Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 182049
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 PM CST THU DEC 18 2014

.SHORT TERM...
249 PM CST

MAINLY CLOUDY CONDITIONS EXPECTED TO PERSIST THROUGH FRIDAY AS
DIRTY HIGH PRESSURE MOVES ACROSS THE REGION. HIGH RES GUIDANCE IS
SHOWING HINTS OF LAKE EFFECT PRECIP DEVELOPING TONIGHT...THOUGH
FORECAST SOUNDINGS SUGGEST THAT LOW INVERSION HEIGHTS WOULD KEEP
THE THREAT OF ANY MEASURABLE LAKE EFFECT PRECIP VERY LOW. STILL
PLAUSIBLE THAT THERE COULD BE SOME SNOW GRAINS/FLURRIES INTO
NORTHEAST PORTER COUNTY TONIGHT AS LOW LEVEL FLOW VEERS MORE
NORTHERLY.

IZZI

&&

.LONG TERM...
249 PM CST

GOING INTO THE WEEKEND FAIRLY QUIET CONDITIONS EXPECTED. WEAK
NORTHERN STREAM SHORTWAVE WILL PASS MAINLY JUST NORTH OF THE REGION
SATURDAY...BUT MOISTURE/FORCING LOOK TOO LIMITED FOR ANY
PRECIP...THOUGH WAA CLOUDINESS LOOKS TO BE A GOOD BET. ANOTHER WEAK
SHORTWAVE PASSES JUST TO OUR NORTH ON SUNDAY WITH GFS SQUEEZING OUT
SOME LIGHT QPF. ECMWF/WRF-NAM AND PARALLEL GFS KEEP LIGHT PRECIP TO
OUR NORTH...SO HAVE OPTED TO HANG ONTO A DRY FORECAST FOR NOW FOR
SUNDAY BUT WITH PLENTY OF CLOUDINESS OF COURSE.


NEXT WEEK A SIGNIFICANT PATTERN CHANGE IS FORECAST TO TAKE PLACE
ACROSS THE NORTHWESTERN HEMISPHERE WITH SIGNIFICANT LONG WAVE TROUGH
SETTING UP OVER THE UPPER MISSISSIPPI VALLEY AND EVENTUALLY THE
EASTERN CONUS. THE SYSTEM THAT WILL EVENTUALLY CARVE OUT THE DEEP
TROUGH OVER THE REGION IS ACTUALLY THE SAME SIGNIFICANT STORM THAT
JUST AFFECTED JAPAN...SO IT HAS A LONG FAIRLY AND DATA SPARSE REGION
OF THE PACIFIC TO TRAVERSE BEFORE ARRIVING IN OUR AREA. AS IS
TYPICAL WITH LARGE SCALE PATTERN CHANGES...THERE HAVE BEEN
SIGNIFICANT RUN TO RUN MODEL VARIATIONS IN THE HANDLING OF THE
DETAILS OF THIS CYCLONE/DEVELOPING TROUGH AND WOULD ANTICIPATE
FURTHER CHANGES IN LATER MODEL RUNS.

AT THIS POINT...FAIRLY HIGH CONFIDENCE THAT A STORMIER AND
EVENTUALLY COLDER PATTERN WILL SETTLE IN NEXT WEEK. INITIALLY LOOKS
TO BE MORE OF A RAIN/SHOWER EVENT EARLY IN THE WEEK TRANSITIONING TO
MORE FLURRIES/SNOW SHOWERS AS THE UPPER LOW SETTLES IN OVER THE
REGION. LATEST RUNS REALLY ARENT LOOKING TOO FOREBODING FOR
SIGNIFICANT SNOWFALL...BUT AT THIS POINT WOULD REALLY CAUTION ABOUT
LATCHING ONTO ANY ONE SOLUTION AS THERE WILL LIKELY BE MORE MODEL
VARIABILITY IN THE COMING DAYS. CERTAINLY SOME POTENTIAL EXISTS FOR
TRAVEL IMPACTS HEADING INTO THE MIDDLE OF NEXT WEEK.

IZZI

&&

.AVIATION...

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

* MVFR CIGS THROUGH PERIOD.

BMD

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

HIGH PRESSURE WILL SLOWLY DRIFT OVER THE TERMINALS THROUGH THE TAF
PERIOD RESULTING IN ALREADY LIGHT WINDS CONTINUING TO TREND
DOWNWARD. A FEW HOLES IN THE MVFR CIGS HAD DEVELOPED EARLIER BUT
HAVE SINCE BEGUN TO FILL IN AND EXPECT MVFR TO REMAIN THROUGH THE
REMAINDER OF THE FORECAST PERIOD...THOUGH CLOUD BASES MAY TREND
DOWNWARD SLIGHTLY OVERNIGHT.

BMD

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

* MEDIUM-HIGH FOR CIGS REMAINING MVFR THROUGH PD.
* HIGH ON LIGHT WINDS THROUGH PD...THOUGH WIND DIRECTION MAY BE
  VARIABLE AT TIMES.

BMD

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

* FRIDAY NIGHT...DRY. MVFR POSSIBLE.
* SATURDAY AND SUNDAY...DRY/VFR. LIGHT SOUTH WINDS.
* MONDAY...CHANCE OF RAIN/SNOW. MVFR LIKELY. GUSTY SOUTHERLY WINDS.
* TUESDAY...CHANCE OF RAIN/SNOW. IFR LIKELY. SOUTHWEST WINDS.
* WEDNESDAY...CHANCE OF SNOW. MVFR LIKELY. STRONG/GUST WEST WINDS.

&&

.MARINE...

230 PM...DEEP LOW PRESSURE IS MOVING NORTHEAST THROUGH NOVA SCOTIA
WHILE A BROAD AREA OF HIGH PRESSURE EXTENDING FROM ONTARIO TO THE
CENTRAL GULF COAST SLOWLY MOVES EAST AND WILL EXTEND FROM QUEBEC
THROUGH THE LOWER MISSISSIPPI VALLEY BY SATURDAY. AS THE HIGH
PRESSURE CONTINUES TO VERY SLOW SPREAD TO THE EAST ACROSS THE
LAKES...WINDS WILL BECOME LIGHT AND VARIABLE FOR A PERIOD FRIDAY
AFTERNOON AND FRIDAY NIGHT. A WEAK TROUGH OF LOW PRESSURE
DEVELOPING OVER THE NORTHERN PLAINS AS THE HIGH BUILDS EAST WILL
SET UP LIGHT SOUTHERLY FLOW OVER THE LAKE. THIS INITIAL TROUGH
WILL MOVE LITTLE THROUGH SATURDAY AND THEN A LOW PRESSURE SYSTEM
IS EXPECTED TO DROP OUT OF THE SOUTHERN CANADIAN ROCKIES BY SUNDAY
EVENING...HELPING TO DEEPEN THE TROUGH INTO A CLOSED LOW. THIS LOW
IS THEN EXPECTED TO TRACK EAST TO WISCONSIN EARLY NEXT WEEK AND AS
THE LOW GETS CLOSER TO THE LAKE...THE SOUTHERLY GRADIENT WILL
STRENGTHEN TO 20 TO 25 KT AS THE LOW DEEPENS AS IT APPROACHES THE
LAKE.

KREIN

&&

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

$$

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