Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 260558
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1258 AM CDT THU MAR 26 2015

.UPDATE...843 PM CDT

GOING FORECAST IN GOOD SHAPE CAPTURING LIGHT RAIN COVERAGE AND
TEMPERATURES. THE LIGHT RAIN SHIELD FROM OVERRUNNING HAS BEEN
MAINLY CONFINED TO SOUTH OF A PONTIAC TO VALPARAISO LINE...WITH
ONLY SPOTTY SPRINKLES NORTH OF THERE. WHILE THIS MAY INCH SLIGHTLY
NORTHWARD DO NOT FORESEE IT MUCH FURTHER AT ALL GIVEN AMPLE
CONVECTION TO THE SOUTH ZAPPING MOISTURE TRANSPORT AS WELL AS
LESS DEEP LAYER MOISTURE FURTHER NORTH.

HAVE MADE MINOR TWEAKS TO SKY COVER WITH TEMPORARY CLEARING IN
THE NORTH CHICAGO METRO...THOUGH VARIABLE CLOUDINESS IS LIKELY TO
FILL BACK IN THROUGH THE REST OF THE NIGHT.

MTF

&&

.SHORT TERM...
228 PM CDT

THROUGH THURSDAY EVENING...

MAIN CONCERN IN THE NEAR TERM WILL BE ANOTHER ROUND OF RAIN
OVERSPREADING SOUTHERN PORTIONS OF THE FORECAST AREA...WITH THE
BEST CHANCES APPEARING ALONG AND SOUTH OF A OTTAWA TO GARY LINE.
THIS AFTERNOON...ONE SURFACE LOW IS ANALYZED OVER LAKE SUPERIOR
WITH A COLD FRONT STRETCHING SOUTH ALONG THE MISSISSIPPI RIVER
VALLEY. MEANWHILE...ANOTHER LOW IS LOCATED NEAR THE TEXAS
PANHANDLE WITH TROUGHING EXTENDING EAST INTO THE MID MISSISSIPPI
VALLEY. WATER VAPOR IMAGERY SHOWS A SHORTWAVE TROUGH OVER SE
WY/NRN CO AND IS PROGGED TO MOVE ACROSS THE CENTRAL PLAINS TONIGHT
WITH A WEAK STABLE WAVE DEVELOPING ALONG THE TROUGH OVER THE MID
MISSISSIPPI VALLEY. AS THIS OCCURS...F-GEN WILL INCREASE NORTH OF
THE SURFACE WAVE WITH PRECIP SPREADING NORTH ACROSS CENTRAL
ILLINOIS LATE THIS EVENING INTO THE EARLY OVERNIGHT HOURS. EXPECT
A SHARP CUTOFF OF PRECIP ON THE NORTH SIDE OF THIS SYSTEM WITH
MUCH OF THE NORTHERN HALF OF THE CWA EXPECTED TO REMAIN DRY
OVERNIGHT. EVEN IN AREAS WITH THE STRONGEST F-GEN...DRY AIR IS
NOTED BELOW 700MB AND WILL TAKE SOME TIME TO SATURATE...SO INITIAL
RADAR RETURNS WILL LIKELY ONLY BE VIRGA AS THE COLUMN SATURATES
TOP-DOWN. PRECIPITATION SHOULD CLEAR THE FORECAST AREA BY AROUND
DAYBREAK THURSDAY WITH ATTENTION TURNING TO TEMPERATURES. COLD
ADVECTION WILL DRIVE 850MB TEMPS FROM AROUND 5C TODAY TO AROUND
-7C BY MID AFTERNOON THURSDAY. COLD ADVECTION WILL RESULT IN STEEP
LAPSE RATES...SO AS MID-HIGH CLOUDS EXIT TO OUR EAST...EXPECT COLD
AIR STRATOCUMULUS TO FILL IN IMMEDIATELY BEHIND RESULTING IN
MOSTLY CLOUDY CONDITIONS THROUGH THE DAY. MIXING DOWN TEMPS FROM
AROUND 900MB RESULTS IN HIGH TEMPS IN THE LOW 40S TOMORROW.

DEUBELBEISS

&&

.LONG TERM...
228 PM CDT

THURSDAY NIGHT THROUGH WEDNESDAY

AN ELONGATED UPPER LEVEL TROUGH WILL EXTEND FROM NORTHERN QUEBEC
THROUGH TEXAS THURSDAY EVENING.  THE TROUGH WILL SLOWLY SHIFT EAST
WITH THE TROUGH AXIS MOVING THROUGH THE REGION FRIDAY MORNING.  HIGH
PRESSURE WILL ALSO BE CENTERED OVER SOUTH CENTRAL CANADA AND DRIFT
SOUTHEAST. WINDS BECOME NORTH TO NORTHEAST RESULTING IN A FAVORABLE
FETCH FOR LAKE EFFECT PRECIP.  NOT OVERLY IMPRESSED WITH THE LAKE
EFFECT PARAMETERS FOR THE IL SIDE OF THE LAKE THURSDAY EVENING SO
CAPPED POPS IN THE SLIGHT CHANCE RANGE.  FORECAST SOUNDINGS FEATURE
A BIT OF LLWS THAT WILL PROBABLY LEAD TO MULTI-BANDED LAKE EFFECT.
PRECIP COULD BEGIN TO FALL AS A RAIN/SNOW MIX AS SFC TEMPS WILL BE A
BIT ABOVE FREEZING AND WE WILL NOT BE SATURATED IN THE DGZ.  HOWEVER
EXPECTING SATURATION TO QUICKLY OCCUR AND TURN THE PRECIP OVER TO
SNOW.

WINDS BECOME DUE NORTH AFTER MIDNIGHT THURSDAY NIGHT LEADING TO A
BETTER CHANCE FOR LAKE EFFECT SNOW OVER NORTHWEST
INDIANA...ESPECIALLY FRIDAY MORNING. WIND SHEAR REDUCES SO LIKING
OUR LOCAL ARW/S SOLUTION OF A SINGLE BAND OVER NORTHWEST INDIANA.
IT/S STILL A BIT FAR OUT TO IDENTIFY EXACTLY WHERE THE BAND WILL SET
UP SO HAVE A BROAD AREA OF CHANCE POPS LATE THURSDAY NIGHT INTO
FRIDAY MORNING. FOR SNOW TOTALS...WENT A BIT LOWER THAN PREVIOUSLY
FORECAST FOR THE IL SIDE WITH TOTALS LESS THAN A HALF INCH.  FOR NW
INDIANA...EXPECTING AROUND AN INCH OF NEW SNOW WITH LOCALLY HIGHER
TOTALS IF A STRONG BAND OF SNOW FORMS.  EXPECTING LAKE EFFECT SNOW
TO DIMINISH IN THE EARLY AFTERNOON AS WE LOSE FORCING BUT SCATTERED
FLURRIES COULD HANG AROUND ALL AFTERNOON.

A SURFACE HIGH MOVES OVER THE REGION FRIDAY EVENING.  WINDS DIMINISH
AND SKIES CLEAR UNDER THE HIGH AND EXPECTING LOW TEMPS FRIDAY NIGHT
TO BE IN THE TEENS...EXCEPT FOR AROUND 20 DOWNTOWN.  TEMPS COULD
CERTAINLY BE A BIT COOLER IF THE SURFACE IS ABLE TO DECOUPLE.  THE
WARM UP BEGINS SATURDAY WITH DRY CONDITIONS AND HIGHS IN THE 30S.
LOCATIONS ALONG AND WEST OF I-39 MAY REACH 40.

THE HIGH CONTINUES SOUTHEAST WITH THE NEXT LOW PASSING OVER SOUTHERN
ONTARIO SUNDAY.  AN UPPER LEVEL SHORTWAVE ALSO SCOOTS THROUGH THE
REGION SUNDAY AFTERNOON.  EXPECTING GUSTY SOUTHWEST WINDS SUNDAY
WITH MAX GUSTS ARND 35 MPH. AMPLE WAA WILL RESULT IN HIGH TEMPS IN
THE MID TO UPPER 40S. THE LOWS COLD FRONT SWINGS THROUGH SUNDAY
AFTERNOON AND EVENING WITH RAIN EXPECTED AHEAD OF AND ALONG THE
FRONT.  FORECAST SOUNDINGS DO NOT FEATURE ANY INSTABILITY...SO KEPT
THUNDERSTORMS OUT OF THE FORECAST.

THE MAJORITY OF COOLER AIR ASSOCIATED WITH THE LOW STAYS TO OUR
NORTH ALLOWING US TO REMAIN AT OR ABOVE NORMAL MONDAY WITH HIGHS IN
THE 50S. THE ECMWF FEATURES AN UPPER LEVEL WAVE WITH PRECIP MOVING
THROUGH MONDAY...BUT IT SEEMS TO BE AN OUTLIER SO KEPT RAIN OUT OF
THE FORECAST FOR EARLY NEXT WEEK.  AN UPPER LEVEL RIDGE MOVES
OVERHEAD TUESDAY LEADING TO HIGH TEMPS IN THE 60S.

JEE

&&

.AVIATION...

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

* MAINLY VFR CIGS THRU OVERNIGHT.

* NORTHWEST WINDS TURNING NORTH AND GUSTING TO 20KT BY MID-
  MORNING.

* POSSIBLE LAKE EFFECT RAIN/SNOW SHOWERS BECOMING ALL SNOW LATE
  THIS EVENING.

BEACHLER

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

IR IMAGERY EARLY THIS MORNING SHOWS THE BULK OF THE STRATUS CLOUDS
SOUTH OF THE TAF SITES...AND WITH THE FLOW TURNING NORTHWESTERLY
THIS SHOULD HELP TO KEEP THE STRATUS SOUTH OF THE TAF SITES
OVERNIGHT. WINDS WILL SLOWLY TURN NORTHERLY BY MID-MORNING WITH
GUSTS DEVELOPING TO 20KT. CLOUDS MAY BRIEFLY THIN FURTHER LATER
THIS MORNING...HOWEVER WITH COOLER AIR WORKING BACK INTO THE
REGION...STRATUS LAKE CLOUDS MAY DEVELOP AND ALSO PRODUCE SOME
LIGHT RAIN/SNOW LATE AFTN. TEMPS WILL COOL INTO THE LOW 30S LATER
THIS EVENING AND MAY TRANSITION THE PRECIP OVER TO ALL SNOW...WITH
ONLY MINOR REDUCTIONS. GIVEN THE CONFIDENCE IS LOW...WILL HOLD OFF
AT THIS TIME ON MENTIONING THIS WITHIN THE CURRENT TAF BUT WILL
MAINTAIN THE STRATUS CLOUDS AND POSSIBLE MVFR CIGS DEVELOPING.

BEACHLER


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

* HIGH CONFIDENCE IN WIND DIR/SPEED...MEDIUM CONFIDENCE IN
  DURATION OF GUSTS MID-MORNING THROUGH MID-AFTERNOON.

* HIGH CONFIDENCE IN CIGS REMAINING VFR THRU 20Z...MEDIUM
  CONFIDENCE IN MVFR CIGS DEVELOPING AFT 00Z WITH PRECIP.

* MEDIUM CONFIDENCE IN PRECIP TIMING.

BEACHLER

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

FRIDAY...VFR. BREEZY NORTH WINDS TURNING NORTHEAST THROUGH THE
AFTERNOON.

SATURDAY...VFR. LIGHT NORTHEAST WINDS TURNING SOUTHEAST.

SUNDAY...CHANCE RAIN THROUGH THE DAY...POSSIBLY MIXING WITH SNOW
EARLY. MVFR CIGS/VIS POSSIBLE. GUSTY SOUTHWEST WINDS.

MONDAY...VFR. WEST WINDS.

TUESDAY...VFR. SOUTHWEST WINDS.

MDB

&&

.MARINE...
228 PM CDT

MODERATE WEST TO SOUTHWEST WINDS ARE IN PLACE TODAY AHEAD OF AN
APPROACHING COLD FRONT WHICH WILL SWEEP ACROSS LAKE MICHIGAN
TONIGHT. WINDS TURN NORTHWEST THEN NORTH TOMORROW WITH 30 KTS
EXPECTED TO SPREAD DOWN THE LAKE BY TOMORROW EVENING. WINDS
GRADUALLY DIMINISH FRIDAY AND FRIDAY NIGHT AS HIGH PRESSURE BUILDS
OVER LAKE MICHIGAN BY SATURDAY MORNING...THEN WINDS TURN BACK TO THE
SOUTH/SOUTHWEST AGAIN BY LATER SATURDAY. ANOTHER COLD FRONT IS
PROGGED TO SWEEP ACROSS LAKE MICHIGAN SUNDAY NIGHT. A PERIOD OF
SOUTHWEST GALES APPEARS POSSIBLE AHEAD OF THE FRONT STARTING EARLY
SUNDAY MORNING...THEN NORTHWEST GALES ARE POSSIBLE BEHIND THE FRONT
SUNDAY NIGHT...EASING MONDAY MORNING.

BMD

&&

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

$$

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