Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 262005
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
305 PM CDT TUE APR 26 2016

.SHORT TERM...
303 PM CDT

THROUGH THURSDAY...

THE MAIN FOCUS DURING THE SHORT TERM PERIOD WILL BE WITH THE
TIMING OF SHOWERS AND THUNDERSTORMS WEDNESDAY INTO THURSDAY OVER
THE AREA.

A LARGE AND POTENT UPPER LEVEL STORM SYSTEM...CURRENTLY NOTED IN
WATER VAPOR IMAGERY SPINNING OVER THE CENTRAL ROCKIES...WILL
CONTINUE TO DRIVE/DEVELOP SURFACE LOW PRESSURE OVER KANSAS TODAY
AND TONIGHT. THE STORM SYSTEM WILL ALSO SUPPORT NUMEROUS SEVERE
THUNDERSTORMS INTO TONIGHT OVER THE PLAINS. ON WEDNESDAY THE
SYSTEM IS EXPECTED TO QUICKLY BECOME VERTICALLY STACKED OVER
...THEN IS FORECAST TO GRADUALLY SHIFT EASTWARD OVER NORTHERN
ILLINOIS BY LATE THURSDAY. ADDITIONALLY...DURING THIS PERIOD...A
LARGE SURFACE RIDGE OF HIGH PRESSURE WILL CONTINUE TO DOMINATE
OVER SOUTHERN CANADA AND THE UPPER GREAT LAKES REGION.

THE PRESSURE PATTERNS DISCUSSED ABOVE WILL CONTINUE TO FAVOR A
PERSISTENT EAST-NORTHEASTERLY LOW-LEVEL FLOW OF COOL LAKE
MODIFIED AIR OVER NORTHERN ILLINOIS. AS A RESULT OF THIS...HIGH
TEMPERATURES WILL CONTINUE TO VARY WIDELY OVER THE REGION OVER THE
NEXT COUPLE OF DAYS. THE COOLEST AREAS WILL BE NEAR LAKE
MICHIGAN...WHERE TEMPERATURES WILL LIKELY REMAIN IN THE MID TO
UPPER 40S. HOWEVER...SOUTH OF INTERSTATE 80...TEMPERATURES COULD
WARM WELL INTO THE 60S WEDNESDAY AND THURSDAY.

IT APPEARS THE THREAT FOR SHOWERS WILL HOLD OFF UNTIL LATE IN THE
DAY ON WEDNESDAY...ESPECIALLY OVER FAR NORTHEASTERN ILLINOIS...BUT
SHOWERS WILL GRADUALLY BECOME LIKELY FROM SOUTHWEST TO NORTHEAST
THROUGH THE DAY AS BETTER MOISTURE TRANSPORT AND WARM AIR
ADVECTION BEGINS TO OCCUR IN RESPONSE TO THE STORM SYSTEM
APPROACHING FROM THE WEST. WEDNESDAY EVENING LOOKS TO BE A RATHER
WET PERIOD OVER THE REGION AS 850 MB WARM FRONT BEGINS TO SHIFT
NORTHWARD OVER THE AREA. IT ALSO APPEARS THERE WILL BE A LOW
THREAT FOR SOME ELEVATED THUNDERSTORMS AS THE 850 MB FRONT MOVES
UP OVER THE REGION. MODEL SOUNDINGS ALSO INDICATE SOME MODEST
STEEPENING MID-LEVEL LAPSE RATES WENDESDAY NIGHT AS THE MID LEVEL
DRY SLOT BEGINS TO SHIFT OVER THE AREA. WITH THIS IN MIND...WE
HAVE ADDED A CHANCE OF THUNDER TO THE FORECAST. IT APPEARS THE
BEST AREAS WILL BE SOUTH...BUT WITH A WARM AIR ADVECTION SETUP
WEDNESDAY NIGHT...WE ADDED A SMALL CHANCE TO THE ENTIRE FORECAST
AREA.

ON THURSDAY THE UPPER AND LOWER LEVEL LOW ARE EXPECTED TO SHIFT
OVER THE AREA. THIS COULD SET UP SOME ADDITIONAL DIURNAL
THUNDERSTORMS OVER SOUTHERN SECTIONS OF THE AREA IN CLOSE
PROXIMATE TO THE SURFACE BOUNDARY. IT ALSO APPEARS HIGH
TEMPERATURES COULD GET INTO THE LOWER 70S SOUTH OF THE SURFACE
FRONT OVER MY FAR SOUTH. FARTHER NORTH 50S ARE LIKELY...AND EVEN
COLDER...IN THE MID TO UPPER 40S NEAR LAKE MICHGAN.

KJB

&&

.LONG TERM...
326 AM CDT

WEDNESDAY NIGHT THROUGH TUESDAY...

THE SAME SYSTEM WILL STILL BE IN THE AREA THURSDAY CONTINUING TO
WEAKEN AND FILL. ENOUGH COLD AIR ALOFT SHOULD BE PRESENT TO
SUPPORT A CONTINUED THREAT OF SHOWERS INTO THE DAY THURSDAY BEFORE
THIS SYSTEM FINALLY DISSIPATES AS IT MOVES EAST AWAY FROM THE AREA
THURSDAY NIGHT. A BREAK IN PRECIP CHANCES IS THEN EXPECTED FRIDAY
AND PROBABLY MOST IF NOT ALL OF SATURDAY AS WELL BEFORE THE NEXT
BIG SHORTWAVE/CLOSED EMERGES TO THE LEE OF THE ROCKIES AND HEADS
TOWARD THE MIDWEST BY LATER IN THE WEEKEND. HAVE TRIED TO SLOW
POPS A BIT FROM BLENDED MODEL GUIDANCE...BUT SUSPECT FURTHER
SLOWING IN THE ARRIVAL OF PRECIP COULD BE NEEDED AS MEDIUM RANGE
MODELS TEND TO SLOW THESE TYPE OF SYSTEMS EASTWARD PROGRESS AT
THIS DISTANCES. ONCE THE SYSTEM DOES EVENTUALLY ARRIVE LATER IN
THE WEEKEND LOOK FOR MORE RAIN AND PERHAPS SOME THUNDER CHANCES AS
WELL.

NOW THAT WINDS ARE SHIFTING TO NORTHEAST BEHIND THE FRONT MOVING
THROUGH THE AREA EARLY THIS MORNING...LOOK FOR THE NORTHEAST OR
EAST WIND REGIME TO REMAIN LOCKED IN THROUGH THE UPCOMING WEEKEND.
THE EASTERLY WINDS AND FREQUENT BOUTS OF CLOUD COVER AND RAIN WILL
KEEP TEMPS BELOW AVERAGE THROUGH THE UPCOMING WEEKEND. NO WHERE
WILL THAT BE THE CASE MORESO THAN NEAR THE LAKE WHERE TEMPERATURES
PROBABLY WONT REACH 50 DEGREES AGAIN THROUGH THE REST OF THE AND
POSSIBLY THROUGH THE WEEKEND AS WELL.

IZZI

&&

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

CONCERNS CENTER AROUND MVFR CEILINGS AND SPECIFIC END
TIME...FOLLOWED BY CONTINUED EAST WINDS. FOCUS SHIFTS TO RAIN
POTENTIAL AND TIMING FOR WEDNESDAY AFTERNOON.

CEILINGS CONTINUE TO RISE PER MODEL GUIDANCE WITH MOST LOCATIONS
INTO THE MVFR CATEGORY AS OF 17Z...WITH THE EXCEPTION BEING RIGHT
AT THE LAKEFRONT WHERE IFR WILL LINGER A BIT LONGER. REMNANTS OF
THE MORNING CONVECTIVE COMPLEX WILL CONTINUE TO DRIFT
EAST/SOUTHEAST TODAY AND WILL NOT IMPACT THE TERMINALS DIRECTLY.
GUIDANCE CONTINUES TO SUGGEST MVFR STRATUS WILL LINGER FOR MOST OF
THE DAY AND AT LEAST THE EARLY EVENING HOURS. GUIDANCE IS MIXED AS
TO WHETHER THE MVFR CIGS WILL LAST INTO THE MORNING
HOURS...POSSIBLY LIFTING TO VFR OVERNIGHT THEN RETURNING TO MVFR
IN THE MORNING FOR A TIME. DEWPOINTS DO NOT DROP MUCH
TONIGHT...BUT COOLING OVERNIGHT WILL BE LIMITED DUE TO CONTINUED
EAST WINDS. THESE FACTORS SUGGEST STATUS QUO OF AT LEAST SOME
SCATTERED LOW VFR/HIGH MVFR CLOUDS BEING AROUND.

THE LARGE STORM SYSTEM TO OUR WEST WILL SLOWLY DRIFT EASTWARD ON
WEDNESDAY. HIGHER CONFIDENCE EXISTS IN SHOWERS/EMBEDDED
THUNDERSTORM CHANCES DURING THE EVENING HOURS...BUT AN ELEVATED
WARM FRONT WILL BEGIN MOVING NORTHWARD DURING THE AFTERNOON. AT
THIS POINT THUNDER CHANCES IN THE AFTERNOON APPEAR TOO LOW TO
INCLUDE IN THE TAF. SOME GUIDANCE EVEN HOLDS OF ON THE SHOWER
ACTIVITY UNTIL LATE IN THE DAY. WILL HANDLE THIS WITH A
COMPROMISE TIMING AROUND 20-21Z IN THE 30 HR ORD TAF.

KMD

&&

.MARINE...
207 PM CDT

NOW THAT THE COLD FRONT HAS CLEARED THE LAKE...WINDS WILL LARGELY
REMAIN NORTHEASTERLY FOR MUCH OF THE PERIOD. HIGH PRESSURE IS
CENTERED OVER WESTERN HUDSON BAY...WITH LOW PRESSURE OVER THE
PLAINS. THIS LOW WILL DEEPEN SOME TONIGHT THEN SLOWLY WEAKEN AS IT
SPREADS FROM THE CENTRAL PLAINS WEDNESDAY TO CENTRAL ILLINOIS
THURSDAY. ONCE THIS LOW MOVES EAST...BROAD HIGH PRESSURE EXTENDING
SOUTH FROM HUDSON BAY WILL REMAIN IN PLACE WHILE ANOTHER LOW FORMS
IN THE PLAINS LATE IN THE WEEK. WINDS OVER THE LAKE NEVER GET TOO
STRONG AS THE GRADIENT IS NOT SUPER STRONG BETWEEN THESE
FEATURES...BUT SPEEDS WILL CERTAINLY SUPPORT OCCASIONAL SMALL
CRAFT ADVISORY LEVEL WAVES >=4FT AND POSSIBLY STRONGER WINDS AT
TIMES. THE GRADIENT WILL BE STRONGEST ACROSS THE SOUTH HALF. WE
HAVE EXTENDED THE CURRENT SMALL CRAFT ADVISORY FOR THE ILLINOIS
NEARSHORE THROUGH THURSDAY AFTERNOON AS THE ENE FETCH WILL
MAINTAIN WAVES GENERALLY AT OR ABOVE 4 FT FOR MOST OF THIS PERIOD
EXCEPT FOR POSSIBLY A BRIEF PERIOD WEDNESDAY EVENING. WE HAVE
MAINTAINED THE INDIANA NEARSHORE EXPIRATION TIME JUST FOR MORE OF
AN EAST WIND CUTTING DOWN WAVES FOR A LONGER PERIOD OF TIME
THOUGH...THOUGH IT IS LIKELY THERE WILL BE ANOTHER PERIOD OF
HIGHER WAVES ON THE INDIANA SHORE THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 5 PM THURSDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM WEDNESDAY.

&&

$$

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