000
FXUS63 KLOT 100118
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
718 PM CST MON DEC 9 2013

.DISCUSSION...
718 PM CST

ONLY ISSUES THUS FAR HAVE BEEN TEMPERATURES TAKING A NOSE DIVE.
RFD DROPPED TO 3 DEGREES ALREADY WITH OTHER STATIONS UNDER CLEAR
SKIES TANKING AS WELL. AS LOWERED LOW TEMPS FOR TONIGHT WITH
OUTLYING AREAS DIPPING JUST BELOW ZERO. BASED ON TRENDS...TEMPS
MAY FALL A BIT LOWER THAN CURRENTLY FORECAST FOR AREAS NORTH OF A
LASALLE TO OHARE AIRPORT LINE. BASICALLY WHERE THE SKY IS CLEAR.
USED HRRR TRENDS WITH A FEW HAND EDITS TO GET TEMP TREND TONIGHT
SINCE AREAS UNDER THE CLOUD COVER WILL COOL VERY SLOWLY.

ISSUED A SPS TO HIGHLIGHT THE COLD TEMPS AND WIND CHILLS SINCE
THIS IS THE COLDEST WE HAVE BEEN THIS SEASON. MIN WIND CHILLS
OF -10 TO -15 ARE EXPECTED FOR AREAS IN AND NORTH OF A LASALLE
COUNTY TO WILL COUNTY LINE. ISOLATED AREAS NORTH OF I-90 MAY EVEN
SEEN MIN WIND CHILLS APPROACHING -20. HOWEVER THE AREA OF -20 WILL
NOT BE WIDESPREAD ENOUGH TO WARRANT A WIND CHILL ADVISORY.

OTHERWISE MADE MINOR ADJUSTMENTS TO SKY COVER AS THE
REST OF THE FORECAST IS ON TRACK. STILL EXPECTING TEMPS TO RISE A
BIT AROUND SUNRISE AS CLOUD COVER ASSOCIATED WITH THE NEXT CLIPPER
MOVE IN.

JEE

&&

.PREV DISCUSSION...
253 PM CST

IT APPEARS WE ARE STUCK IN MOTHER NATURES WINTER PATTERN...AND FOR
THE NEXT SEVERAL DAYS IT DOES NOT APPEAR WE ARE LOOKING AT A BREAK
FROM THIS SETUP. LONG-TERM PATTERN IS BEGINNING TO SHOW JUST A BRIEF
RESPITE...THEN A RETURN TO UNSEASONABLY COLD SETUP.

IT`S THE GIFT THAT KEEPS ON GIVING CLARK.

THIS AFTERNOON/EVENING...WILL REMAIN RELATIVELY QUIET FOR THE
FORECAST AREA...HOWEVER THAT WILL CHANGE TOWARDS DAYBREAK TUESDAY.
SFC RIDGE HAS BECOME CENTERED ACROSS THE MID-MISSOURI
VALLEY...BEGINNING TO STRETCH EAST THROUGH THE OHIO VALLEY. THE
DEPARTING SFC LOW THAT BROUGHT THE FRESH BLANKET OF SNOW HAS LIFTED
NORTHEAST OF LAKE HURON...MEANWHILE A CLIPPER IS BEGINNING TO DIP
INTO THE NORTHERN PLAINS LATE THIS AFTERNOON. IR IMAGERY SHOWS A
CHANNEL OF CLOUDS OVER SAINT LOUIS STRETCHING NORTHEAST THROUGH
SOUTHERN LAKE MICHIGAN...ASSOCIATED WITH A FRONTAL BOUNDARY THAT
CONTINUES TO SLOWLY SLIDE EAST/SOUTHEAST ACROSS THE FORECAST AREA.
TEMPS AHEAD OF THIS BOUNDARY HAVE HELD STEADY IN THE LOW 20S...WHILE
BEHIND THIS BOUNDARY TEMPS HAVE ALREADY FALLEN INTO THE MID/UPR
TEENS. ACROSS THE STATELINE INTO IOWA...TEMPS HAVE HELD IN THE
SINGLE DIGITS ABOVE ZERO.

GUIDANCE HAS TRENDED SLIGHTLY FURTHER SOUTH WITH THE FIRST CLIPPER
TONIGHT...AND AS A RESULT HAVE INCREASED POPS ACROSS THE NORTHERN
CWFA. THE PRESSURE GRADIENT DOES INCREASE THIS EVENING...AND WILL
PERSIST THRU DAYBREAK TUE. THIS WILL LIKELY RESULT IN SOME BLOWING
SNOW. AS NOTED ABOUT INCREASED POPS...THIS HAS RESULTED IN LIGHT
SNOW EXPECTED JUST BEFORE DAYBREAK TUE FOR THE NORTHERN HALF OF THE
CWFA.

USING THE COBB TECHNIQUE WOULD SUGGEST A FEW POINTS BETWEEN 09-12Z
COULD PICK-UP A COUPLE TENTHS OF AN INCH OF SNOWFALL. WITH THE
BREEZY CONDS EXPECTED...AND COLD AIR IN PLACE...TEMPS WILL LIKELY
TUMBLE TO THE SINGLE DIGITS ABOVE ZERO AND WIND CHILL VALUES WELL
BELOW ZERO AND NEARING -15 IN A FEW LOCATIONS WEST OF THE FOX
VALLEY.

CONFIDENCE...HIGH.

TUESDAY THROUGH WEDNESDAY...
500MB TROUGH AXIS HAS TRENDED STRONGER...WHICH HAS ALSO DISPLACED
THE CLIPPER POISED TO ARRIVE ACROSS THE REGION FURTHER SOUTH TUE
MORNING. AS A RESULT HAVE INTRODUCED POPS TO ACCOMMODATE THIS THRU
18Z TUE. BUT IN TRADITIONAL FASHION...THIS CLIPPER SHUD QUICKLY PUSH
EAST BY EARLY AFTN WITH WEAK SFC RIDGING PUSHING BACK INTO THE
FORECAST AREA. SOME WEAK WARMING MAY OCCUR WITH THIS SYSTEM
EARLY...ALLOWING TEMPS TO WARM INTO THE TEENS TO PSBLY LOW 20S ALONG
THE SOUTHERN CWFA TUE AFTN.

THEN YET ANOTHER CLIPPER IS PROGGED TO TRAVERSE THE REGION LATE TUE
NGT/WED...WHICH HAS CONTINUED TO TREND FURTHER SOUTH AND STRONGER.
WITH THE SFC RIDGE DRIFTING SOUTH INTO THE TENN VALLEY...THIS WILL
LIKELY ALLOW THE WAVE TO PUSH ACROSS THE HEART OF THE CWFA. QPF OF
ARND 0.10" FOR THIS SECOND CLIPPER SNOW RATIOS WILL HOVER ARND 15:1
TO 20:1. THE BEST OMEGA/LIFT IS PUSHING INTO THE FAVORED DGZ WED
MORNING...WHICH COULD HELP PRODUCE LARGER DENDRITES AND INCREASE
SNOWFALL ACCUM RATES. AT THIS POINT HAVE ACCUMS GENERALLY BETWEEN
1-3"...AND COULD SEE A FEW LOCATIONS BETWEEN THE I-80 AND I-88
CORRIDOR COULD PICK UP CLOSE TO 4" BY LATE WED MORNING.

THEN HIGH PRESSURE BUILDS BACK INTO THE REGION WED NGT...SETTING THE
STAGE FOR A VERY COLD NIGHT INTO THUR MORNING. THE RIDGE CENTER HAS
ALSO TRENDED SLIGHTLY FURTHER SOUTH...WHICH WILL LIKELY KEEP SOME
WEST/NORTHWEST WIND COMPONENT. DESPITE THIS TEMPS SHUD STILL RADIATE
INTO THE SINGLE DIGITS BELOW ZERO.

CONFIDENCE...HIGH.
CONFIDENCE IN ACCUMULATING SNOWFALL WED...HIGH.

THURSDAY THROUGH SUNDAY...
PREVIOUS GUIDANCE HAD HELD THE SFC RIDGE OVER THE FORECAST AREA THUR
MORNING...WITH DRY WEATHER. HOWEVER AS HAS BEEN THE CASE WITH THE
PRIOR COUPLE OF CLIPPERS...AND PLACEMENT OF THE 500MB TROUGH
AXIS...GUIDANCE HAS NOW INTRODUCED YET ANOTHER CLIPPER SLICING
SOUTHEAST ACROSS THE NORTHERN PLAINS EARLY THUR...AND COULD BRING A
PERIOD OF LIGHT SNOW/FLURRIES INTO NORTHERN IL THUR MORNING. THIS
MAY RESULT IN TEMPS THUR MORNING NOT GETTING AS COLD...BUT THAT WILL
HINGE UPON TIMING AND CLOUD COVER FROM THE AFOREMENTIONED CLIPPER.

THEN A RELATIVELY QUIET PERIOD FOR FRI WITH THE 500MB FLOW TRYING TO
FLATTEN...BUT THIS WILL ONLY BE BRIEF. GUIDANCE IS NOW BEGINNING TO
TREND TOWARDS AN INVERTED TROUGH DEVELOPING IN THE WAKE OF THE SFC
RIDGE FRI...WITH A STRONG SHORTWAVE TAKING SHAPE ACROSS THE SOUTHERN
PLAINS FRIDAY EVENING. THIS SYSTEM WILL NEED TO BE CLOSELY MONITORED
FOR THE UPCOMING WEEKEND...AS THIS COULD SPREAD ACCUMULATING
SNOWFALL THROUGH THE OHIO VALLEY INTO NORTHERN IL/NORTHWEST IN.

THE LATEST GFS INDICATES AN 850MB LOW ASSOCIATED WITH THIS INVERTED
TROUGH...LIFTING NORTHEAST ACROSS CENTRAL IL THEN NORTHEAST INTO
NORTHCENTRAL IN MIDDAY SAT. LLVL FLOW AHEAD OF THIS FEATURE WILL BE
TURNING NORTHEAST SAT...SETTING UP THE POTENTIAL FOR A HYBRID SYSTEM
OF LAKE EFFECT SNOW AND POTENTIALLY SYNOPTIC SNOW SAT.

TEMPS SHUD BEGIN TO WARM TO NEAR 30 DEG...OR POSSIBLY THE FREEZING
POINT FRI THRU SAT. THEN WITH YET ANOTHER ARCTIC AIRMASS POISED TO
PUSH BEHIND THIS SYSTEM SUN.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* WESTERLY WIND GUSTS TO 25 KT DIMINISHING NEXT 1-2 HRS.

* CHANCE FOR SNOW SHOWERS MID/LATE TUESDAY MORNING WITH BRIEF IFR
  VSBY POSSIBLE BUT COVERAGE MAY BE LOW.

* SOUTHWEST WIND GUSTS 25-30 KT BY MID MORNING TURNING WEST AND
  INCREASING TO 30-35 KT EARLY AFTERNOON.

* ACCUMULATING SNOW CHANCES INCREASE TUESDAY NIGHT...IFR LIKELY.

MDB

//DISCUSSION...UPDATED 00Z...

STRONG WEST WINDS ARE BEGINNING TO EASE WITH GUST FREQUENCY
DIMINISHING AS WELL. VFR WILL CONTINUE THROUGH THE NIGHT WITH
WINDS TURNING SOUTHWEST LATE TONIGHT. WIND SPEEDS WILL INCREASE BY
MID TUESDAY MORNING WITH GUSTS OF 25-30 KT DEVELOPING AS AN
ALBERTA CLIPPER REACHES THE AREA. THE BULK OF THE SNOW WITH THIS
SYSTEM WILL BE TO THE NORTH BUT EXPECT THAT THERE WILL BE AT LEAST
A CHANCE FOR SOME SNOW SHOWERS TO EXTEND TOWARD THE TERMINALS
DURING THE MORNING. COVERAGE MAY NOT BE ALL THAT HIGH AND
CONFIDENCE IN OCCURRENCE IS SOMEWHAT LIMITED BUT WILL CONTINUE
WITH VCSH/PROB30 MENTION FOR NOW. SHOULD HAVE BETTER CONFIDENCE
GOING INTO THE OVERNIGHT AS THE SYSTEM TRACKS ACROSS THE DAKOTAS
AND MINNESOTA/IOWA. SHOULD SNOW SHOWERS CROSS THE AREA THEN
INTENSITY COULD BE SUCH THAT IFR VSBY COULD OCCUR FOR A SHORT
TIME. THE SYSTEM WILL QUICKLY EXIT BY EARLY AFTERNOON TURNING
WINDS WESTERLY AND ALLOWING WIND GUSTS TO INCREASE TO 30-35 KT
BEFORE DIMINISHING TUESDAY EVENING. ATTENTION WILL THEN TURN TO A
STRONGER CLIPPER SYSTEM WHICH WILL CROSS THE AREA TUESDAY NIGHT
AND WEDNESDAY MORNING BRINGING MUCH BETTER CHANCES FOR
ACCUMULATING SNOW AND IFR CONDITIONS.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN WIND GUSTS DIMINISHING NEXT FEW HOURS.

* MEDIUM CONFIDENCE THAT THERE WILL BE SOME SNOW SHOWERS IN THE
  AREA MID/LATE TUESDAY MORNING. LOW-MEDIUM CONFIDENCE THAT IF
  SNOW SHOWERS DO OCCUR THEN BRIEF IFR VSBY IS POSSIBLE.

* HIGH CONFIDENCE IN WIND FORECAST TUESDAY.

* HIGH CONFIDENCE IN SNOW CHANCES INCREASING TUESDAY NIGHT AND
  MEDIUM CONFIDENCE IN AT LEAST SOME IFR.

MDB

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

WEDNESDAY...SNOW ENDING TOWARD MIDDAY. BECOMING VFR.

THURSDAY...VFR.

FRIDAY...VFR WITH SNOW CHANCES INCREASING FRIDAY EVENING. IFR
DEVELOPING FRIDAY EVENING.

SATURDAY...CHANCE FOR SNOW. IFR/MVFR.

SUNDAY...IMPROVING TO VFR.

MDB

&&

.MARINE...
145 PM CST

MAIN MARINE FORECAST CONCERNS ARE A COUPLE OF PERIODS OF GALE FORCE
WINDS OVER NORTHERN LAKE MICHIGAN THIS AFTERNOON/EVENING...AND AGAIN
TUESDAY AND TUESDAY NIGHT ACROSS THE ENTIRE LAKE. HAVE UPGRADED GALE
WATCH TO A GALE WARNING FOR TUESDAY AND TUESDAY NIGHT.

STRENGTHENING LOW PRESSURE WAS LOCATED JUST NORTH AND NORTHEAST OF
LAKE SUPERIOR THIS AFTERNOON...AND WILL CONTINUE TO DEEPEN AS IT
LIFTS TOWARD JAMES BAY THIS EVENING. AS THE LOW DEEPENS...A PERIOD
OF TIGHTENING SURFACE PRESSURE GRADIENT WAS RESULTING IN LOW-END
WEST GALES ACROSS MAINLY NORTHERN LAKE MICHIGAN WITH GRAND TRAVERSE
LIGHT GUSTING 34 KTS AS OF NOON CST. GALES WILL LINGER TONIGHT AS
THE LOW PULLS AWAY...GRADUALLY EASING AFTER MIDNIGHT ACROSS THE FAR
NORTHERN PORTION OF THE LAKE AS WEAK HIGH PRESSURE RIDGING MOVES
ACROSS THE WESTERN LAKES. THE LULL LOOKS TO BE BRIEF HOWEVER...AS A
FAST MOVING CLIPPER SYSTEM CURRENTLY MOVING ACROSS FAR SOUTHERN
SASKATCHEWAN TRAVELS QUICKLY TO THE UPPER MISSISSIPPI VALLEY
OVERNIGHT...AND ACROSS THE NORTHERN/WESTERN GREAT LAKES REGION ON
TUESDAY. THIS WILL INDUCE A QUICK RE-TIGHTENING OF THE SURFACE
PRESSURE GRADIENT ACROSS LAKE MICHIGAN TUESDAY MORNING...WITH STRONG
SURFACE-BASED MIXING AND COLD ADVECTION EXPECTED TO PRODUCE WESTERLY
40 KT GALES BASED ON MODEL FORECAST SOUNDINGS. GALES LOOK TO PERSIST
INTO TUESDAY EVENING ACROSS THE SOUTH HALF OF THE LAKE...AND PAST
MIDNIGHT FARTHER NORTH. HIGH PRESSURE THEN BUILDS SOUTHEAST FROM THE
CENTRAL PLAINS THROUGH THE MID/LOWER MISSOURI AND LOWER OHIO RIVER
VALLEYS WEDNESDAY AND WEDNESDAY NIGHT...ALLOWING GALES TO EASE
THOUGH WINDS REMAIN WESTERLY IN THE 20-30 KT RANGE IN THE TIGHTER
GRADIENT NORTH OF THE SURFACE HIGH AND SOUTH OF LOW PRESSURE WHICH
LINGERS OVER HUDSON BAY. WEST WINDS WILL LINGER THROUGH THURSDAY AS
THE HIGH SPREADS EAST THROUGH THE OHIO VALLEY...AND ANOTHER WEAK LOW
CROSSES THE NORTHERN LAKES.

IN THE NEAR TERM...SMALL CRAFT ADVISORIES ARE IN EFFECT FOR THE
ILLINOIS AND INDIANA NEAR SHORE WATERS THROUGH EARLY TUESDAY... WITH
WINDS/WAVES DIMINISHING MORE QUICKLY ALONG THE ILLINOIS SHORE
TONIGHT. THE GALE WARNING TUESDAY/TUESDAY EVENING INCLUDES THE NEAR
SHORE WATERS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565 UNTIL 3
     AM TUESDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...4 PM
     TUESDAY TO 3 AM WEDNESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 8 AM TUESDAY.

     GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
     LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...8 AM TUESDAY TO 9 PM
     TUESDAY.

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

&&

$$

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