Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280312
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 PM CST TUE JAN 27 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 03Z...

* GUSTY SSELY WINDS TOMORROW.

* CHANCE FOR MVFR CIGS OR VIS LATE TONIGHT.

KREIN

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

THE DECK OF MVFR STRATOCU CONTINUES TO ERODE FROM EAST TO WEST PER
LATEST SATELLITE IMAGERY. RFD REMAINS THE ONLY TAF SITE STILL WITH
MVFR CIGS AND IS JUST WEST OF THE EDGE OF THE CLEARING SKIES. THE
EDGE OF THE CLEARING APPEARS TO HAVE SLOWED WITH THE SETTING
SUN...SO HAVE DELAYED IMPROVEMENT OF CIGS THERE UNTIL 04Z...BUT
THE CONFIDENCE IN THE EXACT TIMING IS LOW. AS HIGH PRESSURE
SETTLES OVER THE AREA TONIGHT...WINDS WILL DROP OFF TO
LGT/VRBL...AND WITH THE DECREASING CLOUD COVER...THERE SHOULD BE
ENOUGH RADIATIVE COOLING FOR TEMPERATURES TO DROP LOW ENOUGH OVER
RURAL AREAS TO ALLOW FOR SOME AREA OF BR DEVELOPMENT WITH VIS
DROPPING INTO THE 3-5SM RANGE. ORD/MDW/GYY WILL LIKELY REMAIN VFR
DUE TO URBAN HEAT ISLAND EFFECTS PREVENTING TEMPERATURES FROM
DROPPING OFF AS MUCH.

THE MAIN CONCERN FOR TOMORROW WILL BE WINDS. AS THE HIGH SETTLES
TO THE SOUTH AND LOW PRESSURE TRACKS EWD ACROSS THE CNTRL
PLAINS...A STRENGTHENING SOUTHERLY GRADIENT WILL SET UP...WITH
WINDS INCREASING BY LATE MORNING. THERE SHOULD BE ADEQUATE
SUNSHINE TO ALLOW FOR STRONGER WINDS ABOVE THE SFC TO MIX
DOWN...WITH GUSTS IN THE 20-25KT RANGE LIKELY THROUGH THE
AFTERNOON. THE LOW PRESSURE SYSTEM TRACKING ACROSS THE PLAINS
SHOULD BRING THE NEXT CHANCE FOR PCPN AND REDUCED CIGS/VIS...BUT
THIS WILL LIKELY NOT BE UNTIL AFTER MIDNIGHT TOMORROW NIGHT.

KREIN

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

* MEDIUM CONFIDENCE IN CIGS/VIS TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//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.

KREIN

&&

.MARINE...
318 PM CST

LIGHTER NORTHERLY WINDS IN PLACE THIS AFTERNOON AS HIGH PRESSURE
SPANS THE REGION...WILL FURTHER DIMINISH THIS EVENING AS THIS HIGH
MOVES OVERHEAD. THIS HIGH WILL THEN CONTINUE SOUTHEAST TOWARDS THE
OHIO VALLEY TONIGHT AS A TROUGH OF LOW PRESSURE MOVES EAST ACROSS
THE CENTRAL PLAINS. THIS WILL HELP THE WINDS TO TURN BACK MORE
SOUTHERLY AND THEN BEGIN TO SLOWLY INCREASE LATER TONIGHT INTO
WEDNESDAY. THIS INCREASING TREND WILL CONTINUE THROUGHOUT THE DAY
WEDNESDAY...WITH SOUTHERLY WINDS REALLY INCREASING DURING THE
AFTERNOON TIME FRAME. THIS WILL LIKELY CREATE WINDS HAZARDOUS FOR
SMALL CRAFT...AND SO HAVE ISSUED A SMALL CRAFT ADVISORY FOR
WEDNESDAY AFTERNOON THROUGH LATE WEDNESDAY NIGHT WHEN WINDS WILL
DIMINISH WITH THE APPROACHING LOW PRESSURE. THIS WILL LIKELY BE
BRIEF AS WINDS WILL QUICKLY INCREASE ONCE AGAIN ON THE BACKSIDE OF
THIS SYSTEM THURSDAY. ALSO...SOUTHERLY WINDS ACROSS THE SOUTHERN
HALF OF THE LAKE COULD HOVER AROUND 30 KT A FOR A BRIEF WINDOW
WEDNESDAY NIGHT. WILL NEED TO MONITOR TRENDS DURING THIS
PERIOD...BUT WILL MAKE MENTION OF OCCASIONAL GALE FORCE GUSTS
DURING THIS TIME. EXPECT STRONG WINDS TO BE IN PLACE ON
THURSDAY...REALLY INCREASING INTO THE AFTERNOON AND EVENING HOURS.
GALES ARE APPEARING LIKELY FOR THE ENTIRE LAKE DURING THIS
TIME...EVEN FOR THE NEARSHORE WATERS...BUT WITH SPEEDS DIMINISHING
ONCE AGAIN LATE THURSDAY NIGHT INTO FRIDAY.

RODRIGUEZ

&&

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

&&

$$

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