Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 301803
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
103 PM CDT SAT APR 30 2016

.SHORT TERM...
320 AM CDT

THROUGH SUNDAY NIGHT...

RAINY AND COOL CONDITIONS WILL BE IN PLACE OVER THE WEEKEND. THIS
MORNING...WATER VAPOR IMAGERY SHOWS A CLOSED UPPER LOW OVER
WESTERN KANSAS WITH A LEAD SHORT WAVE LIFTING NORTH ACROSS AR/MO
WITH SHOWERS AND THUNDERSTORMS LIFTING TOWARDS THE REGION. THIS
LEAD SHORTWAVE TROUGH IS PROGGED TO LIFT ACROSS ILLINOIS BY AROUND
MIDDAY. DESPITE A DRY LOW LEVEL NORTHEASTERLY WIND...STRONG
FORCING IS EXPECTED TO OVERSPREAD THE REGION THROUGH THE DAY WITH
UPPER LEVEL DIFLUENCE IN PLACE ALONG WITH DCVA FROM THE
AFOREMENTIONED WAVE AND STRONG MID LEVEL WAA ALL HELPING TO
PROVIDE DEEP ASCENT THROUGHOUT THE AFTERNOON AND INTO THE EVENING.
INSTABILITY WILL BE INCREASINGLY MARGINAL AS YOU HEAD NORTH AND
APPEARS THE BEST CHANCE FOR ANY EMBEDDED ELEVATED THUNDERSTORMS
WOULD BE FROM MID/LATE AFTERNOON THROUGH MID EVENING. MODEST
LOW/MID LEVEL MOISTURE CONVERGENCE WILL OVERSPREAD AREAS MAINLY
ALONG/SOUTH OF THE I-80 CORRIDOR WHERE SEVERAL HUNDRED J/KG MUCAPE
IS PROGGED TO DEVELOP. DO NOT ANTICIPATE ANY SEVERE WEATHER THREAT
TODAY...BUT COULD SEE SOME LOCALLY HEAVIER RAINFALL RATES WITH
EMBEDDED THUNDERSTORMS. OTHERWISE...EXPECT WIDESPREAD TOTALS OF
THREE QUARTERS TO AROUND AN INCH OF RAIN ACROSS NORTHERN ILLINOIS
AND NORTHWEST INDIANA THROUGH DAYBREAK SUNDAY. ON SUNDAY...THE
MAIN UPPER LOW IS PROGGED TO BEGIN TO OPEN UP AS IT MOVES ACROSS
NORTHERN ILLINOIS. THIS WILL RESULT IN ADDITIONAL SCATTERED
SHOWERS...AND POSSIBLY A FEW THUNDERSTORMS...ESPECIALLY ACROSS THE
FAR SOUTHEASTERN COUNTIES IN THE FORECAST AREA WHICH WILL BE NEAR
THE SURFACE LOW TRACK.

DEUBELBEISS

&&

.LONG TERM...
320 AM CDT

MONDAY THROUGH FRIDAY...

AMPLIFIED AND BLOCKY UPPER AIR PATTERN WILL BE IN PLACE MUCH OF
NEXT WEEK WITH A BLOCKING RIDGE IN PLACE ACROSS THE WESTERN HALF
OF THE CONUS TO START THE WEEK AND NORTHWEST FLOW ACROSS THE
EASTERN CONUS. REGIONALLY...SURFACE HIGH AND NORTHWEST FLOW WILL
PROVIDE DRY CONDITIONS MONDAY WITH SLIGHTLY COOLER THAN NORMAL
TEMPERATURES WITH HIGHS IN THE LOW TO MID 60S INLAND AND LOW 50S
LAKEFRONT...THEN BY TUESDAY EXPECT HIGHS TO BE NEAR THE 70 MARK.
MEANWHILE...WHILE THE UPPER RIDGE IS CENTERED OVER BRITISH
COLUMBIA AND ALBERTA EARLY NEXT WEEK...PORTIONS OF THE JET STREAM
TOP THE RIDGE OVER THE ARCTIC CIRCLE AND WILL DISLODGE A COLD
AIRMASS TOWARDS THE REGION SCHEDULED TO ARRIVE AROUND MIDWEEK.
THERE ARE DIFFERENCES IN THE MAGNITUDE AND SOUTHERN EXTENT OF THE
AIRMASS WITH THE GFS BRINGING AROUND -5C H85 AIR SQUARELY INTO THE
MIDWEST BY EARLY THURSDAY...VERSUS THE ECMWF PROVIDING MORE OF A
GLANCING BLOW OF COLD AIR. THIS RESULTS IN QUITE A BIT OF
UNCERTAINTY FOR TEMPERATURES BEYOND MIDWEEK THOUGH BELOW NORMAL IS
HEAVILY FAVORED...AND CURRENT FORECAST FOR THURSDAY AND FRIDAY MAY
BE TOO WARM IF 00Z MODEL TRENDS HOLD. THERE IS NOT A LOT OF
MOISTURE WITH THE COLD FRONT BUT A SLIGHT/LOW CHANCE OF RAIN IS
WARRANTED WITH FROPA. THE UPPER RIDGE IS PROGGED TO GRADUALLY
SHIFT EAST TOWARDS THE MID SECTION OF THE COUNTRY BY LATE IN THE
WEEK AND AS WE SHOULD SEE DRY WEATHER AND A GRADUAL WARMING TREND
TO CLOSE OUT THE WEEK AND AS WE HEAD INTO INTO NEXT WEEKEND.

DEUBELBEISS

&&

.AVIATION...
FOR THE 18Z TAFS...

MAIN CONCERNS FOR THE REMAINDER OF THE AFTERNOON THROUGH THE
OVERNIGHT HOURS WILL BE ON CIGS AND VSBY REDUCTIONS. CONSIDERABLE
MOISTURE AND RAIN CONTINUES TO FEED NORTH/NORTHEAST ACROSS
NORTHERN IL AND NORTHWEST IN THIS AFTERNOON...WHICH HAS BEEN
STEADILY OVERCOMING THE INITIAL DRY LAYER FROM THIS MORNING. CIGS
HAVE BEEN SLOWLY LOWERING TOWARDS MVFR CONDS...BUT EXPECT CLOSER
TO 00Z CIGS WILL BE FLIRTING WITH IFR CONDS. THE STEADIER PRECIP
SHOULD BE DIMINISHING IN COVERAGE BETWEEN 00-02Z...WITH JUST SOME
LINGERING DZ OR LGT RA THROUGH THIS EVENING. WINDS WILL CONTINUE
FROM THE EAST WITH OCCASIONAL GUSTS BETWEEN 20-24KT THIS
AFTERNOON...THEN DIMINISHING AFTER SUNSET. OVERNIGHT PRECIP
COVERAGE SHOULD END WITH JUST PATCHY DZ REMAINING. THIS IS THE
TIME WHEN GUIDANCE HAS BEEN LEANING HEAVILY TOWARDS CIGS FALLING
FURTHER TOWARDS LIFR CONDS...WITH BASES BETWEEN 200-300FT AGL. IT
IS POSSIBLE A FEW SPOTS COULD GO FURTHER DOWN OVERNIGHT. HELPING
CIGS TO LOWER TONIGHT WILL BE THE LIGHTER WINDS THAT DEVELOP AS
THE LOW PRESSURE APPROACHES THE REGION FROM THE
SOUTHWEST...HOWEVER WIND DIRECTIONS WILL REMAIN NORTHEASTERLY AND
SPEEDS WILL BE BETWEEN 6-12KT.

AFTER DAYBREAK SUNDAY WINDS WILL TURN MORE NORTHERLY...WHICH
SHOULD HELP TO LIFT CIGS SLIGHTLY BACK TOWARDS IFR CONDS. BUT WITH
THE CONTINUED LACK OF STRONG MIXING AND A WEAK PRESSURE GRADIENT
THE CONTINUED IFR/LOW END MVFR CIGS WILL PERSIST WITH A FEW
SHOWERS IN THE AREA.

BEACHLER

&&

.MARINE...
242 AM CDT

AN EXPANSIVE AREA OF HIGH PRESSURE WILL REMAIN NORTH OF THE LAKES
TODAY...AS AN AREA OF LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST INTO THE LOWER MISSOURI VALLEY BY EVENING...AND THEN
TRACKS TO THE EASTERN LAKES/UPPER OHIO VALLEY ON SUNDAY. COOL
NORTHEAST FLOW FROM THE HIGH TO THE NORTH WILL INCREASE ESPECIALLY
ACROSS SOUTHERN LAKE MICHIGAN TODAY AS THE LOW APPROACHES FROM THE
SOUTHWEST AND TIGHTENS UP THE GRADIENT. EAST-NORTHEASTERLY FLOW AT
20-25 KT WILL PRODUCE SMALL CRAFT ADVISORY CONDITIONS ON SOUTHERN
LAKE MICHIGAN...LIKELY LINGERING THROUGH SUNDAY AS WINDS BACK MORE
NORTHERLY AND THE FETCH LENGTHENS. WEAK HIGH PRESSURE WILL SPREAD
ACROSS THE LAKES MONDAY ALLOWING WINDS AND WAVES TO SUBSIDE.
ANOTHER ROUND OF MODESTLY STRONG NORTH WINDS APPEARS LIKELY MID-
WEEK.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 1 AM
     MONDAY.

&&

$$

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