Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 272108
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
308 PM CST SAT DEC 27 2014

.SHORT TERM...
307 PM CST

REMAINDER OF THIS AFTERNOON AND TONIGHT...

A STRONG COLD FRONT IS TRACKING ACROSS THE REGION...USHERING IN MUCH
COOLER AIR ALONG WITH SOME SCT LIGHT PCPN.  AS OF 230PM CDT...THE
SFC FRONTAL BOUNDARY EXTENDED FROM WESTERN LOWER MICHIGAN...TO
EAST-CENTRAL IL...TO SERN MO.  WINDS HAVE BEEN GUSTING TO ARND 30
MPH FOLLOWING THE FROPA WHILE VEERING FROM SWLY TO WLY.
TEMPERATURES ARE SLOWLY DROPPING OFF WITH THE FROPA AND THE BULK OF
THE PCPN IS POST-FRONTAL AS A STRONG LOW LEVEL JET HAS SET UP ALONG
AN ELEVATED BAROCLINIC ZONE.  SOME SCT RAIN IS STILL POSSIBLE OVER
NWRN IN AND ECNTRL IL AHEAD OF THE FRONT...BUT AS COOLER AIR FILTERS
IN BEHIND THE BOUNDARY...LIQUID PCPN IN THE POST-SFC FRONTAL
BOUNDARY SHOULD TRANSITION INTO A MIX OF RAIN...SNOW AND POSSIBLE
SOME GRAPPLE.  THE SHARPER TEMPERATURE DROPOFF WILL OCCUR LATER THIS
AFTERNOON AND THROUGH THIS EVENING AS A SECONDARY TROUGH ASSOCIATED
WITH A SURGE OF COOLER AIR PUSHED ACROSS THE EVENING WHICH WILL BE
ACCOMPANIED BY A WIND SHIFT TO WLY-WNWLY.  ANY LINGERING PCPN SHOULD
PUSH END OVER NWRN IL-ECNTRL IL DURG THE LATE EVENING HOURS AND
TEMPERATURES OVERNIGHT SHOULD RANGE FROM ARND 20F OVER THE ROCKFORD
AREA TO THE UPPER 20S EAST OF THE I-55 CORRIDOR.

KREIN

&&

.LONG TERM...
307 PM CST

SUNDAY THROUGH SATURDAY...

THE PASSAGE OF THE SYSTEM CURRENTLY MOVING THROUGH THE REGION IS A
SIGNAL OF A MAJOR PATTERN SHIFT FROM THE UNSEASONABLY WARM
CONDITIONS OF RECENT DAYS BACK TO MORE SEASONABLE CONDITIONS AS THE
SHORT-WAVELENGTH...HIGH AMPLITUDE TROUGH SHEARS OUT INTO BROAD WEAK
TROUGHING ALOFT THROUGH THE REMAINDER OF THE WEEKEND.  THE GENERAL
TEMPERATURE TREND FOR SUNDAY AND INTO EARLY NEXT WEEK WILL BE FOR A
SLOW COOLING TREND UNDER BROAD...WEAK HEIGHT FALLS ALOFT.  A
STRONGER SURGE OF COLD AIR WITH A SERIES OF NRN STREAM SHORTWAVES
WILL USHER IN THE TRUE COLD AIR BY MONDAY NIGHT AND TUESDAY WITH
TEMPERATURES MONDAY MORNING DROPPING OFF INTO THE LOWER TEENS OVER
THE ROCKFORD AREA TO AROUND 20F EAST OF THE I-55 CORRIDOR.  THE
UPPER LEVEL PATTERN WILL SET UP TO MORE ZONAL OVER THE SRN CONUS
AS THE MAIN JET PATTERN SHIFTS TO THE SOUTH WHILE POLAR-SOURCED
SHORT WAVE ENERGY DROPS INTO THE UPPER MISSISSIPPI VALLEY AND
THROUGH THE MIDWEST AND GREAT LAKES REGIONS THROUGH THE REMAINDER OF
NEXT WEEK.  THE LARGE SCALE PATTERN WILL ALSO BECOME LESS
PROGRESSIVE...WITH THE LONGER RANGE GUIDANCE INDICATING A CUT OFF
LOW DIGGING INTO SRN CALIFORNIA AND VERY SLOWLY TRACKING EWD THROUGH
THE DESERT SOUTHWEST BY LATE NEXT WEEK WHILE SUB-TROPICAL HIGH
PRESSURE REMAINS PARKED OVER THE WESTERN CARIBBEAN AND GREATER
ANTILLES.  THE SLOWING PROGRESSION TO THE LONGWAVE PATTERN WILL IN
TURN SET UP A PERIOD WITH A SERIES OF NRN STREAM SHORTWAVES KEEPING
A STEADY STREAM OF SEASONABLY COLD AIR INTO THE REGION.  THE NEXT
CHANCE FOR ANY PCPN ACROSS THE AREA WILL BE MONDAY AFTERNOON INTO
TUESDAY AS A COLD FRONT ON THE LEADING EDGE OF AN ARCTIC AIRMASS
TRIES TO SQUEEZE OUT A LITTLE SNOW IN A RELATIVELY DRY ENVIRONMENT.
LITTLE OR NO ACCUMULATION IS EXPECTED OVER MUCH OF THE AREA...
PERHAPS A  DUSTING WITH SCT SNOW SHOWERS. HOWEVER...AS SFC HIGH
PRESSURE BUILDS ACROSS THE UPPER MISSISSIPPI VALLEY AND INTO THE
GREAT LAKES REGIONS...A PERIOD OF GENERALLY NORTHERLY FLOW WILL SET
UP OVER LAKE MICHIGAN...AND THERE WILL BE A CHANCE FOR SOME LAKE
EFFECT SNOW INITIALLY ALONG THE ILLINOIS LAKE MICHIGAN SHORE MONDAY
EVENING AND THEN GRADUALLY TRANSITIONING TO THE EAST OVER NWRN
INDIANA MONDAY NIGHT INTO TUESDAY MORNING AS FLOW BACKS MORE NWLY.
IT IS STILL A LITTLE EARLY TO DISCUSS ACCUMULATIONS WITH LAKE EFFECT
SNOW AT THIS POINT...BUT HAVE INCREASED POPS TO LIKELY FOR THE
FAVORED LAKE EFFECT AREAS AND WOULD ANTICIPATE SOME MEASURABLE
ACCUMULATION.  MIDWEEK SHOULD BE DRY...BUT WITH THE LOWEST
TEMPERATURES OF THE PERIOD AS THE SFC HIGH PRESSURE SETTLES INTO THE
LOWER MISSISSIPPI VALLEY AND SERN CONUS.  BY LATE NEXT WEEK...THE
LONGER RANGE GUIDANCE IS INDICATING THAT THE CUT OFF LOW DROPPING
INTO THE DESERT SOUTHWEST WILL FINALLY BEGIN TO LIFT OUT TO THE
NORTHEAST WHILE A NRN STREAM SHORTWAVE DROPS THROUGH THE NRN PLAINS
TO THE UPPER MISSISSIPPI VALLEY.  HOWEVER...WHILE THE LONGER RANGE
GUIDANCE IS IN RELATIVELY DECENT AGREEMENT ON THE TREND...THERE ARE
CONSIDERABLE DIFFERENCES IN THE TIMING WITH THE GFS MUCH FASTER THAN
THE ECMWF OR GEM.  GIVEN THAT SOUTHWEST CUT-OFF LOWS TEND TO LINGER
LONGER THAN THE MODELS LIKE TO FORECAST...HAVE TRENDED THE LONGER
TERM FORECAST CLOSER TO THE SLOWER SOLUTIONS...AND WOULD NOT BE
SURPRISED TO SEE THE MODELS TREND EVEN SLOWER THAN CURRENTLY
INDICATED.  SO...WILL LIMIT POPS TO CHANCE LEVELS WITH TEMPERATURES
CONDUCIVE TO SNOW FOR NOW.

KREIN

&&

.AVIATION...

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

* WEST WINDS GUSTING ARND 25 KT THROUGH THE AFTN.

* MVFR CIGS PERSISTING THROUGH THE EVENING.

JEE

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

THE COLD FRONT EXTENDS FROM PWK THROUGH FORD COUNTY IL AND IT WILL
CONTINUE EAST WITH 30KT GUSTS ALONG THE FRONT. SCATTERED LIGHT
SHOWERS ARE ALONG THE FRONT AND STILL NOT EXPECTING ANY
SIGNIFICANT IMPACT FROM THEM AS THEY QUICKLY SHIFT EAST OF THE
TERMINALS. IFR CIGS LIFT TO MVFR BEHIND THE FRONT AS WELL.

VFR CONDITIONS EXTEND FROM CENTRAL MN THROUGH NE AND EXPECTING
CIGS TO SCATTER OUT OVERNIGHT. HIGH PRESSURE SPREADS IN AND NW
WINDS DIMINISH TO LESS THAN 20 KT OVERNIGHT. VERY WEAK
WINDS...LESS THAN 5 KT...VARY FROM WEST OR SOUTHWEST OVER RFD
TOMORROW TO NORTHWEST TO NORTH OVER THE EASTERN TERMINALS.

JEE

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

* HIGH CONFIDENCE IN CIG TRENDS...MEDIUM CONFIDENCE IN TIMING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...VFR.

MONDAY...CHANCE OF -SN OR FLURRIES...ESPECIALLY AT NIGHT. MVFR
CIGS LIKELY.

TUESDAY THROUGH FRIDAY...PREDOMINANTLY VFR.

IZZI

&&

.MARINE...
158 AM CST

LOW OVER EASTERN IOWA WILL QUICKLY DEEPEN THROUGH THIS EVENING
AS IT TRACKS NORTHEAST ACROSS NORTHERN LAKE MICHIGAN AND
EVENTUALLY OFF INTO QUEBEC. DUE TO THE BRIEF BUT RAPID DEEPENING
AND COLD AIR ADVECTION THIS AFTERNOON THERE COULD BE A VERY BRIEF
WINDOW OF GALES BEHIND THE FRONT FOR AN HOUR OR TWO OVER SOUTHERN
PORTIONS OF THE LAKE. DURATION LOOKS TO BE TOO SHORT FOR GALE
WARNING THOUGH SO NO HEADLINE PLANNED FOR OPEN WATERS. WINDS/WAVES
LOOK TO RAPIDLY SUBSIDE TONIGHT INTO MONDAY BEFORE AN ARCTIC FRONT
BEGINS WORKING SOUTH DOWN THE LAKE MONDAY NIGHT INTO TUESDAY.
TIGHT GRADIENT BEHIND THE FRONT ALONG WITH VERY COLD AIR AND
UNSTABLE CONDITIONS SHOULD ALLOW FOR STRONG NORTHERLIES TO
DEVELOP...POSSIBLY TO NEAR GALE FORCE BEHIND THE FRONT. THAT
SHOULD MARK THE START OF AN ACTIVE PERIOD ON THE LAKE WITH LOW
PRESSURE TRACKING ACROSS CANADA MIDWEEK DRAGGING A FRONT ACROSS
THE LAKE AND TIGHTENING THE PRESSURE GRADIENT AND PROBABLY LEADING
TO A PERIOD OF WESTERLY GALES WEDNESDAY/EARLY THURSDAY TIME FRAME.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 4 AM SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 10 PM
     SATURDAY.

&&

$$

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