Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281412
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 AM CDT THU AUG 28 2014

.DISCUSSION...
310 AM CDT

MORE ACTIVE WEATHER WILL TRY TO RETURN TO THE AREA INTO THIS EVENING
FOR AT LEAST PART OF THE AREA FOLLOWING THE RATHER QUIET WEATHER
YESTERDAY. THE FORECAST WILL FOCUS ON TIMING AND COVERAGE OF
SHOWER/THUNDER CHANCES AS WELL AS TEMPERATURES...ESPECIALLY FRIDAY
WHEN THUNDERSTORMS COULD HINDER ANOTHER SUBSTANTIAL WARM UP. THE
MAIN FEATURE ON WATER VAPOR THIS MORNING IS AN UPPER LOW WHICH HAS
BEEN SLOWLY SPINNING EASTWARD ACROSS THE WESTERN U.S. THE LOW IS NOW
MAKING SLIGHTLY FASTER EASTWARD PROGRESS ACROSS COLORADO AND WYOMING
AND AMPLIFYING A RIDGE AHEAD OF IT INTO THE MID AND UPPER
MISSISSIPPI RIVER VALLEY. SEVERAL SMALLER SCALE SHORTWAVES ARE
MOVING NORTHEASTWARD AROUND THE BASE OF THE LOW AND LIFTING INTO
KANSAS AND NEBRASKA. LOOKING FURTHER NORTHWEST...A TROUGH AXIS
EXTENDS SOUTHWESTWARD FROM NORTHERN ALBERTA ACROSS CENTRAL BRITISH
COLUMBIA AND OVER THE PACIFIC WHILE A CLOSED UPPER IS DIGGING
SOUTHEASTWARD OFF THE SOUTHERN ALASKA COAST. AT THE SURFACE...HIGH
PRESSURE IS CENTERED OVER LAKE SUPERIOR WHILE A FRONTAL BOUNDARY
EXTENDS FROM THE MAINE COAST DOWN THE OHIO VALLEY AND BACK INTO THE
CENTRAL PLAINS. SURFACE LOW PRESSURE IS ORGANIZING ACROSS THE
CENTRAL AND SOUTHERN HIGH PLAINS IN CONJUNCTION WITH THE APPROACHING
UPPER LOW.

TODAY AND TONIGHT...THE UPPER RIDGE AXIS WILL BE CRESTING THE AREA
THIS MORNING AS THE ENTIRE RIDGE BROADENS INTO FRIDAY. THE SURFACE
HIGH WILL ACCELERATE EASTWARD AND BE CENTERED OVER THE LOWER ST.
LAWRENCE RIVER VALLEY BY FRIDAY. THE UPPER LOW WILL PUSH INTO THE
CENTRAL PLAINS WHILE THE ATTENDANT SURFACE LOW MOVES NORTHEASTWARD
INTO MINNESOTA TONIGHT. WARM ADVECTION AHEAD OF THE ADVANCING UPPER
TROUGH IS GENERATING SHOWERS AND THUNDERSTORMS ACROSS MUCH OF
NEBRASKA INTO SOUTHERN IOWA AND NORTHERN MISSOURI IN CONJUNCTION
WITH SEVERAL SHORTWAVES. THE WARM ADVECTION WILL SPREAD
NORTHEASTWARD WITH A SURFACE WARM FRONT ALSO MOVING NORTHEASTWARD
AND CROSSING THE LOCAL AREA TODAY. THE FOCUS OF THE ASCENT WILL BE
TO THE WEST AND NORTHWEST OF THE AREA THROUGH THE MORNING KEEPING
THE BULK OF IF NOT ALL OF THE SHOWER ACTIVITY OUT OF THE CWA.
HOWEVER...HAVE BEEN SEEING A FEW LIGHT SPRINKLES/SHOWERS ALONG AND
SOUTH OF THE SOUTHERN CWA BORDER THIS MORNING AS WELL LIKELY IN
CONJUNCTION WITH A SUBTLE MID LEVEL WAVE. EXPECT THESE TO SHIFT EAST
OF THE AREA THROUGH DAYBREAK. PRECIP CHANCES WILL INCREASE THIS
AFTERNOON HOWEVER...MAINLY ACROSS THE WESTERN HALF OF THE AREA AND
IT IS POSSIBLE THIS COULD BE A LITTLE FAST. A BETTER PUSH OF THETA-E
AND INSTABILITY MOVE ACROSS THIS EVENING...ESPECIALLY ACROSS
NORTHERN AREAS SO MAY SEE THE PEAK OF THE ACTIVITY DURING THIS TIME.
SOUTHERN AND EASTERN AREAS MAY END UP STAYING DRY FOR MUCH OF THIS
PERIOD. HIGHS TODAY WILL RANGE FROM THE UPPER 70S NORTH TO LOWER 80S
SOUTH WITH A FAIR AMOUNT OF CLOUD COVER EXPECTED.

FRIDAY...FRIDAY WILL BE A TRICKY FORECAST WITH THE POTENTIAL
FOR A NOTICEABLE WARM UP BUT ALSO A POTENTIAL TO HAVE THAT SPOILED
BY THUNDERSTORMS. THE WESTERN PERIPHERY OF THE MID LEVEL WARM AXIS
WILL BE OVER THE AREA WITH A SOUTH TO SOUTHWEST SURFACE WIND IN
PLACE. H85/H92 HIGH TEMP CLIMATOLOGY SHOWS STRONG SUPPORT FOR HIGHS
NEAR 90 WITH VALUES OF 18/23C. LATEST GUIDANCE SHOWS CONVECTION
DEVELOPING TO THE SOUTH OF THE AREA FRIDAY MORNING AND LIFTING
NORTHWARD ON THE WESTERN FLANK OF THE RIDGE AND CROSSING THE AREA
INTO THE AFTERNOON. TOUGH TO SAY IF THIS WILL BE THE CASE BUT THE
PATTERN IS CERTAINLY SUCH THAT THIS COULD OCCUR SO WILL CONTINUE
WITH POPS PRIMARILY FRIDAY AFTERNOON AND STICK WITH HIGHS IN THE MID
TO UPPER 80S FOR NOW.

FRIDAY NIGHT THROUGH MID NEXT WEEK...LARGER SCALE TROUGHING WILL BE
BUILDING INTO WESTERN NORTH AMERICA INTO SATURDAY WHICH WILL HELP
KICK THE CENTRAL PLAINS UPPER LOW NORTHEASTWARD. ANOTHER SURFACE LOW
WILL DEVELOP AND TRACK NORTHEASTWARD INTO WISCONSIN BY SATURDAY
MORNING. LATE FRIDAY NIGHT THROUGH SATURDAY MORNING WILL PROBABLY
END UP BEING THE BEST CHANCE FOR SHOWERS AND THUNDERSTORMS AS THIS
OCCURS. MORNING FRONTAL PASSAGE IS NOT ALL THAT FAVORABLE FOR SEVERE
WEATHER BUT DO EXPECT THAT SOME SORT OF LINE OR COMPLEX OF STORMS
WOULD AFFECT THE AREA...BRINGING HEAVY RAINFALL IF NOTHING ELSE.
HIGH PRESSURE RIDGING BUILDS IN NORTH OF THE AREA BEHIND THE
DEPARTING LOW. THE BIGGEST ISSUE WITH THIS HAS BEEN TIMING WITH THE
LATEST GUIDANCE FASTER THAN EARLIER RUNS KEEPING THE PRECIP CONFINED
TO SATURDAY MORNING. WILL ADJUST POPS TO BETTER FIT THIS BUT WILL
KEEP CHANCE POPS FOR SATURDAY AFTERNOON FOR NOW. H85 TEMPS COOL
BEHIND THE SYSTEM KEEPING HIGHS IN THE UPPER 70S AND LOWER 80S WITH
SLIGHTLY WARMER TEMPS SUNDAY. THE WESTERN TROUGH WILL AMPLIFY AS IT
MOVES INTO THE NORTHERN PLAINS TAKING A SURFACE LOW NORTHEAST FROM
THE NORTHERN PLAINS TO NORTHWESTERN ONTARIO LATER SUNDAY. TIMING
WILL ONCE AGAIN NEED TO BE BETTER ASSESSED BUT THIS SYSTEM WILL
BRING ANOTHER COOL FRONT ACROSS THE AREA SOME TIME MONDAY. A LOWER
AMPLITUDE UPPER FLOW BECOMES ESTABLISHED AS THE TROUGH DEPARTS WITH
HIGH PRESSURE BUILDING IN AT THE SURFACE. WIDESPREAD POP CHANCES
LOOK LOW INTO MIDWEEK BUT THE FAIRLY ZONAL FLOW WILL BE SUPPORTIVE
OF WEAK PASSING SHORTWAVES WHICH COULD TRIGGER SOME SPOTTY PRECIP AT
TIMES. HIGHS GENERALLY LOOK TO BE AROUND 80 BUT THE FLOW WILL LIKELY
BE WEAK ENOUGH TO SUPPORT LAKE COOLING AS LONG AS THE SURFACE HIGH
IS NEARBY.

MDB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* EASTERLY WINDS AROUND 10KT THRU EARLY EVENING.
* ISOLATED/SCATTERED SHRA THIS EVENING THRU FRIDAY MORNING.
CMS/BEACH

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

GRADIENT HAS TIGHTENED JUST A BIT THIS MORNING WITH EASTERLY WINDS
AROUND 10KT. MAY SEE SOME FLUCTUATION IN WIND SPEEDS BUT OVERALL...
PREVAILING WINDS WILL LIKELY BE EASTERLY AROUND 10KT FOR MUCH OF
THE DAY. WINDS SLOWLY TURN SOUTHEAST THIS EVENING THE SHIFT
SOUTHERLY TOWARD DAYBREAK FRIDAY.

MID CLOUDS WILL VARY FROM SCT TO BKN THIS MORNING BUT SHOULD
EVENTUALLY BECOME BKN/OVC LATER THIS AFTERNOON INTO THIS EVENING
AS THEY SLOWLY LOWER. HIGH MVFR CIGS HAVE DEVELOPED ACROSS EASTERN
IOWA AND FAR WESTERN IL. THESE WILL NEED TO BE MONITORED THIS
MORNING...ESPECIALLY FOR POSSIBLE HIGH MVFR CIGS INTO RFD.

SHRA/TSRA OVER IOWA ARE EXPECTED TO LIFT NORTHEAST THIS AFTERNOON
AND THIS EVENING...POSSIBLY MOVING ACROSS FAR NORTHWEST IL AND
RFD WITH ADDITIONAL SHRA DEVELOPMENT POSSIBLE THRU THE NIGHT AS A
WARM FRONT LIFTS ACROSS THE AREA. OVERALL CONFIDENCE REGARDING
TIMING AND COVERAGE OF PRECIP REMAINS LOW SO MAINTAINED PREVIOUS
PROB MENTION AND ADDED VICINITY MENTION INTO FRIDAY MORNING WITH
THE BEST CHANCES ACROSS FAR NORTHERN IL INTO SOUTHERN WI. CMS

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH FOR WINDS THRU THE PERIOD.
* LOW FOR SHRA THIS EVENING THRU FRIDAY MORNING.
CMS/BEACH

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

* FRIDAY NIGHT...CHANCE OF TSRA.
* SATURDAY...TSRA LIKELY.
* SUNDAY...SLIGHT CHANCE OF TSRA.
* MONDAY AND TUESDAY...CHANCE OF TSRA.
* WEDNESDAY...DRY/VFR.

&&

.MARINE...

300 AM...HIGH PRESSURE OVER THE LAKES REGION WILL MOVE EAST TODAY
AND TONIGHT REACHING NEW ENGLAND FRIDAY MORNING. EAST WINDS 10 TO
15 KTS WILL GRADUALLY TURN SOUTHEASTERLY THIS EVENING THEN MORE
SOUTHERLY OVERNIGHT INTO FRIDAY MORNING AND INCREASE. LOW PRESSURE
OVER THE WESTERN PLAINS WILL MOVE NORTHEAST TO MINNESOTA AND IOWA
BY FRIDAY MORNING THEN TURN NORTHEAST ACROSS THE NORTHERN LAKES
SATURDAY INTO SATURDAY EVENING. THE GRADIENT WILL TIGHTEN AHEAD OF
THIS LOW WITH 15-25KTS EXPECTED FRIDAY. THE GRADIENT WILL SLOWLY
WEAKEN FROM NORTH TO SOUTH FRIDAY NIGHT. A TRAILING COLD FRONT
FROM THIS LOW WILL THEN MOVE SOUTH ACROSS LAKE MICHIGAN SATURDAY
NIGHT INTO SUNDAY MORNING. THIS FRONT WILL THEN LIFT BACK NORTH AS
A WARM FRONT SUNDAY NIGHT AS STRONGER HIGH PRESSURE IS EXPECTED TO
MOVE ACROSS THE NORTHERN LAKES AND ONTARIO SUNDAY NIGHT AND
MONDAY. CMS

&&

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

$$

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