000
FXUS63 KLOT 230556
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1256 AM CDT THU MAY 23 2013

.DISCUSSION...
307 PM CDT

SYNOPSIS...TODAY AND TOMORROW MORNING LOOK LIKE THE LAST OF THE
ACTIVE WEATHER THROUGH AT LEAST LATE THIS WEEK AS A BLOCKING PATTERN
SETS UP ALOFT. BELOW NORMAL TEMPS ARE EXPECTED TOMORROW AS THE UPPER
LEVEL TROUGH PASSES OVERHEAD...BUT TEMPS RETURN TO NEAR NORMAL FOR
MEMORIAL DAY.

TODAY THROUGH THURSDAY...
THE SURFACE LOW STRETCHES FROM NE IOWA THROUGH MICHIGAN THIS
AFTERNOON WHILE ITS COLD FRONT LIES IN WESTERN MO AND EASTERN KS.
THE LOW AND THE UPPER LEVEL TROUGH WILL CONTINUE TO WEAKEN WITH THE
LOW PASSING THROUGH NORTHERN IL TONIGHT.  FOG IS EXPECTED ACROSS THE
LAKE AND MAY MOVE ONSHORE TONIGHT AS WINDS TURN NORTHEAST.  NOT
EXPECTING THE FOG TO MOVE TOO FAR INLAND...MAYBE AN MILE OR TWO.

FOR PRECIP...THE MAJORITY OF CONVECTION HAS MOVED OUT OF THE
CWA...BUT ANOTHER ROUND OF SHOWERS AND POSSIBLY SOME THUNDER IS
POSSIBLE THIS AFTERNOON AND OVERNIGHT.  A BREAK IN THE CLOUD COVER
HAS ALLOWED SOME ISOLATED CONVECTIVE SHOWERS TO FORM MENDOTA SOUTH
THROUGH SOUTHERN IL. LOW LEVEL LAPSE RATES HAVE INCREASED TO 7
DEGREES C PER KM OR GREATER IN THE AREAS THAT HAVE SEEN THE SUN.
THEREFORE EXPECTING SCATTERED SHOWERS AND A FEW THUNDERSTORMS TO
MOVE INTO AREAS ALONG AND SOUTHEAST OF I-55 THIS AFTERNOON.
DEWPOINTS ALONG THIS LINE ARE IN THE MID TO UPPER 50S...BUT THINKING
THESE SHOWERS WILL ALSO PRODUCE BRIEF HEAVY DOWNPOURS LIKE THE
SHOWERS AND STORMS WE EXPERIENCED THIS MORNING.

ANOTHER AXIS OF RAIN WILL STRETCH FROM NORTHERN MICHIGAN THROUGH
SOUTHERN WI AND NORTHEAST IA ON THE BACKSIDE OF THE LOW.  THE LINE
OF SHOWERS WILL GRADUALLY SINK SOUTH...BUT THINKING THE RAIN WILL
NOT INFILTRATE NORTHERN IL UNTIL AFTER MIDNIGHT TONIGHT.  THE RAIN
WILL LIKELY LINGER INTO THURSDAY MORNING AND GRADUALLY EXIT TO THE
SOUTHEAST AS THE LOW MOVES OUT OF THE REGION.  CLOUDS WILL QUICKLY
ERODE WITH IT LEADING TO A MOSTLY SUNNY LATE AFTERNOON/EVENING
THURSDAY.

FOR TEMPS...MUCH COLDER AIR FUNNELS IN TONIGHT AND TOMORROW AS THE
UPPER LEVEL TROUGH PASSES OVERHEAD.  HIGH TEMPS TOMORROW WILL BE
MUCH COOLER IN THE 50S AND 60S...AND COOLER BY THE LAKE DUE TO
ONSHORE FLOW.  TEMPS THURSDAY NIGHT ARE ANOTHER CONCERN GIVEN THE
LIGHT WINDS AND CLEAR SKIES.  WENT A DEGREE OR TWO COOLER...WITH
ONSHORE FLOW KEEPING DOWNTOWN AND AREAS ALONG THE LAKE A BIT
WARMER.  PATCHY FROST IS CERTAINLY POSSIBLE LATE THURSDAY NIGHT INTO
FRIDAY MORNING...ESPECIALLY NORTH OF I-80...BUT THINKING TEMPS WILL
REMAIN ABOVE FREEZING ACROSS THE CWA.

FRIDAY AND SATURDAY...
THE BLOCKING PATTERN BEGINS TO TAKE SHAPE FRIDAY WITH A TROUGH OVER
THE NORTHWEST COAST...THE RIDGE GROWS ACROSS THE GREAT PLAINS...AND
THE TROUGH REMAINS OVER THE EAST COAST.  THE UPPER LEVEL JET IS ALSO
INCREDIBLY WEAK DURING THIS TIME FRAME...WHICH HELPS THE BLOCKING
PATTERN REMAIN IN PLACE.  AT THE SURFACE...A HIGH PRESSURE RIDGE
SINKS SOUTH OVER THE WESTERN GREAT LAKES.  THE RIDGE HELPS PUSH SOME
OF THE COOLER CANADIAN AIR OUT OF THE REGION...BUT TEMPS LOOK TO
REMAIN BELOW NORMAL THROUGH THE END OF THIS WEEK.

GUIDANCE SUGGESTS A WEAK UPPER LEVEL DISTURBANCE MAY TRAVEL AROUND
THE UPPER LEVEL RIDGE AND LEAD TO A CHANCE OF SHOWERS AND
THUNDERSTORMS SATURDAY AND SUNDAY.

EXTENDED...SUNDAY THROUGH TUESDAY...
THE BLOCKING PATTERN BEGINS TO BREAK UP SUNDAY NIGHT INTO MONDAY AS
THE EAST COAST TROUGH FINALLY BEGINS TO SHIFT NORTHEAST.  THIS
ALLOWS THE RIDGE TO OPEN WITH SHORT WAVE TROUGHS PASSING THROUGH OUR
AREA. GUIDANCE DIFFERS ON WHERE AND WHEN THESE DISTURBANCES WILL
PASS...THEREFORE WENT WITH A CHANCE OF SHOWERS AND THUNDERSTORMS
THROUGHOUT THE EXTENDED.  THE BEST DAY FOR PRECIP APPEARS TO BE
TUESDAY OR WEDNESDAY AS AN UPPER LEVEL PASSES THROUGH SOUTHERN WI.

NEXT WEEK BEGINS WITH A WARMING TREND.  NEAR NORMAL TEMPS ARE
EXPECTED FOR MEMORIAL DAY AND BACK INTO THE UPPER 70S OR LOW 80S BY
MID WEEK.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR CIGS THROUGH AROUND 12Z.

* A PERIOD OF SHOWERS 12Z-16Z WITH CIGS LIFTING TO MVFR.

* CLEARING EARLY AFTERNOON.

* NORTHEAST WINDS LESS THAN 10KT THRU 12Z...THEN N TO NNE WINDS
  INCREASING TO 20-30KT BY MID MORNING-AFTN.

ALLSOPP

//DISCUSSION...UPDATED 06Z...

AT 05Z COLD FRONT EXTENDED FROM JUST NORTH OF RFD TO MDW. AHEAD OF
FRONT WINDS WERE WEST 5-10 KT WITH MVFR CIGS 2-3K FT. BEHIND THE
FRONT WINDS WERE NORTHEAST 5-10 KT WITH CIGS DROPPING TO 3-5
HUNDRED FEET AND VSBY 3-5 MILES. LOW CIG ALREADY INTO ORD AND
SHOULD SPREAD INTO RFD...DPA...AND MDW SHORTLY. THESE CONDITIONS
SHOULD THEN PREVAIL THROUGH 12Z. THERE HAVE BEEN REPORTS OF PATCHY
DENSE FOG OVER LAKE MI BUT VSBYS OVER LAND HAVE BEEN HOLDING IN
THE 3-5 SM RANGE FOR THE MOST PART.

THERE ARE A FEW SPOTTY LIGHT SHOWERS OR SPRINKLES OVER NORTHERN IL
BUT THE MAIN AREA OF RAIN WAS STILL ALONG AND N OF AN AXIS FROM
DBQ TO MKE. THIS WILL SHIFT SOUTH AND SOUTHEAST INTO THE CHICAGO
AREA TAFS AROUND DAYBREAK. THIS AREA OF SHOWERS COMES ALONG WITH THE
PUSH OF STRONGER WINDS AND COLDER DRIER AIR. THEREFORE EXPECTING
CIGS AND VSBYS TO IMPROVE SLIGHTLY AFTER AROUND 12Z. COULD SEE
SOME BRIEF LOCAL VSBY REDUCTION IN SHOWERS DURING THE MORNING BUT
OVERALL EXPECT IMPROVING TREND THROUGH THE MORNING HOURS.

SHOWERS WILL END AND WINDS WILL RAMP UP MID TO LATE MORNING. MVFR
CIGS WILL LIFT AND SCATTER OUT QUICKLY BY EARLY AFTERNOON. WINDS
WILL PICK UP TO 20KT WITH GUSTS OF 30 KT OR MORE THROUGH
AFTERNOON. WIND DIRECTION WILL BE 360-020. WINDS WILL DROP OFF
QUICKLY AROUND SUNSET.

ALLSOPP


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CIG FCST.

* MEDIUM CONFIDENCE IN VISIBILITY FORECAST. COULD SEE VSBY DROP TO
  AROUND 3SM AT TIMES IN FOG OVERNIGHT AND AGAIN IN SHOWERS DURING
  THE MORNING.

* MEDIUM CONFIDENCE IN TIMING OF RAIN. COULD BE SOME SPOTTY
  SPRINKLES THROUGH THE OVERNIGHT BUT MAIN AREA OF RAIN IS EXPECTED
  AFTER 12Z.

* MEDIUM CONFIDENCE IN TIMING OF IFR CIG LIFTING TO MVFR THIS
  MORNING AND IN TIMING OF CLEARING THIS AFTERNOON.

* HIGH CONFIDENCE IN WIND FORECAST.

ALLSOPP

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

* FRIDAY...DRY. VFR.
* SATURDAY...SLIGHT CHANCE OF TSRA AFTERNOON/EVENING.
* SUNDAY THROUGH TUESDAY...CHANCE OF SHRA/SLIGHT CHANCE OF TSRA.

&&

.MARINE...
1250 PM CDT

SURFACE LOW WILL MOVE EAST OF THE LAKE TONIGHT WITH STRONG HIGH
PRESSURE BUILDING INTO THE REGION. TIGHT PRESSURE GRADIENT WITH
FAIRLY STRONG LATE SEASON HIGH PRESSURE WILL COMBINE WITH A HEALTHY
SURGE OF COLD AIR LOOKS LIKELY TO RESULT IN A PERIOD OF GALE FORCE
WINDS LATE TONIGHT INTO THURSDAY...PARTICULARLY ACROSS SOUTHERN
PORTIONS OF THE LAKE. WILL BE UPGRADING GALE WATCH TO A WARNING WITH
THE AFTERNOON FORECAST AND INCLUDE THE NSH IN A WARNING...WITH
EXPECTATION THAT A SMALL CRAFT ADV WILL BE NEEDED TOMORROW NIGHT
INTO FRIDAY FOR LINGERING WAVES. BEYOND THIS WIND EVENT AN EXTENDED
PERIOD OF FAIRLY BENIGN CONDITIONS EXPECTED ON THE LAKE THROUGH THE
WEEKEND WITH HIGH PRESSURE OVER THE AREA.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-
     LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-
     LMZ876-LMZ878 UNTIL 3 AM THURSDAY.

     GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...7 AM THURSDAY TO 9 PM THURSDAY.

     GALE WARNING...LMZ366-LMZ565-LMZ567-LMZ669-LMZ868-LMZ870...4 AM
     THURSDAY TO 3 PM THURSDAY.

&&

$$

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