Issued by NWS Chicago, IL
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000
FXUS63 KLOT 130824
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
324 AM CDT WED MAY 13 2009
.DISCUSSION...
856 PM CDT
MINOR UPDATE TO GRIDS/FORECAST TO BRING IN PRECIP A LITTLE FASTER
ACROSS WESTERN IL COUNTIES LATE THIS EVENING...AND TO INCREASE
CLOUD COVER ALL AREAS.
ANALYSIS OF 00Z RAOB DATA...ALONG WITH PROFILER AND WATER VAPOR...
INDICATES MID LEVEL SHORT WAVE TROUGH CURRENTLY PROPAGATING
EASTWARD ACROSS IOWA AND MISSOURI. LARGE AREA OF RAIN AND EMBEDDED
THUNDERSTORMS ACROSS EASTERN IOWA PER REGIONAL MOSAIC OF
88DS...ABOUT TO CROSS RIVER INTO IL. TIMING OF OF LEADING EDGE OF
REFLECTIVITY INDICATES RAIN WILL LIKELY MOVE INTO WESTERN IL
COUNTIES OF CWA SHORTLY...THUS HAVE INCREASED POPS ACROSS THESE
AREAS FOR LATE EVENING HOURS. CG LIGHTNING NETWORK HAS DEPICTED
DECREASING AMOUNT OF LIGHTNING WITH THIS PRECIP LAST COUPLE OF
HOURS...WITH SPC RUC MESOANALYSIS DATA INDICATING RATHER POOR MID
LEVEL LAPSE RATES OF AROUND 5.5 DEG/KM IN 700-500 MB LAYER THUS
WILL LIKELY ONLY SEE ISOLATED/EMBEDDED THUNDER EARLY ON. SHORT
TERM PROGS CONTINUE TO DEPICT 40-50 KNOT LOW LEVEL JET VEERING
INTO IL LATER TONIGHT...09-12Z PERIOD...WITH RELATIVELY STRONG
MOISTURE CONVERGENCE AROUND 850 MB LEVEL INDICATING BETTER FORCING
FOR MORE WIDESPREAD THUNDER DURING PRE-DAWN HOURS OF WEDNESDAY
MORNING. ANY SEVERE POTENTIAL FOR EARLY WEDNESDAY EXPECTED TO BE
IN FORM OF ELEVATED STORMS WITH HAIL.
LITTLE AVAILABLE IN TERMS OF NEW GUIDANCE FOR CONVECTIVE TRENDS
WEDNESDAY SO NO CHANGES BEYOND THE OVERNIGHT FOR NOW.
RATZER
&&
.AVIATION...
0600 UTC TAFS...WILL KEEP THE ONGOING FORECAST IN THE TAFS FOR
NOW. THE RADAR AND SURFACE OBSERVATIONS SHOWS THE RAIN IS LIGHT
AND VISIBILITY IS ABOVE 5 MILES. LIGHTING PLOTS SHOW MOST OF THE
LIGHTNING IS WELL SOUTH OF THE TAFS AREA. WILL ISSUE AN AMENDMENT
FOR THE TAFS CONCERNING THE THUNDERSTORMS FOR LATER THIS AFTERNOON
AND EVENING WHEN THE NEW LOCAL WRF IS COMPLETE AND OTHER MODEL
INFORMATION IS AVAILABLE. AFTER 14 UTC WE STILL EXPECT DRY
WEATHER. THE EARLIER GFS MODEL HAS BEEN VERY GOOD WITH THE WARM
AIR ADVECTION AND WARM FRONTAL TYPE PRECIPITATION.
&&
.MARINE...
320 AM CDT
A STRONG LOW WITH A PRESSURE OVER SOUTHERN MANITOBA WILL MOVE
NORTHEAST TO NORTHERN ONTARIO BY THURSDAY MORNING. THIS LOW WILL
DRAG A FRONT INTO MICHIGAN AND INDIANA BY MIDNIGHT THURSDAY
MORNING. A LARGE HIGH WILL MOVE INTO MISSOURI BY THURSDAY
AFTERNOON. THE COOL WATER HAS SET UP AN INVERSION WHICH PREVENTS
STRONG WIND SPEED ALOFT TO REACH THE LAKE SURFACE. BECAUSE OF THE
INVERSION WE DO NOT EXPECT GALES OR HIGHER WIND SPEEDS AT THIS
TIME. WILL KEEP THE SMALL CRAFT ADVISORY IN EFFECT THROUGH
THURSDAY MORNING.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...7 AM WEDNESDAY TO 7 AM THURSDAY.
&&
$$
