FXUS63 KLOT 051935
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
135 PM CST SAT DEC 5 2009
.DISCUSSION...
247 AM CST
FORECAST CHALLENGES THIS MORNING REVOLVE AROUND WEAK STORM SYSTEM
SLATED TO ARRIVE SUNDAY NIGHT...THEN THE MUCH STRONGER STORM SYSTEM
TO AFFECT THE REGION THE MIDDLE OF NEXT WEEK.
IN THE SHORT TERM...THE STORM SYSTEM THAT HAS PLAGUED OUR REGION FOR
DAYS WILL CONTINUE TO LOOSEN ITS GRIPS ON THE REGION TODAY. 11-3.9
MICRON GOES IMAGERY EARLY THIS MORNING SHOWS THAT THE BACK EDGE OF
THE FLURRYING STATUS DECK IS MAKING GOOD PROGRESS NORTHEASTWARD AND
REALLY DONT SEE ANY REASON THIS TREND WONT CONTINUE THIS MORNING
WITH SKIES CLEARING OUT. STEEP LOW LEVEL LAPSE RATES AND LINGERING
COLD AIR ALOFT WOULD TEND TO FAVOR FAIRLY EXTENSIVE DIURNAL
STRATOCUMULUS...HOWEVER VERY DRY LOW LEVEL AIR MASS IN PLACE SHOULD
TEND TO SOMEWHAT LIMIT DIURNAL STRATOCU DEVELOPMENT.
ATTENTION THEN TURNS TO THE TROUGH/CLOSED LOW CURRENTLY OVER THE
NORTHERN INTERMOUNTAIN WEST POISED TO GET BOOTED EASTWARD ACROSS THE
LOWER GREAT LAKES SUNDAY NIGHT. MODELS ARE ALL GENERALLY DEVELOPING
A WEAK SURFACE REFLECTION AND TRACKING THAT LOW ACROSS NORTHERN
ILLINOIS SUNDAY NIGHT. TRACK OF 500MB VORT MAX AND SURFACE LOW WOULD
BOTH POINT TOWARD BAND OF ACCUMULATING SNOW SETTING UP FROM IOWA ENE
INTO SOUTHERN WISCONSIN AND POSSIBLY BRUSHING FAR NORTHERN ILLINOIS.
WILL GO AHEAD AND CARRY AND AN INCH OR SO OF SNOW ACCUM IN THE GRIDS
ALONG THE WI BORDER FOR SUNDAY NIGHT...BUT IF SFC LOW TRACK REMAINS
UNCHANGED THIS MAY BE A BIT GENEROUS WITH BETTER ACCUMS NORTH OF THE
BORDER.
INTERESTINGLY...MODELS REMAIN RATHER BULLISH WITH QPF ALONG AND
SOUTH OF THE TRACK OF THE SURFACE LOW...WHICH GIVEN NO GOOD MOISTURE
RETURN AND LESS THAN STELLAR FORCING...IT DOES LOOK SUSPICIOUS.
ISENTROPIC ASCENT SHOULD BE MAXIMIZED ALONG TIGHTER THERMAL GRADIENT
ALONG/NORTH OF LOW TRACK WITH ONLY WEAK ISENTROPIC ASCENT SOUTH FROM
THERE...CERTAINLY NOT ENOUGH TO JUSTIFY LIKELY POPS SOUTH OF
FORECAST SURFACE LOW TRACK. AM ALSO SOMEWHAT CONCERNED ABOUT P-TYPE
OVER OUR SOUTHERN COUNTIES...DESPITE FORECAST SOUNDINGS SUGGESTING
ALL SNOW...IT ISN'T COMMON TO SEE SNOW SOUTH OF A SURFACE LOW TRACK
FOLLOWING A GOOD 12+ HOURS OF WARM AIR ADVECTION. WILL LEAVE P-TYPE
AS ALL SNOW IN GRIDS ACROSS THE ENTIRE CWA FOR NOW GIVEN SUCH STRONG
SUPPORT FOR ALL SNOW IN FORECAST SOUNDINGS...BUT WOULDNT BE
SURPRISED IF ANY PRECIP THAT DOES END UP FALLING SOUTH OF THE SFC
LOW ENDS UP MIXING WITH SOME SLEET OR EVEN LIGHT RAIN.
BIGGEST WEATHER STORY CONTINUES TO BE THE STRONG SHORTWAVE CURRENTLY
CRESTING THE ALASKAN RIDGE AND MOVING ACROSS THE NORTHWEST
TERRITORY. THIS SYSTEM IS FORECAST TO CLOSE OFF A MID-LEVEL
CIRCULATION AS IT DIVES SOUTHWARD ALONG THE WESTERN NOAM COAST THIS
WEEKEND. MEDIUM RANGE MODELS THEN DIG THIS SYSTEM A BIT DEEPER INTO
THE DESSERT SOUTHWEST BEFORE EJECTING IT QUICKLY NORTHEAST TOWARD
THE GREAT LAKES BY MIDWEEK. TREND IN THE LAST COUPLE RUNS OF THE GFS
AND ECMWF HAVE BEEN FOR SLIGHTLY LESS AMPLIFICATION WHICH HAS
RESULTED IN A BIT OF A SHIFT TO THE RIGHT IN THE TRACK OF THE
SURFACE LOW WHICH IS ALSO IN LINE WITH THE UKMET. THE
CMC/DGEX/NOGAPS ALL REMAIN MORE AMPLIFIED AND FARTHER TO THE NORTH
WITH THE SURFACE LOW TRACK. REALLY ONLY TALKING ABOUT A DIFFERENCE
OF A COUPLE/FEW HUNDRED MILES IN THE FORECAST TRACK OF THE SURFACE
LOW AMONG THE VARIOUS MODELS...WHICH THIS FAR OUT ISNT ALL THAT
UNUSUAL. AT THIS DISTANCE...REALLY HARD TO HANG MY HAT ON ANY ONE
SOLUTION...THOUGH GIVEN RECENT TRENDS WOULD SUSPECT A SOLUTION MORE
IN LINE WITH THE LATEST GFS/ECMWF/UKMET PROBABLY IS THE WAY TO GO.
SHOULD THE LESS AMPLIFIED/FARTHER SOUTHWARD TRACK IN THE ECMWF AND
GFS VERIFY...THEN MOST IF NOT ALL OF OUR CWA WOULD REMAIN COLD
ENOUGH FOR ALL SNOW. WHILE THE 500MB AND MSLP ANOMALIES SUGGEST
THAT WE WOULD STILL BE LOOKING AT A STRONG SYSTEM...IT WOULD LIKELY
BE MOVING TOO QUICKLY TO REALLY TAP INTO QUALITY GULF MOISTURE. THE
FAST MOVEMENT WOULD ALSO TEND TO ARGUE AGAINST A GANGBUSTERS TYPE
QPF EVENT. THE CMC/NOGAP/DGEX SOLUTION WOULD TAKE THE SFC LOW ON AN
UNFAVORABLE TRACK FOR SNOW FOR OUR CWA...WITH A TRANSITION FROM
SNOW/MIX TO RAIN MORE LIKELY IN THIS MODEL CAMP.
REALLY HARD TO IMPROVE UPON GOING FORECAST AT THIS DISTANCE WITH
LIKELY POPS CERTAINLY JUSTIFIABLE. P-TYPE AND AMOUNTS WILL HINGE ON
THE EVENTUAL TRACK THIS SYSTEM TAKES...WHICH QUITE FRANKLY IS
ANYONES GUESS AT THIS POINT. MODEL TRENDS WILL CERTAINLY NEED TO BE
WATCHED THE NEXT COUPLE/FEW DAYS AS THERE IS DEFINITELY A CHANCE OF
SIGNIFICANT SNOW IN OUR NECK OF THE WOODS. WITH ALL MEDIUM RANGE
MODELS FORECASTING AN INTENSE SURFACE LOW EAST OF THE AREA BY WED
NIGHT INTO THURSDAY IT WOULD SEEM THAT STRONG WINDS ARE PROBABLY THE
ONE THING THAT CAN BE FORECAST WITH A MODERATELY HIGH DEGREE OF
CONFIDENCE AT THIS DISTANCE.
NO CHANGES MADE TO THE FORECAST BEYOND WEDNESDAY.
IZZI
&&
.AVIATION...
18Z TAFS...NO CONCERNS...VFR THRU THE PERIOD. A LARGE RIDGE OF
HIGH PRESSURE EXTENDS FROM THE SOUTHERN LAKES SOUTHWEST TO THE
GULF OF MEXICO. THIS RIDGE WILL SLOWLY MOVE EAST TO THE ATLANTIC
COAST BY SUNDAY EVENING. SOUTHERLY WINDS 10-15KT WITH A FEW
HIGHER GUSTS THIS AFTERNOON WILL DIMINISH UNDER 10KTS WITH SUNSET
THEN INCREASE BACK TO 10-15KTS SUNDAY MORNING. STRATOCU OVER THE
AREA EARLIER THIS MORNING HAS ERODED BUT CU NOW FORMING ACROSS
NORTHEAST IL AND NORTHWEST INDIANA. WHILE THIS CU WILL LIKELY BE
BKN/OVC FOR ANOTHER HR OR SO...OPTED TO CARRY PREVAILING SCATTERED
SINCE VFR CIGS SHOULD BE SHORT-LIVED. OTHERWISE INCREASING HIGH
AND MID CLOUDS TONIGHT AND SUNDAY. CMS
&&
.MARINE...
135 PM...MAIN FORECAST FOCUS/CHALLENGE CONTINUES TO BE A STRONG
AREA OF LOW PRESSURE WHICH WILL MOVE ACROSS THE GREAT LAKES...
WHILE DEEPENING...TUESDAY NIGHT AND WEDNESDAY.
IN THE SHORT TERM...A LARGE RIDGE OF HIGH PRESSURE EXTENDS FROM
THE SOUTHERN LAKES TO THE GULF OF MEXICO. THIS RIDGE WILL SHIFT
EAST TO THE ATLANTIC COAST BY SUNDAY EVENING. A WEAK COLD FRONT
WILL MOVE SOUTHEAST ACROSS THE WESTERN LAKES SUNDAY NIGHT AS A
WEAK AREA OF LOW PRESSURE DEVELOPS ALONG THIS FRONT OVER EASTERN
IA AND WESTERN IL MONDAY MORNING. THIS LOW WILL QUICKLY LIFT
NORTHEAST ACROSS THE EASTERN LAKES BY MONDAY EVENING. COMBINATION
OF A SLIGHTLY TIGHTER GRADIENT ALONG WITH SOME COOLER AIR...WILL
LIKELY ALLOW WINDS TO INCREASE TO 15-25KTS FOR A SHORT TIME...
ESPECIALLY OVER SOUTHERN LAKE MICHIGAN. A FAST MOVING RIDGE OF
HIGH PRESSURE WILL MOVE ACROSS THE LAKES REGION BY TUESDAY
MORNING...THUS WINDS SHOULD QUICKLY DIMINISH BY THIS TIME PERIOD.
AS THIS HIGH SHIFTS EAST...WINDS WILL FLIP AROUND TO EASTERLY AS
A NEW AREA OF LOW PRESSURE OVER THE SOUTHERN PLAINS TUESDAY LIFTS
NORTHEAST ACROSS THE SOUTHERN GREAT LAKES LATE TUESDAY NIGHT INTO
WEDNESDAY. TRENDS HAVE BEEN FAIRLY CONSISTENT SHOWING THIS LOW
DEEPENING AS MOVES THROUGH THE SOUTHERN LAKES...BUT EXTENT OF
DEEPENING AND HOW STRONG IT BECOMES CONTINUES TO VARY FROM RUN TO
RUN AND MODEL TO MODEL. WHILE THE SPECIFICS REGARDING TIMING AND
EXACT TRACK/WIND DIRECTIONS ARE STILL SOMEWHAT UNCERTAIN...
CONFIDENCE CONTINUES TO INCREASE THAT GALES WILL DEVELOP ONCE THE
LOW PASSES...ESPECIALLY OVER SOUTHERN LAKE MICHIGAN. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
