Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 141546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
946 AM CST SUN FEB 14 2016

.UPDATE...
929 AM CST

THE STRONG SOUTHEAST WIND COMPONENT HAS BRIEFLY DELAYED THE
MOISTENING IN THE LOWER LEVELS THIS MORNING...HOWEVER STEADY
ISENTROPIC ASCENT IS PROGGED TO QUICKLY MOISTEN THE ENVIRONMENT
OVER NORTHERN IL AND EVENTUALLY NORTHWEST IN. REGIONAL RADAR
SHOWS THE LEADING EDGE OF THE LIGHT SNOW LIFTING NORTHEAST ALONG
AND WEST OF A ROCKFORD TO LASALLE LINE. JUST WEST OF THIS LINE THE
LOW LEVELS HAVE MOISTENED FURTHER WITH BETTER LAPSE RATES AND
ALLOWED SOME MODERATE TO BRIEFLY HEAVY SNOW TO OCCUR...AND THIS
EXTENDS WEST TO EASTERN IOWA. VISIBILITIES HAVE DIMINISHED TO
AROUND ONE QUARTER MILE IN PLACES ACROSS EASTERN IOWA/FAR WESTERN
IL.

HAVE ONLY MADE MINOR ADJUSTMENTS TO THE PRESENT THINKING OF
SNOWFALL TOTALS BETWEEN 1 TO 3 INCHES IN FAR NORTHEAST IL...WHERE
IT WILL TAKE LONGER TO MOISTEN AND 3 TO 5 WITHIN THE PRESENT
WINTER WEATHER HEADLINE. OUTSIDE OF THE THESE LOCATIONS A GENERAL
2 TO 3 INCHES OF SNOWFALL IS EXPECTED. THE GUSTY WINDS ARE
EXPECTED TO DAMPEN SLIGHTLY ONCE THE BETTER MOISTURE
DEVELOPS...HOWEVER THE SUB 20 DEGREE AIR WILL LIKELY KEEP THE SNOW
RATIOS HIGHER BETWEEN 18:1 TO 20:1 AND RESULT IN A MORE POWDER
LIKE SNOWFALL. THE COMBINATION OF GUSTY WINDS WILL ALLOW THIS TO
CREATE SOME PATCHES OF BLOWING/DRIFTING SNOW...MAINLY FOR OPEN AND
RURAL LOCATIONS.

WITH THE MID-LVL WAVE OPENING UP LATER THIS AFTERNOON/EARLY
EVENING...EXPECT THE MODERATE SNOW TO END SHORTLY AFTER SUNSET
WITH CONTINUED LIGHT SNOW THROUGH THIS EVENING. THE OTHER CONCERN
FOR TONIGHT COULD END UP BEING SOME PATCHY FOG DUE TO THE
LINGERING LOW LEVEL MOISTURE AND DECREASING WINDS FROM THE
SOUTH/SOUTHWEST. BUT THAT WILL BE HIGHLIGHTED IN THE AFTERNOON
PACKAGE.

BEACHLER

&&

.SHORT TERM...
333 AM CST

THROUGH TONIGHT...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH THE SNOW POTENTIAL
TODAY INTO THIS EVENING...WITH NO CHANGES TO THE CURRENT WINTER
WEATHER ADVISORY.

APPROACHING WAVE PUSHING THROUGH THE NORTHERN CONUS EARLY THIS
MORNING IS STILL RATHER VIGOROUS AT THIS TIME...WITH SOME ROBUST
DEVELOPMENT CURRENTLY TIED TO THIS SYSTEM. GUIDANCE STILL
CONSISTENT WITH SHOWING THIS WAVE DAMPENING WITH TIME TODAY...BUT
STILL THINK IT WILL BRING A DECENT SHOT OF SOME GOOD LIFT TO THE
AREA LATER THIS MORNING INTO THE AFTERNOON. WHILE THE LARGER SCALE
FORCING INCREASES THIS MORNING...ISENTROPIC ASCENT CURRENTLY
FOCUSED JUST TO THE WEST WILL LIKEWISE SPREAD EAST ACROSS THE
AREA. THIS PERSISTENT FORCING WILL HELP TO ERODE SOME DRIER IN
PLACE THIS MORNING AND AS THIS OCCURS...SHOULD SEE PRECIP BLOSSOM
AS IT PUSHES EAST OVER THE CWA. LATEST RADAR IMAGERY DEPICTING
SOME RETURNS...BUT WITH NONE OF THIS REACHING THE GROUND OVER THE
CWA AT THIS TIME. ANY SNOW NEAR THE CWA RIGHT NOW IS TIED TO FGEN
BAND WHICH DEVELOPED OVER EASTERN IOWA AND WESTERN ILLINOIS THIS
PAST EVENING. HOWEVER...THIS IS SLIDING TO THE SOUTHEAST AND WILL
CONTINUE TO DO SO OVER THE NEXT COUPLE OF HOURS. DO THINK THERE IS
A COUPLE HOURS HERE WHERE THE CWA WILL BE MOSTLY DRY BUT ONCE
AGAIN AS THIS FORCING SATURATES THE COLUMN...SHOULD SEE AREAS NEAR
STERLING SOUTHEAST TO PONTIAC BEGIN REPORTING SNOW AROUND THE
12-13Z TIME FRAME. ALTHOUGH ASCENT WILL BE SPREADING EAST THROUGH
THE MORNING...THINK AREAS EAST OF THIS INITIAL START TO THE SNOW
MAY HAVE ALSO HAVE A FEW HOURS BEFORE START TIME.
HOWEVER...REMAINING AREAS IN NORTH CENTRAL WILL LIKELY SEE THE
SNOW BEGIN BY MID MORNING...AND THEN WITH REMAINING AREAS IN
NORTHEAST ILLINOIS AND NORTHWEST INDIANA CLOSER TO MIDDAY.

PERIODS OF MODERATE SNOW WILL LIKELY ACCOMPANYING THIS SNOW
TODAY...WITH THIS STILL VIGOROUS WAVE AND STEEPER LAPSE RATES.
SURFACE RIDGE WILL CONTINUE TO SHIFT EAST AND WITH THE SURFACE
GRADIENT BECOMING MORE ORGANIZED TODAY...SOUTHERLY WINDS/GUSTS ARE
ANTICIPATED TO INCREASE SIMILAR TO WHAT IS CURRENTLY OCCURRING
ACROSS IOWA. THIS BETTER SNOWFALL AND SOUTHERLY WINDS COULD BRING
SOME BLOWING SNOW...ESPECIALLY OUT IN OPEN AREAS. AS FORCING
DIMINISHES THIS EVENING SNOW WILL LIKELY BE EASING AS WELL.
HOWEVER...SOME GUIDANCE INDICATING AN ADDITIONAL CHANCE OF MORE
ORGANIZED SNOW DEVELOPMENT. WITH ISENTROPIC ASCENT STILL FOCUSED
OVERHEAD THIS SEEMED REASONABLE...SO DID MAINTAINED HIGHER POPS
THIS EVENING AS WELL AS SLIGHTLY HIGHER QPF/SNOWFALL. SNOWFALL
TOTALS REMAIN SIMILAR TO PREVIOUS FORECAST...BUT AS WAS DISCUSSED
THIS PAST EVENING...SNOWFALL TOTALS ARE SLIGHTLY LOWER. HAVE 3 TO
5 IN THE ADVISORY AREAS AND ELSEWHERE...2 TO 4 INCHES. DO THINK
THERE COULD BE SOME ISOLATED TOTALS SLIGHTLY ABOVE THE 5 INCH
MARK ACROSS THE FAR SOUTHWEST CWA...ALONG AND SOUTHWEST OF A LINE
FROM MENDOTA TO PONTIAC. THIS WOULD BE OWING TO WHERE THE BEST
FORCING WOULD BE...AND POSSIBLE BETTER CONVECTIVE ELEMENTS.

RODRIGUEZ

&&

.LONG TERM...
333 AM CST

MONDAY THROUGH SUNDAY...

RISING TEMPS WILL BE THE TREND THIS MORNING THROUGH MONDAY...WITH
PERSISTENT WAA HELPING TEMPS TO SEE A STEADY RISE. TEMPS
REBOUNDING BACK INTO THE 30S WITH EXPECTED DRY CONDITIONS ON
MONDAY. HOWEVER...WILL NEED TO MONITOR FOR THE POSSIBILITY OF
ADDITIONAL PRECIP MONDAY AFTERNOON AND ESPECIALLY MONDAY NIGHT
ACROSS THE CWA AS CYCLONIC FLOW CONTINUES TO USHER IN ADDITIONAL
SHORTWAVE ENERGY. PATTERN TO LIKELY REMAIN ACTIVE INTO TUESDAY
WITH GUIDANCE STILL ADVERTISING A MORE ROBUST WAVE DROPPING
SOUTHEAST THROUGH THE REGION. AT THIS TIME...BEST FORCING WOULD
RESIDE JUST TO THE SOUTH BUT SOME GUIDANCE IS SHOWING THIS BETTER
FORCING PUSHING DIRECTLY OVERHEAD. DID INCREASE POPS ON TUESDAY
BUT KEPT THEM IN THE CHANCE RANGE. IF THIS PRECIP DOES
MATERIALIZE...LIKELY TYPE WOULD BE SNOW. SLIGHTLY WARMER BOUNDARY
LAYER CONDITIONS COULD HELP FOR A RAIN SNOW MIX ACROSS THE
SOUTHERN CWA THOUGH. TEMPS IN THE 30S STILL EXPECTED THROUGH
MIDWEEK BUT WARMUP STILL ANTICIPATED WITH TEMPS IN THE 50S
APPEARING LIKELY BY FRIDAY...AND POSSIBLY APPROACHING 60S IN SOME
SPOTS.

RODRIGUEZ

&&

.AVIATION...
FOR THE 12Z TAFS...

WINTER STORM SYSTEM TAKING SHAPE ACROSS THE PLAINS EARLY THIS
MORNING...AND WILL RESULT IN SNOW DEVELOPING EASTWARD ACROSS THE
TERMINALS THROUGH THIS MORNING. SOME LIGHT SNOW ALREADY OCCURRING
ALONG A NORTHWEST-SOUTHEAST BAND FROM KALO-KCMI...BUT EXPECT SNOW
TO EXPAND IN COVERAGE FROM THE WEST THROUGH MID-MORNING AS LEAD
WAVE APPROACHES. SNOW EXPECTED TO ARRIVE IN KRFD AREA AROUND 15Z
AND SPREAD INTO THE CHICAGO TERMINALS ROUGHLY 1630-18Z. EXPECTING
A PERIOD OF MVFR/OCCASIONAL IFR CONDITIONS WITH ACCUMULATING
LIGHT-MODERATE SNOW THROUGH EARLY AFTERNOON...WITH A LULL PERHAPS
DURING THE LATE AFTERNOON BEFORE A SECONDARY WAVE APPROACHES WITH
AN INCREASE IN SNOW INTENSITY POSSIBLE EARLY THIS EVENING.

WINDS WILL BECOME GUSTY FROM THE SOUTHEAST TO AROUND 20 KT BY
MIDDAY AND MAY CAUSE SOME BLOWING/DRIFTING OF SNOW. LIGHTER
SNOW/FLURRIES WILL LIKELY CONTINUE MUCH OF THE NIGHT AS COLUMN
REMAINS FAIRLY SATURATED AND WEAK ASCENT PERSISTS. RAW MODEL
SOUNDINGS SUGGEST IFR CIGS ARE LIKELY OVERNIGHT...THOUGH SHOULD
SEE IMPROVEMENT IN VISIBILITY BY LATE EVENING AS SNOW INTENSITY
DECREASES.

RATZER

&&

.MARINE...
233 AM CST

SOUTH-SOUTHEAST WINDS WILL STRENGTHEN QUICKLY TO AROUND 25 KT
TODAY...ON THE BACK SIDE OF A SPRAWLING AREA OF HIGH PRESSURE
WHICH WILL MOVE EAST OF THE LAKES TO SOUTHERN NEW ENGLAND AND THE
MID-ATLANTIC REGION BY TONIGHT. A WEAKENING SURFACE WAVE WILL MOVE
INTO THE MID-MISSISSIPPI VALLEY ON MONDAY...BUT WILL DISSIPATE AS
A SOUTH GRADIENT IS MAINTAINED BETWEEN THE EAST COAST RIDGE AND AN
AREA OF DEEPER LOW PRESSURE MOVING ACROSS HUDSON BAY. AS THIS
CANADIAN LOW MOVES EAST IT WILL EVENTUALLY TRAIL A TROUGH ACROSS
LAKE MICHIGAN TUESDAY...SHIFTING WINDS TO THE NORTH-NORTHWEST AND
BRIEFLY INCREASING TO 20-30 KT TUESDAY NIGHT INTO EARLY WEDNESDAY
BEFORE HIGH PRESSURE MOVES ACROSS THE WESTERN LAKES WEDNESDAY
NIGHT. ANOTHER DEEP LOW IS EXPECTED TO MOVE ACROSS THE UPPER
MIDWEST TOWARD THE END OF THE WEEK...WITH SOUTH-SOUTHEAST WINDS
STRENGTHENING AGAIN LATE THURSDAY AND FRIDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-
     ILZ019-ILZ020-ILZ021-ILZ032-ILZ033-ILZ039 UNTIL MIDNIGHT
     MONDAY.

IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 9 PM SUNDAY.

&&

$$

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