Severe Weather Thread November 7-8

[David Reimer]

Extended range models have been consistent in showing a powerful upper trough moving through the southern plains next weekend. While uncertainty is high on moisture return, I'd be willing to bet that the usual suspect areas for fall severe weather events (LA/AR/MS/TN) will end up getting at least a forced squall line next weekend with the passage of this system. SPC has put out a rather strongly worded extended range discussion for next weekend. I'd paste it here but I'm not in the mood to deal with this forum's shi**y formatting system.

[andyhb]

Could be a doozy. Here's the snippet from the discussion...rather impressive for seven days out.

A GREATER THREAT WILL LIKELY EXIST WITH A LARGER SCALE TROUGH

AMPLIFICATION THAT WILL TAKE PLACE FRI/D6 INTO SAT/D7 FROM THE

ROCKIES INTO THE PLAINS. MODELS ARE IN GENERALLY GOOD AGREEMENT

DEPICTING A POWERFUL MID LEVEL JET MAX OF 90-110 KT EJECTING EWD

ACROSS THE PLAINS AND THEN NEWD INTO THE GREAT LAKES BY SUN/D8.

WHILE IT APPEARS PROBABLE THAT SEVERE WEATHER WILL OCCUR WITH THIS

SYSTEM...THE PRIMARY PREDICTABILITY ISSUE IS TIMING OF THE TROUGH

AND MOISTURE RETURN.

THE DETERMINISTIC GFS MODEL SHOWS VERY ROBUST MOISTURE RETURN WITH

MID 60S F BOUNDARY LAYER DEWPOINTS AS FAR N AS THE KS/OK BORDER BY

SAT MORNING. THIS MAY BE AN OUTLIER SOLUTION AS THE ECMWF SHOWS A

TIGHT MOISTURE GRADIENT FARTHER S INTO NWRN TX AND NEAR THE RED

RIVER AT THAT TIME...WITH MID 60S ONLY INTO CNTRL TX. REGARDLESS OF

TIMING ISSUES...SUFFICIENT MOISTURE IS LIKELY TO RETURN NWD RAPIDLY

ACROSS THE SRN PLAINS...POSSIBLY BEING DRAWN NWD INTO THE MID MS

VALLEY BY LATE SAT. SHEAR PROFILES AS WELL AS FORCING WITH THIS

SYSTEM...AS CURRENTLY PROGGED...WOULD CERTAINLY FAVOR AN EXPANSIVE

AREA OF SEVERE POTENTIAL INCLUDING N TX...OK...KS...AR...MO.

DAMAGING WINDS AND TORNADOES WOULD BE THE MAIN THREATS WITH SUCH

STRONG WIND FIELDS. HOWEVER...GIVEN THIS EVENT IS 7 DAYS

OUT...AFOREMENTIONED PREDICTABILITY ISSUES WITH TROUGH TIMING AND

MOISTURE RETURN WILL FORESTALL ANY SEVERE AREAS UNTIL LATER

OUTLOOKS.

[Helicity]

Could be a great one.

[Helicity]

12z GFS is quite impresive, nice hemispheric flow, no closed low creating B-V-B, looks to get nice moisture return back as well.

[andyhb]

Here's the Canadian:

[JoMo]

hoping its more linearly forced here

[andyhb]

Springfield, MO AFD:

AS WE APPROACH NEXT WEEKEND...MEDIUM RANGE MODELS ARE REALLY

STARTING TO SHOW AN INTERESTING PATTERN. DEEP TROUGHING EVOLVES

ACROSS THE WESTERN CONUS. MEANWHILE...STRONG WARM AIR ADVECTION AND

GULF MOISTURE RETURN OCCURS ACROSS THE OZARKS. THIS AIR MASS SHOULD

HAVE HIGH QUALITY MOISTURE...AS THE GULF WILL HAVE SEVERAL DAYS TO

RECHARGE WITHOUT ANY CHANGE IN AIR MASS FLOWING OVER THIS SOURCE

REGION. WE`RE STILL 7 TO 10 DAYS OUT...BUT IF MODELS ARE

CORRECT...THEN WE WILL HAVE TO MONITOR THE RISK FOR AN EPISODE OF

ORGANIZED STORMS...EITHER NEXT WEEKEND...OR EARLY THE FOLLOWING WORK

WEEK. STAY TUNED

[Radtechwxman]

the million dollar question is if moisture can recover enough after the mid-week storm system. also we got to see if the sfc low goes more north like ECMWF shows or more south like GFS is showing. that will have major implications on the extent and severity of the severe weather. but i must say that coupled jet structure is gorgeous. this system has incredible speed shear.

[David Reimer]

This afternoon's FWD AFD

ECMWF/GFS IN RELATIVELY GOOD AGREEMENT WITH NEXT IMPRESSIVE SYSTEM

LIFTING OUT OF THE ROCKIES AND OVER THE PLAINS LATER SATURDAY AND

SATURDAY NIGHT WHERE SEVERE WEATHER APPEARS POSSIBLE FROM THE RED

RIVER VALLEY NORTH INTO OKLAHOMA/KANSAS/ARKANSAS/AND MISSOURI.

FURTHER NORTH...A SNOWSTORM MAY OCCUR WITHIN COLDER AIRMASS ACROSS

NEBRASKA INTO THE DAKOTAS AND THE UPPER MIDWEST BY SATURDAY NIGHT.

WE WILL FINE TUNE THE FORECAST THROUGH THE WEEK WITH REGARD TO ANY

SEVERE WEATHER POSSIBILITIES NEAR THE RED RIVER VALLEY NEXT WEEKEND.

[andyhb]

Updated Springfield AFD:

A STRONG PRESSURE GRADIENT WILL DEVELOP AND IT WILL BE WARM AND

BREEZY ON SATURDAY WITH DECENT MOISTURE RETURN COMING UP FROM THE

WESTERN GULF OF MEXICO. LOOKING AT PARAMETERS AND FORECAST

SOUNDINGS...CAPE WILL BE RUNNING FROM 500 TO 100O J/KG...0-3KM

STORM REL HELICITIES AROUND 500...PW VALUES AROUND 1.25-1.50

INCHES...GOOD SHEAR ENVIRONMENT...SURFACE DEWPOINTS IN THE LOW 60S

AND A DECENT DRYLINE/FRONT PUNCH FROM THE WEST. INGREDIENTS APPEAR

TO POINT TO POSSIBLE STRONG AND SEVERE STORMS NEXT SATURDAY AND

SOMETHING TO WATCH THROUGH THE WEEK. THE SYSTEM WILL QUICKLY MOVE

OUT BY SUNDAY WITH COOLER AND BREEZY WEATHER.

Little Rock AFD:

UPPER RIDGE WILL DOMINATE FOR FRIDAY AS NEXT UPPER SYSTEM DIGS

THROUGH THE NORTHERN ROCKIES. UPPER SYSTEM WILL MOVE TO THE

NORTHEAST SATURDAY AND TAKE ON A NEGATIVE TILT AS IT DOES. SYSTEM

WILL DRAG A COLD FRONT THROUGH THE AREA SATURDAY WITH PRECIPITATION

RETURNING TO THE FORECAST. CAN NOT RULE OUT STRONG TO POSSIBLY

SEVERE WEATHER WITH FAVORABLE WIND PROFILES FOR STRONG WINDS.

HOWEVER...SINCE WE ARE TALKING DAY SEVEN...WILL NOT GO REAL CRAZY.

FORECAST AREA WILL BE IN THE WARM SECTOR BUT MOISTURE RETURN COULD

BE THE LIMITING FACTOR. FUTURE RUNS WILL OF COURSE DICTATE THE

SEVERE WEATHER THREAT. LOOKS LIKE THE MAV/MEX GUIDANCE IS A LITTLE

TOO WARM AND WILL ADJUST ACCORDINGLY.

[brettjrob]

31/00z GFS rolling in is significantly slower, with phenomenal kinematics for Saturday from eastern KS/NE into IA/MO. At the same time, moisture return is too little too late to take advantage of it. With a 50-70 kt. LLJ over such a wide swath of the warm sector, this obviously bears watching for changes in the moisture situation.

[baroclinic_instability]

31/00z GFS rolling in is significantly slower, with phenomenal kinematics for Saturday from eastern KS/NE into IA/MO. At the same time, moisture return is too little too late to take advantage of it. With a 50-70 kt. LLJ over such a wide swath of the warm sector, this obviously bears watching for changes in the moisture situation.

See the other storm thread. This one is DOA for the exact reason you mentioned...poor trajectories and no moisture = poor wave amplification. Even the impressive ejecting anomaly can't make up for the awful theta-e regime. The day 3 wave absolutely destroys the warm sector.

[brettjrob]

See the other storm thread. This one is DOA for the exact reason you mentioned...poor trajectories and no moisture = poor wave amplification.

Good call... in addition to the much slower progression of the Fri/Sat system, the other thing that jumped out at me this run was the significantly more-amplified eastern trough (D3 system), which always spells moisture trouble.

[baroclinic_instability]

Good call... in addition to the much slower progression of the Fri/Sat system, the other thing that jumped out at me this run was the significantly more-amplified eastern trough (D3 system), which always spells moisture trouble.

I had some hopes that the GFS may be right regarding a low amplitude and much weaker ejecting cutoff wave day 3-4 (see 12Z GFS). Such a solution had some validity as it is quite common for a lot of the arctic air to stay across the intermountain W during strong surges with positive tilt shortwave troughs and high ampitude ridges behind it (not to mention the last system that affected the Front Range with the first winter storm of the season trended much slower and more cut off from the northern stream with more upper level energy remaining across the mtns), but the final wave remained progressive enough and came out pretty intact...intact enough for amplification and strong front to clear well through the GOM. GFS was quite the outlier (although it did suggest this solution for a number of runs), but it was hard to ignore the EC/CMC/NAM and the more progressive and intense solutions. What a difference really. I feel your pain as I know you lament many spring setups where this similar occurrence happens.

[Fred Gossage]

Yep, the position of the lead wave and the short wavelengths between the two systems causes an easterly to northeasterly low-level flow across most of the Gulf of Mexico ahead of the bigger system. The true maritime tropical air gets shunted way southward into the Bay of Campeche while only slightly modified continental air gets recirculated northward into the warm sector of the approaching stronger system.

[Stebo]

Yep, the position of the lead wave and the short wavelengths between the two systems causes an easterly to northeasterly low-level flow across most of the Gulf of Mexico ahead of the bigger system. The true maritime tropical air gets shunted way southward into the Bay of Campeche while only slightly modified continental air gets recirculated northward into the warm sector of the approaching stronger system.

Ideally we'd need the initial system to be weaker however the latest trends look for it to actually be fairly potent. Will be interesting to see if this holds face through the next couple of days as any weakening of that initial wave would allow for weaker CAA and more moisture return for the 2nd system.

[Fred Gossage]

I'm not sure just how much it would help. That strong high in the Northeast is usually not a good sign for quality moisture in the northern parts of the Gulf of Mexico. I'm sure that a weaker lead wave would lead toward slightly less cold air advection into the Gulf, but I'm not sure how much it would matter. With that high pressure in place, you'd still get more of an easterly trajectory closer to the Gulf Coast, than you would a southerly flow. We need the wavelengths to increase so that the ridge is allowed to be flatter... in order to get more significant moisture northward.

[Stebo]

I'm not sure just how much it would help. That strong high in the Northeast is usually not a good sign for quality moisture in the northern parts of the Gulf of Mexico. I'm sure that a weaker lead wave would lead toward slightly less cold air advection into the Gulf, but I'm not sure how much it would matter. With that high pressure in place, you'd still get more of an easterly trajectory closer to the Gulf Coast, than you would a southerly flow. We need the wavelengths to increase so that the ridge is allowed to be flatter... in order to get more significant moisture northward.

Yeah I see your point with respect to the Gulf Coast but a weaker system will probably not scour out the Western Gulf and the deep moisture in place there. Previous runs of the GFS had been showing the Western Gulf not getting scoured out as much which allowed for at least modest moisture return.

[Fred Gossage]

Yeah, your surface dewpoints would be better in a situation like that, but the problem that even those previous runs were showing... was that the moisture was shallow, especially once you get north of the Red River and involved more south-southwesterly to southwesterly winds above 925mb. That shallow moisture would very easily get mixed out in a situation like that. Still... we'd be talking about upper 50 to around 60-61 dewpoints... instead of the upper 40 to lower 50 dewpoints the guidance is starting to now suggest.

[Stebo]

Yeah, your surface dewpoints would be better in a situation like that, but the problem that even those previous runs were showing... was that the moisture was shallow, especially once you get north of the Red River and involved more south-southwesterly to southwesterly winds above 925mb. That shallow moisture would very easily get mixed out in a situation like that. Still... we'd be talking about upper 50 to around 60-61 dewpoints... instead of the upper 40 to lower 50 dewpoints the guidance is starting to now suggest.

With it being late season that might be enough juice (upper 50s to low 60s). It may not be a prolific tornado outbreak but it could be a decent severe weather outbreak with those types of dews. Of course that's a mute point right now as that moisture doesn't return far enough North. Still interesting times ahead with this system.

[Ed Lizard]

With it being late season that might be enough juice (upper 50s to low 60s). It may not be a prolific tornado outbreak but it could be a decent severe weather outbreak with those types of dews. Of course that's a mute point right now as that moisture doesn't return far enough North. Still interesting times ahead with this system.

50ºF dewpoints will return to parts of Iowa and Illinois by late Saturday afternoon, but the 60ºF dewpoints are just to the Red River, and the gap between the storm and moisture just look too far apart for anything meaningul.

Hoping the models come around...

[brettjrob]

Aaaaaaand the 12z GFS goes right back to the old solution with a progressive lead wave allowing for better (though still unimpressive) moisture return. If it were to trend just a bit more in that direction, then AR/MO would probably be looking at a threat worth mentioning.

Following the weekend system, more energy drops into the Desert SW as a GOM ridge builds in, setting the stage for another timeframe with potential around D+8. Moisture should be in greater supply should the pattern evolve similarly to how the GFS how shown over the past day or so, but given that it can't even make up its mind on D+3 right now...

[baroclinic_instability]

Aaaaaaand the 12z GFS goes right back to the old solution with a progressive lead wave allowing for better (though still unimpressive) moisture return. If it were to trend just a bit more in that direction, then AR/MO would probably be looking at a threat worth mentioning.

Following the weekend system, more energy drops into the Desert SW as a GOM ridge builds in, setting the stage for another timeframe with potential around D+8. Moisture should be in greater supply should the pattern evolve similarly to how the GFS how shown over the past day or so, but given that it can't even make up its mind on D+3 right now...

The UKMET still holds out a shred of hope...and it kicks out the cutoff wave out of the Rockies a bnit faster and digs the longwave a bit deeper with a slower jecting wave. It apparentyly has much more moisture return to have a bomb run like this.

[tornadotony]

Aaaaaaand the 12z GFS goes right back to the old solution with a progressive lead wave allowing for better (though still unimpressive) moisture return. If it were to trend just a bit more in that direction, then AR/MO would probably be looking at a threat worth mentioning.

Following the weekend system, more energy drops into the Desert SW as a GOM ridge builds in, setting the stage for another timeframe with potential around D+8. Moisture should be in greater supply should the pattern evolve similarly to how the GFS how shown over the past day or so, but given that it can't even make up its mind on D+3 right now...

Yeah it's hard to take anything past a day or two with more than a grain of salt right now, but it's notable that the overall pattern that the GFS and Euro feature is the harbinger pattern of a lot of significant severe weather episodes, with a "sacrificial" trough, if you will, that lifts NE quickly ahead of another substantial disturbance, with the intermediary time frame featuring potentially robust return flow aided by a large ridge off of the southeastern coast. The pattern certainly bears watching, especially for the disturbance next week, but discussing any specifics would be asinine.

[andyhb]

Yeah it's hard to take anything past a day or two with more than a grain of salt right now, but it's notable that the overall pattern that the GFS and Euro feature is the harbinger pattern of a lot of significant severe weather episodes, with a "sacrificial" trough, if you will, that lifts NE quickly ahead of another substantial disturbance, with the intermediary time frame featuring potentially robust return flow aided by a large ridge off of the southeastern coast. The pattern certainly bears watching, especially for the disturbance next week, but discussing any specifics would be asinine.

The weekend trough would be the sacrificial trough in this scenario, yes? Or am I reading that wrong?

[BeauDodson]

Been watching the Sunday system since October 22nd - had some thoughts it might bring severe but it appears it might lack rich moisture and instability - at least in my area. Still some time to go. The system after that one might be of interest - could be a priming type deal.

I did an analog on the Sunday storm and came up with this

[brettjrob]

I could pick out October 9, 2001, on that map before I even looked at the list. I'd sever my right arm for a repeat, though I don't think climatology would support a truly-comparable event in NOV this far west.

[Stebo]

Yeah it's hard to take anything past a day or two with more than a grain of salt right now, but it's notable that the overall pattern that the GFS and Euro feature is the harbinger pattern of a lot of significant severe weather episodes, with a "sacrificial" trough, if you will, that lifts NE quickly ahead of another substantial disturbance, with the intermediary time frame featuring potentially robust return flow aided by a large ridge off of the southeastern coast. The pattern certainly bears watching, especially for the disturbance next week, but discussing any specifics would be asinine.

I noticed the same thing in the models with respect to the pattern for the next 2 weeks.

[andyhb]

Interesting discussion D4-8 regarding the next trough (following the weekend one) from the SPC:

ON SUN/D6...THIS TROUGH WILL LOSE MOST OF ITS AMPLITUDE AS IT

CONTINUES NEWD ACROSS THE GREAT LAKES...LEAVING A BROAD AREA OF SWLY

FLOW BEHIND EXTENDING SWWD TO THE NEXT UPPER TROUGH FORECAST TO BE

OVER THE SWRN U.S. ON MON/D7. THIS WILL BE A MORE FAVORABLE REGIME

TO ADVECT SUBSTANTIAL LOW LEVEL MOISTURE NWD INTO THE PLAINS...WITH

AT LEAST LOWER 60S F DEWPOINTS LIKELY AS FAR N AS OK AND KS MON

AFTERNOON. LIFT ASSOCIATED WITH THIS RAPID WARM

ADVECTION...HOWEVER...WILL LEAD TO WIDESPREAD CLOUDS AND RAIN.

THUNDERSTORMS WILL BE LIKELY. SIGNIFICANT ENOUGH MODEL DIFFERENCES

EXIST AT D7 NOT TO INTRODUCE ANY SEVERE AREAS. THIS IS MAINLY DUE TO

THE POSSIBILITY OF WIDESPREAD CLOUDS AND RAIN...AND ALSO DIFFERENCES

IN MOISTURE RETURN MAGNITUDE...WITH THE GFS MUCH MORE BULLISH AND

THE ECMWF MUCH LESS SO.

THE UPPER TROUGH IS FORECAST TO MOVE ACROSS THE PLAINS MON NIGHT

INTO TUE/D8...AND THIS WOULD MOST LIKELY BE THE MOST ACTIVE SEVERE

DAY. THIS TYPE OF PATTERN WILL HAVE LESSER CHANCE FOR FAILURE GIVEN

A LONGER DURATION OF MOISTURE RETURN AND SUCH A BROAD BELT OF SWLY

FLOW/SHEAR FORECAST BY THE MODELS. AT THIS POINT...TIMING AND

AMPLIFICATION OF THE TROUGH IS THE MAIN ISSUE...WITH SEVERE WEATHER

POSSIBLE ON D7-D8 ANYWHERE FROM TEXAS NEWD INTO MO AND SRN IL. FOR

NOW...PREDICTABILITY IS TOO LOW TO CONFIDENTLY PLACE ANY SEVERE

AREAS.

..JEWELL.. 11/01/2011

[thewxmann]

The medium range modeling indicates there will be multiple disturbances that will ride the jet stream in the coming weeks. This is probably one of the more active patterns we've seen in awhile. While it is impossible to point out which, if any, of these disturbances will produce a severe weather event at this juncture, I think the potential is higher than what we've seen in recent Novembers.