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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1146 AM CST MON FEB 11 2013

DISCUSSION...
308 AM CST

A VARIETY OF WEATHER WILL CONTINUE THIS FORECAST PERIOD...ESPECIALLY
WITH REGARD TO TEMPERATURES. MORNING WATER VAPOR IMAGERY SHOWS A BIG
CLOSED UPPER LOW SPINNING OVER NORTHERN WISCONSIN AND STEADILY
LIFTING NORTHEASTWARD. A TROUGH AXIS EXTENDS SOUTHWESTWARD TO A
CUTOFF UPPER LOW JUST WEST OF THE FOUR CORNERS REGION. ACTIVE ZONAL
FLOW OVER THE PACIFIC WEST OF BRITISH COLUMBIA IS SHUNTING A RIDGE
AXIS INTO THE CANADIAN PRAIRIES WHICH STEMS FROM AN ANTICYCLONIC
UPPER CIRCULATION OFF THE OREGON/WASHINGTON COAST. AT THE
SURFACE...LOW PRESSURE IS MOVING NORTHEASTWARD ACROSS NORTHERN
WISCONSIN WITH AN OCCLUDED FRONT NOW TO THE EAST OF THE LOCAL AREA.
MEANWHILE...HIGH PRESSURE EXTENDS FROM THE NORTHERN ROCKIES INTO THE
CENTRAL PLAINS.

TODAY AND TONIGHT...THE MAIN CONCERNS WILL BE WINDS THROUGH THE
AFTERNOON ALONG WITH POSSIBLE SNOW SHOWER ACTIVITY. THE SURFACE LOW
WILL CONTINUE NORTHEASTWARD TODAY WITH COLD ADVECTION CONTINUING
FROM THE SOUTHWEST AS THIS OCCURS. H85 TEMPS WILL FALL TO AROUND
-10C BY AFTERNOON. THE LOW WILL MAINTAIN STRENGTH THROUGH THE DAY
AND THE MAIN AREA OF PRESSURE RISES CURRENTLY MOVING TOWARD THE
MID/UPPER MISSISSIPPI RIVER WILL TRANSLATE EAST-NORTHEAST. THIS
COMBINED WITH STEEPENING LOW LEVEL LAPSE RATES WILL KEEP GUSTY WINDS
IN PLACE THROUGH THE DAY WITH FREQUENT GUSTS AROUND 40 KT LIKELY
WITH SOME HIGHER GUSTS POSSIBLE AT TIMES. WILL MAINTAIN THE WIND
ADVISORY. CYCLONIC FLOW AND STEEP LOW LEVEL LAPSE RATES...ALONG WITH
AN INCREASE IN COLUMN MOISTURE WILL PROVIDE SOME SUPPORT FOR SNOW
SHOWERS ACROSS THE NORTHERN HALF OR SO OF THE CWA OR GENERALLY NORTH
OF INTERSTATE 80. THE MAIN FOCUS FOR ACTIVITY WILL LIKELY BE ALONG
AND NORTH OF INTERSTATE 88 HOWEVER. AT THE MOMENT...THERE APPEARS TO
BE AN EMBEDDED VORT MAX DRIVING A FAIRLY ORGANIZED AREA OF LIGHT
SNOW NOW MOVING ACROSS NORTHEAST IOWA AND THIS WILL MOVE ACROSS THE
FAR NORTHERN CWA THIS MORNING. RADAR TRENDS SHOW OTHER AREAS OF
LIGHTER RETURNS ACROSS MUCH OF CENTRAL AND EASTERN IOWA AS WELL.
OVERALL...AREAS THAT ARE DIRECTLY UPSTREAM OF THE CWA ARE SEEING
MINIMAL VSBY REDUCTION AT THIS POINT. EXTRAPOLATION SUPPORTS THE
IDEA OF THE BEST CHANCES BEING ACROSS THE NORTHERN CWA.
COVERAGE/INTENSITY MAY BE AIDED DIURNALLY ACROSS THE LOCAL AREA BY
LATE MORNING. SOME LIGHT ACCUMULATION IS POSSIBLE...ESPECIALLY IF
MORE INTENSE ISOLATED SNOW SHOWERS CAN DEVELOP...WHICH COULD ALSO
BRIEFLY BRING VSBY DOWN TO A FEW MILES. SOME LOCALIZED ACCUMULATION
OF A FEW TENTHS OF AN INCH IS A POSSIBILITY...ESPECIALLY IF THERE IS
SOME DIURNAL ENHANCEMENT LATER THIS MORNING/EARLY THIS AFTERNOON.
WEAK UPPER RIDGING WILL TRAIL THE UPPER LOW THIS EVENING BRINGING
DRIER SUBSIDENT AIR AND AN END TO ANY SNOW SHOWER ACTIVITY. A
WESTERLY BREEZE LOOKS TO REMAIN IN PLACE WITH THE SURFACE HIGH
PASSING SOUTH OF THE AREA. WITH COLDER AIR SPREADING ACROSS THE AREA
NOW...HIGHS WILL LIKELY OCCUR THIS MORNING ACROSS NORTHERN SECTIONS
OF THE CWA WHERE CLOUD COVER WILL BE THICKEST. IT DOES NOT APPEAR
THAT THERE WILL BE A MAJOR COOLING TREND THROUGH THE DAY BUT
PROBABLY MORE OF A STEADY ONE...THOUGH A FEW DEGREES OF COOLING MAY
OCCUR THROUGH THE DAY. SOUTHERN AREAS MAY BE ABLE TO REBOUND A FEW
DEGREES DURING THE MIDDLE PART OF THE DAY. EXPECT OVERNIGHT LOWS IN
THE LOW TO MID 20S.

TUESDAY THROUGH EARLY NEXT WEEK...THE SURFACE HIGH WILL PASS TO THE
SOUTH WHILE LOW PRESSURE MOVES ACROSS HUDSON BAY ON TUESDAY WHICH
WILL RESULT IN WEAK RIDGING CROSSING THE AREA. H85 TEMPS WILL WARM
TO AROUND -4C WITH A WEST TO SOUTHWEST BREEZE. THIS SHOULD RESULT IN
HIGHS IN THE MID TO UPPER 30S WITH SOME AREA OF THE SOUTH REACHING
40. THE AFOREMENTIONED FOUR CORNERS CUTOFF UPPER TROUGH WILL DAMPEN
SLIGHTLY AND MOVE EASTWARD FROM THE TEXAS PANHANDLE TO THE OHIO
VALLEY TUESDAY NIGHT AND WEDNESDAY MORNING. A WEAK FRONT TRAILING
THE HUDSON BAY LOW WILL CROSS THE AREA WEDNESDAY MORNING BUT RESULT
IN LITTLE MORE THAT A SLIGHT WIND SHIFT TO WEST-NORTHWEST AND
PERHAPS SOME CLOUD COVER THANKS TO THE PARENT UPPER TROUGH AXIS. A
CLIPPER WILL QUICKLY MOVE SOUTHEASTWARD IN A NEWLY ESTABLISHED
NORTHWESTERLY UPPER FLOW STRETCHING FROM WESTERN CANADA INTO THE
UPPER MIDWEST WHICH WILL BRING A SLIGHT PUSH OF WARM ADVECTION LATE
WEDNESDAY. EXPECT HIGHS TO BE 5 OR SO DEGREES WARMER WEDNESDAY THAN
TUESDAY DESPITE ALL THESE FEATURES PASSING NEAR THE AREA. THE
SURFACE TROUGH OF THE CLIPPER WILL PASS NORTH OF THE AREA WEDNESDAY
NIGHT AND THURSDAY MORNING KEEPING MOST OF THE MOISTURE TO THE NORTH
BUT A BRIEF PERIOD OF WARM ADVECTION PRECIP IS A LOW POSSIBILITY
ACROSS THE CWA...MAINLY NORTH...WEDNESDAY EVENING/NIGHT. THE
ATTENDANT COLD FRONT THEN SWEEPS ACROSS THURSDAY POTENTIALLY
BRINGING SOME LIGHT PRECIP WITH IT AS WELL. FROM THAT POINT ON A
SERIES OF TROUGHS WILL HELP DIG A LONG WAVE TROUGH INTO THE WESTERN
GREAT LAKES AND LOWER OHIO VALLEY WHICH WILL RESULT IN PERIODIC
LIGHT PRECIP CHANCES THROUGH THE WEEKEND. IN ADDITION...MUCH COLDER
AIR WILL WORK BACK IN WITH H85 TEMPS OF AROUND -16C. THIS WILL LEAD
TO BELOW NORMAL TEMPS FROM FRIDAY THROUGH THE WEEKEND. RIDGING DOES
LOOK TO TRY AND BUILD IN EARLY NEXT WEEK BRINGING MODERATING TEMPS
BUT IT WILL BE FORCED BY ANOTHER TROUGH BUILDING INTO THE ROCKIES SO
ANOTHER MILDER AND ACTIVE WEATHER PERIOD MAY SET UP.

MDB

&&

AVIATION...

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

* STRONG/GUSTY W WINDS THROUGH THE EVENING.

* MVFR CIGS THROUGH THE EVENING INTO OVERNIGHT.


TRS

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

WHILE ORD METAR INCLUDED A G50 THIS IS AN ANOMALY AS REST OF AREA
METARS HAVE PKWND IN 34-38KT RANGE. W WINDS WILL GRADUALLY
DIMINISH THIS AFTERNOON AND EVENING AS THE PRESSURE GRADIENT OVER
THE AREA DECREASES WITH DEEP LOW PRESSURE OVER EASTERN LAKE
SUPERIOR MOVING OFF TO THE NE AND A SURFACE RIDGE BUILDING FROM
THE PLAINS TO THE MS VALLEY. CENTER OF THE PRESSURE RISE CENTER
BETWEEN THE DEPARTING LOW AND THE APPROACHING HIGH HAS BEEN
MOVING NE FROM SE MN TO CENTRAL WI. HOWEVER...DECENT 3 HOUR
PRESSURE RISES OF 3 TO 5MB STILL EXTENDS S OVER SW WI...EASTERN
IA AND W CENTRAL IL SO EXPECT GUSTINESS TO PERSIST...THOUGH
SLOWLY DECREASING IN MAGNITUDE...THIS AFTERNOON AND EARLY
EVENING.

MODELS DEPICT A MINOR WAVE DROPPING SSE FROM SE MN AND W CENTRAL
WI BEFORE TURNING TO THE SE ACROSS S CENTRAL WI AS WELL AS AND N
CENTRAL AND NE IL THIS AFTERNOON. SURFACE OBS FROM SW WI...SE MN
AND NE IA HAVE BEEN REPORTING SOME -SN OVER THE LAST FEW HOURS
BUT CONFIDENCE IN QUALITY OF TOTALLY AUTOMATED OBS NOT THE
GREATEST. NONETHELESS...THERE MAY BE SHORT PERIOD OF P6SM VERY
LIGHT SNOW...BASICALLY FLURRIES...MID AND LATE AFTERNOON AS THIS
NEXT MINOR DISTURBANCE APPROACHES AND MOVES OVERHEAD.

ADVECTION OF INCREASINGLY LOWER DEW POINTS IN PLACE UPSTREAM WILL
OCCUR THIS AFTERNOON AND TONIGHT WHICH IS EXPECTED TO LIFT
CEILINGS BACK TO VFR...AND EVENTUALLY LOSS OF ANY CEILINGS AS
FLOW BOTH IN LOW LEVELS AS WELL AS MID AND UPPER LEVELS BECOMES
SLIGHTLY ANTICYCLONIC BY PRE-DAWN TUE.

TRS

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

* HIGH CONFIDENCE IN WIND DIRECTION...SUSTAINED SPEED AND GUSTINESS.

* HIGH CONFIDENCE IN MVFR CIGS PERSISTING FROM THIS AFTERNOON INTO
  THE OVERNIGHT.

TRS

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

* TUESDAY NIGHT AND WEDNESDAY...DRY/VFR.
* THURSDAY...WIND SHIFT/COLD FRONT. SLIGHT CHANCE OF SNOW. MVFR
  POSSIBLE.
* FRIDAY...CHANCE OF SNOW. MVFR POSSIBLE.
* SATURDAY AND SUNDAY...DRY/VFR.

&&

MARINE...

253 AM...GOING FORECAST/GRIDS/HEADLINES IN GOOD SHAPE THIS
MORNING. STRONG LOW PRESSURE OVER NORTHERN WISCONSIN WILL LIFT
NORTHEAST ACROSS THE UPPER LAKES TODAY AND ACROSS QUEBEC TONIGHT.
A TIGHT GRADIENT COMBINED WITH COLDER AIR SPREADING BACK ACROSS
THE REGION WILL ALLOW FOR GALES 40-45 KTS TO CONTINUE ACROSS THE
SOUTHERN HALF OR SO OF LAKE MICHIGAN INTO THIS EVENING. THE
STRONGER GRADIENT WILL MOVE ACROSS NORTHERN LAKE MICHIGAN LATER
THIS AFTERNOON INTO EARLY THIS EVENING AND THERE COULD BE A SHORT
PERIOD OF TIME WHERE GALES ARE POSSIBLE. AT THIS POINT HAVE
CONTINUED GALE GUST MENTION BUT WILL NEED TO BE MONITORED THROUGH
THE MORNING. AS THIS LOW DEPARTS TONIGHT...THE GRADIENT WILL RELAX
BUT THE NEXT HIGH PRESSURE WILL SLIDE SOUTH OF THE LAKE ACROSS THE
OHIO VALLEY AND EXPECT A PREVAILING WEST/SOUTHWEST WIND INTO MID
WEEK. THE NEXT LOW WILL MOVE ACROSS THE UPPER LAKES/NORTHERN LAKE
MICHIGAN ON THURSDAY. STILL SOME UNCERTAINTY REGARDING THE TRACK
OF THIS LOW AS WELL AS ITS STRENGTH...BUT CONSENSUS FOR ANOTHER
SHOT OF COLD AIR BEHIND THIS LOW THURSDAY NIGHT INTO FRIDAY...
WHICH SHOULD BE SUFFICIENT FOR WINDS TO INCREASE TO AT LEAST
25-30KTS AND DEPENDING ON HOW TIGHT THE GRADIENT BECOMES...PERHAPS
LOW END GALES. CMS

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
     ILZ032-ILZ033-ILZ039 UNTIL 4 PM MONDAY.

IN...WIND ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 4 PM
     MONDAY.

LM...GALE WARNING...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
     LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM MONDAY.

&&

$$