Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 250247
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
847 PM CST WED DEC 24 2014

.UPDATE...
845 PM CST

LOW PRESSURE CONTINUES TO DEEPEN ACROSS EASTERN LAKE HURON THIS
EVENING WHILE HIGH PRESSURE RIDGING MOVES EAST ACROSS THE CENTRAL
PLAINS AND UPPER MISSISSIPPI RIVER VALLEY. THE MAIN UPPER LEVEL
TROUGH AXIS IS NOW PIVOTING TO THE EAST OF THE FORECAST AREA BUT
THERE IS ENOUGH REMNANT LIFT AND LOW LEVEL MOISTURE TO KEEP
DRIZZLE GOING ACROSS MUCH OF THE AREA...WITH SOME VERY SPOTTY
AREAS OF LIGHT RAIN/LIGHT SNOW EMBEDDED. WITH THE TROUGH AXIS
SHIFTING EAST AND UPPER RIDGING QUICKLY APPROACHING FROM THE WEST
DRIZZLE WILL STEADILY END FROM WEST TO EAST EARLY TONIGHT.
TEMPERATURES HAVE BEEN PRETTY STEADY IN THE MID AND UPPER 30S AND
AM NOT ANTICIPATING AREAS TO FALL BELOW FREEZING PRIOR TO DRIZZLE
ENDING AT THIS POINT.

MDB

&&

.SHORT TERM...
257 PM CST

FOR THE REMAINDER OF THE AFTERNOON...THE MAIN FOCUS WILL CENTER ON
THE AREA OF PCPN OVER THE ERN PORTIONS OF THE CWA AND THE CHANCES
FOR SOME LINGERING LIGHT PCPN THIS EVENING.  THE MAIN SFC LOW
CONTINUES TO TRACK THROUGH THE EASTERN GREAT LAKES...BUT IN THE
ABSENCE OF ANY SIGNIFICANT COLD AIR...THE PCPN OVER THE AREA WILL
REMAIN ALL LIQUID THROUGH THE AFTERNOON AND INTO THE EARLY EVENING.
AS THE SFC LOW CONTINUES TO LIFT TO THE NORTH...SOME COOLER AIR
UPSTREAM OVER THE UPPER MISSOURI VALLEY WILL EVENTUALLY FILTER OVER
THE AREA AND SOME LINGERING LIGHT PCPN SHOULD CHANGE OVER TO SOME
SCT LIGHT SNOW...BUT NO ACCUMULATION IS EXPECTED.  AS THE UPPER
TROUGH ASSOCIATED WITH THE SFC LOW CONTINUES TO PUSH TO THE
EAST...BROAD...FLAT UPPER RIDGING WILL BUILD ACROSS THE REGION
TONIGHT.  THE MAIN IMPACT WILL BE TO KEEP TEMPERATURES RELATIVELY
MILD AS WIDESPREAD CLOUD COVER SHOULD BE SLOW TO IMPROVE.  WHILE
TEMPERATURES SHOULD DROP TO AT OR A BIT BELOW THE FREEZING
MARK...WINDS SHOULD REMAIN BREEZY...AROUND 10-15 MPH...SO ANY
RESIDUAL WET SURFACES SHOULD DRY OFF BEFORE THE TEMPS DROP BELOW
FREEZING...SO TRAVEL CONDITIONS OVERNIGHT TONIGHT SHOULD BE
UNIMPEDED.

KREIN

&&

.LONG TERM...
257 PM CST

SINCE THE SYSTEM CURRENTLY IMPACTING THE REGION DID NOT QUITE PAN
OUT AS PREVIOUSLY ANTICIPATED...THE CHANCES FOR A WHITE CHRISTMAS
OVER NRN IL/NWRN IN ARE PRETTY MUCH NIL.  WITH WEAK UPPER RIDGING
CONTINUING TO BUILD ACROSS THE REGION...TEMPERATURES FOR CHRISTMAS
DAY SHOULD BE ALMOST 10 DEGREES ABOVE NORMAL WITH HIGHS IN THE LOWER
40S. AS SFC RIDGING BUILDS TO THE EAST...SFC WINDS WILL ALSO TURN
MORE SOUTHERLY...HELPING TO DRAW WARM AIR INTO THE REGION.
HOWEVER...THIS WILL ALSO SET UP BROAD ISENTROPIC LIFT ACROSS THE
AREA...KEEPING SKIES CLOUDY TO MOSTLY CLOUDY...BUT SOME DRIER AIR
IMPINGING ON THE REGION SHOULD ALLOW FOR AT LEAST SOME PARTIAL
CLEARING AND FILTERED SUNSHINE IN THE AFTERNOON.

THE NEXT CHANCE FOR PCPN WILL LIKELY NOT BE UNTIL LATE FRIDAY NIGHT
OR EARLY SATURDAY.  A STRONG SHORTWAVE CURRENTLY CRASHING INTO THE
PACIFIC NORTHWEST COAST IS EXPECTED TO TAKE A TURN TO THE SOUTHEAST
AND CLOSE OFF OVER THE FOUR CORNERS REGION BY FRIDAY MORNING.
TIMING OF THE NEXT ROUND OF PCPN WILL BE HIGHLY DEPENDENT ON THE
TIMING OF THE SYSTEM EJECTING OUT OF THE FOUR CORNERS AREA.
UNFORTUNATELY...AT THIS POINT...THERE IS LITTLE MODEL CONSENSUS AS
FOR THE TIMING OF THE SYSTEM LIFTING OUT AND REACHING THE LOCAL
AREA...SO HAVE GONE WITH BROAD LOW CHANCE POPS FOR FRIDAY
NIGHT...THOUGH WILL CARRY LIKELY POPS FOR SATURDAY MORNING...LARGELY
IN DEFERENCE TO THE ECMWF/GEM SOLUTIONS WHICH HAVE HAD SOME
RELATIVELY CONSISTENCY WHILE THE GFS IS TRENDING CLOSER TO THE IDEA
OF A WET SATURDAY.  IN A BROAD WARM ADVECTION PATTERN AHEAD OF THE
UPPER TROUGH LIFTING ACROSS THE PLAINS...TEMPERATURES FOR SATURDAY
SHOULD REACH INTO THE 40S...AT LEAST FOR PORTIONS OF THE AREA.  A
COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL BRING IN SOME COOLER
AIR...LATE IN THE DAY...LIKELY KEEPING TEMPERATURES OVER THE NWRN
PORTIONS OF THE CWA A BIT LOWER.

A GENERAL COOLING TREND WILL SET UP BY SATURDAY NIGHT AND CONTINUE
THROUGH THE REMAINDER OF THE FORECAST PERIOD.  FOLLOWING THE PASSAGE
OF THE COLD FRONT SATURDAY...TEMPERATURES WILL DROP OFF...THOUGH NOT
DRAMATICALLY AS THE SYSTEM IS OF PACIFIC ORIGIN.  THE LONGER RANGE
MODELS ARE ADVERTISING A MORE SIGNIFICANT COOL DOWN FOR EARLY NEXT
WEEK AS A NRN STREAM SHORT WAVE TRACKS ACROSS THE UPPER GREAT
LAKES...DRAGGING A COLD FRONT ACROSS THE AREA SUNDAY NIGHT OR MONDAY
MORNING.  THIS SYSTEM WILL USHER IN SIGNIFICANTLY COLDER AIR
ASSOCIATED WITH AN ARCTIC AIRMASS.  BROAD HIGH PRESSURE SHOULD
OVERSPREAD THE REGION AND THE GFS AND ECMWF ARE BOTH INDICATING
850MB TEMPS ARND -10 TO -12C BY TUESDAY MORNING WITH THE COLD
AIRMASS REMAINING OVER THE REGION THROUGH THE REMAINDER OF THE
FORECAST PERIOD.  BY TUESDAY MORNING...ANTICIPATE TEMPERATURES TO
DROP INTO THE UPPER TEENS AND LOWER 20S.  WITH PERSISTENT COLD
ADVECTION...TEMPERATURES COULD DROP INTO THE SINGLE DIGITS BY
WEDNESDAY MORNING. WITH HIGH PRESSURE PREVAILING ACROSS THE REGION
THROUGH MUCH OF THE EXTENDED PERIOD...POPS WILL BE LOW.  THE BEST
CHANCE FOR ANY PCPN...PER THE LATEST LONGER RANGE MODEL SOLUTIONS
WOULD BE FOR SOME LAKE EFFECT SNOW AS A NORTHERLY FETCH SETS UP OVER
LAKE MICHIGAN FOR TUESDAY AND WEDNESDAY.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PATCHY DZ OR LGT RAIN THRU 3Z...THEN JUST SOME ISOLATED DZ.

* LOW END MVFR WITH PATCHY IFR OVERNIGHT.

* LOW END MVFR PERSISTS THRU DAYBREAK.

BEACHLER

//DISCUSSION...UPDATED 00Z...

LOW PRESSURE HAS LIFTED NORTHEAST OF DETROIT...WITH MUCH OF
NORTHERN IL/NORTHWEST IN SEEING THE PRECIP COMING TO AN END.
FORTUNATELY TEMPERATURES HAVE REMAINED WELL ABOVE FREEZING IN MOST
LOCATIONS THAT PRECIP HAS MAINLY FALLEN AS LIGHT RAIN...HOWEVER
TEMPERATURES ARE BEGINNING TO FALL ACROSS NORTHWEST IL...AND MAY
BRING A PERIOD OF LGT SNOW/FLURRIES BEFORE ENDING ARND 3-4Z. THERE
IS SOME CONCERN THAT WITH THE LACK OF STRONG LIFT...THIS MAY
RESULT IN PRECIP BEING LIMITED TO -DZ THRU 3Z. THEN WITH THE LACK
OF A STRONG PUSH OF DRY AIR...SOME PATCHY BR OR PERHAPS DZ WILL
CONTINUE. CIGS HAVE TRIED TO TREND TOWARDS IFR...AND MAY BOUNCE
BETWEEN IFR/LOW-END MVFR OVERNIGHT. GUIDANCE INDICATES THAT JUST
AFT DAYBREAK CIGS MAY START TO INCREASE WITH WEAK HIGH PRESSURE
ARRIVING. HAVE HELD ONTO LOWER CIGS LONGER...THEN GRADUALLY
IMPROVE TO VFR BY MIDDAY CHRISTMAS DAY. WINDS WILL GENERALLY BE
FROM THE WEST...THEN START TO BACK TO SOUTHWEST ARND DAYBREAK.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN WIND DIR/SPEED.

* HIGH CONFIDENCE IN CIGS REMAINING NO BETTER THAN LOW-END
  MVFR...MEDIUM CONFIDENCE IN IFR CIGS TIMING/DURATION.

* MEDIUM/HIGH CONFIDENCE IN PATCHY PRECIP ENDING BY 3Z...LOW
  CONFIDENCE

BEACHLER

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

FRIDAY..MVFR/IFR POSSIBLE.

SATURDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE.

SUNDAY...GENERALLY VFR.

MONDAY AND TUESDAY...MVFR/IFR POSSIBLE. CHANCE OF SNOW TUESDAY.

BEACHLER

&&

.MARINE...

223 PM...LOW PRESSURE NEAR DETROIT IS A BIT WEAKER AND FURTHER
EAST THAN PREVIOUSLY EXPECTED THIS AFTERNOON. THIS LOW WILL
CONTINUE TO DEEPEN AS IT REACHES GEORGIAN BAY TONIGHT. AS IT DOES
THE GRADIENT WILL TIGHTEN AND NORTHWEST WINDS WILL INCREASE UP TO
30 KTS DURING THE EVENING AND CONTINUE INTO THURSDAY MORNING. GALE
POTENTIAL APPEARS TO BE RATHER MARGINAL...AND MAINLY CONFINED TO
THE NORTHERN PORTIONS OF THE LAKE AND WILL BE CANCELING THE GALE
WARNING. THIS LOW WILL CONTINUE TO DEEPEN AS IT MOVES ACROSS
QUEBEC THURSDAY.

ANOTHER WEAKER LOW WILL TRACK FROM MANITOBA TO WESTERN ONTARIO ON
THURSDAY AND BECOME ABSORBED BY THE LOW OVER NORTHERN QUEBEC
THURSDAY NIGHT. HIGH PRESSURE MOVING ACROSS THE GULF COAST WILL
MOVE TO THE CAROLINAS AND MID ATLANTIC FRIDAY MORNING. THE
COMBINATION OF ALL THESE SYSTEMS WILL MAINTAIN STEADY 15-25KT
GRADIENT OVER MUCH OF THE LAKE THROUGH FRIDAY...WHEN A LARGE
TROUGH/COLD FRONT WILL SLOWLY MOVE INTO THE WESTERN LAKES REGION.
A NEW LOW WILL DEVELOP ALONG THIS TROUGH SATURDAY MORNING AND MOVE
NORTHEAST INTO QUEBEC SATURDAY NIGHT. WINDS WILL TURN NORTHWEST
BEHIND THIS TROUGH SATURDAY NIGHT INTO SUNDAY WITH HIGH PRESSURE
BUILDING ACROSS THE PLAINS AND OHIO VALLEY SATURDAY NIGHT INTO
SUNDAY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 PM THURSDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 9 AM
     THURSDAY.

&&

$$

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