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Severe weather potential July 18-20


RyanDe680

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MCD 1464...

MESOSCALE DISCUSSION 1464

NWS STORM PREDICTION CENTER NORMAN OK

1231 PM CDT SAT JUL 18 2015

AREAS AFFECTED...EASTERN IOWA...NORTHERN ILLINOIS...AND SOUTHERN

WISCONSIN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 181731Z - 181930Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP/INTENSIFY THIS

AFTERNOON. VERY LARGE HAIL AND DAMAGING THUNDERSTORM WIND GUSTS WILL

BE THE MAIN THREATS...BUT ONE OR TWO TORNADOES CANNOT BE RULED OUT.

DISCUSSION...THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE NEXT

SEVERAL HOURS AS ASCENT ASSOCIATED WITH A MID-LEVEL VORTICITY

MAXIMUM /CURRENTLY ACROSS NORTH-CENTRAL IOWA/ OVERSPREADS THE AREA.

INITIAL THUNDERSTORMS SHOULD DEVELOP ALONG OR SOUTH OF A DECAYING

OUTFLOW BOUNDARY LEFT OVER FROM OVERNIGHT CONVECTION...WHERE THE

ATMOSPHERE HAS BECOME MODERATELY UNSTABLE AND IS WEAKLY CAPPED.

EFFECTIVE DEEP-LAYER SHEAR IS SUFFICIENT FOR ORGANIZED MULTI-CELL

CLUSTERS AND/OR SUPERCELLS...ALTHOUGH THE LACK OF WIDESPREAD

CONVECTIVE INHIBITION SUGGESTS THUNDERSTORMS SHOULD EVENTUALLY GROW

UPSCALE. THUNDERSTORMS SOUTH OF THE OUTFLOW BOUNDARY WILL HAVE THE

POTENTIAL TO PRODUCE LARGE HAIL AND DAMAGING THUNDERSTORM

WINDS...AND A TORNADO OR TWO CANNOT BE RULED OUT...ESPECIALLY IN THE

VICINITY OF THE REMNANT OUTFLOW BOUNDARY AND/OR LAKE BREEZE...WHERE

LOW-LEVEL VORTICITY MAY BE LOCALLY AUGMENTED. NORTH OF THE OUTFLOW

BOUNDARY...THUNDERSTORMS MAY EXHIBIT CHARACTERISTICS OF ELEVATED

CONVECTION OWING TO THE WORKED-OVER AIRMASS. HERE...THE MAIN THREAT

SHOULD BE LARGE HAIL...ALTHOUGH GIVEN THE STRONGER DEEP-LAYER SHEAR

AND LOWER CLOUD BASES...ISOLATED DAMAGING WIND GUSTS AND A TORNADO

OR TWO WILL BE POSSIBLE.

ONE COMPLICATING FACTOR WILL BE THE EVOLUTION OF THE CLOUD SHIELD

DEVELOPING ACROSS NORTHERN MISSOURI AND NORTHWESTERN ILLINOIS.

SHOULD THIS DEVELOP FARTHER NORTHWARD...OVERSPREADING NORTHERN

ILLINOIS AND SOUTHERN WISCONSIN...THUNDERSTORM DEVELOPMENT MAY END

UP BEING MORE ISOLATED IN NATURE...DELAYING POTENTIAL UPSCALE

GROWTH.

..MARSH/CORFIDI.. 07/18/2015

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FWIW we might want to consider adding Monday (July 20) to this thread--this morning's D3 outlook had a boomerang-shaped slight risk area which includes SE MN, NW and western IA, eastern NE, northeastern Kansas, most of MO, and the southern half of IL.

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

SPC AC 180739   DAY 3 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0239 AM CDT SAT JUL 18 2015   VALID 201200Z - 211200Z   [ . . . ]   ...SRN MN/ERN NEB/IA/ERN KS AND MO TO LOWER OH VALLEY...   STRONGER INSTABILITY IS EXPECTED TO RESIDE ALONG THE   QUASI-STATIONARY BOUNDARY ON MONDAY...THAN WITH POLEWARD EXTENT INTO   SOUTHERN MN WHERE SOME MOISTURE RETURN WILL CONTRIBUTE TO AT LEAST   MODERATE INSTABILITY FROM ERN NEB TO SRN MN.  MODERATELY STRONG   WNWLY 500-MB WINDS ACCOMPANYING THE TRANSIENT MIDLEVEL IMPULSES WILL   SUPPORT STRENGTHENING EFFECTIVE BULK SHEAR FOR AN ORGANIZED   SEVERE-WEATHER THREAT.     TSTMS AND/OR CLUSTERS OF STORMS SHOULD BE ONGOING ACROSS PARTS OF   THE MID MO VALLEY...CENTRAL PLAINS AND LOWER MO VALLEY AT 12Z   MONDAY.  NEW STORM DEVELOPMENT IS FORECAST ALONG THE SEWD-MOVING   FRONT INTO SRN MN TO ERN NEB MONDAY AFTERNOON...WHILE STORMS SHOULD   DEVELOP ALONG THE SRN PERIPHERY OF THE ONGOING   STORMS/CLOUDINESS/DIFFERENTIAL HEATING BOUNDARY IN NERN KS AND NRN   MO TO CENTRAL IL.  AFOREMENTIONED INSTABILITY AND BULK SHEAR WILL   SUPPORT STRONG TO SEVERE STORMS.     STORMS SHOULD DIMINISH IN INTENSITY ACROSS THE UPPER MS VALLEY   MONDAY NIGHT DUE TO WEAKENING INSTABILITY....WHILE FARTHER TO THE   SOUTH...A FORWARD PROPAGATING MCS WILL BE POSSIBLE THROUGH THE MID   MS VALLEY TO LOWER OH VALLEY MONDAY NIGHT.  THIS LATTER AREA COULD   HAVE A DAMAGING-WIND THREAT THROUGH MONDAY EVENING TO PART OF THE   OVERNIGHT PERIOD.   ..PETERS.. 07/18/2015
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MCD 1464...

MESOSCALE DISCUSSION 1464

NWS STORM PREDICTION CENTER NORMAN OK

1231 PM CDT SAT JUL 18 2015

AREAS AFFECTED...EASTERN IOWA...NORTHERN ILLINOIS...AND SOUTHERN

WISCONSIN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 181731Z - 181930Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP/INTENSIFY THIS

AFTERNOON. VERY LARGE HAIL AND DAMAGING THUNDERSTORM WIND GUSTS WILL

BE THE MAIN THREATS...BUT ONE OR TWO TORNADOES CANNOT BE RULED OUT.

DISCUSSION...THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE NEXT

SEVERAL HOURS AS ASCENT ASSOCIATED WITH A MID-LEVEL VORTICITY

MAXIMUM /CURRENTLY ACROSS NORTH-CENTRAL IOWA/ OVERSPREADS THE AREA.

INITIAL THUNDERSTORMS SHOULD DEVELOP ALONG OR SOUTH OF A DECAYING

OUTFLOW BOUNDARY LEFT OVER FROM OVERNIGHT CONVECTION...WHERE THE

ATMOSPHERE HAS BECOME MODERATELY UNSTABLE AND IS WEAKLY CAPPED.

EFFECTIVE DEEP-LAYER SHEAR IS SUFFICIENT FOR ORGANIZED MULTI-CELL

CLUSTERS AND/OR SUPERCELLS...ALTHOUGH THE LACK OF WIDESPREAD

CONVECTIVE INHIBITION SUGGESTS THUNDERSTORMS SHOULD EVENTUALLY GROW

UPSCALE. THUNDERSTORMS SOUTH OF THE OUTFLOW BOUNDARY WILL HAVE THE

POTENTIAL TO PRODUCE LARGE HAIL AND DAMAGING THUNDERSTORM

WINDS...AND A TORNADO OR TWO CANNOT BE RULED OUT...ESPECIALLY IN THE

VICINITY OF THE REMNANT OUTFLOW BOUNDARY AND/OR LAKE BREEZE...WHERE

LOW-LEVEL VORTICITY MAY BE LOCALLY AUGMENTED. NORTH OF THE OUTFLOW

BOUNDARY...THUNDERSTORMS MAY EXHIBIT CHARACTERISTICS OF ELEVATED

CONVECTION OWING TO THE WORKED-OVER AIRMASS. HERE...THE MAIN THREAT

SHOULD BE LARGE HAIL...ALTHOUGH GIVEN THE STRONGER DEEP-LAYER SHEAR

AND LOWER CLOUD BASES...ISOLATED DAMAGING WIND GUSTS AND A TORNADO

OR TWO WILL BE POSSIBLE.

ONE COMPLICATING FACTOR WILL BE THE EVOLUTION OF THE CLOUD SHIELD

DEVELOPING ACROSS NORTHERN MISSOURI AND NORTHWESTERN ILLINOIS.

SHOULD THIS DEVELOP FARTHER NORTHWARD...OVERSPREADING NORTHERN

ILLINOIS AND SOUTHERN WISCONSIN...THUNDERSTORM DEVELOPMENT MAY END

UP BEING MORE ISOLATED IN NATURE...DELAYING POTENTIAL UPSCALE

GROWTH.

..MARSH/CORFIDI.. 07/18/2015

MCD 1463 was issued 5 minutes before the above quoted #1464--watch also possible for parts of N IN, NW OH, and extreme SE Lower MI:

http://www.spc.noaa.gov/products/md/md1463.html

 

 MESOSCALE DISCUSSION 1463   NWS STORM PREDICTION CENTER NORMAN OK   1226 PM CDT SAT JUL 18 2015   AREAS AFFECTED...FAR SERN LOWER MI/NRN AND ERN INDIANA/PARTS OF WRN   OH   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE    VALID 181726Z - 181930Z   PROBABILITY OF WATCH ISSUANCE...40 PERCENT   SUMMARY...SOME INCREASE IN CONVECTION CONTINUES ACROSS THE NERN   INDIANA VICINITY ON THE SRN FRINGE OF AN ONGOING LOWER MI MCS.  WW   MAY BE REQUIRED AS SEVERE RISK GRADUALLY INCREASES THIS AFTERNOON.   DISCUSSION...LATEST SURFACE AND OBJECTIVE ANALYSES REVEAL A VERY   MOIST BOUNDARY LAYER ACROSS THE IN/WRN OH VICINITY ATTM...S AND SE   OF AN OUTFLOW BOUNDARY ASSOCIATED WITH AN MCS MOVING EWD ACROSS   LOWER MI TOWARD/INTO ONTARIO ATTM.  PERSISTENT HEATING OF THE MOIST   BOUNDARY LAYER CONTINUES GIVEN PARTLY CLOUDY CONDITIONS PER VIS   IMAGERY...WITH MIXED-LAYER CAPE NOW EXCEEDING 2000 J/KG ACROSS ALL   OF THE DISCUSSION AREA.     IN CONJUNCTION WITH THE DIURNAL HEATING/DESTABILIZATION...A GRADUAL   UPTICK IN CONVECTIVE INTENSITY HAS BEEN NOTED ACROSS NERN INDIANA   OVER THE PAST HOUR OR SO...JUST TO THE COOL SIDE OF THE LEADING EDGE   OF OUTFLOW.  CONTINUED HEATING WILL LIKELY SUPPORT FURTHER INCREASES   IN STORM COVERAGE/INTENSITY...WITH SSWLY INFLOW AND THE MAIN   INSTABILITY AXIS S OF THE CONVECTION FAVORING UPDRAFT FORMATION TO   THE SW OF ONGOING STORMS -- AND THUS OVERALL SEWD/SSEWD PROPAGATION   OF CONVECTION.  MODERATE BACKGROUND WLYS ALOFT SHOULD SUPPORT AT   LEAST MULTICELL ORGANIZATION -- WITH STRONGER UPDRAFTS CAPABLE OF   YIELDING RISK FOR WIND/HAIL.  WE WILL CONTINUE TO MONITOR CONVECTIVE   EVOLUTION ACROSS THIS AREA...WITH WW ISSUANCE POSSIBLY BECOMING   NECESSARY IN THE NEXT 1-2 HOURS.   ..GOSS/CORFIDI.. 07/18/2015   ATTN...WFO...CLE...ILN...DTX...IWX...IND...
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A fairly notable shift on the Day 2 outlook (not unexpected)...

 

day2otlk_1730.gif?1437243458866

 

day2probotlk_1730_any.gif?1437243578154

 

SPC AC 181726

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1226 PM CDT SAT JUL 18 2015

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OH VALLEY INTO WRN NEW
ENGLAND...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE MID MS VALLEY INTO
THE CNTRL HIGH PLAINS...

...SUMMARY...
SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED SUNDAY ACROSS THE OHIO
VALLEY INTO WESTERN NEW ENGLAND. DAMAGING WINDS ARE EXPECTED WITH
THIS ACTIVITY. ISOLATED STRONG STORMS...CAPABLE OF PRODUCING
LOCALLY STRONG WINDS AND HAIL...SHOULD DEVELOP FROM THE MID
MISSISSIPPI VALLEY INTO THE CENTRAL HIGH PLAINS.

...OH VALLEY INTO WESTERN NEW ENGLAND...

DIFLUENT HIGH-LEVEL FLOW WILL SPREAD ACROSS THE GREAT LAKES INTO THE
NERN U.S. AHEAD OF PROGRESSIVE SPEED MAX THAT WILL TRANSLATE THROUGH
THE BASE OF TROUGH AXIS INTO SERN ONTARIO BY EARLY EVENING. THIS
FEATURE WILL PROGRESS ACROSS UPSTATE NY DURING THE LATTER HALF OF
THE PERIOD. LATEST MODEL GUIDANCE IS FAIRLY AGGRESSIVE WITH THIS
FEATURE AND SOMEWHAT FASTER WITH AIR MASS RECOVERY ACROSS THE NERN
U.S. THAN PERHAPS EARLIER DAY2 OUTLOOK REFLECTS. SUBSTANTIAL
DESTABILIZATION IS EXPECTED ACROSS NY...SWWD INTO THE OH VALLEY
AHEAD OF ASSOCIATED COLD FRONT AND THUNDERSTORMS SHOULD READILY
DEVELOP ALONG/AHEAD OF SURGING WIND SHIFT BY MID DAY AS DIABATIC
HEATING IS MAXIMIZED. FORECAST SOUNDINGS...WHILE NOT STRONGLY
SHEARED...ARE MORE THAN ADEQUATE FOR SUSTAINING ORGANIZED UPDRAFTS
THAT COULD OBTAIN CHARACTERISTICS FAVORABLE FOR BOWING LINE SEGMENTS
AND ORGANIZED MULTI-CELL CLUSTERS. GIVEN THE
STRENGTHENING/DEEPENING WLY FLOW ALONG THE INTERNATIONAL BORDER IT
SEEMS WARRANTED TO EXPAND SEVERE PROBS EWD INTO NEW ENGLAND AS
AFTERNOON CONVECTION THAT EVOLVES OVER NY SHOULD PROPAGATE EAST OF
THE HUDSON VALLEY WITH SUFFICIENT INTENSITY TO WARRANT SEVERE PROBS.
HAVE EXPANDED BOTH THE CATEGORY1 AND CATEGORY2 THREATS ACROSS THIS
REGION AND HIGHER PROBS MAY BE NEEDED IN LATER OUTLOOKS TO REFLECT
GREATER STORM COVERAGE WITHIN THIS DESTABILIZED AIR MASS.

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Looks like we got ourselves a ternader watch now for northern IL/southern WI/far eastern IA/far northwest IN.

 

NAM did hint at possibly bringing those storms here later this evening, but that's assuming the atmosphere recovers sufficiently.

 

I'll probably keep a passive eye on them.

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Some new development north of Rockford near border.  Could be interesting as it's close to that leftover OFB.  

 

Also, a trailing line of TCU from near Dubuque back to Cedar Rapids could blow up at any time.  Nice moisture convergence in that area.

 

EDIT:  If I were chasing I'd want to be on that new cell near WI/IL border.  Already looks pretty interesting.

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Some new development north of Rockford near border. Could be interesting as it's close to that leftover OFB.

Also, a trailing line of TCU from near Dubuque back to Cedar Rapids could blow up at any time. Nice moisture convergence in that area.

EDIT: If I was chasing I'd want to be on that new cell near WI/IL border. Already looks pretty interesting.

South of Rockford now too....could get dicey

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