Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 170915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 AM CST WED DEC 17 2014

.SHORT TERM...
315 AM CST

THROUGH THURSDAY...

THE SYSTEM THAT BROUGHT A RETURN TO MORE SEASONAL TEMPERATURES IS
NOW CENTERED OVER THE EASTERN GREAT LAKES. THIS UPPER LOW IS
ROTATING AROUND A NOW DEEPER BUT SHEARING UPPER LOW CENTERED OVER
MINNESOTA AND WISCONSIN EARLY THIS MORNING. AT THE LOW-LEVELS THIS
SLOW MOVING PATTERN IS HELPING KEEP COLD AIR ADVECTION IN PLACE.
WHILE NOT PARTICULARLY STRONG FOR DECEMBER...THIS ADVECTION WITHIN
CYCLONIC FLOW HAS HELPED KEEP THE CLOUDS AND EVEN SOME FLURRIES.
EARLY MORNING SATELLITE IMAGERY INDICATES THE BACK EDGE CLEARING
FROM MINNEAPOLIS TO DES MOINES AND MAKING LITTLE PROGRESS. UPSTREAM
00Z SOUNDINGS AND CURRENT ACARS DATA FROM RFD INDICATE THE MOISTURE
DEPTH IS VERY SHALLOW. SO CERTAINLY THERE IS POTENTIAL TO SCATTER
FROM WEST TO EAST TODAY AND HIGH RESOLUTION GUIDANCE AND CONDENSATE
FIELDS DO PAINT THIS PICTURE AS WELL. GIVEN FURTHER STRENGTHENING OF
THE SUBSIDENCE INVERSION ON FORECAST SOUNDINGS ACROSS NORTH CENTRAL
ILLINOIS...HAVE GONE WITH FORECAST SCATTERING THERE BY EARLY
AFTERNOON. A LITTLE MORE TRICKY TOWARD CHICAGO AND NORTHWEST INDIANA
AND HAVE FAVORED THAT AREA REMAINING AT LEAST MOSTLY CLOUDY THROUGH
MUCH OF TODAY.

HIGH TEMPERATURES TODAY LOOK TO BE THEIR COOLEST IN ABOUT A WEEK
WITH UPPER 20S AND LOWER 30S SUPPORTED GIVEN LITTLE DIURNAL CLIMB
EXPECTED. THIS IS JUST A TAD BELOW MID-DECEMBER NORMALS. AS FOR
TONIGHT...LIKE A SONG ON REPEAT...THE CONFIDENCE ON CLOUDS ONCE
AGAIN IS LOW. WHILE SOME AREAS MAY SEE NOT MUCH FOR CLOUDS IN THE
EVENING...HIGH CLOUDS LOOK TO MOVE NORTHWARD OVER THE AREA LATE
TONIGHT. WITH LIGHTER WINDS THE POTENTIAL EXISTS FOR TEMPERATURES TO
DROP INTO THE LOWER TO MID TEENS IN OUTLYING AREAS.

THE GREAT LAKES BROAD UPPER LOW WILL MOVE EAST ON THURSDAY WEAKENING
THE CONFLUENT UPPER FLOW OVER THE FORECAST AREA. THIS WILL HELP A
SOUTHERN STREAM SYSTEM...CENTERED IN EASTERN ARIZONA EARLY THIS
MORNING...TO MAKE SOME INROADS WITH MID-LEVEL WARM AND MOIST
ADVECTION UP TO AT LEAST CENTRAL ILLINOIS AND INDIANA. THIS SHOULD
BRING CLOUDS TO MUCH OF THE AREA. HAVE NOT INCLUDED ANY LIGHT SNOW
IN THE FAR SOUTHERN AREA AT THIS TIME AS THE SUPPORT FOR LIFT STAYS
JUST SOUTH ON MOST GUIDANCE SOLUTIONS.

MTF

&&

.LONG TERM...
315 AM CST

FRIDAY THROUGH TUESDAY...

SURFACE HIGH PRESSURE RIDGING BASICALLY MAINTAINS ITSELF OVER THE
AREA THROUGH THE WEEKEND. THE UPPER PATTERN REMAINS SOMEWHAT SPLIT
WITH A SYSTEM LIKELY ENTIRELY PASSING TO OUR SOUTHEAST ON SATURDAY.
A NORTHERN STREAM UPPER LOW IS FORECAST TO BRING SOME PACIFIC
MOISTURE...MAINLY ALOFT...OVER THE AREA SATURDAY EVENING/OVERNIGHT.
LIFT IS WEAK AND MAINLY FOCUSED NORTH SO DO NOT HAVE ANY
POPS...HOWEVER HAVE INCREASED CLOUD COVER IN THE FORECAST AND WITH
THAT FORECAST MINS ON SATURDAY NIGHT.

THE WEATHER PATTERN ACROSS THE CENTRAL CONUS HAS BEEN CONSISTENTLY
FORECAST BY LONG RANGE MODELS AND ENSEMBLES TO BECOME MORE AMPLIFIED
DURING NEXT WEEK. JUST LOOKING ON HEMISPHERIC WATER VAPOR THIS
MORNING...MULTIPLE SYSTEMS ON ACTIVE JET ARE SEEN ACROSS THE
NORTHERN PACIFIC...SO A PATTERN SHIFT SEEMS LIKELY. THE CONSENSUS OF
GUIDANCE FAVORS AN ANOMALOUS SURFACE REFLECTION TO DEVELOP ACROSS
THE MIDWEST MONDAY INTO TUESDAY...THOUGH AS ONE CAN EXPECT THERE ARE
LARGE DIFFERENCES IN PLACEMENT.  HAVE INCREASED FORECAST POPS IN
LINE WITH A SMART GUIDANCE BLEND. GIVEN A CONSENSUS PLACEMENT
THOUGH...IT WOULD SEEM PROFILES WOULD BE MILD ENOUGH FOR MAINLY RAIN
AT FIRST IN OUR AREA. CERTAINLY THIS BECOMES A LOT MORE IN QUESTION
AS THE TROUGH FURTHER AMPLIFIES SUCH AS MODELS SUGGEST INTO
TUESDAY AND CHRISTMAS EVE.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY WEST/NORTHWEST WINDS THRU THIS AFTERNOON.
* MVFR CIGS THRU THIS AFTERNOON. CMS

//DISCUSSION...UPDATED 09Z...

MVFR CIGS HAVE TRENDED A BIT LOWER...NOW IN THE 1500FT RANGE. NOT
EXPECTING IFR CIGS...BUT THEY COULD CONTINUE TO LOWER INTO THE
1000-1200FT RANGE OVER THE NEXT FEW HOURS. ALSO A FEW FLURRIES AT
TIMES...BUT NO RESTRICTION TO VIS EXPECTED. CMS

PREVIOUS 06Z DISCUSSION...

MVFR CIGS REMAIN LOCKED IN ACROSS MUCH OF THE REGION AND FORECAST
SOUNDINGS SUGGEST THESE MAY STAY TRAPPED UNDER AN INVERSION
THROUGH MUCH OF WEDNESDAY. CONFIDENCE IS FAIRLY LOW BUT OPTED TO
CONTINUE BKN CIGS UNTIL EVENING. NORTHWEST WINDS 12-16KTS WILL
SLOWLY DIMINISH WEDNESDAY MORNING INTO THE AFTERNOON. GUSTS ARE
STILL IN THE LOWER/MID 20KT RANGE AND THESE TOO WILL SLOWLY
DIMINISH THRU THE DAY...BUT LIKELY NOT COMPLETELY UNTIL LATE IN
THE AFTERNOON. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM FOR CIGS THRU THE PERIOD.
* HIGH FOR WINDS THRU THE PERIOD. CMS

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

* THURSDAY THROUGH MONDAY...DRY/VFR.

KJB

&&

.MARINE...

210 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE EAST AND BE
ABSORBED BY LOW PRESSURE MOVING NORTH ALONG THE NEW ENGLAND COAST.
THIS LOW WILL THEN SLOWLY LIFT NORTHEAST AND DEEPEN OVER THE NEXT
FEW DAYS. A LARGE AREA OF HIGH PRESSURE EXTENDING FROM MANITOBA
INTO THE CENTRAL PLAINS WILL SLOWLY BUILD EAST ACROSS THE LAKES
REGION THURSDAY AND FRIDAY. NORTHWEST WINDS TO 30 KTS IN BETWEEN
THESE TWO SYSTEMS WILL GRADUALLY DIMINISH TONIGHT INTO THURSDAY.
AS THE HIGH DRIFTS ACROSS THE LAKES REGION...THERE WILL BE A
PERIOD OF LIGHT PERHAPS EVEN CALM WINDS FRIDAY NIGHT INTO SATURDAY
NIGHT UNTIL THE HIGH MOVES EAST SUNDAY AND SUNDAY NIGHT AND THE
FLOW TURNS BACK SOUTHERLY. CMS

&&

.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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