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May 20-21 Severe Threat


IWXwx

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NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL

832 PM CDT TUE MAY 20 2014

.MESOSCALE DISCUSSION...

830 PM CDT

ONE LARGE HP SUPERCELL CONTINUES TO MOVE EAST-SOUTHEAST ACROSS FAR

NORTHERN WILL AND INTO CENTRAL/SOUTHERN COOK COUNTY AT 820 PM CDT.

RADAR SHOWS A STRONG BUT BROAD CIRCULATION WITH AN IMPRESSIVE WIND

MAX ON THE LOWEST SCANS. LOOP OF MDW TDWR SHOWS MULTIPLE

OCCLUSIONS OF THE RFD WHILE MESO NET SITES SHOW THAT THE OUTFLOW

IS RATHER COOL WHICH COMBINED WITH THE BROAD CIRCULATION SUPPORTS

A LOW BUT NOT NECESSARILY ZERO TORNADO THREAT. THIS LOW THREAT

WILL TRANSLATE DOWNSTREAM ACROSS SOUTHERN COOK COUNTY IN THE NEAR

TERM...WITH LAKE COUNTY INDIANA CERTAINLY IN THE THREAT AREA

DEPENDING ON EVOLUTION ACROSS COOK. DAMAGING STRAIGHT LINE WINDS

AND LARGE HAIL ARE STILL THE MAIN THREAT.

OTHERWISE MOIST MID LEVEL WAA CONTINUES TO STREAM NORTHEASTWARD

INTO THE FORECAST AREA WHICH WILL LIKELY RESULT IN AT LEAST CONTINUED

SCATTERED CONVECTIVE DEVELOPMENT ACROSS NORTHEAST IL...WHILE THE

BIGGER SUPERCELL AND ANY ASSOCIATED NEW DEVELOPMENT TRACK INTO

NORTHWEST INDIANA. BEYOND THAT THE SYNOPTIC BOUNDARY REMAINS

STRETCHED ACROSS CENTRAL IOWA WITH SEVERAL OTHER SUPERCELLS LINED

UP ALONG IT. TRAJECTORY OF THESE WOULD TAKE THEM INTO THE NORTHERN

CWA WITH THE NEAREST CELL NEARING LEE/OGLE COUNTY. EARLIER STORMS

ALONG THE SAME TRACK MANAGED TO WEAKEN AS THEY MOVED EAST THANKS

TO WORKED OVER AIR SO THIS MAY BE THE TREND. SEVERAL ADDITIONAL

WAVES OF CONVECTION ARE POSSIBLE INTO THE OVERNIGHT HOURS AS WHAT

APPEARS TO BE A MID LEVEL WAVE ACROSS CENTRAL IOWA TRACKS

EASTWARD.

MDB

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New severe thunderstorm watch for NW OH, Nrn IN, and SE lower MI until 5am. Watch says Moderate pops across the board for wind and hail (including 65kt gusts and 2+ Inch hail). Interested to see if these storms can make it all the way into OH while still being severe.

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 163

NWS STORM PREDICTION CENTER NORMAN OK

945 PM EDT TUE MAY 20 2014

THE NWS STORM PREDICTION CENTER HAS ISSUED A

* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

NORTHERN INDIANA

SOUTHERN LOWER MICHIGAN

NORTHWESTERN OHIO

LAKE MICHIGAN

* EFFECTIVE THIS TUESDAY NIGHT AND WEDNESDAY MORNING FROM 945 PM

UNTIL 500 AM EDT.

* PRIMARY THREATS INCLUDE...

SCATTERED DAMAGING WINDS AND ISOLATED SIGNIFICANT GUSTS TO 75

MPH POSSIBLE

ISOLATED VERY LARGE HAIL EVENTS TO 2.5 INCHES IN DIAMETER

POSSIBLE

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES EITHER SIDE OF A LINE FROM 20 MILES WEST OF SOUTH

BEND INDIANA TO 60 MILES EAST NORTHEAST OF FORT WAYNE INDIANA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU3).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 160...WW 161...WW 162...

DISCUSSION...PRIMARY COMPLEX OF SVR TSTMS INITIALLY OVER CHICAGO

METRO AREA IS EXPECTED TO MOVE EWD TO ESEWD OUT OF WW 161 AND ACROSS

NEW WW THROUGH REMAINDER EVENING. SOME UPSCALE COLD-POOL GROWTH AND

RESULTANT ENHANCEMENT TO WIND-DAMAGE POTENTIAL IS POSSIBLE...IN

ADDITION TO LARGE-HAIL THREAT ALREADY REALIZED DURING PAST COUPLE

HOURS. REF MESOSCALE DISCUSSION 628 FOR MORE INITIAL DETAILS. SVR

HAIL AND STG/DAMAGING GUSTS ALSO ARE POSSIBLE WITH ANY CONVECTION

THAT SURVIVES ITS TREK OVER SRN-LM STABLE LAYER.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 65

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 28035.

...EDWARDS

 

post-4544-0-22717200-1400637830_thumb.gi

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00z NAM and RAP actually look somewhat encouraging for tomorrow, even if we miss out on tonight's activity.
 

It tracks the MCS tonight far enough south to allow for some clearing in its wake by sunrise and the air to rapidly destabilize (2000-3000 J/KG) before the cold front passage. 

 

That instability holds right through 21z - 00z too...

 
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