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Severe Weather Episode Nov 21-22-?


Radtechwxman

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SREF_prob_combined_sigtor__f057.gif

SREF_prob_combined_sigtor__f060.gif

After showing an empty map for several runs yesterday, the SREF's significant tornado ingredients parameter is increasing for Monday. It looks like we have a small '20' contour present on the 03Z graphic. While this convinces me we're going to have a busy severe weather day in my neck of the woods (or in this case, the flat open plains :D ) on Monday, it also makes me concerned the tornado potential may be increasing as well. I'm definitely going to be glued to the 0Z model runs as they come in later this evening.

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yea those hodos are really starting to look nice. if higher instability can be realized, i will def be more impressed. it is one hell of a drive from IL for me and i am on major time constraints thanks to work. i have a close eye on the models. i am still wondering how long discrete supercells would last. storm interference could be an issue. but like last week, new storms could keep forming south of the merging ones.

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This is a duplicate of the discussion I just posted on the Texas Storm Chasers website and is written with the general public in mind.

My thoughts that I posted in this morning’s discussion for Sunday generally remain the same, but a few things are beginning to change for Monday that I wanted to talk briefly about. Please note this is only an update and is meant to supplement this morning’s discussion. I’m planning to have an entirely new discussion posted early tomorrow morning.

View my morning discussion here.

gfsSP_850_spd_54-550x412.gif18Z GFS: 850 Millibar height/wind at 6 PM Monday

This graphic comes from the 18Z GFS, which is still rolling in the door as I type this around 4:30 PM. This graphic shows the 850 millibar output for 6 PM on Monday. If you read my discussion from this morning, you’ll recall that I mentioned that models were increasing the strength of the low level jet each supplemental run. I mentioned that the low level jet was pretty weak, and that the tornado potential would likely remain limited due to the small hodograph sizes, or turning with height. This run of the GFS has increased the low level jet’s strength. Instead of the 30-35 knot low level jet that was being indicated on last night’s North American Model (NAM) for 6 PM on Monday, the new 18Z GFS is showing a 45 to 50 knot low level jet south of the south, veering to the southwest the further west of Fort Worth you go. This is a dramatic increase in the speed of the low level jet and needs to be monitored very closely for consistency.

decatur.png0Z NAM: Simulated hodograph for Decatur, TX at 6 PM Sunday

hodo-550x547.png18Z GFS: Simulated hodograph for Dallas, TX at 6 PM Monday

The first graphic shows the hodograph I used as an example on this morning’s blog post for 6 PM Sunday. I explained how that the hodograph size looked to be limited due to weak lower level shear and that this would likely help limit the tornado threat. This still looks to be the case on Sunday, however there are indications that this may not be the case on Monday. This second graphic shows the simulated hodograph from the 18Z GFS for Dallas at 6 PM on Monday. Do you see how much larger the hodograph is on the second image verses the first? If this type of hodograph was present on Monday and we had adiquite amounts of instability, I could definitely see portions of North Texas having a substantial tornado threat.

HOWEVER, this is just one model run and it takes a lot more then wind shear to create the threat of tornadoes. I just wanted to point out that there is the possibility that we may be dealing with more then I originally thought on Monday. I’d recommend that everyone stay tuned, as Monday is already looking to be a busy severe weather day. Whether or not we deal with a substantial tornado threat is to be determined. I’m going to be posting a new discussion later tonight that will talk in depth about the possibilities for both Sunday and Monday. Stay tuned!

- David

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This is an email that was sent out to the local skywarn groups in North Texas this afternoon...

From: National Weather Service, Fort Worth

Date: Saturday 19 Nov 2011 13:49 CST

A cold front and an upper level storm system will affect North Texas Sunday and Monday and result in the potential for severe thunderstorms Sunday afternoon and night, and again on Monday afternoon and night. Thunderstorms Sunday and Monday will have the potential to produce large hail and damaging winds, with isolated tornadoes not out of the question Sunday. The tornado potential may be higher on Monday as both supercell thunderstorms and bow-echo squall lines are possible. Some areas, especially north of Interstate 20, may experience sufficient rainfall to cause runoff and localized flooding through Monday.

Overview...A cold front currently extends from Iowa into the Oklahoma Panhandle. This front will move into North Texas during the day Sunday before becoming stationary across our area Sunday night and Monday. An upper level disturbance currently over the eastern Pacific Ocean will move onshore tonight and approach North Texas Monday. Moist air from the Gulf of Mexico continues to surge northward and will help contribute to moderate instability Sunday and Monday.

Details and Timing...Widely scattered thunderstorms will be possible as early as tonight across North Texas, with small hail possible from the stronger storms. On Sunday, scattered thunderstorms are expected near and just north of the cold front which should be located generally from near Sherman to Denton to Eastland by late afternoon. The front will sink slowly southward Sunday night before becoming nearly stationary Monday. As the upper level storm system moves across Texas on Monday the most widespread and intense thunderstorms are expected.

Confidence...confidence is moderate on severe thunderstorms Sunday, and moderate to high on Monday. The primary uncertainty is on the exact locations of greatest severe weather risk, which will depend on the cold front location and the strength of the upper level storm system as it moves across our area.

Bottom Line...Monitor our latest forecasts, discussions and outlooks for the latest information on the cold front location since it will impact the severe weather threats and timing. We will keep our web site and Facebook page updated with the latest information.

Useful NWS web sites:

North Texas Hazard Planner

NWS Fort Worth Facebook Page

Graphical Severe Weather Warnings Page (when warnings are in effect; joint venture with NCTCOG)

As always, please give us a call for additional information or support, and Happy Thanksgiving to all!

Bill

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Doubt that quite a bit.

TORCONs for 11/7 (per Dr. Forbes' FB wall https://www.facebook.com/home.php?ref=home#!/twcdrforbes):

Issued Friday 11/4: 5

No posts 11/5

Issued Sunday 11/6: 4

Issued Monday 11/7:5

TORCONs for 11/21 (again per his FB wall):

Issued Yesterday: 5

Issued Today: 4

I'm not positive I understand what it is you doubt. If it's what I said about this being for publicity, then please explain how the TORCON value could be so high so many days out with such forecasting uncertainties and then decrease as we get closer and output begins to look more favorable for an event. I don't doubt Dr. Forbes' knowledge or forecasting expertise, but it seems a tad bit dubious, like throwing out bait to grab people's attention and then keeping them hooked with each passing update. It seems that a day 4 TORCON of 5 is pretty bullish, no matter what time of year, but especially in an area that, though not unheard of, is not the most climatologically-favored area for such an event this time of year.

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Convective forecasting is hard. My first response to a series of altered forecasts would certainly not be "it's for publicity." That's a pretty crass and cynical charge against a widely respected meteorologist.

Exactly, which is why putting a 50% chance of tornadoes within 50mi of a point for a day 4 forecast for a setup that, though it looks favorable for severe weather, has some big question marks to it seems dubious. Maybe it is indeed the cynic in me that somewhat questions the ability to do that.

Also, my original post wasn't so much about Dr. Forbes personally but more about TWC as a whole. I never have questioned, nor would I ever question, whether or not he deserves the respect he has. He is one of the most productive and admirable severe weather researchers in history. I'm not positive, but something tells me that TORCON goes well beyond him. It's been a huge attraction for TWC on the whole since it was debuted. The public doesn't read SPC outlooks or look at SPC probability forecasts on the whole...they do watch for and read about the TORCON. And for that, they frequent TWC...

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Exactly, which is why putting a 50% chance of tornadoes within 50mi of a point for a day 4 forecast for a setup that, though it looks favorable for severe weather, has some big question marks to it seems dubious. Maybe it is indeed the cynic in me that somewhat questions the ability to do that.

Also, my original post wasn't so much about Dr. Forbes personally but more about TWC as a whole. I never have questioned, nor would I ever question, whether or not he deserves the respect he has. He is one of the most productive and admirable severe weather researchers in history. I'm not positive, but something tells me that TORCON goes well beyond him. It's been a huge attraction for TWC on the whole since it was debuted. The public doesn't read SPC outlooks or look at SPC probability forecasts on the whole...they do watch for and read about the TORCON. And for that, they frequent TWC...

Agreed. During the NWA meeting last month in Birmingham, a public forum was held that surveyed multiple victims of the April 27th Super Outbreak. One of the questions was related to how they, as the individual, gauged a potential severe weather threat. More then a few folks responded with the TORCON value from The Weather Channel and how it was the first '10' in the history of the algorithm. Ignoring the question if it has any scientific basis to it, the 'TORCON' algorithm has become a primary indicator of a potential severe weather threat to the general public. I see folks mentioning it on my facebook page all the time. Yesterday when Forbes issued a value of 5 for North Texas, I had multiple people come to the Texas Storm Chasers page and ask what we were expecting for Monday. In terms of Marketing, The Weather Channel has gold mine on their hands. Do I use the TORCON value in explaining my forecasts to the general public? Hell no. My opinion of The Weather Channel revolves around their newsdesk employees along with off air relationships with their on-air talent. I will say that after reviewing their coverage from April 27, May 22, and May 24th I was impressed. If they keep doing the kind of coverage they did those three days, my respect for them as a responsible source of breaking weather news will continue to slowly return. As of now, I don't refer anyone to The Weather Channel for weather information.

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Simulated sounding from the 0Z NAM at 6 PM on Monday for Spinks Airport in Southern Fort Worth (on the Tarrant/Johnson county line). Speaking for residents in North Texas, we have a big problem.

that is a problem indeed. wow. that is something you would see in early spring. that hodo is incredible. based on that, looks like nocturnal tornadoes could be a real threat. that would even support the possibility of strong tornadoes. excellent directional shear. the LLJ really ramps up that time of night. hope everyone plays close attention to the weather. we dont need any more tornado deaths this year...

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that is a problem indeed. wow. that is something you would see in early spring. that hodo is incredible. based on that, looks like nocturnal tornadoes could be a real threat. that would even support the possibility of strong tornadoes. excellent directional shear. the LLJ really ramps up that time of night. hope everyone plays close attention to the weather. we dont need any more tornado deaths this year...

I'm not sure if I buy the nocturnal tornado threat. While the hodographs are definitely impressive, we seem to have a fairly steady consensus that we're going to have a strong QLCS in progress by 6 PM. That would help reduce the tornado threat a bit, although QLCS tornadoes would be quite possible along with very strong straight line winds.

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I'm not sure if I buy the nocturnal tornado threat. While the hodographs are definitely impressive, we seem to have a fairly steady consensus that we're going to have a strong QLCS in progress by 6 PM. That would help reduce the tornado threat a bit, although QLCS tornadoes would be quite possible along with very strong straight line winds.

good point. i forget to mention storm mode in my previous post. with the main trough axis moving over this area around 0z, the forcing will most likely cause storms to line up along or just ahead of the cold front. a QLCS is a good bet. but you gotta watch those tail end charlie's. with an environment as shown on the sounding, any semi discrete storm could quickly go tornadic along with embedded supercells in the line.

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Probably a rather strongly worded Day 2 about to come out.

Day 1:

post-6489-0-52844200-1321768517.gif

post-6489-0-28556400-1321768540.gif

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1130 PM CST SAT NOV 19 2011

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM NRN TX NEWD INTO ERN AR...

...SYNOPSIS...

A CLOSED LOW OFF THE NRN CA COAST IS FORECAST TO MOVE SEWD AND

DEAMPLIFY INTO AN OPEN WAVE AS IT REACHES SRN NV/SRN CA BY EARLY

MON. THIS WILL MAINTAIN 40-50 KT SWLY MID LEVEL FLOW FROM SOUTH OF

AZ/NM NEWD THROUGH THE SRN PLAINS...OH VALLEY AND INTO NEW ENGLAND.

DESPITE THE SWLY FLOW ALOFT...THE DENSITY OF A SHALLOW COLD AIR

MASS...CURRENTLY STRETCHING FROM THE GREAT LAKES SWWD THROUGH

CENTRAL MO AND INTO THE TX PANHANDLE...WILL MOVE SLOWLY SEWD. THE

LEADING EDGE OF THIS COLDER AIR IS EXPECTED TO EXTEND NEAR A JBR-NW

OF LIT-ACT-SJT LINE AT 21/00Z AND WILL PROVIDE THE FOCUS FOR

POSSIBLE SEVERE STORMS THIS FORECAST PERIOD.

...NRN TX NEWD INTO ERN AR...

THERE IS SOME UNCERTAINTY HOW MUCH CONVECTION WILL DEVELOP...

ESPECIALLY NEAR THE FRONT...DUE TO A LACK OF STRONGER DYNAMICAL

FORCING AND NEUTRAL 500 MB HEIGHT CHANGES. HOWEVER...A STRONG

TEMPERATURE CONTRAST NEAR THE BAROCLINIC ZONE AND BROAD LOW LEVEL

WARM ADVECTION MAY BE SUFFICIENT FOR SURFACE BASED STORMS TO

DEVELOP. ANY SURFACE BASED STORMS ARE EXPECTED IN A NARROW AREA

FROM NERN TX NEWD INTO CENTRAL AR. WITH DEWPOINTS IN THE UPPER

60S...SURFACE TEMPERATURES WARMING TO NEAR 80F AND MID LEVEL LAPSE

RATES AROUND 6.5 C/KM WILL RESULT IN A MODERATELY UNSTABLE AIR

MASS...MLCAPES UP TO 2000 J/KG. ALONG WITH THIS INSTABILITY...THE

DEEP LAYER SHEAR WILL FAVOR SUPERCELLS. STORMS THAT DEVELOP WILL

HAVE THE THREAT FOR HAIL...DAMAGING WINDS AND EVEN ISOLATED

TORNADOES...MAINLY FROM 21-03Z.

DURING THE OVERNIGHT HOURS...THE STRENGTHENING LOW LEVEL JET... AND

CONSEQUENT ISENTROPIC/FRONTOGENETIC ASCENT...COMBINED WITH

INSTABILITY LOCATED ABOVE THE SHALLOW COLD AIR MASS...SHOULD RESULT

IN THUNDERSTORMS TO DEVELOP ON THE COLD SIDE OF THE FRONT.

SUFFICIENT SHEAR AND ELEVATED INSTABILITY WILL EXIST FOR STORMS TO

PRODUCE SEVERE HAIL.

..IMY/LEITMAN.. 11/20/201

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Day 2, rather large 30% area, I would expect that a sig-hatched area may eventually be added if the upward trends in the models continue. Good discussion from Edwards.

post-6489-0-15488500-1321769167.gif

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1200 AM CST SUN NOV 20 2011

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS W TX TO WRN AR...

...SYNOPSIS...

AS OF 20/05Z...MOISTURE CHANNEL IMAGERY INDICATED MID-UPPER LOW

ABOUT 125 NM WNW CAPE MENDOCINO...WITH SHORTWAVE TROUGH SWWD ACROSS

PAC. THIS POSITION IS MORE NLY THAN PROGGED BY MOST MODEL RUNS

DURING PREVIOUS DAYS...AS WILL BE INLAND TRACK OF SHORTWAVE TROUGH

THROUGH DAY-2 PERIOD. STG VORTICITY LOBE WILL MOVE S OF CURRENT

SYSTEM-RELATIVE LOW POSITION...RESULTING IN SOMEWHAT

NEGATIVELY-TILTED...HIGH-AMPLITUDE...OPEN-WAVE TROUGH FROM ERN NV TO

NRN GULF OF CA BY BEGINNING OF PERIOD. TROUGH SHOULD MOVE EWD TO

CENTRAL/SRN NM...FAR W TX AND NRN CHIHUAHUA BY 22/00Z...BECOMING

POSITIVELY TILTED FROM ERN KS TO W-CENTRAL TX BY 22/12Z.

STG SFC COLD FRONT NOW MOVING SEWD OVER ERN MO...S-CENTRAL OK AND

SWRN PANHANDLE OF TX WILL DECELERATE THROUGH DAY-1 PERIOD...BECOMING

QUASISTATIONARY BY 21/12Z OVER SRN KY...WRN TN...CENTRAL AR...AND

NERN THROUGH W-CENTRAL TX. OPERATIONAL SPECTRAL/NAM AND ALL SREF

MEMBERS RETREAT BOUNDARY SLOWLY NWD AS WARM FRONT ACROSS N-CENTRAL

TX AND SE OK DURING 21/18Z-22/00Z TIME FRAME. FRONTAL-WAVE LOW

SHOULD DEVELOP OVER W-CENTRAL TO N-CENTRAL TX AROUND 22/00Z...THEN

MOVE NEWD AND STRENGTHEN...REACHING SERN MO BY END OF PERIOD.

BEHIND THIS LOW...COLD FRONT SHOULD SURGE SEWD ACROSS W

TX...REACHING CENTRAL AR...NE TX...AND CENTRAL/SW TX BY 22/12Z. BY

MID-LATE AFTERNOON...SFC DRYLINE SHOULD EXTEND FROM FRONTAL

INTERSECTION OVER W-CENTRAL TX OR ERN PERMIAN BASIN REGION SWD INTO

NRN COAHUILA.

...SRN PLAINS TO MID-SOUTH REGION...

EARLY-PERIOD TSTMS ALONG AND N OF FRONT...FROM RED RIVER REGION

ENEWD ACROSS MID-SOUTH...MAY POST ISOLATED HAIL THREAT. POTENTIAL

FOR SPORADIC HAIL IN THIS REGIME WILL CONTINUE THROUGHOUT PERIOD AS

PLUME OF LOW-LEVEL WAA AND MOISTURE TRANSPORT EXTENDS EWD ACROSS TN.

GREATER SVR THREAT IS FCST TO DEVELOP FROM AROUND MIDDAY

ONWARD...NEAR FRONT. THIS WILL OCCUR AS STG LARGE-SCALE ASCENT AND

INTENSIFYING DEEP-LAYER SHEAR PRECEDE MID-UPPER TROUGH IMPINGE ON

PROGRESSIVELY MORE MOIST/BUOYANT AIR MASS ON BOTH SIDES OF SFC

FRONT. SCATTERED-NUMEROUS TSTMS ARE LIKELY ALONG AND N OF SFC FRONT

DURING AFTERNOON AND EVENING...AMIDST STG DEEP-LAYER ASCENT. SFC

BAROCLINIC ZONE WILL REMAIN QUITE STG EVEN AS IT BECOMES MORE

SHALLOW...BENEATH ELEVATED LOW-LEVEL WAA REGIME THAT WILL PRECEDE

SWRN CONUS TROUGH. AS SUCH...SFC-BASED EFFECTIVE LIFTED PARCELS

WILL DISAPPEAR WITHIN VERY SHORT DISTANCE N OF FRONT...ALTHOUGH

CONSIDERABLE ELEVATED INSTABILITY IS EXPECTED IN PRE-STORM

ENVIRONMENT. SFC DEW POINTS MID-60S F ALREADY HAVE REACHED PORTIONS

N-CENTRAL/NE TX. MID-UPPER 60S DEW POINTS SHOULD BE COMMON ALONG

AND S OF FRONT BY EARLY DAY-2...SUPPORTING 1500-2000 J/KG MLCAPE IN

MOIST SECTOR. ALONG AND S OF FRONT...CORRIDOR OF MULTI-MODAL SVR

THREAT IS EXPECTED...INCLUDING POTENTIAL FOR SUPERCELLS AND BOW

ECHOES...WITH LARGE HAIL...DAMAGING WIND AND THREAT FOR TORNADOES AS

WELL. LARGEST LOW-LEVEL HODOGRAPHS ARE FCST ALONG FRONT...WITH 0-1

KM SRH POTENTIALLY REACHING 200-250 J/KG.

ACTIVITY N OF FRONT WILL POSE THREAT FOR LARGE HAIL...GENERALLY

DECREASING IN PROBABILITY NWD. 50-60 KT EFFECTIVE SHEAR MAGNITUDE

AND ELEVATED MUCAPE 1000-1500 J/KG ARE EXPECTED IN THAT REGIME.

FARTHER S...LINE OF TSTMS SHOULD DEVELOP ALONG COLD FRONT DURING

LATE EVENING/OVERNIGHT HOURS...POTENTIALLY BUILDING SWD INTO

PORTIONS CENTRAL/E TX WITH WIND/HAIL THREAT.

..EDWARDS.. 11/20/2011

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As of now, I don't refer anyone to The Weather Channel for weather information.

Me either. I work at my school and everyone knows im a weather geek and if someone tells me "oh the weather channel or weather.com said blah blah blah" I just shake my head and tell them not to use them for forecasts/info.

And after looking at the 0z runs, I'd target somewhere near ABI to start. Get on em early.

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At the risk of stating the obvious, I'd say Monday hinges a lot on the northward progress of the retreating boundary. The airmass that just invaded central OK this evening is awfully cold (dropped from ~70 F to ~35 F on the W side of the metro since late afternoon), and should probably clear I-20 to a couple counties E of DFW by tomorrow evening. If we see a good last-minute push during the day Monday akin to November 7, with the warm sector reclaiming places like Gainesville and Duncan, this setup looks relatively impressive for tornadoes. If the boundary bisects the Metroplex at showtime, though, I'm not sure I'd say that.

Tough call. The bias with recent events is seemingly toward keeping baroclinic zones in the Southern Plains suppressed too far south, but on the other hand, the NAM has trended decidedly southward with its position tomorrow -- and the RUC backs it up.

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Exactly, which is why putting a 50% chance of tornadoes within 50mi of a point for a day 4 forecast for a setup that, though it looks favorable for severe weather, has some big question marks to it seems dubious. Maybe it is indeed the cynic in me that somewhat questions the ability to do that.

Also, my original post wasn't so much about Dr. Forbes personally but more about TWC as a whole. I never have questioned, nor would I ever question, whether or not he deserves the respect he has. He is one of the most productive and admirable severe weather researchers in history. I'm not positive, but something tells me that TORCON goes well beyond him. It's been a huge attraction for TWC on the whole since it was debuted. The public doesn't read SPC outlooks or look at SPC probability forecasts on the whole...they do watch for and read about the TORCON. And for that, they frequent TWC...

TWC is much more popular than SPC and Forbes makes what's perceived as an aggressive forecast, so it's a ploy for attention? That's quite a jump in logic. I thought you had something else since you presented it like it was factual.

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