Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 270807
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CDT WED AUG 27 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 06Z...

* POSSIBLE MVFR CIGS EARLY THIS MORNING.
* EAST/NORTHEAST WINDS THRU THE PERIOD...POSSIBLY AROUND 10KT THIS
  AFTERNOON. CMS

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

HIGH PRESSURE OVER THE NORTHERN PLAINS WILL MOVE EAST ACROSS THE
LAKES REGION LATER TODAY AND TONIGHT. THIS WILL MAINTAIN EAST/
NORTHEAST WINDS THROUGH THE PERIOD. SPEEDS COULD INCREASE TO 10KTS
OR SLIGHTLY HIGHER THIS AFTERNOON INTO EARLY THIS EVENING WITH A
POSSIBLE LAKE BREEZE.

CIGS AROUND 3KFT HAVE DEVELOPED ACROSS NORTHEAST IL BUT APPEAR TO
BE SHIFTING EAST AND FOR NOW WILL JUST CARRY SCT MENTION. APPEARS
A BKN/OVC MID DECK WILL SPREAD ACROSS MUCH OF THE REGION OVERNIGHT
AND CONTINUE INTO THIS AFTERNOON. SOME FOG IS POSSIBLE WHERE SKIES
REMAIN MOSTLY CLEAR AND GENERALLY SOUTH AND SOUTHEAST OF THE
TERMINALS. CONTINUED FOG MENTION AT GYY BUT CONFIDENCE TOO LOW
ELSEWHERE.

A FEW ECHOS SHOWING UP ON RADAR NEAR THE QUAD CITIES AND ITS
POSSIBLE FOR A LIGHT SHOWER OR SOME SPRINKLES OUT OF THE MID DECK
THRU MID MORNING. CMS

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

* LOW FOR MVFR CIGS EARLY THIS MORNING.
* MEDIUM FOR WINDS THRU THE PERIOD. CMS

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

* THURSDAY THROUGH MONDAY...CHANCE OF TSRA.

KJB

&&

.MARINE...

307 AM...HIGH PRESSURE CENTERED OVER MINNESOTA EARLY THIS MORNING
WILL MOVE ACROSS THE LAKES REGION TODAY AND TONIGHT. AS IT DOES
THE GRADIENT WILL SLOWLY WEAKEN OVER NORTHERN LAKE MICHIGAN WHILE
IT SLOWLY TIGHTENS OVER THE SOUTHERN PORTION OF THE LAKE. SPEEDS
WILL INCREASE INTO THE 10-20KT RANGE. AS THE HIGH SHIFTS EAST...
WINDS WILL TURN MORE EASTERLY BY THURSDAY MORNING THEN SHIFT
SOUTHEAST TO SOUTHERLY THURSDAY NIGHT AS A WARM FRONT LIFTS NORTH
ACROSS THE LAKE. THE GRADIENT COULD TIGHTEN ENOUGH FOR A PERIOD OF
15-25 KTS THURSDAY NIGHT INTO FRIDAY. A FRONTAL BOUNDARY IS THEN
EXPECTED TO MOVE SOUTH ACROSS THE LAKE SATURDAY AFTERNOON INTO
SATURDAY EVENING. BUT AT THE SAME TIME...LOW PRESSURE IS EXPECTED
TO DEVELOP OVER THE WESTERN LAKES AND THEN MOVE ACROSS NORTHERN
LAKE MICHIGAN BY SUNDAY MORNING. THIS MAKES FOR A CHALLENGING WIND
FORECAST. IF THE LOW BEGINS TO DEEPEN...NORTHERLY WINDS MAY
INCREASE INTO THE 15-25KT RANGE. CHANGES CAN BE EXPECTED DURING
THIS TIME PERIOD AS TRENDS EMERGE. WINDS THEN QUICKLY TURN BACK
SOUTHERLY SUNDAY NIGHT INTO MONDAY. CMS

&&

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

$$

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