October 25 Severe Threat?

[Tim from Springfield (IL)]

SPC Day 4-8 is mentioning the potential for "strong/perhaps severe" thunderstorms in the Midwest on Tuesday (Oct. 25)--one day short of the one-year anniversary of the Octobomb.

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

ZCZC SPCSWOD48 ALL ACUS48 KWNS 220843 SPC AC 220843 DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0343 AM CDT SAT OCT 22 2011 VALID 251200Z - 301200Z ...DISCUSSION... PER 00Z ECMWF/GEFS GUIDANCE...AN INITIALLY LOW AMPLITUDE/PROGRESSIVE UPPER FLOW REGIME IS EXPECTED TO YIELD TO A CONSIDERABLE LARGE SCALE PATTERN AMPLIFICATION MID-LATE WEEK AS HIGHLIGHTED BY AN EASTERN STATES LONGWAVE TROUGH. ON DAY 4/TUESDAY...WITH THE CENTRAL CONUS INCREASINGLY COMING UNDER THE INFLUENCE OF CYCLONIC FLOW ALOFT...A WARM/RELATIVELY MOIST AIRMASS IS EXPECTED TO ADVECT NORTHEASTWARD INTO THE MIDWEST/MS VALLEY VICINITY AHEAD OF A POSITIVE-TILT/LOW AMPLITUDE SHORTWAVE TROUGH AND ASSOCIATED COLD FRONT. WHILE MODEST MOISTURE CONTENT/WARM SECTOR CAPPING WILL LIKELY BE LIMITATIONS...SOME STRONG/PERHAPS SEVERE TSTMS COULD OCCUR ACROSS THE MIDWEST NEAR/AHEAD OF THE ADVANCING SURFACE LOW/COLD FRONT ON TUESDAY. WHILE LITTLE SEVERE RISK IS CURRENTLY EXPECTED DAY 5/WEDNESDAY...THERE IS SOME CONCERN THAT A SEVERE THREAT COULD MATERIALIZE ACROSS THE SOUTHEAST STATES ON DAY 6/THURSDAY INTO DAY 7/FRIDAY...POTENTIALLY INCLUDING A CORRIDOR FROM FL TO THE CAROLINAS. THIS WOULD BE AS THE EASTERN STATES UPPER TROUGH AMPLIFIES AND MOISTURE IS DRAWN NORTH/NORTHEASTWARD AHEAD OF AN ADVANCING COLD FRONT. HOWEVER...NUMERICAL GUIDANCE VARIABILITY/LIMITED PREDICTABILITY AT THIS JUNCTURE PRECLUDE A 30 PERCENT EQUIVALENT SEVERE RISK AREA. ..GUYER.. 10/22/2011

[andyhb]

Eh, not too sure on this one, not exactly convinced it deserves a svr thread this far out.

[Tim from Springfield (IL)]

SPC Mesoscale Discussion #2272 (but watch unlikely) for much of western/central Illinois--possible hail involved with scattered storms developing in western/north central Illinois (roughly along a Quincy/Chicago line):

http://www.spc.noaa..../md/md2272.html

MESOSCALE DISCUSSION 2272 NWS STORM PREDICTION CENTER NORMAN OK 0656 PM CDT TUE OCT 25 2011 AREAS AFFECTED...PORTIONS NERN MO...EXTREME SERN IA...WRN/NRN IL. CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY VALID 252356Z - 260230Z TSTMS ARE DEVELOPING OVER WRN PORTIONS DISCUSSION AREA AND WILL MOVE EWD WITH INCREASING COVERAGE THROUGH 02Z. 3-4 HOUR WINDOW APPEARS MOST PROBABLE FOR THREAT OF OCNL/ISOLATED SVR HAIL BEGINNING SHORTLY AFTER 00Z. 23Z SFC MESOANALYSIS SHOWS FRONTAL-WAVE LOW OVER NERN IA...FCST TO MOVE EWD OVER IL/WI BORDER REGION THROUGH REMAINDER EVENING...WHILE TRAILING SFC COLD FRONT MOVES SEWD ACROSS SERN IA AND N-CENTRAL MO. PRE COLD-FRONTAL CONFLUENCE LINE WAS DRAWN FROM WARM-FRONTAL INTERSECTION NEAR RFD SWWD ACROSS QUAD CITIES AREA THEN CURVING SWD ACROSS CLARK COUNTY MO TO NEAR COU. THIS BOUNDARY SHOULD CONTINUE TO REPRESENT WRN BOUND OF MOST DEVELOPMENT POTENTIAL...WITH CONVERGENCE REINFORCED ONCE FRONT CATCHES CONFLUENCE LINE DURING 02Z-04Z PERIOD. MOISTURE CHANNEL IMAGERY INDICATES SUBTLE SHORTWAVE TROUGH...EMBEDDED IN ZONAL FLOW OVER WRN IA...THAT SHOULD CONTRIBUTE TO ASCENT/LAPSE RATES ALOFT. MODIFIED FCST SOUNDINGS SUGGEST LOW-LEVEL WAA AND MOIST ADVECTION...NEAR STRENGTHENING LLJ...SHOULD MAINTAIN SUFFICIENT LOW-LEVEL THETAE TO SUPPORT 500-1000 J/KG MLCAPE THROUGH ABOUT 03Z. 40-50 KT EFFECTIVE SHEAR MAGNITUDES WILL AID FURTHER IN ORGANIZATION OF CONVECTION. AFTER ABOUT 03Z...HAIL POTENTIAL WILL LEVEL OFF THEN SLOWLY DIMINISH. DIABATIC SFC COOLING SHOULD STRENGTHEN MLCINH WITH INFLOW-LAYER PARCELS BECOMING MORE ELEVATED. MEANWHILE MUCH OF CONVECTION MAY OUTRUN RELATIVELY NARROW CORRIDOR WHERE PARCELS NOW ARE SFC-BASED...AS LLJ VEERS. ..EDWARDS.. 10/25/2011

[andyhb]