Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 280802
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
202 AM CST WED JAN 28 2015

.UPDATE...
905 PM CST

LOW CLOUD COVER CONTINUES TO SLOWLY MOVE WESTWARD AND HAS CLEARED
ALL BUT THE WESTERN FRINGES OF THE FORECAST AREA THIS EVENING.
SATELLITE SHOWS SOME HIGHER CLOUD STREAKS APPROACHING FROM THE
NORTHWEST AS UPPER RIDGING SHIFTS EASTWARD BUT COVERAGE LOOKS
LOOKS TO BE SPORADIC THROUGH THE NIGHT AND MAY BE AT A MINIMUM
DURING THE EARLY OVERNIGHT. TEMPERATURES HAVE BEGUN TO DROP OFF
WHERE THANKS TO THE MAINLY CLEAR SKIES WITH SEVERAL SITES IN
NORTH-CENTRAL ILLINOIS NOW IN THE TEENS. GIVEN THAT HIGHER CLOUD
COVER LOOKS INTERMITTENT AND WINDS WILL DROP OFF WITH HIGH
PRESSURE MOVING OVERHEAD HAVE GONE AHEAD AND LOWERED MINS
OVERNIGHT FOR MOST AREAS...THOUGH WESTERN FRINGES MAY SEE LOWER
LEVEL CLOUD COVER LINGER THROUGH THE NIGHT. WILL GO WITH LOWER
TEENS FOR MUCH OF THE WESTERN/CENTRAL CWA AND SOME OF THE
TRADITIONALLY COLDER SPOTS FROM LEE/OGLE COUNTIES TO DEKALB AND
KANE COUNTIES COULD SEE VALUES A LITTLE BIT LOWER IF HIGH CLOUD
COVER REMAINS VERY MINIMAL.

WITH THE LOWER TEMPS AND SPORADIC HIGHER CLOUD COVER...FREEZING
FOG WILL BE A CONCERN. THE COLDEST AREAS WILL LIKELY SEE A QUICK
DROP OFF IN THE NEXT FEW HOURS WHICH MAY LEAD TO MORE FROST
DEPOSITION RATHER THAN FOG FORMATION. WITH LIMITED CONFIDENCE IN
THIS HAPPENING AND REASONABLE SUPPORT FOR SOME FOG
DEVELOPMENT...WILL GO AHEAD AND ADD PATCHY FOG TO MUCH OF THE
CENTRAL AND WESTERN CWA OR FROM THE FAR WESTERN CHICAGO METRO WEST
AND SOUTHWEST FOR NOW. THIS MAY CAUSE SOME SLICK SPOTS ON ROADS
OVERNIGHT.

MDB

&&

.SHORT TERM...
304 PM CST

THROUGH THURSDAY...

PRIMARY CONCERN IN THE NEAR TERM REVOLVES AROUND THE STRATUS DECK
CURRENTLY OVER THE SOUTHWESTERN 2/3RDS OF THE CWA. WOULD ANTICIPATE
A CONTINUED VERY SLOW CLEARING FROM THE EAST FOR A COUPLE MORE HOURS
BEFORE LOW LEVEL FLOW DIMINISHES THIS EVENING BEFORE BACKING TO
SOUTHERLY OVERNIGHT...WHICH MAY WELL SEND STRATUS SLOSHING BACK
NORTH INTO AREAS THAT HAD PREVIOUSLY CLEARED OUT. TRIED TO REFLECT A
TREND LIKE THIS IN THE HOURLY SKY GRIDS AND RESULTANT TEMPERATURE
GRIDS...BUT GIVEN THE POOR MODEL HANDLING OF THIS CLOUDINESS IT
PRETTY MUCH GUARANTEED THAT OUR CURRENT SKY GRIDS WILL BE WRONG
SOMEWHERE AND NEED UPDATING WITH ACCOMPANYING CHANGES NEEDED IN
TEMPS TONIGHT. WHERE SKIES BECOME/STAY CLEAR TONIGHT COULD SEE
FREEZING GROUND FOG DEVELOP GIVEN THE LIGHT WINDS...BUT WILL LET
EVENING SHIFT WATCH TRENDS AND ADD FREEZING FOG AS NEEDED.

FOR WEDNESDAY HAVE OPTED TO BE OPTIMISTIC IN PUSHING STRATUS NORTH
AND BREAKING IT UP IN THE MORNING BUT THIS VERY WELL MAY END UP
BEING TOO OPTIMISTIC. ASSUMING THERE IS SOME SUNSHINE TOMORROW PRIOR
TO THE ARRIVAL OF EXTENSIVE MID AND HIGH LEVEL CLOUDINESS THEN HIGHS
COULD PUSH WELL INTO THE 30S...PARTICULARLY IN THE LESS SNOW COVERED
AND MORE URBANIZED AREAS. DEVELOPING LOW PRESSURE TO OUR WEST
SHOULD RESULT IN TIGHTENING PRESSURE GRADIENT AND STRENGTHENING
SOUTHERLY WINDS WEDNESDAY.

IZZI

&&

.LONG TERM...
304 PM CST

THURSDAY NIGHT THROUGH TUESDAY...

BRISK SOUTH WINDS...WARM AIR ADVECTION...AND CLOUD COVER IN ADVANCE
OF THE SYSTEM WEDNESDAY NIGHT SHOULD RESULT IN NEARLY STEADY TEMPS
IN THE EVENING AND PROBABLY RISING A BIT OVERNIGHT. COULD SEE A BIT
OF LIGHT RAIN OR DRIZZLE IN THE WARM SECTOR WEDNESDAY NIGHT FOLLOWED
BY SOME POTENTIAL FOR A BIT OF WRAP AROUND RAIN OR SNOW SHOWERS
THURSDAY ON THE BACK SIDE OF THE SYSTEM. STILL LOOKS LIKE PRETTY
LIMITED MOISTURE WITH THE SYSTEM AND HIGHEST QPF FOCUSED TO OUR
NORTH WITH LIGHT AMOUNTS IN OUR CWA AND ONLY MINIMAL THREAT OF ANY
ACCUMULATED FROZEN/FREEZING PRECIP GIVEN THE FORECAST TRACK AND
TEMPS.

SHOT OF SEASONABLY COLD AIR WILL KNOCK TEMPS TO JUST A HAIR BELOW
AVERAGE FRIDAY. VIGOROUS ALBERTA CLIPPER IS FORECAST TO RESULT IN
AN AMPLIFYING LONG WAVE TROUGH OVER THE CENTRAL CONUS THIS WEEKEND.
STILL SOME LARGE SPREAD BETWEEN MODELS WITH RESPECT TO THE DETAILS
THIS WEEKEND...BUT THERE HAS BEEN SOME AGREEMENT THE PAST COUPLE
DAYS ON THE GENERAL IDEA OF A LARGE SWATH OF ACCUMULATING SNOW
POTENTIALLY AFFECTING THE REGION SAT NIGHT INTO SUNDAY. ARCTIC AIR
IS FORECAST TO SURGE SOUTH INTO THE AREA IN THE WAKE OF THIS SYSTEM
EARLY NEXT WEEK...BUT THE DURATION AND MAGNITUDE OF THIS ARCTIC
INTRUSION ARE DEPENDENT ON WHICH MODEL YOU LOOK AT MEANING FAIRLY
LOW FORECAST CONFIDENCE AT THIS POINT.

IZZI

&&

.AVIATION...

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

* CHANCE FOR 1500-2500 FT CIGS BEFORE 14Z.

* GUSTY SOUTH-SOUTHEAST SURFACE WINDS DEVELOPING BY 18Z.

* CHANCE FOR SCATTERED LIGHT RAIN SHOWERS BEGINNING LATE WEDNESDAY
  EVENING.

* SOUTH-SOUTHWEST WINDS OF AT LEAST 50 KT AROUND 2000 FT WEDNESDAY
  EVENING THAT MAY CREATE LOW-LEVEL WIND SHEAR.

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

AS HIGH PRESSURE MOVES EAST OVERNIGHT...SOUTHERLY WINDS WILL
START TO BRING CLOUDS ACROSS NORTHWEST AND WEST CENTRAL ILLINOIS
BACK NORTH TO NORTHEASTWARD. WHILE THE CLOUDS ARE THIN...THEY ARE
UNDER A STRONG INVERSION OF 8C/1000 FT...SO NOT ENVISIONING MUCH
MORE EROSION OVERNIGHT. RFD SHOULD GO BACK TO BROKEN OR EVEN
OVERCAST AS THESE CLOUDS EXPAND BACK NORTHWARD AND IT IS POSSIBLE
ORD AND DPA DO AS WELL.

WITH THE APPROACH OF LOW PRESSURE...SOUTH-SOUTHEAST WINDS WILL
INCREASE WEDNESDAY WITH GUSTS LIKELY IN THE AFTERNOON AND
PERSISTING INTO THE EVENING AS STRONG PRESSURE FALLS SPREAD OVER.
GIVEN THE CURRENT AND FORECAST PLACEMENT OF THE LOW PRESSURE...THE
WIND DIRECTION SHOULD BE EAST OF SOUTH MUCH OF WEDNESDAY AND EARLY
WEDNESDAY EVENING...BEFORE GRADUALLY VEERING DURING LATER
WEDNESDAY NIGHT. A COLD FRONT WILL PASS IN THE PRE-DAWN HOURS.
AHEAD...ALONG...AND BEHIND THIS FRONT WILL BE POTENTIAL FOR
SCATTERED RAIN SHOWERS...WITH THAT CHANGING TO A RAIN AND SNOW
SHOWER CHANCE DURING THE DAY THURSDAY.

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

* MEDIUM THAT IF MVFR CIGS DO RETURN PRIOR TO 14Z THEY WOULD BE
  TEMPORARY.

* HIGH IN WIND SPEED AND IN WIND DIRECTION BEING SLIGHTLY EAST OF
  SOUTH THROUGH THE DAY WEDNESDAY. MEDIUM IN WIND DIRECTION
  WEDNESDAY EVENING.

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

THURSDAY...CHANCE OF RAIN/SNOW. MVFR LIKELY/IFR POSSIBLE.

FRIDAY...VFR. WX NIL.

SATURDAY...CHANCE OF SNOW IN THE AFTERNOON AND OVERNIGHT. VFR
EARLY THEN MVFR LIKELY/IFR POSSIBLE.

SUNDAY...CHANCE OF SNOW. IFR POSSIBLE.

MONDAY...VFR. WX NIL.

MTF/KREIN

&&

.MARINE...
158 AM CST

AN ACTIVE PERIOD WILL UNFOLD OVER LAKE MICHIGAN THROUGH THIS
FORECAST THANKS TO THE PROGRESSIVE NATURE IN THE WEATHER PATTERN.
HIGH PRESSURE EARLY THIS MORNING WILL EXIT THE PICTURE AND A QUICKLY
APPROACHING LOW PRESSURE FROM THE WEST WILL BRING INCREASING
SOUTHERLY WINDS LATER TODAY INTO THIS EVENING. DURING THE EVENING
THERE IS A PERIOD WHERE OCCASIONAL GALES SHOULD OCCUR ACROSS THE
SOUTHERN HALF AS SOME INSTABILITY WILL BE PRESENT WITH GALE FORCE
WINDS ONLY 1000-1500 FT OFF THE WATER SURFACE. THE LOW SHOULD BE
ELONGATED RIGHT DOWN THE AXIS OF THE LAKE AROUND 6 AM THURSDAY
BEFORE IT QUICKLY MOVES EAST. THIS WILL RESULT IN STOUT NORTHWEST
WINDS AND COLD ADVECTION ACROSS THE LAKE WITH WHAT LOOKS LIKE
DEFINITE GALES FOR AT LEAST THE OPEN WATER...INCLUDING 40 KTS
WITH 45 KTS EVEN POSSIBLE ESPECIALLY IN THE NORTH.

HAVE OPTED TO GO WITH A GALE WATCH FOR BEHIND THE LOW PRESSURE AS
THAT TIME PERIOD WILL BE THE HIGHEST WINDS WITH THE SYSTEM. WILL
JUST MENTION OCCASIONAL GALES ON THE FRONT SIDE DURING THIS
EVENING ACROSS MAINLY THE SOUTH HALF. SMALL CRAFT ADVISORY
CONDITIONS WILL OBVIOUSLY EXIST A GOOD AMOUNT OF THIS TIME ON THE
ILLINOIS AND INDIANA NEAR SHORES. WITH A SHORT 4-6 HOUR RESPITE
CENTERED ON DAYBREAK THURSDAY AS THE LOW PASSES...HAVE OPTED TO NOT
EXTEND THE CURRENT SMALL CRAFT ADVISORY...BUT ONE WILL DEFINITELY
BE NEEDED FOR THURSDAY AFTERNOON AND NIGHT...AND FOR THE INDIANA
SHORE INTO FRIDAY.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...NOON WEDNESDAY TO 4 AM THURSDAY.

     GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...NOON THURSDAY TO 3 AM
     FRIDAY.

&&

$$

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