Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 132009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
209 PM 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 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...NONE.
IN...NONE.
LM...NONE.
&&

$$

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