FXUS63 KLOT 111146
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
546 AM CST FRI DEC 11 2009
.DISCUSSION...
335 AM CST
PRIMARY FORECAST CHALLENGES THIS MORNING REVOLVE AROUND TEMPERATURES
THE NEXT SEVERAL DAYS AS WELL AS SMALL PRECIP CHANCES/TYPE SAT NIGHT
INTO SUN MORNING AND AGAIN SUNDAY NIGHT INTO MONDAY.
WARM AIR ADVECTION ALREADY UNDERWAY AS HEART OF THE ARCTIC AIRMASS
RETREATS NORTHEASTWARD INTO CANADA. DESPITE THE FRESH SNOWPACK
STEADY W TO SW WINDS HAVE HELPED HOLD TEMPS STEADY MOSTLY IN THE
SINGLE DIGITS ABOVE ZERO OVER SNOWPACK AND IN THE TEENS SE COUNTIES
WHERE LESS SNOW COVER EXISTS. EVEN WITH THE SOMEWHAT MILDER START
TODAY AND FULL SUNSHINE EXPECT THAT THE SNOW PACK WILL STILL RETARD
OUR WARM UP WITH DEEP SNOW COVERED AREAS PROBABLY NOT REACHING 20F
THIS AFTERNOON.
TEMP FORECAST TONIGHT WILL AGAIN BE TRICKY AS WARM AIR ADVECTION
KEEPS TEMPS WARMING ALOFT...HOWEVER CLEAR SKIES AND LIGHTER WINDS
THIS EVENING MAY ALLOW FOR A RAPID CRASH IN TEMPERATURES OVER THE
SNOW PACK AND HAVE CONTINUED TO UNDERCUT GUIDANCE. STILL WORRIED
THAT IF WE DECOUPLE SUFFICIENTLY THIS EVENING THAT TEMPS COULD BE
EVEN COLDER THAN WHAT I HAVE IN THE GRIDS...BUT DIDN'T WANT TO GET
TOO CARRIED AWAY WITH TEMPS AS SOUTHERLY GRADIENT IS PROGGED TO
TIGHTEN OVERNIGHT.
WARM AIR ADVECTION WILL CONTINUE THROUGH THE DAY SATURDAY IN ADVANCE
OF A WEAK SHORTWAVE RIDING THE SUBTROPICAL JET TOWARD THE REGION
SAT NIGHT INTO SUNDAY. FORECAST SOUNDINGS SUGGEST TOP-DOWN
SATURATION WILL BE TAKING PLACE HOWEVER IT ALSO APPEARS THAT BY
THE TIME THE LOW LEVELS HAVE MOISTENED SUFFICIENTLY FOR PRECIP TO
REACH THE GROUND THAT WE COULD BE LOSING MID/UPPER LEVEL MOISTURE
AND THUS ICE CRYSTALS IN THE CLOUDS. OVERALL DOESNT LOOK TO BE ALL
THAT IMPRESSIVE OF A PRECIP EVENT WITH A TRACE TO COUPLE/FEW
HUNDREDTHS OF AN INCH EVENT APPEARING TO BE THE WORST CASE
SCENARIO. P-TYPE ALSO NOT STRAIGHT FORWARD WITH WARM ADVECTION
TENDING TO PUSH TEMPERATURES ABOVE FREEZING ALOFT...THOUGH
EVAPORATIVE COOLING WILL BE WORKING TO COUNTERACT THAT. GIVEN TOP-
DOWN SATURATION WOULDNT BE SURPRISED IF WE SAW A BIT OF
GRAUPEL...FREEZING SPRINKLES OR FLURRIES. ASSUMING LOW LEVELS
SATURATE FULLY...FORECAST SOUNDINGS SUGGEST A STRATUS DECK WILL
LINGER INTO SUNDAY MORNING WITH SOME LIGHT DRIZZLE OR FREEZING
DRIZZLE A POSSIBILITY.
NEXT MORE SIGNIFICANT NORTHERN STREAM TROUGH FORECAST TO LEAD TO SFC
CYCLOGENESIS OVER THE CENTRAL HIGH PLAINS SUNDAY NIGHT. LOW IS THEN
FORECAST TO TRACK INTO WISCONSIN ON MONDAY WITH FAIRLY STRONG WARM
AIR ADVECTION IN ADVANCE OF THIS SYSTEM LIKELY LEADING TO A NICE
REBOUND IN TEMPS. MEX GUIDANCE HAS OUR SOUTHERN CWA CLIMBING INTO
THE 50S...WITH H8 TEMPS EVEN MILDER ON THE 00Z ECMWF. HAVE NUDGED
HIGHS MONDAY UP INTO THE 40S OVER THE URBAN AND NON-SNOW COVERED
AREAS WITH MID/UPPER 30S ELSEWHERE...THOUGH GIVEN LATEST MODEL
GUIDANCE THESE TEMPS MAY EVEN BE CONSERVATIVE.
GFS BRINGS IN ANOTHER SHOT OF BITTERLY COLD AIR BEHIND THIS FRONT
TUESDAY INTO WEDNESDAY. MEX GUIDANCE KNOCKING HIGHS BACK DOWN INTO
THE TEENS AND LOWS IN THE SINGLE DIGITS. GEM/ECMWF/DGEX ALL MUCH LESS
INTENSE WITH THE ARCTIC INTRUSION SO HAVE NUDGED GOING FORECAST
TEMPS DOWN SLIGHTLY THOUGH KEPT THEM WELL ABOVE WHAT THE OUTLIER GFS
MODEL WOULD SUGGEST IS POSSIBLE.
NO CHANGES MADE TO GOING FORECAST BEYOND TUESDAY...
IZZI
&&
.AVIATION...
1200 UTC TAFS...VFR CONDITIONS ANTICIPATED THROUGH LATE SATURDAY WITH
A RIDGE OF HIGH PRESSURE MOVING OVER THE AREA. WINDS ALSO WILL CONTINUE
TO DIMINISH TODAY AND THEN TURN SOUTHWEST TO SOUTH BY SATURDAY
MORNING BEFORE PICKING UP AGAIN SATURDAY NIGHT INTO SUNDAY AHEAD
OF THE NEXT TROUGH OF LOW PRESSURE. SATURDAY NIGHT ALSO OFFERS A
POSSIBLE QUICK SHOT OF LIGHT WINTER PRECIP IN SOME
FORM...PERHAPS EVEN FREEZING DRIZZLE. THIS APPEARS TO MOVE OUT
VERY EARLY SUNDAY BEFORE THE NEXT SYSTEM APPROACHES ON MONDAY.
LENNING
&&
.MARINE...
318 AM CST
A BROAD AREA OF HIGH PRESSURE CENTERED OVER THE SOUTHEASTERN
US WILL DRIFT TOWARD THE MID ATLANTIC STATES OVER THE NEXT COUPLE
OF DAYS. THE NORTHWESTERN EXTENT OF THIS RIDGE WILL MOVE OVER LAKE
MICHIGAN AND ALLOW WEST WINDS TO SUBSIDE SUBSTANTIALLY BY LATE
FRIDAY. WINDS TURN SOUTH TO SOUTHWEST AND THE PRESSURE GRADIENT
TIGHTENS AGAIN BY SATURDAY AFTERNOON AS A TROUGH OF LOW PRESSURE
DEVELOPS OVER THE NORTHWESTERN GREAT LAKES. THIS TROUGH CROSSES
LAKE MICHIGAN ON SUNDAY AND WINDS AGAIN VEER WEST TO
NORTHWEST...THEN EVENTUALLY AROUND TO THE EAST BY MONDAY MORNING
AHEAD OF THE NEXT APPROACHING LOW PRESSURE SYSTEM. DEPENDING ON
THE EXACT STRENGTH AND TRACK OF THIS SYSTEM AS THE LOW PRESSURE
CENTER CROSSES THE LAKE LATE MONDAY OR EARLY TUESDAY...WINDS COULD
AGAIN INCREASE TOWARD GALE THRESHOLDS.
LENNING
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL MIDNIGHT SATURDAY.
SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL MIDNIGHT SATURDAY.
&&
$$
