FXUS63 KLOT 290829
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
229 AM CST SUN NOV 29 2009
.DISCUSSION...
228 AM CST
AS ANTICIPATED...INCREASING CLOUDINESS IS OVERSPREADING THE MS VLY
AND GREAT LAKES REGION AHEAD OF AN APPROACHING COLD FRONT. THIS
FRONT STRETCHED FROM CENTRAL LAKE MICHIGAN SW THRU THE MILWAUKEE
AREA TO TOPEKA KANSAS AROUND MIDNIGHT. SOUTH WINDS AHEAD OF THIS
FRONT ARE KEEPING DEWPTS IN THE 30S WITH UPR 30S PROMPTING SOME
DENSER FOG SOUTH OF I-88 THIS EARLY MORNING. THE DENSER FOG IS
PRESENTLY QUITE PATCHY WITH VISIBILITIES VARYING FROM A QUARTER
MILE TO 3 MILES IN ANY GIVEN LOCATION. TIME WILL TELL HOW
WIDESPREAD THE DENSE FOG BECOMES...AND WHETHER A DENSE FOG
ADVISORY IS NEEDED.
THE NATIONAL RADAR MOSAIC INDICATES RAIN DEVELOPMENT IS POST
FRONTAL...PHASING WITH A MID LVL TROF ADVECTING ACROSS THE PLAINS
AND INTO THE MS VLY THIS MRNG. SFC FRONTAL PASSAGE IS EXPECTED SOON
AT ROCKFORD AND NEAR SUNUP IN THE CHICAGO AREA AND BY NOONTIME
THROUGH NORTHWEST INDIANA. WITH THE APPROACH OF THE MID LVL
TROF...RAIN IS PROBABLY AT A MINIMAL CHANCE BY NOONTIME ACROSS
NORTHERN IL AND NW INDIANA...BEING RATHER LIGHT AND SHORTLIVED.
THIS IS A FAIRLY PROGRESSIVE UPR TROF AND DRYING SHUD BE
FORTHCOMING THIS EVENING AS TEMPERATURES FALL. FCST SOUNDINGS
INDICATE NO HIGH RH IN THE CRYSTAL FORMING TEMPS...SO A RAIN AND
SNOW MIXTURE IS PROBABLY NOT LIKELY AS PCPN ENDS THIS EVENING.
SFC HIGH PRESSURE BUILDING ACROSS THE PLAINS AND INTO THE MIDWEST
LATE TONIGHT AND MONDAY WILL PUSH ANTICYCLONIC FLOW OVER THE AREA
AND HELP CLEAR SKIES AS THE UPR TROF SWINGS THRU. HOWEVER A SHORT
TURNABOUT WILL CLOUD UP SKIES AGAIN FOR THE LATE AFTN AND EVENING ON
MONDAY AS ANOTHER SFC LOW WORKS EAST ACROSS SRN CANADA INTO ONTARIO.
ANY PCPN HOWEVER SHUD REMAIN NORTH OF ILLINOIS AS HIGH PRESSURE
STRETCHED ACROSS OUR SOUTH GUIDES ACTIVITY AROUND THE FORECAST AREA.
RIDGING IN FACT RETURNS THE CLEARING LATE MON NGT...RESTORING
ANTICYCLONIC FLOW TO THE FORECAST AREA. A RETURN OF SLY FLOW
ALOFT SUGGESTS THAT HIGHS TUESDAY WILL BE APPROACHING THE 50 MARK
AGAIN.
MODELS VARY A BIT MORE SIGNIFICANTLY AFTER MONDAY NIGHT THOUGH. A
TWO STREAM ENVIRONMENT TO THE NORTH AND SOUTH OF ILLINOIS GIVES
MODELS A LOT OF OPTIONS IN DEVELOPING A CONSISTENT AND...
SUBSEQUENTLY ASSUMED...AN ACCURATE SCENARIO THAT WE CAN HANG A HAT
ON.
A NORTHERN STREAM LOW MAKING LANDFALL IN THE PACIFIC NORTHWEST IS
EXPECTED TO GLIDE EAST ACROSS THE NRN CONUS TUESDAY THRU WEDNESDAY.
THE SRN STREAM EJECTS A CLOSED LOW OUT OF THE BAJA MON NIGHT AND
ACROSS TEXAS TUESDAY AND INTO THE LOWER MS VLY TUES NGT INTO
WEDNESDAY. THE TRAJECTORY OF THIS SFC LOW TO THE SOUTH WILL
DETERMINE HOW MUCH COLD AIR IS PULLED DOWN INTO ILLINOIS WHILE
WRAPPING GULF MSTR INTO THIS COLD REGIME. A MORE NORTHERLY TRACK
WILL MAKE FOR A SNOWIER FORECAST FOR ILLINOIS AND INDIANA THAN A
NORTHEAST TRACK THRU THE TN AND OHIO VALLEYS TO OUR SOUTHEAST.
CURRENT LEANINGS IN THE EXTENDED FORECAST FAVOR THE SLIGHTLY NORTHERLY
TRACK. FURTHER MODELS RUNS SHOULD RESOLVE THE INCONSISTENCIES.
RLB
&&
.AVIATION...
0600 UTC TAFS...WEAK FRONT CONTINUES TO SLOWLY MOVE ACROSS THE
AREA WITH BROAD REGION OF WEAK PRESSURE GRADIENT ALLOWING WINDS TO
GO NEARLY CALM. CALM WINDS...LONG LATE NOV NIGHT...AND ONLY SCT
CIRRUS DECK IS ALLOWING FOR VERY EFFICIENT RADIATIONAL COOLING AND
MAY ALLOW FOR SOME LIGHT FOG TO DEVELOP TONIGHT...MAINLY AT
DPA/RFD AWAY FROM THE MORE URBANIZED AREAS. HAVE RECENTLY BEGUN TO
SEE SOME LIFR STRATUS DEVELOP IN SPOTS OVER NORTHERN IOWA...WHICH
IS WHAT MODELS SUGGEST WILL BE THE BEGINNINGS OF OUR STRATUS DECK
SUNDAY. HAVE INTRODUCED LOWER CIGS EARLIER IN THE DAY BUT STILL
GOING TO ERR ON THE OPTIMISTIC SIDE WITH LOW END MVFR CIGS WHICH
IS WHAT MOS PROBABILITY TABLES SUGGEST HAVE THE HIGHEST CHANCE OF
VERIFYING DESPITE RAW MOS OUTPUT OF IFR CIGS. OVERNIGHT SHIFT WILL
BE ABLE TO MONITOR STRATUS DEVELOPMENT AND HAVE A BETTER HANDLE ON
IFR POTENTIAL WITH SUBSEQUENT TAF ISSUANCES. STILL APPEARS AS
THOUGH SOME LIGHT RAIN COULD DEVELOP AS THE WEAK SFC LOW MOVES UP
THE FRONT SUNDAY...THOUGH NOT ANTICIPATING A SIGNIFICANT PRECIP
EVENT AT THIS TIME. CIGS SHOULD CLIMB DURING THE AFTERNOON AS COLD
AIR MASS AND BOUNDARY LAYER DEEPEN CAUSING STRATUS DECK TO LIFT.
AS SFC LOW MOVES OUT LOOK FOR NW WINDS TO PICK UP DURING THE
AFTERNOON SUNDAY WITH A BIT OF GUSTINESS EXPECTED IN STRENGTHENING
COLD AIR ADVECTION REGIME.
IZZI
&&
.MARINE...
232 PM CST
A FRONT WILL MOVE THROUGH LAKE MICHIGAN TONIGHT. A LOW WILL MOVE
ACROSS WISCONSIN AND ANOTHER MAY MOVE ACROSS NORTHERN ILLINOIS.
THIS WILL BRING A WIND SHIFT FROM THE SOUTH AROUND 10 KNOTS TO THE
NORTH AND INCREASING TO 15 TO 25 KNOTS BY SUNDAY AFTERNOON. THERE
WILL BE AREAS OF RAIN. THE WAVES WILL BE 1 TO 3 FEET. A NORTH WIND
WILL BECOME SOUTHWEST DURING THE DAY MONDAY. WE EXPECT AN INCREASE
IN SPEED TO 15 TO 25 KNOTS FROM THE SOUTHWEST BY MONDAY AFTERNOON.
THIS IS IN RESPONSE TO A HIGH BUILDING OVER OKLAHOMA BY MONDAY
AFTERNOON.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
