Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 011949
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 PM CDT SAT AUG 1 2015

.UPDATE...
1105 AM CDT

GOING FORECAST LARGELY IN GOOD SHAPE...AND JUST MADE TWEAKS TO
HOURLY TEMPERATURE...DEWPOINT AND SKY TRENDS. STILL EXPECTING
HIGHS IN THE MID 80S TO AROUND 90...HIGHEST IN THE CHICAGO HEAT
ISLAND AS HAS BEEN TYPICAL THE PAST WEEK. IN FACT...IF MIDWAY AND
THE MIDWAY COOP REACH 90 AGAIN TODAY...IT WILL BE THE 6TH
CONSECUTIVE 90 DEGREE DAY AT THOSE SITES. DEWPOINTS ARE TRYING TO
CREEP UP SOME TODAY...BUT DRY WEDGE ALOFT NOTED ON 12Z RAOBS
CONTINUING TO KEEP DEWPOINTS IN 50S TO LOW 60S. THUS ANOTHER DAY
OF WARM TEMPERATURES BUT COMFORTABLE HUMIDITY LEVELS FOR THE FIRST
DAY OF AUGUST.

W/V SHOWS WEAK DISTURBANCE OVER SOUTHERN WISCONSIN PRODUCING
MIDLEVEL CLOUD COVER OVER SOUTHERN WI AND PORTIONS OF NORTHERN IL.
TRAJECTORY OF ISOLATED SHOWER ACTIVITY OVER SOUTHERN WI FAVORS
THESE SHOWERS AT MOST CLIPPING FAR NORTHEAST ILLINOIS OVER THE
NEXT 1 TO POSSIBLY 2 HOURS...SO JUST HAVE SLIGHT CHANCE POPS IN
THAT AREA...WITH DRY CONDITIONS EXPECTED THE REST OF THE AFTERNOON
AND EVENING BEHIND THIS WAVE.

RC

&&

.SHORT TERM...
330 AM CDT

THROUGH SUNDAY...

THE MAIN FOCUS DURING THE SHORT TERM PERIOD WILL BE WITH REGARDS TO
CONVECTIVE CHANCES LATER TONIGHT THROUGH SUNDAY...WITH THE
POTENTIAL OF SEVERE STORMS...ESPECIALLY SUNDAY AFTERNOON/EVENING.

TODAY LOOKS TO BE ANOTHER WARM AND DRY DAY ACROSS THE REGION.
HOWEVER...THE CURRENT FORECAST HAS A SLIGHT CHANCE MENTION OF A
SHOWER OR TWO THIS MORNING OVER FAR NORTHERN ILLINOIS AND I HAVE
OPTED TO LEAVE THIS CHANCE GOING AS A WEAK DISTURBANCE SHIFTS EAST-
SOUTHEASTWARD ACROSS SOUTHERN WISCONSIN AND OVER SOUTHERN LAKE
MICHIGAN LATER THIS MORNING. REGIONAL RADAR IMAGERY INDICATES THAT A
FEW ISOLATED SHOWERS HAVE DEVELOPED OVER SOUTHEASTERN MINNESOTA...IN
ASSOCIATION WITH THIS DISTURBANCE. ANY SHOWERS THAT OCCUR WILL BE
SHORT LIVED AND SPOTTY IN COVERAGE...SO IT SHOULD NOT BE A BIG DEAL.
OTHERWISE...EXPECT TEMPERATURES TO AGAIN CLIMB INTO THE MID TO UPPER
80S AGAIN UNDER MAINLY SUNNY SKIES. DEWPOINTS WILL BEGIN A SLOW
INCREASE TODAY AS THE FLOW BEGINS TO SHIFT WEST-
SOUTHWESTERLY...THOUGH THE BETTER DEWPOINTS WILL LIKELY NOT GET HERE
UNTIL TONIGHT INTO SUNDAY.

A FAST NORTHWESTERLY UPPER LEVEL PATTERN WILL PERSIST ACROSS THE
CENTRAL CONUS THROUGH THE PERIOD. WITHIN THIS PATTERN...MID LEVEL
HEIGHT FALLS ASSOCIATED WITH A SHORT WAVE IMPULSE...CURRENTLY OVER
MONTANA...IS EXPECTED TO FOCUS/ENHANCE A VEERING WEST-SOUTHWESTERLY
LOW LEVEL JET ACROSS THE MID MISSOURI AND INTO THE UPPER MISSISSIPPI
VALLEYS TONIGHT. THIS SHOULD PROMOTE A FOCUS FOR THUNDERSTORMS TO
GROW UPSCALE INTO ONE OR TWO MCS`S OVER NORTHERN IOWA AND ADJACENT
PORTIONS OF SOUTHERN MINNESOTA AND WISCONSIN OVERNIGHT. THESE STORMS
WILL THEN LIKELY TREND TO THE EAST-SOUTHEAST TOWARDS NORTHERN
ILLINOIS BY EARLY SUNDAY MORNING. THE MAIN THREAT FROM THESE STORMS
WOULD BE STRONG GUSTY WINDS OVER FAR NORTHERN ILLINOIS.
HOWEVER...THESE STORMS COULD END UP COMING ACROSS NORTHERN ILLINOIS
EARLY SUNDAY MORNING IN A WEAKENING PHASE...SO THE EXTENT OF ANY
STRONG TO SEVERE STORMS WITH THIS FIRST WAVE IS UNCERTAIN.

THIS INITIAL WAVE OF REMNANT STORMS IS EXPECTED TO DISSIPATE AND
SHIFT OUT OF THE AREA BY MIDDAY SUNDAY. ATTENTION THEN TURNS TO
ANOTHER SIGNIFICANT DISTURBANCE EXPECTED TO DIG SOUTHEASTWARD OVER
THE UPPER GREAT LAKES REGION DURING THE DAY SUNDAY. STRONG HEIGHT
FALLS ASSOCIATED WITH THIS DISTURBANCE WILL LIKELY STRENGTHEN A
SURFACE COLD FRONTAL TROUGH OVER THE GREAT LAKES REGION AND DRIVE
IT SOUTHWARD OVER THE REGION BY SUNDAY EVENING. THE PREFRONTAL
AIRMASS LOOKS TO BECOME QUITE UNSTABLE ACROSS THE AREA AS STEEP
MID-LEVEL LAPSE RATES ASSOCIATED WITH AN EML GET ADVECTED EASTWARD
ATOP A VERY WARM AND MOIST BOUNDARY LAYER. ASSUMING THAT ANY
MORNING CLOUD COVER FROM REMNANT NOCTURNAL CONVECTION CLEARS
OFF...WHICH IT CURRENTLY APPEARS WILL BE THE CASE...TEMPERATURES
COULD WARM INTO THE UPPER 80S TO POSSIBLY LOW 90S...WITH DEW
POINTS LIKELY TO RECOVER BACK INTO THE MID TO UPPER 60S. THIS
WOULD SUGGEST THAT MLCAPE VALUES COULD GET IN EXCESS OF 2500 J/KG
BY SUNDAY AFTERNOON OVER THE AREA. SO...WITH THE PRESENCE OF STEEP
MID-LEVEL LAPSE RATES...ALONG WITH 30-35 KT OF BULK LAYER
SHEAR...THERE CERTAINLY APPEARS TO BE SOME POTENTIAL FOR SOME
STRONG TO SEVERE THUNDERSTORMS OVER THE AREA LATE SUNDAY AFTERNOON
AND INTO THE EVENING AS THE COLD FRONT SHIFTS OVER THE AREA. AT
THIS TIME...IT APPEARS THAT LARGE HAIL AND DAMAGING WINDS WOULD BE
THE MAIN THREATS WITH THESE POTENTIAL STORMS.

IT ALSO APPEARS THAT IT WILL BE A BIT ON THE WINDY SIDE OVER THE
AREA ON SUNDAY. WITH THE COLD FRONTAL TROUGH OF LOW PRESSURE
EXPECTED TO STRENGTHEN OVER WISCONSIN SUNDAY...THE PRESSURE GRADIENT
WILL STRENGTHEN...AND THIS LOOKS TO SUPPORT SOME HEALTHY
SOUTHWESTERLY SURFACE WINDS. CURRENTLY IT APPEARS THAT 20 TO 25 MPH
WINDS WITH GUSTS OF 35 MPH CAN BE EXPECTED SUNDAY AFTERNOON.

KJB

&&

.LONG TERM...
248 PM CDT

LATE SUNDAY NIGHT THROUGH SATURDAY...

PERIOD WILL BEGIN WITH SHOWER/THUNDERSTORM ACTIVITY LIKELY
EXITING TO THE EAST WITH EASTWARD MOVING SURFACE TROUGH/FRONTAL
BOUNDARY. DID LEAVE CHANCE POPS ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA WITH SLIGHT CHANCE ACROSS PORTIONS OF NORTHERN
ILLINOIS AFTER THE MIDNIGHT TIME FRAME. HOWEVER...THERE IS THE
POTENTIAL FOR ANY THUNDERSTORM DEVELOPMENT TO DEPART THE AREA
SLIGHTLY SOONER...ESPECIALLY IF A LINE OF CONVECTION WERE TO
DEVELOP. AFTER THIS POTENTIAL FOR PRECIP...EARLY NEXT WEEK APPEARS
TO BE ON THE DRIER SIDE...AND HAVE REMOVED POPS DURING THIS TIME.
NORTHWEST FLOW WILL BE IN PLACE ACROSS THE AREA AS LARGE SCALE
PATTERN WILL BE DICTATED BY LARGE UPPER LEVEL CENTER SLOWLY
DROPPING SOUTHEAST THROUGH SOUTHERN CANADA. WITH ANY STRONGER MID
LEVEL FEATURES REMAINING TO THE NORTH AND TO THE SOUTHWEST OF THE
AREA...PRECIP DEVELOPMENT WILL STAY OUTSIDE OF THE CWA.
HOWEVER...THIS WILL PROVIDE COOLER AND DRIER CONDITIONS WITH
INITIALLY NORMAL HIGH TEMPS IN THE LOW 80S LIKELY ON MONDAY...BUT
WITH A TREND TOWARDS BELOW NORMAL HIGH TEMPS IN THE 70S BY MID
WEEK. GUIDANCE IN FAIR AGREEMENT WITH TAKING THIS UPPER LEVEL LOW
TO THE EAST LATER IN THE WORK WEEK...WITH BETTER POTENTIAL FOR
UPSTREAM ENERGY AND PRECIP TO WORK ITS WAY TOWARDS THE AREA.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* WSWLY WINDS WITH SPEEDS ARND 10-12 KT AND GUSTS TO ARND 18KT
  VEERING BACK TO WNWLY THROUGH THE AFTERNOON. GUSTINESS SUBSIDING
  AT SUNSET.

* WINDS TURN SOUTHWEST EARLY SUNDAY MORNING AND INCREASING 15-20KT
  SUSTAINED WITH GUSTS UP TO 25-30KT.

* ANOTHER CHANCE FOR THUNDERSTORMS SUNDAY EVENING.

KREIN

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

STRENGTHENING WLY-WNWLY WINDS ARE INCREASING ACROSS THE REGION AS
DEEP LOW PRESSURE SITS OVER HUDSON BAY AND HIGH PRESSURE SETTLES
INTO THE MIDDLE MISSISSIPPI AND OHIO VALLEYS. A VERY WEAK MID
LEVEL IMPULSE MOVING THROUGH THE FAST NWLY FLOW ALOFT HAS
GENERATED SOME MID CLOUD WITH BASES ARND 8KFT AND A FEW ISOLD
SHRA. HOWEVER...WHAT LITTLE MID LEVEL FORCING THERE IS ASSOCIATED
WITH THE WEAK IMPULSE WILL REMAIN NORTHEAST OF THE TERMINALS AND
NO PCPN IS EXPECTED. THE REMAINDER OF THE NIGHT SHOULD BE QUIET
WITH WINDS DIMINISHING TO ARND 10KT AT SUNSET.

THE NEXT CONCERN WILL BE THE POTENTIAL FOR THUNDERSTORMS OVER THE
AREA TOMORROW. THERE IS STILL SOME SPREAD IN THE FORECAST MODEL
SOLUTIONS FOR THE EXACT TIMING OF TS OVER NRN IL/IN.  HOWEVER...
THE GENERAL IDEA IS FOR A STRONGER MID LEVEL IMPULSE TO CROSS NRN
IL/IN TOMORROW MORNING WHICH SHOULD GENERATE SOME SHOWERS AND
THUNDERSTORMS. THE MAIN ISSUE IS TIMING. SOME GUIDANCE IS
SUGGESTING THAT THE PREFERRED TIMING WILL BE DURG THE EARLY
MORNING HOURS WHILE OTHER MODELS FAVOR A SLOWER SOLUTION WITH THE
HIGHER TS POTENTIAL DURG THE LATE MORNING HOURS. GIVEN THE TIMING
UNCERTAINTY AT THIS POINT...WILL MAINTAIN THE TIMING OF THE GOING
FORECAST. THE REMAINDER OF SUNDAY ALSO HAS SOME UNCERTAINTY FOR
THE POTENTIAL FOR ADDITIONAL TS CHANCES THROUGH THE REMAINDER OF
THE DAY. STRONG SWLY FLOW AT 5KFT AND INCREASING SFC HEAT AND
HUMIDITY WILL BE CONDUCIVE TO TS DEVELOPMENT AHEAD OF A COLD
FRONT DROPPING SOUTH THROUGH THE UPPER MISSISSIPPI VALLEY AND
WESTERN GREAT LAKES. LATEST MODEL SOUNDINGS INDICATE THAT THERE
SHOULD BE AN ELEVATED INVERSION...WHICH COULD DELAY ANY TS UNTIL
THE FRONT ACTUALLY CROSSES THE AREA TOMORROW EVENING.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS THROUGH 06Z SUNDAY.

* LOW CONFIDENCE IN TIMING/COVERAGE/DURATION OF TS IMPACTING THE
  TERMINALS SUNDAY MORNING.

KREIN

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

SUNDAY NIGHT...MAINLY VFR. CHANCE OF SHRA/TSRA EARLY IN THE
EVENING.

MONDAY...MAINLY VFR. NORTHWEST WINDS.

TUESDAY...SLIGHT CHANCE OF SHRA. NORTHWEST WINDS BECOMING NORTHEAST.

WEDNESDAY...CHANCE OF SHRA/SLIGHT CHANCE OF TSRA. NORTHEAST
            WINDS.
THURSDAY AND FRIDAY...CHANCE OF SHRA. EAST WINDS.

BEACHLER

&&

.MARINE...
248 PM CDT

WESTERLY WINDS IN PLACE TODAY AS LOW PRESSURE REMAINS TO THE
NORTH AND WHILE HIGH PRESSURE IS SITUATED OVER THE SOUTHERN PLAINS
TO THE MID MISSISSIPPI VALLEY. EXPECT WINDS TO BECOME MORE
SOUTHWEST THROUGH THE AFTERNOON AND INTO THE EVENING...WITH SPEEDS
THEN EXPECTED TO INCREASE THROUGH THE NIGHT. SOUTHWEST WINDS WILL
THEN REALLY INCREASE ON SUNDAY WITH THE APPROACH OF A SEPARATE
SYSTEM AND WITH THE HIGHEST WINDS/GUSTS LIKELY FROM LATE SUNDAY
MORNING THROUGH EARLY SUNDAY EVENING. HAVE INCREASED WINDS DURING
THIS TIME FRAME TO 30KT FOR BOTH THE NEARSHORE AND OPEN
WATERS...BUT PRIMARILY FOR THE SOUTHERN HALF. THERE IS SOME
POTENTIAL FOR OCCASIONAL GALE FORCE GUSTS IN THE AFTERNOON...BUT
THIS WILL BE MAINLY FOR THE NEARSHORE WATERS. WINDS WILL DIMINISH
SUNDAY NIGHT INTO MONDAY...WHILE THEY TURN MORE WEST/NORTHWEST.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM SUNDAY TO 10 PM SUNDAY.

&&

$$

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