Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CST SUN JAN 25 2015

.SHORT TERM...
329 AM CST

THROUGH TONIGHT...

HAVE FURTHERED THE DIMINISHING SNOWFALL TREND IN THE FORECAST FOR
TODAY...MAINLY NORTH OF INTERSTATE 80. ACROSS THE ENTIRE AREA THIS
LOOKS TO BE A MAINLY LOW IMPACT...NUISANCE TYPE SNOW...WITH SOME
COMMUNITIES IN THE NORTH QUITE POSSIBLY NOT SEEING ANY
ACCUMULATION. HAVE CONTINUED A SPECIAL WEATHER STATEMENT FOR AREAS
ALONG AND SOUTH OF I-80.

SATELLITE IMAGERY THIS MORNING DEPICTS THE CLOSED UPPER CIRCULATION
ACROSS WESTERN IA WITH AN AREA OF COOLING CLOUD TOPS IN ADVANCE OF
THIS MOVING INTO NORTHWEST IL. THIS IS CORRELATING WITH MAINLY LIGHT
RAIN OR RAIN/SNOW MIX IN THE SMALL WINDOW OF DEEPER MOIST
ADVECTION AHEAD OF THE LOW. SIMPLE EXTRAPOLATION OF THE CURRENT
AREA OF PRECIP IN IOWA AND THE DEVELOPING DEFORMATION ON THE
BACKSIDE CLEARLY INDICATE THE SOUTHERN CWA IS MORE SUPPORTED FOR
PRECIPITATION THAN THE NORTH. AT THE SURFACE...TEMPERATURES ARE
AROUND OR JUST ABOVE FREEZING ACROSS MUCH OF THE FORECAST AREA. A
DEVELOPING COLD FRONT IS ADVANCING SOUTHWARD INTO NORTHERN IL WITH
DEW POINTS IN THE MID TO UPPER 20S NORTH OF THIS FEATURE...ANOTHER
HINDRANCE OF APPRECIABLE PRECIPITATION IN NORTHERN AREAS OF THE
FORECAST AREA.

SHORT RANGE GUIDANCE LIKE ITS LONG RANGE COUNTERPARTS THE PAST
SEVERAL DAYS SHOW A FAIR AMOUNT OF DISCREPANCY...NAMELY ON COVERAGE
OF PRECIP TODAY AND PRECIP TYPE IN THE SOUTHERN CWA THIS
MORNING...BUT THEY LEND SUPPORT TO THE OBSERVATIONAL TRENDS. AS
THE AREA OF RAIN ASSOCIATED WITH ELEVATED ISENTROPIC ASCENT MOVES
INTO THE SOUTHERN FORECAST AREA...PROFILES SUPPORT A PERIOD OF
RAIN OR MIX INITIALLY...AND SOME LOCATIONS MIGHT HAVE AIR
TEMPERATURES RIGHT AT FREEZING. WOULD EXPECT ANY FREEZING RAIN
THREAT TO BE SHORT LIVED AS PROFILES TREND TOWARD SNOW. MESOSCALE
CONVERGENCE AND BAROCLINIC FORCING FOR INDUCED LIFT WOULD BECOME
MORE FAVORED JUST TO THE NORTHEAST OF THE CLOSED 850MB
CIRCULATION AS IT PIVOTS MORE EASTWARD. THAT IS FAVORED ACROSS
THE SOUTHERN TIER OR TWO OF COUNTIES LATER THIS MORNING INTO
EARLY AFTERNOON. PROFILES ARE MILD FOR IDEAL SNOW GROWTH...AND
MAYBE EVEN FOR SNOW AT ALL DOWN TOWARD GIBSON CITY FOR MUCH OF THE
MORNING. HAVE SNOW TOTALS AROUND ONE TO TWO INCHES FROM PERU TO
RENSSELAER AND SOUTHWARD FOR TODAY...WITH SNOW DEPARTING NEAR OR
SOON AFTER SUNDOWN.

AS FOR AREAS NORTH OF INTERSTATE 80...SHOULD SEE A GRADUAL INCREASE
IN LIGHT SNOW AREAWIDE BY MID-MORNING. DRY CORRIDOR NEAR 850MB
SEEN ON EARLY MORNING AMDAR SOUNDINGS OVER CHICAGO SHOULD LIMIT
INTENSITY OF ANY SNOW IN THE NORTHERN FORECAST AREA...AS WILL JUST
LESS FORCING. AREAS OF NORTHEAST ILLINOIS STILL LOOK TO HAVE
ONSHORE FLOW BEHIND THE COLD FRONT...BUT FORECAST INVERSION
HEIGHTS AS WELL AS ADAPTED ONES FROM THE 00Z GRB RAOB LAST
EVE...INDICATE VERY MARGINAL DEPTH OF CONVECTIVE CLOUDS. THUS NOT
EXPECTING MUCH IF ANY ENHANCEMENT TO ALREADY MINIMAL SYNOPTIC
FORCING OVER NORTHEAST IL. COULD SEE SOME DISORGANIZED LIGHT SNOW
OR FLURRIES LATE THIS AFTERNOON INTO THIS EVENING AS PROFILES OF
THE LAKE INDUCED STRATOCU COOL INTO THE ICE INITIATION LAYER...BUT
THIS SHOULD NOT BE A BIG DEAL.

AREAWIDE THE NORTHEAST WINDS WILL INCREASE TO 30 MPH AND MAYBE EVEN
A LITTLE HIGHER JUST OF THE LAKE. WITH MINIMAL SNOW NORTH NOT
EXPECTING ANY BLOWING SNOW ISSUES...AND SOUTH THE LOW SNOW-TO-
LIQUID RATIOS SHOULD SUPPRESS MUCH FOR BLOWING ISSUES...THOUGH
COULD LEAD TO MORE REDUCED VISIBILITY DURING THE TIME OF FALLING
SNOW THIS AFTERNOON.

MTF

&&

.LONG TERM...
329 AM CST

MONDAY THROUGH SATURDAY...

THE DISTURBED FLOW PATTERN WILL TURN MORE NORTHWESTERLY MONDAY AND
TUESDAY AS A MAJOR SYSTEM IS EXPECTED TO DEVELOP OFF THE NORTHEAST
COAST. GIVEN THIS POSSIBLY LEADING TO A SLOWER PATTERN...AS WELL
AS THE TREND OF TODAYS SYSTEM...IT IS QUITE CONCEIVABLE THAT THE
NEXT DISTURBANCE FOR MONDAY AFTERNOON AND NIGHT TRENDS WEST AS
WELL...WHICH THE EC HAS HAD IN ITS SOLUTION FOR THREE CONSECUTIVE
RUNS. THIS SYSTEM THOUGH IS NOT AS STRONG AS TODAYS AS IT IS MORE
OF A SHEARED AREA OF VORTICITY ALONG THE LINGERING BAROCLINIC
ZONE. FORCING FOR PRECIP LOOKS PRETTY LIGHT ONCE AGAIN MONDAY
AFTERNOON AND NIGHT BUT ENOUGH TO GO A LITTLE HIGHER ON POPS FOR
NORTHERN PARTS OF THE FORECAST AREA. RIGHT NOW GUIDANCE IS IN
DECENT AGREEMENT WITH SATURATING DEEP ENOUGH FOR PRECIP TYPE TO BE
LIGHT SNOW IF IT CAN OCCUR...BUT NEED TO KEEP AN EYE OUT FOR SOME
FREEZING DRIZZLE POTENTIAL IN THESE LIGHT ASCENT SITUATIONS.

A SLOW MODERATION LOOKS TO OCCUR TUESDAY INTO WEDNESDAY AND THIS
COULD BE VERY MINIMAL DEPENDING ON CLOUD COVER WHICH REMAINS A BIG
QUESTION MARK. HAVE LEANED MORE CLOUDY TUESDAY BUT STILL THINK
WITH A WESTERLY PUSH WEDNESDAY WOULD HAVE SUN POTENTIAL. LONG
RANGE GUIDANCE INDICATES A PACIFIC SYSTEM TO BE THE NEXT ONE TO
POSSIBLY BRING PRECIPITATION TO THE AREA WEDNESDAY NIGHT INTO
THURSDAY. CONTINUE POPS DURING THIS TIME FRAME AND AT THIS POINT
PROFILES ARE NEAR THE BORDER FOR RAIN OR SNOW...SO DID NOT GET TOO
FANCY WITH THE FORECAST PRECIPITATION TYPE. BEHIND THIS SYSTEM IT
SEEMS FAVORED FOR TEMPERATURES TO COOL SOME DURING THE LATTER
HALF OF THE WEEK...TO SLIGHTLY BELOW NORMAL VALUES. OBVIOUSLY ANY
FRESH SNOW COVER WOULD HELP LEAN THAT MORE TOWARD BELOW NORMAL.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LIGHT SNOW TAPERING TO FLURRIES THIS AFTERNOON.
* MVFR CIGS LIFTING THIS AFTERNOON THEN SCATTERING OUT TONIGHT.
* STRONG/GUSTY NORTHEAST WINDS THRU MID EVENING.
* LIGHT SNOW LATE MONDAY AFTERNOON. CMS

//DISCUSSION...UPDATED 18Z...

LOW PRESSURE NEAR STL WILL SLOWLY TRACK EAST ACROSS THE OHIO
VALLEY THIS AFTERNOON INTO TONIGHT. AS IT DOES...LIGHT SNOW WILL
SLOWLY TAPER OFF TO FLURRIES. NORTHEAST WINDS OFF THE LAKE MAY
ALLOW SOME LIGHT SNOW SHOWERS TO CONTINUE NEAR THE LAKE BUT NOT
EXPECTING ANYTHING SIGNIFICANT. HAVE MAINTAINED MENTION OF VFR
LIGHT SNOW THROUGH EARLY EVENING THOUGH CONFIDENCE REGARDING END
TIME IS FAIRLY LOW. VISIBILITIES AND CIGS ARE SLOWLY TRENDING UP
AND THIS WILL CONTINUE THRU THE AFTERNOON WITH PREVAILING MVFR
EXPECTED. NORTHEAST WINDS WILL REMAIN STRONG AND GUSTY WITH GUSTS
INTO THE MID/UPPER 20 KT RANGE THROUGH LATE AFTERNOON WITH A SLOW
RELAXING OF THE SPEEDS/GUSTS THRU THE EVENING. A RIDGE AXIS WILL
MOVE ACROSS THE AREA TOWARD DAYBREAK WITH WINDS BECOMING LIGHT AND
VARIABLE AND THEN SWITCHING TO SOUTHERLY MID/LATE MONDAY MORNING.

A WEAK CLIPPER SYSTEM WILL MOVE SOUTHEAST ACROSS THE WESTERN LAKES
MONDAY AFTERNOON INTO MONDAY NIGHT AND WHILE THIS FEATURE HAS BEEN
CONSISTENT FOR A FEW DAYS...IT HAS LIMITED MOISTURE. HOWEVER...
THERE COULD BE A PERIOD OF LIGHT SNOW BY MID/LATE AFTERNOON ACROSS
NORTHERN IL THAT CONTINUES INTO MONDAY EVENING. THE CLOUD LAYERS
APPEAR DEEP ENOUGH FOR LIGHT SNOW BUT AS THE MID LEVELS DRY OUT IN
THE EVENING...PRECIP COULD TRANSITION TO LIGHT FREEZING DRIZZLE.
STILL SOME UNCERTAINTY HOW THIS PLAYS OUT...BUT OPTED TO INCLUDE A
PROB30 IN THE 30HR ORD TAF. CMS

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH FOR LIGHT SNOW TAPERING TO FLURRIES THIS AFTERNOON...LOW
  FOR SPECIFIC TIMING AND ASSOCIATED CIGS/VIS.
* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD.
* MEDIUM FOR LIGHT SNOW MONDAY AFTERNOON...LOW FOR ASSOCIATED
  CIGS/VIS. CMS

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...CHANCE LIGHT SNOW/MVFR.

TUESDAY...MVFR CIGS POSSIBLE.

WEDNESDAY...MAINLY VFR DURING THE DAY THEN CHANCE OF -RASN AND
MVFR/IFR AT NIGHT.

THURSDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS.

SATURDAY...CHANCE OF LIGHT SNOW/MVFR.

RATZER

&&

.MARINE...
131 PM CST

A QUICK MOVING CLIPPER SYSTEM...CURRENTLY CENTERED ACROSS SOUTHERN
ILLINOIS...WILL RAPIDLY SHIFT EASTWARD TOWARDS THE ATLANTIC COAST
BY MONDAY MORNING. NORTHEASTERLY WINDS OF 30-35 KT CONTINUE ACROSS
THE SOUTHERN 1/3RD OF LAKE MICHIGAN...AND THESE WINDS LOOK TO
CONTINUE FOR THE NEXT FEW HOURS...BEFORE A DIMINISHING TREND BEGINS
EARLY THIS EVENING. ANOTHER WEAKENING LOW WILL SHIFT SOUTHWARD JUST
WEST OF THE LAKE LATE MONDAY AND MONDAY NIGHT. THIS WILL RESULT IN A
PERIOD OF SOUTHERLY WINDS OVER THE LAKE DURING THIS PERIOD. LATER IN
THE WEEK ANOTHER LOW IS EXPECTED TO IMPACT THE GREAT LAKES REGION.
THIS SYSTEM STILL HAS THE POTENTIAL TO PRODUCE A PERIOD OF STRONG
SOUTHERLY WINDS LATE WEDNESDAY AND WEDNESDAY NIGHT...FOLLOWED BY A
PERIOD OF STRONG NORTHERLY WINDS THURSDAY INTO EARLY FRIDAY.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878 UNTIL 6 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...6 PM SUNDAY TO 9 AM MONDAY.

&&

$$

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