Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 271744
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1244 PM CDT WED AUG 27 2014

.DISCUSSION...
321 AM CDT

CONVECTIVE TRENDS REMAIN THE MAIN FOCUS OF THE FORECAST THROUGH THE
WEEKEND. WATER VAPOR IMAGERY SHOWS A SPLIT UPPER FLOW WITH A
NORTHERN STREAM OF PROGRESSIVE FLOW RUNNING ACROSS SOUTHERN CANADA
INTO THE UPPER GREAT LAKES. A LOW AMPLITUDE TROUGH AXIS IS
TRAVERSING THE FLOW AND MOVING INTO WISCONSIN AT THE CURRENT TIME.
THE SOUTHERN STREAM FEATURES A CUTOFF UPPER LOW WHICH IS OVER UTAH
AND SLOWLY MOVING EASTWARD. UPPER RIDGING IS STARTING TO BUILD JUST
DOWNSTREAM OF THE UPPER LOW WITH SEVERAL EMBEDDED WAVES MOVING
NORTHEASTWARD AHEAD OF THE LOW. AT THE SURFACE...THE FRONTAL
BOUNDARY WHICH HAS BEEN DISCUSSED OVER THE PAST SEVERAL DAYS IS NOW
SOUTH OF THE CWA AND RUNS EAST-NORTHEAST ACROSS THE LOWER GREAT
LAKES AND ST. LAWRENCE RIVER VALLEY. HIGH PRESSURE HAS SPREAD ACROSS
THE UPPER MIDWEST WITH ITS SOUTHERN FLANK INTO THE FORECAST AREA.

TODAY...THE NORTHERN STREAM UPPER TROUGH AXIS WILL
CROSS THE LOCAL AREA THIS MORNING. THE GREATEST ASCENT ASSOCIATED
WITH IT IS TO THE NORTH AND IS GENERATING BANDS OF SHOWERS ACROSS
WISCONSIN...WITH ADDITIONAL RETURNS WORKING ACROSS CENTRAL IOWA INTO
NORTHERN ILLINOIS. THIS ACTIVITY SEEMS TO BE IN BETTER CONJUNCTION
WITH THE RIGHT ENTRANCE REGION OF AN UPPER JET MAX TO THE NORTH IN
ADDITION TO A BROAD AREA OF HEIGHT FALLS INDUCED BY THE UPPER
TROUGH. A CLUSTER OF THUNDERSTORMS HAS ALSO DEVELOPED ACROSS SW IOWA
IN RESPONSE TO BETTER FOCUSED MID LEVEL WARM ADVECTION. MOST OF THIS
UPPER SUPPORT WILL BE PASSING BY THIS MORNING RESULTING IN A
DECREASE IN ACTIVITY. WITH THE SURFACE FRONT TO THE SOUTH THE
INSTABILITY GRADIENT IS ALSO TO THE SOUTH WITH A WESTERLY LOW LEVEL
JET ABOVE IT SUGGESTING THAT THE CONVECTION ACROSS SOUTHWEST IOWA
WOULD NOT BE A FACTOR TOO FAR NORTH OF ITS CURRENT LATITUDE. ONCE
THE CURRENT SHOWER ACTIVITY EXITS IT APPEARS THAT MOST AREAS WILL
REMAIN DRY FOR THE REST OF THE DAY BUT FAR SOUTHERN AREAS DO HAVE A
CHANCE TO SEE SOME SHOWERS AND STORMS THIS MORNING GIVEN THE
WESTERLY LOW LEVEL JET ALONG THE BOUNDARY AND MID LEVEL MOISTURE
GRADIENT BUT WARM/MOIST ADVECTION IS PRETTY WEAK. HIGH TEMPERATURES
WILL RANGE FROM THE UPPER 70S NORTH TO MID 80S SOUTH WITH A
NORTHEAST WIND HOLDING LAKEFRONT AREAS TO THE LOWER TO MID 70S.

TONIGHT AND THURSDAY...AS THE UPPER TROUGH SHIFTS EAST THE RIDGING
DOWNSTREAM OF THE CUTOFF LOW TO THE WEST WILL PIVOT ACROSS THE
CENTRAL PLAINS. SURFACE LOW PRESSURE WILL BE DEVELOPING ACROSS
EASTERN COLORADO AND WESTERN KANSAS WHICH WILL DRIVE THE FRONTAL
BOUNDARY NORTHEASTWARD ACROSS THE CENTRAL PLAINS WITH THE NEARBY
PORTION OF THE FRONT REMAINING SOUTH OF THE AREA INTO THURSDAY
EVENING. WITH WARM ADVECTION INCREASING ALOFT WITH THE RIDGE
BUILDING BACK IN TONIGHT SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
BE MOVING EAST-NORTHEAST ACROSS IOWA/MISSOURI. SOME OF THIS ACTIVITY
MAY REACH THE WESTERN CWA VERY LATE TONIGHT AND MAY END UP SEEING A
SIMILAR SITUATION TO RECENT DAYS WITH REMNANT CONVECTION FESTERING
AND/OR SPAWNING NEW DEVELOPMENT ACROSS THE CWA THURSDAY
MORNING/AFTERNOON. THE MAIN SURFACE LOW AND UPPER WAVE IS EXPECTED
TO BE MOVING ACROSS IOWA/MINNESOTA/WISCONSIN SO THE BULK OF THE
CONVECTION MAY STAY TO THE NORTHWEST OF THE LOCAL AREA. WILL FOCUS
HIGHEST POPS ACROSS THE WESTERN CWA AND SLOW DOWN THE ARRIVAL UNTIL
LATER TONIGHT. THURSDAY LOOKS TO BE SLIGHTLY WARMER...ESPECIALLY
WITH CONVECTION LOOKING TO BE MORE SCATTERED IN COVERAGE.

FRIDAY THROUGH EARLY NEXT WEEK...THE UPPER TROUGH WILL START TO MAKE
QUICKER EAST-NORTHEAST PROGRESS THANKS TO ANOTHER LARGE SCALE UPPER
TROUGH PUSHING INTO THE WESTERN U.S./CANADA. THIS WILL TAKE ANOTHER
SURFACE LOW NORTHEASTWARD WITH IT WHICH WILL LIKELY TRACK NORTHWEST
OF THE AREA SATURDAY. FRIDAY SHOULD SEE A NOTICEABLE WARM UP WITH
ANOTHER LULL IN WIDESPREAD CONVECTION WITH IT FOCUSING TO THE NORTH
AND WEST. WILL HAVE HIGHER POPS SATURDAY WITH THE LOW PASSING BUT AM
SEEING MIXED SIGNALS IN THE TRACK WHICH WILL AFFECT PRECIP COVERAGE.
CHANCES WILL DIMINISH SATURDAY NIGHT WITH QUESTION MARKS SURROUNDING
SUNDAY INTO EARLY NEXT WEEK WITH THE GFS SHOWING A MORE ACTIVE FLOW
WHILE THE ECMWF IS QUIETER THOUGH IT DOES BRING A FRONT THROUGH THE
AREA TUESDAY. DO NOT SEE MUCH OF A COOL DOWN OVERALL AND A DRY
FORECAST SUNDAY/MONDAY WOULD COINCIDE WITH A WARMING TREND IF IT
COMES TO PASS. WILL CONTINUE WITH MID TO UPPER 80S FRIDAY WITH
READINGS SEVERAL DEGREES COOLER SATURDAY AND SUNDAY.

MDB

&&

.AVIATION...

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

* E WINDS ARND 10 KT EXPECTED BY MID AFTN.

JEE

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

HIGH PRESSURE IS SPREADING OVER THE REGION WITH VFR CONDITIONS
ACROSS THE REGION. EAST WINDS WILL CONTINUE THROUGH THE PERIOD. AS
WARMING CONTINUES...EXPECTING WINDS TO PICK UP TO ARND 10 KT BY
MID AFTN. WINDS THEN DIMINISH THIS EVENING...AND THEN WILL BE ARND
8 KT TOMORROW.

THE HIGH SHIFTS EAST TONIGHT INTO TOMORROW WITH LOW PRESSURE
APPROACHING FROM THE SOUTHWEST. GUIDANCE HAS THE WARM FRONT
REMAINING SOUTH OF THE TERMINALS THROUGH TOMORROW AFTERNOON.
HOWEVER...SOME MODELS SHOW STORMS REACHING RFD BY LATE
MORNING/EARLY AFTN SO HAVE A PROB30 FOR THOSE. NOT OVERLY
CONFIDENT IN THE TSRA CHANCES AT RFD. THE OTHER TERMINALS WILL SEE
PRECIP PUSH IN AFTER 00Z FRIDAY.

JEE


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

* MEDIUM CONFIDENCE IN WHEN EAST WINDS WILL BE ARND 10 KT THIS AFTN.

* HIGH CONFIDENCE IN ALL OTHER FORECAST PARAMETERS.

JEE

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

* THURSDAY NIGHT AND FRIDAY...CHANCE OF TSRA.
* SATURDAY...TSRA LIKELY.
* SUNDAY THROUGH TUESDAY...CHANCE OF TSRA.

&&

.MARINE...

307 AM...HIGH PRESSURE CENTERED OVER MINNESOTA EARLY THIS MORNING
WILL MOVE ACROSS THE LAKES REGION TODAY AND TONIGHT. AS IT DOES
THE GRADIENT WILL SLOWLY WEAKEN OVER NORTHERN LAKE MICHIGAN WHILE
IT SLOWLY TIGHTENS OVER THE SOUTHERN PORTION OF THE LAKE. SPEEDS
WILL INCREASE INTO THE 10-20KT RANGE. AS THE HIGH SHIFTS EAST...
WINDS WILL TURN MORE EASTERLY BY THURSDAY MORNING THEN SHIFT
SOUTHEAST TO SOUTHERLY THURSDAY NIGHT AS A WARM FRONT LIFTS NORTH
ACROSS THE LAKE. THE GRADIENT COULD TIGHTEN ENOUGH FOR A PERIOD OF
15-25 KTS THURSDAY NIGHT INTO FRIDAY. A FRONTAL BOUNDARY IS THEN
EXPECTED TO MOVE SOUTH ACROSS THE LAKE SATURDAY AFTERNOON INTO
SATURDAY EVENING. BUT AT THE SAME TIME...LOW PRESSURE IS EXPECTED
TO DEVELOP OVER THE WESTERN LAKES AND THEN MOVE ACROSS NORTHERN
LAKE MICHIGAN BY SUNDAY MORNING. THIS MAKES FOR A CHALLENGING WIND
FORECAST. IF THE LOW BEGINS TO DEEPEN...NORTHERLY WINDS MAY
INCREASE INTO THE 15-25KT RANGE. CHANGES CAN BE EXPECTED DURING
THIS TIME PERIOD AS TRENDS EMERGE. WINDS THEN QUICKLY TURN BACK
SOUTHERLY SUNDAY NIGHT INTO MONDAY. CMS

&&

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

$$

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