Area Forecast Discussion
Issued by NWS Chicago, IL

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665
FXUS63 KLOT 132057
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
257 PM CST SAT FEB 13 2016

.SHORT TERM...

TONIGHT THROUGH MONDAY...

257 PM...MAIN FORECAST CONCERN IS SNOWFALL AMOUNTS SUNDAY THROUGH
SUNDAY NIGHT.

CLIPPER SYSTEM TO AFFECT THE REGION IN TWO PARTS WITH THE FIRST
AREA OF SNOW EXTENDING FROM IA INTO CENTRAL IL LATE TONIGHT AND
THEN SWING EAST THRU THE CWA DURING SUNDAY MORNING AND EARLY
SUNDAY AFTERNOON. THIS WILL LIKELY PRODUCE A PERIOD OF MODERATE
SNOW BEFORE DIMINISHING SOME IN THE AFTERNOON...THOUGH STILL
SNOWING LIGHTLY. AS THE SURFACE LOW/TROUGH APPROACHES SUNDAY
NIGHT...THERE WILL LIKELY BE ANOTHER PROLONGED PERIOD OF LIGHT
SNOW...PERHAPS BRIEFLY MODERATE. MODEL QPF FORECASTS HAVE FOCUSED
THE HIGHER AMOUNTS...TWO TO THREE TENTHS...MORE ON NORTHWEST IL
INTO CENTRAL IL WITH AMOUNTS GENERALLY UNDER TWO TENTHS ACROSS
NORTHEAST IL AND NORTHWEST INDIANA. AS A RESULT...SNOWFALL TOTALS
NOW APPEAR TO BE JUST A BIT LOWER FOR THE IMMEDIATE CHICAGO AREA
AND LIKELY IN THE 2 TO 4 INCH RANGE...PERHAPS CLOSER TO 2 INCHES
ACROSS NORTHWEST INDIANA. THESE AMOUNTS ARE ALSO IN LINE WITH
LOWER AMOUNTS FROM WPC. BUT SNOWFALL AMOUNTS ACROSS THE WESTERN
AND SOUTHWEST CWA...WHILE ALSO JUST A BIT LOWER...ARE STILL IN
THE 3-5 INCH RANGE AND HAVE ISSUED A WINTER WEATHER ADVISORY
FROM BOONE SOUTH TO GRUNDY/IROQUOIS. IF LATER MODEL RUNS END UP
BRINGING HIGHER QPF AMOUNTS FURTHER EAST...ITS POSSIBLE THE
ADVISORY MAY NEED TO BE EXTENDED FURTHER EAST.

AS THE SNOW SPREADS EAST ACROSS THE CWA SUNDAY MORNING...THERE
COULD BE A PERIOD OR BURST OF MODERATE SNOW AND THIS IS WHEN
SNOWFALL RATES MAY APPROACH ONE INCH AN HOUR FOR AT LEAST A FEW
HOURS. THE SNOW WILL ALSO BE FAIRLY DRY/FLUFFY AND INCREASING
SOUTHEAST WINDS...PERHAPS GUSTING TO 25 MPH RANGE...WILL LIKELY
LEAD TO SOME BLOWING AND DRIFTING SNOW.

TEMPS WILL LIKELY DROP INTO THE SINGLE DIGITS THIS EVENING...
LEVEL OFF AND THEN START SLOWING RISING AS CLOUD COVER INCREASES
OVERNIGHT. BUT OVERALL TREND IN TEMPS ESPECIALLY THIS EVENING IS
LOW. AFTER LIGHT WINDS THIS EVENING...SOUTHEASTERLY WINDS WILL
LIKELY KEEP WIND CHILLS NEAR ZERO OR SLIGHTLY BELOW ZERO OVERNIGHT
INTO SUNDAY MORNING. TEMPS RISE INTO THE LOWER 20S SUNDAY AND
THEN END UP STEADY TO SLOWLY RISING SUNDAY NIGHT INTO MONDAY AS A
BIT MORE MILD AIR ADVECTS IN BEHIND THIS CLIPPER. DESPITE A NEW
SNOW PACK AND PROBABLY EXTENSIVE CLOUD COVER...THERMAL FIELDS
SUGGEST LOW/MID 30S FOR HIGHS ON MONDAY. CMS

&&

.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 THE 18Z TAFS...

VFR CONDS WILL PREVAIL THROUGH TONIGHT AS HIGH PRESSURE CONTINUES
TO SLOWLY BUILD IN FROM THE WEST. SKIES WILL REMAIN MOSTLY CLEAR
WITH A FEW CIRRUS CLOUDS AT 20KFT BEGINNING TO ARRIVE OVERNIGHT.
WINDS WILL BE MAINLY FROM THE WEST/NORTHWEST AROUND 5 TO 10KT THEN
AROUND SUNSET FURTHER DIMINISH TO LGT AND VARIABLE FROM 2-4KT.
HIGH PRESSURE THEN SLIDES EAST BY EARLY SUNDAY MORNING WITH CLOUDS
STEADILY THICKENING AND CIGS LOWERING TOWARDS MVFR BY 15Z. WINDS
WILL BE TURNING SOUTH TO SOUTHEAST AND INCREASING IN ADVANCE OF A
LOW PRESSURE SYSTEM. MIXING WILL BE ON THE INCREASE JUST AFTER
DAYBREAK SUNDAY AND SHOULD PUSH WINDS INTO THE 12-15KT RANGE WITH
GUSTS NEARING 20KT INITIALLY...THEN AS CLOUD BASES LOWER TOWARDS
1200-1500FT AGL GUSTS WILL COME DOWN SLIGHTLY TO ARND 17-19KT.
LIGHT SNOW IS EXPECTED TO OVERSPREAD NORTHWEST IL BY 14-15Z
SUN...EVENTUALLY REACHING ORD/MDW BY 17Z. GUIDANCE CONTINUES TO
FOCUS ON STEADIER SNOW ARRIVING BETWEEN 18-22Z WHERE VSBYS COULD
BE REDUCED TO ARND 1SM OR AT TIMES LOWER. HAVE ACCOUNTED FOR THIS
WITH A TEMPO GROUP...ALTHOUGH THIS MAY TREND TOWARDS A PREVAILING
GROUP. LIGHT SNOW WILL THEN PERSIST WITH CIGS LINGERING ARND LOW
END MVFR BORDERLINE IFR INTO SUN EVE.

BEACHLER

&&

.MARINE...
209 PM CST

HIGH PRESSURE HAS ARRIVED OVER THE WESTERN GREAT LAKES THIS
AFTERNOON...HOWEVER IT IS EXPECTED TO CONTINUE TO DRIFT EAST
OVERNIGHT AND ALLOW THE LIGHT WEST WINDS TO STEADILY TURN SOUTHWEST
TO SOUTH BY DAYBREAK SUNDAY. ANOTHER LOW PRESSURE SYSTEM WILL SLIDE
SOUTH FROM CENTRAL CANADA INTO THE NORTHERN PLAINS LATE
TONIGHT...AND CONTINUE TO SLIDE EAST TOWARDS IOWA/CENTRAL ILLINOIS
BY SUNDAY MORNING. THIS WILL ALLOW AN INCREASING PRESSURE GRADIENT
TO DEVELOP AND INCREASE WINDS OVER THE LAKE DURING THE DAY SUNDAY.
CURRENT INDICATIONS ARE THAT WINDS WILL BE GENERALLY BETWEEN 15 TO
25 KT...HOWEVER THERE COULD BE A PERIOD OF 30KT WINDS FOR THE OPEN
WATERS SUN DURING THE DAY. LOW PRESSURE THEN SLIDES EAST ACROSS THE
CENTRAL/SOUTHERN PORTIONS OF LAKE MICHIGAN...ALLOWING A BRIEF LULL
IN THE WINDS FOR THE CENTRAL/SOUTHERN HALF OF THE LAKE ALTHOUGH
ALONG THE NORTHERN PORTIONS OF THE LAKE WINDS WILL PERSIST FROM THE
NORTHEAST. THE LOW IS EXPECTED TO LIFT NORTHEAST ACROSS LOWER
MICHIGAN TOWARDS LAKE HURON BY MIDDAY MONDAY ALLOWING WINDS TO
MAINLY BE WESTERLY TO SOUTHWESTERLY BUT WITH A LIGHTER
GRADIENT...WINDS WILL SETTLE TO A 10-20KT RANGE SUNDAY NIGHT INTO
MONDAY.

LATE MONDAY NIGHT INTO TUESDAY ANOTHER LOW PRESSURE SYSTEM WILL
QUICKLY SLIDE SOUTH FROM CENTRAL CANADA INTO THE NORTHERN PLAINS AND
MOVE EAST TOWARDS THE OHIO VALLEY TUESDAY. THIS WILL CAUSE WINDS TO
TURN NORTH/NORTHEASTERLY OVER THE LAKE...WITH A TIGHTENING PRESSURE
GRADIENT ALONG THE SOUTHERN HALF OF THE LAKE. IT IS POSSIBLE THAT A
PERIOD OF HAZARDOUS WINDS TO SMALL CRAFT MAY OCCUR...AND WITH THE
NORTHEAST/EAST WIND DIRECTION...THIS COULD ALSO RESULT IN HAZARDOUS
WAVES ALONG THE ILLINOIS/NORTHWEST INDIANA NEARSHORE WATERS TUESDAY
AFTERNOON/EVENING. HIGH PRESSURE THEN ARRIVES WEDNESDAY AND LINGERS
OVER THE GREAT LAKES THROUGH THURSDAY WITH MUCH LIGHTER WINDS AND
LESS WAVE ACTION EXPECTED.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-
     ILZ019-ILZ020-ILZ021-ILZ032-ILZ033-ILZ039...6 AM SUNDAY TO
     MIDNIGHT MONDAY.

IN...NONE.
LM...NONE.
&&

$$

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