Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 182029
AFDLOT

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

.SHORT TERM...
445 AM CST

THROUGH FRIDAY NIGHT...

APOLOGIES FOR THE LATE AFD THIS MORNING DUE TO EQUIPMENT PROBLEMS.

SURFACE RIDGING IS IN PLACE OVER THE AREA AND AS HAS BEEN THE CASE
WITH RECENT HIGHS THIS ONE REMAINS LITTERED WITH CLOUDS. CONFLUENT
UPPER FLOW ATOP THE AREA TODAY WILL HELP TO STIFLE THE NORTHWARD
PROGRESSION OF AN UPPER WAVE CENTERED NEAR KANSAS CITY EARLY THIS
MORNING. A HIGH TO MID CLOUD DECK WILL STILL SPREAD OVER THE AREA
BRINGING MOSTLY CLOUDY CONDITIONS TO SOME LOCATIONS THAT ARE
FORTUNATE ENOUGH TO HAVE SCATTERED LOW CLOUDS EARLY THIS MORNING.
LIGHT SNOW SHOULD REMAIN TO THE SOUTH OF THE FORECAST AREA WHERE
700-600MB FRONTOGENESIS AND DEEPER MOISTURE ARE DEPICTED...HOWEVER
LIGHT RADAR ECHOES WILL LIKELY TRAVERSE SOUTHERN COUNTIES FOR A
GOOD PART OF THE DAY. WITH CLOUD COVER AND A LIGHT WIND REGIME
LIMITING MIXING...AND ALREADY ONE OF THE SHORTEST DAYLIGHT AMOUNTS
OF THE YEAR...ANOTHER SMALL DIURNAL RANGE IS ON TAP. HIGHS SHOULD
MAX OUT MAINLY IN THE UPPER 20S.

TONIGHT THROUGH FRIDAY REMAINS CHALLENGING WITH CLOUD COVER AS THE
LOW-LEVEL FLOW WILL REMAIN LIGHT. HAVE LEANED MORE TOWARD CLOUDY
THAN SCATTERING GIVEN THE RECENT BULLISHNESS OF CLOUDS AND NULL
ADVECTION. AS EARLY THIS MORNING SHOWED ACROSS THE
REGION...PLACES THAT CLEAR DURING THE NIGHT WITH DROP WELL INTO
THE TEENS IN THIS COOL AIR MASS. HAVE LEANED A LITTLE CLOSER TO
THAT TONIGHT BUT AGAIN OVERALL CONFIDENCE ON CLOUD AND TEMPERATURE
SPECIFICS IS LOW.

MTF

&&

.LONG TERM...
441 AM CST

SATURDAY THROUGH WEDNESDAY...

THE WEEKEND CONTINUES TO LOOK QUIET AND SEASONAL WITH ATTENTION
MORE ON NEXT WEEK. A STRONG NORTH PACIFIC JET WILL MOVE INTO THE
NORTHWEST U.S. EARLY NEXT WEEK AND DIVE INTO THE PLAINS STATES BY
TUESDAY...AMPLIFYING THE PATTERN. AS SUCH...AN UPPER TROUGH IS
FORECAST TO TAKE SHAPE ACROSS THE NORTHERN U.S AND THEN LIKELY
INTO A CLOSED LOW ACROSS THE UPPER MIDWEST OR GREAT LAKES REGION
BY AROUND TUESDAY OR SO. DESPITE OBVIOUS DIFFERENCES IN SPECIFICS
AND PLACEMENT ON LONG RANGE MODEL GUIDANCE...THERE IS SOLID
CONSISTENCY IN A DEEPENING TREND OF THE UPPER LOW THROUGH TUESDAY
AND PHASING BEYOND THAT WITH A LOW DEVELOPING UP THE EASTERN
SEABOARD MIDWEEK. WITH RAPIDLY STRENGTHENING BAROCLINICTY IN THE
MODELS...THEY HAVE CONSISTENTLY FORECAST A DEEP LOW TO DEVELOP.
FOUR CONSECUTIVE RUNS OF THE GFS AND EC HAVE SHOWN 975MB OR DEEPER
LOWS BY 12Z ON CHRISTMAS MORNING ACROSS THE GREAT LAKES/SOUTHERN
ONTARIO/NORTHEAST U.S. REGION. BOTH OF THESE MODEL ENSEMBLES ALSO
ARE DEPICTING GOOD CONSISTENCY IN THAT DEEPENING TREND TUESDAY
THROUGH WEDNESDAY. HOW EXACTLY WE GET TO THAT DEEP LOW FORECAST ON
CHRISTMAS MORNING...AND ITS NOTABLE IMPACTS OVER OUR REGION...IF
ANY...STILL ARE HIGHLY UNCERTAIN.

FOR THE FORECAST HAVE INCREASED POPS DURING THE MONDAY NIGHT PERIOD
IN PARTICULAR...AS GUIDANCE SHOWS GOOD OVERLAP /EVEN ACCOUNTING
FOR A SLOWING TREND/ IN PWAT AND MOISTURE FLUX ANOMALIES AND
OVERSPREADING FORCING. THE FORCING MAY BE ENOUGH TO KEEP
TEMPERATURES DOWN TOO. HAVE OPTED NOT TO GET FANCY AND KEPT
RAIN/SNOW FOR A GOOD PART OF THE AREA AT FIRST AND TREND TO RAIN
IN THE LIKELY STRONG SOUTHERLY FLOW. INTO TUESDAY AND TUESDAY
NIGHT WE TREND BACK TO SNOW IN THE COLD ADVECTION PART OF THE
SYSTEM. HAVE FOLLOWED A SLOWER TREND IN THE DETAILS CLOSER TO THE
18.00 EC AS OFTEN WITH A CLOSED/CLOSING WOUND UP SYSTEM IN THE
EXTENDED PORTION OF THE FORECAST IT CAN END UP SLOWER. CERTAINLY A
SYSTEM TO KEEP TABS ON...ESPECIALLY FOR HOLIDAY TRAVELERS.

MTF

&&

.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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