Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291921
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 PM CDT WED JUL 29 2015

.SHORT TERM...
221 PM CDT

TONIGHT THROUGH FRIDAY...

COLD FRONT MOVING EAST OF THE FORECAST AREA THIS AFTERNOON...WITH
SURFACE HIGH PRESSURE RIDGE EXPANDING FROM THE CENTRAL PLAINS INTO
CENTRAL IL/IN. SOUTHERN PERIPHERY OF MID-LEVEL TROUGH ASSOCIATED
WITH CLOSED UPPER LOW OVER ONTARIO WILL SWEEP ACROSS THE REGION
TONIGHT...THOUGH GENERALLY DRY ATMOSPHERE UPSTREAM PER OAX 12Z
RAOB AND EXPECT ONLY A FEW PATCHY MID-HIGH CLOUDS WITH WEAK HEIGHT
FALLS AHEAD OF TROUGH AND BENEATH RIGHT ENTRANCE TO UPPER LEVEL
JET STREAK LIFTING THROUGH THE NORTHERN LAKES. SURFACE DEW POINTS
CONTINUE TO DROP OFF INTO THE 50S ON BREEZY WEST-NORTHWEST
WINDS...SETTING THE STAGE FOR A LESS HUMID NIGHT WITH LOWS NEAR
AVERAGE IN THE LOW-MID 60S.

UPPER PATTERN SETTLES INTO A RIDGE IN THE WEST/TROUGH IN THE EAST
CONFIGURATION THROUGH THE END OF THE WEEK...WITH A COUPLE OF MINOR
AMPLITUDE SHORT WAVES DEPICTED IN GUIDANCE FOR THURSDAY AND
FRIDAY. MODELS INDICATE A RATHER WEAK SURFACE TROUGH REFLECTION
WITH THE WAVE TOMORROW...WITH A LITTLE MORE OF A WEAK COLD FRONTAL
TROUGH INDICATED FRIDAY. GFS IS MORE BULLISH WITH DEVELOPING
CONVECTION ALONG THE FRONT FRIDAY AFTERNOON...THOUGH AM A LITTLE
SUSPICIOUS GIVEN OVERALL DRYNESS OF SOUNDINGS AND WEAK LOW-LEVEL
CONVERGENCE IN WESTERLY WINDS ALONG SOUTHWEST-NORTHEAST ORIENTED
BOUNDARY. SURFACE RIDGE TO OUR SOUTH PREVENTS ANY SIGNIFICANT
MOISTURE RETURN...WITH CURRENT UPSTREAM DEW POINTS OVER THE PLAINS
IN THE 30S AND 40S ACROSS NEBRASKA. THE WRF...WHICH OFTEN OVERDOES
LOW LEVEL MOISTURE/CAPES IS DRY WITH NO CAPE AND FOR NOW AM
MAINTAINING A DRY FORECAST. IT DOES LOOK FAIRLY BREEZY...WITH
WINDS IN THE 25 KT RANGE WITHIN THE MIXED LAYER FOR
FRIDAY...LIKELY GOOD FOR GUSTS 20+ MPH. 850 MB TEMPS RANGE FROM
+16/18 C THURSDAY TO AROUND +18 C FRIDAY...MIXING DOWN TO MID-
UPPER 80S FOR HIGHS BOTH DAYS AND A GOOD DEAL OF SUNSHINE.

RATZER

&&

.LONG TERM...
332 AM CDT

THURSDAY THROUGH TUESDAY...

SUNNY AND VERY WARM WEATHER IS ON TAP FOR THURSDAY WITH
COMFORTABLE HUMIDITY LEVELS BY LATE JULY STANDARDS. FRIDAY LOOKS
TO BE A CARBON COPY OF THURSDAY WITH PERHAPS JUST A FEW MORE
CLOUDS BUT STILL A LOT OF SUNSHINE. PROGGED 925MB TEMPS IN THE
LOW-MID 20S CELSIUS SUPPORTS HIGHS IN THE UPPER 80S TO LOWER 90S
AND GIVEN SUCH LOW DEWPOINTS AND AMPLE SUNSHINE HAVE LEANED CLOSER
TO WARMER GUIDANCE BOTH PERIOD.

WEAK COLD FRONT SLIDES THROUGH FRIDAY NIGHT AND CANNOT TOTALLY
RULE OUT SOME ISOLATED CONVECTION WITH IT...THE FACT ITS COMING
THROUGH AT DIURNALLY UNFAVORABLE TIME OF DAY AND WITH NO RETURN
MOISTURE WORK AGAINST INTRODUCING POPS AT THIS TIME. AFTER
COORDINATION WITH MKX IT WAS DECIDED TO KEEP POPS IN THE 10-15
PERCENT RANGE IN THE GRIDS...BELOW MENTIONABLE THRESHOLD IN THE
TEXT FORECAST FOR NOW. A COUPLE OF MORE WEAK NORTHWEST FLOW FRONT
ARE SLATED TO MOVE ACROSS THE CWA SUNDAY AFTERNOON AND TUESDAY
AFTERNOON...BOTH OF WHICH COULD BRING SOME SCATTERED STORMS BUT
NEITHER LOOKING LIKE BIG TIME WASHOUTS FROM WIDESPREAD RAIN
EITHER. FOR NOW HELD ONTO MODEL CONSENSUS LOWER END CHANCE POPS
FOR BOTH FRONTS. NO SIGNIFICANT COOL DOWNS EXPECTED WITH EITHER
FRONT AT THIS TIME.

IZZI

&&

.AVIATION...

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

* NW WINDS GUSTING TO ARND 20 KT THROUGH THE EARLY EVENING.

* NW WINDS GUSTING TO 20 TO 25 KT FROM MID MORNING THROUGH THE
  LATE AFTN THURSDAY.

JEE

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

HIGH PRESSURE CURRENTLY OVER THE PLAINS WILL SPREAD OVERHEAD
TONIGHT WITH CLEAR SKIES AND GUSTY NW WINDS DIMINISHING TO ARND
8 KT. CLEAR SKIES CONTINUE TOMORROW ALLOWING AMPLE MIXING TO TAKE
PLACE SO THINKING WE WILL SEE NW WINDS GUSTING AGAIN TO ARND 20-25
KT BY THE LATE MORNING. SOME GUIDANCE MEMBERS FEATURE SLIGHTLY
HIGHER WINDS...BUT THINKING WE WILL NOT MIX THAT MUCH.

JEE

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

JEE

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

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY AND MONDAY...CHANCE OF TSRA. WESTERLY WINDS.
* TUESDAY...SLIGHT CHANCE OF TSRA. NORTH/NORTHEAST WINDS.

&&

.MARINE...

233 AM...DEEP LOW PRESSURE OVER MANITOBA WILL MOVE NORTHEAST TO
HUDSON BAY THURSDAY AS A TRAILING COLD FRONT MOVES ACROSS THE LAKE
TODAY. SOUTHERLY WINDS 15-25 KTS OVER THE NORTHERN PORTION OF THE
LAKE WILL REMAIN AT THOSE SPEEDS BUT ONLY GRADUALLY TURN WESTERLY
BY THIS EVENING. THIS LOW WILL REMAIN OVER HUDSON BAY THROUGH THE
END OF THE WEEK...WHILE SLOWLY WEAKENING. HIGH PRESSURE WILL BUILD
ACROSS THE CENTRAL PLAINS TODAY AND TONIGHT AND GRADUALLY SPREAD
INTO THE OHIO VALLEY THURSDAY AND FRIDAY. THIS WILL MAINTAIN A
WESTERLY FLOW ACROSS LAKE MICHIGAN WITH PERIODS OF 15-25 KTS
POSSIBLE INTO THURSDAY. THE GRADIENT WILL THEN RELAX WITH SPEEDS
DIMINISHING. A WEAK TROUGH/FRONT WILL MOVE ACROSS THE LAKE FRIDAY
NIGHT...BRIEFLY TURNING WINDS TO THE NORTHWEST BEFORE TURNING BACK
TO THE SOUTHWEST SATURDAY. CMS

&&

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

$$

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