Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 172215
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 PM CST WED DEC 17 2014

.SHORT TERM...
230 PM CST

THROUGH FRIDAY...

RELATIVELY BENIGN WEATHER ON TAP IN THE NEAR TERM UNDER THE
INFLUENCE OF HIGH PRESSURE WHICH WILL REMAIN OVER THE REGION INTO
THE WEEKEND. SURFACE RIDGE EXTENDS FROM MANITOBA INTO THE LOWER
MISSISSIPPI VALLEY THIS AFTERNOON WHILE ALOFT A SHEARED VORT MAX IS
DIGGING SOUTHEAST ACROSS FAR NORTHERN ILLINOIS. SOUNDINGS INDICATE
STEEP LOW LEVEL LAPSE RATES UP TO AROUND 900MB THIS AFTERNOON AND
RADAR IMAGERY DOES SHOW SIGNS OF SOME CONVECTIVE ROLLS WITH VERY
WEAK WIND PARALLEL RETURNS. WITH THESE INGREDIENTS IN PLACE...A FEW
FLURRIES HAVE BEEN NOTED ACROSS THE AREA...BUT NOTHING OF
CONSEQUENCE. ANY FLURRIES SHOULD TAPER BY MID-LATE AFTERNOON AS
INVERSION HEIGHTS BEGIN TO COME DOWN IN RESPONSE TO MODERATE TO
STRONG MID LEVEL HEIGHT RISES BEHIND DEPARTING SHORTWAVE. STRATUS
DECK REMAINS IN PLACE TODAY BUT HAS BEGUN TO THIN AND ERODE NEAR
THE WESTERN COUNTIES. ANY PEAKS OF SUNSHINE TODAY THOUGH ARE
EXPECTED TO BE BRIEF AS MID LEVEL CLOUD COVER INCREASES FROM THE
NORTH AS A WEAK TROUGH EMBEDDED ON THE EASTERN PERIPHERY OF THE
HIGH SAGS SOUTH ACROSS LAKE MICHIGAN...AND FROM THE SOUTHWEST AS
ANOTHER SHORTWAVE TROUGH CURRENTLY LIFTING ACROSS THE PANHANDLES
OF TX/OK PUSHES ACROSS CENTRAL ILLINOIS MIDDAY THURSDAY. PRECIP
WITH THIS SYSTEM IS EXPECTED TO STAY SOUTH OF THE CWA...TAPERING
AS IT OVERRIDES THE SURFACE RIDGE. CLOUD COVER MAY CONTINUE TO
REMAIN LOCKED IN UNDER THE INVERSION FRIDAY...BUT OTHERWISE EXPECT
VERY LIGHT WINDS AND DRY CONDITIONS ON SQUARELY UNDER THE SURFACE
HIGH.

DEUBELBEISS

&&

.LONG TERM...
230 PM CST

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE WILL CONTINUE TO SLOWLY SHIFT EAST ACROSS THE REGION
OVER THE WEEKEND WITH RETURN FLOW BRINGING WARMER TEMPERATURES
ESPECIALLY BY SUNDAY. MEANWHILE...THE PATTERN IS PROGGED TO BEGIN
AMPLIFYING BY LATE IN THE WEEKEND AS LONGWAVE TROUGH DEEPENS ACROSS
THE MID SECTION OF THE COUNTRY DOWNSTREAM OF A BUILDING RIDGE ALONG
THE WEST COAST. THE JET STREAM WILL DIVE TOWARDS THE GULF STATES BY
TUESDAY WITH SURFACE LOW DEEPENING IN RESPONSE EARLY NEXT WEEK.
THERE REMAIN SIGNIFICANT DIFFERENCES AS WELL AS RUN-TO-RUN
VARIABILITY IN THE TIMING AND TRACK OF THE LOW AS IT LIFTS ACROSS
THE MIDWEST MIDWEEK...WITH COMPLICATIONS AS THE MODELS DEAL WITH
PHASING THE SOUTHERN LOW WITH A CLIPPER LIKE SYSTEM. WILL
CERTAINLY HAVE TO KEEP AN EYE ON THE POTENTIAL FOR ACCUMULATING
SNOW TUESDAY INTO WEDNESDAY OVER THE NEXT SEVERAL DAYS AS MODELS
HOPEFULLY BEGIN TO HONE IN ON A SOLUTION. A RETURN TO BELOW NORMAL
CONDITIONS SEEMS LIKELY FOR THE LATTER HALF OF THE WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* MVFR CEILING TRENDS AND POSSIBLE SCATTERING.

* WIND TRENDS...GUSTINESS TODAY AND VARIABLE LATE TONIGHT.

LENNING

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

CEILINGS ARE HANGING IN THE MVFR RANGE BUT SHOWING SIGNS OF
SCATTERING OUT IN AREAS WEST OF THE ORD/MDW TERMINALS. GIVEN THE
PERSISTENCE OF THIS CLOUD SHIELD IT IS HARD TO PUSH THE CLEARING
INTO THE AREA BEFORE WE ACTUALLY SEE IT HAPPENING...SO FOR NOW
WILL MAINTAIN CURRENT TRENDS INTO THE OVERNIGHT HOURS. WINDS
REMAIN WESTERLY TO NORTHWESTERLY FOR MOST OF THE PERIOD...BUT BY
TOMORROW A WEAKENING PRESSURE GRADIENT MAY ALLOW WINDS TO GO
VARIABLE FOR A TIME...THOUGH LIKELY CONTINUE TO FAVOR A WESTERLY
COMPONENT.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* HIGHER CONFIDENCE IN WIND TRENDS.

LENNING

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

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. LIGHT/VRB WINDS.
* SUNDAY...DRY. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY...CHANCE OF RAIN. MVFR LIKELY. GUSTY SOUTH WINDS.
* TUESDAY...CHANCE OF RAIN. IFR POSSIBLE. SOUTHWEST WINDS.

&&

.MARINE...
210 PM CST

THE LOW PRESSURE THAT PASSED THROUGH THE GREAT LAKES REGION OVER THE
PAST COUPLE DAYS IS IN THE PROCESS OF MERGING WITH ANOTHER LOW OVER
THE NEW ENGLAND COAST.  THIS LOW WILL GRADUALLY DEEPEN AND SLOWLY
MOVE NORTH ALONG THE NEW ENGLAND COAST AS HIGH PRESSURE SPREADS FROM
THE NORTHERN PLAINS AND ACROSS THE WESTERN GREAT LAKES BY THURSDAY
MORNING.  WINDS ARE SLOWLY SUBSIDING OVER THE LAKE...BUT A SECONDARY
TROUGH AND SURGE OF COOLER AIR MOVING DOWN THE LAKE THIS AFTERNOON
AND EVENING WILL KEEP RELATIVELY BRISK NLY-NLWY WINDS OVER THE LAKE
THROUGH THE NIGHT TONIGHT.  WINDS SHOULD WEAKEN TO THE 10-15KT RANGE
THURSDAY NIGHT AND FRIDAY AS THE HIGH GRADUALLY SPREADS EAST...WHILE
MAINTAINING A NLY DIRECTION.  THE HIGH WILL SPREAD ACROSS LAKE
MICHIGAN THURSDAY NIGHT AND FRIDAY...LEADING TO MORE LGT/VRBL WINDS
OVER THE LAKE.  HIGH PRESSURE WILL VERY SLOWLY SPREAD EWD...BUT
STILL CONTROLLING FLOW OVER THE LAKE...KEEPING WINDS GENERALLY LIGHT
AND VARIABLE INTO THE WEEKEND.  BY SUNDAY...THE HIGH WILL FINALLY
PUSH EAST OF LAKE MICHIGAN AS A TROUGH OF LOW PRESSURE DEVELOPS OVER
THE NORTHERN PLAINS.  THIS WILL SET UP INCREASING SLY FLOW OVER THE
LAKE BY SUNDAY.  A DEVELOPING LOW IS EXPECTED TO TRACK ACROSS THE
NRN PLAINS SUNDAY NIGHT AND MONDAY...REACHING THE MIDDLE MISSISSIPPI
VALLEY BY TUESDAY.  THIS WILL KEEP GENERALLY SOUTHERLY WINDS OVER
THE LAKE THROUGH EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

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