Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 242052
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
252 PM CST SAT JAN 24 2015

.SHORT TERM...
250 PM CST

THROUGH SUNDAY...

MAIN FORECAST CONCERN WILL BE PASSAGE OF A CLIPPER SYSTEM ACROSS THE
MIDWEST BRINGING ACCUMULATING SNOWFALL AND FOR SOME AREAS A WINTRY
MIX OF PRECIPITATION. CLOUD COVER WILL CONTINUE TO INCREASE THE
REMAINDER OF THE TODAY AS THE LOW DIVES ACROSS THE DAKOTAS INTO
MINNESOTA. MODELS ARE IN DECENT AGREEMENT TRACKING THE SURFACE LOW
ACROSS FAR NE MO LATE TONIGHT INTO DOWNSTATE IL BY SUNDAY AFTERNOON.
1000MB-700MB LAYER MAX WETBULBS ARE UP TO 2C SOUTH OF THE I-80
CORRIDOR THROUGH LATE MORNING/EARLY AFTERNOON SUNDAY...THEN START TO
FALL QUICKLY FROM THE NORTH THROUGH THE AFTERNOON HOURS. WITH THAT
IN MIND...THINK THAT PRECIP WILL BEGIN AS PRIMARILY SNOW NORTH OF
THE I-80 CORRIDOR WITH RAIN/SLEET TO THE SOUTH...EVENTUALLY CHANGING
OVER TO ALL SNOW. MODELS IN GENERAL HAVE THE AXIS OF HIGHEST QPF
SOUTH OF I-80...BUT WITH WARMER TEMPERATURES...IT APPEARS THE
HIGHEST SNOWFALL MAY OCCUR A LITTLE FARTHER NORTH. DID BUMP UP SNOW
TOTALS ACROSS PORTIONS OF THE CHICAGO METRO WHERE MODELS CONTINUE TO
ADVERTISE AN INCREASE IN THE LOW LEVEL LAPSE RATES AS WINDS TURN NE
OFF LAKE MICHIGAN WITH LAKE ENHANCEMENT APPEARING AT LEAST POSSIBLE.
NAM AND REGIONAL GEM GUIDANCE BOTH SHOW A SLIGHT MAX IN THE QPF
VALUES OVER THE AREA AND HAVE BEEN CONSISTENTLY ADVERTISING A BUMP IN
THE LOW LEVEL OMEGA STARTING LATE MORNING INTO THE AFTERNOON.
FORECAST SNOW TOTALS FOR THIS EVENT WILL BE 1-3 INCHES WEST OF A
WAUKEGAN TO STREATOR LINE...AND 2-4 INCHES EAST. WILL HAVE TO
MONITOR THE MESOSCALE BANDING THREAT FOR SOME LOCALLY HIGHER
AMOUNTS. NAM GUIDANCE IN PARTICULAR WAS HINTING AT AN AREA OF LOW
LEVEL FGEN DEVELOPING FOR EAST CENTRAL IL AND NORTHWEST
INDIANA...BUT LAPSE RATES UPSTAIRS ARENT OVERLY IMPRESSIVE IN THE
LATEST MODELS RUNS. ALSO SURFACE LOW SLOWLY FILLING AS IT MOVES
TOWARDS THE OHIO VALLEY WILL ALSO BE A LIMITING FACTOR. WILL ISSUE
AN UPDATED SPS THIS AFTERNOON FOR THE SNOWFALL. AS MENTIONED...STILL
CANNOT RULE OUT SOME LOCALLY HIGHER AMOUNTS THAT MIGHT REQUIRE AN
ADVISORY HOWEVER DONT HAVE MUCH CONFIDENCE WHERE OR EVEN IF THIS
WOULD OCCUR.

WINDS WILL START TO RAMP UP FROM EARLY MORNING ON OUT OF THE
NORTHEAST AS A TIGHT GRADIENT SWEEPS ACROSS THE REGION ON THE BACK
SIDE OF THE LOW. NORTHEAST WINDS ARE EXPECTED TO GUST 30-35 MPH AT
TIMES ACROSS THE AREA. THESE MODERATELY STRONG NORTHEAST WINDS OVER
LAKE MICHIGAN WILL DRIVE 8-11 FOOT WAVES INTO THE NEARSHORE WATERS
AND SOME OF THESE WAVES MAY RESULT IN SOME MINOR LAKESHORE FLOODING
TO EXPOSED AREAS. IN ADDITION...BLOWING SNOW MAY BECOME A PROBLEM
ESPECIALLY IN OPEN AREAS. WETTER THAN AVERAGE SNOW...PARTICULARLY
SOUTH OF I-80 MAY HELP LIMIT THE BLOWING SNOW SOME.

DEUBELBEISS

&&

.LONG TERM...

SUNDAY NIGHT THROUGH SATURDAY...

250 PM...FORECAST CONCERNS INCLUDE A CHANCE OF LIGHT SNOW MONDAY
AFTERNOON INTO MONDAY NIGHT AND THEN THE POTENTIAL FOR A WINTRY
MIX WEDNESDAY NIGHT.

LIGHT SNOW WILL BE ENDING ACROSS THE SOUTHEAST CWA SUNDAY EVENING
AS NORTHEAST WINDS STEADILY DIMINISH SUNDAY EVENING. LAKE EFFECT
CLOUDS AND PERHAPS A FEW FLURRIES ARE POSSIBLE SUNDAY EVENING. LOWS
BY MONDAY MORNING WILL DIP INTO THE TEENS MOST LOCATIONS BUT AS A
WEAK RIDGE PASSES ACROSS THE AREA AND WINDS BECOME LIGHT OR CALM...
LOWS COULD BE SEVERAL DEGREES COLDER DEPENDING ON CLOUD COVER.

ANOTHER WEAK CLIPPER SYSTEM MOVES SOUTHEAST ACROSS THE WESTERN
LAKES MONDAY AFTERNOON INTO MONDAY NIGHT AS IT SLOWLY BEGINS TO
WEAKEN. MODELS VARY SOME ON TIMING AND PRECIP ARRIVAL. A CONSENSUS
WOULD HAVE THE ARRIVAL DURING MONDAY AFTERNOON. INITIALLY THE
SATURATION IS DEEP ENOUGH THAT PRECIP SHOULD BEGIN AS LIGHT SNOW.
BUT INTO THE EVENING...MID LEVELS BEGIN TO DRY OUT SOME AND PRECIP
COULD TRANSITION MORE TO A LIGHT SNOW MIXED WITH OR JUST FREEZING
DRIZZLE. FAIRLY LOW CONFIDENCE AT THIS POINT...SO MAINTAINED JUST
LIGHT SNOW FOR THE ENTIRE DURATION FOR NOW.

PROGRESSIVE PATTERN BRINGS ANOTHER RIDGE OF HIGH PRESSURE ACROSS
THE REGION TUESDAY NIGHT INTO WEDNESDAY AND THEN ANOTHER STORM
SYSTEM WEDNESDAY NIGHT INTO THURSDAY MORNING. MODELS CURRENTLY IN
DECENT AGREEMENT WITH THE TRACK OF THIS LOW GENERALLY RIGHT ACROSS
THE CWA EARLY THURSDAY MORNING. WITH THIS TRACK...TEMPS LIKELY TO
REMAIN FAIRLY STEADY IN THE LOWER/MID 30S WEDNESDAY NIGHT AND
THERMAL PROFILES WOULD SUGGEST PRECIP WOULD BE MAINLY RAIN OR
PERHAPS FREEZING RAIN...IF SURFACE TEMPS REMAINED BELOW FREEZING.
AND ALSO COULD BE SOME SNOW IF THE LOW WERE TO SPEED UP AND/OR
TRACK FURTHER SOUTH. THUS DID NOT GET TOO SPECIFIC WITH PRECIP
TYPE WEDNESDAY NIGHT INTO THURSDAY BUT A WINTRY MIX IS POSSIBLE.
CMS

&&

.AVIATION...

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

* MVFR CIGS WILL LOWER TOWARDS 700-1000FT AGL ARND 21Z THEN
  POSSIBLY DIP FURTHER TO NEAR 400-600FT AFT 6Z.

* WEST WINDS ARND 5-10KT...QUICKLY SHIFTING EAST AFTER MIDNIGHT
  AND INCREASING TO 10-18KT GUSTS TO 25KT BY DAYBREAK SUN. GUSTS
  INCREASE TOWARDS 30KT SUN MORNING.

* SNOW DEVELOPS JUST BEFORE DAYBREAK SUN...WITH PEAK TIMING
  BETWEEN 14-17Z FROM PERIODS OF STEADIER SNOW. CIGS WILL LOWER
  TOWARDS IFR CONDS WITH POSSIBLE IFR VSBYS FROM STEADY SNOW.

BEACHLER

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

VISIBLE IMAGERY INDICATES SOME CLEARING HAS TAKEN PLACE LATE THIS
MORNING ACROSS NORTHEAST IL/NORTHWEST IN...HOWEVER THERE IS A
WEDGE OF MVFR CIGS STARTING TO CREEP SOUTHEAST ACROSS NORTHWEST
IL. GUIDANCE AND TIMING WOULD INDICATE THE MVFR CIGS RETURNING TO
ORD/MDW ARND 19Z. THEN THE FOCUS WILL TURN TOWARDS THE APPROACHING
WINTER STORM SYSTEM. GUIDANCE CONTINUES TO SHIFT THE TRACK OF THE
SYSTEM FURTHER SOUTH/SOUTHWEST OF CHICAGO. THIS WILL LIKELY
DICTATE WHERE THE STEADIER/TIMING OF SNOW WILL OCCUR SUN MORNING.
AT THIS TIME HAVE ONLY MADE MINOR ADJUSTMENTS TO THE GOING
FORECAST...WITH SNOW DEVELOPING AFTER MIDNIGHT. POSSIBLY SEEING
REDUCED VSBYS FROM STEADIER SNOW BETWEEN 13-17Z. AS THE LOW PASSES
TO THE SOUTH...THE PRESSURE GRADIENT WILL RAPIDLY INCREASE ALONG
THE NORTHERN TIER OR NEAR THE TAF SITES. THIS WILL RESULT IN A
QUICK SHIFT TO EAST WINDS AND GUSTS APPROACHING 20KT ARND
DAYBREAK...THEN INCREASING TO NEAR 30KT BY MID TO LATE MORNING.

IFR CIGS WILL REMAIN ACROSS THE TAF SITES INTO SUN MIDDAY...THEN
SOME DRIER AIR WILL BEGIN TO FILTER INTO THE REGION AND BRING CIGS
BACK TO MVFR LATE SUN AFTN.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS RETURNING TO MVFR CONDS...MEDIUM
  CONFIDENCE IN PRECISE TIMING OF MVFR CIGS.

* MEDIUM CONFIDENCE IN IFR CIGS DEVELOPING THIS AFTN...ALONG WITH
  DURATION OF IFR CIGS.

* MEDIUM CONFIDENCE IN TIMING OF CIGS LOWERING FURTHER TO IFR
  CONDS LATER TONIGHT.

* HIGH CONFIDENCE IN SNOW DEVELOPING AFTER MIDNIGHT...MEDIUM
  CONFIDENCE IN PRECISE TIMING OF STEADIER SNOW BETWEEN 13-17Z.

* HIGH CONFIDENCE IN WINDS QUICKLY TURNING EAST AND GUSTS
  DEVELOPING.

BEACHLER

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

SUNDAY NIGHT...MVFR CIGS POSSIBLE.

MONDAY...CHANCE OF LIGHT SNOW IN THE AFTERNOON. MVFR POSSIBLE.

TUESDAY...MVFR CIGS POSSIBLE.

WEDNESDAY...MAINLY VFR...CHANCE OF SNOW AND MVFR/IFR AT NIGHT.

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

FRIDAY...PRIMARILY VFR.

RATZER

&&

.MARINE...
127 PM CST

A COLD FRONT WILL BEGIN TO SHIFT SOUTHWARD DOWN LAKE MICHIGAN LATE
THIS AFTERNOON...WITH WINDS EXPECTED TO PICK UP OUT OF THE NORTH
INTO TONIGHT. WINDS OVER THE LAKE WILL THEN CONTINUE TO INCREASE
INTO SUNDAY AS A QUICK MOVING CLIPPER SYSTEM TRACKS SOUTHEASTWARD
ACROSS SOUTHERN ILLINOIS. THIS WILL RESULT IN NORTHEASTERLY WINDS UP
TO 30 KT BY EARLY SUNDAY MORNING ACROSS MOST OF THE LAKE...WITH THE
STRONGEST WINDS EXPECTED ACROSS THE SOUTHERN END OF THE LAKE...WHERE
A FEW GALE FORCE GUSTS TO 35 KT ARE POSSIBLE ON SUNDAY. THIS WILL
RESULT IN WAVES UP TO 10 FEET INTO THE NORTHEAST ILLINOIS SHORES
THROUGH SUNDAY EVENING. THE WINDS WILL QUICKLY ABATE ACROSS THE LAKE
SUNDAY NIGHT AS THE LOW SHIFTS TOWARDS THE EASTERN SEABOARD.

ANOTHER WEAKENING LOW WILL SHIFT SOUTHWARD OVER OR JUST WEST OF THE
LAKE LATE MONDAY AND MONDAY NIGHT. THIS WILL RESULT IN A PERIOD OF
LIGHT 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 WEDNESDAY NIGHT...FOLLOWED BY STRONG NORTHERLY WINDS
THURSDAY INTO FRIDAY.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...6 AM SUNDAY TO 9 AM MONDAY.

&&

$$

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