Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 150858
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 AM CDT MON SEP 15 2014

.DISCUSSION...
311 AM CDT

DISMAL AND SHOWERY WEATHER ON TAP TODAY FOLLOWED BY PRETTY
SPECTACULAR WEATHER THE REMAINDER OF THE WEEK.

FAIRLY ENERGETIC SHORTWAVE TROUGH OVER THE DAKOTAS THIS MORNING
WILL DIG SOUTHEASTWARD INTO THE LOWER LAKES LATER TODAY BEFORE
SHIFTING EAST OF THE REGION TONIGHT. LOW-MID LEVEL FRONTOGENESIS IN
THE RIGHT ENTRANCE REGION OF 100KT+ 250MB JET IS ALREADY SUPPORTING
A BAND OF RAIN FROM EASTERN SD EAST INTO CENTRAL WISCONSIN. IN
ADDITION...SECOND AREA OF SHOWERS AND THUNDERSTORMS DEVELOPING OVER
IOWA IN ASSOCIATED WITH STRENGTHENING LOW LEVEL JET/WAA. THESE TWO
REGIONS OF PRECIP ARE LIKELY TO CONGEAL AND SPREAD ACROSS OUR CWA
LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON. SOME WEAK
ELEVATED INSTABILITY COULD SUPPORT AN ISOLATED THUNDERSTORM SOUTH
BUT CHANCES AND AREAL COVERAGE OF THUNDER APPEAR LOW. AS TROUGH AXIS
TRANSLATE QUICKLY EASTWARD LOOK FOR RAIN/SHOWERS TO END...POSSIBLY
AS A PERIOD OF DRIZZLE LATER THIS AFTERNOON. TEMPS ARE TRICKY AND
WILL HINGE ON HOW MUCH THEY CAN RISE BEFORE RAIN STARTS AND THEY
LOSE A LITTLE GROUND THIS AFTERNOON.

STRONG SUBSIDENCE AND DRYING ARE FORECAST IN THE WAKE OF THE TROUGH
WHICH SHOULD LEAD TO RAPID CLEARING THIS EVENING WITH ANOTHER FAIRLY
HEALTHY PUSH OF EARLY SEASON COLD AIR ARRIVING TONIGHT. ONCE AGAIN
LOOKING FOR LOWS TO DROP INTO THE 30S OVER WESTERN PORTIONS OF THE
CWA...PARTICULARLY THE TYPICALLY FAVORED COOL SPOTS. CANT RULE OUT A
TOUCH OF FROST IN THE SHELTERED COOL SPOTS...ESPECIALLY ON ELEVATED
OBJECTS...BUT NOT EXPECTED TO BE A BIG ENOUGH DEAL TO INCLUDE IN
GRIDS.

TUESDAY LOOKS TO BE SUNNY AND UNSEASONABLY COOL...BUT NOT AS CHILLY
AS LAST WEEK. A SLOW BUT STEADY WARMING TREND WILL COMMENCE
WEDNESDAY AND CONTINUE INTO THE WEEKEND WITH HIGHS EVENTUALLY
REBOUNDING BACK TOWARD IF NOT A BIT ABOVE AVERAGE TOWARD THE
WEEKEND. NO RAIN IS EXPECTED THROUGH FRIDAY WITH PLENTY OF SUNSHINE
AND ALL AROUND PLEASANT WEATHER. MEDIUM RANGE MODELS DO SUGGEST
PATTERN COULD TURN POTENTIALLY STORMIER NEXT WEEKEND AS FLOW
FLATTENS OUT A BIT AND WARM AIR ADVECTION STRENGTHENS IN ADVANCE OF
TROUGH DIGGING INTO THE NORTHERN/CENTRAL PLAINS. STILL SOME
DISAGREEMENT IN THE DETAILS...NOT SURPRISINGLY THIS FAR OUT...SO
KEPT POPS MODEST FOR NOW UNTIL DETAILS CAN BE BETTER PINNED DOWN IN
THE COMING DAYS.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* COLD FRONT MIDDAY MONDAY BRINGING A WIND SHIFT TO THE NW OR NNE
  ALONG WITH MVFR POSSIBLY BRIEFLY IFR CONDITIONS AND RAIN.

BMD

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

OVERNIGHT THROUGH AROUND MID MORNING MONDAY EXPECT STEADY STATE
CONDITIONS WITH VERY LIGHT SSW FLOW AND VFR CONDITIONS. AN UPPER
LEVEL WAVE WILL MOVE ACROSS THE REGION MONDAY BRINGING SHOWERS TO
THE AREA BY LATE MORNING OR EARLY AFTERNOON. CIGS ARE EXPECTED TO
LOWER TO AT LEAST MVFR AND SOME MODELS SUGGEST THE POSSIBILITY OF A
COUPLE HOURS OF IFR CIGS AS THE SURFACE TROUGH DROPS ACROSS THE
AREA. CIGS ARE EXPECTED TO QUICKLY SCATTER OUT THOUGH EARLY TO MID
EVENING BEHIND THE FRONT. WINDS WILL BE TRICKY DURING THE DAY
MONDAY. WINDS ARE EXPECTED TO SHIFT TO SOME SORT OF NORTHERLY
COMPONENT BUT NOT QUITE SURE AT THIS POINT IF IT WILL BE NW OR NNE
AT THE CHICAGO TERMINALS WHERE SOME GUIDANCE SHOWS THE FRONT SURGING
AHEAD AND TURNING WINDS NNE OFF OF LAKE MICHIGAN. GIVEN THE RELATIVE
WARMTH OF THE LAKE RELATIVE TO THE AIRMASS...WILL LEAN AWAY FROM
THIS SOLUTION IN THE MEANTIME...BUT IF WINDS DO END UP TURNING MORE
NNE IT WOULD LIKELY BE DURING THE AFTERNOON...THEN WINDS SHOULD
EVENTUALLY SETTLE BACK TOWARDS THE NW LATER IN THE EVENING.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* LOW CONFIDENCE IN WIND DIRECTION POST FRONTAL MONDAY AFTERNOON.
  GUIDANCE RANGES FROM NW TO NNE.
* MEDIUM CONFIDENCE IN MVFR CONDITIONS AND RAIN...LOW CONFIDENCE
  IN IFR.

BMD

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. NORTHWEST WINDS BECOMING WEST.

WEDNESDAY...VFR. WEST WINDS BECOMING NORTHEAST.

THURSDAY...VFR. EAST WINDS.

FRIDAY...VFR. SOUTHEAST WINDS.

SATURDAY...VFR. BREEZY SOUTH-SOUTHWEST WINDS. CHANCE OF
THUNDERSTORMS.

MDB

&&

.MARINE...
303 AM CDT

LOW PRESSURE NEAR JAMES BAY THIS MORNING WILL DRAG A COLD FRONT
ACROSS LAKE MICHIGAN. WINDS WILL TURN NORTHWEST TO NORTH BEHIND THE
FRONT...AND MAY BRIEFLY INCREASE INTO THE 20 TO 25 KT RANGE
ESPECIALLY ON THE SOUTH END OF THE LAKE THIS EVENING. HIGH PRESSURE
WILL BUILD IN BEHIND THE FRONT ALLOWING WINDS TO REMAIN MODEST FOR A
PERIOD BEFORE SOUTHWEST FLOW BEGINS TO FRESHEN UP AGAIN OVER THE
NORTH HALF OF LAKE MICHIGAN MIDDAY TUESDAY. ANOTHER COLD FRONT WILL
DIVE SOUTH ACROSS LAKE MICHIGAN ON WEDNESDAY TURNING WINDS NORTH TO
NORTHEAST AND INCREASING FOR A SHORT PERIOD TO AROUND 30 KT ONCE
AGAIN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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