000
FXUS63 KLOT 052345
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
545 PM CST WED JAN 5 2011
.DISCUSSION...
310 PM CST
MAIN FORECAST CONCERN ACROSS THE CWA WILL BE WITH SEVERAL CHANCES
FOR LIGHT SNOW OVER THE NEXT SEVERAL DAYS...BUT WITH NO REAL
ACCUMULATION EXPECTED FROM ANY CHANCE.
CURRENT SATELLITE IMAGERY DEPICTING FIRST OF SEVERAL MID LEVEL
WAVES MOVING ACROSS THE REGION...PROPAGATING THROUGH PORTIONS OF
NORTHERN ILLINOIS. THIS WILL CONTINUE TO SHIFT EAST ACROSS
ILLINOIS LATE THIS AFTERNOON...BUT ONLY BRINGING WITH IT SOME MID
AND HIGH LEVEL CLOUD COVER. 12Z SOUNDING OUT OF LINCOLN THIS
MORNING SHOWING SOME DRIER AIR ACROSS THE REGION WHICH WILL LIMIT
ANY PRECIP DEVELOPMENT IN THE NEAR TERM. THEN SECOND WAVE TO
AFFECT NORTHERN ILLINOIS AND NORTHWEST INDIANA...CONTINUES TO DROP
SOUTHEAST THROUGH MINNESOTA AND WISCONSIN WITH ATTENDANT SURFACE
LOW/TROUGH OBSERVED FROM NORTHERN ILLINOIS SOUTHWEST INTO
SOUTHEAST MINNESOTA. LATEST RADAR IMAGERY AND OBSERVATIONS
INDICATE THAT LIGHT TO MODERATE IS FALLING WITH SOME DECENT VIS
RESTRICTIONS AND HEAVIER SNOW CLOSER TO THE LOW.
TONIGHT...BETTER FORCING WILL CONTINUE TO BE LOCATED TO THE NORTH
CLOSER TO THE ILLINOIS/WISCONSIN BORDER WHERE LIGHT SNOW WILL
CONTINUE TO BE OBSERVED...AND WILL TAPER OFF AS YOU GO FURTHER
SOUTH. ALTHOUGH...IT WOULDNT BE OUT OF THE QUESTION FOR PORTIONS
OF THE SOUTHERN CWA TO OBSERVE A FLURRY OR TWO TONIGHT...LOW
CHANCE AT THIS TIME SO HAVE LEFT OUT OF THE FORECAST. DONT
ANTICIPATE ANY REAL ACCUMULATION AS THIS WAVE PUSHES THROUGH EARLY
TONIGHT AS FORCING WILL BE QUICK WITH MOISTURE LIMITED AND
DECREASING SIGNIFICANTLY AFTER MIDNIGHT. THEN WITH WAVE EXITING
OFF TO THE SOUTHEAST EARLY THURSDAY...LAKE EFFECT SNOW FOR THE
EASTERN HALF OF THE LAKE WILL PERSIST. ALTHOUGH BOUNDARY LAYER
FLOW WILL KEEP ANY CHANCE OF THIS TO THE EAST OF THE CWA.
THEN A THIRD WAVE DROPS SOUTHEAST OUT OF MINNESOTA AND IOWA
THURSDAY MORNING BRINGING WITH IT ANOTHER CHANCE OF LIGHT SNOW.
ALTHOUGH THIS WILL BE JUST A SLIGHT CHANCE AS OVERALL MOISTURE
WILL REMAIN LIMITED. DID KEEP A SLIGHT CHANCE AS THIS WAVE WHICH
WILL MOVE THROUGH WILL BE A FAIRLY DECENT WAVE. SO THINK THAT
EITHER FLURRIES OR LIGHT SNOW WILL BE ABLE TO BE SQUEEZED
OUT...BUT WITH ONCE AGAIN NO REAL ACCUMULATION EXPECTED.
IT APPEARS AS IF WE WILL REMAIN IN A SIMILAR UPPER LEVEL PATTERN
OVER THE NEXT SEVERAL DAYS WITH SEVERAL SHORT WAVE TROUGHS TO
CONTINUE TO TRAVERSE THE REGION. CURRENT UPPER LEVEL LOW ACROSS
SOUTHEASTERN QUEBEC WILL SLOWLY RETROGRADE BACK TO THE WEST
THURSDAY REACHING ONTARIO THURSDAY NIGHT AS IT PHASES WITH ANOTHER
WAVE MOVING FROM THE NORTHWEST...AND THEN WILL CONTINUE WEST OVER
THE UPPER MIDWEST/CENTRAL GREAT LAKES REGION BY LATE FRIDAY. THE
REGION WILL REMAIN UNDER ITS INFLUENCE THROUGH THE WEEKEND UNTIL
THIS UPPER LEVEL LOW BEGINS TO BREAK DOWN WITH OVERALL UPPER LEVEL
FLOW BECOMING MORE WEAK/DIFFUSE BY MONDAY. THIS CYCLONIC FLOW WILL
BRING YET AGAIN MORE CHANCES FOR FLURRIES OR LIGHT SNOW FRIDAY
INTO SATURDAY. THEN IT LOOKS AS IF LAKE EFFECT REALLY GETS RAMPING
UP LATE SATURDAY INTO SUNDAY FOR PORTIONS OF FAR NORTHEAST
ILLINOIS AND NORTHWEST INDIANA.
RODRIGUEZ
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 00Z...
* TIMING OF THE COLD FRONTAL PASSAGE LATER THIS EVENING.
* POTENTIAL FOR GUSTY NORTHWEST WINDS BEHIND THE FRONT.
* THE POTENTIAL FOR LOW MVFR CIGS AFTER 06 UTC TONIGHT.
KJB
//DISCUSSION...UPDATED 00Z...
...MAIN CONCERNS THIS EVENING ARE TIMING THE WIND SHIFT ASSOCIATED
WITH A COLD FRONTAL PASSAGE LATER THIS EVENING...AS WELL AS THE
POTENTIAL FOR LOW MVFR CIGS AFTER MIDNIGHT TONIGHT...
AN AREA OF LOW PRESSURE ACROSS THE UPPER PENINSULA OF MICHIGAN WILL
PUSH A COLD FRONT ACROSS NORTHERN ILLINOIS AFTER 10 PM TONIGHT.
CURRENTLY IT APPEARS THE FRONT WILL PASS THROUGH KRFD BETWEEN 10 AND
11 PM THIS EVENING...AND ACROSS KORD...KMDW...KDPA AND KGYY BETWEEN
11 PM AND 1 AM TONIGHT. AHEAD OF THIS FRONT SOUTH WINDS WILL
GRADUALLY VEER TO THE WEST THROUGH THE EVENING. FOLLOWING THE
FRONTAL PASSAGE...WINDS WILL BECOME GUSTY OUT OF THE NORTHWEST.
THESE GUSTY NORTHWEST WINDS WILL CONTINUE ON THURSDAY.
THE OTHER CONCERN IS FOR LOW MVFR CIGS MOVING ACROSS THE AREA
TONIGHT IN THE WAKE OF THE FRONT. CURRENT OBSERVATIONS ACROSS
SOUTHERN MN AND IA HAVE SHOWN CIGS DROP RAPIDLY TO BETWEEN 1,500
AND 2,000 FT AGL BEHIND THE FRONT. CURRENT FORECAST GUIDANCE
INDICATES THAT THESE CIGS WILL MOVE ACROSS NORTHERN IL AFTER
MIDNIGHT TONIGHT AND COULD CONTINUE THROUGH MID-MORNING ON
THURSDAY BEFORE CIGS LIFT ABOVE 3,000 FT. IN SPITE OF THIS...I
HAVE DECIDED TO GO WITH 2,000 FT PREVAILING FROM 06 UTC THROUGH
15 UTC DUE TO UNCERTAINTY ON HOW LOW THE CLOUDS WILL BE LATER
TONIGHT AS THEY MOVE FARTHER SOUTH AND EAST. THE POTENTIAL IS
THERE TO SEE CIGS DROP BELOW 2,000 FT. I WILL CONTINUE TO MONITOR
THIS AS THE FRONT APPROACHES THIS EVENING.
A LESSER CONCERN IS THE POTENTIAL FOR SNOW THIS EVENING. CURRENT
RADAR SHOWS WEAK RETURNS ACROSS THE AREA...BUT NOT MANY PLACES ARE
REPORTING ANY SNOW UNTIL YOU GET INTO SOUTHERN WI. I WOULD NOT BE
SURPRISED TO SEE A BRIEF PERIOD OF VERY LIGHT SNOW EARLY THIS
EVENING. HOWEVER...RAPID DRYING ALOFT WILL END THE CHANCES LATER
THIS EVENING.
KJB
//ORD AND MDW CONFIDENCE...UPDATED 00Z...
* MEDIUM CONFIDENCE ON TIMING OF FRONTAL PASSAGE.
* MEDIUM CONFIDENCE THAT MVFR CIGS OF 2,000 FT AGL WILL DEVELOP AFTER
06 UTC.
* LOW CONFIDENCE THAT CIGS WILL DROP BELOW 2,000 AGL TONIGHT.
* HIGH CONFIDENCE ON GUSTY NORTHWEST WINDS LATE TONIGHT AND ON
THURSDAY.
KJB
//OUTLOOK FOR ORD/MDW FOR 06Z FRIDAY-12Z TUESDAY...UPDATED 18Z...
THURSDAY NIGHT...CHANCE OF LIGHT SNOW/FLURRIES. MVFR POSSIBLE.
FRIDAY...CHANCE OF LIGHT SNOW/FLURRIES. MVFR POSSIBLE.
SATURDAY...VFR.
SUNDAY...VFR.
MONDAY...CHANCE OF SNOW.
TUESDAY...VFR.
PAW
&&
.MARINE...
208 PM...PERSISTENT NORTH/NORTHWEST FLOW IS EXPECTED ACROSS THE
WESTERN LAKES INTO THIS WEEKEND WITH PERIODS OF WINDS TO 30 KTS
LIKELY. LOW PRESSURE OVER WESTERN LAKE SUPERIOR WILL SLOWLY MOVE
EAST TO GEORGIAN BAY BY THURSDAY EVENING. A COLD FRONT WILL MOVE
ACROSS THE LAKE TONIGHT SWITCHING WINDS TO NORTHWEST. AS THE
GRADIENT TIGHTENS AND COLDER AIR SPREADS ACROSS THE REGION...
WINDS EXPECTED TO INCREASE TO 30 KTS BY THURSDAY MORNING. WINDS
SLOWLY DIMINISH THURSDAY NIGHT INTO FRIDAY AND SHIFT BACK WESTERLY
AS A SECOND AREA OF LOW PRESSURE MOVES SOUTH FROM JAMES BAY TO
LAKE SUPERIOR FRIDAY. THIS LOW WILL WEAKEN BUT SLOWLY MOVE
SOUTHEAST ACROSS THE EASTERN LAKES FRIDAY NIGHT INTO SATURDAY
BEFORE BEING ABSORBED BY STRONG LOW PRESSURE OFF THE ATLANTIC
COAST. THE GRADIENT IS EXPECTED TO TIGHTEN AGAIN FRIDAY NIGHT INTO
SATURDAY WITH ANOTHER PUSH OF COLD AIR WITH WINDS ONCE AGAIN
INCREASING TO 30 KTS...MAINLY OVER SOUTHERN LAKE MICHIGAN. HIGH
PRESSURE WILL MOVE SOUTHEAST ACROSS SOUTHERN CANADA AND THE
NORTHERN PLAINS SATURDAY AND THEN ACROSS THE WESTERN LAKES SUNDAY
INTO MONDAY.
BY THURSDAY NIGHT...THE STRONG WINDS COMBINED WITH THE COLDER
TEMPS WILL LIKELY LEAD TO THE POTENTIAL FOR FREEZING SPRAY AND
THIS POTENTIAL WILL CONTINUE THRU AT LEAST SATURDAY UNTIL WIND
SPEEDS BEGIN TO DIMINISH. ALSO WILL BE HOISTING A SMALL CRAFT
ADVISORY THRU SUNDAY MORNING FOR THE ILLINOIS AND INDIANA
NEARSHORE WATERS. WELL BEYOND THE 48 HR NEARSHORE FORECAST...BUT
CRITERIA EXPECTED DURING THIS ENTIRE TIME. END TIME WILL BE
DEPENDENT ON HOW FAST WAVE ACTION SUBSIDES WHICH MAY BE DEPENDENT
ON HOW MUCH ICE FORMS/MOVES AROUND IN THE NEARSHORE WATERS. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...MIDNIGHT THURSDAY TO 9 AM SUNDAY.
&&
$$
