September 6-7 Severe Weather

[snowlover2]

Could be an active day.

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0100 AM CDT THU SEP 06 2012

VALID 071200Z - 081200Z

...THERE IS A SLGT RISK OF SVR TSTMS MID AND LOWER OH/MID MS VALLEYS

SWWD INTO THE OZARKS...

...SYNOPSIS...

THE SYNOPTIC-SCALE ENVIRONMENT IS FORECAST TO UNDERGO STRENGTHENING

THIS PERIOD...AS A ROBUST UPPER SHORT-WAVE TROUGH DIGS SEWD OUT OF

THE PLAINS/UPPER MS VALLEY REGION AND INTO THE MID MS/OH VALLEYS.

AS THIS OCCURS...A COLD FRONT -- INITIALLY STRETCHING FROM THE UPPER

GREAT LAKES REGION SWWD ACROSS THE TX PANHANDLE -- WILL STRENGTHEN

WHILE SHIFTING RAPIDLY EWD/SEWD WITH TIME. BY LATE IN THE

PERIOD...THIS FRONT SHOULD EXTEND FROM THE LOWER GREAT LAKES REGION

SWWD ACROSS THE TN/LOWER MS VALLEYS. THIS STORM SYSTEM SHOULD FOCUS

A BROAD AREA OF ACTIVE/LOCALLY-SEVERE STORMS -- MAINLY FROM

AFTERNOON THROUGH LATE EVENING.

...MID AND LOWER OH/MID MS VALLEYS AND THE OZARKS REGION...

SHOWERS AND THUNDERSTORMS SHOULD BE ONGOING AT THE START OF THE

PERIOD ACROSS PARTS OF KS/MO AND VICINITY...WITHIN ZONE OF STRONG QG

FORCING AHEAD OF THE SURFACE COLD FRONT. AS THE UPPER TROUGH DIGS

SEWD AND THE COLD FRONT SHARPENS/ADVANCES ACROSS THE MID MS/OH

VALLEYS AND OZARKS INTO THE AFTERNOON HOURS...A DESTABILIZING

ENVIRONMENT SHOULD SUPPORT AN INCREASE/REDEVELOPMENT OF STORMS.

WITH STRONGER FLOW ALOFT ROTATING AROUND THE BASE OF THE TROUGH AND

ATOP THE WARM SECTOR...SHEAR WILL BECOME SUPPORTIVE OF

ORGANIZED/SEVERE STORMS -- WITH DAMAGING WINDS EXPECTED TO BECOME

THE PRIMARY THREAT ALONG WITH SOME HAIL. WHILE THE DETAILS

REGARDING EVOLUTION OF THIS CONVECTIVE THREAT THROUGH THE AFTERNOON

AND INTO THE EVENING ARE SOMEWHAT DIFFICULT TO DISCERN DUE TO THE

DYNAMIC/STRENGTHENING SYNOPTIC-SCALE ENVIRONMENT DURING THE

PERIOD...WILL INTRODUCE A FAIRLY LARGE SLIGHT RISK AREA FROM THE

OZARKS NEWD INTO THE MID OH VALLEY AREA TO COVER THIS EVOLVING

SEVERE WEATHER SCENARIO.

...PARTS OF THE LOWER GREAT LAKES REGION...

SCATTERED SHOWERS AND THUNDERSTORMS SHOULD EVOLVE THROUGH THE DAY

ACROSS THE LOWER GREAT LAKES/UPPER OH VALLEY REGION DAY 2...AS

AFTERNOON AIRMASS DESTABILIZATION PUSHES MIXED-LAYER CAPE VALUES

INTO THE 1000 TO 1500 J/KG RANGE IN MOST AREAS. WITH A LACK OF A

CLEAR LOW-LEVEL FOCUSING MECHANISM DURING THE DAY AND MODEST FLOW

ALOFT...ONLY A VERY ISOLATED WIND/HAIL THREAT IS EVIDENT THROUGH THE

FIRST HALF OF THE PERIOD.

OVERNIGHT...AS THE COLD FRONT APPROACHES FROM THE WEST...STORMS MAY

BECOME MORE NUMEROUS ALONG THIS BOUNDARY. FLOW ALOFT WILL INCREASE

THROUGH THE EVENING AND INTO THE OVERNIGHT HOURS AS WELL...BUT WITH

THIS OCCURRING DURING THE DIURNALLY LESS FAVORABLE THERMODYNAMIC

ENVIRONMENT...SEVERE THREAT SHOULD REMAIN LIMITED AFTER DARK --

PRIMARILY IN THE FORM OF ISOLATED GUSTY WINDS.

[Jim Martin]

12z Hillsdale, Michigan sounding valid at 5:00pm tomorrow...

Yet the 06z Sounding for the same time period for Hillsdale showing a completely different picture. Could the NAM be overdoing this threat?

[Tim from Springfield (IL)]

You might want to go ahead and add today to this thread--two separate slight risk areas are now knocking on the door of the region (with the larger one now including eastern Iowa and northwestern Illinois). Latest Day 1:

http://www.spc.noaa.gov/products/outlook/day1otlk.html

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1129 AM CDT THU SEP 06 2012

VALID 061630Z - 071200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL AND SRN

PLNS...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE OZARKS...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE LWR GRT

LKS/NORTHERN NEW ENGLAND...

...MID MO/MID MS VLYS TNGT/EARLY FRI...

TSTMS SHOULD INCREASE IN COVERAGE AND STRENGTH OVER PARTS OF ERN

NE...SE SD...IA AND MN AFTER 00Z FRI AS SWLY LLJ/MOISTURE INFLOW

INCREASE WITH THE CONTINUED APPROACH OF AMPLIFYING UPR TROUGH.

STORMS SHOULD FOCUS NEAR/E OF SFC LOW MOVING ESE FROM NEB/SD... AND

MAY BE SLIGHTLY ELEVATED. NEVERTHELESS...WITH MUCAPE AROUND 1000

J/KG AND STRONG CLOUD-LAYER SHEAR /500 MB WNW FLOW AOA 50

KTS/...POTENTIAL WILL EXIST FOR SVR HAIL AND POSSIBLY LOCALLY DMGG

WIND. THIS ACTIVITY COULD REACH NW IL BY THE END OF THE PERIOD.

...OZARKS THIS AFTN...

SATELLITE SHOWS A SRN STREAM IMPULSE NOW IN SE KS THAT SHOULD

CONTINUE E ACROSS THE OZARKS LATER TODAY. ASSUMING THAT THE 12Z SGF

RAOB IS AND WILL REMAIN REPRESENTATIVE OF THE DOWNSTREAM ENVIRONMENT

THROUGH LATER TODAY...AMPLE INSTABILITY SHOULD DEVELOP TO SUPPORT A

CONDITIONAL RISK FOR SVR STORMS GIVEN DEEP EML AND RICH LOW-LVL

MOISTURE. EXPECT THAT SFC HEATING WILL FOSTER ADDITIONAL STORM

DEVELOPMENT ON DOWNWIND SIDE OF EXISTING SLIGHTLY ELEVATED STORM

CLUSTER NOW IN SE KS. THIS ACTIVITY SHOULD FOCUS ALONG AND N OF WEAK

W-E FRONT STALLED OVER THE REGION. THE STORMS MAY GROW INTO A SMALL

MCS CAPABLE OF SVR HAIL AND WIND THAT MOVES ESE TOWARD THE MS RVR.

...LWR OH VLY TO LWR GRT LKS THIS AFTN...

WDLY SCTD TO SCTD TSTMS SHOULD FORM OVER PARTS OF OH...NRN PA...AND

UPSTATE NY...WHERE MODERATE DEEP WLY FLOW WILL PREVAIL ON SRN FRINGE

OF ELONGATED UPR LOW OVER ONT. LARGE SCALE FORCING FOR ASCENT

APPEARS NEUTRAL AT BEST...PER SATELLITE AND MODEL DATA.

NEVERTHELESS...AREA SOUNDING SHOW AMPLE MOISTURE PRESENT FOR STORMS

AND MINIMAL CIN. WITH DEEP FLOW LARGELY PARALLEL TO THE LONG AXES OF

THE LAKES...EXPECT THAT LAKE BOUNDARIES MAY SERVE AS THE MAIN FOCI

FOR LOW-LVL UPLIFT/STORM DEVELOPMENT. THIS ACTIVITY MAY ORGANIZE

SEVERAL SHORT BANDS. WITH AFTN SBCAPE AVERAGING AROUND 1500 J/KG AND

30 KT WLY DEEP SHEAR...SETUP COULD YIELD A FEW SMALL BOWS WITH

LOCALLY DMGG WIND.

DEEP SHEAR SHOULD DIMINISH WITH SW EXTENT THROUGH THE OH VLY...

BUT BOTH INSTABILITY AND SHEAR MAY PROVE SUFFICIENT FOR

ISOLD/BRIEFLY SVR STORMS.

[Hoosier]

Tomorrow seems like a decent setup per my quick 10 minute look at it...maybe even worthy of a moderate risk if no debris issues etc? Could have all modes/facets of severe on the table. Nice to start seeing better shear as we head toward fall.

[A-L-E-K]

Tomorrow seems like a decent setup per my quick 10 minute look at it...maybe even worthy of a moderate risk if no debris issues etc? Could have all modes/facets of severe on the table. Nice to start seeing better shear as we head toward fall.

I think debris is a given...thinks look awfully messy after 6z tonight with no real breaks.

[Stebo]

I think debris is a given...thinks look awfully messy after 6z tonight with no real breaks.

Agree, however if the Northern part of the risk area were to have surface based convection, with the amount of shear in the atmosphere it could get interesting. SPC's new day 2 from earlier today alluded to this potential.

[Hoosier]

NAM really trying to back the low level winds in some spots tomorrow.

This is a pretty decent environment if it pans out.

[Hoosier]

Time to bust out an old friend. Highlighting an area close to the track of the surface low.

[Hoosier]

Pretty nice line in southeastern Missouri.

[Indystorm]

80/57 here in Dunlap now with a nw wind. I may be just north of the retreating warm front given the position of the low on Friday and things may certainly bear watching. Somewhat surprised. Usually think of the second tor peak around Halloween into early Nov. But given the strange anomalies this year who knows.

[Indystorm]

Sig tor parameter already up to 5 or 6 just se of Des Moines at 12z Friday on current RUC. That will only increase as the low pressure moves eastward and stronger insolation occurs.

[Chicago WX]

FWIW, and it may not be much, HIRES NAM trying to bring two rounds of storms through here tomorrow, one morning and one late afternoon/evening. We'll see.

[Hoosier]

FWIW, and it may not be much, HIRES NAM trying to bring two rounds of storms through here tomorrow, one morning and one late afternoon/evening. We'll see.

I can probably count on one hand the number of times I've been this interested in a severe threat in this area in the past 6 months. Maybe that is more a reflection of how things have gone for much of spring/summer. Interesting to see the GFS also spitting out high CAPE tomorrow.

[Chicago WX]

I can probably count on one hand the number of times I've been this interested in a severe threat in this area in the past 6 months. Maybe that is more a reflection of how things have gone for much of spring/summer. Interesting to see the GFS also spitting out high CAPE tomorrow.

Good. Now I'm interested.

[Hoosier]

Good. Now I'm interested.

Really hope we can avoid a morning spoiler.

[Chicago WX]

Really hope we can avoid a morning spoiler.

Yeah, a repeat of yesterday would be a bummer. Have to wait and see I guess.

[A-L-E-K]

On the down side…I thing a complex somewhere in or around the region in the morning is a pretty good bet….on the plus side, the vort looks much stronger so even if instability is limited, things should get going again later for you all/

[Powerball]

If all of this can just come a bit further NW, I'll be a happy camper.

[andyhb]

00z NAM isn't nearly as impressive with parameters as the 12z.

[tornadotony]

00z NAM isn't nearly as impressive with parameters as the 12z.

The parameters are plenty impressive. They're just focused farther south because the frontal wave the NAM develops that backs the sfc winds is slower this run. That's something that will have to be nowcasted. What's important is that is still shows plenty of destabilization by mid-late afternoon.

[andyhb]

The parameters are plenty impressive. They're just focused farther south because the frontal wave the NAM develops that backs the sfc winds is slower this run. That's something that will have to be nowcasted. What's important is that is still shows plenty of destabilization by mid-late afternoon.

It certainly has slowed down the progression of the upper level trough since 12z, somewhat supporting the trend the GFS has shown with recent runs.

[Stebo]

The 4km-wrf has a line going up over night near Iowa and racing East, it seems like it is about 6-9 hours faster than any other model too. Not sure how much weight you can put on it...

[Thundersnow12]

4km NAM is interesting, just started using this site btw. Has a complex come through here and looks like it then develops a few discrete cells in the afternoon in extreme eastern IL into IN ahead of the big main line at night.

http://www.weatherbellmodels.com/weather/hires/2012090700/east/hires_ref_east_mouse.php

[Stebo]

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0100 AM CDT FRI SEP 07 2012

VALID 071200Z - 081200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SERN LOWER MI/OH TO

OZARKS AND MID-SOUTH......

...SYNOPSIS...

DOMINANT UPPER-AIR FEATURE FOR THIS FCST WILL BE STG SHORTWAVE

TROUGH -- NOW VERY POSITIVELY TILTED FROM NWRN ONT WSWWD ACROSS SRN

MB...MT AND CENTRAL ID. AS HEIGHTS RISE ACROSS MOST OF

INTERMOUNTAIN W...500-MB TROUGH WILL TRANSLATE SEWD WITH ITS ERN

PORTION INTENSIFYING. BY 8/00Z...TROUGH SHOULD EXTEND FROM NRN ONT

SWWD ACROSS LS...THROUGH PRIMARY VORTICITY FIELD OVER WI...ACROSS

IA...TO SWRN NEB/NWRN KS REGION. PERTURBATION WILL DEEPEN FURTHER

AND BECOME LESS POSITIVELY TILTED WITH TIME...SUCH THAT BY

8/12Z...VORTICITY CENTER SHOULD ARRIVE AT NRN INDIANA...WITH TROUGH

ARCHING SWD/SWWD OVER SERN INDIANA...SERN MO AND NRN OK.

RELATED SFC COLD FRONT AT START OF PERIOD SHOULD EXTEND SWWD FROM

FRONTAL-WAVE LOW OVER SRN IA THROUGH CENTRAL/SWRN KS TO NERN NM. AS

LOW MOVES EWD TO NRN INDIANA BY 8/00Z...COLD FRONT SHOULD REACH SERN

PORTIONS MO/OK/NM...WHILE WARM FRONT EXTENDS E OF LOW INVOF MI/OH

BORDER AND LE. OVERNIGHT...COLD FRONT WILL SWEEP SEWD TO S TX...WRN

LA...MID TN...AND OH...CONNECTING WITH DEEPENING SFC CYCLONE OVER

SRN ONT BY 12Z.

...DIURNAL...LOWER MI AND INDIANA TO OZARKS AND OK...

STRENGTHENING COLD FRONT IS EXPECTED TO MOVE SEWD INTO PROGRESSIVELY

HIGHER-THETAE AIR MASS DURING DAY...WHILE DIABATIC SFC HEATING

BOOSTS BUOYANCY AND REDUCES CINH. NET RESULT SHOULD BE DEVELOPMENT

OF SCATTERED TSTMS INVOF FRONT DURING AFTERNOON...BUILDING NEWD AND

SWWD WITH TIME INTO LENGTHY BAND OF SCATTERED-NUMEROUS STG-SVR

TSTMS. MAIN THREAT WILL BE DAMAGING GUSTS...ALTHOUGH LOW-LEVEL AND

DEEP SHEAR WILL SUPPORT SUPERCELL POTENTIAL GENERALLY N OF OH RIVER

AND E OF MS RIVER FOR LOCALLY ENHANCED HAIL THREAT AND CONDITIONAL

TORNADO POTENTIAL. LARGEST HODOGRAPHS SHOULD BE INVOF WARM FRONT

DURING AFTERNOON...THEN AS LLJ STRENGTHENS FROM ABOUT 00Z

ONWARD...IN SW-NE CORRIDOR ACROSS PORTIONS KY...INDIANA AND OH. SFC

DEW POINTS UPPER 60S TO LOW 70S F ALREADY ARE IN PLACE ACROSS BROAD

AREA OF MID-SOUTH AND OH VALLEY REGIONS. RELATED LOW-LEVEL MOISTURE

WILL BE ADVECTED/TRANSPORTED POLEWARD AND AGAINST SFC WARM FRONT BY

MID-LATE AFTERNOON. ACCORDINGLY MODIFIED MODEL SOUNDINGS YIELD

2500-3500 J/KG MLCAPE WITH LOCALLY HIGHER VALUES AHEAD OF COLD

FRONT.

EXAMINING AREAS SWWD FROM CATEGORICAL OUTLOOK AREA ACROSS

OK...PREFRONTAL AIR MASS WILL BE CHARACTERIZED BY HOTTER AND MORE

DEEPLY MIXED BOUNDARY LAYER. COMPARED TO FARTHER NE...EXPECT LESS

MOISTURE...LOWER MLCAPE...AND MORE VEERED SFC FLOW CONTRIBUTING TO

WEAKER CONVERGENCE. STILL...COMBINATION OF INTENSE

PREFRONTAL/DIABATIC HEATING AND FRONTAL LIFT WILL LEAD TO AT LEAST

WIDELY SCATTERED TSTM DEVELOPMENT WITH SPORADIC SVR GUSTS/HAIL PSBL.

THIS THREAT WILL BE MORE LIMITED IN SPACE AND TIME THAN OVER

CATEGORICAL OUTLOOK AREA...AND SHOULD DIMINISH AFTER DARK.

...OH TO MID-SOUTH REGION OVERNIGHT...

LATE IN PERIOD...FROM ABOUT 8/06Z ONWARD...STRENGTHENING WIND FIELDS

ALOFT WILL OVERSPREAD LARGER PROPORTION OF WARM SECTOR AS NRN PART

OF MID-UPPER LEVEL SHORTWAVE PERTURBATION DEEPENS AND APCHS NEUTRAL

TILT. THIS CAUSES SOME CONCERN FOR SVR THREAT EXTENDING INTO

OVERNIGHT HOURS ACROSS PORTIONS OH...CENTRAL/ERN KY AND MIDDLE

TN...EVEN THOUGH FOREGOING AIR MASS WILL BE CHARACTERIZED BY

SOMEWHAT WEAKER AMBIENT THETAE...AND INSTABILITY WILL DECREASE DUE

TO DIABATIC SFC COOLING. FCST SOUNDINGS STILL SHOW EFFECTIVE INFLOW

PARCELS SFC-BASED OR VERY NEARLY SO EVEN AS LATE AS AROUND

8/09Z...IN NARROW CORRIDOR AHEAD OF FRONT/CONVERGENCE LINE. LAPSE

RATES AND BUOYANCY EACH WILL BE WEAK...WITH MLCAPE GENERALLY AOB 300

J/KG. SOME CAPPING IN 750-850 MB LAYER IS EVIDENT IN PROGS...WHICH

MAY BE OVERCOME BY FRONTAL FORCING. GIVEN THESE UNCERTAINTIES...SVR

PROBABILITIES AT CATEGORICAL THRESHOLDS ARE EXPANDED FARTHER E...BUT

LOWER THAN PRIOR AFTERNOON/EVENING DUE TO CONDITIONAL NATURE OF

INSTABILITY.

[Jim Martin]

For what it is worth... the significant tornado parameter not that particularly high for this evening into tonight for the Great Lakes region.

[A-L-E-K]

I don't see the northern edge happening you guys

[Indystorm]

Option One....morning MCS ruins opportunities for decent destabilization later in the day for northern area just like what happened the other day.. Option Two...MCS comes through, gets out of way in time for recharging the atmosphere and we have a late evening/night main show. Place your bets.

[KokomoWX]

Option One....morning MCS ruins opportunities for decent destabilization later in the day for northern area just like what happened the other day.. Option Two...MCS comes through, gets out of way in time for recharging the atmosphere and we have a late evening/night main show. Place your bets.

It is difficult to bet against option one but today I will go with option two.

[Bryan Wood]

Think the northern areas are going to be affected by morning convection, seeing major bust potential there. Positive tilt trough also not the greatest for chaseable storms. Looks like the warm front or maybe a localized differential heating boundary would be the spots to watch today. I really want to chase today, but I foresee busting in the future if I do.

[Chicago WX]

It is difficult to bet against option one but today I will go with option two.

But the last HRRR run is whiffing on this morning's complex.

Anyways, if that complex maintains itself, it's coming through here late morning. Also see a outflow kicking out ahead of the central IL storms right now. I'll take option #1 for MBY.