Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 240257
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
957 PM CDT SAT MAY 23 2015

.SHORT TERM...
236 PM CDT

TONIGHT AND SUNDAY...
PRECIPITATION TIMING AND COVERAGE WILL BE THE MAIN FOCUS THROUGH THE
DAY SUNDAY. AFTERNOON WATER VAPOR IMAGERY SHOWS A LARGE UPPER LOW
SPINNING OVER UTAH/COLORADO WITH AN UPPER RIDGE AMPLIFYING OVER THE
EASTERN PLAINS AND TRANSLATING NORTHEAST. THIS CREATES A SOUTH TO
SOUTHWESTERLY UPPER FLOW FROM WEST TEXAS/NEW MEXICO INTO THE MIDWEST
WITH AN EMBEDDED UPPER WAVE MOVING NORTHEAST FROM EASTERN
KANSAS/OKLAHOMA. AT THE SURFACE...LOW PRESSURE IS OVER WEST
TEXAS/NEW MEXICO WITH A WARM FRONT DEVELOPING EASTWARD INTO
OKLAHOMA. THE LOW WILL LIFT NORTHEAST INTO THE CENTRAL HIGH PLAINS
TONIGHT AND SUNDAY MORNING. MID LEVEL WARM ADVECTION WILL INCREASE
LATE TONIGHT AS THE SYSTEM ADVANCES NORTHEAST WITH THE LOW LEVEL JET
DEVELOPING ACROSS THE MID/UPPER MISSISSIPPI RIVER VALLEY. THUS THE
BULK OF THE OVERNIGHT PRECIPITATION/CONVECTION WILL LIKELY STAY TO
THE WEST OF THE FORECAST AREA BUT SOME SCATTERED ACTIVITY WILL BE
POSSIBLE LOCALLY OVERNIGHT...MAINLY OVER WESTERN AREAS...THANKS TO
THE INCREASED WARM ADVECTION AND MOISTURE FLUX. THE THREAT REMAINS
MINIMAL SO WILL ONLY MENTION SLIGHT POPS WEST LATE TONIGHT THROUGH
DAYBREAK SUNDAY.

WARM ADVECTION STRENGTHENS ACROSS THE AREA SUNDAY...ESPECIALLY FROM
LATE MORNING THROUGH THE AFTERNOON. THE WARM FRONTAL BOUNDARY WILL
BE FOCUSED ACROSS IOWA AND LOSE DEFINITION TO THE EAST. HIGH RES
GUIDANCE RANGES FROM VERY LITTLE PRECIP ACTIVITY THROUGH THE DAY TO
WELL ORGANIZED ACTIVITY...MAINLY IN THE AFTERNOON. AM THINKING THAT
THERE MAY BE SOME LINGERING SPOTTY ACTIVITY AFTER DAYBREAK...MAINLY
NORTH/WEST...WITH A WINDOW FOR MINIMAL COVERAGE MID/LATE MORNING.
CHANCES/COVERAGE THEN INCREASE DURING THE AFTERNOON AS BETTER
FORCING SPREADS IN. STILL TOUGH TO PIN DOWN THE BEST WINDOWS FOR
PRECIP BUT PREFER THE AFTERNOON HOURS OVERALL...BUT WILL START TO
RAMP UP POPS DURING THE EARLY AFTERNOON. NORTHWEST INDIANA WILL
LIKELY HAVE THE LOWEST PRECIP CHANCE OF ANYWHERE IN THE CWA.
MORNING ACTIVITY WOULD PRIMARILY BE SHOWERS WITH THUNDER POTENTIAL
SPREADING FROM SOUTHWEST TO NORTHEAST THROUGH THE AFTERNOON. THE
MOST ABUNDANT CLOUD COVER WILL BE WEST AS WILL THE OVERALL BEST
CHANCE OF RAIN SO TEMPS WILL LIKELY BE LIMITED TO THE MID 70S THERE
...WHILE THE REST OF THE INLAND CWA SEES UPPER 70S/AROUND 80. A
SOUTHEAST WIND WILL ONCE AGAIN KEEP ILLINOIS LAKESHORE AREAS COOL
WITH COOLING EXTENDING FURTHER INLAND ACROSS EASTERN LAKE COUNTY IL.

MDB

&&

.LONG TERM...
236 PM CDT

SUNDAY NIGHT THROUGH FRIDAY...

THE EXTENDED LOOKS UNSETTLED WITH NUMEROUS CHANCES OF RAIN AND
THUNDERSTORMS. AN UPPER LEVEL RIDGE REMAINS OVER THE REGION SUNDAY
NIGHT WITH A CLOSED LOW OVER THE ROCKIES.  AS THE LOW PUSHES OVER
THE DAKOTAS MONDAY MORNING...A SERIES OF SHORTWAVE TROUGHS BEGINS TO
MARCH OVER THE REGION. EXPECTING THE SHORTWAVE TROUGH TRAIN TO
CONTINUE THROUGH THURSDAY UNTIL THE UPPER LEVEL TROUGH PUSHES EAST
OF THE REGION.

HIGH PRESSURE WILL BE OVER THE EASTERN THIRD OF THE CONUS SUNDAY
NIGHT WITH A SURFACE LOW FORMING OVER THE CENTRAL PLAINS EARLY
MONDAY MORNING.  THE LOWS WARM FRONT LIFTS NORTH THROUGH THE REGION
EARLY MONDAY MORNING AS WELL. A LOW LEVEL JET SHIFTS EAST THROUGH
THE CWA SUNDAY NIGHT AND EXPECTING TO SEE SHOWERS AND PERHAPS A FEW
THUNDERSTORMS FIRE AND THEN FESTER NORTH OF THE JET/S NOSE.
FORECASTED CAPE IS NOT OVERLY IMPRESSIVE WITH ONLY A COUPLE OF
HUNDRED OF J/KG TO WORK WITH.  WINDS WILL BE IN EXCESS OF 40 KT JUST
A COUPLE THOUSAND FEET OFF OF THE GROUND SO MY MAIN CONCERN FOR ANY
SEVERE WEATHER WOULD BE HIGHER WINDS MIXING DOWN TO THE SFC.

EXPECTING A LULL IN ACTIVITY MONDAY AFTN AS THE MAIN VORTICITY
STREAMER AND LOW LEVEL JET SHIFT EAST OF THE CWA.  SOUTHWEST WINDS
WILL BE GUSTING TO ARND 30 MPH MONDAY AFTN. HAVE LOW CONFIDENCE IN
SKY COVER AND SKY COVER WILL PLAY A BIG PART IN HOW WARM WE GET
MONDAY. DECIDED TO GO A COUPLE OF DEGREES WARMER SO ALL AREAS ARE
AROUND 80. HOWEVER LOCAL CLIMATE STUDIES SUGGEST IF WE ARE
SUNNY...WE COULD SEE MID 80S.  IN ADDITION TO WARMER TEMPS...THE
AMPLE SUNSHINE COULD KICK OFF MORE THUNDERSTORMS...BUT THINKING WE
WILL HAVE ENOUGH CLOUD COVERAGE TO KEEP CONVECTION AND TEMPS IN
CHECK.

ADDITIONAL SHOWERS AND THUNDERSTORMS ARE POSSIBLE MONDAY NIGHT BUT
THINKING THE MAJORITY OF ACTIVITY WILL BE OVER CENTRAL IL CLOSER TO
THE UPPER LEVEL VORTICITY. DID RAISE POPS SOUTH OF I-80 TO AROUND 30
PERCENT IN CASE ANY OF THE ACTIVITY TO OUR SOUTH BLEEDS INTO THE
CWA. WE REMAIN IN THE WARM SECTOR SO KEPT MIN TEMPS MILD IN THE MID
60S.

TUESDAY WILL BE ANOTHER DAY SPENT IN THE WARM SECTOR WITH
THUNDERSTORM CHANCES INCREASING THROUGH THE AFTERNOON. SOUTHWEST
WINDS WILL STILL BE GUSTY...BUT ONLY BTWN 25 AND 30 MPH. THINKING
CLOUD COVER WILL BE MORE PROMINENT TUESDAY SO LOWERED HIGHS INTO THE
UPPER 70S.  PWAT VALUES INCREASE TO OVER 1.5 INCHES TUESDAY SO COULD
SEE SOME HEAVY DOWNPOURS.

SHOWERS AND STORMS SHIFT EAST AS THE COLD FRONT SWINGS THROUGH LATE
TUESDAY NIGHT INTO WEDNESDAY MORNING.  ADDITIONAL SHOWERS AND STORMS
ARE PSBL WEDNESDAY AS THE UPPER LEVEL TROUGH FINALLY MOVES
THROUGH...BUT HAVE LOW CONFIDENCE IN OCCURRENCE AND COVERAGE SINCE WE
MAY BE STABLE.  TEMPS WILL NOT FALL MUCH BEHIND THE COLD FRONT WITH
HIGHS IN THE UPPER 70S AWAY FROM THE LAKE. SOME GUIDANCE MEMBERS
SUGGEST WINDS WILL TURN OFF OF THE LAKE SO HAVE HIGHS IN THE LOW 70S
ALONG THE LAKE SHORE. HAVE LOW CONFIDENCE IN WIND DIRECTION ALONG
THE LAKE FRONT WEDNESDAY.

LATE NEXT WEEK LOOKS WARM WITH HIGH TEMPS IN THE 80S.  COULD SEE
ISOLATED SHOWERS AND STORMS THURSDAY BUT THE BETTER CHANCE FOR
PRECIP IS FRIDAY WHEN A BOUNDARY APPROACHES FROM THE NORTHWEST.
GUIDANCE DIFFERS IN HOW QUICKLY THE BOUNDARY WILL SHIFT EAST SO
CAPPED POPS IN THE CHANCE RANGE.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* SOUTHEAST WINDS INCREASING TO 10 KT+ BY EARLY AFTERNOON SUNDAY.

* CHANCE OF -SHRA SUNDAY MORNING THEN SLOWLY INCREASING CHANCES
  INCLUDING TSRA LATE IN THE DAY AND MORE SO AFTER DARK.


//DISCUSSION...UPDATED 00Z...

THE LAKE BREEZE BOUNDARY WILL CONTINUE TO INCH WESTWARD BEFORE
FADING AROUND OR SOON AFTER SUNDOWN. AS THAT OCCURS...THE EASTERLY
WINDS AT ORD AND MDW WILL EASE IN SPEED AND GRADUALLY VEER. SO 10
KT+ SPEEDS SHOULD BE FADING BETWEEN 01Z-02Z. OTHERWISE A QUIET
NIGHT IS IN STORE FOR AREA TAF SITES.

THE SUNDAY FORECAST IS CHALLENGING AS THERE ARE CHANCES FOR LIGHT
SHRA THROUGH MID AFTERNOON AND THEN CHANCES FOR SHRA/TSRA AFTER
THAT POINT. ONGOING WIDESPREAD STORMS ACROSS THE SOUTHERN PLAINS
ARE LIKELY TO HOLD BACK THE ELEVATED WARM FRONT AND ASSOCIATED
MOISTURE RETURN THROUGH TONIGHT AND EVEN INTO SUNDAY. THIS MAY BE
ENOUGH TO PREVENT MUCH SHOWER COVERAGE IN THE AFTERNOON AND EVEN
THE EVENING. FEEL RFD HAS THE BEST CHANCES FOR GETTING INTO SOME
CONVECTIVE ACTIVITY LATE IN THE DAY AND INTO SUNDAY
EVENING...WHILE AREAWIDE OVERNIGHT SUNDAY. OVERALL CONFIDENCE IS
LOW ON SPECIFIC TIMING AND COVERAGE DURING THE DAY SUNDAY...BUT
HAVE FELT A LITTLE STRONGER LEANING TOWARD THE MAINLY DRY ROUTE
DURING THE DAY FOR CHICAGO AREA TAF SITES.

WINDS ON THE REGIONAL SCALE WILL BECOME SOUTHEAST ON SUNDAY AND
GRADUALLY INCREASE IN SPEED WITH THE PRESSURE GRADIENT. THE
DIRECTION WILL FAVOR A LAKE BREEZE AGAIN IN NORTHEAST
ILLINOIS...WHICH WOULD TURN WINDS MORE DUE EASTERLY IF IT CAN
REACH ORD AND MDW. AT THIS TIME HAVE HELD MORE OF A SOUTHEAST
WIND IN THE TAFS...WHICH SHOULD IN ITSELF BE OVER 10 KT WITH SOME
PERIODIC GUSTS.


//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM IN WINDS ON SUNDAY AND TIMING OF 10+ KTS.

* HIGH THAT ANY TSRA CHANCES WOULD BE AFTER 21Z ON SUNDAY...BUT
  LOW ON SHRA TIMING AND COVERAGE ON SUNDAY AND SUNDAY EVENING.


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

MONDAY...TSRA AND MVFR LIKELY IN THE MORNING. IFR POSSIBLE. GUSTY
         SOUTHWEST WINDS.
TUESDAY... TSRA LIKELY. GUSTY SOUTHWEST WINDS.
WEDNESDAY...CHANCE OF TSRA. WEST WINDS TURNING EAST.
THURSDAY...SLIGHT CHANCE OF TSRA. EAST WINDS.
FRIDAY...CHANCE OF TSRA. WEST WINDS.

MTF

&&

.MARINE...
236 PM CDT

HIGH PRESSURE OVER THE LOWER GREAT LAKES AND APPALACHIANS
WILL SHIFT OFF THE EAST COAST TONIGHT WHILE A SURFACE RIDGE AXIS
LINGERS ACROSS THE WESTERN LAKES. LOW PRESSURE WILL MOVE
NORTHEASTWARD FROM THE SOUTHERN HIGH PLAINS AND EVENTUALLY TO
WESTERN LAKE SUPERIOR BY MONDAY EVENING. A TROUGH OF LOW PRESSURE
MOVING ACROSS EASTERN ONTARIO THIS AFTERNOON HAS HELPED TO TIGHTEN
THE PRESSURE GRADIENT ACROSS NORTHERN LAKE MICHIGAN WHICH HAS
ALLOWED STEADY/BREEZY SOUTHWEST WINDS WHILE A WEAKER GRADIENT TO
THE SOUTH HAS ALLOWED FOR AN ONSHORE FLOW. WINDS WILL DIMINISH
TONIGHT AS THE GRADIENT WEAKENS BUT THE GRADIENT WILL TIGHTEN LATER
SUNDAY ALLOWING WINDS TO COME UP A BIT. DIRECTION WILL REMAIN
SOUTHERLY...FAVORING SOUTHWEST WINDS NORTH AND SOUTHEAST WINDS
SOUTH. WITH THE LOW PASSING WEST OF THE LAKE MONDAY SPEEDS WILL
FURTHER INCREASE AND MAY REACH SMALL CRAFT ADVISORY LEVELS FROM THE
SOUTH AND SOUTHWEST. A WARM AND MOIST AIRMASS WILL ADVECT IN WITH A
SHALLOW STABLE LAYER HOLDING IN PLACE OVER THE LAKE WHICH WILL
LIKELY RESULT IN FOG DEVELOPING...PERHAPS AS EARLY AS SUNDAY
AFTERNOON...BUT MORE SO SUNDAY NIGHT THROUGH MONDAY. ANOTHER LOW IS
FORECAST TO CROSS THE REGION TOWARD WEDNESDAY RESULTING IN NORTHERLY
WINDS TO THE NORTH OF THE TRACK AND SOUTHERLY WINDS TO THE SOUTH.
HIGH PRESSURE QUICKLY CROSSES BEHIND THE LOW LATER IN THE WEEK
BRINGING A RETURN TO SOUTHERLY WINDS AS IT MOVES OFF TO THE EAST.

MDB

&&

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

$$

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