573
FXUS63 KLOT 210415
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1015 PM CST FRI NOV 20 2009
DISCUSSION
243 PM CST
SHOULD BE A GREAT NOVEMBER WEEKEND ON TAP AS HIGH PRESSURE SETTLES
IN ACROSS THE REGION. WITH LIGHT WINDS AND MAINLY CLEAR SKIES
OVERNIGHT TO GO ALONG WITH SOME SURFACE MOISTURE AND A SHARP LOW
LEVEL INVERSION...WILL LIKELY SEE SOME AREAS OF FOG SATURDAY
MORNING. CONSIDERED ADDING THE MENTION OF SOME DENSE FOG FURTHER
SOUTH WHERE THERE WAS HEAVIER RAIN THIS PAST WEEK...BUT WILL HOLD
OFF FOR THE TIME BEING AND ALLOW FOR THE EVENING SHIFT TO MONITOR
CONDITIONS.
AFTER THE FOG MIXES OUT TOWARD MID MORNING...TEMPERATURES WILL
CLIMB BACK WELL ABOVE NORMAL IN THE AFTERNOON INTO THE MID 50S
WITH SUNNY SKIES AND A LIGHT SOUTH TO SOUTHEAST WIND. THESE
PLEASANT CONDITIONS ARE EXPECTED TO PERSIST INTO SUNDAY AND EVEN
INTO MONDAY...ALTHOUGH SKIES WILL BE BECOMING CLOUDIER THROUGH THE
DAY MONDAY. SOME FOG CAN'T BE RULED OUT FOR SUNDAY MORNING...BUT
WILL HOLD OFF ON ANY MENTION AT THIS POINT AND SEE HOW THE FOG
SITUATION PANS OUT TOMORROW MORNING.
NEXT CHANCE FOR PRECIP COMES IN ON MONDAY NIGHT/TUESDAY MORNING AS
A WEAK SHORTWAVE TROF MOVES INTO THE REGION AND COULD PRODUCE A
FEW SHOWERS. NOTHING MAJOR HERE WITH PERHAPS AROUND A TENTH OF AN
INCH OF RAIN POSSIBLE.
MAIN STORY/FORECAST CHALLENGE REMAINS WITH THE MID WEEK SYSTEM
THAT IS CURRENTLY PROPAGATING THROUGH THE ALEUTIAN ISLANDS IN
ALASKA. THIS SYSTEM IS EXPECTED TO CARVE OUT AN UPPER LEVEL TROF
OVER THE PLAINS TOWARD THE MIDDLE OF THIS UPCOMING WEEK. THE MAIN
PROBLEM HAS BEEN THAT THE GFS/DGEX HAVE HAD DIFFERENT PLANS
COMPARED TO THE ECMWF/GEM MODELS. THE GFS/DGEX SOLUTION IS MUCH
MORE PROGRESSIVE AND BRINGS THE SFC/UPPER LOW THROUGH EARLIER IN
THE WEEK WHILE THE ECMWF/GEM CUTS OFF THE UPPER LOW AND IS MUCH
SLOWER BRINGING IT THROUGH. SO...WHILE CONFIDENCE IS HIGH THAT
SOME SORT OF DECENT STORM SYSTEM WILL DEVELOP THIS UPCOMING
WEEK...A LOT OF UNCERTAINTY EXISTS FOR WHEN IT WILL TRACK THROUGH
THE REGION AND WHAT PATH IT WILL TAKE. FOR NOW...HAVE GONE ALONG
WITH HPC'S THINKING AND HAVE TRENDED TOWARD THEIR USE OF THE 00Z
ECMWF/GEM MODELS. HOWEVER...THE 12Z ECMWF HAS COME IN EVEN
SLOWER...BUT AT THIS POINT WILL NOT FALL INTO FLIP-FLOP MODE.
REGARDLESS...LOOKS LIKE WE'LL SEE AN EXTENDED PERIOD OF RAIN AS
THIS SYSTEM DEVELOPS AND ENTERS THE MIDWEST...FOLLOWED BY A
SECONDARY SHOT OF COLD AIR ON THE BACK SIDE OF THE LOW WHICH
SHOULD PROVIDE A CHANCE FOR SOME LIGHT SNOW SHOWERS TO MIX IN.
GIVEN THE SETUP...WOULDN'T EXPECT MUCH/IF ANY ACCUMULATIONS...BUT
MORE OF A HEADACHE FOR TRAVELERS WITH THE SLOPPY WEATHER GIVEN
THAT THIS SCENARIO PANS OUT.
HALBACH
AVIATION
0600 UTC TAFS...MAIN CONCERN FOR THE REMAINDER OF THE NIGHT
CONTINUES TO FOCUS ON VISIBILITY...PARTICULARLY AT RFD/DPA AND
DURING THE EARLY MORNING HOURS.
THE LATEST SATELLITE IMAGERY SHOWS QUICKLY CLEARING. THIS WILL
ENHANCE RADIATIVE COOLING...AND WHEN COMBINED WITH SATURATED
GROUND AND WINDS QUICKLY BECOME LGT/VRBL...VISIBILITY SHOULD DROP
TO MVFR AT RFD/DPA SHORTLY AFTER MIDNIGHT. DUE TO URBAN
INFLUENCES...ORD/MDW SHOULD BE A LITTLE SLOWER TO RESPOND AND NOT
DROP TO MVFR UNTIL A FEW HOURS LATER. ORD/MDW SHOULD REMAIN AT
MVFR WITH RFD/DPA HAVING A BETTER CHANCE TO DROP TO
IFR...ESPECIALLY DURG THE PRE-DAWN HOURS.
THE FOG SHOULD BURN OFF SHORTLY AFTER SUNRISE AND THE REMAINDER OF
THE DAY WILL BE QUIET FOR AVIATION WEATHER CONCERNS.
KREIN
MARINE
1255 PM CST
RATHER WEAK UPR RIDGING OVER THE MIDWEST TODAY AND TONIGHT BUT
EFFECTIVE ENUF TO SUBDUE CU FORMATION AND DIMINISH SC SHIELD NOW
DISSIPATING ALONG WI AND IL BORDER NR RFD. SO SHUD ONLY BE WORKING
WITH BKN CI TODAY AND EARLY TNGT. SCT SKY CONDS ALONG WITH LGT AND
VRBL WINDS WILL PERMIT RADIATING OUT TONIGHT AND THUS LIKELY
GENERATE SOME GROUND FOG PAST MIDNIGHT THRU SUNRISE. DID NOT
REDUCE VSBY TO LESS THAN 1 MILE BUT IS PSBL ESP IN DPA AND RFD.
WINDS W TO SW UNDER 10 KTS TODAY UNDER INFLUENCE OF SFC HIGH
PRESSURE TO THE SOUTH. THEN WINDS LGT AND VRBL OVERNIGHT...PICKING
UP FROM THE SE SATURDAY MRNG BUT STILL RATHER LIGHT.
RLB
LOT WATCHES/WARNINGS/ADVISORIES
IL...DENSE FOG ADVISORY...ILZ008-ILZ010-ILZ019-ILZ032-ILZ039 UNTIL 9
AM SATURDAY.
IN...NONE.
LM...NONE.
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