000
FXUS63 KLOT 201303
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
703 AM CST THU NOV 20 2008
.DISCUSSION...
109 AM CST
PRELIMINARY OVERVIEW OF CURRENT FORECAST COMPARED TO LATEST MODEL
OUTPUT SHOWS NO NEED FOR ANY SIGNIFICANT CHANGES NEEDED.
SHORT WAVE MOVING SOUTHEAST INTO THE LOWER GREAT LAKES REACHES THE
UPPER ST. LAWRENCE VALLEY BY 18Z...WHILE A COMPACT UPPER LOW SEEN
DROPPING SOUTH-SOUTHEAST ACROSS THE BORDER AND OVER NORTH DAKOTA
IN WATER VAPOR SATELLITE IMAGERY IS PROGGED BY MODELS TO OPEN
INTO A WAVE WITH THE TROUGH AXIS OVER SOUTHERN WISCONSIN AND
NORTHERN IOWA AT MIDDAY. THIS SHORT WAVE TROUGH CONTINUES TO MOVE
OVER THE MIDWEST DURING THE AFTERNOON...REACHING THE OHIO VALLEY
THIS EVENING.
COLD AIR ADVECTION FOLLOWING THE COLD FRONT THAT DROPPED
SOUTRHEASTWARD ACROSS THE LOCAL FORECAST AREA DURING WEDNESDAY
AFTERNOON NOT PARTICULARLY STRONG AS CORE OF COLD AIR IS STILL
LOCATED OVER MANITOBA AND WESTERN ONTARIO. LAKE EFFECT HAS STARTED
UP AGAIN OFF OF LAKE SUPERIOR AND NORTHERN LAKE MICHIGAN AS MID
LEVELS COOL AND ALLOW DEEPER CONVECTIVE CELLS TO DEVELOP. THIS
DEEP COLD ADVECTION WILL BE SPREADING FURTHER SOUTHEAST ACROSS THE
UPPER GREAT LAKES TODAY...ARRIVING OVER THE LOCAL FORECAST AREA
WITH THE UPSTREAM SHORT WAVE TROUGH PASSAGE.
EXCEPT FOR A GAP OVER EASTERN WISCONSIN AND ADJACENT WESTERN LAKE
MICHIGAN...WIDESPREAD STRATOCUMULUS HAS COVERED THE REGION AS THE
LOW LEVEL COLD ADVECTION SPREAD SOUTH AND SOUTHEAST. OUTSIDE OF
THE LAKE EFFECT...ONLY SOME FLURRIES OCCURRING UPSTREAM ASSOCIATED
WITH THE NEXT SHORT WAVE AND FOLLOWING STRONGER COLD ADVECTION.
ANTICIPATE WIDESPREAD CLOUDS TODAY INTO THIS EVENING WITH A CHANCE
OF SOME FLURRIES FROM LATER MORNING ON.
LAKE EFFECT SNOW WILL STAY EAST OF PORTER COUNTY...OUT OF THE LOCAL
FORECAST AREA...AS FAIRLY STRONG MEAN LOW LEVEL NORTHWEST FLOW KEEPS
IT OVER THE EASTERN SIDE OF THE LAKE. WITH ANOTHER SHORT WAVE
PASSAGE LATER TODAY FLOW VEERS A BIT BUT MODELS SUGGEST A WEAK
SURFACE TROUGH EXTENDING WESTWARD ACROSS THE LAKES OFTEN OBSERVED DUE
TO THERMAL IMPACT OF RELATIVELY WARM WATERS OF THE LAKES ON THE
REGIONAL WIND FIELD. MODELS DO DEPICT LIGHTER LAKE EFFECT SNOWS
BACKING INTO LAKE COUNTY INDIANA LATE AFTERNOON...BUT THE TAIL OF
THE HEAVY SNOW BAND AXIS SHOWN REMAINING ACROSS BERRIEN AND
LAPORTE COUNTIES TONIGHT.
ELSEWHERE...CLOUDS TO CLEAR TONIGHT AS DRY AIR SPREAD IN AS
SURFACE RIDGE BUILDS ACROSS THE UPPER MISSISSIPPI AND LOWER
MISSOURI VALLEYS DURING THE NIGHT.
STRONG SHORT WAVE CURRENTLY ABOUT 300 MILES OFF THE PACIFIC
NORTHWEST COAST HANDLED FAIRLY SIMILARLY BY VARIOUS MODELS IS
MOVING IT EAST TO OVER THE DAKOTAS BY FRIDAY EVENING...THEN
SOUTHEAST FROM IOWA ACROSS ILLINOIS AND INDIANA DURING THE DAY
SATURDAY. EVEN THOUGH THE MODELS ARE DEPICTING A LOW LEVEL
CIRCULATION IN ASSOCIATION WITH THIS STRONG DISTURBANCE FRIDAY
NIGHT AND EARLY SATURDAY...IT QUICKLY DISSIPATES SATURDAY AS IT
MOVES INTO THE LARGE ANTICYCLONE OVER THE OHIO VALLEY. ONLY EXPECT
A PERIOD OF MID AND HIGH CLOUDS FROM IT AS THE LOW LEVELS WILL BE
QUITE DRY WITH THE HIGH PRESSURE RIDGE.
MODELS SIMILAR IN BRINGING MAIN UPPER LOW/TROUGH...CURRENTLY
OVER GULF OF ALASKA...EAST ACROSS THE CANADIAN ROCKIES AND EAST-
SOUTHEAST PRAIRIE PROVIDENCES DURING SATURDAY AND SUNDAY. THIS
TROUGH THEN PROGGED TO DROP SOUTHEAST ACROSS THE UPPER MIDWEST AND
WESTERN GREAT LAKES S ONTARIO SUNDAY NIGHT AND MONDAY.
LOW LEVEL MOISTURE WILL HAVE TIME TO ADVECT NORTHEASTWARD AS THE
SURFACE RIDGE WILL BE OVER THE ATLANTIC COAST BY SUNDAY NIGHT.
MILDER AIR ALSO TO RETURN AS FLOW BACKS AHEAD OF THIS SYSTEM SO
ANY PRECIPITATION SHOULD BE MAINLY LIQUID SUNDAY NIGHT...THOUGH
MAY MIX/CHANGE TO SNOW ON THE TAIL END AS COLUMN COOLS FOLLOWING
A COLD FRONTAL PASSAGE DURING THE NIGHT.
RETURN TO PREVAILING NORTHWEST FLOW FOR MONDAY AND TUESDAY MEANS
BACK TO COLDER TEMPERATURES THOUGH CORE OF COLD AIR WILL BE
FURTHER EAST WITH THE UPPER TROUGH AXIS OVER THE NORTHEASTERN U.S.
BACKING FLOW WEDNESDAY NIGHT AND THURSDAY ADVERTISES AT LEAST
NORM OR A BIT ABOVE NORMAL TEMPS BY MID WEEK.
TRS
&&
.AVIATION...
1200 UTC TAFS...
A LARGE HIGH OVER SASKATCHEWAN WILL MOVE INTO MISSOURI. THIS WILL
BRING COLDER AIR INTO NORTH CENTRAL...NORTHEAST ILLINOIS AND
NORTHWEST INDIANA. THIS MEANS THE WIND WILL FROM THE NORTHWEST AT
SPEEDS OF 10 TO 20 KNOTS. THERE WILL BE GUSTS OF 20 TO 30 KNOTS.
AS THIS COLD AIR MOVES SOUTH INTO NORTHERN ILLINOIS AND NORTHWEST
INDIANA VFR CEILINGS OF AROUND 3500 FEET AND SOME MVFR CEILINGS
WILL MOVE INTO NORTHERN ILLINOIS AND NORTHWEST INDIANA THIS
AFTERNOON. THERE WILL BE SOME SCATTERED SNOW FLURRIES. WE WILL ADD
A TEMPO GROUP TO THE TERMINAL FORECASTS FOR 6 MILES IN LIGHT SNOW
FOR THIS AFTERNOON. AS THE UPPER AIR DISTURBANCE MOVE EAST OF THE
THE REGION BY FRIDAY AFTERNOON. THE SKY WILL BECOME PARTLY CLOUDY.
AS THE SURFACE HIGH MOVES INTO MISSOURI BY FRIDAY MORNING THE WIND
WILL DECREASE IN SPEED AFTER MIDNIGHT.
&&
.MARINE...
329 AM CST
A LOW OVER LAKE HURON WILL MOVE EAST TO NEW YORK AND WILL BE
ABSORBED INTO A LARGER LOW CENTERED OVER NEWFOUNDLAND BY THIS
EVENING. A LARGE HIGH OVER NORTHERN SASKATCHEWAN WILL MOVE INTO
NORTH DAKOTA BY THIS EVENING. THIS HIGH WILL MOVE TO EASTERN
KANSAS AND SPREAD ACROSS THE WESTERN ONTARIO AND THE ENTIRE
MISSISSIPPI VALLEY BY FRIDAY MORNING.
THE WIND WILL HAVE NUMEROUS GUSTS TO 35 KNOTS TODAY AND
TONIGHT.THE PRESSURE GRADIENT BETWEEN THE LOW AND THE HIGH WILL
SUPPORT A WIND OF 25 TO 30 KNOTS WITH GUSTS TO 35 KNOTS. THE FETCH
OF THIS NORTH WIND AND THE WIND WILL BE AT THE 25 TO 30 KNOTS
RANGE THROUGH TODAY WILL PRODUCE LARGE WAVES OF 10 TO 14 FEET.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...LAKE EFFECT SNOW ADVISORY...INZ002...NOON THURSDAY TO 9 AM
FRIDAY.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ744-LMZ745-LMZ777-
LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 10
PM THURSDAY.
SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 6 PM
FRIDAY.
SMALL CRAFT ADVISORY...LMZ744-LMZ745...10 PM THURSDAY TO 6 PM
FRIDAY.
&&
$$
