Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 300557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT SAT AUG 30 2014

.DISCUSSION...
221 PM CDT

SYNOPSIS...UNSETTLED WEATHER CONTINUES THROUGH TOMORROW WITH
SCATTERED THUNDERSTORMS EXPECTED.  CONFIDENCE REMAINS LOW IN WHEN
AND WHERE THUNDERSTORMS WILL FORM.  SUNDAY STILL LOOKS DRY BUT
MULTIPLE CHANCES FOR STORMS RETURN MONDAY THROUGH THE END OF THE
WEEK. ABOVE NORMAL TEMPERATURES ARE ALSO EXPECTED THROUGH THE PERIOD
AS WELL.

//NEAR TERM FORECAST//

THROUGH TONIGHT...
A LARGE RIDGE IS OVER THE EAST COAST WHILE A TROUGH IS OVER THE
PLAINS.  THE TROUGH WILL WEAKEN AS IT APPROACHES OUR AREA AND PASS
OVERHEAD LATE SATURDAY NIGHT INTO SUNDAY MORNING. AT THE SURFACE THE
HIGH HAS PUSHED EAST WHILE A DEVELOPING LOW PRESSURE SYSTEM IS OVER
MINNESOTA.  THE LOWS WARM FRONT LIES TO OUR SOUTH ACROSS SOUTHERN
IL...AND IT WILL LIFT NORTH THROUGH THE REGION THIS AFTERNOON.

HAVE VERY LOW CONFIDENCE IN EXACT TIMING AND LOCATION OF
THUNDERSTORMS THROUGH THIS EVENING.  THERE IS NO CLEAR FORCING
MECHANISM BUT WITH AROUND 2000 J/KG OF CAPE AVAILABLE...STORMS ARE
CERTAINLY POSSIBLE. PWAT VALUES ARE AROUND 2 INCHES SO THE MAIN
CONCERN REMAINS HEAVY DOWNPOURS. THE STRONGEST STORMS MAY PRODUCE
WIND GUSTS TO 50 KT BUT NO SEVERE WEATHER IS EXPECTED AS WIND SHEAR
IS BASICALLY NIL.

FOR POPS USED A BLEND OF NEAR TERM GUIDANCE WHICH HAS BEEN DOING
REASONABLY WELL THIS MORNING.  HOWEVER...KEPT A CHANCE OF STORMS
ACROSS THE REGION THIS AFTERNOON AND EVENING DUE TO THE SCATTERED
NATURE OF THE STORMS THAT ARE EXPECTED.  A WASH OUT IS NOT
EXPECTED.  THE BEST CHANCE FOR WIDESPREAD STORMS WILL BE OVERNIGHT
AS THE UPPER LEVEL TROUGH APPROACHES. IN FACT THE STORMS ASSOCIATED
WITH THE TROUGH STRETCH FROM MINNESOTA THROUGH ARKANSAS.  MODELS
DIFFER IN HOW WELL THIS AREA OF PRECIP WILL HOLD TOGETHER SO LIMITED
POPS TO THE LIKELY CATEGORY.

LOWS WILL BE IN THE UPPER 60S TO LOWER 70S TONIGHT AND FOG IS
POSSIBLE. GIVEN THAT WE HAVE NOT SEEN MUCH RAIN TODAY...HAVE LIMITED
CONFIDENCE SO LEFT FOG OUT OF THE FORECAST FOR NOW.

SATURDAY AND SATURDAY NIGHT...
THE SURFACE LOW PASSES OVER LAKE MICHIGAN SATURDAY AFTERNOON WHILE
ITS COLD FRONT GETS DRAGGED THROUGH THE AREA SATURDAY
AFTERNOON/EVENING.  SCATTERED STORMS ARE AGAIN POSSIBLE IN THE
MORNING IN THE WARM AND MOIST ENVIRONMENT WITH LINGERING 2 INCH PWAT
VALUES. STORMS WILL THEN FORM ALONG THE COLD FRONT SOUTH OF A GARY
IN TO PONTIAC IL LINE. STORMS ARE POSSIBLE NORTH AND WEST OF THIS
LINE...BUT CONFIDENCE IS SIGNIFICANTLY LOWER.

CAPE VALUES WILL BE AROUND 1000 J/KG TOMORROW WITH WEAK SHEAR ONCE
AGAIN. THEREFORE EXPECTING STORMS TO PRODUCE HEAVY DOWNPOURS AND THE
STRONGEST MAY BE CAPABLE OF GUSTY WINDS.  SEVERE WEATHER IS NOT
EXPECTED.

TOMORROW LOOKS LIKE ANOTHER WARM AND STICKY DAY AHEAD OF THE COLD
FRONT.  LOWS WILL BE IN THE 60S AND FOG IS POSSIBLE OVERNIGHT.

JEE

//EXTENDED FORECAST//

SUNDAY...
EXPECT A BRIEF LULL IN THE PRECIP CHANCES DURING MUCH OF THE DAY
SUNDAY AS THE FIRST COLD FRONT DEPARTS TO THE EAST AND ANOTHER LOW
TAKES SHAPE OVER THE NORTHERN PLAINS. IN BETWEEN THESE TWO
SYSTEMS...WEAK INDUCED SURFACE HIGH SHOULD RESULT IN QUIET WEATHER
LOCALLY...WITH THE H85 THERMAL RIDGE ADVECTING OVERHEARD THROUGHOUT
THE DAY. RETURN FLOW WILL HELP PUSH THE DEWPOINTS BACK UP TO AROUND
70 WITH AFTERNOON HIGH TEMPS EXPECTED TO BE IN THE MID 80S. STEEP
LOW/MID LEVEL LAPSE RATES WILL RESULT IN MODERATE INSTABILITY
DEVELOPING DURING THE AFTERNOON...BUT MODEST SBCIN IS PROGGED TO
STAY IN PLACE CAPPING ANY SURFACE BASED CONVECTION. IN ADDITION...
THE AREA SHOULD BE SQUARELY UNDER AREA OF MID LEVEL HEIGHT RISES
WHICH SHOULD HELP REINFORCE THE INVERSION...AND NO SIGNIFICANT
FORCING NOTED OVER THE AREA.

MONDAY...
TROUGHING CURRENTLY MOVING ONSHORE OVER THE PAC NORTHWEST TODAY WILL
MOVE ACROSS THE CENTRAL PLAINS THIS WEEKEND...THEN BEGIN TO LIFT
ACROSS THE UPPER MIDWEST EARLY NEXT WEEK. SURFACE LOW IS PROGGED TO
DEEPEN FROM THE NORTHERN PLAINS SUNDAY AS IT LIFTS TO NEAR HUDSON
BAY LATE ON MONDAY. THIS WILL DRAG A COLD FRONT ACROSS THE REGION ON
MONDAY. WITH THE LOW LIFTING AWAY FROM THE AREA...CONVERGENCE ALONG
THE FRONT IS PROGGED TO WEAKEN AS IT COMES ACROSS NORTHERN ILLINOIS
EARLY MONDAY WITH THE BETTER DYNAMICS STAYING TO OUR NORTH.
MEANWHILE...THE LOCAL AREA APPEARS TO LIE ON THE NORTHERN PERIPHERY
OF THE BETTER INSTABILITY TO OUR SOUTH. GFS SHOWS SOME HINTS THAT
PARTICULARLY NORTH CENTRAL ILLINOIS MAY BE SPLIT BY THE
PRECIP...ESPECIALLY CONSIDERING THE CAPPING EARLY IN THE DAY...BUT
WILL HOLD OFF ON FINE TUNING THIS DETAIL FOR NOW. IN ADDITION...THE
REGION DOES FALL WITHIN AN OVERLAPPED AREA OF FAVORABLE
SHEAR/INSTABILITY THAT COULD POTENTIALLY SUPPORT A SEVERE WEATHER
THREAT.

TUESDAY THROUGH FRIDAY...
FRONTAL BOUNDARY IS PROGGED TO STALL ACROSS/NEAR CENTRAL ILLINOIS
TUESDAY GRADUALLY LIFTING BACK NORTH ACROSS THE FORECAST AREA BY THE
END OF THE WORK WEEK AS A SERIES OF UPPER LEVEL DISTURBANCES MOVE
ACROSS THE REGION. THIS WILL RESULT IN PERIODIC CHANCES FOR SHOWERS
AND THUNDERSTORMS ACROSS THE AREA...THOUGH TIMING AND LOCATION
DETAILS WILL BE DIFFICULT TO PIN DOWN THIS FAR OUT GIVEN THE
PATTERN. THE ATMOSPHERE REMAINS QUITE SOUPY IN THE VICINITY OF THE
FRONT WHERE PWATS REMAIN AROUND 2 INCHES. THUS THE HEAVY RAIN AND
FLOODING THREAT WILL HAVE TO BE CLOSELY MONITORED THROUGH MUCH OF
THE UPCOMING WEEK.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* CHANCE OF SHRA/TSRA MIDDAY SATURDAY

* SWLY WINDS GUSTING TO 20KT SATURDAY AFTERNOON.

KREIN

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

SCT SHRA AND ISOLD TSRA CONTINUE AS THE AREA REMAINS ENTRENCHED IN
A WARM/MOIST AIRMASS. IN THE ABSENCE OF ANY SFC OR MID LEVEL
FOCUS...PCPN SHOULD REMAIN FAIRLY ISOLATED. HAVE BEEN TRACKING A
A FEW PATCHES OF PERSISTENT RAIN MOVING INTO NCNTRL/NERN IL WHICH
SHOULD HOLD TOGETHER LONG ENOUGH TO BRING SOME WETTING RAIN TO
THE CHICAGO AREA TERMINALS. HOWEVER...ANY PCPN SHOULD BE FLEETING.
FOR THE REMAINDER OF THE NIGHT AND INTO SATURDAY MORNING...WILL
CARRY A DRY FORECAST THOUGH THERE SHOULD BE SOME SCT SHRA OR ISOLD
TSRA WITH LITTLE CHANGE IN THE AIRMASS.

BY TOMORROW MORNING...THE SHORT TERM MODEL GUIDANCE IS PUSHING A
WEAK COLD FRONT ACROSS THE AREA IN ASSOCIATION WITH A STRONGER
UPPER LEVEL TROUGH. THE UPPER TROUGH AND SFC FRONT SHOULD PROVIDE
BETTER FOCUS FOR MORE ORGANIZED THUNDERSTORMS ACTIVITY.
HOWEVER...THE TIMING OF THE FRONT WILL PLAY A SIGNIFICANT ROLE IN
THE TS COVERAGE AS IT SHOULD MOVE NRN IL BY LATE MORNING...AT A
TIME BEFORE MAX DIURNAL WARMING. THE HIGH RESOLUTION MODEL
GUIDANCE SUGGESTS THAT TS COVERAGE SHOULD INCREASE AS THE FRONT
MOVES THROUGH ECNTRL IL AND NWRN IN DURG THE EARLY AFTERNOON
HOURS. SO...WILL MAINTAIN THE PROB30 GROUP FOR THE TIME THAT THE
FRONT SHOULD BE INVOF THE TERMINALS...THOUGH THERE IS A BETTER
CHANCE FOR MORE ORGANIZED...WIDESPREAD TS INVOF THE COLD FRONT AS
IT PUSHES SOUTH AND EAST OF THE TERMINALS SATURDAY AFTERNOON.

WINDS SHOULD GENERALLY BE SOUTHERLY AT LESS THAN 10KT THROUGH THE
REMAINDER OF THE NIGHT AND INTO SATURDAY MORNING. AS THE TROUGH
ASSOCIATED WITH THE COLD FRONT APPROACHES THE REGION...WINDS
SHOULD BECOME MORE SWLY WITH GUSTS TO ARND 20KT FOR THE LATE
MORNING INTO EARLY EVENING. WINDS SHOULD DROP OFF AND BECOME
LGT/VRBL OVERNIGHT SATURDAY NIGHT AS HIGH PRESSURE SPREADS ACROSS
THE AREA.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* LOW-MEDIUM CONFIDENCE IN PRECIP TRENDS.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

KREIN

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

SUNDAY...VFR.

MONDAY...PERIOD OF TSRA LIKELY.

TUESDAY AND WEDNESDAY...PREDOMINANTLY VFR.

THURSDAY...CHANCE TSRA.

IZZI

&&

.MARINE...
221 PM CDT

MODERATE SOUTHERLY WINDS ARE IN PLACE TODAY AHEAD OF LOW PRESSURE
OVER THE NORTHERN PLAINS. SOUTH TO SOUTHWEST WINDS 20 TO 25 KT
WITH AN OCCASIONAL 30 KT GUSTS POSSIBLE WILL BE IN PLACE THROUGH
TOMORROW...THEN A COLD FRONT WILL START TO PUSH ACROSS THE LAKE
TURNING WINDS NORTHWESTERLY. HIGH PRESSURE WILL PROVIDE A BRIEF
LULL IN THE WINDS SUNDAY ALLOWING LAKE BREEZES TO DEVELOP...BUT
THEN SOUTHERLY WINDS RAMP BACK UP TO 25 TO 30 KT SUNDAY NIGHT INTO
MONDAY AHEAD OF ANOTHER LOW. THIS LOW IS PROGGED TO DEEPEN AS IT
LIFTS FROM THE NORTHERN PLAINS SUNDAY TO HUDSON BAY LATE MONDAY.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS UNTIL 3 AM SATURDAY.

&&

$$

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