Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300826
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
326 AM CDT TUE JUN 30 2015

.SHORT TERM...
325 AM CDT

THROUGH WEDNESDAY...

PRIMARY CONCERN IN THE NEAR TERM REVOLVES AROUND PRECIP CHANCES
TODAY. NORTHWEST FLOW ALOFT CONTINUES WITH SERIES OF DISTURBANCES
PIVOTING AROUND EASTERN NOAM UPPER TROUGH. ONE SUCH VORT EVIDENT ON
WATER VAPOR IMAGERY OVER NORTHERN WISCONSIN WILL DROP SOUTH INTO THE
AREA LATER TODAY AND COULD SPARK SOME ISOLATED SHOWER AND PERHAPS T-
STORM DEVELOPMENT THIS AFTERNOON. AT THE SURFACE...BROAD LOW
PRESSURE OVER WESTERN LAKES WILL BEGIN SLOWLY BEGIN MOVING EASTWARD
ALLOWING WEAK NORTHWESTERLY WINDS AT THE SURFACE TO BEGIN PROCESS OF
ADVECTING IN DRIER AIR MASS TODAY...WHICH SHOULD RESULT IN BEST
INSTABILITY OVER SOUTHEASTERN CWA. WATER VAPOR ALSO SHOWS DRY MID-
UPPER LEVEL AIR ADVECTING SE INTO THE AREA WHICH SHOULD ALSO TEND TO
LIMIT THE COVERAGE AND INTENSITY OF SHOWERS THIS AFTERNOON.
GENERALLY FOCUSED CHANCE POPS TODAY IN SE CWA WHERE BEST COMBO OF
INSTABILITY AND MOISTURE WILL EXIST...THOUGH DO HOLD ONTO A TONGUE
OF SLIGHT CHANCE POPS NORTH INTO NORTHEAST ILLINOIS IN CASE MORE
FOCUSED LOW LEVEL CONVERGENCE ALONG THE LAKE BREEZE ENDS UP BEING
ENOUGH TO POP SOME WEAK AFTERNOON CONVECTION.

STRONGER SHORTWAVE WILL RIDE THE NORTHWEST FLOW INTO THE MISSOURI
AND LOWER OHIO VALLEY REGION TONIGHT...BUT LOOKS TO PASS FAR ENOUGH
SOUTHWEST OF OUR REGION TO PROVIDE LITTLE THREAT OF PRECIPITATION.
DRY AND SEASONABLY COOL WEATHER WILL BE THE DOMINANT WEATHER STORY
TOMORROW WITH WINDS OFF THE LAKE KEEPING TEMPS AT THE BEACHES PRETTY
CHILLY BY JULY STANDARDS.

IZZI

&&

.LONG TERM...
325 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

EXTENDED PERIOD OF DRY AND SEASONABLY COOL WEATHER EXPECTED TO
CONTINUE INTO THE WEEKEND AS UPPER TROUGH SLOWLY DEAMPLIFIES BUT
WEAK CANADIAN HIGH PRESSURE REMAINS IN CONTROL OF THE WEATHER. WINDS
OFF THE LAKE WILL KEEP IT CONSISTENTLY COOLER BY THE LAKE WITH HIGHS
GENERALLY IN THE 70S INLAND AND 60S RIGHT ALONG THE LAKE. MODERATING
TREND IN TEMPS EXPECTED HEADING INTO THE WEEKEND AS DEVELOPING LOW
PRESSURE OVER THE PLAINS FLIPS WINDS TO SOUTHERLY DIRECTION AND
BRINGS A RETURN TO MORE SEASONABLE TEMPERATURES OVER THE WEEKEND
ALONG WITH A THREAT OF SOME SHOWERS AND THUNDERSTORMS BY SUNDAY
NIGHT INTO MONDAY.

IZZI

&&

.AVIATION...

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

* FOG OVERNIGHT.
* SCATTERED SHRA/ISOL TSRA TUESDAY AFTERNOON.

BMD

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

SCATTERED SHOWERS SHOULD CONTINUE TO DIMINISH OVER THE NEXT
COUPLE HOURS ACROSS NORTHERN ILLINOIS AS A WEAK SURFACE TROUGH
DROPS SOUTHEAST ACROSS THE REGION. WINDS WILL BE LIGHT WITHIN THE
FRONTAL TROUGH THEN SHOULD TURN NORTHWESTERLY LATER OVERNIGHT OR
EARLY TUESDAY. MAIN CONCERN OVERNIGHT SEEMS TO BE FOG DEVELOPMENT
WITH CONDITIONS ALREADY NEAR SATURATION AND MID LEVEL CLOUD COVER
PROGGED TO CLEAR THE TERMINALS IN THE NEXT 3-4 HOURS. THE
COMBINATION OF LIGHT WINDS AND CLEARING SKIES WILL SET THE STAGE
FOR RADIATION FOG DEVELOPING. AT THIS POINT...NONE OF THE MOS
GUIDANCE IS PICKING UP ON FOG AND THE RAW VSBY GUIDANCE FROM THE
MODELS IS HIT OR MISS. TRENDED VSBY DOWN IN THE LATEST VERSION OF
THE TAFS...BUT CONCERNED AT LEAST PATCHY DENSE FOG OF 1/2 TO 1/4
OF A MILE WILL BE IN PLACE IF NOT MORE WIDESPREAD. WILL WATCH
TRENDS OVER NEXT COUPLE HOURS TO SEE IF FURTHER REDUCTION OF VSBY
IS NEEDED IN THE FORECAST.

TUESDAY SHOULD START OUT WITH NORTHWEST FLOW AND EXPECT TO
GRADUALLY IMPROVE BACK TO VFR BY AROUND MID MORNING. A LAKE BREEZE
IS EXPECTED TO TURN WINDS NE LATE AFTERNOON OR EARLY EVENING FOR
ORD/MDW...AND EARLY AFTERNOON AT GYY. COULD BE SOME SCATTERED
SHOWERS WITH ISOLATED THUNDERSTORMS AGAIN TOMORROW...MAINLY IN THE
AFTERNOON WHEN INSTABILITY PEAKS.

BMD

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

* INCREASING CONFIDENCE IN MVFR/IFR FOG OVERNIGHT. LOW CONFIDENCE
  IN LIFR VSBY.
* LOW-MEDIUM CONFIDENCE IN PRECIP AT TERMINALS TUESDAY AFTERNOON.

BMD

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

* WEDNESDAY AND THURSDAY...DRY/VFR. NORTHEAST WINDS.
* FRIDAY...SLIGHT CHANCE OF SHRA/TSRA. NORTHEAST WINDS.
* SATURDAY...SLIGHT CHANCE OF SHRA. EAST WINDS.
* SUNDAY...SLIGHT SHRA/TSRA. SOUTHEAST WINDS.

&&

.MARINE...
259 AM CDT

A WEAK TROUGH WILL PUSH ACROSS LAKE MICHIGAN TODAY WITH NORTHWEST
TO NORTH WINDS OVERSPREADING THE LAKE THROUGH THE DAY. WINDS
FRESHEN UP TO 15 TO 20 KT ACROSS THE LAKE THIS AFTERNOON AND
EVENING AS THE LOW DEEPENS OVER THE EASTERN LAKES REGION AND HIGH
PRESSURE BUILDS SOUTH FROM MANITOBA. MODEST NORTH TO NORTHEAST
WINDS WILL REMAIN IN PLACE THROUGH WEDNESDAY NIGHT...THEN WILL
BEGIN TO DIMINISH FROM THE NORTH. A GRADIENT WILL HOLD ON ACROSS
THE FAR SOUTH END OF LAKE MICHIGAN THURSDAY AS LOW PRESSURE MOVES
ACROSS THE MID MISSISSIPPI VALLEY...BUT EXPECT WINDS TO DIMINISH
ACROSS THE SOUTH END BY THURSDAY NIGHT AS THE RIDGE CONTINUES TO
BUILD SOUTH.

BMD

&&

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

$$

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