Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 240549
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1149 PM CST FRI JAN 23 2015

.SHORT TERM...

TONIGHT AND SATURDAY...

305 PM...NO CONCERNS THROUGH SATURDAY EVENING. LOW CLOUDS CONTINUE
TO ERODE FROM THE NORTH AND THE SOUTHWEST THIS AFTERNOON. THIS
TREND WILL CONTINUE THIS EVENING AS THE BACK EDGE PUSHES EAST.
HOWEVER...AN EXTENSIVE BAND OF MID CLOUDS WILL SPREAD BACK ACROSS
THE AREA THIS EVENING AHEAD OF AN APPROACHING COLD FRONT. VERY
LIMITED MOISTURE WITH THIS FRONT AND NOT EXPECTING ANY PRECIP
THOUGH A SPRINKLE OR FLURRY CAN/T BE COMPLETED RULED OUT...BUT NO
MENTION IN THE FORECAST. CLOUD COVER HELPED HOLD HIGHS TODAY IN
THE LOWER/MID 30S AND WITH SOME PARTIAL CLEARING AT TIMES...EXPECT
LOWS TONIGHT TO DIP INTO THE MID/UPPER 20S...THOUGH SOME
UNCERTAINTY WITH APPROACHING MID CLOUDS AND THEN ANOTHER AREA OF
LOW CLOUDS OVER THE UPPER MIDWEST WHICH WILL BE SPREADING SOUTH
ACROSS THE AREA SATURDAY MORNING. IF THIS CLOUD COVER DOES BECOME
OVERCAST...HIGHS ON SATURDAY WILL LIKELY BE TEMPERED SOME AS
WELL...PERHAPS ONLY IN THE MID 30S. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH FRIDAY...

305 PM...MAIN FORECAST CONCERN IS ACCUMULATING SNOW LATE SATURDAY
NIGHT THROUGH SUNDAY AFTERNOON...WITH POSSIBLE LAKE EFFECT SNOW
SHOWERS SUNDAY NIGHT AND ANOTHER WEAKER CLIPPER SYSTEM MONDAY
NIGHT...FOLLOWED BY MODERATE/MILD TEMPS MIDDLE OF NEXT WEEK.

DECENT AGREEMENT WITH THE TRACK OF THE SURFACE LOW OF THE NEXT
CLIPPER SYSTEM SATURDAY NIGHT INTO SUNDAY WITH THE 12Z GFS A BIT
FURTHER SOUTHWEST OF THE REST OF THE MODELS...WHICH TRACK THE LOW
FROM ROUGHLY MLI TO IND SUNDAY MORNING. THERMAL PROFILES SUGGEST
PRECIP TYPE WILL BE ALL SNOW...BUT INITIALLY COULD BE SOME RAIN
MIXED IN ACROSS THE SOUTHERN CWA. IN ADDITION...SNOW/WATER RATIOS
COULD BE RATHER LOW TO START...YIELDING A WETTER SNOW. BUT AS THE
LOW TRACKS TO THE SOUTHEAST...COLDER AIR WILL SLOWLY SPREAD ACROSS
THE AREA WITH THE SNOW LIKELY BECOMING DRIER BY LATE MORNING AND
INTO THE AFTERNOON. THIS MAKES SNOWFALL AMOUNTS A BIT TRICKY...
ESPECIALLY IF THE TRACK OF THE LOW ENDS UP A LITTLE FURTHER SOUTH
AS THE GFS SUGGESTS...COLDER AIR WOULD ARRIVE SOONER. POSSIBLE
LAKE ENHANCEMENT WITH NORTHEAST FLOW ALSO ADDS TO THE UNCERTAINTY
REGARDING AMOUNTS. THEREFORE...DIDN/T MAKE ANY SIGNIFICANT
CHANGES TO THE GOING FORECAST WITH 2-4 INCHES NORTH OF A SQI/IKK
LINE...1-2 INCHES SOUTH OF THAT LINE. BUT AS IS ALWAYS THE
CASE...MINOR CHANGES IN THE TRACK COULD CAUSE LARGE CHANGES TO THE
FORECAST AS TRENDS EMERGE.

TEMPERATURES BEGIN TO FALL BY MID/LATE SUNDAY AFTERNOON ACROSS THE
NORTH. NORTHEASTERLY WINDS INCREASE WITH GUSTS TO 30 MPH AND
DEPENDING ON HOW DRY THE SNOW BECOMES...THERE COULD BE SOME
BLOWING SNOW BUT AGAIN...ITS TOO EARLY FOR SPECIFICS OR HOW MUCH
OF A PROBLEM THIS COULD BECOME.

THE NORTHEAST AND THEN NORTHERLY WINDS MAY ALLOW SOME LAKE EFFECT
SNOW SHOWERS TO DEVELOP SUNDAY EVENING ACROSS NORTHEAST IL AND
THEN INTO NORTHWEST INDIANA. BUT INVERSION HEIGHTS ARE RATHER
LOW...PERHAPS NO HIGHER THAN 4KFT AND WINDS BEGIN TO TURN BACK
EASTERLY BY MONDAY MORNING. THUS ANY LAKE EFFECT POTENTIAL LOOKS
MINIMAL.

ANOTHER CLIPPER QUICKLY DROPS SOUTHEAST ACROSS THE WESTERN LAKES
MONDAY AFTERNOON INTO MONDAY NIGHT...AS IT BEGINS TO WEAKEN. A
BAND OF LIGHT SNOW IS POSSIBLE WITH THIS FEATURE ESPECIALLY MONDAY
EVENING AND SOME AREAS MAY SEE AN INCH OR TWO DEPENDING ON WHERE
IT TRACKS. HAVE INCLUDED JUST LIGHT QPF AMOUNTS FOR NOW.

HIGH PRESSURE MOVES ACROSS THE AREA TUESDAY AND TUESDAY NIGHT AS
FLOW TURNS BACK SOUTH WEDNESDAY AND TEMPS MODIFY BACK INTO THE 30S
THOUGH WITH AN EXPECTED SNOW PACK BY THEN...LOW CONFIDENCE ON HOW
WARM TEMPS WILL BECOME. ANOTHER CLIPPER SYSTEM MOVES ACROSS THE
LAKES REGION WEDNESDAY NIGHT AND THURSDAY...WITH A CHANCE OF LIGHT
RAIN OR LIGHT SNOW WEDNESDAY NIGHT INTO THURSDAY MORNING. CMS

&&

.AVIATION...

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

* MVFR CEILINGS MOVING IN FROM THE NORTHWEST AROUND 08Z AND
  LINGERING THROUGH SATURDAY MORNING.

* WESTERLY WINDS NEAR 10 KTS TODAY...DIMINISHING AND EVENTUALLY
  BECOMING EAST-NORTHEAST AFTER MIDNIGHT SATURDAY AND BECOMING
  GUSTY TOWARD MORNING.

* SNOW DEVELOPING TOWARD 12Z SUNDAY. IFR/LIFR CONDITIONS LIKELY
  IN SNOW JUST BEYOND END OF ORD 30 OUR TAF PERIOD.

RATZER

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

SURFACE LOW PRESSURE WAS MOVING EAST INTO EASTERN CANADA LATE THIS
EVENING...WITH A WEAKER TROUGH OF LOW PRESSURE TRAILING SOUTHWEST
INTO THE WESTERN GREAT LAKES REGION. THIS TROUGH WILL MOVE
SOUTHEAST ACROSS THE TERMINAL SITES EARLY THIS MORNING WITH A
SUBTLE WIND SHIFT FROM WEST-SOUTHWEST TO WEST-NORTHWEST...AS WELL
AS AN AREA OF MVFR STRATUS WHICH WILL SPREAD ACROSS THE AREA IN
THE 07-09Z TIME FRAME PER EXTRAPOLATION OF SATELLITE IMAGERY. SOME
LARGE BREAKS IN THE STRATUS BACK ACROSS WESTERN/NORTHWEST WISCONSIN
SUGGEST IT MAY TEND TO ALLOW SOME BREAKS TO VFR CONDITIONS BY
MIDDAY...THOUGH MODEL SOUNDINGS REMAIN FAIRLY MOIST IN THE LOWEST
FEW THOUSAND FEET NEAR THE GROUND.

OF GREATER CONFIDENCE IS THE APPROACH OF A DIGGING MID-LEVEL
DISTURBANCE TONIGHT...WITH ASSOCIATED DEEPENING SURFACE LOW
PRESSURE EXPECTED TO PASS SOUTHWEST OF TERMINALS EARLY SUNDAY
MORNING. MODELS HAVE BEEN FAIRLY CONSISTENT IN SATURATING THE
COLUMN DURING THE PRE-DAWN HOURS OF SUNDAY MORNING WITH SNOW
EXPECTED TO DEVELOP BY 12Z. IFR/LIFR CONDITIONS EXPECTED IN
SNOW SHORTLY THEREAFTER...JUST BEYOND END OF CURRENT TAF PERIODS.
IN ADDITION...DEEPENING OF THE SURFACE LOW TO THE SOUTHWEST OF THE
TERMINALS WILL RESULT IN WINDS SHIFTING TO THE EAST-NORTHEAST AND
INCREASING EARLY SUNDAY MORNING...LIKELY GUSTING 25-30 KT BY MID-
MORNING SUNDAY.

RATZER


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

* HIGH IN WIND TRENDS...THOUGH MEDIUM-LOW IN DIRECTION SATURDAY
  EVENING AS SHIFT TO EAST-NORTHEAST OCCURS.

* MEDIUM-HIGH IN TIMING OF MVFR DECK EARLY THIS MORNING. LOW IN
  DISSIPATION TIMING LATER TODAY.

* MEDIUM-HIGH IN TIMING SNOW TO DEVELOP BEFORE SUNRISE SUNDAY.

RATZER

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

SUNDAY...SNOW. IFR LIKELY PERIODIC LIFR POSSIBLE.

MONDAY...SLIGHT CHANCE OF -SN. MVFR PROBABLE W/CHANCE OF IFR.

TUESDAY THROUGH THURSDAY...PRIMARILY VFR. MAINLY DRY.

IZZI

&&

.MARINE...
122 PM CST

SOUTHWESTERLY WINDS WILL GRADUALLY WEAKEN TONIGHT...THEN A COLD
FRONT WILL SHIFT OVER THE LAKE ON SATURDAY AS THE PARENT SURFACE LOW
TRACKS ACROSS NORTHERN QUEBEC. THIS WILL SET UP A NORTHERLY FLOW
DOWN THE LAKE LATER SATURDAY. A FAST MOVING STOUT CLIPPER SYSTEM
WILL MOVE SOUTH OF THE LAKE ON SUNDAY MORNING...AND THIS LOOKS TO
SET THE STAGE FOR A PERIOD OF STRONG NORTHEASTERLY WINDS UP AROUND
30 KT OVER THE LAKE. THIS WILL LIKELY PRODUCE HIGH WAVES OVER 5 FEET
ACROSS MUCH OF SOUTHERN END OF LAKE MICHIGAN SUNDAY AND SUNDAY NIGHT.
FOLLOWING THIS SYSTEM...ANOTHER STORM SYSTEM IS EXPECTED TO IMPACT
THE GREAT LAKES REGION FOR THE MIDDLE TO END OF NEXT WEEK. IT
APPEARS THIS COULD PRODUCE SOUTHERLY GALE FORCE WINDS OVER MUCH OF
THE LAKE LATE WEDNESDAY AND WEDNESDAY NIGHT...FOLLOWED BY A PERIOD
OF POTENTIALLY GALE FORCE NORTHERLY WINDS THURSDAY AS THE SYSTEM
PASSES OVER THE EASTERN LAKES.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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