Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 281715
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1215 PM CDT TUE OCT 28 2014

.DISCUSSION...
625 AM CDT

SHORT TERM...THROUGH TUESDAY NIGHT...FOR THE REMAINDER OF THE NIGHT
AND INTO TUESDAY MORNING...THE MAIN FORECAST ISSUE WILL BE ASSOCIATED
WITH PCPN AHEAD OF A COLD FRONT MOVING THROUGH THE REGION.  FOR MUCH
OF THE EVENING...THE BAND OF PCPN HAS BEEN OUT AHEAD OF THE COLD
FRONT...MORE ALIGNED WITH THE WARM ADVECTION...ISENTROPIC LIFT
COINCIDENT WITH THE LOW LEVEL JET.  SOME SHOWERS AND THUNDERSTORMS
HAD DEVELOPED UNDER THE MAIN UPPER LOW...BUT THAT ACTIVITY HAS BEEN
WELL NORTH OF THE AREA.  THERE HAS BEEN LITTLE IN THE WAY OF THUNDER
WITHIN THE PCPN SHIED...WITH THE GREATER CONCENTRATION OF THUNDER
WELL TO THE SOUTH INVOF A MID LEVEL JET STREAK AS HAVE BEEN EVIDENT
IN SATELLITE IMAGERY AS A WELL DEVELOPED BAROCLINIC LEAF.  AS THE
MID LEVEL JET STREAM MOVES NORTHEAST THROUGH THE REMAINDER OF THE
OVERNIGHT HOURS...THERE WILL STILL BE A CHANCE FOR SOME
THUNDER...BUT THIS WILL LIKELY BE LIMITED TO PORTIONS OF THE
CWA SOUTH OF A LINE FROM GARY TO PONTIAC.  LATEST SFC ANALYSIS
INDICATES THAT THE COLD FRONT IS QUICKLY MOVING THROUGH NWRN IL AND
IS ACTUALLY CATCHING UP WITH THE PCPN BAND OVER LIVINGSTON
COUNTY...WHICH IS LIKELY HELPING THE TS DEVELOPMENT THERE.  THIS IS
ALSO INDICATIVE THAT THE LONGWAVE PATTERN IS BECOMING MORE
PROGRESSIVE...AND THAT THE PCPN BAND THAT HAS BEEN LINGERING FROM
THE SRN CHICAGO METRO AREA TO THE ST LOUIS AREA WILL ALSO BEGIN TO
PROGRESS TO THE EAST.  BASED ON THE LATEST TRENDS...ANTICIPATE THAT
THE PCPN SHOULD PUSH OUT OF THE SERN PORTION OF THE CWA BY LATE
TUESDAY MORNING.

WITH THE FROPA...WINDS WILL QUICKLY PICK UP AS STRONG COLD ADVECTION
AND PRESSURE RISES SET UP ACROSS THE REGION WITH THE MAIN SFC LOW
LIFTING INTO THE UPPER GREAT LAKES REGION.  LATEST OBS ALREADY SHOW
WINDS OVER NWRN AND WCNTRL IL SHIFTING TO WLWY AND GUSTING TO ARND
25KT.  THIS IS THE FIRST INDICATIONS OF HOW THE REMAINDER OF TUESDAY
WILL SHAPE UP.  AS THE FRONT PASSES EWD...THE STRONGER GUSTY
WLY-WNWLY WINDS WILL OVERSPREAD THE REGION.  ALSO...A MID LEVEL DRY
SLOT WILL ALSO MOVE OVER THE REGION...ALLOWING FOR A DECREASE IN
CLOUD COVER.  THIS WILL THEN ALLOW FOR DEEP LAYER MIXING...AND WIND
GUSTS SHOULD INCREASE FURTHER TO ARND 30KT OR SO FROM LATE MORNING
THROUGH THE REMAINDER OF THE DAYLIGHT HOURS.  THERE SHOULD BE SOME
WRAP AROUND MOISTURE ON THE SWRN PERIPHERY OF THE PARENT UPPER
LOW...WHICH COULD BRING INCRG STRATOCU AND AND SOME SHRA THROUGH
MN/WI...BUT AT THIS POINT...FEEL THAT THE BETTER POTENTIAL FOR ANY
SCT INSTABILITY SHRA WILL REMAIN NORTH OF THE CWA...AND THAT ALL THE
LOCAL AREA WILL SEE WILL BE SCT STRATOCU DEVELOPMENT THROUGH THE
AFTERNOON.

FOR TEMPERATURES...WITH THE STRONG COLD ADVECTION SETTING UP BEHIND
THE FROPA...THERE SHOULD BE LITTLE DIURNAL VARIATION TO TEMPERATURES
THROUGH THE DAY TODAY. THERE MAY BE SOME OPPORTUNITY FOR A LITTLE
WARMING AS SKIES CLEAR OUT UNDER THE THE DRY SLOTTING...BUT THIS
WILL LIKELY AMOUNT TO ONLY A COUPLE DEGREES OF WARMING THIS
AFTERNOON.  OVERNIGHT TONIGHT...TEMPERATURES SHOULD DROP OFF
SIGNIFICANTLY AS MUCH COOLER AIR IS DRAWN INTO THE REGION.  LOOKING
UPSTREAM...TEMPERATURES OVER NRN ND/MN HAVE ALREADY DROPPED INTO THE
MIDDLE 30S BEHIND A SECONDARY COLD FRONT.  WHILE THE AIRMASS SHOULD
MODIFY A LITTLE BY THE TIME THIS SECONDARY COLD FRONT PUSHED ACROSS
THE AREA LATE TONIGHT...EXPECT THAT TEMPERATURES SHOULD DROP INTO
THE UPPER 30S TO LOWER 40S.

KREIN

WEDNESDAY THROUGH FRIDAY...
LARGE 500MB TROUGH POISED TO INFLUENCE MOST OF THE GREAT LAKES
REGION WED...WITH SFC RIDGING SLIDING SOUTHEAST OF THE FORECAST
AREA. THIS SHUD KEEP A LIGHT WEST FLOW AT THE SFC WED...HOWEVER WITH
THE AFOREMENTIONED TROUGHING ACROSS THE REGION A LOBE OF VORTICITY
IS PROGGED TO QUICKLY SLIDE SOUTH FROM CENTRAL CANADA TOWARDS THE
WESTERN GREAT LAKES MIDDAY THUR. SOME SPREAD AMONGST THE SOLUTIONS
REMAINS ON WHETHER THIS WOULD PRODUCE PRECIP THUR OR JUST REMAIN
CLOUDS...BUT THERE IS SOME WEAK WARM AIR TRYING TO BE ADVECTED ALONG
THE NOSE OF THE VORT. WILL NUDGE POPS TO 14 AND MENTION SPRINKLES IN
THE WESTERN CWFA. GUIDANCE THEN PAINTS A STRONGER LOBE OF VORTICITY
SLIDING ACROSS THE UPPER MIDWEST THUR EVE INTO LOWER MICHIGAN FRI
MORNING. MOTHER NATURE WILL BE PROVIDING A FEW TRICKS OF HER OWN FRI
WITH THE ARRIVAL OF A STRONG CANADIAN HIGH PRESSURE...THAT WILL
LIKELY TREAT US TO HIGHS STRUGGLING TO REACH THE MID 40S FRI. 850MB
TEMPS CRASH FRI WITH A SLUG OF -6 TO -10 DEG C ADVECTING SOUTHEAST
ACROSS THE REGION. FORTUNATELY WITH HIGH PRESSURE BUILDING
IN...THERE WILL BE ENOUGH DRY AIR TO QUICKLY ERODE THE CLOUDS AND
PROVIDE ABUNDANT SUNSHINE. IF THIS WERE NOT THE CASE...TEMPS MAY
STRUGGLE TO REACH 40 DEG FRI AFTN. STRONG NORTHWEST/NORTH WINDS WILL
LIKELY PRODUCE BREEZY CONDS...AND WIND CHILLS FRI AFTN IN THE UPR
20S/LOW 30S.

THE POTENTIAL FOR LAKE EFFECT CLOUDS/LGT PRECIP DOES EXIST FRI
MIDDAY. THE QUESTION WILL BE RESONANCE TIME OVER THE LAKE...WHICH
COULD RESULT IN MORE CELLULAR LIKE LGT PRECIP DUE TO THE BREEZY
CONDS. HIGH PRESSURE WILL BE NEARLY OVERHEAD FRI NGT...WITH WINDS
SLOWLY DIMINISHING. CURRENTLY EXPECT OVERNIGHT LOWS FRI NGT TO DIP
INTO THE MID/UPR 20S...HOWEVER IF WINDS DECOUPLE EARLIER...TEMPS MAY
BE A FEW DEGREES COOLER IN THE LOW 20S WITH DEW POINTS DROPPING INTO
THE UPPER TEENS.

CONFIDENCE...HIGH.

SATURDAY THROUGH EARLY NEXT WEEK...
ENSEMBLES HAVE CONTINUED TO PROG THE HIGH AMPLITUDE RIDGE OVER
HUDSON BAY SAT/SUN AND THE DEPARTING TROUGH TO BOTH MARGINALLY
WEAKEN LATE IN THE WEEKEND. MEANWHILE GUIDANCE HAS BEEN HINTING AT A
SECONDARY TROUGH DEVELOPING ACROSS THE SOUTHWEST CONUS...WITH
MINIMAL SPREAD AMONGST ENSEMBLE MEMBERS. THERE DOES REMAIN
CONSIDERABLE SPREAD AMONGST GUIDANCE DOWNSTREAM OF THIS FEATURE IN
THE WAKE OF THE NORTHEAST TROUGH. WHILE THE WEEKEND WILL LIKELY
KICK-OFF UNSEASONABLY COOL WITH HIGHS SAT IN THE
40S...SOUTH/SOUTHWEST FLOW DEVELOPING SUN/MON SHUD AID IN A SLOW
MODERATION BACK TOWARDS SEASONAL CONDS. LOW CHC FOR PRECIP RETURNING
SUN/MON.

BEECHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* WEST WINDS GUSTING TO ARND 27KT LATE MORNING THRU SUNSET.

KJB

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

WEST WINDS WILL CONTINUE TO BE GUSTY UP AROUND 25 KT THROUGH THE
AFTERNOON AS A POTENT AREA OF LOW PRESSURE CONTINUES SHIFTING OVER
EASTERN ONTARIO. HOWEVER...WIND SPEEDS SHOULD QUICKLY ABATE WITH
SUNSET. EXPECT A WEST-NORTHWESTERLY WIND TO CONTINUE THROUGH THE
REMAINDER OF THE FORECAST PERIOD. OVERALL VFR CONDITIONS ARE ALSO
EXPECTED DURING THE PERIOD. HOWEVER...SOME CLOUD COVER MAY TRY TO
MOVE IN ACROSS KRFD AND KORD LATER THIS AFTERNOON. IT APPEARS THAT
IF THIS CLOUD COVER RESULTS IN A BKN CIG LATER TODAY IT WILL LIKELY
REMAIN JUST ABOVE 3,000 FT AGL.

KJB


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KJB

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

WEDNESDAY NIGHT...VFR. WX NIL. LGT/VRBL WINDS.

THURSDAY...VFR. WX NIL. SWLY WINDS BECMG NWLY.

FRIDAY...VFR. WX NIL. NLY WINDS.

SATURDAY...VFR. WX NIL. SELY WINDS.

SUNDAY...SLIGHT CHANCE OF SHRA. SLY WINDS.

MONDAY...CHANCE OF SHRA. SWLY WINDS.

KREIN

&&

.MARINE...
214 AM CDT

LOW PRESSURE HAS BEEN SLUGGISH TO LIFT NORTHEAST...AND EARLY THIS
MORNING WAS JUST PUSHING EAST ACROSS CENTRAL LAKE MICHIGAN. THIS
LOW WILL THEN LIFT NORTHEAST AND DEEPEN. A TRAILING FRONTAL
BOUNDARY WILL PUSH EAST ACROSS THE LAKE BY DAYBREAK OR SHORTLY
AFTER DAYBREAK...WITH WINDS TURNING WEST AND INCREASING. SURFACE
OBSERVATIONS WEST OF THE FRONT HAVE BEEN GUSTING FROM THE WEST TO
25-30KT. AS THE LOW CONTINUES TO LIFT NORTHEAST...BY MIDDAY THE
GRADIENT TIGHTENS FURTHER ACROSS THE NORTHERN SECTIONS OF THE LAKE
AND COULD PRODUCE A PERIOD OF GALES TO 35KT EARLY THIS AFTN. BY
LATE THIS EVENING THE GRADIENT WILL CONTINUE TO DIMINISH...WITH
HIGH PRESSURE BUILDING INTO THE MID-MISSOURI VALLEY. THIS WILL
KEEP THE LAKE IN A WEST/NORTHWEST FLOW...WITH WINDS GENERALLY
REMAINING 15-25 KT OVERNIGHT INTO DAYBREAK WED.

WINDS REMAIN GENERALLY WESTERLY AND CONDITIONS GRADUALLY RELAX
THROUGH THE REMAINDER OF THE WEEK UNDER THE INFLUENCE OF AN
APPROACHING RIDGE UNTIL ANOTHER LOW CROSSES THE LAKE THURSDAY
NIGHT. COLD NORTHERLY FLOW THEN DEVELOPS FOR FRIDAY AND MOST OF
SATURDAY. THIS WILL LIKELY PRODUCE LARGER WAVES FOR A LONGER
PERIOD OF TIME ACROSS THE CENTRAL/SOUTHERN PORTIONS OF THE LAKE
GIVEN THE COLD AIR SLIDING SOUTH ACROSS THE WARMER LAKE SURFACE.

BEACHLER

&&

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

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.