Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 022245
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
445 PM CST MON MAR 2 2015

.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 DEWPOINTS 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...
417 PM CST

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 22Z...

* LIGHT/VARIABLE WINDS THIS AFTERNOON BEFORE FLOPPING SOUTHEAST BY
  EARLY EVENING. SOUTH-SOUTHEAST WINDS BECOMING GUSTY 20-25 KT BY
  TUESDAY MORNING.

* SNOW...MIXING WITH SLEET THEN CHANGING TO FREEZING RAIN/RAIN
  EARLY TUESDAY MORNING. VFR CONDITIONS TO QUICKLY DETERIORATE TO
  IFR/LIFR IN PRECIP.

KJB

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

IT WILL CONTINUE TO BE A QUIET WEATHER DAY ACROSS THE AREA TODAY. A
SURFACE RIDGE OF HIGH PRESSURE PUSHING ACROSS THE AREA THIS
AFTERNOON WILL RESULT IN A PERIOD OF LIGHT AND VARIABLE
WINDS...THOUGH THE WINDS SHOULD SETTLE INTO A SOUTHEASTERLY DIRECTION
BY EARLY THIS EVENING. OTHERWISE VFR CONDITIONS EXPECTED.

THE WEATHER WILL BECOME MUCH MORE PROBLEMATIC BY DAYBREAK TUESDAY.
WINDS WILL INCREASE OUT OF THE SOUTHEAST AND BECOME GUSTY DURING THE
MORNING. SNOW WILL ALSO DEVELOP OVER THE AREA JUST PRIOR TO
DAYBREAK...BEFORE MIXING WITH SLEET AND CHANGING OVER TO A PERIOD OF
FREEZING RAIN BY MID MORNING TUESDAY. IT CURRENTLY APPEARS THAT
ABOUT A 1 TO 3 HOUR PERIOD OF SNOW AND SLEET WILL OCCUR FROM ROUGHLY
11 UTC THROUGH 13 TO 15 UTC. DURING THIS PERIOD IFR VIS IN SNOW AND
LOWERING CIGS ARE LIKELY. CIGS WILL CONTINUE TO DETERIORATE INTO THE
IFR AND LIFR CATEGORIES DURING THE MORNING AS WARMER AIR ALOFT
BEGINS TO CHANGE THE SNOW AND SLEET OVER TO SOME FREEZING RAIN.
SURFACE TEMPERATURES SHOULD ALSO BE ON A WARMING TREND DURING THE
MORNING...AND ARE EXPECTED TO WARM ABOVE FREEZING BY MIDDAY...SO ANY
LINGERING PRECIP AFTER THIS TIME WILL LIKELY NO LONGER PRODUCE A
FREEZING THREAT.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH IN PRECIP TIMING/TREND EARLY TUESDAY. MEDIUM IN
  CIG/VIS IMPACTS.

* HIGH ALL OTHER ELEMENTS.

KJB

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

TUESDAY NIGHT...MVFR CIGS. GUSTY WEST WINDS.

WEDNESDAY...MVFR CIGS.

THURSDAY AND FRIDAY...VFR.

SATURDAY AND SUNDAY...MVFR CIGS POSSIBLE.

RATZER

&&

.MARINE...

224 PM...HIGH PRESSURE OVER THE SOUTHERN LAKES AND OHIO VALLEY
WILL MOVE EAST TO THE MID ATLANTIC AND NEW ENGLAND TUESDAY MORNING
AS LOW PRESSURE FORMS OVER THE CENTRAL PLAINS TONIGHT. THIS LOW
WILL QUICKLY MOVE NORTHEAST TUESDAY AND BE ABSORBED BY STRONGER
LOW PRESSURE OVER NORTHERN ONTARIO...AS A COLD FRONT MOVES ACROSS
LAKE MICHIGAN. THE GRADIENT WILL SLOWLY INCREASE AHEAD OF THIS LOW
TONIGHT INTO TUESDAY MORNING WITH 30 KTS EXPECTED BY TUESDAY
MORNING AND THERE COULD BE SOME LOW END GALE GUSTS BUT CONFIDENCE
REGARDING FREQUENCY IS LOW. WINDS WILL SHIFT TO THE SOUTHWEST IN
THE AFTERNOON AND THEN TO THE NORTHWEST TUESDAY NIGHT. SPEEDS WILL
LIKELY REMAIN IN THE 30 KT RANGE...ESPECIALLY ACROSS THE SOUTHERN
TWO THIRDS...AS HIGH PRESSURE BUILDS ACROSS THE PLAINS WEDNESDAY
AND COLD AIR OVERSPREADS THE REGION. THIS HIGH WILL EXTEND FROM
THE SOUTHERN PLAINS TO THE OHIO VALLEY THURSDAY AS WINDS TURN MORE
WESTERLY AND BEGIN TO SLOWLY DIMINISH. BUT AS THE HIGH DEPARTS
THURSDAY NIGHT...THE GRADIENT WILL TIGHTEN AS LOW PRESSURE MOVES
ACROSS NORTHERN ONTARIO WITH A PERIOD OF SOUTHWEST WINDS TO 30 KTS
ON FRIDAY...WITH SOME LOW END GALES POSSIBLE. CMS

&&

.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...3 AM TUESDAY TO NOON
     TUESDAY.

IN...WINTER WEATHER ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019...3
     AM TUESDAY TO NOON TUESDAY.

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

&&

$$

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