Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 110914
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
414 AM CDT FRI JUL 11 2014

.DISCUSSION...
259 AM CDT

TODAY...
LARGEST FOCUS FOR THE DAY WILL BE ON THE GRADUAL DEPARTURE TO THE
SFC RIDGE...WHICH GUIDANCE HAS SLOWED SLIGHTLY. THIS SHUD ALLOW FOR
A MOSTLY DRY DAY...HOWEVER AS THE EVENING PROGRESSES AND HIGHER DEW
PTS STEADILY ADVECT NORTH ACROSS THE FORECAST AREA...PRECIP CHANCES
WILL STEADILY INCREASE. AT THIS TIME CONFIDENCE IS HIGH THAT ANY
PRECIP WILL NOW HOLD OFF UNTIL AFT 00Z...SO HAVE PUSHED THE TIMING
BACK A FEW HOURS. THE THERMAL TROUGH THAT HELPED TO KEEP TEMPS DOWN
A FEW DEGREES WILL ALSO DEPART TODAY...HOWEVER CLOUDS WILL BE
STEADILY ON THE INCREASE THROUGHOUT THE AFTERNOON. BUT EXPECT TEMPS
REBOUNDING INTO THE UPR 70S TO LOW 80S. WINDS SHUD BE GENERALLY
SOUTHERLY...THE ONLY EXCEPTION COULD BE FAR NORTHEAST IL WHERE WINDS
MAY BE SLIGHTLY TURNED FROM THE SOUTHEAST AND USHER IN SLIGHTLY
COOLER AIR INTO NORTHEAST LAKE COUNTY.

TONIGHT THROUGH SATURDAY...
AS PREVIOUSLY NOTED...HAVE PUSHED BACK THE TIMING OF THE PRECIP
UNTIL AFT 00Z. SOME WEAK DIFFLUENCE IN THE MID-LVLS IS STILL
PRESENT...ALTHOUGH STEADILY WEAKENING AS THE EVENING PROGRESSES.
WARM/MOIST AIR WILL CONTINUE TO ADVECT NORTH INTO THE FORECAST
AREA...WITH SKIES BECOMING MOSTLY CLOUDY. INSTABILITY AT THE ONSET
IS NOT SIGNIFICANT...SO EXPECT THE LEADING EDGE OF THE PRECIP TO
PERHAPS NOT HAVE MUCH CONVECTION WITH IT. THIS WILL HOWEVER CHANGE
AS THE OVERNIGHT HOURS PROGRESS INTO SAT MORNING. HI-RES LCL ARW8KM
HAS FOR A FEW CYCLES BEEN SUGGESTIVE OF A LOBE OF VORTICITY SLIDING
EAST/SOUTHEAST ACROSS IA/CENTRAL IL AFT 09Z SAT THEN TURNING
SOUTHEAST. PWAT VALUES CONTINUE TO BE PROGGED AT 3 TO 4 SIGMA...OR
HOVERING AT 2" FOR MUCH OF THE FORECAST AREA. SO ANY CONVECTION THAT
DEVELOPS COULD EASILY PRODUCE SOME BRIEF HEAVY DOWNPOURS.

SAT MORNING MAY FEATURE A BRIEF LULL IN THE ACTIVITY...DESPITE THE
HIGH DEW PTS THAT WILL CONTINUE TO ADVECT NORTH/NORTHEAST ACROSS THE
REGION. A FEW SOLUTIONS HAVE CONTINUED TO POINT TOWARDS DEW PTS
NEARING THE MID 70S BY SAT AFTN. SO A VERY HUMID ENVIRONMENT IS IN
SHAPE FOR SAT...FORTUNATELY ABUNDANT CLOUD COVER WILL KEEP TEMPS
FROM GETTING TOO OUT OF CONTROL. THUS HAVE ONLY MADE MINOR
ADJUSTMENTS TO THE AFTN HIGHS...WHICH WILL GENERALLY BE IN THE
LOW/MID 80S.

THE FOCUS FOR ADDTL CONVECTIVE DEVELOPMENT WILL BE ON THE SHORTWAVE
PROGGED TO BE LIFTING INTO THE CENTRAL PLAINS SAT AFTN. THE MAIN
TROUGH AXIS WILL BE STARTING TO DIG INTO THE NORTHERN PLAINS SAT
AFTN/EVE...WHICH WILL AID IN INCREASING THE SOUTHWEST LLVL FLOW SAT
EVE FOR THE FORECAST AREA. THIS COUPLED WITH INCREASING
SHEAR...COULD AID IN THE POTENTIAL FOR STRONG TO PERHAPS SEVERE
STORMS TO DEVELOP SAT EVE. GENERAL STORM MOTION SHOULD BE WEST-EAST.

CONFIDENCE...MEDIUM/HIGH.

SUNDAY THROUGH THURSDAY...
FOCUS FOR THE SECOND HALF OF THE WEEKEND INTO NEXT WEEK WILL BE THE
UNSEASONABLY COOL WEATHER EXPECTED FOR NEXT WEEK. ALTHOUGH PRIOR TO
THE ARRIVAL...SUN WILL FEATURE A COUPLE BOUNDARIES PUSHING EAST
ACROSS THE REGION. A WEAK BOUNDARY SHUD BE ORIENTED FROM NORTHERN MO
STRETCHING NORTHEAST THRU SOUTHERN MI...WITH A SECONDARY WAVE
APPROACHING THE REGION LATE SUN NGT/EARLY MON. THE 500MB VORT WILL
BE ARRIVING OVER THE UPPER MIDWEST LATE SUN...WITH A FEW WEAK LOBES
OF VORTICITY PIVOTING ARND THE AXIS. 850MB THERMAL TROUGH WILL ONLY
CONTINUE TO COOL AS TIME PROGRESSES...AND EXPECT BY TUE TEMPS ALOFT
TO NEAR -3 SIGMA. ENSEMBLES HAVE MAINTAINED A HIGH CONFIDENCE WITH
MINIMAL SPREAD FOR NUMEROUS CYCLES. BASED ON THE PATTERN OF A HIGH
AMPLITUDE RIDGE DEVELOPING ACROSS THE WESTERN CONUS/CANADA...THIS
WILL TRANSLATE INTO A DEEP/STRONG TROUGH FOR THE GREAT LAKES. EXPECT
TEMPS TUE TO STRUGGLE TO WARM BEYOND THE UPR 60S FOR SOME LOCATIONS
NORTH OF I-80...AND PERHAPS ARND 70 ELSEWHERE.

AS THE EXTENDED PERIODS PROGRESS...THE POTENCY OF THE TROUGH BEGINS
TO MODERATE AND TEMPS START TO WARM GENERALLY INTO THE MID 70S WITH
BROAD SFC RIDGING BUILDING IN.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* POTENTIAL FOR A LAKE BREEZE THIS AFTERNOON/EVENING


KMD

//DISCUSSION...UPDATED 06Z...

VFR CONDITIONS WILL PREVAIL AT THE TERMINALS THROUGH AT LEAST THE
NEXT 24 HOURS WITH HIGH PRESSURE INCHING EAST AWAY FROM THE
REGION. E TO ESE WINDS WILL CONTINUE TO DROP OFF AND LIKELY GO
LIGHT AND VARIABLE IN MANY LOCATIONS THOUGH DIRECTION SHOULD
GENERALLY VEER TOWARDS THE SOUTH. WINDS WILL PICK UP OUT OF THE
SOUTH AROUND 10 KT OR SO DURING THE DAY FRIDAY. A LAKE BREEZE IS
EXPECTED TO FORM...HOWEVER IT IS UNSURE AT THIS POINT WHETHER OR
NOT IT WILL HAVE A STRONG ENOUGH PUSH TO MAKE IT ACROSS THE
TERMINALS. SOME OF THE HIGHER RESOLUTION GUIDANCE IS HINTING AT A
SHIFT TO SE WINDS AT KMDW BUT GENERALLY KEEPS SPEEDS ON THE
LIGHTER SIDE. WITH A SSW WIND AROUND OR SLIGHTLY ABOVE 10 KT...A
LAKE BREEZE WOULD LIKELY SLOWLY PUSH INTO NORTHERN COOK COUNTY
TOWARDS ORD...BUT MAY BE STOPPED SHY OF THE TERMINAL. WILL
CONTINUE WITH THIS REASONING FOR NOW BUT OBVIOUSLY THIS IS A SITUATION
THAT WILL HAVE TO BE MONITORED...AND THE PICTURE MAY BECOME MORE
CLEAR AS IT STARTS TO COME IN RANGE OF MORE OF THE HIGHER-RES
MODEL SOLUTIONS OVERNIGHT AND EARLY TOMORROW.

CONCERNS WILL SHIFT TO POTENTIAL FOR THUNDERSTORMS AFTER 6Z...BUT
WILL GIVE THIS A CLOSER LOOK WITH THE 12Z TAF PACKAGE.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* LOW CONFIDENCE IN LAKE BREEZE REACHING TERMINALS FRIDAY.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

KMD

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

SATURDAY...TSRA. MVFR/IFR PSBL.
SUNDAY THROUGH TUESDAY...PERIODIC CHANCES FOR TSRA/SHRA. PRIMARILY VFR.
WEDNESDAY...VFR.

BMD

&&

.MARINE...
332 AM CDT

HIGH PRESSURE HAS SHIFTED TO THE EASTERN GREAT LAKES EARLY THIS
MORNING...AND WINDS HAVE TURNED MORE SOUTHERLY ACROSS THE LAKE.
EXPECT SPEEDS TO INCREASE TODAY IN RESPONSE TO A STRONGER GRADIENT
CREATED BY LOW PRESSURE CENTERED IN NORTHERN MANITOBA AND INTO THE
NORTHERN PLAINS. THE STRONGER GRADIENT WILL BE OVER THE NORTHERN
HALF OF THE LAKE...WHERE SOUTH WINDS INCREASE TO 15 TO 25 KT...WHILE
THE SOUTH HALF WILL SEE S TO SE WINDS AT 10-20 KT. WINDS DIMINISH
SATURDAY AS A TROUGH OF LOW PRESSURE MOVES OVERHEAD AND BECOME
SOUTHWEST SATURDAY NIGHT.

A LOW PASSES WELL NORTH OF THE LAKE SATURDAY NIGHT AND SUNDAY AND
ITS COLD FRONT SWINGS OVER THE LAKE SUNDAY MORNING. WINDS BECOME
WEST BEHIND THE FRONT MAINLY FOR THE NORTHERN HALF...AND THEN A
SECOND FRONT PUSHES DOWN THE LAKE SUNDAY NIGHT INTO MONDAY BEFORE
FINALLY CLEARING THE LAKE MONDAY EVENING.  WINDS WILL BECOME NORTH
TO NORTHWEST 10-20 KT BEHIND THE FRONT.  WINDS DIMINISH LATE TUESDAY
NIGHT AND THEN HIGH PRESSURE MOVES OVER THE LAKE WEDNESDAY NIGHT.

KMD

&&

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

$$

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