Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 290302
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
902 PM CST FRI NOV 28 2014

.EVENING UPDATE...
820 PM CST

FORECAST GENERALLY ON TRACK FOR THE REMAINDER OF THE NIGHT.
TEMPERATURE TRENDS WILL BE A LITTLE TRICKY AS PERSISTENT WARM
ADVECTION AND INCREASING SLY FLOW WILL KEEP TEMPS STEADY OR SLOWLY
RISE THROUGH THE NIGHT. DEWPOINTS SHOULD ALSO BE ON A SLOW UPWARD
TREND AS WELL. WILL CONTINUE TO CARRY SOME MENTION OF PATCHY FOG
FOR GENERALLY THE NORTHERN AND WESTERN PORTIONS OF THE
CWA...ESPECIALLY LOCATIONS THAT HAD A LITTLE SNOW COVER.  HOWEVER...
FEEL THAT ANY PATCHY FOG THAT MAY DEVELOP WILL NOT BE PARTICULARLY
DENSE...WITH VISIBILITY DROPPING INTO THE 3-5SM RANGE. ANY FOG
FORMATION WOULD ALSO BE DEPENDENT ON WHETHER THE HIGH CLOUD
CURRENTLY STREAMING OVER THE AREA CAN CLEAR OUT ENOUGH TO ALLOW AT
LEAST A LITTLE DIURNAL COOLING DURG THE EARLY MORNING HOURS.

KREIN

&&

.SHORT TERM...
300 PM CST

THROUGH SUNDAY...

A TEMPERATURE ROLLER COASTER RIDE OVER THE NEXT FEW DAYS IS THE MAIN
FOCUS OF THE FORECAST.

TONIGHT AND SATURDAY...

W/V IMAGERY SHOWS THAT HIGHLY AMPLIFIED PATTERN THAT
RESULTED IN ALL THE COLD AIR THE PAST FEW WEEKS IS RAPIDLY BEING
REPLACED BY ZONAL MID AND UPPER FLOW. A VERY WARM AND DRY AIR MASS
OVER THE CENTRAL PLAINS THIS MORNING WILL RAPIDLY BE ADVECTED INTO
THE AREA TONIGHT INTO SATURDAY BY DECENT SOUTHWEST FLOW AT H85. IN
ADDITION...A SFC WARM FRONTAL FEATURE IS ALSO BEGINNING THE
PROCESS OF LIFTING WARMER AND MORE MOIST AIR NORTHWARD THIS
AFTERNOON...WHICH RESULTED IN PATCHY LOW CLOUD DEVELOPMENT FOR A
TIME. STILL SOME CONCERN FOR LIGHT QPF EARLY THIS EVENING IN THE
FAR NORTH...WHICH IF ANY COULD REACH THE GROUND WOULD LIKELY BE IN
THE FORM OF LIGHT SNOW OR PELLETS DUE TO WET BULB PROCESSES. THINK
THE FOCUS WILL BE JUST NORTH OF THE CWA SO HAVE REMOVED SLIGHT
POPS BUT WILL NEED TO MONITOR THIS. THE MODELS APPEAR TO BE
STRUGGLING GREATLY WITH AMOUNT OF SNOW COVER ON THE GROUND OVER
THE CWA...ESPECIALLY THE NAM AND RAP. EXPECTING THAT SKIES WILL
TREND TO PARTLY CLOUDY TONIGHT...WHICH DESPITE STEADY SOUTHERLY
WINDS...COULD SET THE STAGE FOR PATCHY GROUND FOG OVER STILL SNOW
COVERED AREAS. TEMPERATURES ARE EXPECTED TO REMAIN STEADY OR
SLOWLY RISE OVERNIGHT.

THE SNOW COVER/CLOUD COVER ISSUE COMES TO A HEAD ON SATURDAY.
LOOKING IN THE WARM SECTOR OF THE DEVELOPING HIGH PLAINS LOW
TODAY...THERE IS LITTLE IN THE WAY OF CLOUD COVER. HOWEVER...MANY
MODELS INSIST ON BREAKING OUT LOW CLOUDS/LOW LEVEL SATURATION. WITH
A +12 TO +15C AIR MASS AT 850 MB MOVING INTO THE AREA...SUSPECT THAT
MUCH OF THE GUIDANCE IS BIASED FAR TOO COLD TOMORROW. IT SEEMS THAT
THE CANADIAN GLOBAL AND REGIONAL MODELS...WHICH TYPICALLY DO BETTER
IN COOL SEASON WARM-UPS...HAVE A MUCH BETTER HANDLE ON LIKELY LACK
OF LOW LEVEL CLOUD COVER...WHICH CAN BE SEEN ON FORECAST SOUNDINGS.
HAVE BUMPED UP TEMPERATURES IN THE LOW-MID 50S AREA WIDE...EXCEPT
FOR NEAR 50 ALONG IMMEDIATE WI BORDER WHERE 2-4 INCHES OF SNOW DEPTH
WERE REPORTED TODAY. HAVE CONSERVATIVELY LOWERED SKY COVER
PERCENTAGE AS WELL...AS OTHER THAN SOME MID/HIGH CLOUDS...IT APPEARS
A DECENT AMOUNT OF SUN COULD BE IN STORE.

SATURDAY NIGHT AND SUNDAY...

A VERY MILD SATURDAY NIGHT WILL ALLOW FOR A ANOTHER WARM SUNDAY
FOR PARTS OF THE CWA. HOWEVER...THERE WILL BE AN ARCTIC FRONT
SURGING SOUTHWARD AHEAD OF EXPANSIVE AND STRONG HIGH PRESSURE OVER
THE NORTHERN PLAINS. TIMING OF THIS FRONT IS KEY AND NOW THINK IT
WILL BE INTO THE NORTHERN CWA BY LATE AM/MID DAY...CAPPING HIGHS
NEAR 40/LOW 40S THERE. FAR SOUTHERN CWA COULD CONCEIVABLY APPROACH
60 DEGREES GIVEN MORE TIME TO WARM UP AHEAD OF THE FRONT. UPPER
FORCING IS NOT IMPRESSIVE WITH THE FRONT BUT LOW LEVEL MOISTURE
CONVERGENCE AND DECENT LOW/MID F-GEN DUE TO QUICKLY TIGHTENING
THERMAL GRADIENT COULD BE ENOUGH FOR ISOLATED/WIDELY SCT`D RAIN
SHOWERS MAINLY IN AFTERNOON IN SOUTHEAST 1/3 OF CWA.

RC

&&

.LONG TERM...
249 PM CST

SUNDAY NIGHT THROUGH FRIDAY...

LOW LEVEL ARCTIC AIR MASS WILL QUICKLY SPILL SOUTHWARD SUNDAY NIGHT
AS UPPER TROUGH BRIEFLY DIGS ACROSS NORTHERN TIER AND STRONG HIGH
PRESSURE SPREADS SOUTHEAST. AIR MASS LOOKS FAIRLY DRY OVER THE
LAKE...BUT LAKE EFFECT PARAMETERS ARE MARGINALLY FAVORABLE FOR SOME
LAKE EFFECT SNOW SHOWERS SUNDAY NIGHT INTO MONDAY MORNING FOR THE
SOUTHEAST TIP OF THE LAKE. TEMPERATURES WILL TUMBLE INTO THE TEENS
AND 20S BY MONDAY MORNING...WITH CONTINUED COLD ADVECTION RESULTING
IN A WELL BELOW NORMAL START TO METEOROLOGICAL WINTER. HIGHS WILL
LIKELY  BE IN 20S CWA WIDE/IF NOT COLDER IN FAR NORTH...FOLLOWED BY
A COLD NIGHT MONDAY NIGHT AS 1040 MB+ HIGH PRESSURE MOVES OVERHEAD.
PATTERN WILL QUICKLY TURN ZONAL AGAIN BUT COLD AIR REMAINING JUST TO
NORTH SHOULD KEEP TEMPERATURES ON THE COOLER SIDE THROUGH MID WEEK.
BIG TIMING DIFFERENCES IN THE LATE WEEK TIMEFRAME WITH ECMWF AND
GFS/GEFS...AS ECMWF KEEPS DRY/COOL HIGH LOCKED IN TIL THURSDAY
MORNING...WHILE GFS BREAKS OUT PRECIP ALONG BAROCLINIC ZONE
WEDNESDAY NIGHT INTO THURSDAY. HAVE MAINTAINED LOW GUIDANCE BLEND
POPS BUT CONFIDENCE IS FAIRLY LOW IN TEMPS AND SENSIBLE WX
WEDS-THURSDAY...THOUGH A MILD PERIOD DOES LOOK TO BE IN THE CARDS
LATE NEXT WORK WEEK INTO THE WEEKEND.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CHANCE FOR MVFR VISIBILITY LATER TONIGHT INTO EARLY SATURDAY
  MORNING.

* LOW CHANCE FOR MVFR CIGS ON SATURDAY AND SATURDAY EVENING.

* SOUTH-SOUTHEAST WINDS TONIGHT BECOMING SOUTH-SOUTHWEST AND
  GUSTY ON SATURDAY.


//DISCUSSION...UPDATED 00Z...

WARM AND MOIST AIR IS GRADUALLY RETURNING TO THE REGION AS LOW
PRESSURE ORGANIZES ACROSS THE PLAINS. AN INITIAL WARM FRONT IS
DRAPED FROM JUST SOUTH OF THE QUAD CITIES TO NORTHWEST INDIANA AND
IMMEDIATELY NORTH OF THIS IS AN AREA OF MVFR CIGS. DUE TO THE
LIKELIHOOD OF THIS WARM FRONT NOT RUSHING NORTHWARD THIS
EVENING...HAVE EXTENDED THE DURATION OF MVFR CIGS. WHILE THERE
COULD BE SOME GRADUAL LOWERING IN THESE CIGS THEY SHOULD REMAIN IN
THE MVFR CATEGORY. EXPECT THESE CIGS TO SLOWLY INCH THEIR WAY
NORTHWARD BY LATE THIS EVENING OR OVERNIGHT AS SOUTH-SOUTHEAST
SURFACE WINDS CONTINUE. INCREASING SURFACE DEW POINTS HAVE HELPED
ALREADY RESULT IN SOME LIGHT HAZE AND DO THINK MVFR FOG WILL
BECOME MORE WIDESPREAD NORTH OF INTERSTATE 80 WITH SOME IFR
POTENTIAL...THOUGH MAINLY ONLY AT OUTLYING TAF SITES.

MORE STRATUS IS EXPECTED TO DEVELOP ACROSS THE ARKLATEX REGION
LATER TONIGHT AND EXPAND NORTHEAST BEHIND THE PRIMARY WARM FRONT.
MODEL DEPICTED LOW-LEVEL MOISTURE VS ACARS OBSERVED MOISTURE OVER
THIS REGION INDICATE THE MODELS ARE ALREADY TOO MOIST WHICH LEADS
TO QUESTIONS ON HOW WIDESPREAD AND FAR NORTH STRATUS WILL REACH ON
SATURDAY. FOR RIGHT NOW HAVE LEANED TOWARD NORTHERN ILLINOIS
REMAINING OUT OF THE WIDESPREAD STRATUS ALTHOUGH SOME IS PROBABLE
DOWNSTATE AND INTO INDIANA. SOUTH-SOUTHWEST WINDS WILL BE GUSTY
ON SATURDAY ESPECIALLY IF THERE IS NO WIDESPREAD STRATUS.


//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM-HIGH IN VISIBILITY FORECAST TONIGHT.

* MEDIUM THAT ANY IFR/MVFR STRATUS WILL STAY SOUTH OF ORD AND MDW
  ON SATURDAY AND SATURDAY EVENING.

* HIGH IN SUSTAINED WIND SPEEDS AND MEDIUM IN GUSTS ON
  SATURDAY...AS THAT WILL DEPEND ON DEGREE OF CLOUD COVER.


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

SUNDAY...MVFR CIGS POSSIBLE. SOUTHWEST WINDS BECOMING NORTHWEST.
MONDAY...VFR. NORTHWEST WINDS BECOMING NORTH BY EVENING.
TUESDAY...VFR. SOUTH WINDS.
WEDNESDAY...VFR. WEST WINDS.
THURSDAY...CHANCE OF RAIN AND SNOW. EAST WINDS.

MTF

&&

.MARINE...
123 PM CST

SOUTHERLY WINDS WILL REMAIN ELEVATED IN THE 20 TO 30 KT RANGE
THROUGH SATURDAY NIGHT AS AN AREA OF LOW PRESSURE TRACKS
NORTHEASTWARD FROM THE DAKOTAS TO NEAR JAMES BAY. THIS LOW WILL
DRIVE A COLD FRONT SOUTHWARD ACROSS LAKE MICHIGAN DURING THE DAY ON
SUNDAY. MUCH COLDER AIR AND STRONG NORTHERLY WINDS WILL SET UP IN
THE WAKE OF THIS FRONT AS A STOUT 30.71+ INCH HIGH BUILDS OVER THE
PLAINS AND UPPER MIDWEST. THIS SHOULD RESULT IN 30 KT WINDS LATER
SUNDAY INTO MONDAY...THOUGH A PERIOD OF GALE FORCE WINDS SUNDAY
NIGHT AS THE HEART OF THE COLD AIRMASS SPILLS OVER THE LAKE.

THE SURFACE HIGH WILL SHIFT EASTWARD OVER LAKE MICHIGAN BY AROUND
MONDAY EVENING...LEADING TO A PERIOD OF ABATING WINDS. HOWEVER...AS
THIS HIGH SHIFTS EAST OF THE LAKE...IT APPEARS THAT WINDS WILL
INCREASE OUT OF THE SOUTH AGAIN BY TUESDAY AS IT APPEARS ANOTHER
DECENT STORM SYSTEM WILL TRACK NORTHEASTWARD INTO SOUTHERN CANADA.
THIS COULD RESULT IN ANOTHER PERIOD OF GALE OR NEAR GALE FORCE
SOUTHERLY WINDS...ESPECIALLY ACROSS NORTHERN LAKE MICHIGAN.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 PM SATURDAY.

&&

$$

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