Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 011142
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
642 AM CDT SAT AUG 1 2015

.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...
234 AM CDT

SUNDAY NIGHT THROUGH FRIDAY...

THE ACTIVITY LEVEL WILL PERSIST FOR THE SECOND HALF OF THE
WEEKEND...AS THE 500MB TROUGH RETURNS TO THE GREAT LAKES WITH A
ROBUST SFC LOW QUICKLY LIFTING NORTHEAST ACROSS THE LOWER GREAT
LAKES REGION. ENSEMBLES CONTINUE A HIGH CONFIDENCE WITH PRECIP
SHIFTING EAST LATE SUN NGT...WITH ANTI-CYCLONIC FLOW BUILDING IN
FROM THE WEST. HAVE HELD ONTO PRECIP THRU DAYBREAK MON...HOWEVER
WITH THE NORTHWEST FLOW ARRIVING AND GENERALLY A MORE PROGRESSIVE
FLOW...IT IS POSSIBLE PRECIP MAY END SHORTLY AFTER MIDNIGHT SUN NGT.

MINIMAL SPREAD AMONGST THE ENSEMBLE MEMBERS CONTINUES IN THE
LONGWAVE PATTERN...WITH A HIGH AMPLITUDE RIDGE REMAINING ACROSS THE
WESTERN CONUS/ALASKA. THIS WILL ALLOW AN ANOMALOUSLY STRONG TROUGH
TO DIG INTO THE GREAT LAKES AND PRODUCE COOLER AIR FOR MUCH OF THE
REGION FROM TUE THRU FRI. OPERATIONAL SOLUTIONS INDICATE THE
SOUTHERN STREAM WILL BECOME SOMEWHAT ACTIVE...WITH A SERIES OF WAVES
RIDING ALONG A QUASI-STATIONARY BOUNDARY OVER THE TENN VALLEY NEXT
WEEK. CURRENTLY ANTICIPATE THE BULK OF THIS PRECIP WILL REMAIN
FURTHER SOUTH...HOWEVER A BUCKLE IN THE WAVE MAY OCCUR TUE INTO
EARLY WED AND COULD BRING A LOW CHC OF SHOWERS/THUNDER BACK TO THE
FORECAST AREA. FEEL THAT THIS MAY END UP TRENDING BACK SOUTH AS IT
APPEARS MORE FAVORABLE THAT NORTHERN IL WILL BE UNDER A STRONGER
INFLUENCE FROM THE SFC RIDGE.

MON APPEARS TO BE THE WARMEST DAY OF THE EXTENDED PERIOD...WITH
TEMPS GENERALLY IN THE LOW 80S. THEN THE 850MB THERMAL TROUGH
ARRIVES WITH WINDS SHIFTING NORTH/NORTHEAST...AND TEMPS FOR THE BULK
OF NEXT WEEK WILL BE IN THE MID/UPR 70S. LOWS WILL GENERALLY BE IN
THE UPR 50S TO LOW 60S THROUGHOUT THE EXTENDED.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* WEST WINDS PERSIST WITH SPEEDS BETWEEN 7-10KT...GUSTS DEVELOP
  MID-MORNING TO AROUND 20KT.

* BRIEF POCKET OF CIGS ARND 8KFT AGL MID-MORNING.

* WINDS TURN SOUTHWEST EARLY SUNDAY MORNING...INCREASING CHANCES
  FOR THUNDERSTORMS AFTER DAYBREAK SUNDAY.

BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE REMAINS CENTERED ACROSS THE TENN VALLEY...ALLOWING
WINDS TO REMAIN WESTERLY AGAIN TODAY. MIXING IS EXPECTED TO
INCREASE AND ALLOW WINDS TO BECOME GUSTY AT TIMES...NEARING
20-24KT. EARLY THIS MORNING A POCKET OF LIGHT RAIN WAS SLIDING
SOUTHEAST ACROSS SOUTHEAST MINNESOTA/SOUTHWEST WISC...ALTHOUGH IT
APPEARS THIS AREA OF PRECIP WAS DISSIPATING AS IT MOVED INTO MUCH
DRIER AIR. SOME CLOUDS ARND 8KFT AGL WILL ARRIVE ASSOCIATED WITH
THE DECAYING SHOWERS LATER THIS MORNING...HOWEVER NOT EXPECTED TO
LOWER VFR CONDS.

HIGH PRESSURE DRIFTS EAST TONIGHT...WITH WINDS SLOWLY TURNING
SOUTHWESTERLY. A LOW PRESSURE WILL DEVELOP OVER THE PLAINS EARLY
SUNDAY...WITH AN AREA OF SHOWERS AND THUNDERSTORMS EXPECTED TO
DEVELOP WITH THIS LOW. THE BEST TIMING TO ARRIVE ACROSS NORTHERN
IL/NORTHWEST IN DOES NOT APPEAR TO BE UNTIL AFTER DAYBREAK
SUN...AND MAY END UP BEING LATE MORNING SUNDAY. CONFIDENCE SEEMS
FAVORABLE FOR THUNDERSTORMS...SO HAVE GONE AHEAD AND MENTIONED A
PROB30 GROUP WITH THE CURRENT 30HR TAF AT ORD.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS THROUGH 00Z SUN.

* MEDIUM CONFIDENCE IN TAF SITES REMAINING DRY THRU LATE SUN
  NGT...THEN BEST TIMING FOR THUNDERSTORMS APPEARS TO BE AFTER
  DAYBREAK SUN.

BEACHLER

//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...
234 AM CDT

WEST WINDS WILL PERSIST ACROSS THE LAKE AGAIN TODAY...AS
HIGH PRESSURE CENTERED OVER THE OHIO VALLEY. WINDS WILL BECOME GUSTY
AGAIN TODAY...BUT SHOULD REMAIN WITHIN A 15 TO 25 KT RANGE. SO WILL
NOT HOIST ANY SMALL CRAFT ADVISORY AT THIS TIME.

TONIGHT THE HIGH WILL SHIFT FURTHER EAST...ALLOWING WINDS TO SLOWLY
TURN SOUTHWESTERLY. A MUCH STRONGER LOW PRESSURE SYSTEM WILL ARRIVE
ACROSS THE WESTERN GREAT LAKES SUNDAY AND PASS OVER THE NORTHERN
PORTIONS OF THE LAKE SUN AFTERNOON/EVENING. THIS WILL PRODUCE A
TIGHT GRADIENT FOR THE SOUTHERN HALF OF THE LAKE...AND COULD ALLOW
GUSTS TO APPROACH 30KT WITH A FEW GALE FORCE GUSTS POSSIBLE. WILL
LIKELY NEED TO ISSUE A SMALL CRAFT ADVISORY FOR SUNDAY AND MAY
LINGER INTO SUNDAY NIGHT. THE LOW THEN QUICKLY LIFTS NORTHEAST BY
EARLY MONDAY...AS WINDS SHIFT NORTHWEST TO NORTH EARLY NEXT WEEK.
THEN WINDS WILL MAINLY BE FROM THE NORTH THROUGH MUCH OF THE
UPCOMING WEEK.

BEACHLER

&&

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

$$

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