Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 011926
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
226 PM CDT FRI AUG 1 2014

.DISCUSSION...
143 PM CDT

THIS EVENING THROUGH TONIGHT...
VISIBLE IMAGERY THIS AFTERNOON SHOWS A CIRRUS SHIELD FLOATING
OVERHEAD...WITH SOME POCKETS OF CUMULUS BUILDING ACROSS THE REGION.
THE LAKE BREEZE WAS BEGINNING TO BE DEPICTED WELL ALONG THE
LAKESHORE...WHICH WAS CREATING A LLVL CONVERGENCE ZONE AND ALLOWING
SOME OF THE CUMULUS CLOUDS TO ENHANCE SLIGHTLY. SFC TEMPS THIS AFTN
HAVE BEEN ABLE TO WARM INTO THE UPR 70S TO LOW 80S...WITH DEW POINTS
GENERALLY AROUND 60 DEGREES. ACARS SOUNDINGS INDICATE THE MORNING
CAPPED ENVIRONMENT HAS DISSOLVED WITH VERY SKINNY CAPE ACROSS THE
FORECAST AREA. GIVEN THE LACK OF SHEAR THROUGHOUT THE
COLUMN...AROUND 10-20KTS...IT DOES NOT APPEAR ANY CONVECTION THAT
DEVELOPS WILL BE ABLE TO PUSH TOWARDS SEVERE LIMITS. HOWEVER A FEW
HAVE BEEN ABLE TO STRENGTHEN AND PRODUCE AROUND 0.5" DIAMETER HAIL
AND A BRIEF GUST TO 50 MPH. THE LARGEST CONCERN OF ANY WILL BE THE
SLOW MOVING NATURE OF THE CONVECTION...WHICH WILL LIKELY INCREASE
THE CONCERN FOR LOCALIZED PONDING/FLOODING.

THE ATMOSPHERE WILL REMAIN UNSTABLE THROUGH EARLY THIS EVENING...AND
EXPECT ONCE SUNSET OCCURS THE MINIMAL COVERAGE OF STORMS WILL BECOME
EVEN LESS THROUGHOUT THE LATE EVENING HOURS.

TONIGHT...INSTABILITY WILL CONTINUE TO WEAKEN THROUGH THE OVERNIGHT
HOURS. MID-LVL TROUGH AXIS WILL CONTINUE TO PIVOT EAST OVER THE
FORECAST AREA TONIGHT...WHICH WILL ALSO BRING LESS FOCUS FOR PRECIP.
SO HAVE TRENDED DRY OVERNIGHT. HOWEVER WITH THE LACK OF DRYING AT
THE SFC...LLVL MOISTURE SHUD REMAIN AND THE COMBINATION OF LIGHT
WINDS WILL LIKELY ALLOW FOR PATCHY FOG TO DEVELOP. AT THIS TIME
EXPECT VSBYS TO NOT GO BELOW 2SM...ALTHOUGH COULD SEE A FEW POCKETS
WHERE AFTN RAINFALL COULD FURTHER REDUCE VSBYS TO ARND 1SM.

SATURDAY THROUGH SUNDAY...
HIGH AMPLITUDE RIDGE ACROSS THE WESTERN CONUS WILL KEEP THE
CONTINUED NORTHWEST FLOW IN PLACE FOR THE GREAT LAKES REGION THROUGH
SAT AND LIKELY INTO SUN. GUIDANCE CONTINUES TO INDICATE A LULL IN
ACTIVITY TO START THE DAY SAT...WITH A LACK OF ANY WAVES OVERHEAD.
ALTHOUGH BY MIDDAY SAT THERE IS A WEAK MID-LVL WAVE SLIDING
SOUTHEAST ACROSS THE WESTERN GREAT LAKES. THIS COMBINED WITH WEAK
SFC INSTABILITY COULD LEAD TO A FEW SPOTTY SHOWERS/THUNDERSTORMS TO
ONCE AGAIN DEVELOP. THERE DOES APPEAR TO BE ANOTHER LAKE BREEZE FOR
SAT/SUN...WHICH WOULD ALSO ADD TO THE LOCALIZED CONVERGENCE AND
FOCUS A FEW PULSE STORMS. TEMPS SHUD AGAIN NEAR SEASONAL CONDS
SAT/SUN WITH HIGHS GENERALLY ARND 80 BOTH DAYS. DEPENDING ON THE
TIMING OF THE LAKE BREEZE...TEMPS DOWNTOWN CHICAGO COULD HOLD IN THE
UPR 70S BEFORE FALLING INTO THE LOW 70S BEHIND THE LAKE BREEZE.

MONDAY THROUGH END OF NEXT WEEK...
ENSEMBLES IN THE LONG RANGE APPEAR TO BE SUGGESTING THE NORTHERN
ATLANTIC BLOCK WILL WEAKEN...ALLOWING THE PERSISTENT TROUGH OVER THE
GREAT LAKES TO PIVOT EAST AND FLATTEN THE WESTERN RIDGE LATER IN THE
WEEK. THIS POINTS TOWARDS AN INCREASE IN THE ACTIVITY OF SYSTEMS
SLIDING WEST TO EAST ACROSS THE NORTHERN CONUS. SO PERIODIC CHANCES
FOR SHOWERS/STORMS IN THE EXTENDED LOOKS PROBABLE. TEMPS SHOULD BE
SLIGHTLY SUB-SEASONAL THROUGH THE FIRST HALF OF NEXT WEEK...THEN
SLOWLY WARM BACK INTO THE LOWER 80S TOWARDS THE END OF THE EXTENDED
PERIODS.

BEACHLER

&&

.AVIATION...

//OED AND MD CONCERNS...UPDATED 18Z...

* SCATTERED SHRA/TSRA THIS AFTERNOON.
* LAKE BREEZE LIKELY BY MID-LATE AFTERNOON.
* WIND DIRECTION MAY BE BRIEFLY COMPLICATED BY TSRA OUTFLOW WITH
  HIGHER SPEEDS UP TO 30 KT POSSIBLE.

KJB

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

SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP ACROSS THE AREA
THIS AFTERNOON AS AN UPPER LEVEL DISTURBANCE MOVES ACROSS THE AREA.
A LAKE BREEZE IS EVIDENT CURRENTLY RIGHT ALONG THE LAKE SHORE AND
THE EXPECTATION IS THAT THE LIGHT WIND REGIME WILL ALLOW THIS
BOUNDARY TO PUSH INLAND OVER THE EASTERN TERMINALS BY MID TO LATE
THIS AFTERNOON. UNFORTUNATELY...HOWEVER...THE TIMING OF THIS BOUNDARY
MOVING OVER THE TERMINALS THIS AFTERNOON HAS DIMINISHED SOME...AS IT
APPEARS SOME OF THE OUTFLOW FROM THE STORM CURRENTLY MOVING OVER MDW
COULD DELAY OR PUSH THE LAKE BREEZE BOUNDARY BACK OVER THE LAKE FOR
A PERIOD. ONCE THIS BOUNDARY DOES MOVE OVER THE TERMINALS...THE MAIN
THREAT FOR SCATTERED CONVECTIVE ACTIVE SHOULD SHIFT TO THE WEST AND
SOUTH OF THE MAIN EASTERN TERMINALS WITH AN EASTERLY WIND SHIFT.

KJB

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

* MEDIUM WITH TSRA NEAR THE TERMINALS THROUGH AROUND 21 UTC THIS
  AFTERNOON.
* LOW-MEDIUM WITH LAKE BREEZE TIMING THIS AFTERNOON.
* LOW CONFIDENCE IN WIND DIRECTION IF AFFECTED BY TSRA OUTFLOW.

KJB

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

SATURDAY NIGHT...DRY/VFR.

SUNDAY...SLGT CHC AFTN/EVE TSRA...OTHERWISE VFR.

MONDAY THROUGH THURSDAY...CHANCE OF SHRA/TSRA.

RATZER

&&

.MARINE...
226 PM CDT

NO MAJOR CONCERNS FOR THE LAKE THROUGH THE PERIOD. A WEAK SURFACE
TROUGH WILL PASS THROUGH THE LAKE THROUGH TONIGHT. BROAD HIGH
PRESSURE ACROSS THE PLAINS AND EXTENDING INTO THE UPPER MIDWEST AND
THROUGH THE OHIO VALLEY WILL MOVE OVERHEAD SATURDAY AND THROUGH THE
WEEKEND. AS THE HIGH BUILDS IN...WINDS WILL TURN NORTHERLY ACROSS
THE LAKE...AND THEN GENERALLY BECOME LIGHT AND VARIABLE SATURDAY
NIGHT. WITH THE WEAK PRESSURE GRADIENT EXPECT LAKE BREEZES TO
CONTINUE INTO SUNDAY. ANOTHER WEAK LOW WILL PASS BY TO THE NORTH OF
THE LAKE EARLY SUNDAY THAT WILL TIGHTEN THE GRADIENT WILL BIT SUNDAY
ACROSS THE NORTHERN PART OF THE LAKE IN WITH SOUTH WINDS INCREASING
BUT STILL REMAINING UNDER 15 KT OR SO. A WEAK FRONT ASSOCIATED WITH
THIS LOW WILL THEN DISSIPATE WITH THE GRADIENT AGAIN BECOMING RATHER
WEAK SUNDAY NIGHT INTO MONDAY. LONGER RANGE GUIDANCE HAS BACKED OFF
ON THE EASTWARD MOVEMENT OF A SOMEWHAT STRONGER LOW OVER THE
PLAINS...THUS WITH HIGH PRESSURE TO THE NORTH OR OVERHEAD EXPECT
NORTH TO NORTHEAST WINDS FOR SOMETIME BEFORE SHIFTING MORE SOUTHERLY
LATER IN THE WEEK. WAVES GENERALLY REMAIN 2 FT OR LESS FOR THE
FORSEEABLE FUTURE.

KMD

&&

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

$$

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