177
FXUS63 KLOT 071831
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1231 PM CST SAT NOV 7 2009
DISCUSSION
152 AM CST
MODELS APPEAR TO HOLD ON TO CONSISTENCY WITH THE SFC TROF ACROSS
THE UPPER MS VLY AND GREAT LAKES REGION FLATTENING OUT AND
EJECTING NE INTO ONTARIO TODAY WHILE DRAPING A WEAK FRONTAL
BOUNDARY DOWN ACROSS NRN IL. THIS FRONT IS LITTLE MORE THAN A WEAK
WIND SHIFT TO THE WEST IN AN OTHERWISE WEAK PRESSURE GRADIENT AND
SUBSEQUENT LIGHTER WIND PATTERN BE ESTABLISHED BY LATE AFTN.
HOWEVER BRISK WINDS THIS EARLY MRNG SHUD KEEP LOW TEMPS UP TO
AROUND 50 IN MOST LOCATIONS...PROVIDING A GOOD START FOR AMPLE
SUNSHINE TO PUSH HIGHS TO AROUND 70 THIS AFTN.
ON A SIDE NOTE...PREVIOUS DISCUSSION WAS CONCERNED ABOUT LOW STRATUS
FORMING OVERNIGHT AND CAUSING A CLOUDY START TO THE MRNG. HOWEVER
MIXING STILL GOING STRONG IN VIGOROUS WIND FIELD AND NO SIGNS OF
BLACK STRATUS ON SATL FOG PRODUCT AS YET. THUS APPEARS NOT TO BE A
CONCERN THIS MRNG AND WILL EXPECT A SUNNY START TO THE DAY.
WITH HIGH PRESSURE BUILDING BACK INTO THE MIDWEST AND GREAT LAKES
REGION TONIGHT...WILL MAINTAIN CLEAR SKIES. ABSENCE OF POST FRONTAL
COLD AIR ADVECTION WILL LIKELY ONLY DROP LOWS TO AROUND 50 WITH SOME
LOW LYING MID 40S POSSIBLE CONSIDERING WEAKER WIND PATTERN.
SUNDAY IS STILL REINFORCING UPPER RIDGING EAST OF THE MS RIVER VLY
AND TILTING UPPER FLOW TO A MORE SWLY PATTERN OVER THE PLAINS AND
MIDWEST. AND OF COURSE A LEE SIDE LOW PRESSURE SYSTEM IS FORECAST TO
EJECT NE ALONG THIS UPPER PATTERN FROM THE HIGH PLAINS LATE TONIGHT
AND SUNDAY. THIS WILL PUSH OUR WEAK COLD FRONT BACK NORTH ON SUNDAY
AS A WARM FRONT. HIGHS NEAR 70 ARE AGAIN PROBABLE FOR SUNDAY AS A
RESULT DESPITE AN EXPECTED INCREASE IN AFTN WAA CLOUD COVER AHEAD OF
THIS SYSTEM. AS THE FRONT CONTINUES TO LIFT NORTH LATE SUNDAY...MODELS
DEPICTING RISING HEIGHTS OVER ILLINOIS...HELPING TO PUSH WAA
CLOUDINESS NORTHWARD. AN INTENSIFYING LLJ FROM THE GULF THRU THE
SRN PLAINS TO THE MID AND UPR MS VLY SHUD FEED GULF MSTR INTO THE
REGION SUNDAY INTO MONDAY. ANY OVERRUNNING PCPN SUNDAY WILL BE IN
THE COOLER AIR NORTH OF THIS OLD FRONTAL BOUNDARY IN WISCONSIN.
THE WARM FEED OF GULF MSTR INTO ILLINOIS WILL LIKELY KEEP NIGHTTIME
TEMPS UP TO AROUND 50 SUNDAY NIGHT.
THINGS CHANGE ON MONDAY HOWEVER AS A DEEPENING UPR TROF DIVES SE
FROM WRN CANADA AND SETS THIS PLAINS SYSTEM IN MOTION TO THE SE. A
SHOT OF RAIN IS POSSIBLE MONDAY THRU EARLY TUESDAY AS THIS SYSTEM IS
PUSHED SE BY THIS DIVING AMPLIFIED UPR TROF. POST FRONTAL CAA WILL
PUT AN END TO ANYMORE 60S FOR DAYTIME HIGHS THIS WEEK. WHILE A
WARMUP APPEARS TO BE SETTING UP FOR THURSDAY...ANOTHER SHOT OF RAIN
AND POST FRONTAL CAA ON FRIDAY APPEARS TO FOIL ANY WEEKEND PROSPECTS
FOR A RETURN OF THESE CONDITIONS.
RLB
AVIATION
1200 PM CST
1800 UTC TAFS...MAIN CONCERN AGAIN TODAY IS WITH WIND FCST.
CURRENT SFC ANALYSIS SHOWS A RATHER WEAK AND DIFFUSE COLD FRONTAL
BOUNDARY WORKING ITS WAY SEWD ACROSS ERN WI AND NWRN IL. THIS
FEATURE WILL CONTINUE TO WEAKEN AS IT SETTLES ACROSS REMAINDER OF
AREA THIS AFTN. AS THE FRONT APPROACHES...STRONGER SWLY
WINDS...GUSTING TO AOA 20 KTS...WILL BEGIN TO DIMINISH. WE/RE
ALREADY SEEING THIS OCCUR ACROSS NRN IL...TO W OF FOX RIVER
VALLEY. WINDS TO DIMINISH FURTHER HEADING INTO THIS EVENING. WITH
CLR SKIES AND WEAKENING GRADIENT...SFC/BOUNDARY LYR AIR WILL
DECOUPLE EARLY THIS EVENING ALLOWING WINDS TO DROP OFF TO LGT AND
VRBL. BY LATE TONIGHT...COMBINATION OF SFC RIDGE MOVING E OF
AREA...AND WEAK LOW PRESSURE FORMING ACROSS CNTRL PLAINS...WILL
RESULT IN PREVAILING WIND BCMG SELY BLO 10 KTS BY SUNRISE
SUNDAY...THEN TURNING SLY AND INCRG TO 10-20 KT RANGE BY 18Z AS
TODAY/S COLD FRONT LIFTS BACK NWD AND AREA ONCE AGAIN LIES WITHIN
WARM SECTOR.
SATLT IMAGERY SHOWS NEAREST UPSTREAM CLOUDS OVER 500 MI AWAY...SO
WILL GO WITH VFR CLR CONDITIONS THROUGH THIS EVENING. AS WARM
ADVECTION RE-STRENGTHENS LATER TONIGHT AHEAD OF NEXT
WAVE...SUSPECT SOME MID LVL CLOUDINESS WILL INCR ACROSS MID MS VLY
AND SRN GRTLKS REGION. THIS WILL LIFT N OF REGION BY 18Z AS WARM
FRONT LIFTS THRU.
OF MORE CONCERN TONIGHT WILL BE VIS. UNLIKE LAST NIGHT WHEN SFC
WINDS STAYED ELEVATED THROUGH HE NIGHT...DECOUPLING OF LLVL AIR
MASS...LIGHT WINDS AND SFC DEW POINTS NR 50 F SUGGEST HAZE/FOG
WILL DVLP OVERNIGHT. THIS DOESN/T LOOK LIKE A DENSE FOG SITN...BUT
WE PROBABLY WILL HAVE VIS DROPPING INTO MVFR RANGE LATE TONIGHT
THROUGH EARLY SUNDAY.
MERZLOCK
MARINE
1148 AM CST
A LOW PRESSURE APPROACHING HUDSON BAY WILL CONTINUE TO TRACK
NORTHEAST TODAY AND TONIGHT. A TRAILING TROUGH OF LOW PRESSURE
WILL DROP SOUTHEASTWARD ACROSS LAKE MICHIGAN THIS AFTERNOON AS IT
SLOWLY WEAKENS. A WEAK RIDGE OF HIGH PRESSURE WILL THEN BUILD
ACROSS THE NORTHERN PLAINS...REACHING THE GREAT LAKES REGION
TONIGHT. ON SUNDAY...ANOTHER WEAK AREA OF LOW PRESSURE IS EXPECTED
LIFT FROM THE CENTRAL PLAINS STATES...NORTHEASTWARD ACROSS THE
UPPER MIDWEST. THIS WILL SWING WINDS BACK INTO THE S AND SE WITH
SPEEDS INCREASING INTO 15 TO 25 KT RANGE...BUT STAYING MUCH
LIGHTER THAN WINDS YESTERDAY AND LAST NIGHT. A MORE SIGNIFICANT
WEATHER DISTURBANCE WILL TO MOVE ACROSS SOUTHERN CANADA ON MONDAY.
IN RESPONSE...SFC HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN
PLAINS AND UPPER MISSISSIPPI VALLEY ALLOWING A STRONGER...MORE
SUSTAINED NORTH TO NORTHWEST AIR FLOW TO EVOLVE HEADING INTO MID
WEEK.
MERZLOCK
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL NOON SATURDAY.
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