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Early May (1st-7th) Severe Chances


Stebo

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LOT hinting at severe weather Thursday night.

LONG TERM...THURSDAY NIGHT THROUGH MONDAY

THE ACTIVE PATTERN LOOKS TO CONTINUE LATE THIS WEEK INTO EARLY

NEXT WEEK WITH A POTENTIAL FOR SOME COOLER AIR OVER THE WEEKEND

INTO EARLY NEXT WEEK...ESPECIALLY FOR THE NORTHERN CWA/NEAR THE

LAKE.

BROAD MID/UPPER LEVEL RIDGING OVER THE EASTERN CONUS WILL FLATTEN

OUT AND IT APPEARS FAIRLY DEEP TROUGHING WILL DIG INTO THE NORTHEAST

US OR SOUTHEASTERN CANADA BY THE WEEKEND. AT THE SAME TIME...A

TROUGH WILL DIG INTO THE WESTERN CONUS. THESE DEVELOPMENTS WILL

SUPPORT RENEWED RIDGING EXTENDING FROM MEXICO UP THROUGH THE

CENTRAL CONUS. AT THE SURFACE...A QUASI STATIONARY FRONTAL

BOUNDARY IS EXPECTED TO SET UP JUST NORTH OF THE CWA AND THEN

GRADUALLY SAG SOUTH OVER THE WEEKEND AS LARGE SURFACE HIGH

PRESSURE TRIES TO BUILD DOWN FROM CENTRAL CANADA. THIS WILL BRING

SYNOPTIC ONSHORE/NE FLOW BY LATE SATURDAY...ENDING THE STRING OF

UNSEASONABLE WARMTH...WITH THIS MOST LIKELY TO OCCUR FOR THE

NORTHERN HALF OF THE CWA AND/OR LOCATIONS CLOSER TO THE LAKE. WEAK

WAVES OF SURFACE LOW PRESSURE WILL OCCASIONALLY RIDE ALONG THE

BOUNDARY INTO EARLY NEXT WEEK...BRINGING ANOTHER EXTENDED FORECAST

WITH POPS THROUGHOUT. IT IS A DIFFICULT PATTERN TO HANDLE

INDIVIDUAL FEATURES OF NOTE...SO THE MODELS REALLY DO NOT HAVE

MUCH AGREEMENT IN TERMS OF PLACEMENT AND TIMING OF FEATURES THAT

WILL IMPACT OUR SENSIBLE WEATHER. ALTHOUGH POPS HAVE AGAIN BEEN

INCLUDED FOR EVERY PERIOD...THERE WILL CERTAINLY BE DRY

TIMES...WITH REFINEMENT OF DETAILS OCCURRING AS WE GET CLOSER IN

THE FORECAST.

THE BIG STORY WILL BE THE SUMMER HEAT AND HUMIDITY SOUTH OF THAT

BOUNDARY...WITH 850 MB TEMPERATURES IN THE MID TEENS SUPPORTING HIGH

TEMPERATURES IN THE 70S AND 80S FRIDAY AND SATURDAY...ALONG WITH

DEWPOINTS WELL INTO THE 60S. THE CONCERN IS THERE FOR ORGANIZED

CONVECTION POTENTIALLY PRODUCING HEAVY RAIN ON THE NOSE OF 30-40 KT

LOW LEVEL JET ON THURSDAY EVENING/NIGHT. PWATS AND 850 MB MOISTURE

FLUX CONTINUE TO BE ADVERTISED WELL ABOVE CLIMO AT 2 SD OR

HIGHER...AND SOUNDINGS SHOW PLENTY OF INSTABILITY TO BE TAPPED INTO.

CANNOT RULE OUT SEVERE THUNDERSTORMS LATE THURSDAY...WITH

POSSIBILITY OF DECENT LOW LEVEL SHEAR AND CAPE AT OR IN EXCESS OF

2000 J/KG. HOWEVER...WITH CORE OF JET STREAM WELL TO

NORTH...MIDLEVEL FLOW WILL ONLY BE ON THE ORDER OF 35 KT OR SO...SO

DEEP LAYER SHEAR PROFILES WILL BE MARGINAL. BIGGEST THREAT MAY

BECOME THAT OF HEAVY AND POSSIBLY FLOODING RAINS. HIGH CAPE CAN BE

EXPECTED FRIDAY AS WELL...AND THEN SOUTH OF WHEREVER THE BOUNDARY

SETS UP SATURDAY AND SUNDAY...SO AT LEAST ISOLATED STRONGER STORMS

CAPABLE OF PRODUCING VERY HEAVY RAIN CANNOT BE RULED OUT THOSE DAYS

EITHER.

RC

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MKX severe weather disco:

TUESDAY NIGHT...FORECAST CONFIDENCE MEDIUM TO HIGH.

EXPECT ONGOING CONVECTION FROM TUESDAY AFTERNOON IN MN/NW WI ON NOSE

OF LLJ AND PORTION OF SURFACE WARM FRONT NEAREST SURFACE LOW TO

DEVELOP BACK THROUGH IA ALONG TRAILING SURFACE TROUGH/COOL FRONT.

STORMS IN WISCONSIN TO MOVE EAST ALONG WARM FRONT...AND FARTHER

SOUTH WITH 1000-850 MB THETA-E ADVECTION/CONVERGENCE AS SOUTHERLY

850 MB WINDS VEER SOUTHWEST BEHIND PASSING SHORT WAVE. FORECAST CAPE

VALUES HIGHER OVER WESTERN CWA...THOUGH MAGNITUDE IS SUSPECT AS

MODEL 2M DEW POINTS AND SFC DEW POINTS ON FORECAST SOUNDINGS LOOK

TOO MOIST. WILL TREND CLOSER TO LOWER MOS GUIDANCE. STILL ENOUGH

INSTABILITY...STEEP MID-LEVEL LAPSE RATES AND SHEAR FOR MAINLY

ELEVATED STRONG STORMS WITH THE POTENTIAL OF LARGE HAIL...ESPECIALLY

WEST.

FOLLOWED NEIGHBORING OFFICES AND WENT WITH 3-HOURLY POPS. LIKELY

POPS AFTER MIDNIGHT IN THE FAR NORTH LINE UP WELL WITH STRONGER

LAYER Q-VECTOR CONVERGENCE...MAINLY ALONG SURFACE AND 850 MB

FRONTS...THAT WEAKENS AS IT MOVES SOUTHEAST OVER THE REMAINDER OF

THE CWA OVERNIGHT...LEADING TO CHANCE POPS ELSEWHERE.

WEDNESDAY AND WEDNESDAY NIGHT...FORECAST CONFIDENCE MEDIUM

WHERE THE EFFECTIVE SURFACE WARM FRONT SETS UP DUE TO OUTFLOW AND

CLOUD DEBRIS FROM TUESDAY NIGHT INTO WEDNESDAY MORNING CONVECTION

WILL BE CRITICAL TO AMOUNT OF WARMING AND INSTABILITY AND SUBSEQUENT

DEVELOPMENT OF CONVECTION...AND DICTATE MOST-LIKELY LOCATION OF

SEVERE WITH NEXT WARM AIR/MOISTURE ADVECTION SURGE LATE WEDNESDAY

AFTERNOON AND EVENING. SPC DAY 3 OUTLOOK COVERS MOST OF THE STATE TO

ACCOUNT FOR BOTH MORNING SEVERE POTENTIAL IN THE CENTRAL AND

NORTH...AND THE AFTERNOON/EVENING POTENTIAL SOUTH AND CENTRAL.

BEST CHANCES FOR SEVERE IN THE SOUTH IN THE LATE

AFTERNOON/EVENING...WITH THE HIGHER VALUES ON LOCAL CWASP SEVERE

CHECK LIST ALIGNING WELL WITH CONVERGENCE ON LEADING EDGE OF 40 KT

LOW-LEVEL JET AND ALONG SURFACE WARM FRONT THAT PASSES SOUTH TO

NORTH THROUGH FORECAST AREA BETWEEN 00Z AND 06Z THURSDAY. VEERING

WIND PROFILE SUGGEST SUPER CELL STORMS LIKELY WITH SUFFICIENT 0-6KM

BULK SHEAR OF 35 TO 40 KNOTS. LARGE HAIL AND STRONG WINDS...WITH THE

POTENTIAL FOR TORNADOES WITH LOW LEVEL VEERING ALONG THE SURFACE

WARM FRONT PRODUCING 0-1KM SHEAR OF 25 TO 35 KNOTS AND 0-1 KM EHI

BETWEEN 1.5 AND 2.25.

Sounds like several chance at severe weather in different areas. Should keep local forecast offices quite busy!

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I'm not sure I agree. The lapse rate between the lake water and the air just above (like feet above) is often very steep. Over the lake, the slice of the atmosphere affected by the lake is usually thin. Not saying development over the lake is never retarded but I think you are overblowing it.

I think you guys are taking what I'm saying the wrong way. The lake is less likely to effect convection that's being fed by unstable air being advected in from elsewhere and converging over the lake. However, for the air to be converging over the lake in the first place there has to be some kind of meso or synoptic scale forcing going on. Or, as in the Chicago case there was already a boundary that formed over the land and was advected over the lake by offshore flow. The same thing can happen on the east side of the lake, but it's more unusual to have an offshore flow since the prevailing flow usually has some westerly component.

Anyways, if you ever look at visible satellite view of the cu field during peak heating you'll get what I'm saying. If there is a SW flow the cu field pretty much vanishes by the time the air reaches the middle of the lake and doesn't redevelop until the air gets about 20 miles inland on the leeward side. It's pretty hard for convection to initiate in that cu field hole. It usually has to initiate in Wisconsin and then move across the lake.

Also, even if the actual marine layer is too thin to reduce the stability of the layer above directly, it does create a boundary layer meso-high circulation due to differential heating. It may be that the differential heating of lake-vs-land does more to inhibit convection than the absolute reduction in CAPE. You could have 2200 ML CAPE over the lake and 2500 ML CAPE over the land. The 2200 ML CAPE over the lake is still plenty of juice for strong convection, yet the convection might still have trouble initiating over the lake because the heating differential is just enough to increase the CINH so that parcels have more trouble reaching the level of free convection.

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Not sure about this discussion about convection forming over the lake, I don't expect that to be the case this week so it is an irrelevant topic to this week's potentials.

The current expectation with the stuff this week will be that it moves in from the West or forms over Michigan.

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t0pb3k.jpg

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1258 AM CDT TUE MAY 01 2012

VALID 021200Z - 031200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM A PORTION OF THE CNTRL

PLAINS INTO THE UPPER MS VALLEY AND GREAT LAKES...

...SYNOPSIS...

BELT OF BROAD CYCLONIC FLOW WILL PERSIST OVER THE NRN THIRD OF THE

COUNTRY. SEVERAL IMPULSES WILL MOVE THROUGH THIS REGIME AND TEND TO

MODULATE THE SEVERE POTENTIAL FROM THE CNTRL PLAINS INTO THE UPPER

MS VALLEY AND GREAT LAKES. FRONT WILL LIKELY STALL FROM NEB NEWD

THROUGH MN AND WI. DRYLINE WILL PERSIST OVER THE SRN PLAINS NWD INTO

SWRN NEB WHERE IT WILL INTERSECT THE FRONT. A WARM FRONT WILL

CONTINUE LIFTING NEWD THROUGH THE GREAT LAKES.

...CNTRL PLAINS THROUGH UPPER MS VALLEY AND GREAT LAKES...

IT STILL APPEARS LEAD IMPULSE WILL EJECT INTO SWRN QUEBEC EARLY

WEDNESDAY WITH SWLY FLOW ALOFT BECOMING NEAR PARALLEL TO FRONT THAT

WILL EXTEND FROM WI AND MN SWWD INTO THE CNTRL PLAINS. A MOIST WARM

SECTOR WITH LOW TO MID 60S DEWPOINTS WILL RESIDE SOUTH OF FRONT. A

FEW STORMS WILL PROBABLY BE ONGOING EARLY IN PERIOD AND MIGHT

CONTRIBUTE TO EFFECTIVE BOUNDARY RESIDING SOUTH OF THE SYNOPTIC

FRONT. INITIAL CONVECTION WILL SHIFT EWD AND WEAKEN ALLOWING

BOUNDARY LAYER DESTABILIZATION IN ITS WAKE. STEEP LAPSE RATES WILL

ADVECT ABOVE THE MOIST AXIS RESULTING IN MODERATE TO STRONG

INSTABILITY AS THE BOUNDARY LAYER WARMS. LOW AMPLITUDE SHORTWAVE

RIDGING WILL MOVE THROUGH THE AREA BEFORE THE NEXT UPSTREAM TROUGH

APPROACHES BY EVENING. ADDITIONAL STORMS WILL LIKELY DEVELOP ALONG

THE FRONT AND RESIDUAL OUTFLOW BOUNDARIES FROM NEB INTO THE UPPER MS

VALLEY BY LATE AFTERNOON. NRN EXTENT OF WARM SECTOR WILL REMAIN

WITHIN BELT OF STRONGER WLYS...AND DEEP LAYER WINDS WILL STRENGTHEN

AS THE NEXT UPSTREAM SHORTWAVE TROUGH APPROACHES THE NRN PLAINS.

VERTICAL SHEAR FROM 35-40 KT WILL PROMOTE ORGANIZED SEVERE STORMS

INCLUDING SUPERCELLS...BUT SOME OF THE STORMS MAY EVENTUALLY GROW

UPSCALE INTO ONE OR MORE MCS CLUSTERS SUPPORTED BY STRENGTHENING

LLJ. LARGE HAIL...DAMAGING WIND AS WELL AS A FEW TORNADOES WILL BE

POSSIBLE.

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Beat me to it. Placement of the slight risk and higher 30% and hatched area seems very reasonable. Northern IL portion of slight will likely be too capped and very marginal shear, but with steep midlevel lapse rates and high CAPE, still seems warranted to keep part of the LOT CWA in the 15% probs. From NAM and GFS soundings, Thursday looks like it will have even more instability and steeper mid level lapse rates than Weds, but similar capping and marginal shear issues. As Hoosier alluded to earlier though, if any updrafts can be sustained on Weds and Thurs, large hail would be a good bet. This period also looks like a pretty good set-up for nocturnal MCS's for somewhere in the region with plenty of elevated instability remaining overnight and the low level jet ramping up.

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liking chances for an MCS to come through during the early morning hours...probably not severe through.

Skyvision on Milwaukee's local Fox 6 affiliate shows a nice line coming through in the early morning hours around sunrise as well. Wasn't confident in it happening, but now might reconsider the chances.

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Skyvision on Milwaukee's local Fox 6 affiliate shows a nice line coming through in the early morning hours around sunrise as well. Wasn't confident in it happening, but now might reconsider the chances.

most of the previous high res runs had something

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most of the previous high res runs had something

That's true, I wasn't sure whether to trust the GFS repeated dry runs or the hi-res models a bit beyond their useful range. Oh well, if not overnight tonight, we should still have chances late Wednesday and Thursday for an MCS.

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Not sure about this discussion about convection forming over the lake, I don't expect that to be the case this week so it is an irrelevant topic to this week's potentials.

The current expectation with the stuff this week will be that it moves in from the West or forms over Michigan.

The cursed t-storm killing lake is relevant to me considering my location. :P It's a rare case when it's a positive factor (i.e. backed SSE flow setting up a lake breeze) rather than a negative. I guess I'll be happy to get a nocturnal MCS or weakening squall line rolling in from Wisconsin. Discrete afternoon popups are much more interesting to watch but they usually require getting in the car and driving east 20-30 miles or so.

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That's true, I wasn't sure whether to trust the GFS repeated dry runs or the hi-res models a bit beyond their useful range. Oh well, if not overnight tonight, we should still have chances late Wednesday and Thursday for an MCS.

latest NMM and ARW runs both bring an MCS across the region tonight, with the former further north across northern IL / southern WI and the latter diving an aggressive outflow south.

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BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE INDIANAPOLIS IN

322 PM EDT TUE MAY 1 2012

THE NATIONAL WEATHER SERVICE IN INDIANAPOLIS HAS ISSUED A

* TORNADO WARNING FOR...

NORTHWESTERN BARTHOLOMEW COUNTY IN CENTRAL INDIANA...

CENTRAL BROWN COUNTY IN SOUTH CENTRAL INDIANA...

* UNTIL 345 PM EDT

* AT 321 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED NEAR NASHVILLE...OR 12 MILES EAST OF BLOOMINGTON...AND MOVING EAST AT 55 MPH.

* LOCATIONS IMPACTED INCLUDE...

NASHVILLE...

GNAW BONE...

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Mesoscale Discussion 646

mcd0646.gif

MESOSCALE DISCUSSION 0646

NWS STORM PREDICTION CENTER NORMAN OK

0230 PM CDT TUE MAY 01 2012

AREAS AFFECTED...FAR ERN SD...SW MN...NW IA...NE NEB

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 011930Z - 012030Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...SCATTERED THUNDERSTORM DEVELOPMENT IS EXPECTED DURING THE

NEXT FEW HOURS WITH THE POSSIBILITY OF A FEW SEVERE STORMS CAPABLE

OF PRODUCING HAIL AND STRONG WINDS. PART OR ALL OF THIS AREA WILL

LIKELY NEED A WW BY 21Z.

DISCUSSION...19Z SURFACE ANALYSIS DEPICTS AN AREA OF LOW PRESSURE

OVER N-CNTRL SD WITH A WARM FRONT EXTENDING FROM MBG EWD TO ETH AND

THEN SEWD TO AXA AND A COLD FRONT EXTENDING SWWD TO OGA.

TEMPERATURES HAVE CLIMBED INTO THE MID TO UPPER 70S SOUTH OF THIS

FRONT WITH DEWPOINT VALUES IN THE UPPER 50S TO LOW 60S. AS A

RESULT...AN AXIS OF INSTABILITY EXISTS ACROSS THE DISCUSSION AREA

WITH THE HIGHEST MLCAPE VALUES /AROUND 1000 J/KG/ IN AND AROUND FSD.

CONTINUED HEATING SHOULD ALLOW FOR INCREASED DESTABILIZATION SOUTH

OF THE WARM FRONT WITH CONVECTIVE INITIATION BECOMING MORE LIKELY.

SHEAR PROFILES INDICATE STORM ORGANIZATION IS PROBABLE WITH PRIMARY

THREATS OF SEVERE HAIL AND STRONG WIND GUSTS. FARTHER E /ACROSS

MN/...BACKED LOW-LEVEL FLOW INDICATES AN ENHANCED TORNADO

THREAT...ESPECIALLY ALONG AND JUST AHEAD OF THE ADVANCING WARM

FRONT. HOWEVER...THIS AREA WILL LIKELY REMAIN CAPPED UNTIL AFTER THE

WARM FRONT MOVES THROUGH. AS SUCH...VEERING WINDS ALONG AND BEHIND

THE FRONT SHOULD KEEP THE TORNADO THREAT ISOLATED.

..MOSIER/BUNTING/MEAD.. 05/01/2012

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PRELIMINARY LOCAL STORM REPORT

NATIONAL WEATHER SERVICE INDIANAPOLIS IN

400 PM EDT TUE MAY 01 2012

.TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON

.DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.

..REMARKS..

0353 PM TORNADO 1 W COLUMBUS 39.21N 85.93W

05/01/2012 BARTHOLOMEW IN TRAINED SPOTTER

BRIEF TOUCHDOWN REPORTED WEST SIDE OF COLUMBUS

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WFUS53 KILX 012101

TORILX

ILC019-012145-

/O.NEW.KILX.TO.W.0007.120501T2101Z-120501T2145Z/

BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE LINCOLN IL

401 PM CDT TUE MAY 1 2012

THE NATIONAL WEATHER SERVICE IN LINCOLN HAS ISSUED A

* TORNADO WARNING FOR...

SOUTHERN CHAMPAIGN COUNTY IN EAST CENTRAL ILLINOIS...

* UNTIL 445 PM CDT.

* AT 359 PM CDT...TRAINED WEATHER SPOTTERS REPORTED A FUNNEL CLOUD 8

MILES SOUTHEAST OF WHITE HEATH...OR 8 MILES SOUTHEAST OF

MONTICELLO. A TORNADO MAY DEVELOP AT ANY TIME. DOPPLER RADAR SHOWED

THIS DANGEROUS STORM MOVING NORTHEAST AT 30 MPH.

* LOCATIONS IMPACTED INCLUDE...

CHAMPAIGN...TOLONO...SAVOY...PHILO...URBANA...SIDNEY...ST.

JOSEPH...OGDEN...HOMER...SADORUS...WILLARD AIRPORT...ROYAL AND

FLATVILLE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A

STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR

OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT

YOURSELF FROM FLYING DEBRIS.

&&

LAT...LON 3988 8842 3988 8846 4008 8846 4028 8797

4022 8794 4002 8794

TIME...MOT...LOC 2101Z 246DEG 25KT 3999 8842

$$

BAK

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BULLETIN - EAS ACTIVATION REQUESTED

TORNADO WARNING

NATIONAL WEATHER SERVICE LOUISVILLE KY

524 PM EDT TUE MAY 1 2012

THE NATIONAL WEATHER SERVICE IN LOUISVILLE HAS ISSUED A

* TORNADO WARNING FOR...

NORTHWESTERN WASHINGTON COUNTY IN SOUTH CENTRAL INDIANA...

* UNTIL 545 PM EDT...

* AT 518 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED 7 MILES WEST OF MOUNT CARMEL...MOVING NORTHEAST AT 40 MPH.

* THIS TORNADIC STORM WILL ALSO IMPACT...

MCKINLEY...

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