Tim from Springfield (IL) Posted April 4, 2015 Share Posted April 4, 2015 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 Link to comment Share on other sites More sharing options...
TimChgo9 Posted April 4, 2015 Share Posted April 4, 2015 My son sent me the info on this. Looks like a setup for some of the subforum. Keeping an eye on this to see what develop. Link to comment Share on other sites More sharing options...
Chargers09 Posted April 5, 2015 Share Posted April 5, 2015 Is this progged to continue east into Friday? Link to comment Share on other sites More sharing options...
JasonOH Posted April 5, 2015 Share Posted April 5, 2015 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. Link to comment Share on other sites More sharing options...
Tim from Springfield (IL) Posted April 5, 2015 Author Share Posted April 5, 2015 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 Link to comment Share on other sites More sharing options...
Tim from Springfield (IL) Posted April 5, 2015 Author Share Posted April 5, 2015 On his FB page, Tom Skilling has linked to WGN's Paul Dailey's article on Wednesday-Thursday. Dailey's thoughts: http://chicagoweathercenter.com/blog/chicago-area-included-in-severe-weather-area-outlook-for-this-coming-thursday Link to comment Share on other sites More sharing options...
snowlover2 Posted April 6, 2015 Share Posted April 6, 2015 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 Link to comment Share on other sites More sharing options...
Gilbertfly Posted April 6, 2015 Share Posted April 6, 2015 12k with 2M temps in the mid 70s into northern IL thursday at 21z...fwiw at this range obv Link to comment Share on other sites More sharing options...
A-L-E-K Posted April 6, 2015 Share Posted April 6, 2015 non-event for mby Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 6, 2015 Share Posted April 6, 2015 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 Link to comment Share on other sites More sharing options...
cyclone77 Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
cyclone77 Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
cyclone77 Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
cyclone77 Posted April 6, 2015 Share Posted April 6, 2015 12z GEM is a little slower, and would keep the highest threat over the eastern half of Iowa. Link to comment Share on other sites More sharing options...
Hoosier Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
huronicane Posted April 6, 2015 Share Posted April 6, 2015 Link to comment Share on other sites More sharing options...
Stebo Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
huronicane Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
RCNYILWX Posted April 6, 2015 Share Posted April 6, 2015 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. Link to comment Share on other sites More sharing options...
huronicane Posted April 6, 2015 Share Posted April 6, 2015 Agreed. EHIs in the 5s is ominous for anywhere, let alone NE IL in April. A storm riding along the boundary could spell trouble. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
Indystorm Posted April 7, 2015 Share Posted April 7, 2015 I've waited many months for Gil Sebenste of NIU in DeKalb IL to say the things he does in his blog concerning the Midwest this Monday. http://weather.admin.niu.edu/forecast.txt Link to comment Share on other sites More sharing options...
Stebo Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
cyclone77 Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
cyclone77 Posted April 7, 2015 Share Posted April 7, 2015 925mb theta-e. Very impressive to say the least. This is of course conditional based on what happens with Wednesday/Wednesday night's Plains leftovers. Hopefully it doesn't muddle things up too much for Thu. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted April 7, 2015 Share Posted April 7, 2015 Yeah the fcst soundings and hodographs in and around RFD look very impressive Link to comment Share on other sites More sharing options...
Hoosier Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
RCNYILWX Posted April 7, 2015 Share Posted April 7, 2015 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. Link to comment Share on other sites More sharing options...
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