000
FXUS63 KLOT 072251
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
551 PM CDT SUN SEP 7 2008
.DISCUSSION...
251 PM CDT
LITTLE OR NO CHG TO GOING FCST THRU TONIGHT. DIURNAL CU FIELD
SHOULD DISSIPATE ERLY THIS EVENING AHD OF CLOUD BAND ASSD WITH
FRONT NOW MOVG INTO UPR MS VLY. FOCUS OF CONCERN THIS FCST
ISSUANCE IS WITH UPCOMING RAIN EVENT MONDAY INTO MONDAY NIGHT.
CURRENT WATER VAPOR IMAGERY SHOWS SHORT WAVE OVR WRN ONTARIO
LIFTING ENEWD. THIS WILL CONTINUE TO PUSH FRONT SEWD ACROSS UPR
GRTLKS...AND ACROSS FA MONDAY MRNG. MEANWHILE...OF GREATER
IMPORTANCE...IS ANOTHER JET MAX INDICATED IN WATER VAPOR IMAGERY
EMERGING EWD FROM SRN MT/NRN WY. THIS FEATURE IS FCST TO AMPLIFY
AS IT HEADS EWD TNGT...CAUSING LLVL FLOW TO BACK AND INCR
OVERNIGHT...WITH DEEPER LLVL MOISTURE FROM OZARKS...SWD STARTING
TO ADVECT NWD INTO MO VLY BY 12Z MON. AS SFC WAVE MOVES ENEWD ALG
FRONTAL BOUNDARY...FRONTOGENETIC FORCING TO INCR OVR
FA...PARTICULARLY OVR NCNTRL AND EXTRM NERN IL...WITH STG MOISTURE
CONVERGENCE OVERRIDING THIS BOUNDARY DURG AFTN AND EVENING. AS A
RESULT...WILL GO WITH CATEGORICAL POPS RFD-CHI AREAS. FCST
SOUNDINGS SHOW LTL OR NO INSTABILITY...BUT GIVEN INCR IN LLVL FLOW
INTO FRONTAL ZONE...WILL AT LEAST MENTION SO ISOL THUNDER OVR
SRN/ERN PORTIONS OF FA WHERE THERE MAY BE ENUF LIMITED SUNSHINE TO
ALLOW SFC TEMPS TO RISE TO ARND 80. AS SHRT WAVE CONTINUES TO
AMPLIFY AND BCM NEG TILTED AS IT PASSES ACROSS WRN GRTLKS ON
MON...DECENT PRESSURE COUPLET EXPECTED TO DVLP THAT WILL BRING A
PERIOD OF RAPID SFC PRESSURE RISES ACROSS AREA MON NGT ALONG WITH
RATHER BREEZY CONDITIONS AND DRYING BY TUESDAY MRNG. BUILDING SFC
HI PRESSURE THEN DOMINATES OUR WX TUES AFTN-WED WITH CLRG SKIES
AND COOL...ALMOST FALL LIKE CONDITIONS.
A LTL LESS CONFIDENCE IN THU-SUN FCST. ANOTHER COLD FRONT WILL BE
MOVING EWD INTO UPR MS VLY ON THURSDAY...BRINGING AT LEAST A CHC
OF SOME SHWRS. THIS IS FOLLOWED BY SOME CLRG FRI-FRI NIGHT BEFORE
MID LVL RIDGING DVLPS FROM OZARKS SEWD ACROSS SERN U.S. AS THIS
RIDGING DVLPS...LLVL FLOW SHOULD BACK AND ALLOW MORE TRPCL AIR
MASS TO DVLP NWD ACROSS MIDWEST...THUS INCRSG PCPN CHCS OVR NXT
WEEKEND. COMBINATION OF SOME MODEL INCONSISTENCY...AND POTL
INTERACTION WITH HURCN IKE...FCST BY GFS/EUROPEAN TO BE APCHG TX
COAST AS A MAJOR HURCN ON SAT...MAKE EXTENDED FCST A BIT
PROBLEMATIC.
MERZLOCK
&&
.AVIATION...
0000 UTC TAFS...VFR CONDITIONS AND GENERALLY GOOD FLYING WEATHER
TONIGHT WILL GIVE WAY TO DETERIORATING CONDITIONS MONDAY. MID-
LEVEL DECK OVER IA WILL OVERSPREAD TERMINALS TONIGHT WITH BKN-OVC
VFR DECK LIKELY MUCH OF TONIGHT. CLOUD BASES WILL BEGIN TO LOWER
WITH RAIN SPREADING EASTWARD ACROSS N IL MONDAY MORNING. RAIN WILL
INITIALLY BE LIGHT WITH CIGS/VSBY LIKELY TO STAY VFR. WITH TIME
RAIN WILL INCREASE IN INTENSITY DURING THE AFTERNOON WITH FALLING
CIGS/VSBY LIKELY. HAVE BROUGHT FLIGHT CATS DOWN TO LOWER END MVFR
FOR NOW...BUT IFR CONDITIONS CERTAINLY PLAUSIBLE BY THE END OF
THIS TAF PERIOD.
IZZI
&&
.MARINE...
200 PM...MONDAY AFTERNOON THROUGH TUESDAY MORNING REMAINS THE TIME
PERIOD OF CONCERN WITH THIS FORECAST. IN THE SHORT TERM HOWEVER...
WEAK LOW PRESSURE OVER NORTHERN ONTARIO WILL MOVE EAST ACROSS
NORTHERN QUEBEC TONIGHT AND MONDAY. A TROUGH OF LOW PRESSURE WILL
MOVE ACROSS THE WESTERN LAKES AND LAKE MICHIGAN OVERNIGHT. AHEAD
OF THIS TROUGH...WEST/SOUTHWEST WINDS WILL CONTINUE AND THE
GRADIENT WILL LIKELY TIGHTEN SOME ON THE NORTH END...THUS 15-25KTS
LOOKS REASONABLE. WINDS THEN TURN NORTHWEST AND DIMINISH MONDAY
MORNING AS A WEAK RIDGE OF HIGH PRESSURE BUILDS ACROSS THE UPPER
LAKES BY MONDAY AFTERNOON.
THE TROUGH STALLS ACROSS SOUTHERN LAKE MICHIGAN AND NORTHERN IL
BY MONDAY AFTERNOON. NEW LOW PRESSURE DEVELOPS OVER THE PLAINS
TONIGHT THEN LIFTS NORTHEAST ALONG THIS TROUGH/BOUNDARY MONDAY
AFTERNOON/EVENING. THE EXTENT TO WHICH THIS LOW DEEPENS IS STILL
UNCERTAIN...THOUGH LATEST MODEL TRENDS DO NOT DEEPEN IT AS MUCH AS
THEY DID 24 HRS AGO. HOWEVER...WITH THE LOW PASSING NEAR OR JUST
SOUTH OF SOUTHERN LAKE MICHIGAN...ALONG WITH HIGH PRESSURE OVER
THE PLAINS BUILDING INTO THE WESTERN LAKES TUESDAY...EXPECT
GRADIENT TO STILL SUPPORT 30KTS...PERHAPS FOR A SHORTER TIME
PERIOD...OVER SOUTHERN LAKE MICHIGAN MONDAY NIGHT. SHOULD THIS
LOW DEEPEN MORE THAN EXPECTED...THEN A SHORT PERIOD OF GALES IS
POSSIBLE. LIKEWISE...IF LITTLE DEEPEN OCCURS OR IT DEEPENS FURTHER
EAST...WINDS SPEEDS MAY END UP BEING LOWER THAN CURRENTLY
EXPECTED. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
