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000
FXUS63 KLOT 121145
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
645 AM CDT WED MAR 12 2014

.DISCUSSION...
350 AM CDT

HAVE MADE SOME ADJUSTMENTS TO HEADLINES...NAMELY TO BRING UP
EXPIRATION TIMES...INCLUDING WARNING FOR THE CHICAGO AREA. ALSO
DID DOWNGRADE THE WARNING IN A HANDFUL OF COUNTIES THAT EITHER 1.
RECEIVED CONSIDERABLY LESS SNOWFALL THAN ORIGINALLY FORECAST OR 2.
WILL HAVE AN EARLIER END TIME WITH LESS BLOWING SNOW THAN INITIALLY
THOUGHT AND THUS IMPACTS AFTER SUNRISE WILL BE CONSIDERABLY
LESS...SO DID NOT FEEL WARNING WAS ANY LONGER APPROPRIATE FOR
THOSE AREAS.

THE VERY WELL-DEFINED UPPER LOW IS ENTERING WESTERN IL AS OF 330
AM WITH FURTHER AMPLIFICATION OCCURRING AS NORTHERN STREAM SHORT
WAVE FROM MN DIGS SOUTHEAST TOWARD/INTO THIS SYSTEM. THE
DEFORMATION AREA SEEMS TO BE FOLLOWING SUIT...WITH INCREASED
REFLECTIVITY SINCE 300 AM IN A SOUTHWEST TO NORTHEAST CORRIDOR
ALIGNING WITH FRONTOGENESIS...INCLUDING OVER CHICAGO. HAVE HAD A
COUPLE LIGHTNING STRIKES NEAR PONTIAC IN THE PAST COUPLE HOURS AND
JUST PRIOR TO THAT SEVERAL REPORTS THROUGH SOCIAL MEDIA OF HEARING
THUNDER. SO SOME EMBEDDED HEAVIER RATES ARE LIKELY WITHIN THIS
AXIS GIVEN REFLECTIVITY AND JUST WHAT IS OCCURRING OUT THE WINDOW
IN ROMEOVILLE...INCLUDING WITH LARGE FLAKES COMMON OF HIGH MIXING
RATIO SCENARIOS.

CONTINUE THE WARNING FOR THE CHICAGO METRO AREA AND FAR NORTHWEST
INDIANA BUT MOVE UP THE EXPIRATION TIME TO 11 AM...AND IT COULD
END UP BEING CANCELLED EVEN EARLIER IF BLOWING SNOW AND ATTENDANT
IMPACTS ARE DETERMINED TO BE LESS.

FURTHER TO THE SOUTHEAST...MAINLY SOUTH OF A PONTIAC TO RENSSELAER
LINE...GREATER ELEVATED INSTABILITY IS PRESENT PER LOOK OF RADAR
ECHOES AND RAP ANALYSIS. MUCH OF THIS AREA HOWEVER CHANGED OVER
TO ALL SNOW ONLY AT 2-330 AM AND THUS ACCUMULATIONS LOOK
LIMITED...WHICH WE KNEW WOULD COULD OCCUR. SOME OF THE HEAVIEST
CONVECTION JUST MISSED OVERRIDING THIS AREA HAS NOW SKIRTED INTO
NORTHERN INDIANA. SO FOR THAT REASON AND REPORTS RECEIVED THROUGH
DISPATCH...HAVE DOWNGRADED THOSE SOUTHERN AREAS...AS BLOWING SNOW
SHOULD BE QUITE LIMITED THIS MORNING.

REST OF TODAY...

THE PRIMARY CHANGES IN THE FORECAST WERE A QUICKER DIMINISHING OF
ANY LIGHT SNOW CHANCES AS WELL AS TO BUMP UP TEMPERATURES NAMELY
THIS MORNING. DEEP DRY AIR AND SUPPRESSION LOOK TO MOVE QUICKLY
INTO THE AREA BY LATE MORNING BEHIND THIS SYSTEM. CONTINUING LOW-
LEVEL CYCLOGENESIS OFF TO THE EAST WILL DRIVE COLD AIR ADVECTION
INTO THE REGION...AND PROFILES WILL BE SUPPORTIVE OF KEEPING
STRATOCU AND MAYBE SOME FLURRIES INTO EARLY TO MID AFTERNOON.
TEMPERATURES ARE FAIRLY HOMOGENEOUS UP TO CENTRAL/SOUTHERN WI
EARLY THIS MORNING...SO LOW-LEVEL THERMAL ADVECTION LOOKS TO BE
NEUTRAL THROUGH DAYBREAK AND THEN SLIGHT COLD AIR ADVECTION THIS
MORNING. TEMPERATURES SHOULD LEVEL OUT THIS AFTERNOON AS AT LEAST
SOME MARCH SUNSHINE OFFSETS ANY COLD AIR ADVECTION. WITH NOT AS
COLD OF AIR QUICKLY COMING INTO THE AREA...THE POSSIBILITY OF LAKE
EFFECT SNOW SHOWERS INTO NORTHWEST INDIANA LOOKS QUITE SMALL...BUT
POSSIBLY SOME CLOUDS GENERATING INTO LAKE AND PORTER COUNTIES THIS
AFTERNOON.

TONIGHT...

HIGH PRESSURE WILL MOVE OVER THE REGION TONIGHT AND SET THE STAGE
FOR A COLD NIGHT BY MID-MARCH STANDARDS. HIGH CLOUDS DO LOOK TO
SPILL INTO THE WESTERN FORECAST AREA AS THE NIGHT PROGRESSES AS A
SHEARED WEAK SHORTWAVE DROPS SOUTHWARD ON THE BACKSIDE OF THE
DEVELOPING LONGWAVE TROUGH. BUT IT LOOKS TO BE A LITTLE TOO LATE
TO STOP TEMPERATURES FROM DROPPING NICELY OVER FRESH SNOW COVER
THIS EVE INTO EARLY OVERNIGHT. FORECAST TEMPERATURES WITH MODEST
CONFIDENCE ARE SINGLE DIGITS IN OUTLYING AREAS TO 10 TO 15 IN THE
CHICAGO METRO. THAT LINES UP WITH THE 850MB TEMPERATURES OF -12C
TO -15C ACROSS THE FORECAST AREA BY TONIGHT...WHICH ARE WELL BELOW
CLIMO. IF CLOUDS WERE TO MOVE IN QUICKER IT WOULD RESULT IN MINS
POTENTIALLY QUITE A BIT WARMER.

THURSDAY AND BEYOND...

WHILE THE UPPER FLOW PATTERN BECOMES NORTHWEST AND REMAINS DECENTLY
ACTIVE THROUGH THE REST OF THE FORECAST PERIOD...WE REMAIN ON THE
ANTICYCLONIC SIDE. THUS WE LOOK TO FREQUENTLY MISS THE BEST
FORCING AND DEEPER SATURATION OF EACH QUICK-MOVING SYSTEM. IT DOES
MAKE FOR A CHALLENGE WITH TEMPERATURES...ESPECIALLY WEIGHING
RECENT SNOW COVER AND OCCASIONALLY PASSING CLOUD COVER. DO
MAINTAIN A SMALL CHANCE FOR LIGHT SNOW THURSDAY MORNING IN
NORTHERN AREAS AS WARM AIR ADVECTION ALOFT MOVES IN BEHIND THE
TROUGH. SATURATION LOOKS TO BE A PROBLEM...BUT THE ISENTROPIC
ASCENT IS PRETTY STRONG AND SATURATION ON BOTH THE NAM AND GFS IS
DEPICTED TO BE LOW ENOUGH FOR SOME LIGHT SNOW TO REACH THE
GROUND...IF IT CAN MATERIALIZE.

FRIDAY LOOKS MILD WITH TEMPERATURES POTENTIALLY PUSHING 50 DEGREES
AS WEST SOUTHWEST LOW-LEVEL FLOW BRING A WARM SECTOR OF ONE OF
THE QUICK-MOVING SYSTEMS INTO OUR AREA.

HAVE GONE WITH AN GFS/EC BLEND FOR THE WEEKEND INTO EARLY NEXT
WEEK. THE GFS IS CONSIDERABLY COLDER FOR SUNDAY AND SUNDAY NIGHT
WITH A STRONG CANADIAN HIGH PASSING OVER THE AREA...WHILE THE EC
FAVORS THIS FEATURE TO BE MUCH FURTHER NORTH AND WEAKER.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LIGHT SNOW ENDING BY 13Z.
* BLOWING SNOW THIS MORNING.
* MVFR CIGS THROUGH THIS AFTERNOON.
* STRONG/GUSTY NORTHERLY WINDS THROUGH MID/LATE AFTERNOON. CMS

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

BACK EDGE OF LIGHT SNOW WILL BE MOVING EAST OF MDW/GYY BY 13Z.
STILL THE POTENTIAL FOR SOME FLURRIES OR VERY LIGHT SNOW THROUGH
MID MORNING BUT NOT EXPECTING ANY VIS/CIGS RESTRICTIONS. BLOWING
SNOW/LOW DRIFTING SNOW WILL CONTINUE INTO THIS AFTERNOON. ONCE
SNOW ENDS...MVFR CIGS WILL CONTINUE INTO THIS AFTERNOON THEN
SCATTER OUT BY EVENING WITH SKC EXPECTED TONIGHT.

STRONG/GUSTY NORTHERLY WINDS WILL CONTINUE THROUGH MUCH OF THE DAY
WITH GUSTS AS HIGH AS 30KTS FOR THE NEXT FEW HOURS...THEN GUSTS
WILL DIMINISH INTO THE MID/UPPER 20KT RANGE BY LATE MORNING...
SLOWLY AND STEADILY DIMINISHING THROUGH AFTERNOON WITH GUSTS
ENDING WITH SUNSET. WINDS WILL BECOME LIGHT AND VARIABLE OVERNIGHT
AS A RIDGE OF HIGH PRESSURE MOVES ACROSS THE AREA. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH FOR SNOW END TIMING.
* HIGH FOR CIG TRENDS.
* HIGH FOR WINDS SPEEDS/GUSTS/DIRECTIONS. CMS

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

* THURSDAY NIGHT...DRY/VFR.
* FRIDAY...DRY/VFR. GUSTY WESTERLY WINDS.
* SATURDAY THROUGH SUNDAY...DRY/VFR.
* TUESDAY...CHANCE OF RAIN/SNOW. MVFR POSSIBLE.

&&

.MARINE...
210 PM CDT

LOW PRESSURE OVER THE CENTRAL PLAINS WILL CONTINUE TO DEEPEN AS IT
TRACKS EAST ACROSS SOUTHERN ILLINOIS TONIGHT AND INTO THE OHIO
VALLEY WEDNESDAY.  AS THE LOW TRACKS SOUTH AND THEN SOUTHEAST OF THE
LAKE...HIGH PRESSURE WILL ALSO BUILD ACROSS THE UPPER GREAT LAKES
REGION...SETTING UP STRONG NORTH WINDS.  THE COMBINATION OF A STRONG
GRADIENT AND STRONG COLD ADVECTION WILL LEAD TO WINDS QUICKLY
INCREASING TO GALES BY LATE THIS EVENING.  THE LATEST GUIDANCE HAS
BEEN RELATIVELY CONSISTENT IN INDICATING THE POTENTIAL FOR HIGH END
GALES BY LATE WEDNESDAY MORNING AND EARLY AFTERNOON...WITH THE
STRONGEST GALES OVER THE SOUTHERN PORTIONS OF THE LAKE...INCLUDING
THE NEARSHORE WATERS.  BY WEDNESDAY EVENING...THE HIGH PRESSURE WILL
BEGIN TO SPREAD ACROSS LAKE MICHIGAN ALLOWING WINDS TO SUBSIDE BELOW
GALE FORCE.  BY THURSDAY NIGHT...THE HIGH WILL PUSH TO THE SOUTHEAST
OF THE LAKE AS A CLIPPER DROPS OUT OF NORTHERN ALBERTA AND SWINGS
JUST NORTH OF THE UPPER GREAT LAKES ON FRIDAY.  WITH THE SFC HIGH
SAGGING OFF THE SERN COAST...A PERIOD OF SWLY WINDS WILL DEVELOP
AHEAD OF AN APPROACHING COLD FRONT TRAILING FROM THE CLIPPER.
ANTICIPATE A PERIOD OF BRISK SLY TO SWLY WINDS FOR THURSDAY NIGHT
THROUGH FRIDAY...BUT MORE GALES ARE NOT EXPECTED AT THIS TIME.  AS
THE CLIPPER TURNS NEWD INTO QUEBEC...IT WILL DRAG A WEAK COLD FRONT
DOWN THE LAKE WITH ANOTHER ARCTIC HIGH BUILDING IN BEHIND THE
FRONT.  25-30KT NORTH WINDS WILL SET UP FOLLOWING THE FROPA FOR
SATURDAY NIGHT AND SUNDAY...BUT AS THE HIGH SPREADS ACROSS THE GREAT
LAKES SUNDAY NIGHT...WINDS SHOULD BECOME MORE LIGHT AND VARIABLE.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ013-ILZ014-ILZ020-ILZ021-ILZ022-ILZ023
     UNTIL 11 AM WEDNESDAY.

     WINTER WEATHER ADVISORY...ILZ006-ILZ011-ILZ012 UNTIL 7 AM
     WEDNESDAY.

     WINTER WEATHER ADVISORY...ILZ019-ILZ032-ILZ033-ILZ039 UNTIL 11
     AM WEDNESDAY.

IN...WINTER STORM WARNING...INZ001-INZ002 UNTIL 11 AM WEDNESDAY.

     WINTER WEATHER ADVISORY...INZ010-INZ011-INZ019 UNTIL 11 AM
     WEDNESDAY.

LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878 UNTIL 10 PM WEDNESDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868 UNTIL 7 PM WEDNESDAY.

&&

$$

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