm in Spring and it looks like the system to the southwest is moving far north of us? What am I missing?

N of I-10 still looks like we could see some strong storms if the high resolution rapid refresh meso guidance is correct. These storms would come tonight as the upper low nears our area.

[srainhoutx]

Severe Thunderstorm Watch issued to our S and W.

Code: Select all

BULLETIN - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 557
   NWS STORM PREDICTION CENTER NORMAN OK
   310 PM CST SAT NOV 22 2014

   SEVERE THUNDERSTORM WATCH 557 IS IN EFFECT UNTIL 1000 PM CST
   FOR THE FOLLOWING LOCATIONS

   TXC047-061-127-131-137-163-215-247-249-261-271-283-311-323-325-
   385-427-463-465-479-489-505-507-230400-
   /O.NEW.KWNS.SV.A.0557.141122T2110Z-141123T0400Z/

   TX 
   .    TEXAS COUNTIES INCLUDED ARE

   BROOKS               CAMERON             DIMMIT              
   DUVAL                EDWARDS             FRIO                
   HIDALGO              JIM HOGG            JIM WELLS           
   KENEDY               KINNEY              LA SALLE            
   MAVERICK             MCMULLEN            MEDINA              
   REAL                 STARR               UVALDE              
   VAL VERDE            WEBB                WILLACY             
   ZAPATA               ZAVALA              

[srainhoutx]

Update from Jeff:

A few isolated supercells have erupted in the last hour over the western portions of SE TX.

Storm over Lavaca county is showing strong low level rotation on Doppler radar and will be moving into Colorado County shortly. Radar shows a strong couplet and notch on the southern flank of the cell with tight enough rotation to require a tornado warning for this cell. This cell appears to be in the process of crossing a NW to SE boundary laying from near College Station to Sugar Land to Freeport which is the dividing line between the drier air to the NE and the moist unstable warm sector to the SW. Storms crossing such boundaries with backed low level flow can at times quickly become tornadic. Additional cells are rapidly developing in warm sector from Matagorda Bay NNE toward Wharton and these will be closely watched for severe and tornado potential.

Expect widespread development to continue for the next several hours with our western and northwestern counties favored. Strong energy is preparing to cross the Rio Grande and SPC will be issuing a either a tornado or severe thunderstorm watch for much of SW/S TX shortly as severe storms have rapidly developed over the mountains of NE MX and will be moving toward a moderately unstable air mass as they cross the Rio Grande. It is likely these storms will grow upscale into a squall line this evening and impact much of the region with a damaging wind threat.

[singlemom]

N of I-10 still looks like we could see some strong storms if the high resolution rapid refresh meso guidance is correct. These storms would come tonight as the upper low nears our area.[/quote]

Thanks, again, S'rain for clearing things up. We've had a string of "Yikes! Weather!" forecasts that have not necessarily come true....but I guess that's forecasting for ya'.

[Andrew]

Some very nice clearing to our West. That will be a good area to keep an eye on for stronger storms.

http://www.ssd.noaa.gov/goes/east/sc/mflash-vis.html

[Heat Miser]

Looking to the southwest for our future. Still believe we'll see some very serious storms fire up and move our way a little later. Heck, I prefer thunderstorms at night anyway.