August 22-31 Severe Weather Thread

[Tim from Springfield (IL)]

Per the latest Day 4-8, possibly some severe weather again in the Dakotas on Monday:

http://www.spc.noaa.gov/products/exper/day4-8/

DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0337 AM CDT FRI AUG 19 2011 VALID 221200Z - 271200Z ...DISCUSSION... FORECAST MODELS ARE IN DECENT AGREEMENT THROUGH MON/D4...DEPICTING A LARGE UPPER TROUGH OVER THE LOWER GREAT LAKES INTO NEW ENGLAND...AND A FLAT UPPER RIDGE FROM THE ROCKIES INTO THE PLAINS. A COLD FRONT WILL EXIT NEW ENGLAND EARLY MONDAY...WITH RAIN AND STORMS BUT WEAK INSTABILITY FOR SEVERE. TO THE W...SLY RETURN FLOW ACROSS THE NRN PLAINS WILL HELP MAINTAIN INSTABILITY WITH SCATTERED THUNDERSTORMS...SOME POSSIBLY SEVERE ACROSS THE DAKOTAS. WITH LITTLE IN THE WAY OF UPPER SUPPORT...THIS SET APPEARS TOO MARGINAL FOR A LONG RANGE OUTLOOK. FROM TUE/D5 ON...MODELS DISAGREE ON TIMING...BUT DO SUGGEST AN AMPLIFICATION OF A TROUGH DIGGING INTO THE MID TO LOWER MO VALLEY. FORCING WITH A COLD FRONT AND AMPLE INSTABILITY AHEAD WOULD YIELD SEVERE STORMS CAPABLE OF HAIL AND WIND. HOWEVER...WILL DEFER TO LATER OUTLOOKS AS MODEL GUIDANCE COMES INTO BETTER AGREEMENT. THE AFOREMENTIONED TROUGH ON D5 WILL CONTINUE EWD INTO THE OH VALLEY REGION BY D6...BUT PREDICTABILITY IS TOO LOW AT THIS TIME. ..JEWELL.. 08/19/2011

[andyhb]

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0311 AM CDT SAT AUG 20 2011

VALID 231200Z - 281200Z

...DISCUSSION...

THE ECMWF AND GFS ARE IN GOOD AGREEMENT ON TUE/D4 SHOWING A

SHORTWAVE TROUGH MOVING SEWD ACROSS THE UPPER MS VALLEY INTO THE

LOWER OH VALLEY LATE TUE INTO EARLY WED/D5. AMPLE MOISTURE AND

INSTABILITY WILL BE IN PLACE FOR STRONG TO SEVERE THUNDERSTORMS. AT

THIS TIME...IT APPEARS STORMS MAY FORM LATE AFTERNOON/EARLY EVENING

NEAR A COLD FRONT OVER SRN MN/IA...WITH A POSSIBLE MCS DEVELOPING

SEWD ACROSS THE MS RIVER AND INTO IL OVERNIGHT TUE. HOWEVER...THERE

IS TIMING DISAGREEMENT BETWEEN MODELS...WITH SOME FIRING CONVECTION

MUCH EARLIER. GIVEN THESE DISCREPANCIES...WILL DEFER TO LATER

OUTLOOKS FOR POSSIBLE SEVERE AREAS.

THE AFOREMENTIONED D4 WAVE WILL CONTINUE SEWD INTO THE OH/TN

VALLEY...POSSIBLY ACCOMPANIED BY AN ONGOING MCS DEPENDING ON HOW THE

D4 STORMS EVOLVE.

PREDICTABILITY CONTINUES TO DECREASE AFTER THE D5 PERIOD.

[Amped]

It's Canado season in the SE That is a similar track to Ivan, which produced a preddy good low end tornado outbreak.

[wisconsinwx]

The NAM looks pretty solid for much of Wisconsin on Tuesday. Of course, given this summer, I don't think these progs will last.

[Chicago Storm]

The NAM looks pretty solid for much of Wisconsin on Tuesday. Of course, given this summer, I don't think these progs will last.

good. stop posting about it.

[Tim from Springfield (IL)]

Day 3 slight risk for the northern half of Illinois, southern WI, NE Missouri, most of Iowa and SE Minnesota:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

[wisconsinwx]

For a 15% slight risk event, both MKX and ORD have some pretty strong wording in their morning AFDs.

[Thundersnow12]

For a 15% slight risk event, both MKX and ORD have some pretty strong wording in their morning AFDs.

its LOT not ORD...

and here was the AFD

GUIDANCE HAS BEEN REMARKABLY CONSISTENT WITH THE GENERAL

IDEA OF THIS FEATURE AND MOST MODELS MAINTAIN A FAIRLY SIGNIFICANT

SHORTWAVE FOR THIS TIME OF YEAR WITH IMPRESSIVE MID-UPPER LEVEL

SPEED MAX PROVIDING FOR STRONG SHEAR PROFILES. WOULD BE ABSURD TO

TRY AND GET TOO SPECIFIC THIS FAR OUT WITH IF/WHERE STRONG

SHEAR/INSTABILITY AND FORCING WOULD ALL BECOME FAVORABLY

JUXTAPOSED. CERTAINLY AGREE WITH SWODY3'S SLIGHT RISK FOR THE AREA

AS THE POTENTIAL EXISTS FOR A RATHER SIGNIFICANT SEVERE WEATHER

EVENT SOMEWHERE IN THE MIDWEST TUESDAY AFTERNOON AND NIGHT. WORTH

NOTING THAT THE SLU'S WARM SEASON ANALOG GUIDANCE DOES SHOW A

PRETTY GOOD SIGNAL FOR SEVERE WEATHER OVER THE MIDWEST BASED ON

THE THE 00Z GFS DATA.

[Thundersnow12]

18z NAM has a nice storm complex from southwest WI to northern IL tuesday evening, really nice amounts of shear but instability is less the further east you go.

[IMADreamer]

Well we missed Saturday's sure thing rain so maybe Wednesday will prove better. We are in the slight risk area. No measurable rain since mid July at the farm.

[Baum]

The NAM looks pretty solid for much of Wisconsin on Tuesday. Of course, given this summer, I don't think these progs will last.

good call.

[Thundersnow12]

0z NAM for tuesday..

[wisconsinwx]

good call.

It might work out to be reverse psychology.

[andyhb]

0z NAM for tuesday..

Quite the setup if that comes into fruition...

Snippet from the MKX discussion:

MON NT THROUGH WED...FORECAST CONFIDENCE MEDIUM

A SHORTWAVE TROUGH WITHIN NW FLOW WILL APPROACH WI WITH LOW LEVEL SSWLY

FLOW AND WARM...MOIST ADVECTION AHEAD OF IT FOR LATE MON NT AND TUE.

PWS TO INCREASE TO NEARLY 1.8 INCHES WITH ELEVATED CAPE RISING TO

1500 J/KG LATE MON NT INTO TUE AM. AFOREMENTIONED QG PROCESSES AND

LIFT ARE SUFFICIENT FOR NUMEROUS TO WIDESPREAD SHOWERS AND TSTORMS

FOR TUE.

SOME SUNSHINE EXPECTED BY MID AFTERNOON BEHIND MAIN WARM ADVECTION

PRECIPITATION AREA WITH SHORTWAVE TROUGH STILL TO PASS DURING THE

LATE AFTERNOON AND EVENING. THUS REDEVELOPMENT IS POSSIBLE SO KEPT

CHANCE POPS INTO THE EVENING. CONTINUED WARM AND MOIST ADVECTION

MAY BOOST MLCAPE VALUES TO 2000-4000 J/KG WITH MDT DEEP LAYER

SHEAR...INCLUDING 0-3 KM/0-1 KM SRH OF 200/100 M2/S2. THUS IF

STORMS DEVELOP...SUPERCELLS ARE PROBABLE WITH THE FULL RANGE OF

SVR POSSIBILITIES INCLUDING ISOLATED TORNADOES.

BY LATE TUE NT AND WED A VERY WARM CAP OF 12C AT 700 MB WILL

PREVAIL OVER THE PASSING WEAK COLD FRONT THAT HAS NO UPPER

SUPPORT. THE DEPTH OF THE LOW LEVEL MOISTURE WILL ALSO BE

DECREASING DURING THIS TIME SO OPTED TO GO WITH A DRY FRONTAL

PASSAGE. TEMPS WILL WARM EACH DAY WITH VERY WARM CONDITIONS FOR

WED.

[wisconsinwx]

Quite the setup if that comes into fruition...

Snippet from the MKX discussion:

Madison looks to be in a favorable position right now pending early day convection on Tuesday.

[wisconsinwx]

SREF starting to pick up on the threat.

[Thundersnow12]

MKX might want to check the 0-3km helicity values again...coupled with MLCAPE values AOA 2500 j/kg, over 90 degrees of turning from the sfc to H5, 45kts of shear, and a 45kt LLJ..

the problem is going to be getting sustained surface based convection, the cap only continues to strengthen throughout the evening and we get a southeast bound MCS riding down the edge of the EML/instability gradient.

0z NAM

[wisconsinwx]

MKX might want to check the 0-3km helicity values again...coupled with MLCAPE values AOA 2500 j/kg, over 90 degrees of turning from the sfc to H5, 45kts of shear, and a 45kt LLJ..

the problem is going to be getting sustained surface based convection, the cap only continues to strengthen throughout the evening and we get a southeast bound MCS riding down the edge of the EML/instability gradient.

0z NAM

Do you think the NAM's phase shift bias comes into play here?

[Thundersnow12]

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1229 AM CDT MON AUG 22 2011

VALID 231200Z - 241200Z

..THERE IS A SLGT RISK OF SVR TSTMS FOR MUCH OF WI...NRN IL

ERN

IA...SERN MN...

..SYNOPSIS

STRONG WNWLY FLOW WILL EXIST ON THE NRN PERIPHERY OF AN EXPANSIVE

FOUR CORNERS RIDGE...WITH A 60-70 KT MID LEVEL JET EXTENDING FROM

THE WRN U.S./CANADIAN BORDER INTO THE UPPER MS VALLEY. AN EMBEDDED

SHORTWAVE TROUGH AND SLOW MOVING SURFACE COLD FRONT WILL PROVIDE

LIFT FOR SEVERE THUNDERSTORMS FROM MN INTO IL.

..SERN MN/WI INTO ERN IA AND NRN IL

A LARGE POOL OF MOISTURE AND INSTABILITY WILL EXIST ACROSS THE NRN

PLAINS/UPPER MS VALLEY...WITH UPPER 60S BL DEWPOINTS BENEATH

RELATIVELY COOL AIR ALOFT. A SWLY LOW LEVEL JET ON THE ORDER OF 30

KT WILL EXIST TUE MORNING...PRODUCING LIFT AND THE POSSIBILITY OF

ELEVATED THUNDERSTORMS FROM MN INTO WI. THIS ACTIVITY MAY ALREADY BE

PRODUCING SEVERE HAIL.

EXISTING ACTIVITY...AND/OR NEW ACTIVITY FORMING ON RELATED OUTFLOW

AND WITH APPROACHING COLD FRONT...WILL LIKELY GROW UPSCALE WITH

SUPERCELLS AND PERHAPS A SEVERE MCS POSSIBLE. DAMAGING WINDS AND

LARGE HAIL WILL BE LIKELY. MODEL CONSENSUS MAINTAINS THE GREATEST

THREAT AREA FROM WI INTO NRN IL INCLUDING THE CHICAGO AREA...BUT

WILL DEFER HIGHER PROBABILITIES TO LATER OUTLOOKS WHEN DETAILS

BECOME CLEARER.

..JEWELL.. 08/22/2011

[Tim from Springfield (IL)]

Wednesday now has a Day 3 slight risk for most of Lower Michigan plus the Chicagoland area and small parts of north IN and NW OH:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

[andyhb]

New discussion from ARX for Tuesday:

22.00 MODELS CONTINUE TO SHOW DIFFERING SOLUTIONS ON TUESDAY. IF THE

MCS DEVELOPS LATE TONIGHT AND MOVES ACROSS THE FORECAST AREA DURING

THE MORNING HOURS ON TUESDAY...THIS WOULD LIMIT THUNDERSTORM

DEVELOPMENT TUESDAY AFTERNOON. THE NAM FIRES AN MCS ACROSS NORTHERN

MINNESOTA AND BRINGS IT SOUTHEASTWARD IMPACTING LOCATIONS MAINLY

ALONG AND EAST OF THE MISSISSIPPI RIVER. GIVEN THE MODEL UNCERTAINTY

WILL MAINTAIN CURRENT POPS...FAVORING THE GFS SOLUTION. LOOK FOR

WIDESPREAD SHOWERS AND THUNDERSTORMS EARLY TUESDAY MORNING...MOVING

EAST LATE IN THE MORNING WITH ADDITIONAL SHOWER AND THUNDERSTORM

DEVELOPMENT POSSIBLE IN THE AFTERNOON HOURS. SEVERE THUNDERSTORMS

ARE POSSIBLE EARLY TUESDAY MORNING AND AGAIN TUESDAY AFTERNOON WITH

HEAVY RAIN AND LARGE HAIL THE MAIN THREATS. IF STORMS CAN BECOME

SURFACE BASED TUESDAY AFTERNOON...LOW LEVEL WIND SHEAR WOULD SUPPORT

AN ISOLATED TORNADO OR TWO ACROSS EXTREME NORTHEAST IOWA AND

SOUTHWEST WISCONSIN...WITH 0-1 KM BULK SHEAR INCREASING INTO THE

20-25KT RANGE BY 00Z. THE SHOWERS AND THUNDERSTORM WILL MOVE EAST OF

THE FORECAST AREA TUESDAY EVENING AS A COLD FRONT PUSHES ACROSS THE

AREA DURING THE OVERNIGHT HOURS. HIGH TEMPERATURES ON TUESDAY WILL

LARGELY DEPEND ON THE TIMING AND LOCATION OF SHOWERS AND

THUNDERSTORMS. AT THIS TIME IT APPEARS THE CONVECTION SHOULD CLEAR

LOCATIONS WEST OF THE MISSISSIPPI RIVER BY EARLY AFTERNOON WITH

CAPPING MOVING INTO THOSE AREAS. SHOULD SEE TEMPERATURES CLIMB

INTO THE MIDDLE 80S ACROSS THESE AREAS. KEPT TEMPERATURES IN THE

UPPER 70S TO LOWER 80S EAST OF THE RIVER WHERE CONVECTION IS

EXPECTED TO LINGER INTO THE EARLY AFTERNOON WITH ADDITIONAL

DEVELOPMENT POSSIBLE. LOW TEMPERATURES WILL RANGE FROM THE UPPER 60S

ACROSS NORTH CENTRAL WISCONSIN TO THE LOWER 70S ACROSS NORTHEAST

IOWA.

Disc. from MKX:

TUESDAY AND TUESDAY NIGHT...FORECAST CONFIDENCE MEDIUM TO HIGH.

POPS WILL BE HIGHLY DEPENDENT UPON WHERE CONVECTION DEVELOPS

TONIGHT. BEST GUESS IS THAT ONGOING CONVECTION OVER MN/WEST CENTRAL

WI AT THE NOSE OF THE LLJ AND WITHIN THE STRONGEST AREA OF WARM AIR

ADVECTION WILL MOVE ACROSS SOUTHERN WI TUESDAY MORNING. LIKELY POPS

BETWEEN 12 AND 18Z TUE. NOT SURE OF THE SEVERITY OF THE STORMS

DURING THIS TIME PERIOD. IF THERE IS AN ONGOING MESOSCALE CONVECTIVE

SYSTEM...THEN DAMAGING WINDS ARE THE PRIMARY THREAT. IF IT IS POP-UP

CONVECTION FROM ELEVATED ACCAS /ALTOCUMULUS CASTELLANUS/

CLOUDS...THEN STORMS WOULD PROBABLY NOT BE SEVERE DURING THIS TIME.

DEPENDING ON THE TIMING OF THE FIRST ROUND OF STORMS...THERE COULD

BE A BIG ENOUGH BREAK TO ALLOW FOR DAYTIME HEATING AHEAD OF THE MAIN

SHORTWAVE TROUGH DROPPING SOUTHEASTWARD ACROSS WI ON TUE. MODEL

SNDGS SHOW SFC BASED CAPE VALUES INCREASING TO OVER 3000J/KG WITH

40KT 0-6KM BULK SHEAR AND HIGH HELICITY. WITH THE TROUGH REACHING

SOUTHERN WI DURING PEAK DAYTIME HEATING AND WITHIN A VERY MOIST

AIRMASS...SEVERE WEATHER IS POSSIBLE/LIKELY. SPC CONTINUES SOUTHERN

WI IN THE SLIGHT RISK FOR SEVERE STORMS AREA.

CONVECTION WILL WIND DOWN TUE EVENING...BUT A FEW SHOWERS COULD

LINGER IN THE UNSTABLE NW FLOW BEHIND THE MAIN TROUGH.

Disc. from LOT:

THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS WILL INCREASE OVERNIGHT

MONDAY NIGHT INTO TUESDAY AS A STRONG SHORTWAVE DROPS OUT OF THE

NORTHERN PLAINS AND INTO THE UPPER MIDWEST. THE COMBINATION OF THE

INCREASING WARM/MOIST ADVECTION IN THE LOWER LEVELS AND THE STRONG

SHORTWAVE...HAVE INCREASED POPS TO LIKELY...PARTICULARLY AS THE SFC

COLD FRONT SWEEPS ACROSS THE CWA. WHILE THE WARM/MOIST ADVECTION

AND ISENTROPIC LIFT WILL BE STRONG ENOUGH TO MAINTAIN THE CHANCE

POPS FOR TUESDAY...THE ADDED FORCING OF THE SFC COLD FRONT SHOULD BE

ADEQUATE TO JUSTIFY INCREASING POPS TO LIKELY FOR TUESDAY NIGHT WITH

THE FRONTAL PASSAGE. THE POSSIBILITY OF THUNDERSTORMS REACHING

SEVERE LEVELS WILL NEED TO BE CONSIDERED FOR TUESDAY AFTERNOON AND

EVENING AS ANY ONGOING UPSTREAM THUNDERSTORMS WILL MOVE INTO A

VOLATILE ENVIRONMENT OF COPIOUS LOW LEVEL HEAT AND HUMIDITY AS WELL

AS A SWLY LOW LEVEL JET OF 35-40KT. THE POTENTIAL FOR LARGE HAIL

AND STRONG WIND GUSTS WILL NEED TO BE MONITORED.

[wisconsinwx]

I'll take an order of the 06z ARW please:

[A-L-E-K]

Going to have to see what goes on tonight over Iowa/Minn before getting too into details but i'm liking the Wisc/Iowa/Ill border area.

[Stebo]

Going to have to see what goes on tonight over Iowa/Minn before getting too into details but i'm liking the Wisc/Iowa/Ill border area.

This, also for Wednesday I am liking Central/SW Michigan moving into SE Michigan late Wed Eve.

[wisconsinwx]

Going to have to see what goes on tonight over Iowa/Minn before getting too into details but i'm liking the Wisc/Iowa/Ill border area.

SW Wisconsin, NE Iowa, and NW Illinois probably have the best chance for supercell development tomorrow afternoon, but it looks quite possible an MCS will develop farther north and east that might affect cities like MKE and ORD tomorrow evening.

[A-L-E-K]

SW Wisconsin, NE Iowa, and NW Illinois probably have the best chance for supercell development tomorrow afternoon, but it looks quite possible an MCS will develop farther north and east that might affect cities like MKE and ORD tomorrow evening.

If supercell development takes places over SW Wisconsin, NE Iowa, and NW Illinois, I don't see an MCS developing north of there. The cells would grow upscale into an MCS and push across N. Illinois or S. Wisconsin. I'm not buying what that ARW run was showing with the linear MCS pushing due south.

[Thundersnow12]

[wisconsinwx]

All the models show something different, but it's interesting the RUC shows some pop up showers and storms in the morning, with still enough sunshine to destabilize and form two separate lines of storms in the late afternoon.

[Thundersnow12]

It's the RUC/GFS vs the NAM regarding amount of instability here tomorrow afternoon and evening with the NAM being alot less bullish.

[a mighty wind]

All the models show something different, but it's interesting the RUC shows some pop up showers and storms in the morning, with still enough sunshine to destabilize and form two separate lines of storms in the late afternoon.

Great post!

Very descriptive. I'll be sure to watch THAT area.