Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 282141
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
341 PM CST WED JAN 28 2015

.SHORT TERM...
340 PM CST

THROUGH FRIDAY...

MAIN FORECAST CONCERNS ARE WITH PRECIP POTENTIAL AND TEMP TRENDS
TONIGHT...LINGERING LAKE EFFECT SNOW SHOWERS THURSDAY INTO EARLY
FRIDAY...AND POSSIBLE ACCUMULATING SNOW THIS WEEKEND.

RELATIVELY QUIET CONDITIONS THIS AFTERNOON...WITH INCREASING
MID/HIGH LEVEL CLOUD COVER OUT AHEAD OF APPROACHING SYSTEM OVER
THE CENTRAL PLAINS. SURFACE LOW OVER EASTERN NEBRASKA WILL
CONTINUE TO SHIFT EAST TOWARDS THE AREA THIS EVENING AS MID/UPPER
LEVEL TROUGH SWING EAST THROUGH THE CENTRAL CONUS. AS THIS
OCCURS...STRONG ISENTROPIC ASCENT OUT AHEAD OF IT WILL GRADUALLY
SHIFT EAST ACROSS THE CWA LATER THIS EVENING. INITIAL DRY
CONDITIONS IN PLACE WILL NEED TO BE OVERCOME THIS EVENING BUT
INCREASING ASCENT THIS EVENING SHOULD ALLOW FOR THE COLUMN TO
SATURATE...WITH DEVELOPING PRECIP TO THEN SPREAD OVER THE REGION.
GUIDANCE DOES VARY WITH REGARDS TO WHEN THE DRIER AIR WILL BE
OVERCOME...WITH SOME INDICATING THIS WILL OCCUR AS EARLY AS THIS
EVENING AND WITH OTHERS POINTING AT THE DEVELOPMENT AFTER THE
MIDNIGHT TIME FRAME. HAVE TRENDED TOWARDS THE PREVIOUS FORECAST
WITH THE POSSIBILITY OF PRECIP DEVELOPING BY MID TO LATE
EVENING...STRAYING AWAY FROM THE DRIER GUIDANCE. PERSISTENT
FORCING THROUGH THIS EVENING SHOULD ALLOW FOR AT LEAST LIGHT
DEVELOPMENT ACROSS A GOOD PORTION OF THE CWA. RAIN DOES APPEAR TO
BE THE PREDOMINANT PRECIP TYPE OVERNIGHT TONIGHT AS STRONG WARM
ADVECTION OUT AHEAD OF THIS SYSTEM OCCURS...AND ESPECIALLY AS
SOUTHERLY FLOW CONTINUES TO RAMP UP AHEAD OF THE SURFACE LOW.
HOWEVER...DO ANTICIPATE FOR SOME SLIGHT COOLING OF THE CURRENT MID
30 TEMPS LATE THIS AFTERNOON INTO THE EARLY EVENING BEFORE A
STEADY TEMP RISE IS OBSERVED FOR ALL AREAS. IF THE PRECIP WERE TO
OCCUR SLIGHTLY EARLIER THAN CURRENT THINKING...THEN A BETTER
CHANCE FOR LIGHT FREEZING RAIN COULD OCCUR. THIS TIME FRAME WOULD
BE IN THE 1-4Z PERIOD WHERE LOW TEMPS IN THE LOW 30S WILL BE
OBSERVED...BEFORE A RISE TO THE MID TO UPPER 30S WILL OCCUR. THIS
TEMP RISE SHOULD LIMIT ANY FREEZING RAIN POTENTIAL TO A SMALL
SEVERAL HOUR WINDOW...WITH ONCE AGAIN RAIN THEN EXPECTED EVEN INTO
EARLY THURSDAY MORNING.

EXPECT BEST DEVELOPMENT TO OCCUR MORE TOWARDS EARLY THURSDAY
MORNING INTO MID MORNING AS SURFACE LOW AND SURFACE BOUNDARIES
PUSH THROUGH...WITH THE RAIN BECOMING ALL SNOW THROUGH MID TO LATE
MORNING. PRECIP SHIELD SHOULD BE EXITING DURING THIS TRANSITION
WITH ANY SNOW ACCUMULATION EXPECTED TO NO MORE THAN A COUPLE OF
TENTHS OF AN INCH. LIGHT SNOW COULD LINGER INTO NORTHWEST INDIANA
AS LAKE EFFECT POTENTIAL INCREASES...BUT BETTER FOCUS WILL
INITIALLY BE FURTHER TO THE EAST. AS COLDER AIR SPILLS SOUTH AND
BOUNDARY LAYER FLOW SHIFTS...FOCUS FOR BETTER LAKE EFFECT SNOW
DEVELOPMENT WILL MOVE INTO THE CWA...WITH THE PORTER COUNTY AREA
WITHIN THE CWA LIKELY OBSERVING THIS BEST DEVELOPMENT. BUILDING
HIGH PRESSURE WITH BACKING LOW LEVEL FLOW WILL GRADUALLY HELP THIS
SNOW TO DIMINISH WHILE SHIFTING EAST THROUGHOUT THE DAY ON FRIDAY.

RODRIGUEZ

&&

.LONG TERM...
340 PM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

MAIN CONCERN TO START THE PERIOD WILL BE FOR THE POTENTIAL FOR
ACCUMULATING SNOW SATURDAY NIGHT INTO SUNDAY. THERE STILL APPEARS
TO BE THE POTENTIAL FOR SNOW DURING THIS PERIOD...BUT WITH
CONFIDENCE OF THIS POTENTIAL FOR THE CWA LOWERING TODAY. PREVIOUS
CONSISTENCY AMONG VARYING GUIDANCE IS NOT PRESENT TODAY...WITH
GUIDANCE RANGING FROM LIGHT ACCUMULATIONS TO VERY LITTLE TO NONE.
AM NOT TOTALLY CONVINCED IN THE SHIFT WITH THE STORM TRACK AND
POTENTIAL PRECIP ADVERTISED TODAY AND DID NOT CHANGE POPS TOO MUCH
DURING THIS PERIOD...AS GUIDANCE COULD SHIFT BACK ONCE AGAIN.
WOULD LIKE TO SEE CONSISTENCY OF THIS POTENTIAL BEFORE POPS ARE
LOWERED. CURRENTLY HAVE THE HIGHEST POPS FOR THE SOUTHERN HALF OF
THE CWA...WITH A MORE FAVORED SOUTHERLY TRACK OF THIS SYSTEM.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY SOUTH-SOUTHEAST SURFACE WINDS THIS AFTERNOON...POSSIBLY STRENGTHENING
  INTO EVENING.

* SCATTERED LIGHT RAIN SHOWERS LIKELY AND MVFR CIGS DEVELOPING
  OVERNIGHT...AND THE POSSIBILITY OF A BRIEF MIX WITH SNOW AND IFR BEFORE
  ENDING THURSDAY MORNING.

* SOUTH-SOUTHWEST WINDS AT 2000 FT OF AT LEAST 40-45 KT THIS EVENING
  INTO OVERNIGHT THAT MAY CREATE LOW-LEVEL WIND SHEAR.

* NORTHWEST WINDS GUSTING TO AROUND 30 KT DURING THE DAY
  THURSDAY.

KMD

//DISCUSSION...UPDATED 18Z...

QUITE A FEW AVIATION CONCERNS FOR THIS TAF CYCLE. THE FIRST
CENTERS AROUND WINDS. SE WINDS WILL GRADUALLY RAMP UP THIS
AFTERNOON AND EVENING WITH SUSTAINED WINDS HOLDING IN THE MID
TEENS AND GUSTS INTO 22-24 KT RANGE AHEAD OF LOW PRESSURE MOVING
EAST THROUGH THE PLAINS. THE LOW MOVES THROUGH LATE TONIGHT WITH A
TRAILING COLD FRONT INTO TOMORROW MORNING. AFTER A PERIOD OF
LIGHTER WINDS...NW WINDS RAMP UP QUICKLY MID MORNING THROUGH THE
AFTERNOON. NAM/GFS FORECAST SOUNDINGS SHOW GOOD MIXING THAT WILL
SUPPORT 30 KT OR SO GUSTS THROUGH THE AFTERNOON. AT THIS POINT
LLWS HAS NOT BEEN INTRODUCED AS WINDS AT 2000 FT WILL REACH 40-45
KT WHICH IS ON THE THRESHOLD...BUT WITH THE CONTINUED GUSTINESS IT
IS MARGINAL AT THIS POINT. DURING PERIODS OF LESS FREQUENT GUSTS
THERE COULD BE SOME LLWS.

OTHER CONCERNS REVOLVE AROUND PRECIPITATION EVOLUTION AND TYPE
THROUGH EARLY THURSDAY. SEVERAL MODELS SHOW SOME DECENT LIFT IN
THE WARM ADVECTIVE REGIME THIS EVENING. IN SPITE OF
THIS...GUIDANCE IS MIXED AS TO HOW MUCH MOISTURE THERE WILL
ACTUALLY BE TO SUPPORT PRECIPITATION DURING THIS INITIAL TIME
FRAME. IF PRECIP WERE TO DEVELOP IN THE 4Z-8Z TIME FRAME...SURFACE
TEMPERATURES COULD SUPPORT FZRA. HAVE ONLY GONE WITH A VCSH GIVEN
THE LACK OF MOISTURE ON SOME GUIDANCE...BUT WILL BE A PERIOD TO
WATCH. BETTER CHANCES OF PRECIPITATION COME WITH THE COLD FRONT
LATE TONIGHT INTO EARLY THURSDAY. PRECIP LOOKS TO BE A RAIN OR
DRIZZLE BEFORE TAPERING TO A RAIN SNOW MIX. SURFACE TEMPS HOLD AT
OR ABOVE 32 FOR MOST OF THE PRECIP THUS LITTLE TO NO ACCUMULATION
IS EXPECTED.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH IN WIND DIRECTION AND SPEED THROUGH THIS
  EVENING...INCLUDING THE WIND DIRECTION REMAINING SLIGHTLY EAST
  OF SOUTH.

* MEDIUM IN PRECIPITATION OCCURRING AT THE AIRFIELD LATER TONIGHT
  AND EARLY THURSDAY MORNING. MEDIUM ON PRECIPITATION TYPE.

* MEDIUM THAT LLWS WILL REMAIN MARGINAL THROUGH THE EVENING.

* HIGH IN MVFR CIGS LATE TONIGHT INTO THURSDAY MORNING THOUGH
  MEDIUM ON TIMING. MEDIUM IN ANY IFR OCCURRING.

KMD

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

THURSDAY NIGHT...MAINLY VFR. NORTH-NORTHWEST WINDS.
FRIDAY...VFR. NORTHWEST WINDS.
SATURDAY...CHANCE OF SNOW AND IFR DURING THE NIGHT. SOUTHWEST
           WINDS.
SUNDAY...SNOW AND IFR LIKELY. NORTHEAST WINDS.
MONDAY...CHANCE OF SNOW WITH MVFR LIKELY. IFR POSSIBLE. NORTHWEST
         WINDS.
TUESDAY...CHANCE OF SNOW DURING THE NIGHT. SOUTHWEST WINDS.

MTF

&&

.MARINE...
211 PM CST

I HAVE UPGRADED THE GALE WATCH TO A WARNING FOR THURSDAY
AFTERNOON AND NIGHT. AN AREA OF LOW PRESSURE APPROACHING THE LAKES
REGION FROM THE PLAINS WILL PRODUCE A PERIOD OF STRONG SOUTHERLY
WINDS AROUND 30 KT TONIGHT...THEN A PERIOD OF NORTHERLY GALE FORCE
WINDS THURSDAY AFTERNOON AND NIGHT AS MUCH COLD AIR SPILLS IN OVER
THE LAKES IN THE WAKE OF THIS LOW. I HAVE INCLUDED MY ILLINOIS
NEAR SHORES IN THIS GALE WARNING AS IT APPEARS THE OFF SHORE
COMPONENT OF THE WIND WILL BE STRONG ENOUGH TO SUPPORT SOME LOW
END GALES.

SURFACE HIGH PRESSURE WILL GRADUALLY BUILD EASTWARD ACROSS THE PLAINS
AND UPPER MIDWEST LATER THURSDAY AND THURSDAY NIGHT...AND THIS
SHOULD ALLOW FOR SOME STRONGER WINDS TO CONTINUE INTO EARLY
FRIDAY...BEFORE DIMINISHING BY FRIDAY AFTERNOON. ANOTHER COLD FRONT
LOOKS TO DROP ACROSS THE LAKES ON SUNDAY...AND A PERIOD OF STRONGER
NORTHERLY WINDS (25 TO 30 KT) APPEAR LIKELY IN ITS WAKE AS A VERY
COLD AIRMASS MOVES SOUTHWARD OVER THE LAKE.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 11 AM THURSDAY.

     GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878...11 AM THURSDAY TO 3 AM FRIDAY.

     HEAVY FREEZING SPRAY WARNING...LMZ261-LMZ362-LMZ364-LMZ366-
     LMZ563-LMZ565-LMZ567-LMZ868...2 PM THURSDAY TO 3 AM FRIDAY.

&&

$$

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