Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 271554
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
954 AM CST SAT DEC 27 2014

.SHORT TERM...
245 AM CST

THROUGH SUNDAY...

WE ARE LIVING ON BORROWED TIME WITH 850 MB TEMPS SITTING ABOVE
ZERO...BUT THAT WILL BE A THING OF THE PAST COME THIS AFTERNOON. BUT
FIRST OFF...LIGHT RAIN/DRIZZLE IN EAST CENTRAL ILLINOIS AND INTO NW
INDY IS ASSOCIATED WITH THE SLIGHTLY BETTER ISENTROPIC LIFT/MOISTURE
ADVECTION.  THIS WILL DRIFT OFF TO THE EAST THIS MORNING AND WILL
GRAZE OUR SE COUNTIES. MEANWHILE A SECOND AREA OF LIGHT RAIN
CONTINUES OVER NORTHWEST/NORTH CENTRAL ILLINOIS CLOSER TO THE NORTHWARD
MOVING LOW AND EASTWARD ADVANCING COLD FRONT. MUCH OF OUR AREA FINDS
ITSELF IN AN AREA OF WEAKER ISENTROPIC LIFT AND A BIT REMOVED FROM
THE FRONTAL INFLUENCE. THEREFORE...EXPECT SCATTERED LIGHT
RAIN/DRIZZLE IN BETWEEN THAT SHOULD BE LESS ORGANIZED THAN THESE TWO
AREAS.

THE SURFACE LOW IN IOWA CONTINUES TO DEEPEN AND PUSH NE TO NORTHERN
LAKE MICHIGAN THIS MORNING. THE BETTER UPPER DYNAMICS WITH THE
FRONT ARE WITH THE SHORTWAVE MOVING THROUGH IOWA...AND THIS HEADS
NORTHWEST OF OUR AREA TODAY AS WELL. ENOUGH FRONTAL CONVERGENCE
EXISTS TO CARRY A LOW POP RAIN MENTION THROUGH THE MORNING THOUGH
MANY AREAS STAY DRY. THE BETTER MID LEVEL FORCING/FRONTOGENESIS
ARRIVES WITH THE FRONT THIS AFTERNOON BUT MOISTURE IS
LACKING...THEREFORE EXPECT A LARGELY DRY AFTERNOON EXCEPT IN NW
INDIANA AND EASTERN PORTIONS OF ILLINOIS. WITH A STRENGTHENING
UPPER JET OVERHEAD...EXPECT BREEZY SOUTHWEST WINDS AHEAD OF THE
FRONT...THEN GUSTY WEST WINDS BEHIND IT. AFTER A PLEASANT WARM UP
THE LAST FEW DAYS...THIS FRONT DOES HAVE SOME KICK TO IT...AND
WHILE THE COLD AIR DOES NOT NECESSARILY COME SCREAMING IN...DO
EXPECT A RETURN TO REALITY AND MORE SEASONAL CONDITIONS.

THE COLD FRONT WILL BE THROUGH TONIGHT. ANY LINGERING PRECIP IN OUR
FAR SE COUNTIES OF NW INDIANA MAY SEE A LIGHT RAIN/SNOW MIX BEFORE
PRECIP ENDS. OTHERWISE HIGH PRESSURE NOSES IN FROM THE WEST BRINGING
GRADUAL CLEARING OVERNIGHT. READINGS OVERNIGHT DROP INTO THE 20S
TO AROUND 30. SUNDAY LOOKS TO BE GENERALLY SUNNY BUT SEASONALLY
COLD AS THE MAIN UPPER LOW PASSES THROUGH SOUTHERN CANADA.

KMD

&&

.LONG TERM...
245 AM CST

SUNDAY NIGHT THROUGH FRIDAY...

STRONGER CANADIAN HIGH PRESSURE...WILL BE KNOCKING AT OUR DOOR ON
SUNDAY NIGHT...AND WILL SEND A WEAK BACK DOOR COLD FRONT DOWN THE
LAKE. THE LEADING EDGE OF THIS SECONDARY SURGE OF COLD AIR WILL
TRIGGER A SIGNIFICANTLY COLDER STRETCH OF WEATHER TO KICK OFF THE
LAST FEW DAYS OF 2014. THERE MAY BE SOME WEAK LAKE EFFECT SNOW
SHOWERS GETTING INTO NE ILLINOIS...OTHERWISE INCREASING CLOUDS AND
COLDER. THEN AS THE TRULY ARCTIC AIR SPILLS IN MONDAY NIGHT...WE MAY
SEE SOME SNOW SHOWERS ALONG THE BAROCLINIC ZONE. MOISTURE IS NOT
IMPRESSIVE WITH THE FRONT...BUT THE COMBINED NE FLOW OFF THE LAKE
WITH MORE SIGNIFICANT INVERSION HEIGHTS AND MUCH COLDER AIR MAY
ALLOW FOR LAKE ENHANCEMENT AND SOME BETTER ACCUMULATION POTENTIAL.

THEN THE CHILL ENSUES FOR SEVERAL DAYS OF HIGHS ON EITHER SIDE OF 20
AND LOWS IN THE SINGLE DIGITS AND TEENS AS WE REMAIN IN NW FLOW. THE
UPSIDE...LIKELY SOME MORE SUN TO ENJOY TO END THE YEAR...AS ANY
SHORTWAVE ENERGY ROTATING THROUGH FROM THE CANADIAN VORTEX WILL
EITHER REMAIN NORTH OR GENERALLY BE WEAK AS THE ONE THAT COMES
THROUGH TUESDAY NIGHT. SOME MODIFICATION TO THE COLD AIR MASS
ARRIVES ON NEW YEARS DAY AND MORE SO FRIDAY AS WE RETURN TO
SOUTHERLY FLOW. AS THIS OCCURS...WILL HAVE TO WATCH IF LOW
PRESSURE THAT CLOSES OFF OVER CALIFORNIA EARLIER IN THE WEEK
PHASES WITH THE NORTHERN STREAM LOW OR REMAINS FARTHER SOUTH AS
THIS WILL HAVE IMPLICATIONS FOR ANY PRECIPITATION CHANCES TOWARD
WEEKS END.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* IFR CIGS IMPROVE TO MVFR BY LATE MORNING/EARLY AFTN.

* MVFR CIGS LINGER TODAY AND PSBLY INTO TONIGHT.

* SCATTERED SHRA ALONG THE FRONT THIS MORNING.

* GUSTY WEST WINDS THROUGH THIS AFTN.

JEE

//DISCUSSION...UPDATED 12Z...

COLD FRONT WILL SWEEP ACROSS THE TERMINALS MID-LATE MORNING
PROBABLY ACCOMPANIED BY A BAND OF SHRA ALONG THE FRONT AND QUICKLY
FOLLOWED BY STRONG/GUSTY WEST WINDS. COULD BE A BRIEF PERIOD OF
GUSTS AROUND 30KT BEFORE PREVAILING GUSTS TEND TO SETTLE MORE IN
THE MID-UPPER 20 KNOT RANGE. IFR CIGS THIS MORNING COULD LIFT
SLIGHTLY TO LOW END MVFR PRIOR TO THE FRONT MOVING THROUGH BUT
LIKELY LIFT TO MVFR IN THE WAKE OF THE FRONT. MVFR CIGS WILL
PROBABLY LINGER INTO AT LEAST THIS EVENING BUT COULD POTENTIALLY
CLEAR OUT LATER TONIGHT...BUT CONFIDENCE IN LOW IN CLEARING TIME
SO HELD ON TO MVFR CIGS FOR NOW.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN CIG TRENDS...MEDIUM CONFIDENCE IN TIMING.
  LOW CONFIDENCE IN MVFR CIGS TONIGHT...COULD BE HIGHER.

* MEDIUM CONFIDENCE IN SCATTERED SHRA IMPACTING THE TERMINALS.

* 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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