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Severe Weather Threat in Dixie Alley/OV Feb 27 - Mar 1


Fred Gossage

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Just pushed out a 06Z SmartModel run with severe weather output. I am seeing two areas of potential for some severe criteria convection. First area is E. OK, AR, and S. MO. and the second area is C. MO to C. IL. Still trying to nail down potential winds, hail and tornado threats for those areas.

I have seen you talking about your smart model a lot. Care to talk a little more about it? What models are you using? Any plots?

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We're going to be really close tomorrow evening with convection initiating on whether or not convection will initiate on the dryline. The 12Z NAM has convective temperatures around 68F for 0Z tomorrow indicating the cap is somewhat weaker. Here's the oh so useful cap strength graphic from Earl.

CENTRAL_ETA212_ATMOS_LSI_36HR.gif

Perhaps an important thing to note is that the models seem to be underdoing the amount of wind behind the dryline, thus underestimating the amount of convergence, in addition to the possibility under doing surface temperatures. Looking at data, I'm still planning on being in Oklahoma tomorrow afternoon hoping for a storm to form off the dryline. Another possible play may end up being the warm front out in MO.

CENTRAL_ETA212_ATMOS_LSI_36HR.gif

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Well, I've got to drive down to Indpls for a conference from tomorrow evening until late Tues. Will not be happy if I get some elevated hailers on my vehicle and I will not be able to access internet during that time so I think I will exhibit withdrawal symptoms not being able to see what is happening with this interesting system during that time period.:arrowhead:

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The 12z run of the NAM really ups the anty for Monday across KY, TN, and probably nrn AL. Low-level and overall CAPE just explodes on this run compared to previous runs in vicinity of very strong low-level and deep-layer shear.

New GFS looks very squirrelly. Has weakened the overall system substantially versus previous runs and has a strange looking farther south, weaker secondary low plodding east through the TN valley into Monday. Neither run looks much like the 00Z ECMWF, although the NAM certainly maintains a much stronger looking system which is more like the ECMWF, although the timing is slower. At 00Z Tue the 12Z GFS has a 994 mb low just east of Downeast ME, a secondary 1004 mb low over central VA, with a weird looking positively tilted surface trough SW out of it into far SE MS. At the same time, the 00Z ECMWF had a well organized "double barrel" 993 over upstate NY/W PA with a good cold front down into GA/FL Panhandle. The NAM has a 998 mb surface low over KHTS with a front extending S into AL. The upper systems are also light years apart, GFS is way weaker than either the NAM or ECMWF. I love it when the model spread increases the closer to an event one gets.

Anyway, the ECMWF seems to be more consistent, although its ensemble mean would seem to allow for a somewhat weaker solution than its op run shows. Of the 12Z models in so far, I would lean right now towards a somewhat faster version of the NAM - will be interested to see the 12Z ECMWF.

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Yeah I'd love to see some maps with regards to this. Would be nice to get a visual representation.

I have added a overall map on the site that will update on each run I perform. The plots are values based on the environmental factors, for severe weather. I use adjusted upper air model data, which is data that has been refined by pireps, surface observations, and sometime Artymet, which is the Army version of the ROAB in away, I analyze 27 severe weather indicies and 38 synoptic scale factors such as sheer, wind speeds, direction, moisture, dry air and such. It then outputs a value, the highest output is a 1, which means every single environment factor has been met for severe weather.

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DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1130 AM CST SAT FEB 26 2011

VALID 271200Z - 281200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF EASTERN

OK/MUCH OF AR/SOUTHERN MO/SOUTHERN IL/FAR SOUTHWEST INDIANA/WESTERN

KY/WESTERN TN/NORTHERN MS...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS TO THE

LOWER/MIDDLE MS VALLEY AND LOWER OH VALLEY...

...SYNOPSIS...

CLOSED UPPER LOW CURRENTLY CENTERED OVER CA IS EXPECTED TO

OPEN/SHIFT EASTWARD OVER AZ/NM DURING THE DAY ON SUNDAY...AND TAKE

ON MORE OF A NEUTRAL/SLIGHT NEGATIVE TILT AS IT REACHES THE SOUTHERN

PLAINS/OZARKS LATE SUNDAY NIGHT. A REGIONAL OUTBREAK OF SEVERE

TSTMS...INCLUDING THE POSSIBILITY OF WIDESPREAD DAMAGING

WINDS/STRONG TORNADOES...SEEMS PROBABLE LATE SUNDAY AFTERNOON AND

ESPECIALLY SUNDAY NIGHT.

...SOUTHERN PLAINS/ARKLATEX/OZARKS/MID-SOUTH/LOWER OH VALLEY...

THE POSSIBILITY OF WIDESPREAD DAMAGING WINDS AND TORNADOES

/INCLUDING SOME STRONG/...IN ADDITION TO AN INITIAL BOUT OF LARGE

HAIL...WILL BEGIN LATE SUNDAY AFTERNOON...AND CONTINUE WELL THROUGH

THE NIGHT/EARLY MORNING HOURS OF MONDAY ACROSS PORTIONS OF THE

OZARKS/MID-SOUTH TO MIDDLE MS VALLEY/LOWER OH VALLEY.

INITIAL/DIURNAL DEEP CONVECTIVE COVERAGE IS A STILL A BIT UNCERTAIN

ALONG THE DRYLINE ACROSS OK/NORTH TX/FAR SOUTHERN KS DURING THE

DAYLIGHT HOURS...AS MUCH OF THE WARM SECTOR SHOULD REMAIN CAPPED

BENEATH AN ELEVATED MIXED LAYER. NONETHELESS...CURRENT THINKING IS

THAT AT LEAST AN ISOLATED INITIAL THREAT FOR SEVERE TSTMS WILL

DEVELOP BY SUNSET...WITH INITIALLY ISOLATED SUPERCELLS CAPABLE OF

LARGE HAIL AND A TORNADO THREAT ACROSS PORTIONS OF OK/FAR NORTH TX

AND PERHAPS FAR SOUTHERN KS.

OTHERWISE...A SEASONALLY MOIST LOW LEVEL AIRMASS...GENERALLY

CHARACTERIZED BY LOWER 60S F SURFACE DEWPOINTS...WILL BECOME

ESTABLISHED WITHIN A RELATIVELY BROAD WARM SECTOR ACROSS THE REGION

DURING THE AFTERNOON/NIGHT. A CONSIDERABLE INCREASE IN DEEP

CONVECTIVE COVERAGE/INTENSITY IS ANTICIPATED THROUGH THE

EVENING...AS LARGE SCALE FORCING FOR ASCENT/DEEP TROPOSPHERIC WIND

FIELD DRAMATICALLY INCREASE ATTENDANT TO THE ADVANCING UPPER

TROUGH/POLAR JET. WITH DEEP LAYER SHEAR ON THE ORDER OF 50-70

KT...SUFFICIENT INSTABILITY ON THE ORDER OF 750-1250 J/KG MLCAPE

WILL SUPPORT A POTENTIALLY WIDESPREAD SEVERE THREAT. GIVEN STRONG

LOW LEVEL SRH AS AIDED BY A STRENGTHENING 60+ KT LOW LEVEL JET...A

MIXED CONVECTIVE MODE INCLUDING QUASI-LINEAR BOWING

SEGMENTS/LINE-LEADING SEMI-DISCRETE SUPERCELLS WILL BE CAPABLE OF

WIDESPREAD DAMAGING WINDS/STRONG TORNADOES...AS THE SEVERE THREAT

CONTINUES WELL INTO THE EARLY MORNING HOURS OF MONDAY TOWARD THE

MIDDLE/LOWER MS AND TN/LOWER OH RIVER VALLEYS.

..GUYER.. 02/26/2011

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We have a chase team together and ATM will be setting up between Bootheel of MO. area to near Cape Girardeau. Will have to see local meso features and timing. Will be a long night looks like..

Side note, our location Thursday night as reported picked up 85-95 mph winds in AR. according to NWS MEM damage assessment team. Amazing how quick it formed into a QLCS when interacted with the LLJ. Some of the highest winds We have ever experienced in 12 years

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We have a chase team together and ATM will be setting up between Bootheel of MO. area to near Cape Girardeau. Will have to see local meso features and timing. Will be a long night looks like..

Side note, our location Thursday night as reported picked up 85-95 mph winds in AR. according to NWS MEM damage assessment team. Amazing how quick it formed into a QLCS when interacted with the LLJ. Some of the highest winds We have ever experienced in 12 years

Kevin, I'm sending you a PM in regards to chasing.

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Interesting note. Notice surface winds during afternoon, CAP looks fairly weak here through day. If a discreet cell gets going the winds are very much backed in W. KY and So.IL in afternoon tomorrow..

...except you are missing any kind of forcing or lift. The severe weather for that region won't arrive until the overnight hours.

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For Sunday/Sun night:

It looks very possible that a QLCS will be the primary mode with high winds being the primary threat with possible embedded tornadoes. If the cap can break over OK/SE KS/MO during the afternoon/evening then we could see some discrete supercells with an increased tornado risk (some strong).

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Yeah basing on PAH wondering if anything may form pre trigger. But still remains more backed here closer to triple point as opposed to further south. Worth noting I think?

Yes, but you need something more than backed surface winds to trigger storms. The main trough and shortwave doesn't arrive until much later.

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NAM forecast soundings are depicting 0-1 km SRH of 400 in some areas tomorrow night along with adequate instability. Depending on what things look like tomorrow, would not be surprised to see a high risk area.

I wouldn't be surprised either. I'm very curious as to see if we can get CI to occur along the dryline around sunset or if it holds off till after.

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NAM forecast soundings are depicting 0-1 km SRH of 400 in some areas tomorrow night along with adequate instability. Depending on what things look like tomorrow, would not be surprised to see a high risk area.

I'm glad someone else has these thoughts... it'll be an interesting day for sure. At this point, it's somewhat difficult to go with any model's forecast soundings, as it seems like we'll have to take a blend of some of the models (NAM, Euro, SREF as we have been) in order to get the most accurate/realistic scenario for tomorrow. It's a little hard to imagine the resulting sounding without having modification software...

The Day 1 will probably start off as a moderate risk, and I'll give it a 50/50 of upgrading to a High Risk in later products.

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