Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 162006
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
206 PM CST TUE DEC 16 2014

.SHORT TERM...
329 AM CST

THROUGH WEDNESDAY...

SLOWLY OCCLUDING AND BROADENING STACKED LOW PRESSURE IS CENTERED
DIRECTLY OVER THE AREA AS OF 3 AM. DRIZZLE AND CORRIDORS OF ROTATING
SHOWERS ASSOCIATED WITH MID-LEVEL VORTICITY SPOKES AND MOISTURE
CONVERGENCE WILL CONTINUE TO SLOWLY MOVE EAST WITH THE LOW THIS
MORNING. MOST COMMUNITIES SHOULD SEE MORNING RAIN...ESPECIALLY
NORTH OF I-80...THOUGH MUCH OF IT SHOULD BE LIGHT. THE WEAK WIND
FIELD HAS ALLOWED AREAS OF DENSE FOG TO DEVELOP THOUGH THAT SHOULD
DISSIPATE NOT LONG AFTER DAYBREAK AS THE WINDS BEGIN TO INCREASE
BEHIND THE LOW PASSAGE.

BAROCLINICITY WITH THE SYSTEM IS GRADUALLY WEAKENING THOUGH STILL A
MODEST COLD AIR PUSH /GIVEN RECENT DAYS/ WILL MOVE EAST ACROSS THE
FORECAST AREA LATER THIS MORNING AND EARLY AFTERNOON. WINDS WILL
TURN NORTHWEST WITH GUSTS OF 30-35 MPH EXPECTED AND TEMPERATURES
DROPPING THROUGH THE 30S. WHILE THERE ARE A COUPLE OBSERVATIONS OF A
MIX IN IA EARLY THIS MORNING...THE OVERLAP OF CLOUD ICE PRESENCE AND
FORCING FOR PRECIPITATION WILL TRANSLATE MAINLY NORTH OF THE AREA
THIS AFTERNOON. HAVE FOLLOWED THE PREVIOUS SHIFT WITH ONLY KEEPING A
BRIEF CHANCE FOR A RAIN/SNOW MIX IN FAR NORTHERN ILLINOIS BEFORE
PRECIPITATION ENDS THIS AFTERNOON. SOME LAKE EFFECT SHOWERS STILL
LOOK LIKE THEY COULD IMPACT PORTER COUNTY INDIANA THIS EVE THOUGH
TEMPERATURES DO NOT LOOK TO FAVOR ANY SNOW ACCUMULATION.

NORTHWEST WINDS AND COLD AIR ADVECTION WILL CONTINUE TONIGHT AS
WINDS STAY UP...SO TEMPERATURES WILL CONTINUE TO FALL. CLOUDS WILL
MAKE A DIFFERENCE ON HOW FAR THEY DROP AND IF CLEARING TEENS COULD
BE REALIZED. SATELLITE INDICATES CLOUDS ALL THE WAY BACK TO SOUTHERN
CANADA AND THE DAKOTAS IN THE CYCLONIC FLOW...WHICH USUALLY FAVORS
STAYING IN CLOUDS FOR A LONGER PERIOD BEHIND A SYSTEM...BUT GUIDANCE
ALSO FORECASTS QUITE A BIT OF SUPPRESSION COMING IN THIS EVENING AND
DRY ADVECTION ON LOW-LEVEL WINDS. SO JUST DO NOT HAVE A GOOD FEEL
AND HAVE LEANED TOWARD GRADUAL SCATTERING OCCURRING...ESPECIALLY
ACROSS NORTH CENTRAL ILLINOIS.

NORTHWEST WINDS WILL EASE ON WEDNESDAY AS THE LOW-LEVEL FLOW BECOMES
MORE ANTICYCLONIC. THE 925MB TEMPERATURES AROUND -9C FAVOR HIGHS
AROUND 30...THOUGH CLOUD COVER AGAIN IS IN QUESTION. DO THINK SOME
AREAS WILL SEE PERIODS OF SUNSHINE WHICH IS A BIG DEAL SO FAR THIS
MONTH. LIGHTER WINDS ARE CERTAINLY ON TAP WEDNESDAY NIGHT AND LOWS
IN THE TEENS LOOK MORE PROBABLE IF CLOUDS HAVE ERODED.

MTF

&&

.LONG TERM...
329 AM CST

THURSDAY THROUGH MONDAY...

WHILE SEVERAL LITTLE NUISANCES IN THIS PART OF THE FORECAST...ANY
HIGH IMPACT WEATHER IS NOT PROBABLE THROUGH THE WEEKEND. THE UPPER
FLOW PATTERN REMAINS SOMEWHAT SPLIT OVER THE U.S...WITH A MORE
ACTIVE AND FAST-PACED SOUTHERN JET TO OUR SOUTH WITH MULTIPLE
SYSTEMS TRANSLATING SOUTH OF THE REGION. LIGHT PRECIP CHANCES MAY
ENCROACH FROM THE SOUTH THURSDAY AND AGAIN FRIDAY NIGHT...BUT
CONSISTENCY AND TRENDS IN GUIDANCE INCLUDING ENSEMBLES LEANS THE
FORECAST TOWARD DRY. SEA-LEVEL PRESSURES ARE BASICALLY EXPECTED TO
REMAIN 1024MB OR HIGHER FROM THURSDAY THROUGH SUNDAY INDICATIVE OF
THE AREA NOT BEING IMPACTED MUCH BY ANY REAL ADVECTION...SO
TEMPERATURES LOOK TO BE FAIRLY STEADY.

JUST SOME GLANCES AT LONG RANGE GUIDANCE INTO THE HOLIDAY WEEK SHOWS
A PROBABLE MORE ACTIVE PATTERN ACROSS THE CENTRAL PART OF THE
COUNTRY WITH A STRONG PACIFIC JET FORECAST TO DEVELOP INTO THE
NORTHWEST. MULTIPLE SYSTEMS ARE PRESENTLY FORECAST BY GUIDANCE BUT
OBVIOUSLY TOO FAR OUT TO LATCH ONTO ANYTHING AND WILL LIKELY REMAIN
SO FOR AT LEAST A FEW DAYS.

MTF

&&

.AVIATION...

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

* MVFR CEILINGS THROUGH MUCH OF THE FORECAST PERIOD.

* LINGERING SHOWERS EXITING THIS AFTERNOON.

* STRONG WEST/NORTHWEST WINDS THIS AFTERNOON.

RODRIGUEZ

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

SURFACE LOW AND FRONTAL BOUNDARY CONTINUE TO PUSH THROUGH THE
REGION EARLY THIS AFTERNOON...WITH CEILINGS AND SHOWERS STILL
LINGERING ACROSS THE TERMINALS AND WHILE WEST NORTHWEST WINDS
BEGIN TO INCREASE. EXPECT ANY LINGERING PRECIP TO EXIT OVER THE
NEXT SEVERAL HOURS WHILE CURRENT LOW END MVFR CEILINGS OBSERVE A
SLOW RISING TREND THIS AFTERNOON. DID KEEP MVFR CEILINGS IN
THROUGH TOMORROW AS A FAIR AMOUNT OF STRATUS DOES REMAIN UPSTREAM.
THE CURRENT HOLES DEVELOPING ON THE WESTERN EDGE COULD BE A
PREVAILING FEATURE ON WEDNESDAY...POSSIBLY REACHING THE TERMINALS
WEDNESDAY AFTERNOON. POST FRONTAL WEST NORTHWEST WINDS ARE
INCREASING EARLY THIS AFTERNOON AND EXPECT THIS INCREASE TO
CONTINUE...WITH GUSTS LIKELY PERSISTING OVERNIGHT INTO WEDNESDAY
MORNING.

RODRIGUEZ

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

* HIGH CONFIDENCE WITH MVFR CEILINGS TODAY AND TONIGHT...MEDIUM
  CONFIDENCE OF DURATION ON WEDNESDAY.

* HIGH CONFIDENCE WITH SHOWER TRENDS.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

RODRIGUEZ

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

* WEDNESDAY NIGHT THROUGH MONDAY...DRY/VFR.

&&

.MARINE...
130 PM CST

LOW PRESSURE AND A COLD FRONT HAVE PASSES EAST OF LAKE MICHIGAN AND
WINDS HAVE SHIFTED NORTHWESTERLY.  STRONG COLD ADVECTION AND STRONG
PRESSURE RISES AS THE LOW PULLS AWAY TO THE EAST AND HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS WILL COMBINE TO DRIVE WINDS TO
30KT FOR THE REMAINDER OF THE AFTERNOON THROUGH TONIGHT AND MUCH OF
TOMORROW.  THERE IS THE POTENTIAL FOR A FEW GALE FORCE GUSTS...BUT
IN GENERAL...DO NOT EXPECT ENOUGH PREVAILING GALE FORCE WINDS TO
NECESSITATE A GALE WARNING.  HOWEVER...A SMALL CRAFT ADVISORY HAS
ALREADY BEEN ISSUED FOR THE NEARSHORE WATERS AND EXPECT THAT TO PLAY
OUT AS CURRENTLY ADVERTISED.  THE OVERALL PATTERN WILL BE SLOWLY
PROGRESSIVE...SO BRISK WINDS WILL REMAIN OVER THE LAKE THROUGH
THURSDAY...BUT AS HIGH PRESSURE BEGINS TO BUILD ACROSS THE WESTERN
GREAT LAKES...WINDS SHOULD DROP OFF AND BECOME MORE VARIABLE IN
DIRECTION.  HIGH PRESSURE WILL PREVAIL ACROSS THE GREAT LAKES FROM
LATE THURSDAY THROUGH THE WEEKEND...KEEPING WINDS RELATIVELY LIGHT
IN SPEED AND VARIABLE IN DIRECTION.  BY EARLY NEXT WEEK...THE HIGH
SHOULD FINALLY PUSH EAST OF LAKE MICHIGAN AS LOW PRESSURE BEGINS TO
DEVELOP OVER THE NORTHERN PLAINS.  THIS SHOULD SET UP A PERIOD OF
INCREASING SOUTHERLY WINDS FOR EARLY NEXT WEEK AS A LOW PRESSURE
SYSTEM DEEPENS WHILE CROSSING THE NORTHERN PLAINS AND DRAGGING A
TRAILING COLD FRONT ACROSS THE CENTRAL PLAINS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM THURSDAY.

&&

$$

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