Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
257 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 06Z...

* EAST/SOUTHEAST WINDS AROUND 10KT TODAY.
* CHANCE OF TSRA LATE TONIGHT INTO WEDNESDAY MORNING. CMS

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

WEAK HIGH PRESSURE OVER THE CENTRAL AND EASTERN GREAT LAKES WILL
SLOWLY MOVE EAST TODAY AND TONIGHT WHILE LOW PRESSURE OVER THE
WESTERN PLAINS MOVES NORTHEAST INTO CANADA TONIGHT AND WEDNESDAY.
THIS WILL ALLOW WINDS TO TURN A BIT MORE SOUTHEASTERLY THIS
MORNING...POSSIBLY SHIFTING BACK EASTERLY THIS AFTERNOON. SPEEDS
THOUGH WILL REMAIN AROUND 10KTS. WINDS WILL DIMINISH UNDER 10 KT
THIS EVENING TURNING SOUTHERLY IN THE EVENING AND SOUTHWESTERLY
OVERNIGHT.

A TRAILING COLD FRONT FROM THE LOW NOTED ABOVE WILL MOVE ACROSS
THE AREA WEDNESDAY MORNING. SHOWERS AND THUNDERSTORMS ARE EXPECTED
TO DEVELOP ALONG AND AHEAD OF THIS FRONT THIS AFTERNOON AND THIS
EVENING TO THE NORTHWEST....MOVING ACROSS THE TERMINALS TONIGHT
INTO WEDNESDAY MORNING. THERE STILL REMAINS SOME UNCERTAINTY
REGARDING WHERE AND WHEN THESE STORMS WILL AFFECT THE TERMINALS.
SOME GUIDANCE SUGGESTS A COMPLEX OF STORMS PASSING JUST SOUTH OF
THE TERMINALS. DURATION ALSO COULD END UP BEING JUST A FEW HOURS.
SO FOR NOW HAVE INCLUDED A TEMPO AT THE END OF THE PERIOD AT RFD
AND THEN A PROB AT ORD AT THE END OF ITS 30 HR TAF.

PATCHY FOG IS AGAIN POSSIBLE OVERNIGHT INTO THIS MORNING...MAINLY
AT GYY AND SOUTH OF THE TERMINALS. CONFIDENCE REGARDING HOW
WIDESPREAD IT MAY BECOME IS LOW AND LEFT OUT MENTION WITH THIS
FORECAST. CMS

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

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

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

WEDNESDAY...CHANCE OF TSRA IN THE MORNING.

THURSDAY...VFR.

FRIDAY...VFR.

SATURDAY...CHANCE OF TSRA.

SUNDAY...CHANCE OF TSRA.

RODRIGUEZ

&&

.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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