FXUS63 KLOT 060821
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 AM CST SUN DEC 6 2009
.DISCUSSION...
206 AM CST
THERE WILL BE SNOW TONIGHT MOST OF WHICH WILL FALL IN THE NORTH
HALF OF OUR FORECAST AREA. ANOTHER LOW WILL PRODUCE SNOW TUESDAY
THROUGH WEDNESDAY.
TODAY AND TONIGHT...THE 300 MB JET STREAM IS OVER ILLINOIS.
THE JET STREAM WILL MOVE EAST TODAY. THERE WAS A SOUTH WIND OVER
ILLINOIS THIS MORNING. THE PROFILER AT WOLCOTT INDIANA SHOWS THE
WIND VEERING WITH HEIGHT. THIS WARM AIR ADVECTION WILL INCREASE
THE VORTICITY AT 925 MB AND INCREASING THE STRENGTH OF THE COLD
FRONT THAT LIES FROM WISCONSIN TO THE OKLAHOMA PANHANDLE. BY
THIS EVENING THE FRONT WILL BE A STRONG ENOUGH BAROCLINIC ZONE TO
SUPPORT A CYCLONE OVER NORTH CENTRAL ILLINOIS BY MONDAY MORNING. A
SHORT WAVE OVER NEVADA THIS MORNING WILL MOVE INTO ILLINOIS
MONDAY. MORNING. ANOTHER 300 MB JET STREAM WILL SPREAD OVER
ILLINOIS MONDAY MORNING. THIS WILL BE A SHORT LIVED EVENT. THE LOW
IS FORECAST TO MOVE QUICKLY. THE NAM...GFS...SREF AND ECMWF SHOW
THIS TO BE A WEAK LOW. WE WILL FORECAST 1 TO 2 INCHES OF SNOW.
THERE IS FORECAST OMEGA OF AROUND -3 MB/S DUE TO ISENTROPIC LIFT
FROM THE NAM MODEL. THE SOUNDING FORECAST HAS SIGNIFICANT MOISTURE
WITH A ONE DEGREE SPREAD AT 800 MB FOR EARLY MONDAY MORNING. WITH
A 12 TO 17 DEGREE TEMPERATURE FROM 1700 METERS TO 3300 METERS WE
EXPECT SOME DENDRITE SNOW CRYSTALS. THE SREF AND NAM MODELS ARE SIMILAR
IN THIS FORECAST. WE WILL FORECAST HIGH TEMPERATURES IN THE MIDDLE
TO UPPER 30S AND LOW TEMPERATURES IN THE MIDDLE TO UPPER 20S
TONIGHT.
MONDAY THROUGH TUESDAY NIGHT...MONDAY AND MONDAY NIGHT THE WEATHER
WILL BE DRY. THE NEXT CYCLONE WILL DEVELOP IN OKLAHOMA IN THE
BAROCLINIC ZONE OF THE SOUTHERN JET STREAM. COLD AIR WILL BE IN
PLACE OVER NORTH CENTRAL ILLINOIS AND NORTHWEST INDIANA. A 500 MB
LONG WAVE TROUGH IS FORECAST TO MOVE INTO THE CENTRAL PLAINS. THE
LONGWAVE TROUGH IS FORECAST TO CHANGE ITS ORIENTATION AS IT MOVES
INTO THE MISSISSIPPI VALLEY. WE EXPECT THE CYCLONE TO DEEPEN AND
MOVE INTO NORTHERN ILLINOIS OR NORTHERN INDIANA BY WEDNESDAY
MORNING. THIS COULD BE A SIGNIFICANT CYCLONE WITH HEAVY SNOW. WE
WILL NOT ISSUE A WINTER STORM WATCH AT THIS TIME. WE WILL WAIT TO
SEE WHERE THE CYCLONE WILL TRACK. WE WILL ADJUST THE PRECIPITATION
TYPE A LITTLE BASED ON A COMPROMISE OF THE GFS AND NAM WITH THE
SREF AND ECMWF MODELS. THIS STORM WILL BRING SIGNIFICANT WIND AS
WELL. THERE MAY BE BLOWING AND DRIFTING SNOW. THE SOUTHEAST
COUNTIES MAY HAVE RAIN AND SNOW MIXED BEFORE TURNING TO ALL SNOW
BY WEDNESDAY MORNING.
WEDNESDAY THROUGH THURSDAY...THE SNOW WILL MOVE OUT WEDNESDAY NIGHT.
EXTREMELY COLD AIR WILL MOVE TO NORTHERN ILLINOIS AND NORTHWEST
INDIANA...AS A BIG HIGH MOVES INTO THE MISSISSIPPI VALLEY
THURSDAY. WE MAY HAVE LOW TEMPERATURES IN THE SINGLE DIGITS AND
HIGH IN THE LOWER 20S.
&&
.AVIATION...
0600 UTC TAFS...VFR CONDITIONS TO CONTINUE OVERNIGHT DUE TO LARGE
HIGH PRESSURE SYSTEM ANCHORED OVER THE OHIO VALLEY. ONE WEAK UPPER
LEVEL DISTURBANCE SHEARING OUT ACROSS THE GREAT LAKES OVERNIGHT
JUST BRINGING SOME PATCHES OF MID CLOUD ACROSS THE AREA. MORE
SUBSTANTIAL UPPER WAVE COMING OUT OF THE SW US WILL SPREAD A MORE
SOLID MID AND HIGH CLOUD DECK INTO THE REGION SUNDAY AND SUNDAY
NIGHT. THIS WILL EVENTUALLY BRING SOME LIGHT SNOW TO THE AREA LATE
SUNDAY NIGHT AND MONDAY MORNING...MAINLY BEYOND THE RANGE OF THIS
FORECAST. THE BULK OF THE SNOW WILL IMPACT WISCONSIN AND FAR NORTHERN
IL INCLUDING ROCKFORD. LOOKS TO BE MINIMAL IMPACT ON THE CHICAGO
AREA AIRPORTS.
WITH THE STRONG SURFACE HIGH DRIFTING EAST AND A SURFACE TROF/COLD
FRONT APPROACHING FROM THE NORTHWEST...PRESSURE GRADIENT WILL
SUSTAIN S TO SW WINDS AROUND 10 KTS REST OF TONIGHT INTO SUNDAY
MORNING. AS THE FRONT APPROACHES WINDS WILL DIMINISH SUNDAY
AFTERNOON...ESPECIALLY IN THE RFD AREA. FRONT WILL BECOME NEARLY
STATIONARY OVER THE CHICAGO AREA SUNDAY NIGHT AS A WEAK LOW
PRESSURE AREA MOVES THROUGH EARLY MONDAY MORNING.
ALLSOPP
&&
.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.
&&
$$
