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Tim from Springfield (IL)

April 8-10 Severe threat

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SPC already has a 30% D6 risk from roughly Chicago to Texarkana for Thursday (Apr. 9), plus some D5 15% that includes most of MO.  Looks like Thursday could be the first severe threat of 2015 in central Illinois if current trends hold:

 

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

 

ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 040858
   SPC AC 040858

   DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0358 AM CDT SAT APR 04 2015

   VALID 071200Z - 121200Z

   ...DISCUSSION...
   LATEST RUNS OF THE MEDIUM-RANGE MODELS EXHIBIT DECENT AGREEMENT INTO
   THE DAY 6 /THU. 4-9/ TIME PERIOD...PROJECTING THE WRN U.S. TROUGH TO
   BECOME PROGRESSIVE AND TRAVERSE THE ROCKIES THROUGH DAY 5 BEFORE
   SHIFTING INTO THE PLAINS DAY 6.  FROM LATE IN THE DAY 6 PERIOD
   ONWARD...SPREAD IN THE MODEL SOLUTIONS INCREASES SUCH THAT LOW
   FORECAST CONFIDENCE PREVAILS DAYS 7 AND 8.

   SEVERE-WEATHER RISK APPEARS RELATIVELY LOW EARLY IN THE PERIOD --
   BUT A GRADUAL RAMP-UP IN RISK EACH AFTERNOON/EVENING THROUGH DAY 6
   APPEARS LIKELY ACROSS THE U.S. AS THE WRN TROUGH APPROACHES -- AND
   EVENTUALLY REACHES -- THE CENTRAL CONUS.  THOUGH AIRMASS ACROSS THE
   OK/ERN KS/MO/AR/N TX VICINITY DURING THE AFTERNOON ON DAY 4 /TUE.
   4-7/ WILL LIKELY BECOME STRONGLY UNSTABLE...WEAK RIDGING PERSISTING
   ALOFT -- AND ASSOCIATED/WEAK SUBSIDENCE -- SHOULD PERMIT CAPPING AT
   THE BOTTOM OF THE EML LAYER TO PERSIST IN MOST AREAS.  THIS SUGGESTS
   THAT STORM INITIATION /AND ASSOCIATED SEVERE RISK/ SHOULD REMAIN
   RELATIVELY ISOLATED.

   SLIGHTLY MORE WIDESPREAD STORM DEVELOPMENT WILL BE POSSIBLE DURING
   THE AFTERNOON ON DAY 5 /WED. 4-8/...AS WEAK HEIGHT FALLS BEGIN AHEAD
   OF THE APPROACHING UPPER SYSTEM.  WHILE EJECTION OF ANY APPRECIABLE
   LEAD WAVE IS NOT EVIDENT ATTM...A LESS SUBSIDENT/MORE NEUTRAL
   BACKGROUND LARGE-SCALE UVV SUGGESTS GREATER POTENTIAL FOR CAP
   BREACHES/STORM INITIATION -- PRIMARILY ACROSS THE ERN KS/MO/OK
   VICINITY.  WITH STRONG INSTABILITY AND MODERATELY STRONG SHEAR
   EXPECTED...ENVIRONMENT WILL FAVOR SUPERCELLS...AND ASSOCIATED RISK
   FOR LARGE HAIL...DAMAGING WINDS...AND POSSIBLE TORNADOES.

   WHILE ONGOING CONVECTION OVERNIGHT DAY 5 AND INTO EARLY DAY 6
   LIKELY...ASCERTAINING DEGREE AND LOCATION OF SEVERE RISK DAY 6
   PRESENTS SOME DIFFICULTY ATTM.  WITH THAT SAID...THE ADVANCE OF THE
   WRN TROUGH AND ASSOCIATED UVV INTO THE INTO THE CENTRAL PLAINS
   DURING THE AFTERNOON AND EVENING WILL PERMIT WIDESPREAD CONVECTIVE
   INITIATION -- FOCUSED INVOF THE COLD FRONT FORECAST TO BE ADVANCING
   ACROSS ERN KS/CENTRAL OK NEAR PEAK HEATING.  WITH SUBSTANTIAL
   INSTABILITY LIKELY TO BE PRESENT AND A FAVORABLY SHEARED
   ENVIRONMENT...A FAIRLY BROAD AFTERNOON AND EVENING ZONE OF RISK FOR
   LARGE HAIL AND DAMAGING WINDS ALONG WITH A FEW TORNADOES IS EVIDENT
   -- EXTENDING FROM IL SWWD ACROSS MO/AR INTO SERN KS/ERN OK AND
   POSSIBLY INTO N CENTRAL/NERN TX.

   ..GOSS.. 04/04/2015

   CLICK TO GET WUUS48 PTSD48 PRODUCT
 

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The 78 and 81 hour of the 18z nam should be saved for those of us in western OH. Classic end of crazy uncle nam run.

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New D4 for Wednesday now has west-central Illinois (as far east as SPI, ILX, and almost to PIA) in the 15% risk, mainly for that night.  Thursday's D5 pretty much unchanged in this region at this time:

 

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

 

ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 050858
   SPC AC 050858

   DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0358 AM CDT SUN APR 05 2015

   VALID 081200Z - 131200Z

   ...DISCUSSION...
   APPRECIABLE SPREAD -- EVEN MORE THAN 24 HOURS PRIOR -- IS EVIDENT
   AMONGST THE MEDIUM-RANGE MODELS THIS FORECAST...WITH THE GFS
   SHIFTING THE WRN TROUGH INTO THE PLAINS FASTER AND WITH MORE OF A
   POSITIVE TILT...WHILE THE UKMET AND PARTICULARLY THE ECMWF DEPICT A
   SLOWER AND MORE NEUTRAL TO NEGATIVE TILT PROGRESSION.  AS A RESULT
   OF THESE DIFFERENCES -- AND THE ASSOCIATED VARIANCES IN SURFACE
   FEATURE LOCATIONS IN THE DAY 4-5 TIME FRAME...SPECIFICS OF THE
   SEVERE WEATHER FORECAST WITH RESPECT TO TIMING/LOCATION REMAIN
   DIFFICULT TO ASCERTAIN.

   DESPITE TIMING DIFFERENCES WITH RESPECT TO THE MAIN UPPER
   LOW/TROUGH...CONFIDENCE HAS INCREASED THIS FORECAST WITH RESPECT TO
   SEVERE RISK FOR DAY 4 /WED 4-8/ ACROSS CENTRAL AND ERN OK/ERN KS/MO.
    ALL MODELS INDICATE MID-LEVEL HEIGHT FALLS ACROSS THIS AREA...AND
   AT LEAST HINTS OF A SUBTLE/EMBEDDED WAVE CROSSING THE REGION NEAR
   PEAK HEATING.  ATTM...EXPECT RESULTING UVV TO BE SUFFICIENT ATOP THE
   EWD-MIXING DRYLINE TO PERMIT CAP WEAKENING SUFFICIENT TO YIELD
   ISOLATED TO SCATTERED STORM DEVELOPMENT BY LATE AFTERNOON.  WITH A
   VERY MOIST BOUNDARY LAYER AHEAD OF THE DRYLINE TOPPED BY STEEP LAPSE
   RATES...AND A KINEMATIC ENVIRONMENT FEATURING FLOW THAT VEERS
   SUBSTANTIALLY AND INCREASES STEADILY WITH HEIGHT...SHEAR WILL FAVOR
   LONG-LIVED SUPERCELLS AND ATTENDANT RISK FOR VERY LARGE
   HAIL...DAMAGING WINDS...AND TORNADOES.  GIVEN UNCERTAINTY DUE TO
   STORM COVERAGE...WILL MAINTAIN ONLY 15% PROBABILITY AREA ATTM --
   DESPITE SIGNIFICANT SEVERE WEATHER POTENTIAL WITH ANY STORM THAT
   DOES DEVELOP.

   THE LIKELIHOOD FOR MORE WIDESPREAD STORMS -- BUT WITH GREATER
   UNCERTAINTY IN TERMS OF TIMING AND AREA -- EXISTS DAY 5 /THU 4-9/.
   DEEPENING OF THE SURFACE LOW IN THE KS/NEB/IA VICINITY AND ADVANCE
   OF A TRAILING COLD FRONT INTO THE CENTRAL/SRN PLAINS WILL FACILITATE
   A BROAD ZONE OF STORM INITIATION...GIVEN THE MOIST/FAVORABLY
   UNSTABLE AIRMASS EXPECTED.  WITH STRONGER FLOW ALOFT AS COMPARED TO
   DAY 4 GIVEN PROGRESSION OF THE MAIN MID-LEVEL JET STREAK INTO THE
   CENTRAL STATES...SUPERCELL STORMS AND ASSOCIATED RISK FOR VERY LARGE
   HAIL...DAMAGING WINDS...AND TORNADOES CAN BE EXPECTED.

   MODELS CONTINUE TO DIVERGE DAY 6 AND BEYOND...AND GIVEN THE
   INCREASING SPREAD IN SOLUTIONS BETWEEN THEM...LOW CONFIDENCE EXISTS
   WITH RESPECT TO EVOLUTION OF SEVERE RISK THROUGH THE SECOND HALF OF
   THE PERIOD.  THUS...LOW PREDICTABILITY PRECLUDES ATTEMPTS TO
   HIGHLIGHT THREAT AREAS BEYOND DAY 5.

   ..GOSS.. 04/05/2015
 

 

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New day 3

 

 

 

DAY 3 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0233 AM CDT MON APR 06 2015  
 
VALID 081200Z - 091200Z  

 
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID AND LOWER MO/MID  
MS VALLEY REGION SWWD ACROSS ERN KS/CENTRAL OK...  
 
...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLIGHT RISK  
AREA...FROM THE MIDWEST WWD INTO THE MID MO VALLEY...AND SWD ACROSS  
CENTRAL TX...  
   
..SUMMARY
 
 
SCATTERED SHOWERS AND STORMS ARE FORECAST ACROSS A LARGE PORTION OF  
THE CENTRAL AND EASTERN UNITED STATES...INCLUDING AN AREA OF SEVERE  
STORMS OVER THE CENTER OF THE COUNTRY. SHOWERS AND THUNDERSTORMS  
ARE ALSO FORECAST ACROSS PORTIONS OF THE INTERMOUNTAIN WEST  
WEDNESDAY.  
   
..SYNOPSIS
 
 
STEADY EWD ADVANCE OF A LARGE WRN U.S. UPPER TROUGH IS FORECAST TO  
CONTINUE DAY 3 /WED/. SUBSTANTIAL HEIGHT FALLS ARE FORECAST TO  
OCCUR AHEAD OF THIS FEATURE OVER THE PLAINS...WITH THE TROUGH  
PROGGED TO REACH/CROSS THE NRN AND CENTRAL HIGH PLAINS LATE IN THE  
PERIOD. DOWNSTREAM...RIDGING IS FORECAST TO INCREASE E OF THE MS  
VALLEY...AS THE OVERALL PATTERN AMPLIFIES CONUS-WIDE.  
 
AT THE SURFACE...CYCLOGENESIS IS FORECAST IN RESPONSE TO THE  
APPROACHING UPPER SYSTEM -- INITIALLY OVER THE CENTRAL HIGH PLAINS  
DURING THE DAY AND THEN SHIFTING NEWD TO BECOME CENTERED NEAR THE  
ERN NEB/NERN KS/NWRN MO/WRN IA BORDER REGION BY THE END OF THE  
PERIOD. S OF THIS LOW...A DRYLINE IS PROGGED TO MIX EWD INTO  
CENTRAL KS/CENTRAL OK THROUGH THE AFTERNOON...TO BECOME OVERTAKEN BY  
A SEWD-MOVING COLD FRONT OVERNIGHT. MEANWHILE...A NWD ADVANCE OF A  
WARM FRONT ACROSS THE KS/MO VICINITY IS FORECAST WITH TIME AS THE  
SURFACE LOW DEEPENS/SHIFTS NEWD ACROSS KS.  
   
..THE MIDWEST/MID AND LOWER MO VALLEY/CENTRAL AND SRN PLAINS
 
 
A MOIST BOUNDARY LAYER WILL REMAIN IN PLACE ACROSS THE CENTRAL AND  
SRN PLAINS AND MID/LOWER MO VALLEY REGION AHEAD OF THE DRYLINE AS IT  
MIXES EWD THROUGH THE AFTERNOON. AS HEIGHT FALLS ALOFT OCCUR AHEAD  
OF THE ADVANCING UPPER TROUGH...RESULTING ASCENT WILL SUPPORT  
WEAKENING OF CAPPING AT THE BASE OF THE EML LAYER -- PARTICULARLY  
FROM SRN OK NWD INTO KS. EVENTUALLY...ASCENT SHOULD PROVE  
SUFFICIENT TO ALLOW LOCAL BREACHES IN CAPPING -- AND RESULTING/RAPID  
DEVELOPMENT OF ISOLATED STORMS. GIVEN A VERY UNSTABLE AIRMASS/STEEP  
LAPSE RATES ALOFT...AND AIDED BY FAVORABLY STRENGTHENING/VEERING  
FLOW WITH HEIGHT...STORMS SHOULD RAPIDLY BECOME SUPERCELLS. ALONG  
WITH LOCALLY DAMAGING WINDS...VERY LARGE HAIL IS EXPECTED. IN  
ADDITION...THE AMPLY MOIST BOUNDARY LAYER AND FAVORABLE LOW-LEVEL  
SHEAR -- PARTICULARLY NWD INTO KS NEARER THE ADVANCING SURFACE LOW  
-- WILL LIKELY BE SUFFICIENT TO SUPPORT RISK FOR TORNADOES. WHILE  
OVERALL STORM COVERAGE SHOULD REMAIN WIDELY SCATTERED TO  
ISOLATED...SIGNIFICANT SEVERE WEATHER IS EXPECTED WITH ANY STORM  
WHICH DOES DEVELOP.  
 
OVERNIGHT...INCREASING WARM ADVECTION AHEAD OF THE ADVANCING LOW --  
PARTICULARLY NEAR/N OF THE WARM FRONT -- SUGGESTS INCREASING  
CONVECTIVE COVERAGE. THIS WILL ALLOW WARM-SECTOR RISK TO  
CONTINUE/SPREAD EWD INTO MO THROUGH THE EVENING/OVERNIGHT...WHILE  
ELEVATED STORMS POSING A LARGE HAIL RISK MAY DEVELOP AS FAR N AS  
NEB/IA/SRN MN...AND EWD INTO THE OH VALLEY STATES.  
 
..GOSS.. 04/06/2015

 

post-4544-0-54931500-1428306149_thumb.pn

post-4544-0-98297500-1428306165_thumb.pn

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Northern IL looks pretty interesting for good severe on the new 12z NAM. 

 

Rapidly deepening sfc low backing the sfc low with plenty of instability and almost what looks like a pseudo dryline 

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I love it when a surface low is rapidly deepening in one of these events.  Will keep surface flow nicely backed, with a very nice H5 punch coming in later in the afternoon.  Wind profiles show plenty of stretching, with nicely curved hodos in the lower 2-3km.  12z NAM showing over 3000j/kg cape over IL as well, which is very respectable for early-mid April this far north.  Shear vectors are pointing away from the front, so hopefully that will keep things discrete for several hours.  I think as long as we don't have any major changes to the overall setup, and there isn't too much leftover precip/cloudiness from Wed we should have a very nice setup for IL on Thu.

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I love it when a surface low is rapidly deepening in one of these events.  Will keep surface flow nicely backed, with a very nice H5 punch coming in later in the afternoon.  Wind profiles show plenty of stretching, with nicely curved hodos in the lower 2-3km.  12z NAM showing over 3000j/kg cape over IL as well, which is very respectable for early-mid April this far north.  Shear vectors are pointing away from the front, so hopefully that will keep things discrete for several hours.  I think as long as we don't have any major changes to the overall setup, and there isn't too much leftover precip/cloudiness from Wed we should have a very nice setup for IL on Thu.

 

Always seems to come down to this. Would possibly be somewhat faster storm motions but with the strong upper flow, they would be vented nicely as well. 

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Always seems to come down to this. Would possibly be somewhat faster storm motions but with the strong upper flow, they would be vented nicely as well. 

 

Yeah the 12z NAM would imply some decent classic sup type potential, which would be very nice.  Us IL chasers are used to the fast storm motions, especially this time of year lol.  At least the road network is very good in this state.

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GFS is less aggressive with surface low strengthening, and keeps the surface flow more veered.  I think it has a tendency to over-veer the surface flow though, so not too concerned about that at this point.  It would point more towards closely spaced, quickly congealing supercells that would probably be QLCS in nature after a short time.  Wind damage potential would still be pretty impressive with that H5 jet streak nearly on top of the convection by late afternoon.

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Thursday looks a bit messy perhaps but certainly some decent potential.  We might be able to keep a threat going a while after dark as well especially as a strong/deepening surface low would help keep the low levels mixed.

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With things slowing down for Wednesday to the west, things in our subforum are actually looking a bit up for Thursday compared to previous runs. I like Eastern IA/Northern IL a lot actually on the latest runs.

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Fox Valley sounding looks pretty impressive at 00z Friday, hodo could use a little work, but all-in-all a really nice setup for the Chicago metro going into Thursday evening.

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Fox Valley sounding looks pretty impressive at 00z Friday, hodo could use a little work, but all-in-all a really nice setup for the Chicago metro going into Thursday evening.

Good low level veering on the 18z NAM due to decently backed surface winds from deepening low, but then pretty unidirectional from h8 to h5. Overall, still an ominous look for here with the CAPE low level shear combo. The 18z NAM also portrays the warm front being kept farther south as a lake enhanced boundary in extreme northeast IL, which could make things interesting.

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Agreed. EHIs in the 5s is ominous for anywhere, let alone NE IL in April. A storm riding along the boundary could spell trouble.

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It will be interesting to see what solution wins out for Thursday. The 12z NAM was the most bullish, the 18z run still interesting but lost the backed sfc flow as that will be the key to the tornado threat with as RC said, the more undirectional profile above 850mb or so. It will depend how quickly the sfc low deepens inducing p-falls along with the placement and track of it. 

 

 

Also, think we have a solid shot and some good elevated, possibly severe storms here tomorrow night as plenty of MUCAPE advects northward along with 50kts of shear. 

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Agreed. EHIs in the 5s is ominous for anywhere, let alone NE IL in April. A storm riding along the boundary could spell trouble.

 

Yeah but given the shear vectors and the orientation of the possible lake breeze boundary, the storm would cross it and go elevated into the colder air.

 

IMO lake breeze boundaries are much more interesting for tornado potential in late spring, mainly summer when we get the storm motions out of the W, WNW, or NW. 

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Yeah but given the shear vectors and the orientation of the possible lake breeze boundary, the storm would cross it and go elevated into the colder air.

 

IMO lake breeze boundaries are much more interesting for tornado potential in late spring, mainly summer when we get the storm motions out of the W, WNW, or NW. 

Yeah locally for you guys, but if something comes out of Kankakee area towards SW lower MI there is a better chance it could ride the boundary in the shadow of the lake on this side of Lake Michigan. Of course that is a highly detailed scenario. I do think the warm front itself across MI could have potential as well. Pretty good convergence along that boundary.

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00z NAM back to looking really nice like it did with the 12z.  Very nice vort max in IA over the deepening surface low Thu afternoon.  Verbatim there's no doubt in my mind that a solution like the 00z NAM would yield several tornadoes over IL with this.  Let's hope trends with the NAM continue.

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Best threat on Thursday looks like it may be west of Chicago proper but if the timing speeds up at all, then things would look different.  As is, the western suburbs may be in a higher threat zone.

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Yeah the fcst soundings and hodographs in and around RFD look very impressive

One of the more impressive soundings I've seen locally in my 5 years out here. I'd say this is probably the best looking April setup in the region since 4/10/11, but the surface low will be farther south this time than that one, which ended up being a big event near Green Bay. Gonna probably need a 12z 4/6 and 00z 4/7 NAM-like solution to maximize the severe/tornado potential given the unidirectional flow above 850 mb.

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