Severe Threats Apr. 24-May 1

[Tim from Springfield (IL)]

Catch-all thread for multiple severe threat possibilities next week (Apr. 24-30) that may affect parts of the subforum.

Starting the thread with Sunday (Apr. 24) in case the D3 slight in SW Iowa/NW Missouri southwestward makes it farther east than anticipated:

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

DAY 3 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0153 AM CDT FRI APR 22 2016

   VALID 241200Z - 251200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM NORTH-CENTRAL OK AND
   EASTERN KS INTO THE MID-MO VALLEY...

   ...THERE IS A MRGL RISK OF SVR TSTMS FROM WESTERN OK TO THE MID-MO
   VALLEY...

   ...SUMMARY...
   STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AND
   EVENING ACROSS PARTS OF OKLAHOMA AND EASTERN KANSAS INTO THE MIDDLE
   MISSOURI VALLEY.

   ...PORTIONS OF THE SRN PLAINS TO MID-MO VALLEY...

   THE UPPER LOW OVER THE CENTRAL ROCKIES/HIGH PLAINS EARLY SUNDAY
   MORNING WILL SHIFT EASTWARD ACROSS THE CENTRAL PLAINS TOWARD THE
   MID-MO VALLEY BY 12Z MON. AS THE 50+ KT MIDLEVEL JET OVERSPREADS
   OK/KS INTO MO/IA/NEB...SOUTHERLY LOW-LEVEL FLOW WILL TRANSPORT UPPER
   50S TO LOW 60S DEWPOINTS NORTHWARD IN A NARROW CORRIDOR AHEAD OF A
   DRYLINE. ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED TO
   DEVELOP IN WEAK CONVERGENCE ALONG THE DRYLINE FROM NORTH-CENTRAL OK
   NORTH/NORTHEAST INTO SOUTHWEST IA. STEEP LAPSE RATES WILL BE IN
   PLACE AND SHEAR PROFILES WILL FAVOR SUPERCELLS WITH THE MAIN CONCERN
   BEING LARGE HAIL. THE THREAT FURTHER SOUTHWEST INTO WESTERN/CENTRAL
   OK APPEARS MORE CONDITIONAL DUE TO CAPPING CONCERNS. SHOULD A STORM
   DEVELOP HOWEVER...LARGE HAIL AND STRONG WINDS WILL BE POSSIBLE. 

   ADDITIONAL THUNDERSTORMS ARE POSSIBLE NEAR THE WARM FRONT ACROSS
   PARTS OF EASTERN SD INTO NORTHERN IA AND SOUTHERN MN.
   HOWEVER...MODEL VARIABILITY WITH REGARDS TO MOISTURE AND WEAKER
   LOW/MID-LEVEL FLOW WILL PRECLUDE ADDITION OF PROBS AT THIS TIME.

   ..LEITMAN.. 04/22/2016

[Tim from Springfield (IL)]

D6 still has a 15% for SE Iowa/MO/IL for Wednesday, and severe can't be ruled out the rest of next week:

...DAY 6/WEDNESDAY...   THE SEVERE THREAT IS EXPECTED TO SHIFT EASTWARD ON DAY 6/WED ACROSS   PARTS OF THE MIDDLE MS VALLEY TO NORTHEAST TX AHEAD OF THE   EASTWARD-ADVANCING SURFACE LOW AND COLD FRONT. CONVECTION WILL   LIKELY BE ONGOING WEDNESDAY MORNING ACROSS PARTS OF THE MID-MS   VALLEY...BUT GUIDANCE IS IN REASONABLE AGREEMENT THAT THIS   CONVECTION WILL SHIFT EAST AND ALLOW FOR SOME AIRMASS RECOVERY BY   AFTERNOON. THE AIRMASS WILL REMAIN MORE PRISTINE WITH SOUTHWESTWARD   EXTENT INTO SRN MO/AR/SE OK/NE TX AND THE BETTER SEVERE THREAT MAY   ULTIMATELY UNFOLD ACROSS THAT AREA. GUIDANCE DOES SUGGEST SLIGHTLY   MORE VEERED LOW-LEVEL FLOW...BUT PARAMETERS SHOULD STILL BE   FAVORABLE FOR ALL SEVERE HAZARDS.    ...DAY 7/THURSDAY - DAY 8/FRIDAY...   STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE ON DAY   7/THU...THOUGH PREDICTABILITY IS LOW GIVEN TWO DAYS OF PRIOR   CONVECTION ACROSS PARTS OF THE PLAINS/MS VALLEY REGION. GUIDANCE   SUGGESTS SHORTWAVE RIDGING OVER THE PLAINS AS THE UPPER TROUGH OVER   THE UPPER MIDWEST/GREAT LAKES SHIFTS EASTWARD TOWARD NEW ENGLAND.   BETTER MOISTURE WILL LIKELY REMAIN OVER TX AND THE LOWER MS VALLEY   WHERE STRONG TO SEVERE STORMS COULD DEVELOP ALONG THE COLD FRONT   AND/OR OUTFLOW FROM PREVIOUS DAYS CONVECTION. WHERE THIS MAY OCCUR   IS UNCERTAIN HOWEVER. THIS UNCERTAINTY AND MULTI-MODEL VARIABILITY   CONTINUES INTO DAY 8/FRI...WITH GUIDANCE DIFFERING IN THE EVOLUTION   OF ANOTHER WESTERN TROUGH EJECTING EASTWARD TOWARD THE PLAINS.   ..LEITMAN.. 04/22/2016

[A-L-E-K]

zzzzzzzzzz for this sub

[cyclone77]

zzzzzzzzzz for this sub

 

Monday and Wednesday both look decent to me.  Nice little remnant mid-level vort/jet max rolling through on Monday could be interesting.  Wednesday still a little up in the air, but there should be at least a low-end severe threat. 

[Stebo]

zzzzzzzzzz for this sub

Depends what happens with the mess to our NE, I do think we aren't in the bullseye but portions of the subforum should cash in. Especially if you live near STL or from Central IL to Central KY. Our chances will come once the -NAO relaxes.

[ClicheVortex2014]

Wednesday looks good for part of this sub-forum.

 

 

TWC

 

Wednesday

• Severe t-storms could again be rather numerous from the mid-Mississippi Valley to the southern Plains
• Overall outbreak potential: Moderate
• Threats: Tornadoes, large hail, damaging winds

 

 

[Chicago Storm]

Looks like a decent non-tor severe threat on Monday around here.

[HillsdaleMIWeather]

18Z GFS came in looking better for around the subforum on the 28th

[Thundersnow12]

Near Rochelle, IL on Monday off the 18z NAM..

 

[RCNYILWX]

Near Rochelle, IL on Monday off the 18z NAM..

rochelle area.png

Not too shabby. Instability is much higher on the NAM than on the Euro and GFS as it typically is. Lake enhanced backdoor cold front is not usually favorable for more than a wind and maybe hail threat so we'll have to see if anything can form earlier in the warm sector.

Also think that the GFS runs today and the 12z Euro looked pretty interesting along the warm front on Wednesday in central IL and IN. Pooled mid 60s dewpoints with CAPE up around 2000 j/kg and decent looking wind fields/shear profiles.

[cyclone77]

00z NAM now has cape up to 3000j/kg over eastern Iowa on Monday.  Models have been pretty consistent in developing convection ahead of the cold front from southern WI down into eastern Iowa for several runs now.  Shear looks sufficient for organized severe, but tornado threat looks pretty minimal.  Large hail looks pretty meager as well, with less than impressive mid-level laps.  Could still get brief bursts of large hail in any severe storm though given the amount of cape that looks to be available.  The main severe threat looks to be wind, and very heavy rainfall.  Storm speeds look to be relatively slow for this time of the year, so some areas could get quite a bit of rainfall if caught underneath for a length of time.  

[cyclone77]

Love the new addition of low/mid-level lapse rate forecasts on COD.  Not only convenient for a case by case forecast, but also pretty cool in how it really illustrates the evolution of the LR plume.  

 

For example, the Sunday setup over the western MW/Plains will have some fairly steep mid-level lapse rates to work with.  The lapse rate plume on Sunday originate from the day before, where they develop over the southern Rockies.  

 

This is at 21z on Sat, look at that beautiful sea of strong LRS developing over the southern Rockies.  These slowly float northeast, and over-top the instability axis during the day on Sunday.

 

Monday's setup over the MW looks to have a piss poor mid-level lapse rate pool to access.  Why?  Just look at upstream from the day before on Sunday.  Unlike on Saturday, the southern Rockies do not generate a nice sea of steep LRS, as the trough has cooled most of the column by that time over that area.  So, after the original LR plume from Saturday get used up we are left with jack squat for Monday.  

 

The COD LR model output really does a great job in showing how these very important parameters evolve over time.

[HillsdaleMIWeather]

The 0Z GFS came in really interesting looking Thursday, with a dramatic uptick in instability in the subforum.

[cyclone77]

Pretty surprised SPC didn't at least include a MRGL risk over the corn belt for Day 3.  IMO it deserves a slight.  Still looks like a decent setup for a small area of severe thunderstorm potential from southern WI down into eastern IA/northern IL.  NAM continues to show a decent mid-level wave, and instability over 2000j/kg.  Even if the instability is a little overdone, there should still be at least a small threat for severe given the shear profiles.  Moisture should pool up nicely over the instability axis, as we'll have a collapsing cool front from the north, and the incoming cool front from the west.  Dews AOA 60 seem reasonable to me.

[Thundersnow12]

Continuing to get some interesting look soundings in northern IL on Monday. 

 

Here is the 18z NAM gain for near Rochelle...that could get it done. 

 

45kts of 0-6km shear, 179 m2/s2 0-1km SRH, good directional shear and CAPE values > 2,000 J/kg. 

 

[HillsdaleMIWeather]

The 18Z GFS does look a little better on Monday night, with a widespread around 1000 CAPE. Hopefully the NAM verifies.

[Tim from Springfield (IL)]

Interestingly (although I am convinced tomorrow's first D2 for Monday will be a different story), SPC's Day 3 outlook didn't have any severe listed at this time.  However, the local Weather Channel forecasts for Monday include a chance of severe here in Springfield--although from the D3 SPC didn't seem too impressed for my area.

 

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

DAY 3 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0240 AM CDT SAT APR 23 2016   VALID 251200Z - 261200Z   ...NO SVR TSTM AREAS FORECAST...   ...SUMMARY...   SEVERE STORMS ARE NOT EXPECTED ACROSS THE CONTIGUOUS UNITED STATES   ON MONDAY AND MONDAY NIGHT.   ...SYNOPSIS...   THE MID- TO UPPER-LEVEL TROUGH AMPLIFYING ACROSS THE WESTERN STATES   DURING DAY 2 IS EXPECTED TO SHIFT EAST/SOUTHEAST ON MONDAY AND   MONDAY NIGHT TOWARD THE CENTRAL ROCKIES AND FOUR CORNERS REGION.  A   MEAN RIDGE POSITION WILL BE MAINTAINED ACROSS THE GREAT PLAINS TO   CENTRAL CANADA DURING DAY 3 WITH HEIGHT RISES EXPECTED ACROSS THE   UPPER MIDWEST TO THE MID MS VALLEY.  THESE RISES WILL OCCUR AS A SD   UPPER LOW AND A LEAD SHORTWAVE TROUGH EACH WEAKEN/DAMPEN IN   AMPLITUDE...AS THEY TRACK EASTWARD INTO A CONFLUENT FLOW REGIME   ACROSS THE GREAT LAKES/OH VALLEY REGION.   ...PART OF THE UPPER MS VALLEY/GREAT LAKES AND OH VALLEY...   SHOWERS AND EMBEDDED THUNDERSTORMS SHOULD BE ONGOING ACROSS PARTS OF   THE UPPER MS VALLEY AND UPPER GREAT LAKES AT 12Z MONDAY...WITHIN A   LOW-LEVEL WARM ADVECTION REGIME /NEAR AND NORTH OF THE EASTWARD-   EXTENDING QUASISTATIONARY BOUNDARY.  DESPITE THE LIKELIHOOD FOR WEAK   UPPER FORCING...GIVEN THE DAMPENING OF THE PROGRESSIVE MIDLEVEL   LOW/TROUGH...PERSISTENT LOW-LEVEL WAA SHOULD SUPPORT ADDITIONAL   SHOWERS AND STORMS THROUGH MONDAY AFTERNOON AND EARLY EVENING.    GENERALLY WEAK INSTABILITY AND 30-35 KT OF EFFECTIVE BULK SHEAR   ORIENTED NEARLY PARALLEL TO THE SURFACE FRONT SUGGEST LINE SEGMENTS   WILL BE POSSIBLE.  HOWEVER...MODEL UNCERTAINTY WITH THE SOUTHWARD   MOVEMENT OF THE FRONT ACROSS THE SOUTHERN GREAT LAKES AND WEAK   DESTABILIZATION PRECLUDES THE INTRODUCTION OF SEVERE PROBABILITIES   AT THIS TIME.   ...EASTERN MO/WEST-CENTRAL IL...   LINGERING SHOWERS AND THUNDERSTORMS SHOULD WEAKEN ACROSS THIS REGION   MONDAY MORNING...WHILE HEIGHT RISES SUPPORT A STRENGTHENING CAP FROM   THE SOUTHWEST INTO MONDAY AFTERNOON.  THIS SHOULD LIMIT THE   DEVELOPMENT OF NEW THUNDERSTORMS.

[Hoosier]

Pretty surprised SPC didn't at least include a MRGL risk over the corn belt for Day 3.  IMO it deserves a slight.  Still looks like a decent setup for a small area of severe thunderstorm potential from southern WI down into eastern IA/northern IL.  NAM continues to show a decent mid-level wave, and instability over 2000j/kg.  Even if the instability is a little overdone, there should still be at least a small threat for severe given the shear profiles.  Moisture should pool up nicely over the instability axis, as we'll have a collapsing cool front from the north, and the incoming cool front from the west.  Dews AOA 60 seem reasonable to me.

 

 

I'm sure it'll be coming on subsequent outlooks.  Marginal to slight potential written all over it. 

[RyanDe680]

Best cape that we've seen in a while.

[Geos]

4km NAM firing off some boomers Monday afternoon.

 

 

[HillsdaleMIWeather]

The 0Z NAM had higher supercell composites and higher CAPE all over. 

[Geos]

Definitely some CAPE to work with.

 

[Geos]

GFS not as impressed.

 

 

[HillsdaleMIWeather]

SPC Day 2's out on Kamala

 

..FAR EASTERN IA...SRN WI...NRN IL/IND  
SRN LOWER MI AND FAR NW  
OHIO...  
 
THERE IS STILL SOME UNCERTAINTY WITH REGARDS TO WHERE EXACTLY THE  
SURFACE LOW AND ATTENDANT SYNOPTIC SFC BOUNDARIES WILL BE LOCATED ON  
MONDAY WITH MODERATE SPREAD AMONGST GUIDANCE IN THE EVOLUTION OF  
THIS SYSTEM. CONFIDENCE IS HIGH ENOUGH HOWEVER GIVEN THE OVERALL  
PATTERN TO INCLUDE A MARGINAL AREA. SCATTERED CLOUDINESS MAY LIMIT  
INSTABILITY DESPITE A MOIST BOUNDARY LAYER AND MODEST MIDLEVEL LAPSE  
RATES...BUT WILL STILL BE SUFFICIENT FOR THUNDERSTORM DEVELOPMENT  
NEAR THE SFC LOW AND/OR AHEAD OF THE SOUTHWARD SAGGING FRONT.  
DEEP-LAYER SHEAR WILL INCREASE THROUGH THE DAY /0-6 KM SHEAR NEAR 40  
KT/ AS THE SHORTWAVE APPROACHES WITH GENERALLY UNIDIRECTIONAL  
PROFILES FORECAST. THE EXCEPTION WILL BE NEAR THE FRONT AND SURFACE  
LOW WHERE LOW LEVEL DIRECTIONAL SHEAR WILL BE SOMEWHAT BETTER. THIS  
SHOULD LEAD TO AT LEAST SOME ISOLATED CELLS CAPABLE OF HAIL AND  
GUSTY WINDS. AN UPGRADE TO SLIGHT RISK MAY BE NEEDED FOR PORTIONS OF  
THIS AREA IN FUTURE OUTLOOKS SHOULD CONFIDENCE INCREASE AND FINER  
DETAILS BECOME MORE CERTAIN.  

[wisconsinwx]

Tomorrow starting to look a bit interesting around here. Many of the models, hi-res and global, seem to be honing in on a complex developing in C Wisconsin tomorrow afternoon and then shifting E/SE. Being projected on the southern flank of this we could definitely get some good garden variety storms at the very least.

[Geos]

0z EURO fires a thunderstorm line off in SE MN just west of DLL and extreme NE IA at mid-day and it looks like it takes it ESE from there.

 

Showing a tongue of 500-1000 SB CAPE values extending along the front with some elevated SB CINH. 60° dewpoints into N IL back down into MO.

 

A secondary area gets going from PIA to GRR in the evening.

[Geos]

12z EURO

 

Has a slight to moderate risk of severe weather from SE WI to western MI late tomorrow afternoon. SB CAPE never gets above 750 in the sub, except maybe southeast Iowa. Some CIN less than -50 j/Kg from NE IL into WI and western MI.

 

Dew points get into the low 60s ahead of the front. Storm fire in similar areas to the 0z run^.

[HillsdaleMIWeather]

18Z GFS did up the CAPE like the 12Z did, if you want good severe weather tomorrow hope the NAM verifies.

[Hoosier]

12z EURO

 

Has a slight to moderate risk of severe weather from SE WI to western MI late tomorrow afternoon. SB CAPE never gets above 750 in the sub, except maybe southeast Iowa. Some CIN less than -50 j/Kg from NE IL into WI and western MI.

 

Dew points get into the low 60s ahead of the front. Storm fire in similar areas to the 0z run^.

 

 

Are those your own categories or something?

[cyclone77]

27hr RAP breaks out convection from southern WI down into eastern IA late tomorrow afternoon.  Has a nice ribbon of 60+dews, and 1500-2000j/kg cape ahead of the cool front.