Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 131135
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
535 AM CST SAT FEB 13 2016

.SHORT TERM...
339 AM CST

THROUGH TONIGHT...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH THE COLD TEMPS/LOW
WIND CHILLS THIS MORNING...LAKE EFFECT SNOW CONTINUING IN
NORTHWEST INDIANA...AND THEN ACCUMULATING SNOW LIKELY SUNDAY INTO
SUNDAY NIGHT.

IN THE NEAR TERM...LAKE EFFECT SNOW SHOWERS STILL PERSISTING
ACROSS NORTHWEST INDIANA. ALTHOUGH SNOW HAS BEEN FALLING ACROSS
SEVERAL COUNTIES IN THE CWA...THE BULK OF ANY STRONGER DEVELOPMENT
HAS OCCURRED ACROSS NORTHEAST PORTER COUNTY. HIGH DELTA TS AND
INVERSION HEIGHTS WITH PERSISTENT CONVERGENCE OVERNIGHT HAS
ALLOWED FOR SOME STRONGER ELEMENTS TO MOVE ACROSS THE CWA.
HOWEVER...THE STRONGER CONVERGENCE HAS BEEN SITUATED JUST TO THE
EAST...WITH THE MORE FOCUSED DEVELOPMENT LIKEWISE STAYING TO THE
EAST. INSTABILITY WILL REMAIN IN PLACE THIS MORNING BUT GUIDANCE
IN GOOD AGREEMENT WITH INVERSION HEIGHTS QUICKLY COMING DOWN OVER
THE NEXT SEVERAL HOURS. ALTHOUGH BOUNDARY LAYER FLOW WILL ALLOW
FOR CONTINUED SNOW SHOWERS TO MOVE ACROSS PORTER COUNTY THIS
MORNING THROUGH MIDDAY ANY ADDITIONAL SNOW AMOUNTS WILL LIKELY
REMAIN MINOR AROUND ONE INCH TO AT MOST ONE TO TWO INCHES...LIKELY
NORTHEAST OF CHESTERTON.

OUTSIDE OF THE LAKE EFFECT SNOW...SKIES HAVE REMAINED CLEAR WITH
TEMPS STEADILY FALLING. HOWEVER...TIGHTER GRADIENT AND STRONGER
NORTHWEST WINDS LIKELY LIMITING HOW QUICKLY TEMPS HAVE FALLEN.
GRADIENT IS RELAXING AT THIS TIME AND EXPECT THIS TO CONTINUE WITH
TEMPS EXPECTED TO FALL TO AROUND ZERO IN THE ADVISORY LOCATION.
THIS WILL RESULT IN MIN WIND CHILLS APPROACHING THE 20 BELOW MARK.
DESPITE SUNNY SKIES THIS MORNING...ONGOING CAA WILL CONTINUE
THROUGH MID MORNING AND LIMIT UPWARD TEMP/WIND CHILL TRENDS. WITH
THIS EXPECTED...END TIME OF THE WIND CHILL ADVISORY STILL APPEARS
TO BE ON TRACK. OUTSIDE OF THE LAKE EFFECT CLOUDS IN NORTHWEST
INDIANA...SUNNY SKIES WILL PREVAIL TODAY WHILE TEMPS MAX OUT IN
THE TEENS. BOUNDARY LAYER FLOW WILL FINALLY BACK ENOUGH FOR ANY
REMAINING LIGHT LAKE EFFECT SNOW OR FLURRIES TO PUSH WELL EAST OF
THE CWA LATE THIS AFTERNOON INTO THE EARLY EVENING. ANOTHER COLD
NIGHT WITH LOWS IN THE SINGLE DIGITS AND SUBZERO WIND CHILLS ARE
EXPECTED...WHILE CLOUD COVER INCREASES OUT AHEAD OF THE NEXT
SYSTEM TO IMPACT THE REGION SUNDAY.

RODRIGUEZ

&&

.LONG TERM...
339 AM CST

SUNDAY THROUGH SATURDAY...

SYSTEM TO IMPACT THE AREA SUNDAY INTO SUNDAY NIGHT IS CURRENTLY
MOVING IN OFF THE PACIFIC AND PUSHING INTO THE NORTHWEST CONUS.
GUIDANCE IN FAIR AGREEMENT WITH THIS SYSTEM DROPPING
EAST/SOUTHEAST INTO THE NORTHERN PLAINS BY TONIGHT AND THEN
PUSHING INTO THE REGION SUNDAY MORNING. AT THIS TIME...ITS STILL
APPEARING THAT A LONGER DURATION THAT THE AREA WILL SEE A LONGER
DURATION WARM ADVECTION SNOW WITH THE APPROACH OF THIS LARGER
SCALE ASCENT. LARGE SCALE FORCING REALLY RAMPS UP OVER THE WESTERN
CWA AFTER MIDNIGHT BUT WILL INITIALLY ACT TO ERODE SOME RATHER DRY
AIR IN PLACE. HOWEVER...THIS WILL EASILY BE OVERCOME BY AROUND THE
12Z TIME FROM FROM AREAS NEAR ROCKFORD SOUTH TO PONTIAC. THIS
TREND WILL SPREAD EAST WITH AREAS IN THE REMAINING CWA LIKELY
SEEING SNOW START BY MID TO LATE MORNING. A STEADY LIGHT TO AT
TIMES MODERATE SNOW IS STILL EXPECTED WITH THE AFTERNOON TIME
FRAME THE LIKELY TIME FOR THIS BETTER DEVELOPMENT.

FORCING WILL SHIFT TO THE EAST THROUGH THE EVENING AND SHOULD SEE
SNOW TAPER FROM WEST TO EAST DURING THIS TIME. HOWEVER...WILL NEED
TO MONITOR THE EVENING PERIOD AS ITS POSSIBLE FOR SOME ADDITIONAL
BETTER DEVELOPMENT. ALTHOUGH A HIGH RATIO SNOW IS STILL
ANTICIPATED...EVENING GUIDANCE WAS SHOWING THAT THE STRONGEST LIFT
COULD BE OUTSIDE OF THE SNOW GROWTH ZONE. NONETHELESS...LATEST
FORECAST STILL ON TRACK FOR STORM TOTALS OF 2 TO 5 INCHES ACROSS
THE CWA WITH THE HIGHEST AMOUNTS EXPECTED ACROSS NORTH CENTRAL AND
NORTHWEST ILLINOIS. GIVEN THE START TIME OF THE SNOW...MAINLY
SUNDAY...HAVE OPTED TO HOLD OFF ON ANY HEADLINES THIS MORNING.
HOWEVER...IF SIMILAR TRENDS CONTINUE TODAY...COULD SEE HEADLINES
ISSUED LATER TODAY.

RODRIGUEZ

&&

.AVIATION...

FOR 12Z TAFS...

QUIET AVIATION WEATHER CONDITIONS IN STORE FOR THE REGION OVER THE
NEXT 24 HOURS...AFTER WHICH CONDITIONS WILL BE QUICK TO
DETERIORATE AS SNOW DEVELOPS SUNDAY MORNING/MID-DAY.

SPRAWLING SURFACE HIGH PRESSURE OVER THE UPPER MIDWEST WILL DRIFT
SOUTHEAST ACROSS THE FORECAST AREA THROUGH THIS EVENING. THIS WILL
ALLOW NORTHWEST WINDS TO GRADUALLY DIMINISH FROM 10-12 KT THIS
MORNING TO LESS THAN 10 KT THIS AFTERNOON. SURFACE RIDGE WILL PASS
ACROSS THE TERMINALS THIS EVENING WITH A PERIOD OF LIGHT/VARIABLE
WINDS BEFORE DIRECTION SHIFTS SOUTHEAST AND SPEEDS BEGIN TO
INCREASE AGAIN THROUGH SUNDAY MORNING. CLEAR SKIES THROUGH THE DAY
TODAY WILL SEE VFR HIGH/MID CLOUDS DEVELOP LATER THIS EVENING AND
LOWER AND THICKEN OVERNIGHT. FAIRLY GOOD AGREEMENT AMONGST MODEL
GUIDANCE IN DEVELOPING SNOW INTO THE ROCKFORD AREA AT/SHORTLY
AFTER 12Z SUNDAY...AND INTO THE CHICAGO TERMINALS IN THE 16-18Z
PERIOD. CONFIDENCE IS FAIRLY HIGH THAT VISIBILITY WILL QUICKLY
DETERIORATE TO IFR AS SNOW DEVELOPS...WITH A LOW MVFR CEILING
QUICKLY FOLLOWING. HAVE INDICATED THIS AT THE END OF O`HARE 30
HOUR TAF...WITH IFR/LOW MVFR CONDITIONS LIKELY SUNDAY AFTERNOON.

RATZER

&&

.MARINE...
309 AM CST

THE MARINE WEATHER FORECAST FOR LAKE MICHIGAN FOCUSES ON A COUPLE
OF PERIODS OF STRONGER WINDS...INITIALLY TODAY WITH NORTH-
NORTHWEST WINDS TO 30 KT EARLY...AND THEN A PERIOD OF 25-30 KT
SOUTH- SOUTHEAST WINDS SUNDAY AND SUNDAY NIGHT. HAVE CANCELLED
GALE WARNING EARLY AS OBSERVATIONAL TRENDS INDICATE WINDS HAVE
LARGELY DIMINISHED TO 25-30 KT.

NORTH-NORTHWEST WINDS WERE SLOWLY DIMINISHING EARLY THIS MORNING
ACROSS THE LAKE...WITHIN A TIGHT SURFACE PRESSURE GRADIENT WEST OF
A DEPARTING AREA OF LOW PRESSURE OVER NORTHERN NEW ENGLAND AND AN
EXPANSIVE CANADIAN HIGH PRESSURE SYSTEM SPREADING SOUTHEAST FROM
THE NORTHERN PLAINS AND PRAIRIE PROVINCES. THIS HIGH WILL CONTINUE
TO MOVE SOUTHEAST TODAY...REACHING THE WESTERN LAKES THIS EVENING
WITH DIMINISHING WINDS. WINDS WILL SHIFT TO THE SOUTH- SOUTHEAST
SUNDAY AS THE HIGH MOVES OFF TO THE EAST...AND A TROUGH OF LOW
PRESSURE DEVELOPS OVER THE PLAINS. WINDS WILL INCREASE AGAIN INTO
THE 20-25 KT RANGE FOR THE MOST PART AS THE TROUGH MOVES EAST
EVENTUALLY REACHING NORTHERN ILLINOIS BY EARLY MONDAY AND ALLOWING
WINDS TO DIMINISH. DEEPER LOW PRESSURE WILL PRESS EAST ACROSS
MANITOBA AND NORTHERN ONTARIO DURING THIS TIME...AND WILL TRAIL A
COLD FRONTAL TROUGH ACROSS THE WESTERN LAKES BY MONDAY NIGHT. A
PERIOD OF STRONGER NORTHERLY WINDS IS POSSIBLE TUESDAY NIGHT...AS
ANOTHER HIGH PRESSURE AREA BUILDS SOUTHEAST FROM CENTRAL CANADA
AND EVENTUALLY CROSSES THE LAKE LATE WEDNESDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014 UNTIL 9 AM SATURDAY.

IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 9 AM
     SATURDAY.

     HEAVY FREEZING SPRAY WARNING...LMZ744-LMZ745-LMZ777-LMZ779 UNTIL
     6 AM SATURDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL NOON SATURDAY.

&&

$$

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