FXUS63 KLOT 302049
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 PM CST MON NOV 30 2009

.DISCUSSION...
159 PM CST

TONIGHT...THE SKY HAS BECOME MOSTLY CLEAR THIS AFTERNOON. WE
EXPECT THE LOW TEMPERATURES TO FALL TO AROUND 30. WE EXPECT DRY
WEATHER. 

TUESDAY THROUGH WEDNESDAY...WE FOUND THE EMF MODEL TO BE THE MOST
CONSISTENT DURING THE LAST DAY. WE WILL USE THE ECMWF FOR THE
MOVEMENT OF THE UPPER AIR RIDGES AND TROUGHS. THE UPPER AIR LONG
WAVE WILL MOVE INTO SOUTHERN MISSOURI WITH A LOW MOVING INTO
KENTUCKY BY WEDNESDAY EVENING. WE WILL ADD A CHANCE OF SNOW IN THE 
SOUTHEAST TWO THIRDS OF OUR COUNTY WARNING AREA AND A SLIGHT
CHANCE OF SNOW IN NORTHWEST ONE THIRD. WE EXPECT THE SNOW TO
ACCUMULATE IN THE EXTREME SOUTHEAST PART OF OUR COUNTY WARNING
AREA. 

WEDNESDAY NIGHT THROUGH FRIDAY... THE SURFACE LOW WILL MOVE INTO
NEW YORK BY THURSDAY MORNING. DUE TO THE UNCERTAINLY OF THE MODELS 
WE WILL STILL USE THE ECMWF FORECAST WITH SOME CAUTION. FORECAST
SOUNDINGS SHOW ENOUGH COLD AIR FOR SNOW. AN 700 MB FRONTOGENICAL
ZONE DOES PASS OVER THE FORECAST AREA WEDNESDAY AFTERNOON AND
EVENING. WE EXPECT THE SNOW TO FALL IN THIS REGION. BY 12 UTC THIS 
ZONE IS TO THE EAST OF OUR FORECAST AREA. WE WILL FORECAST 25 TO
30 PERCENT CHANCE OF SNOW THURSDAY THROUGH FRIDAY AS A 700 MB SHORT
WAVE TROUGH MOVES THROUGH AND THE 500 MB LONG WAVE PASSES OVER
NORTHERN ILLINOIS AND NORTHWEST INDIANA. WE WILL BE CAUTIOUS ABOUT
FORECAST SNOW AMOUNTS AT THIS TIME. 

FRIDAY THROUGH SUNDAY...WE EXPECT COLD WEATHER FRIDAY. THE WEATHER 
IS FORECAST TO BECOME WARMER SUNDAY AND MONDAY. WE EXPECT A CHANCE 
OF SNOW FOR MONDAY. A 500 MB TROUGH WILL MOVE ACROSS NORTHERN ILLINOIS
AND NORTHWEST INDIANA MONDAY. 

&&

.AVIATION...
1215 PM CST

WIND DIRECTION TRENDS WILL BE THE MAIN AVIATION FORECAST ISSUE OVER 
THE NEXT 36 HOURS. 

SURFACE HIGH BUILDING ACROSS CENTRAL PLAINS WILL CONTINUE TO SLOWLY 
TRACK EASTWARD TODAY WHICH WILL ALLOW FOR CONTINUED BACKING OF LOW 
LEVEL WINDS FROM NORTHWEST DIRECTIONS THIS MORNING...TO SOUTHWEST 
THIS AFTERNOON. THE COMBINATION OF SFC HIGH TRACKING SOUTH OF THE 
AREA...AND NEXT SFC TROUGH MOVING INTO THE UPPER MIDWEST FROM THE 
NORTHERN PLAINS WILL KEEP SOME STRENGTH TO GRADIENT IN PLACE
THROUGH THE AFTERNOON. IN ADDITION...DESPITE WARM ADVECTION
STRENGTHENING THIS AFTERNOON...MIXED LAYER HEIGHTS ARE EXPECTED TO
REMAIN AROUND 4K FT THIS AFTERNOON WHICH SHOULD PROMOTE SOME GUSTS
TO 15 TO 20 KT DURING THE AFTERNOON HOURS FROM THE SOUTHWEST. WITH
SFC TROUGH MOVING INTO THE WESTERN GREAT LAKES THIS EVENING...DID
MAINTAIN SOME GUSTS IN THIS GENERAL RANGE INTO THIS EVENING BEFORE
DIMINISHING LATE EVENING AS SFC TROUGH MOVES OFF TO THE EAST. IN
TERMS OF SKY COVER...SOME VFR STRATOCU AROUND 4K FT WILL CONTINUE
TO OVERSPREAD NORTHEAST ILLINOIS EARLY THIS AFTERNOON JUST IN
ADVANCE OF FAIRLY STRONG SHORT WAVE MOVING THROUGH MID MS RIVER
VALLEY. MORNING SOUNDING FROM DVN INDICATING SATURATION LAYER IS
RELATIVELY THIN AND COULD TEND TO SEE THESE VFR CLOUDS DISSIPATE
OVER NEXT SEVERAL HOURS AS LOW LEVEL WARM ADVECTION INCREASES.
SOME MID CLOUD ALSO EXPECTED TO INCREASE LATER THIS
AFTERNOON/EARLY EVENING...BUT OTHER THAN THIS JUST EXPECTING SOME
HIGH CLOUDINESS OVERNIGHT INTO TOMORROW MORNING.

MARSILI

&&

.MARINE...
120 PM CST

POTENTIAL OF GALES TONIGHT...AND THEN STRONG NORTH WINDS POSSIBLE
AGAIN WED/THU WILL BE THE MAIN MARINE FORECAST ISSUES THROUGH THE
REMAINDER OF THE WEEK.

CENTER OF SFC ANTICYCLONE WILL MOVE ACROSS THE LOWER MS RIVER VALLEY
TONIGHT AS AREA OF LOW PRESSURE AND ACCOMPANYING SFC TROUGH
APPROACHES THE WESTERN GREAT LAKES. THE COMBINATION OF THESE TWO
PRESSURE SYSTEMS WILL RESULT IN A FAIRLY STRONG SFC PRESSURE
GRADIENT ACROSS LAKE MICHIGAN TONIGHT. A MID/UPPER LEVEL JET MAX
WILL ALSO BE CUTTING THROUGH THE REGION TONIGHT IN ASSOCIATION
WITH AN UPPER LEVEL DISTURBANCE THAT WILL ENHANCE WINDS DURING
THE EVENING. GIVEN THE ABOVE FACTORS AND FAIRLY GOOD MIXING OVER THE
LAKE...DID GO AHEAD AND ISSUE A GALE WARNING FOR THE OPEN WATERS
FOR THE 00Z TO 09Z TIME PERIOD TONIGHT...ALTHOUGH TIME PERIOD OF
GREATEST THREAT FOR WEST SOUTHWEST GALES APPEARS TO BE IN THE 00Z
TO 06Z TIME FRAME. WEAK SFC RIDGE WILL THEN BUILD INTO THE REGION
ON TUESDAY BEHIND THIS SYSTEM AS NEXT SFC LOW TAKES SHAPE ACROSS
THE NORTHERN PLAINS. THIS LOW WILL APPROACH WESTERN LAKE SUPERIOR
TUESDAY NIGHT...AND SHOULD SEE SOUTH WINDS INCREASE IN RESPONSE
BACK INTO 10 TO 20 KT RANGE WITH SOME GUSTS TO 25 KT POSSIBLE.

ATTENTION WILL THEN SHIFT TO ANOTHER LOW LIFTING NORTHEAST FROM
THE LOWER MS RIVER VALLEY ON WEDNESDAY. CURRENT INDICATIONS
SUGGEST THIS LOW WILL MOVE INTO THE OHIO RIVER VALLEY WEDNESDAY
NIGHT WITH COLDER AIR/GUSTY WINDS BEING WRAPPED AROUND BACKSIDE OF
THIS SYSTEM ACROSS THE WESTERN GREAT LAKES. DID INCREASE WINDS A
BIT FOR THIS TIME PERIOD TO 30 KT.

IN TERMS OF THE NEARSHORE WATERS...SMALL CRAFT ADVISORIES WILL
REMAIN IN EFFECT THROUGH LATE TONIGHT...WITH ANOTHER PERIOD OF
HAZARDOUS WINDS AND WAVES FOR SMALL CRAFT POSSIBLE IN ASSOCIATION
WITH THE MID WEEK SYSTEM.

MARSILI

&&

.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...6 PM MONDAY TO 3 AM 
     TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 6 AM TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 4 AM 
     TUESDAY.

&&

$$