Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 172010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 PM 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 20Z...

* 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 20Z...

* 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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