Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 030815
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
215 AM CST TUE MAR 3 2015

.UPDATE...
758 PM CST

THE FORECAST REMAINS ON TRACK WITH THE NEXT SYSTEM OVER COLORADO
THIS EVENING. GUIDANCE CONTINUES TO SUGGEST THAT THE LOW WILL
REACH SOUTHERN WISCONSIN MID-DAY TUESDAY AND MERGE WITH A
STRONGER LOW PUSHING EAST ACROSS ONTARIO. PRECIP WILL SPREAD
ACROSS THE REGION FROM SOUTHWEST TO NORTHEAST EARLY TUESDAY
MORNING. PRECIP SHOULD INITIALLY FALL AS SNOW...BUT WILL QUICKLY
TURN OVER TO A WINTRY MIX AS TEMPERATURES WARM TO ABOVE ZERO ALOFT
AND WE LOSE SATURATION IN THE DGZ. WILL KEEP THE WINTER WEATHER
ADVISORY AS IS.

JEE

&&

.SHORT TERM...
317 PM CST

THROUGH WEDNESDAY...

.SHORT TERM...THROUGH WEDNESDAY

AS MENTIONED IN THE EARLIER UPDATE... A WINTER WEATHER ADVISORY
WAS ISSUED FOR THE ENTIRE AREA EARLIER IN THE SHIFT FOR LATE
TONIGHT THROUGH TUESDAY MORNING. MODELS ARE STILL SHOWING
PRECIPITATION BEGINNING AS SNOW NORTH OF INTERSTATE 80...AND SOME
FORM OF SNOW...SLEET OR FREEZING RAIN IN THE FAR SOUTH. IT COULD
BE A PRETTY GOOD BURST OF WET SNOW INITIALLY BEFORE THE TRANSITION
BEGINS.

A WARM FRONT WILL LIFT THROUGH THE AREA DURING THE MORNING HOURS.
THIS IS THE PERIOD WHERE MODELS A SHOWING A MORE SIGNIFICANT PUSH
OF PRECIPITATION. WE ARE COMING OUT OF A PRETTY COLD AIR
MASS..AND DEW POINTS ARE STILL VERY LOW ACROSS THE AREA...WITH
DEWPOINTS ABOVE FREEZING NOT VERY CLOSE. TEMPERATURES LOOK TO
REMAIN BELOW FREEZING THROUGH AT LEAST MID MORNING AREA WIDE.
MODEST PRECIPITABLE WATER VALUES IN EXCESS OF 0.75 INCHES COUPLED
WITH A 35-40 KT LOW LEVEL JET FEEDING INTO THE LOW LEVEL FRONTAL
ZONE WOULD SUGGEST MODEST PRECIPITATION RATES DURING THIS TIME WHEN
THE LOW LEVEL (925-850 MB) TEMPERATURES ARE HEADING ABOVE
FREEZING. SOME OF THE RECENT NAM/GFS WAS SLIGHTLY COOLER IN THE
THERMAL PROFILE FOR THIS PERIOD SUGGESTING THAT SNOW/SLEET MAY
DOMINATE...ESPECIALLY FOR THE NORTHERN METRO AREA AND POINTS NORTH
TOWARD WISCONSIN... AND IF PRECIPITATION RATES CONTINUE A BIT
HEAVIER THIS MAY SLOW THE LOW LEVEL WARMING. BUT THE SIGNAL IS
STILL THERE FOR A SNOW-SLEET-FZRA TRANSITION AND ICE ACCUMULATION
POTENTIAL.

WHERE THE UNCERTAINTIES REMAIN IS IN REGARDS TO HOW MUCH ICE
ACCUMULATION WILL OCCUR AND HOW FAR NORTH THE IMPACTS ARE FELT. ICE IS
EXPECTED TO BE THE LEAST NORTH TOWARDS WISCONSIN AND IN THE
ROCKFORD AREA WHERE IT MAY JUST BE AN ALL SNOW/SLEET SITUATION
WHERE ADVISORY CRITERIA MAY NOT BE TECHNICALLY SATISFIED. GIVEN
THE UNCERTAINTY AND THE RUSH-HOUR TIME...FEEL IT IS THE SAFER CALL
WITH SOME SNOW/SLEET AS WELL. AND IN NW INDIANA...THE BETTER
MOISTURE ADVECTION IS FOCUSED HERE WHERE THERE IS HIGHER POTENTIAL
FOR ICE ACCUMULATION...BUT IT WILL BE A RACE AGAINST SURFACE TEMPS
AS WELL WHICH LOOK TO WARM THROUGH THE MORNING. AS MENTIONED
EARLIER...MEANWHILE...THE ECMWF/GEM ARE MORE SUPPORTIVE OF A
SNOW/SLEET SOLUTION IN MANY AREAS...ESPECIALLY NORTH OF INTERSTATE
80. IT LOOKS LIKE THE TRANSITION TIME FOR MIXED PRECIPITATION
SOUTH OF I-80 WILL OCCUR BEFORE DAYBREAK BASED ON THE NAM AND
EARLY LOOKS AT THE RAP CLOSE TO THAT TIME FRAME. IT WOULD LIKELY
BE AFTER 6-7 AM WHEN THAT TRANSITION OCCURS IN THE METRO
AREA...BUT CONFIDENCE ON THAT TIMING IS NOT SUPER HIGH.

WHILE WE ARE LOSING THE DEEPER MOISTURE IN THE AFTERNOON...WE ARE
GETTING SOME DECENT MID LEVEL FRONTOGENESIS WHICH SHOULD STILL ALLOW
US TO WRING OUT SOME PRECIPITATION IN THE AFTERNOON WHICH COULD BE A
SNOW-RAIN MIX IN THE NW...LIKELY RAIN IN THE SE...WITH EVEN SOME
-SN/DZ/FZDZ POSSIBLE ACROSS THE CHICAGO METRO AREA LATE IN THE
AFTERNOON AND EVENING.

THE UPPER TROUGH AXIS WILL GRADUALLY MOVE THROUGH THE AREA WHILE
SURFACE HIGH PRESSURE NOSES IN FROM THE NORTHWEST. EXPECT COLDER
CONDITIONS WITH SOME HIGH CLOUDS MOVING THROUGH. HIGHS WILL BE IN
THE TEENS WEDNESDAY AND THURSDAY...WITH LOWS EARLY THURSDAY MORNING
BOTTOMING OUT AT OR BELOW ZERO. WITH THE HIGH STILL TO THE
EAST...WIND CHILLS...YES WE ARE STILL DISCUSSING WIND CHILLS IN
EARLY MARCH...GET DOWN TO -10 TO -20 BELOW. A CLIMATE SECTION TO
THE AFD WILL BE FORTHCOMING.

KMD

&&

.LONG TERM...
317 PM CST

THURSDAY THROUGH MONDAY...

THE EXTENDED PERIOD WILL START OUT VERY COLD AS A 1040 MB ARCTIC
HIGH SHIFTS ACROSS THE REGION. WITH 925 AND 850 MB TEMPERATURES
PROGGED TO BE AROUND -18 CELSIUS...THIS SHOULD ONLY ALLOW FOR HIGHS
IN THE MIDDLE TO UPPER TEENS...FOLLOWING A BITTERLY COLD AND
POTENTIALLY RECORD COLD MORNING. THE GOOD NEWS IS THAT THIS WILL BE
A PROGRESSIVE HIT OF ARCTIC AIR. IN FACT...TEMPERATURES SHOULD
QUICKLY RECOVER BY FRIDAY AS A GUSTY SOUTH-SOUTHWESTERLY FLOW SETS
UP ALONG THE NORTHWESTERN PERIPHERY OF THE EXITING SURFACE RIDGE OF
HIGH PRESSURE. THIS SHOULD SUPPORT HIGHS INTO THE LOW 30S
FRIDAY...AND POSSIBLY WELL INTO THE 30S FOR THE WEEKEND. A WEAK COLD
FRONT MAY DROP ACROSS THE AREA OVER THE WEEKEND...BUT IT APPEARS THE
DEEPER COLD WILL BE AIMED TO OUR NORTHEAST. PRECIPITATION CHANCES
ALSO APPEAR TO BE MINIMAL DURING MUCH OF THE EXTENDED PERIOD.

KJB

&&

.CLIMATE...

A FEW RECORD LOW AND AND RECORD LOW MAXIMUM TEMPERATURES ARE IN
JEOPARDY ON WEDNESDAY AND THURSDAY.

HERE ARE THE CURRENT RECORDS FOR ROCKFORD AND CHICAGO. THE ONES THAT
STAND THE BEST CHANCE TO BE REACHED ORBROKEN HAVE A STAR (*) NEXT TO
THEM.

  WED 3/4  THU 3/5
ROCKFORD

RECORD LOW-11 (2002)-11 (2002)
RECORD LOW MAX 14 (2002)* 17 (1960)*

CHICAGO
RECORD LOW-12 (1873)  0 (1978)*
RECORD LOW MAX 17 (1890)* 12 (1901)

KMD/KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* SNOW EXPECTED TO DEVELOP DURING PREDAWN HOURS...QUICKLY
  TRANSITIONING TO A SNOW/SLEET MIX AND THEN FREEZING RAIN DURING
  THE MORNING. TEMPS RISE TO/ABOVE FREEZING BY MIDDAY WITH PRECIP
  CHANGING TO RAIN/DRIZZLE.

* CIG/VIS EXPECTED TO DETERIORATE FAIRLY QUICKLY FROM VFR TO
  IFR/LIFR WITH PRECIPITATION THIS MORNING. SLOW IMPROVEMENT IN
  CONDITIONS EXPECTED LATER THIS AFTERNOON/EVENING...WITH MVFR
  CIGS LIKELY LINGERING TONIGHT.

* SOUTH-SOUTHEAST WINDS INCREASING 10-15 KT EARLY THIS MORNING AND
  BECOMING GUSTY AROUND 20 KTS AT TIMES WHILE BACKING SOUTH LATE
  THIS MORNING. SOUTHWEST WINDS GUSTING AROUND 20 KTS THIS
  AFTERNOON BECOME WEST-NORTHWEST BY EARLY EVENING AND REMAINING
  GUSTY.

RATZER

//DISCUSSION...UPDATED 06Z...

LOW PRESSURE WAS DEVELOPING OVER EASTERN COLORADO AROUND MIDNIGHT...
WITH SOUTH-SOUTHEAST WINDS INCREASING ACROSS THE PLAINS AND MIDWEST
AND STARTING TO PULL MOISTURE NORTHWARD FROM THE WESTERN GULF.
REGIONAL RADAR MOSAIC SHOWS PRECIPITATION BLOSSOMING ACROSS THE
MID-MISSISSIPPI VALLEY AND LIFTING NORTHEAST AHEAD OF WARM FRONT
DEVELOPING ACROSS MISSOURI AND KANSAS. FORECAST MODELS CONTINUE TO
DEPICT PRECIPITATION SPREADING ACROSS THE LOCAL TERMINALS ROUGHLY
10-12Z...WITH THERMAL PROFILES SUPPORTING INITIALLY SNOW...QUICKLY
MIXING WITH SLEET AND FREEZING RAIN AS TEMPERATURES WARM ALOFT.
SURFACE TEMPS LOOK TO CLIMB TO/ABOVE FREEZING BY LATE MORNING OR
MIDDAY WITH ANY LINGERING PRECIPITATION IN THE FORM OF RAIN OR
DRIZZLE AS THE BETTER FORCING WITH THE ELEVATED WARM FRONT LIFTS
NORTH OF THE AREA.

WITH DEVELOPMENT OF PRECIPITATION...GUIDANCE REMAINS STEADFAST IN
A RAPID DETERIORATION OF VFR CONDITIONS TO IFR/LIFR WITHIN A FEW
HOURS OF ONSET. CIGS SHOULD LIFT ABOVE LIFR THIS AFTERNOON AS WARM
FRONT MOVES NORTH...AND EVENTUALLY TO MVFR LATE THIS AFTERNOON AND
THIS EVENING AS A COLD FRONT PUSHES EAST ACROSS THE AREA.

SOUTH-SOUTHEAST WINDS WILL BACK MORE SOUTHEAST EARLY THIS MORNING
AND INCREASE INTO THE 10-15 KT RANGE AS THE LOW MOVES QUICKLY
ACROSS THE PLAINS. WINDS WILL BACK SOUTH BY LATE MORNING/EARLY
AFTERNOON AS THE LOW PASSES NORTH ACROSS WISCONSIN. FORECAST
SOUNDINGS SUPPORT GUSTS AROUND 20 KTS BY LATE MORNING...AND
CONTINUE TO INDICATE GUSTY CONDITIONS AS WINDS SHIFT SOUTHWEST
THIS AFTERNOON AND WEST-NORTHWEST THIS EVENING.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN TIMING PRECIP DEVELOPMENT AND TRANSITION OF P-TYPES AS
  WELL AS CIG/VIS IMPACTS.

* HIGH IN WINDS...AND DRY WEATHER WITH LINGERING MVFR CIGS THIS
  EVENING.

RATZER

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

WEDNESDAY...MVFR CIGS.

THURSDAY AND FRIDAY...VFR.

SATURDAY AND SUNDAY...MVFR CIGS POSSIBLE.

BEACHLER

&&

.MARINE...
214 AM CST

MAIN FOCUS FOR THE LAKE MICHIGAN FORECAST REMAINS IN THE NEAR
TERM...AS SOUTH WINDS INCREASE QUICKLY THIS MORNING IN ADVANCE OF AN
AREA OF LOW PRESSURE MOVING QUICKLY FROM THE PLAINS TO THE WESTERN
LAKES BY THIS EVENING. SOUTH WINDS TO 30 KT...WITH A FEW GALE FORCE
GUSTS TO 35 KT...ARE EXPECTED ON MAINLY THE SOUTHERN PORTION OF THE
LAKE. THE LOW WILL TRAIL A COLD FRONT ACROSS THE LAKE EARLY THIS
EVENING WHICH WILL SHIFT WINDS TO THE WEST INITIALLY AND MORE
NORTHWEST OVERNIGHT AND WEDNESDAY...AS THE GRADIENT CONTINUES TO
SUPPORT 25-30 KT WINDS AS HIGH PRESSURE SLOWLY BUILDS FROM THE
NORTHERN PLAINS TO THE OHIO VALLEY. THE HIGH WILL PASS SOUTHWEST OF
THE LAKES THURSDAY AND THURSDAY NIGHT ALLOWING WINDS TO EASE AND
BACK SOUTHWEST BY EARLY FRIDAY. THE GRADIENT WILL TIGHTEN UP ONCE
AGAIN FRIDAY HOWEVER...BETWEEN THE HIGH RETREATING TO THE SOUTHEAST
AND AN AREA OF LOW PRESSURE MOVING NORTH OF THE LAKES ACROSS
ONTARIO. 30 KT SOUTHWESTERLIES LIKELY FRIDAY...BEFORE THE LOW TRAILS
A COLD FRONTAL TROUGH INTO THE AREA EARLY SATURDAY AND ALLOWS WINDS
TO RELAX A BIT AND SHIFT TO THE WEST.

SMALL CRAFT HEADLINES REMAIN UP FOR THE ILLINOIS AND INDIANA
NEARSHORE TODAY THROUGH WEDNESDAY EVENING FOR THE 25-30 KT WINDS.
RECENT POLAR-ORBITING SATELLITE IMAGERY FROM MONDAY AFTERNOON SHOWS
A GOOD PORTION OF THE ILLINOIS SHORE TO BE MAINLY OPEN WATER OR THIN
ICE FLOES...THUS HAVE INCLUDED WAVE FORECAST FOR ILLINOIS WATERS
WHILE INDIANA SHORE APPEARS TO REMAIN LARGELY ICE-COVERED. THE SAME
GOES FOR WESTERN PORTIONS OF NORTHERN LAKE MICHIGAN...WHICH APPEAR
TO HAVE A FAIR AMOUNT OF OPEN WATER.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL NOON TUESDAY.

IN...WINTER WEATHER ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019
     UNTIL NOON TUESDAY.

LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...6 AM TUESDAY TO 6 PM WEDNESDAY.

&&

$$

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