Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 310323
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1023 PM CDT THU JUL 30 2015

.SHORT TERM...
226 PM CDT

THROUGH FRIDAY...

FORECAST PERIOD WILL REMAIN RELATIVELY QUIET...WITH DRY
CONDITIONS EXPECTED. INCREASING WESTERLY WINDS AT THIS TIME WILL
LIKELY REACH THEIR PEAK OVER THE NEXT COUPLE OF HOURS WITH A
DIMINISHING TREND THEN EXPECTED INTO THE EARLY EVENING. A FEW CU
HAVE DEVELOPED THIS AFTERNOON BUT THESE WILL QUICKLY ERODE WITH
CLEAR SKIES EXPECTED ONCE AGAIN TONIGHT. GUIDANCE IS HINTING AT
SOME PASSING MID/HIGH LEVEL CLOUD COVER LATE TONIGHT INTO FRIDAY
MORNING. HOWEVER...FEEL IT MAY BE A BIT AGGRESSIVE AND DONT THINK
IT WILL AMOUNT TO MUCH BEYOND A WINDOW OF PARTLY CLOUDY SKIES.
SUNNY SKIES WILL HELP TEMPS ACROSS THE AREA TO BE SOMEWHAT OF A
MIRROR OF TODAY...WITH OFFSHORE FLOW KEEPING ANY LAKE COOLING
LIMITED ACROSS PORTIONS OF NORTHWEST INDIANA. DEWPOINTS WILL TRY
TO INCREASE THROUGHOUT THE DAY BUT SHOULD BE LIMITED TO THE LOWER
60S BEFORE DAYTIME MIXING ALLOWS DRIER AIR TO MIX DOWN...WITH THIS
LOWER DEWPOINT AIR ALSO LIMITING HEAT INDICES. WAS A LITTLE
CONCERNED THAT PREVIOUS RUNS OF GUIDANCE WERE NOT QUITE HANDLING
PRECIP POTENTIAL FRIDAY AFTERNOON QUITE WELL BUT 12Z GUIDANCE
TODAY HAS CONTINUED A SIMILAR TREND...KEEPING ANY DEVELOPMENT OUT
AHEAD OF APPROACHING TROUGH/BOUNDARY OUTSIDE OF THE CWA. WITH LOW
TO MID LEVEL FLOW ALREADY WEST TO NORTHWEST ON FRIDAY...LOW/MID
LEVEL CONVERGENCE WILL REMAIN RATHER WEAK. ALSO...SUPPORT ALOFT
APPEARS TO BE LACKING. SO HAVE BACKED AWAY ON THUNDERSTORM CHANCES
FRIDAY AFTERNOON FOR THE CWA BUT IF ANY BRIEF/ISOLATED DEVELOPMENT
WERE TO OCCUR...IT WOULD BE ALONG THE FORD/IROQUOIS TO BENTON
COUNTY LINE.

RODRIGUEZ

&&

.LONG TERM...
305 PM CDT

FRIDAY NIGHT THROUGH THURSDAY...

MAIN FORECAST CONCERN OVER THE WEEKEND IS CONVECTIVE CHANCES LATE
SATURDAY THROUGH SUNDAY. AFTER A SEASONABLY WARM START TO THE
FIRST WORK WEEK OF AUGUST...THE REST OF NEXT WEEK LOOKS TO BE
COOLER BUT POTENTIALLY ACTIVE AT TIMES. MID AND UPPER LEVEL
PATTERN WILL FEATURE PRIMARILY NORTHWEST FLOW AROUND LARGE
INITIALLY QUASISTATIONARY UPPER LOW NEAR HUDSON BAY THAT WILL
THEN PIVOT SOUTHEAST DURING THE WORK WEEK.

COLD FRONT...ALBEIT WITH NOT MUCH COOLER AIR BEHIND IT...WILL BE
CLEARING SOUTHEAST CWA FRIDAY EVENING. FOCUS FOR ANY CONVECTION
LOOKS TO BE OFF TO EAST AND SOUTHEAST OF THE AREA ASSOCIATED WITH
BETTER CONVERGENCE ALONG THE FRONT. ANTICIPATING MOSTLY CLEAR
SKIES AND NEAR SEASONABLE LOWS. HAVE CONTINUED WITH A DRY
FORECAST FOR SATURDAY DAYTIME HOURS DESPITE SOME MODELS INDICATING
QPF...AS FORCING APPEARS WEAK AND DEWPOINTS COULD BE OVERDONE
LEADING TO TOO MUCH INSTABILITY. 925 MB TEMPS OF +20 TO +22
CELSIUS SUPPORT HIGHS IN MID 80S WITH UPPER 80S POSSIBLE IN
CHICAGO HEAT ISLAND. TIMING OF NEXT COLD FRONT AND UPPER WAVE HAS
SPED UP ON SOME GUIDANCE TO FAVOR EVENING AND OVERNIGHT FOR
SHRA/TSRA CHANCES...WITH MID-HIGH CHANCE POPS NORTH OF INTERSTATE
80. CONFIDENCE IS FAIRLY LOW ON CONVECTIVE EVOLUTION/TIMING...SO
HAVE NOT ADDED TEMPORAL RESOLUTION TO POPS. SPC CURRENTLY HAS A
MARGINAL RISK WEST OF CWA...THOUGH ~40 KT OF DEEP LAYER SHEAR
COULD SUPPORT A THREAT FOR ISOLATED STRONG TO SEVERE STORMS WITHIN
CWA DEPENDING ON MESOSCALE DETAILS.

UPPER WAVE AND ASSOCIATED FORCING APPEARS TO FAVOR SOUTHEAST CWA
FOR HIGHER POPS ON SUNDAY...THOUGH 12Z ECMWF IS MUCH
SLOWER/POSSIBLY AN OUTLIER. DEPENDING ON CLOUD COVER/CONVECTIVE
TRENDS...THERMAL PROGS COULD SUPPORT HIGHS A BIT WARMER THAN
CURRENT FORECAST MID 80S. SIMILAR SITUATION ON MONDAY...AS COLD
FRONT WILL BE MOVING THROUGH BUT VERY WARM THERMAL PROFILES/925 MB
TEMPS IN LOWER-MID 20S CELSIUS COULD YIELD AT LEAST MID-UPPER
80S. HAVE MAINTAINED SLIGHT TO CHANCE POPS FROM BLENDED GUIDANCE
INTO MONDAY NIGHT. UPPER LOW DIVING SOUTHEAST IN THE MID WEEK
PERIOD NEXT WEEK WILL SEND MUCH COOLER AIRMASS THAN WE HAVE BEEN
EXPERIENCING LATELY SOUTHWARD...BUT WITH UNCERTAINTY ON JUST HOW
COOL. CURRENTLY LOOKING AT UPPER 70S-LOWER 80S ON TUESDAY AND
MID-UPPER 70S ON WEDNESDAY AND THURSDAY...ALONG WITH STEADY
ONSHORE WINDS. MODELS ARE OVER THE PLACE ON DAY TO DAY
DETAILS...BUT PERIODIC SLIGHT TO CHANCE POPS SEEM REASONABLE GIVEN
SOMEWHAT DISTURBED NORTHWEST FLOW PATTERN.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* WEST TO NORTHWEST WINDS GUSTING TO AROUND 20 KT ON FRIDAY

KMD

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE OVER THE REGION...MAINLY CENTERED JUST TO WEST OF
OUR AREA...WILL REMAIN IN PLACE THROUGH THE TAF CYCLE. WEST TO NW
WINDS WILL BE GUSTING INTO THE MID 20 KT RANGE FOR AN HOUR OR TWO
LONGER AND THEN DIMINISH TO LESS THAN 10 KT THIS EVENING. WEST
WINDS THEN BEGIN GUSTING AGAIN INTO THE LOW 20 KT RANGE MID FRIDAY
MORNING THROUGH THE AFTN. A DRY COLD FRONT WILL PASS THROUGH
FRIDAY AFTERNOON WITH A SLIGHT SHIFT TO MORE OF A NW COMPONENT TO
THE WIND IN THE AFTERNOON EARLY EVENING PERIOD. OTHERWISE VFR
CONDITIONS ARE EXPECTED.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH IN ALL FORECAST ELEMENTS

KMD

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

* SATURDAY...VFR. WEST WINDS. CHANCE TSRA OVERNIGHT.
* SUNDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
* MONDAY...CHANCE OF TSRA. NORTHWEST WINDS.
* TUESDAY...DRY/VFR. NORTHEAST WINDS.
* WEDNESDAY...CHANCE OF TSRA. EASTERLY WINDS.

KMD

&&

.MARINE...
226 PM CDT

OVERALL FLOW OVER THE LAKE HAS DIMINISHED TODAY...BUT WITH
WESTERLY WINDS ALONG THE NEARSHORE IN ILLINOIS INCREASING AT THIS
TIME. THESE INCREASING WESTERLY WINDS WILL LIKELY REACH THEIR PEAK
OVER THE NEXT COUPLE OF HOURS WITH A DIMINISHING TREND THEN
EXPECTED INTO THE EARLY EVENING...WITH THE CURRENT SMALL CRAFT
ADVISORY END TIME STILL ON TRACK TODAY. WESTERLY WINDS OF 10 TO 20
KT WILL LIKELY REMAIN THE GENERAL TREND TONIGHT INTO FRIDAY OVER
THE LAKE...WHILE A TROUGH/FRONTAL BOUNDARY APPROACH ON FRIDAY. OUT
AHEAD OF THESE FEATURES...WEST/NORTHWEST WINDS WILL LIKELY
INCREASE TO THE 20-25KT RANGE BY EARLY FRIDAY AFTERNOON...WITH
HAZARDOUS CONDITIONS FOR SMALL CRAFT BECOMING LIKELY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...10 AM
     FRIDAY TO 7 PM FRIDAY.

&&

$$

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