Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281136
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
636 AM CDT TUE JUL 28 2015

.SHORT TERM...
257 AM CDT

THROUGH WEDNESDAY...

HIGH CONFIDENCE IN SYNOPTIC EVOLUTION NEXT 24 HOURS...HOWEVER
MESOSCALE DETAILS WITH CONVECTION CONFIDENCE IS LOW ON EXACT
EVOLUTION. A SEASONABLY STRONG MID LATITUDE CYCLONE WILL SLOWLY LIFT
NORTHEAST FROM THE NORTHERN PLAINS THIS MORNING TOWARD HUDSON BAY BY
WEDNESDAY EVENING. TRAILING COLD FRONT WILL PUSH SOUTHEAST ACROSS
THE UPPER MISSISSIPPI VALLEY TODAY AND ACROSS THE MIDWEST AND
WESTERN LAKES LATE TONIGHT INTO WEDNESDAY MORNING.

LARGE MCS ONGOING OVER NORTHERN PLAINS SHOULD CONTINUE TO TRACK EAST-
SOUTHEASTWARD TOWARD IOWA THIS MORNING. CONVECTIVE COMPLEX LIKELY TO
WEAKEN WITH TIME THIS MORNING AS IT ENCOUNTERS LESS INSTABILITY AND
LOW LEVEL JET BEGINS TO DIURNALLY VEER AND WEAKEN AFTER SUNRISE.
SOME CONVECTIVE ALLOWING GUIDANCE STILL SUGGESTS SOME SHOWERS FROM
THIS ACTIVITY COULD MAKE IT INTO FAR WESTERN CWA THIS AFTERNOON SO
HAVE MAINTAINED SLIGHT CHANCE POPS...THOUGH THINK THE MORE LIKELY
SCENARIO IS JUST SOME DEBRIS CLOUDINESS.

ADDITIONAL CONVECTION IS LIKELY TO DEVELOP THIS AFTERNOON FROM UPPER
MS VALLEY SOUTH INTO IOWA AND THEN TRACK EAST-SOUTHEAST TOWARD OUR
CWA LATE THIS EVENING INTO THE OVERNIGHT HOURS. WIDE ARRAY OF
SOLUTIONS FROM CONVECTIVE ALLOWING GUIDANCE TONIGHT...LIKELY DUE IN
PART TO WEAKER LARGE SCALE ASCENT AND HEIGHT FALLS THIS FAR SOUTH
LEADING TO MORE MESOSCALE FORCED CONVECTION AND A GREATER DEGREE OF
UNCERTAINTY REGARDING COVERAGE OVER OUR CWA TONIGHT. INSTABILITY IS
LIKELY TO BE WEAKENING DIURNALLY AND GUIDANCE SUGGESTS ONLY A WEAK
LOW LEVEL JET LEADING WHICH COULD ALLOW STORMS TO FADE TONIGHT AND
PERHAPS KEEP COVERAGE OF PRECIP DOWN SOME OVER MAINLY SE CWA.
LINGERING THREAT OF CONVECTION WILL CONTINUE INTO WED
MORNING...MAINLY SE CWA BEFORE SYNOPTIC FRONT CLEARS THE AREA AND
ALLOWS DRIER AND MORE STABLE AIR TO FILTER INTO THE REGION IN ITS
WAKE.

TEMPERATURES TODAY WILL BE A BIT TRICKY AS DEBRIS CLOUDINESS FROM N
PLAINS MCS COULD HOLD TEMPS BACK FROM REACHING THEIR FULL
POTENTIAL...ESPECIALLY WESTERN CWA. GENERALLY MADE FEW CHANGES FROM
GOING FORECAST WHICH WAS WELL IN LINE WITH CONSENSUS GUIDANCE WITH
HIGHS IN THE UPPER 80S/NEAR 90. MOISTURE ADVECTION AND
EVAPOTRANSPIRATION SHOULD RESULT IN DEWPOINTS CLIMBING INTO THE MID
TO UPPER 70S OVER WESTERN AND SOUTHERN CWA...WHICH ASSUMING TEMP
FORECAST VERIFIES WOULD SEND HEAT INDICES OVER 100 DEGREES THIS
AFTERNOON. SLIGHTLY LOW DEWPOINTS IN THE CHGO METRO AREA AND A LAKE
BREEZE WILL LIKELY MEAN HEAT INDICES MAINLY IN THE 95-100 RANGE AWAY
FROM THE LAKE WHERE HIGHS WILL LIKELY ONLY REACH THE LOWER 80S VS
NEAR 90 INLAND 5-10 MILES. AIRMASS BEHIND THE FRONT WEDNESDAY LOOKS
TO BE LESS HUMID BUT NOT MUCH COOLER WITH 925MB TEMPS SUPPORTING
HIGHS ONCE AGAIN IN THE MID-UPPER 80S...THOUGH LOWER AND FALLING
DEWPOINTS WILL MAKE IT FEEL MORE COMFORTABLE THAN THIS AFTERNOON.

IZZI

&&

.LONG TERM...
257 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

DRY AND WARM CONDITIONS EXPECTED THURSDAY-SATURDAY WITH COMFORTABLE
HUMIDITY LEVELS BY LATE JULY/EARLY AUGUST STANDARDS. WESTERLY
GRADIENT APPEARS LIKELY TO BE STRONG ENOUGH TO PREVENT ANY
APPRECIABLE LAKE BREEZES SENDING THE WARMTH RIGHT UP TO THE CHICAGO
BEACHES. WEAK COLD FRONT LOOKS LIKE IT COULD MAKE A RUN AT THE
REGION SUNDAY INTO MONDAY...THOUGH HIGH PRESSURE OVER THE SOUTHEAST
STATES PROMISES TO KEEP DEEP GULF MOISTURE AT BAY. DESPITE THE LACK
OF RETURN MOISTURE...CORN-FED DEWPOINTS ARE LIKELY TO CREEP UP OVER
THE WEEKEND AND POTENTIALLY POOL ALONG THE WEAK FRONT PROVIDING
ENOUGH MOISTURE AND INSTABILITY TO JUSTIFY AT LEAST CHANCES POPS AT
THIS DISTANCE.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* EAST/SOUTHEAST WINDS AROUND 10KT MID MORNING THRU EARLY THIS
  EVENING.
* CHANCE OF TSRA OVERNIGHT INTO WEDNESDAY MORNING. CMS

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE OVER THE EASTERN LAKES WILL MOVE EAST TODAY AND
TONIGHT AS LOW PRESSURE OVER THE NORTHERN PLAINS MOVE NORTHEAST
INTO CANADA. EASTERLY WINDS WILL CONTINUE THROUGH MUCH OF TODAY
ACROSS THE CHICAGO TERMINALS...MORE SOUTHEAST AT DPA AND RFD.
SPEEDS ARE ALSO EXPECTED TO INCREASE TO 10KTS THIS MORNING...
THEN DIMINISH THIS EVENING. WINDS WILL TURN MORE SOUTHERLY
TONIGHT AND THEN SHIFT WESTERLY WEDNESDAY MORNING AS A COLD
FRONT MOVES ACROSS THE AREA.

THUNDERSTORMS CURRENTLY OVER NORTHEAST AND WESTERN IA ARE
EXPECTED TO DISSIPATE THIS MORNING BEFORE REACHING ANY OF THE
TERMINALS. HOWEVER...IT IS POSSIBLE FOR AN ISOLATED SHOWER OR
THUNDERSTORM THIS AFTERNOON AND IF THESE OCCUR...THEY WOULD BE
MOST LIKELY SOUTHWEST AND SOUTH OF THE TERMINALS.

ADDITIONAL THUNDERSTORMS ARE EXPECTED TO DEVELOP NORTHWEST OF
THE TERMINALS THIS AFTERNOON OR THIS EVENING AND THEN MOVE
SOUTHEAST ACROSS THE AREA LATE THIS EVENING ACROSS NORTHWEST IL
AND RFD AND THEN OVERNIGHT ACROSS THE CHICAGO AREA. THERE STILL
REMAINS UNCERTAINTY FOR COVERAGE AND FOR THAT REASON OPTED TO
MAINTAIN PROB30 MENTION. TIMING SEEMS TO BE CENTERED ON THE 09Z-
12Z PERIOD FOR CHICAGO...BUT ADDITIONAL CHANGES CAN BE EXPECTED
WITH LATER FORECASTS AND ONCE ACTIVITY EMERGES LATER TODAY/THIS
EVENING. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM FOR WINDS THRU THE PERIOD.
* MEDIUM FOR TSRA OVERNIGHT/WEDNESDAY MORNING...LOW FOR TIMING
  AND DURATION. CMS

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

* WEDNESDAY NIGHT THROUGH SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
* MONDAY...CHANCE OF TSRA. LAKE BREEZE POSSIBLE.

&&

.MARINE...

217 AM...HIGH PRESSURE OVER THE EASTERN LAKES WILL SLOWLY MOVE
EAST TODAY AND TONIGHT WHILE A LARGE TROUGH OF LOW PRESSURE OVER
THE WESTERN PLAINS CONSOLIDATES INTO A LOW IN SOUTHERN CANADA.
THIS LOW WILL THEN MOVE NORTHEAST TONIGHT REACHING HUDSON BAY
WEDNESDAY EVENING. A TRAILING COLD FRONT FROM THIS LOW WILL MOVE
ACROSS LAKE MICHIGAN WEDNESDAY. THE GRADIENT WILL TIGHTEN AHEAD
OF THIS FRONT LATER TONIGHT INTO WEDNESDAY MORNING WITH A PERIOD
OF 15-25 KTS STILL EXPECTED ACROSS NORTHERN PORTIONS OF THE LAKE.
WINDS WILL SHIFT WESTERLY WEDNESDAY AFTERNOON INTO WEDNESDAY
EVENING. ANOTHER COLD FRONT IS EXPECTED TO MOVE ACROSS THE LAKES
FRIDAY AFTERNOON INTO FRIDAY NIGHT. CMS

&&

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

$$

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