Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 261955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT TUE AUG 26 2014

.DISCUSSION...
255 PM CDT

AS HAS BEEN THE NORM IN THE PAST WEEK TO TEN DAYS...THE PRIMARY
FORECAST CHALLENGES ARE TRYING TO DETECT WHEN BETTER THUNDERSTORM
CHANCES MAY BE AND WHAT INFLUENCE THOSE HAVE...IF ANY...ON
TEMPERATURES.

.TONIGHT...

THE INITIAL SYNOPTIC COLD FRONT HAS APPEARED TO CLEAR THE
FORECAST AREA. THIS SURGE WAS CONVECTIVELY ENHANCED AND LINGERING
HIGH DEW POINT AIR...E.G. UPPER 60S TO LOWER 70S...REMAINS ACROSS
THE SOUTH. THERE ALSO ARE ONE OR TWO WESTWARD-PROPAGATING OUTFLOW
BOUNDARIES THAT ARE LIKELY TO LAST INTO LATE THIS AFTERNOON.
CUMULUS HAS FORMED NEAR PONTIAC AND GIBSON CITY...AND BACK TOWARD
PRINCETON TO MENDOTA...WITH THESE FEATURES. WOULD NOT BE TOTALLY
SURPRISED TO SEE ISOLATED STORMS POP ON THESE AS MIXED LAYER
INHIBITION APPEARS SHALLOW WITH RECOVERING TEMPERATURES INTO THE
MID 80S AND EVEN 88 AT PONTIAC. A COUPLE SUBTLE SHORT WAVES ARE
NOTED ON WATER VAPOR...WITH ONE A LITTLE BETTER DEFINED ON
VISIBLE SATELLITE NEARING THE MISSISSIPPI RIVER FROM IA ASSOCIATED
WITH A 35 KT 500MB SPEED MAXIMUM. THIS LOOKS TO PASS OVER NORTH
CENTRAL IL EARLY THIS EVE AND COULD SEE SOME SHOWER/STORM ACTIVITY
WITH THAT...ALTHOUGH CONFIDENCE IS LOW FOR SHORT TERM STORM
CHANCES...SO HAVE KEPT POPS FAIRLY LOW. CONFLUENT 700-850MB FLOW
CONTINUES OVERNIGHT WITH ANOTHER LITTLE RIPPLE IN THE FLOW
FORECAST TO MOVE OVER THE AREA. SO CONTINUE CHANCE FOR A STORM
THROUGH THE ENTIRE NIGHT...BUT NOT EXPECTING ANYTHING WIDESPREAD.

INCOMING CLOUDS FROM THE DISTURBED MID-LEVEL FLOW SHOULD KEEP THE FOG
THREAT MINIMAL...AND TEMP/DEW POINT SPREADS LOOK TO BE MODESTLY
HIGH GOING INTO TONIGHT IN MOST AREAS...OUTSIDE OF THE FAR SOUTH.

MTF

.WEDNESDAY THROUGH TUESDAY...

THE LONGWAVE PATTERN OVER THE CENTRAL CONUS HAS BECOME MORE ZONAL
WITH TROPICAL SYSTEM OVER SERN ATLANTIC...NERN PACIFIC WHILE A BROAD
HIGH SITS OVER THE SRN CONUS AND A CLOSED UPPER LOW SWINGS THROUGH
THE GREAT BASIN.  THE SENSIBLE WEATHER OVER THE CWA WILL CONTINUE TO
BE UNSETTLED AS A STRONG SHORTWAVE QUICKLY MOVES ACROSS THE UPPER
MISSISSIPPI VALLEY AND GREAT LAKES WEDNESDAY.  UPPER RIDGING SHOULD
BUILD ACROSS THE MIDWEST ON THURSDAY AS MORE SHORT WAVE ENERGY
OVERTOPS THE RIDGE AND TRACKS ACROSS THE UPPER MIDWEST AND THE LOWER
GREAT LAKES REGIONS.  BY THURSDAY NIGHT AND FRIDAY...THE UPPER RIDGE
SHOULD BUILD TO THE EAST OF THE REGION AS THE UPPER LOW OVER THE
GREAT BASIN FINALLY OPENS UP AND LIFTS EAST ACROSS THE CENTRAL
PLAINS AS AN OPEN WAVE FRIDAY AND FRIDAY NIGHT.  THIS WAVE WILL
CROSS THE UPPER MIDWEST INTO THE WESTERN GREAT LAKES BY SUNDAY.  THE
LONGER RANGE GUIDANCE SUGGESTS THAT THIS WAVE WILL PHASE WITH
ANOTHER NORTHERN STREAM SHORTWAVE OVER THE UPPER GREAT LAKES BY
SUNDAY.  THE PROGRESSIVE AND RELATIVELY LOW AMPLITUDE UPPER LEVEL
PATTERN OVER THE CONUS WILL LEAD TO A CONTINUES ACTIVE WEATHER
PATTERN FOR THE LOCAL AREA...WITH PERIODIC CHANCES FOR SHOWERS AND
THUNDERSTORMS THROUGH MUCH OF THE PERIOD.  THE SOUTHERN PORTIONS OF
THE CWA WILL BE MORE FAVORABLE FOR ADDITIONAL PCPN WEDNESDAY AS SFC
HIGH PRESSURE SPREADS ACROSS THE GREAT LAKES REGION AND THE OLD
FRONTAL BOUNDARY LAYS OUT ALONG THE OHIO VALLEY INTO SRN ILLINOIS.
AS A SFC LOW DEEPENS OVER THE CENTRAL PLAINS ON THURSDAY...IT WILL
DRAG THE FRONT NORTH AGAIN AS A WARM FRONT...BRINGING GREATER
CHANCES FOR MORE WIDESPREAD PCPN TO THE AREA FOR THURSDAY AND
THURSDAY NIGHT.  WHILE THE FRONT REMAINS TO THE SOUTH AND HIGH
PRESSURE SPREADS ACROSS THE GREAT LAKES REGION...TEMPERATURES WILL
DIP BACK INTO THE MIDDLE 70S ACROSS THE NORTHERN PORTIONS OF THE CWA
WHILE THE SOUTHERN LOCATIONS MAY REACH THE LOWER 80S.  BY
FRIDAY...WHEN THE WARM FRONT LIFTS NORTH OF THE CWA...HOT AND HUMID
CONDITIONS WILL RETURN...WITH HIGHS IN THE MIDDLE 80S...DEWPOINTS IN
THE LOWER 70S AND MAX HEAT INDEX VALUES INTO THE LOWER 90S.  THE
DEVELOPING SFC LOW IS EXPECTED TO SLOWLY LIFT ACROSS THE UPPER
MISSISSIPPI VALLEY ON SATURDAY...KEEPING THE LOCAL AREA UNDER WARM
SECTOR AIR AHEAD OF AN ASSOCIATED COLD FRONT.  WHILE THE AREA
REMAINS IN THE WARM SECTOR THROUGH THE WEEKEND...THERE WILL CONTINUE
TO BE CHANCES FOR SCATTERED SHOWERS AND THUNDERSTORMS...BUT WITHOUT
A STRONG FOCUSING MECHANISM...WILL KEEP POPS IN THE CHANCE RANGE.
BY EARLY NEXT WEEK...THE LONG RANGE GUIDANCE IS SUGGESTING THAT THE
COLD FRONT SHOULD FINALLY PUSH THROUGH THE AREA...BUT THERE SHOULD
BE LITTLE IN THE WAY OF AIRMASS CHANGE WITH THE FROPA AS ANOTHER
DEEPENING TROUGH OVER THE NORTHERN PLAINS SHOULD QUICKLY BRING A
RETURN TO WARM...MOIST SOUTHERLY FLOW FOR EARLY NEXT WEEK...WHICH
WILL...IN TURN...KEEP CONTINUES CHANCES FOR PCPN ACROSS THE REGION.

KREIN

&&

.AVIATION...

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

* E TO ESE WINDS ARND 10 KT DIMINISH TO LESS THAN 10 KT THIS AFTN.

* EAST WINDS AROUND 10 KT EXPECTED AGAIN TOMORROW.

JEE

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

THE FRONT AND ASSOCIATED STORMS HAVE PUSHED EAST OF THE TERMINALS.
ADDITIONAL CONVECTION IS POSSIBLE WELL SOUTH OF THE
TERMINALS...SOUTH OF A GARY TO PONTIAC LINE. NO ADDITIONAL
CONVECTION IS EXPECTED AT THE TERMINALS. WINDS ARE E TO ESE BEHIND
THE CONVECTION WITH SPEEDS AT 10-15 KT. BASED ON UPSTREAM
OBS...EXPECTING WINDS TO RETURN TO NE ARND 7 KT BY MID AFTN. A
LAKE BREEZE MAY FORM BUT THINKING IT WILL ONLY SHIFT ALREADY NE
WINDS TO EAST LESS THAN 10 KT. GYY AND MDW WILL BE THE MOST
SUSCEPTIBLE TO THE LAKE BREEZE.

HIGH PRESSURE MOVES OVER THE REGION TONIGHT AND EXPECTING VFR
CONDITIONS WITH LIGHT NE WINDS. AS MIXING DEVELOPS MID TOMORROW
MORNING...THINKING NE WINDS WILL BE ARND 10 KT.

JEE

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

* LOW CONFIDENCE IN ANY PRECIP OVERNIGHT INTO TOMORROW MORNING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

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

* WEDNESDAY NIGHT...SLIGHT CHANCE OF TSRA.
* THURSDAY THROUGH MONDAY...CHANCE OF TSRA.

&&

.MARINE...
250 PM CDT

LOW PRESSURE CONTINUES TO TRACK OUT OF NORTHERN QUEBEC AS A TRAILING
COLD FRONT EXTENDS SOUTHWEST THROUGH NORTHERN INDIANA AND INTO
SOUTHERN ILLINOIS.  THE FRONT SHOULD STALL OUT OVER THE OHIO VALLEY
OVERNIGHT TONIGHT AND HIGH PRESSURE BUILDS ACROSS UPPER MISSISSIPPI
VALLEY AND WESTERN GREAT LAKES.  WINDS OVER THE LAKE HAVE BEEN
DISRUPTED BY THUNDERSTORM ACTIVITY TODAY...BUT SHOULD SETTLE INTO A
MORE NORTHERLY TO NORTHEASTERLY DIRECTION OVERNIGHT TONIGHT.  THE
HIGH IS EXPECTED TO BUILD ACROSS THE UPPER GREAT LAKES WEDNESDAY
NIGHT WHILE LOW PRESSURE DEEPENS OVER THE CENTRAL PLAINS.  WINDS
OVER THE NORTHERN PORTIONS OF THE LAKE SHOULD THEN BECOME SOMEWHAT
VARIABLE IN DIRECTION AS THE CENTER OF THE HIGH MOVES OVER THE FAR
NORTHERN PORTION OF THE LAKE...BUT THE SOUTHERN PORTIONS OF THE LAKE
SHOULD MAINTAIN A NORTHEASTERLY TO EASTERLY FETCH.  THE PERSISTENT
NORTHEASTERLY TO EASTERLY FETCH SHOULD CAUSE WINDS TO PILE UP OVER
THE WESTERN SHORE OF THE LAKE...APPROACHING 3-4FT AS WINDS REACH
10-20KT.  THE HIGH WILL CONTINUE TO BUILD TO THE EAST THURSDAY AND
FRIDAY AS LOW PRESSURE TRACKS NEWD ONTO THE UPPER MISSOURI VALLEY.
THIS WILL...IN TURN...LIFT THE OLD FRONTAL BOUNDARY THAT HAD GONE
STATIONARY OVER THE OHIO VALLEY TO LIFT NORTH AS A WARM FRONT TURING
WINDS THROUGH SOUTHEASTERLY TO SOUTHERLY BY FRIDAY.


AS HAS BEEN THE NORM IN THE PAST WEEK TO TEN DAYS...THE PRIMARY
FORECAST CHALLENGES ARE MUCH WHAT THEY HAVE BEEN...TRYING TO DETECT
WHEN BETTER THUNDERSTORM CHANCES MAY BE AND WHAT INFLUENCE THOSE
CONVECTIVE CHANCES HAVE ON TEMPERATURES.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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