Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 260743
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
143 AM CST MON JAN 26 2015

.UPDATE...
820 PM CST

PCPN IS WINDING DOWN ACROSS THE AREA WITH ONLY SOME LINGERING
LIGHT SNOW SOUTH OF THE KANKAKEE RIVER. WHILE WINDS ARE CURRENTLY
STILL RATHER BREEZY ACROSS THE AREA...THE GENERAL TREND OF THE
REMAINDER OF THE EVENING AND OVERNIGHT SHOULD BE FOR WINDS TO
DIMINISH AND ANY LINGERING SNOW SHOULD PUSH OUT OF THE AREA.
TEMPERATURES SHOULD ALSO DROP OFF WITH PARTIALLY CLEARING SKIES
AND SOME COOLER AIR FILTERING IN AS THE LOW PRESSURE CENTER
ASSOCIATED WITH THE SYSTEM THAT BROUGHT TODAY`S PRECIPITATION
MOVES OFF TO THE SOUTHEAST.

HAVE MADE SOME CHANGES TO THE GOING FORECAST FOR TOMORROW. THE
LATEST 00Z MODEL RUNS ARE TRENDING TOWARD THE NEXT CLIPPER
DROPPING A LITTLE FARTHER SOUTH...WITH SOME MODEST LIFT IN THE
ZONE AHEAD OF A WEAK WARM FRONT ASSOCIATED WITH THE NEXT CLIPPER.
SO HAVE INCREASED POPS...WITH LIKELY POPS FOR THE AFTERNOON HOURS
ACROSS MUCH OF THE AREA...WITH THE EXCEPTION OF THE FAR SOUTHERN
PORTIONS OF THE CWA. ALSO...THE THERMAL PROFILES IN THE LATEST
MODEL SOUNDINGS SUGGEST THAT THE PCPN SHOULD BE ALL SNOW...WITH A
DEEP ENOUGH SATURATED LAYER TO SUPPORT ALL SNOW...AND LESSER
CHANCES FOR FREEZING DRIZZLE. SO...HAVE REMOVED THE FREEZING
DRIZZLE MENTION FOR THE DAYTIME HOURS. STILL FEEL THAT THERE IS A
BETTER CHANCE FOR FREEZING DRIZZLE TOMORROW NIGHT AS DRIER AIR
ALOFT LOWERS THE DEPTH OF THE SATURATED LAYER ENOUGH TO MINIMIZE
THE CHANCE FOR ICE PRODUCTION IN THE SATURATED LAYER. WHILE POPS
HAVE BEEN RAISED...THERE IS LITTLE AVAILABLE DEEP LAYER
MOISTURE...SO ACTUAL SNOWFALL AMOUNTS SHOULD BE LIGHT...ONLY
PERHAPS A COUPLE TENTHS OF AN INCH OF ACCUMULATION.

KREIN

&&

.SHORT TERM...
206 PM CST

TONIGHT THROUGH MONDAY NIGHT...

COOL AIR HAS STRUGGLED TO SLIDE SOUTH THIS AFTERNOON...HOWEVER TEMPS
ARE BEGINNING TO FALL INTO THE UPR 20S ACROSS FAR NORTHEAST IL.
ACROSS THE CENTRAL/SOUTHERN CWFA TEMPS REMAIN IN THE LOW 30S WITH
DEW POINT DEPRESSIONS NOT MUCH MORE THAN 1 TO 2 DEGREES. NORTH OF
I-80 PRECIP IS MAINLY FLURRIES...WITH A RAIN/SNOW MIX SLOWLY
CHANGING TO ALL SNOW LATER THIS AFTERNOON ACROSS THE SOUTHERN CWFA.
THE SHORTWAVE THAT BROUGHT THE LIGHT SNOW CONTINUES TO SLIDE EAST
ACROSS SOUTHERN IL...AND WILL STEADILY BRING AN END TO THE PRECIP
ACROSS THE FORECAST AREA THIS EVENING FROM NORTHWEST TO SOUTHEAST.
WINDS WILL GRADUALLY DIMINISH AS WELL AS THE PRESSURE GRADIENT
RELAXES.

SFC RIDGE CENTERED TO THE NORTH THIS AFTERNOON...WILL SAG SOUTH AND
EXPAND TO COVER A PORTION OF THE WESTERN GREAT LAKES/MISSOURI VALLEY
OVERNIGHT. WHILE SOME EROSION TO THE CLOUDS IS PROBABLE NORTH OF THE
FORECAST AREA...EXPECT SOME DECREASE IN CLOUDS CLOSER TO DAYBREAK
MON. CURRENTLY EXPECT OVERNIGHT LOWS TO DIP INTO THE MID/UPR
TEENS...HOWEVER THIS WILL LIKELY NOT OCCUR UNTIL CLOSER TO DAYBREAK
MON.

THE BRIEF BREAK IN CLOUDS MON MORNING WILL QUICKLY GIVE WAY TO THE
NEXT CLIPPER SYSTEM ARRIVING MON AFTN/EVE. GUIDANCE HAS MAINTAINED A
PROGRESSIVE LOOK TO THIS NEXT WAVE...HOWEVER OPERATIONAL SOLUTIONS
ARE EQUALLY BULLISH ON EROSION OF MOISTURE WITHIN THE LOWEST FEW
LAYERS OF THE ATMOS LATE MON NGT. HAVE SOME CONCERN ABOUT P-TYPE MON
AFTN/EVE. AT THE ONSET MOISTURE WILL QUICKLY SATURATE THRU THE -10
DEG C LAYER AND TOUCH THE FAVORED DGZ...HOWEVER THE DEPTH OF THE
MOISTURE BECOMES MORE SHALLOW MON EVE. ALONG WITH THE LACK OF GOOD
LIFT AND SHALLOW MOISTURE...IT IS LOOKING MORE LIKELY THAT PRECIP
MAY BE A MIX OF FREEZING DRIZZLE/LGT-SNOW.

A WEAK THERMAL RIDGE TRIES TO PUSH OVERHEAD MON AFTN...AS LLVL FLOW
TURNS SOUTHWESTERLY. TEMPS SHUD HOVER ARND FREEZING...HOWEVER THIS
WILL HINGE ON CLOUD COVER ARRIVAL AND DEVELOPMENT OF PRECIP. IF THIS
IS DELAYED...TEMPS COULD PUSH A FEW DEGREES WARMER MON EARLY AFTN.

HEIGHTS SLOWLY INCREASE MON NGT...WITH THE MOISTURE PEELING EAST
ALONG WITH THE WEAKENING SHORTWAVE. AT THIS TIME HAVE MAINTAINED A
MENTION OF LGT SNOW OR PATCHY FREEZING DRIZZLE MON NGT...BUT COULD
END UP WITH A DRY PERIOD.

BEACHLER

&&

.LONG TERM...
206 PM CST

TUESDAY THROUGH SUNDAY...
TOWARDS THE MIDDLE OF THE WEEK ENSEMBLES MAINTAIN A HIGH CONFIDENCE
IN THE TROUGH ALONG THE SOUTHEAST CONUS WEAKENING WITH RIDGING
EXPANDING EAST ACROSS THE CENTRAL PLAINS. THIS SHUD PLACE THE BULK
OF THE REGION INTO A WEAK SFC RIDGE TUE/WED. WED AFTN THE SFC RIDGE
QUICKLY SLIDES SOUTHEAST...WHICH COULD ALLOW SOME WARM AIR TO ADVECT
NORTHEAST INTO THE CWFA AND PUSH SFC TEMPS CLOSE TO 40 DEG.

WITH A QUASI-ZONAL SETUP WED NGT/THUR...GUIDANCE SUGGESTS A ROBUST
MID-LVL VORT WILL QUICKLY SLIDE EAST FROM THE ROCKIES TOWARDS THE
PLAINS WED EVE. GUIDANCE THEN FURTHER STRENGTHENS THIS WAVE AND
LIFTS NORTHEAST ACROSS THE FORECAST AREA THUR. SOUNDINGS SUGGESTS
THAT PRECIP COULD START AS MAINLY RAIN WITH THIS SYSTEM...THEN
DYNAMICALLY COOL OVERNIGHT INTO THUR AND TRANSITION PRECIP OVER TO
LGT SNOW.

A RELATIVELY ACTIVE PATTERN CONTINUES TOWARDS THE END OF THE WEEK
INTO EARLY NEXT WEEKEND...WITH TEMPS GENERALLY IN THE UPR 20S/LOW
30S.

BEACHLER

&&

.AVIATION...

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

* BRIEF HIGH-END MVFR CIGS OFF LAKE MICHIGAN SHOULD SCATTER BY
  SUNRISE.

* PERIOD OF LIGHT SNOW POSSIBLE THIS AFTERNOON/EVENING WITH
  REDEVELOPMENT OF MVFR CIGS WHICH LINGER TONIGHT.

RATZER

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

WEAK HIGH PRESSURE RIDGE QUICKLY MOVING INTO FORECAST AREA FROM
THE NORTHWEST OVERNIGHT...THOUGH NORTHEAST WINDS HAVE RESULTED IN
A LAKE-INDUCED PLUME OF MVFR STRATOCU FROM ABOUT ORD EAST...WITH
BASES AROUND 2500 FT. THESE CIGS WILL LIKELY AFFECT ORD/MDW/GYY
UNTIL ABOUT SUNRISE...WHEN MODELS DEPICT NORTHEAST FLOW QUICKLY
BECOMING DISORGANIZED WITH APPROACH OF SFC RIDGE. SFC WINDS TO
BECOME LIGHT/VARIABLE FOR A TIME THIS MORNING AS THE SURFACE HIGH
PRESSURE RIDGE MOVES ACROSS THE TERMINALS...GENERALLY FLOPPING
FROM LIGHT NORTHERLY TO LIGHT SOUTHERLY BY MID-DAY.

IR SATELLITE PICS ALREADY SHOWING HIGH CLOUDS SPILLING INTO THE
REGION FROM THE NORTHWEST AHEAD OF THE NEXT WEAK CLIPPER SYSTEM
WHICH WILL AFFECT THE AREA MONDAY AFTERNOON/EVENING. LOW LEVELS
ARE INITIALLY DRY AND WILL TAKE SOME WORK TO SATURATE FROM ABOVE
AS MID-LEVEL FORCING INCREASES MID-DAY INTO EARLY AFTERNOON. MOST
GUIDANCE DOES INDICATE SOME LIGHT SNOW DEVELOPING DURING THE
PERIOD...THOUGH A COMBINATION OF WEAKENING FORCING AND FORCING
FOCUSED BELOW TEMP LAYER CONDUCIVE TO LARGER SNOWFLAKE GROWTH
SUGGESTS THIS WILL BE RATHER LIGHT. WHILE A FEW INCONSEQUENTIAL
FLURRIES COULD BEGIN SOONER...THE TIMING OF THE PERIOD MOST
LIKELY TO SEE SOME LIGHT SNOW AND MVFR CIG/POSSIBLE IFR VSBY LOOKS
TO BE DURING THE AFTERNOON AT RFD...AND DURING THE LATE AFTN/EARLY
EVENING FOR CHICAGO TERMINALS. SNOW SHOULD TAPER OFF DURING THE
EVENING AT RFD AND BY LATE EVENING FOR CHICAGO TERMINALS...WITH
LOSS OF STRONGER LIFT AND DRYING IN MID-LEVELS. SOME INDICATION
THAT THERE COULD BE A BRIEF PERIOD OF FREEZING DRIZZLE AS THE SNOW
ENDS ESPECIALLY AT RFD WHERE MID-LEVELS DRY A LITTLE MORE
QUICKLY...THOUGH MODELS MAY BE OVERDOING THE DEGREE OF SATURATION
IN THE BOUNDARY LAYER AND CONFIDENCE IS LOW THAT FZDZ WOULD OCCUR.
IT DOES HOWEVER APPEAR THAT SOME SORT OF HIGH-IFR OR LOW-MVFR CIG
MAY LINGER DURING THE NIGHT.

RATZER

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

* HIGH IN WIND TRENDS.

* MEDIUM-LOW IN SNOW TIMING/INTENSITY THIS AFTERNOON AND EVENING.

RATZER

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

TUESDAY...MVFR CIGS POSSIBLE.

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

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

FRIDAY...CHANCE OF MVFR CIGS...ESPECIALLY EARLY.

SATURDAY...CHANCE OF LIGHT SNOW/MVFR CIGS.

IZZI

&&

.MARINE...
143 AM CST

ONLY MARINE FORECAST CONCERNS ARE A BRIEF PERIOD OF ENHANCED
SOUTH-SOUTHEAST WINDS THIS AFTERNOON AND EVENING ESPECIALLY ON THE
NORTHERN PORTION OF THE LAKE...AND AGAIN WEDNESDAY AFTERNOON. GUSTY
NORTH WINDS NEAR 30 KT ARE ALSO LIKELY THURSDAY AND THURSDAY
NIGHT.

WINDS CONTINUE TO DIMINISH QUICKLY ACROSS LAKE MICHIGAN EARLY THIS
MORNING...AS WEAK HIGH PRESSURE RIDING SLIDES SOUTHEAST ACROSS THE
LAKE. THIS RIDGE WILL ALSO PASS QUICKLY OFF TO THE SOUTHEAST THIS
AFTERNOON IN WHAT REMAINS A PROGRESSIVE WEATHER PATTERN...WITH
ANOTHER LOW PRESSURE SYSTEM CURRENTLY NEAR LAKE WINNIPEG MOVING
QUICKLY SOUTHEAST INTO ILLINOIS BY MIDNIGHT TONIGHT WHILE FILLING.
THIS WILL RESULT IN WINDS BECOMING SOUTH AND INCREASING TO AROUND 20
KTS ON THE LAKE THIS AFTERNOON...THEN DECREASING AND BACKING TO THE
NORTHEAST INTO TUESDAY MORNING AS THE LOW PASSES AND WEAKENS.
ANOTHER HIGH PRESSURE RIDGE WILL SETTLE ACROSS THE WESTERN LAKES BY
TUESDAY EVENING.

ANOTHER MORE DEVELOPED LOW WILL FORM ACROSS THE LAKES TUESDAY
NIGHT...AND WILL DEEPEN SLIGHTLY AS IT APPROACHES FROM THE WEST
WEDNESDAY AND PASSES JUST SOUTH OF LAKE MICHIGAN EARLY THURSDAY
MORNING. THIS WILL AGAIN RESULT IN WINDS INITIALLY BECOMING SOUTH
AND INCREASING TO 20-25 KT WEDNESDAY AFTERNOON AND EVENING...THEN
BACKING TO THE NORTH EARLY THURSDAY AND GUSTING NEAR 30 KT AS THE
LOW PULLS AWAY ACROSS THE EASTERN LAKES AND UPPER OHIO VALLEY
THROUGH THURSDAY AFTERNOON AND NIGHT. HIGH PRESSURE THEN SPREADS
ACROSS THE REGION BY FRIDAY AFTERNOON.

FOR THE ILLINOIS AND NORTHWEST INDIANA NEARSHORE WATERS...AS SMALL
CRAFT ADVISORY REMAINS IN EFFECT UNTIL MID-MORNING TODAY...AS WAVES
CONTINUE TO SUBSIDE FROM YESTERDAY/LAST EVENINGS STRONG NORTHEAST
WINDS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 9 AM MONDAY.

&&

$$

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