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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1128 AM CST SUN FEB 17 2013

DISCUSSION...
1108 AM CST

FOR MORNING UPDATE...

LITTLE/NO CHANGE TO GOING FORECAST TODAY. SURFACE HIGH PRESSURE
RIDGE DRIFTING EAST ACROSS THE FORECAST AREA PRODUCING LIGHT WINDS
AND MAINLY SUNNY SKIES ACROSS THE REGION. WILL SEE AN INCREASE IN
THIN CIRRUS THIS AFTERNOON AS HIGH LEVEL MOISTURE SPILLS ACROSS
THE UPPER RIDGE AXIS...THOUGH SHOULD STILL SEE A GOOD DEAL OF SUN
THROUGH THE PATCHY HIGH CLOUDS. AFTERNOON HIGHS FROM THE LOW/MID
30S FAR SOUTHWEST TO THE UPPER 20S ACROSS NORTHEAST SECTIONS OF
THE CWA STILL APPEAR REASONABLE AND ON TRACK PER 12Z GUIDANCE LOW
LEVEL THERMAL FIELDS. ISSUED UPDATED ZFP MAINLY TO CLEAN UP WINDS
WITH THE RIDGE MOVING THROUGH...OTHERWISE GOING FORECAST IS IN
FINE SHAPE.

RATZER

//PREV DISCUSSION...
322 AM CST

THE MAIN FORECAST CONCERNS DURING THE PERIOD CONTINUES TO FOCUS ON
THE ACTIVE WEATHER PERIOD EXPECTED DURING THE UPCOMING WEEK ALONG
WITH SOME BIG TEMPERATURE SWINGS...ESPECIALLY OVER THE NEXT 48
HOURS.

A SURFACE RIDGE OF HIGH PRESSURE CENTERED ACROSS THE
REGION...COMBINED WITH CLEAR SKIES HAS LEAD TO A VERY COLD
MORNING...WITH MANY AREAS ACROSS NORTHERN ILLINOIS IN THE SINGLE
DIGITS. THIS COLD AIRMASS HAS ALSO SET UP VERY FAVORABLE
THERMODYNAMIC CONDITIONS FOR LAKE EFFECT SNOW SHOWERS ACROSS LAKE
MICHIGAN OVERNIGHT. THE LIGHT WIND FIELD HAS ALLOWED FOR A SHORE
BREEZE CONVERGENCE ZONE ACROSS THE SOUTHERN PORTION OF LAKE
MICHIGAN. REGIONAL RADAR IMAGERY SHOWS A DECENT AND WELL DEVELOPED
SINGLE BAND RUNNING ONSHORE ACROSS FAR SOUTHWESTERN MI AND PORTIONS
OF NORTH CENTRAL INDIANA. THIS BAND OF SNOW HAS STAYED TO THE EAST
OF MY AREA THROUGH THE NIGHT. IT IS STILL POSSIBLE THAT THE BAND
COULD SHIFT FAR ENOUGH WEST TO CLIP PORTIONS OF PORTER COUNTY
INDIANA EARLY THIS MORNING...SO I INCREASED POPS SOME DURING THE
EARLY MORNING HOURS TO ACCOUNT FOR THIS POTENTIAL. IF THE BAND DOES
MAKE IT INTO PORTER COUNTY A QUICK INCH OR SO COULD FALL...BUT OVERALL
CONFIDENCE ON THE BAND OF HEAVIER SNOW SHOWERS GETTING INTO PORTER
COUNTY IS LOW.

THE FLOW ACROSS THE LAKE WILL QUICKLY BECOME WESTERLY BY LATE
MORNING AND SOUTHERLY THIS AFTERNOON AS THE SURFACE RIDGE OF HIGH
PRESSURE SHIFTS TO THE SOUTHEAST ACROSS THE OHIO VALLEY THROUGH THE
DAY. THEREFORE...THE CONVERGENT BAND OF LAKE EFFECT SNOW WILL
QUICKLY WEAKEN BY MID TO LATE MORNING ENDING THE THREAT.

THINGS WILL BEGIN TO WARM TODAY AS THE FLOW TURNS
SOUTHEAST BY EARLY AFTERNOON OUT AHEAD OF LOW PRESSURE TAKING SHAPE
ACROSS THE PLAINS STATES. HOWEVER...THE EXTENT OF THE WARMTH WILL BE
LIMITED TODAY AS THE REAL WARMTH WILL NOT ARRIVE UNTIL
MONDAY. THE COMBINATION OF THE UNFAVORABLE SOUTHEASTERLY COMPONENT
TO THE WIND AND THE VERY COLD START THIS MORNING WILL MAKE IT HARD
FOR TEMPERATURES TO WARM MUCH ABOVE 30 DEGREES THIS AFTERNOON. IN
FACT NORTHERN ILLINOIS MAY ONLY GET INTO THE UPPER 20S.

TONIGHT TEMPERATURES WILL LIKELY NOT DROP MUCH...AND WILL LIKELY END
UP RISING THROUGH THE NIGHT AS WARM AIR ADVECTION
INCREASES ACROSS THE AREA. THE SURFACE WARM FRONT SHOULD PUSH ACROSS
THE REGION BY EARLY MONDAY...AND VERY WARM CONDITIONS WILL SET UP IN
THE WAKE OF THIS FRONT. IT STILL APPEARS THAT MANY AREAS ACROSS
CENTRAL ILLINOIS WILL GET INTO AT LEAST THE LOWER 50S...WITH
SLIGHTLY COOLER CONDITIONS IN THE MID TO UPPER 40S ACROSS NORTHERN
ILLINOIS. I CONTINUED THE TREND OF RAISING TEMPERATURES AS THE
STRONG WARM PUSH AHEAD OF THE APPROACHING LOW...WITH NO SNOW COVER
..SHOULD EASILY SUPPORT TEMPERATURES WELL ABOVE AVERAGE FOR THIS
TIME OF YEAR.

THE OTHER STORY ON MONDAY WILL BE THE STRONG SOUTHERLY WINDS AND
RAIN...ESPECIALLY DURING THE AFTERNOON. THERE LOOKS TO BE A VERY
IMPRESSIVE SURGE OF MOISTURE NORTHWARD FROM THE WESTERN GULF OF
MEXICO ON MONDAY...AS GUIDANCE SUGGESTS THAT A 50 TO 60 KT LOW LEVEL
JET WILL DEVELOPS AHEAD OF THE APPROACHING TROUGH. STRONG ISENTROPIC
ASCENT WILL LIKELY LEAD TO RAIN DEVELOPMENT BY LATE MORNING OR EARLY
AFTERNOON ACROSS THE CWA. THIS WILL RESULT IN A WARM AND BREEZY
AFTERNOON...BUT ALSO A FAIRLY WET ONE AS WELL. WITH THE STRONG SURGE
OF MOISTURE...I WILL NOT BE SURPRISED TO SEE RAINFALL AMOUNTS
APPROACH A HALF INCH IN SOME AREAS.

THE SURFACE LOW WILL TRACK NORTH OF THE AREA ACROSS NORTHERN
PORTIONS OF WISCONSIN DURING THE AFTERNOON. THE ASSOCIATED COLD
FRONT STILL LOOKS ON TRACK TO MOVE FROM WEST TO EAST ACROSS MY AREA
DURING THE EVENING HOURS. THERE WILL BE A GOOD PUSH OF COLD AIR IN
THE WAKE OF THIS FRONT...WHICH SHOULD ALLOW FOR THE RAIN TO CHANGE
TO SOME SNOW ON THE BACK SIDE OF THE SYSTEM. SNOW SHOWERS AND
FLURRIES MAY ACTUALLY CONTINUE INTO TUESDAY AS IT APPEARS THAT SOME
UPPER LEVEL ENERGY WILL LAG THE COLD FRONTAL PASSAGE AND RESULT IN
RENEWED DEVELOPMENT WELL BEHIND THE FRONT. STEEP LOW LEVEL LAPSE
RATES WITHIN THE COLD AIRMASS SHOULD LEAD TO MORE SHOWERY SNOW INTO
TUESDAY. THIS STILL DOES NOT LOOK TO BE A GOOD SNOWFALL EVENT FOR
US...BUT THERE COULD BE SOME MINOR ACCUMULATIONS WITH THE SNOW
SHOWER ACTIVITY.

THE WINDS LOOK TO ALSO REMAIN FAIRLY STRONG MONDAY NIGHT INTO
TUESDAY IN THE WAKE OF THE COLD FRONT. THE GUIDANCE CURRENTLY
SUGGESTS WINDS SHOULD BE SUB ADVISORY CRITERIA...BUT DECENT
ISALLOBARIC PRESSURE RISES AND STRONG COLD AIR ADVECTION COULD
RESULT IN A PERIOD OF FAIRLY STRONG WINDS...POSSIBLY HIGHER THAN
GUIDANCE CURRENTLY SUGGESTS. THE STRONG WINDS AND MUCH COLDER
TEMPERATURES WILL ALSO RESULT IN SOME FAIRLY COLD WIND
CHILLS...POSSIBLE NEAR OR JUST BELOW ZERO AT TIMES.

THE MAIN STORY IN THE EXTEND PERIOD CONTINUES TO BE WITH THE NEXT
POTENT SYSTEM EXPECTED TO DIG ACROSS THE WESTERN CONUS ON TUESDAY
AND THEN EJECT OUT ACROSS THE SOUTHERN ROCKIES BY MIDWEEK. OVERALL
NOT MUCH HAS CHANGED IN THE CURRENT THINKING.  THE GUIDANCE
CONTINUES TO SUGGEST A SYSTEM THAT LIFTS NORTH NORTHEASTWARD ACROSS
THE MID MISSOURI VALLEY AND UPPER MISSISSIPPI VALLEY BY WEEKS END.
OVERALL...THIS TRACK WOULD NOT BE FAVORABLE FOR VERY LARGE AMOUNTS
OF SNOW ACROSS THE AREA. HOWEVER...THERE COULD STILL BE A DECENT
PERIOD OF SNOW ACROSS THE AREA ASSOCIATED WITH THE STRONG ISENTROPIC
UPGLIDE/WARM AIR ADVECTION AHEAD OF THE APPROACHING SYSTEM. THE
CURRENTLY TIMING WOULD PRODUCE THE BEST CHANCES DURING THE EVENING
HOURS ON THURSDAY.

ONE THING TO KEEP IN MIND ABOUT THE CURRENT FORECASTS FROM THE
OPERATIONAL SOLUTIONS IS THAT THERE IS STILL A DECENT AMOUNT OF
SPREAD AMONGST THE ENSEMBLE SOLUTIONS. SO...ALTHOUGH CONFIDENCE IN
INCREASING IN PERIOD OF PRECIPITATION FROM THIS SYSTEM LATER
THURSDAY. CONFIDENCE IN THE CURRENT TRACK OF THE SYSTEM INTO FRIDAY
REMAINS LOW AT THIS TIME.

IT APPEARS THAT WE WILL REMAIN IN A RATHER ACTIVE SOUTHERN STREAM STORM
TRACK...EVEN BEYOND THE CURRENT FORECAST PERIOD AS A NEGATIVE PNA
PATTERN LOOKS TO CONTINUE TO DRIVE DIGGING SYSTEMS IN ACROSS THE
WESTERN CONUS AND THEN OUT ACROSS THE CENTRAL CONUS.

KJB

&&

AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LLWS TONIGHT
* STRONG/GUSTY SOUTHERLY WINDS SUNDAY
* -SHRA/MVFR DEVELOPING SUNDAY AFTERNOON

IZZI

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

MID/HIGH LEVEL CLOUDINESS WILL INCREASE THROUGH TONIGHT AS
DEVELOPING STORM OVER THE PLAINS BEGINS TO MAKE PROGRESS EAST
TOWARD THE REGION. SOUTH/SOUTHEAST WINDS WILL DEVELOP TODAY AND
SLOWLY RAMP UP TONIGHT...PARTICULARLY JUST ABOVE THE SFC WHERE LOW
LEVEL JET WILL RESULT IN 50KT+ SOUTHERLY WINDS JUST OFF THE DECK
TONIGHT. THOSE HIGHER WINDS WILL BEGIN MIXING TO THE SFC AS GUSTS
OF 25KT+ BY MID-LATE MORNING SUNDAY AND CONTINUE INTO SUNDAY
AFTERNOON. SHOWERS ARE EXPECTED TO MOVE INTO THE CHICAGO AREA
SUNDAY AFTERNOON WITH CORRESPONDING INCREASE IN LOW LEVEL MOISTURE
LIKELY TO RESULT IN MVFR CIGS DEVELOPING.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE THROUGH EARLY SUNDAY MORNING
* LOWER CONFIDENCE ON CIGS SUNDAY AND TIMING OF LOWER CIGS
  ARRIVING

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN ENDING...POSSIBLY AS A TOUCH OF SNOW. MVFR
LIKELY AND IFR POSSIBLE. STRONG WINDS.

TUESDAY...MVFR CIGS. STRONG WEST WINDS.

WEDNESDAY...VFR.

THURSDAY...SNOW DEVELOPING IN THE LATE AFTERNOON/EARLY EVENING.
IFR CONDITIONS LIKELY BY EVENING. STRONG EAST WINDS LIKELY.

FRIDAY...IFR/LIFR POSSIBLE WITH DZ/-RA.

SATURDAY...MVFR CIGS POSSIBLE.

IZZI

&&

MARINE...
310 AM CST

HIGH PRESSURE STRETCHES FROM JAMES BAY...THROUGH THE WESTERN
GREAT LAKES...SOUTH INTO THE LOWER MISSISSIPPI VALLEY. THIS RIDGE
WILL PASS EAST ACROSS LAKE MICHIGAN DURING THE EARLY MORNING
HOURS...ALLOWING WINDS TO SHIFT FROM NORTHWESTERLY TO MORE
SOUTHERLY. AS WINDS SHIFT TO A MORE OFFSHORE ORIENTATION...WAVES
OVER THE SOUTHERN TIP OF THE LAKE WILL SUBSIDE...BRINGING AND END
TO THE GOING SMALL CRAFT ADVISORY. THE HIGH WILL THEN PROCEED TO
THE EASTERN SEABOARD BY MONDAY AFTERNOON WHILE STRENGTHENING TO
30.5 INCHES. MEANWHILE...LOW PRESSURE OVER SOUTHERN SASKATCHEWAN
WILL DROP SOUTHEAST TO NORTHERN MINNESOTA BY MONDAY MORNING. THIS
WILL LEAD TO A STRENGTHENING SOUTHERLY GRADIENT OVER THE LAKE WITH
WINDS INCREASING TO 30KT LATE SUNDAY NIGHT AND MONDAY MORNING. A
SMALL CRAFT ADVISORY WILL GO INTO EFFECT LATE SUNDAY NIGHT AS
WINDS INCREASE TO 30 KT AND THERE IS A CHANCE FOR OCCASIONAL
SOUTHERLY GALE FORCE GUSTS OVER THE SOUTHERN TWO THIRDS OF THE OPEN
WATERS THROUGH MONDAY. AS THE LOW CONTINUES EAST...DRAGGING A
STRONG COLD FRONT ACROSS THE LAKE MONDAY EVENING AS THE LOW
DEEPENS TO 29.2 INCHES. THERE WILL BE A BRIEF LULL IN THE WINDS AS
THE FRONTAL TROUGH CROSSES THE LAKE...BUT WINDS WILL QUICKLY RISE
TO WEST GALES AS THE STRONG PUSH OF COLD AIR SPREADS ACROSS THE
LAKE. WEST TO NORTHWEST GALES SHOULD PERSIST UNTIL EARLY WEDNESDAY
MORNING WHEN THE LOW LIFTS NORTHEAST ACROSS SOUTHERN QUEBEC AND
WEAKENS. HIGH PRESSURE WILL THEN BUILD IN BEHIND THE FRONT...
SPREADING ACROSS THE WESTERN GREAT LAKES WEDNESDAY AND WEDNESDAY
NIGHT.

KREIN

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...MIDNIGHT MONDAY TO 10 AM WEDNESDAY.

     GALE WATCH...LMZ080-LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-
     LMZ675-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-
     LMZ878...3 AM MONDAY TO 3 PM MONDAY.

&&

$$