Area Forecast Discussion
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FXUS63 KLOT 010734
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
134 AM CST SUN FEB 1 2015

.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...

MONDAY NIGHT THROUGH SATURDAY...

134 AM...FORECAST CONCERNS INCLUDE A CHANCE OF LIGHT SNOW MONDAY
NIGHT INTO TUESDAY...THEN A BETTER CHANCE FOR ACCUMULATING LIGHT
SNOW TUESDAY NIGHT INTO WEDNESDAY MORNING.

A RIDGE OF HIGH PRESSURE WILL BE MOVING SOUTHEAST OF THE AREA
MONDAY EVENING AS A WEAK WAVE MOVES ACROSS THE REGION MONDAY NIGHT.
FAIRLY LIGHT QPF FROM ALL THE MODELS WITH THIS WAVE BUT PLENTY COLD
ENOUGH FOR THE LOW QPF AMOUNTS TO POTENTIALLY FLUFF UP TO A HALF
INCH MONDAY NIGHT. WHILE TEMPS BY THIS TIME WILL LIKELY BE IN THE
SINGLE DIGITS OR LOW TEENS...CLOUD COVER AND WEAK WARM AIR ADVECTION
MAY ALLOW TEMPS TO HOLD STEADY OR RISE A FEW DEGREES OVERNIGHT.

NEXT WAVE QUICKLY SHIFTS SOUTHEAST ACROSS THE AREA BY TUESDAY
EVENING WITH QPF AMOUNTS BETWEEN ONE AND TWO TENTHS. THIS HAS BEEN
A FAIRLY CONSISTENT FEATURE ON THE MODELS AND IF THIS MATERIALIZES
AS ADVERTISED...A FEW INCHES OF SNOW WILL BE POSSIBLE. TIMING AND
LOCATION ALSO ARE A BIT UNCERTAIN...EARLIER COULD IMPACT THE TUESDAY
EVENING RUSH...LATER COULD IMPACT THE WEDNESDAY MORNING RUSH. BUT
GIVEN THE POTENTIAL FOR SOME ACCUMULATION...OPTED TO BUMP POPS UP TO
LIKELY FOR TUESDAY NIGHT.

HIGH PRESSURE THEN SETTLES SOUTH ACROSS THE MIDWEST AND LAKES REGION
WEDNESDAY INTO THURSDAY AND WITH IT...SOME VERY COLD AIR. WITH A
DEEP SNOWPACK BY THAT TIME AND DIMINISHING WINDS WEDNESDAY NIGHT
INTO THURSDAY...EXPECT MANY LOCATIONS TO DROP BELOW ZERO FOR LOWS
THURSDAY MORNING. THE AIRMASS MODIFIES/WARMS SOME THURSDAY BUT
STILL EXPECTING LOWS IN THE LOWER SINGLE DIGITS THURSDAY EVENING...
POSSIBLY BELOW ZERO BUT WARM AIR ADVECTION BY MORNING WITH
INCREASING SOUTHERLY WINDS MAY PUT THE BRAKES ON HOW LOW TEMPS FALL
THURSDAY NIGHT. STRONG SOUTHERLY WINDS CONTINUE INTO SATURDAY WITH
WARMING TEMPS...THAT WILL LIKELY BE MUTED SOME BY THE SNOWPACK. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SNOW THRU THE PERIOD. VISIBILITIES UNDER 3/4SM.
* STRONG NORTHEAST WINDS SUNDAY...GUSTING 30-35 KT.
* BLOWING SNOW SUNDAY AND SUNDAY NIGHT.
* IFR/LIFR CIGS THRU THE PERIOD. CMS

//DISCUSSION...UPDATED 06Z...

LONG DURATION SNOW EVENT UNDERWAY AS LOW PRESSURE OVER KANSAS
MOVES EAST TO SOUTHERN INDIANA BY SUNDAY EVENING AS IT SLOWLY
STRENGTHENS. MOISTURE STREAMING NORTH FROM THE GULF WILL ALLOW
THIS SYSTEM TO PRODUCE MODERATE SNOW THROUGH SUNDAY EVENING...
BEFORE SLOWLY TAPERING OFF LATE SUNDAY EVENING AND EARLY MONDAY
MORNING. VISIBILITIES WILL LIKELY FLUCTUATE FROM TIME TO TIME
BUT PREVAILING VIS LIKELY TO BE AROUND 1/2SM FOR MUCH OF THE
EVENT.

AS THE GRADIENT STRENGTHENS SUNDAY MORNING...NORTHEAST WINDS
WILL INCREASE UP TO 20KTS WITH GUSTS 30-35KTS FOR MUCH OF THE
AFTERNOON AND EVENING. THESE STRONG WINDS WILL PRODUCE BLOWING
AND DRIFTING SNOW THAT MAY REDUCE VISIBILITIES UNDER 1/2SM AT
TIMES. THE WINDS WILL TURN MORE NORTHERLY SUNDAY EVENING AND
THEN BEGIN TO DIMINISH EARLY MONDAY MORNING. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR SNOW/VIS THRU THE PERIOD.
* HIGH FOR WINDS/GUSTS THRU THE PERIOD.
* HIGH FOR BLOWING SNOW SUNDAY/SUNDAY NIGHT. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY...IFR VSBY
POSSIBLE.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

MDB

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039 UNTIL 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL
     6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

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