Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 231924
AFDLOT

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

.SHORT TERM...
251 AM CDT

SATURDAY AND SATURDAY NIGHT...

SATURDAY IS SHAPING UP TO BE A RELATIVELY QUIET DAY.  WITH HIGH
PRESSURE OVER THE EASTERN GREAT LAKES GRADUALLY SLIDING SOUTHEAST
OFF THE MID ATLANTIC COAST AND LEE CYCLOGENESIS OVER THE WESTERN
PLAINS...WINDS WILL...SYNOPTICALLY...VEER FROM EASTERLY TO SOUTHERLY
THROUGH THE DAY TODAY.  HOWEVER...BY THIS AFTERNOON...SFC RIDGING
EXTENDING FROM THE HIGH CENTER THROUGH THE UPPER MISSISSIPPI VALLEY
WILL SET UP A WEAK SOUTHERLY PRESSURE GRADIENT OVER THE REGION.
SO...WHILE THE SYNOPTIC WINDS SHOULD REMAIN SOUTHERLY AROUND 10KT
THROUGH THE DAY...SOME LAKE INFLUENCE SHOULD SET UP A LAKE BREEZE.
UNDER THE EXPECTED SFC PATTERN...A NW-SE ORIENTED BOUNDARY IS
EXPECTED TO SET PUSH...PUSHING INLAND INTO LAKE COUNTY...KEEPING THE
WAUKEEGAN AREA ON THE COOLER SIDE.  THERE IS SOME QUESTION AS TO HOW
FAR INLAND THE LAKE BREEZE WILL PUSH INTO COOK COUNTY...BUT THE
LATEST HIGH RES SFC WIND GUIDANCE DOES SUGGEST THAT THE LAKE BREEZE
COULD PUSH AS FAR WEST AS ORD...SO...HAVE KEPT MAX TEMPS OVER ERN
COOK AND LAKE COUNTIES...INCLUDING DOWNTOWN CHICAGO ONLY IN THE
LOWER 60S.  THE REMAINDER OF THE AREA SHOULD SEE TEMPERATURES A BIT
HIGHER THAN YESTERDAY UNDER THE PREVAILING SOUTHERLY
FLOW...ESPECIALLY LOCATIONS OVER NERN IL WHICH WERE IMPACTED BY THE
LAKE BREEZE THAT HAD PUSHED PRETTY MUCH THROUGH ALL OF NERN IL AND
NWRN IN BY EARLY LAST EVENING.  SO...WITH THE EXCEPTION OF THE SMALL
AREA OF FAR NERN IL REMAINING COOLED BY THE LAKE BREEZE...THE HIGHS
IN THE MIDDLE TO UPPER 70S ARE EXPECTED TODAY.  CONDITIONS ARE
EXPECTED TO REMAIN DRY THROUGH THE DAY...THOUGH THICKENING MID AND
HIGH CLOUDINESS IS EXPECTED WITH CLOUD BASES GRADUALLY LOWERING
THROUGH THE DAY AND INTO TONIGHT AS DEEP LAYER MOISTURE INCREASES IN
ADVANCE OF THE SYSTEM DEVELOPING OVER THE WESTERN PLAINS.

BY LATE THIS EVENING...THE SOUTHERN STREAM JET WILL TAKE A TO THE
NORTHEAST AS UPPER RIDGING BUILDS FROM THE SERN CONUS BACK THROUGH
THE UPPER MISSISSIPPI VALLEY.  THIS WILL SHUNT THE DEEP LAYER
MOISTURE TRANSPORT ON A MORE NORTHEASTERLY TRAJECTORY FROM THE WRN
GULFMEX AND TX INTO THE MIDDLE MISSISSIPPI VALLEY.  THIS WILL BE THE
SOURCE MOISTURE FOR INCREASING PRECIPITATION CHANCES GOING INTO
EARLY SUNDAY MORNING.  THE INITIAL PCPN CHANCES SHOULD BEGIN WEST OF
THE I-39 CORRIDOR AFTER MIDNIGHT TONIGHT AND INTO THE EARLY MORNING
HOURS.  THERE COULD BE A FEW TSRA WITH THIS INITIAL PCPN...BUT
GENERALLY...SHOWERS ARE MORE LIKELY...WITH THE INCREASING TS CHANCES
INTO THE DAY ON SUNDAY.  INCREASING AND THICKENING CLOUD COVER ALONG
WITH DEWPOINTS RISING BACK INTO THE 50S OVERNIGHT TONIGHT INTO
SUNDAY MORNING...OVERNIGHT LOW TEMPS WILL BE A BIT MORE
SEASONABLE...WITH LOWS IN THE LOWER 50S...EXPECT THE WAUKEEGAN AREA
WHICH COULD STILL BE UNDER THE INFLUENCE OF LAKE-COOLED AIR...WITH
LOWS IN THE UPPER 40S.

KREIN

&&

.LONG TERM...
253 AM CDT

SUNDAY THROUGH FRIDAY...

SUNDAY THROUGH MEMORIAL DAY...
MAIN CONCERN FOR THE SECOND HALF OF THE HOLIDAY WEEKEND WILL BE
PRECIP CHANCES/TIMING/COVERAGE. 500MB HEIGHTS WILL NUDGE UP A LITTLE
SUN...WHICH LIKELY WILL SIGNAL A DELAY IN THE ONSET OF PRECIP FOR
THE BULK OF THE FORECAST AREA. FURTHER WEST ACROSS THE CENTRAL
CONUS...HEIGHT FALLS WILL BE NOTED WITH AN ATMOSPHERIC PLUME OF
MOISTURE STREAMING NORTH FROM THE WESTERN GULF ALONG RETURN FLOW
MOISTURE FROM THE DOWNSTREAM SFC RIDGE. GUIDANCE HAS BECOME LESS
ORGANIZED WITH THE SFC WAVE AND SHIFTED FURTHER WEST ACROSS THE
FRONT RANGE OF THE ROCKIES MIDDAY SUN...ALL POINTING TOWARDS
DELAYING THE PRECIP UNTIL MAINLY LATE AFTN AND POSSIBLY MORE TOWARDS
THE LATE EVENING HOURS. 500MB TROUGH WILL BE DRIFTING EAST/NORTHEAST
SUN EVE/EARLY MON...WITH HEIGHT FALLS BEGINNING TO OCCUR OVER THE
BULK OF THE FORECAST AREA.

THIS COUPLED WITH AN ANOMALOUSLY STRONG LVLL NOCTURNAL 40KT JET AND
THE SOUTHERLY WIND COMPONENT PROGGED AT NEARLY 4 SIGMA...SIGNALS
THAT OVERNIGHT SUN/EARLY MON IF AN ATMOSPHERIC WAVE CAN DEVELOP IT
WOULD LIKELY TRIGGER SOME BRIEF DOWNPOURS IN THIS TIMEFRAME. HOWEVER
THE SFC FEATURES CONTINUE TO BE LACKING IN ORGANIZATION...BUT WILL
MAINTAIN LIKELY POPS THRU DAYBREAK MON GIVEN THE PATTERN SETUP. BUT
COULD SEE THIS BEING LESS COVERAGE AND POSSIBLY ONLY EMBEDDED
THUNDER. SFC MOISTURE WILL STILL BE FELT AS DEW POINTS IN THE
LOW/MID 60S WILL ADVECT NORTH ACROSS THE REGION. AFTN TEMPS WILL BE
SLIGHTLY DIFFICULT GIVEN THE HIGH WATER CONTENT WITHIN
PARCELS...HOWEVER GUIDANCE HAS MAINTAINED A HIGH CONFIDENCE IN TEMPS
PUSHING THE UPR 70S TO ARND 80 BOTH SUN/MON.

LLVL JET WILL BEGIN TO PEEL NORTH/NORTHEAST OF THE REGION MON...WITH
A PROGGED DRY WEDGE LIFTING NORTHEAST ACROSS THE CENTRAL CONUS
TOWARDS THE FORECAST AREA BY MIDDAY MON. HAVE REFLECTED THIS WITH
SLIGHTLY LESS POPS IN THE MON AFTN TIMEFRAME...AND COULD SEE THE
AFTN/EVE HOURS END UP BEING DRY. ENSEMBLES ARE CURRENTLY INDICATING
LESS CONFIDENCE IN PRECIP IN THE EVENING HOURS...SO THE LATER
FORECASTS MAY INDEED FURTHER TRIM POPS FOR MON AFTN/EVE.

TUESDAY THROUGH FRIDAY... 500MB TROUGH WILL CONTINUE TO DRIFT EAST
TUE...WITH THE AXIS PIVOTING OVER THE CENTRAL CONUS. THIS WILL ALLOW
HEIGHTS TO FALL SLIGHTLY WITH MOIST SOUTHERLY CONTINUING ACROSS THE
REGION THROUGH THE MIDDLE OF NEXT WEEK. HIGH AMPLITUDE RIDGING
REMAINS ACROSS WESTERN CANADA WITH DOWNSTREAM RIDGING DEVELOPING
OVER THE SOUTHEAST CONUS. THIS WILL ALLOW A PERSISTENT SOUTHWEST
FLOW FOR THE SECOND HALF OF NEXT WEEK...WITH PERIODIC CHANCES FOR
SHOWERS AND THUNDERSTORMS.

TEMPERATURES WILL GENERALLY BE IN THE 70S WITH A FEW AFTERNOONS
TOUCHING 80 DEGREES NEXT WEEK. WITH GENERALLY AN OFFSHORE FLOW
EXPECTED FOR THE BULK OF THE EXTENDED...AREAS ADJACENT TO LAKE
MICHIGAN WILL BE ABLE TO MAINTAIN THE WARMTH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SW WINDS BACKING TO SE LATE THIS AFTERNOON/EARLY
  EVENING...THOUGH VARIABLE FOR A TIME TODAY.
* SHOWERS LATE TONIGHT INTO EARLY SUNDAY
* ANOTHER ROUND OF SHOWERS WITH EMBEDDED THUNDER PSBL SUNDAY AFTN

KMD

//DISCUSSION...UPDATED 18Z...

THE BATTLE OF THE LAKE INFLUENCE AND WARM SYNOPTIC SOUTHERLY FLOW
IS PLAYING OUT WITH THE ORD AND MDW ON THE BORDER OF THESE TWO
VARYING INFLUENCES ON WINDS. AN EARLIER LAKE BREEZE HAS STALLED
OUT CLOSER TO I-94 AND MAKING LITTLE PROGRESS AT THIS TIME. WINDS
ARE GENERALLY SSW ON THE WEST SIDE OF THE LAKE BREEZE AND ANYWHERE
FROM NE TO SE BEHIND IT. VARIABLE WINDS HAVE RESULTED AT TIMES
WITH THIS. GENERALLY EXPECT THAT WESTERN TAF SITES WILL HOLD THE
SSW WINDS THROUGH THE AFTERNOON WITH THE SE WINDS TAKING MORE
CONTROL FROM ORD EASTWARD LATE THIS AFTERNOON AND EVENING...THOUGH
TIMING ON THIS REMAINS A CHALLENGE. ALSO...WINDS BEHIND THE LAKE
BREEZE ARE NOT VERY STRONG...SO IT SHOULD BE LOW OPERATIONAL
IMPACT.

ATTENTION TURNS TO SHOWER/THUNDER POTENTIAL SUNDAY. THE LEADING
EDGE OF LOW LEVEL WARM AIR SURGES NORTHWARD LATE TONIGHT...AND
ALONG THIS BOUNDARY SOME SHOWERS ARE EXPECTED IN THE 10Z-15Z TIME
FRAME SOUTH TO NORTH. COVERAGE WILL NOT BE WIDESPREAD...THUS THE
VCSH MENTION. THEN AFTER A LULL...EXPECT THAT AS LOW LEVEL
MOISTURE ADVECTION INCREASES ANOTHER ROUND OF SHOWERS WITH
EMBEDDED THUNDERSTORMS CAN BE EXPECTED SUNDAY AFTERNOON. THOUGH
CONFIDENCE IS HIGH IN A PERIOD OF SHOWERS AND THUNDERSTORMS GUIDANCE
VARIES WITH WHETHER THIS BEGINS AT 18Z OR HOLDS OFF UNTIL CLOSER
TO 0Z THUS HAVE CARRIED A -SHRA MENTION IN THE ORD 30 HR TAF FOR
NOW TO ACCOUNT FOR UNCERTAINTY IN TIMING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM ON WIND SPEED AND DIRECTION.
* MEDIUM ON SHOWER POTENTIAL AND TIMING IN THE TAFS
* HIGH IN NO THUNDER UNTIL SUNDAY AFTERNOON...BUT LOW ON IF/WHEN IT
  WILL OCCUR AT THE TERMINAL SUNDAY PM.

KMD

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

SUNDAY NIGHT...CHANCE OF SHRA/TSRA. SOUTH-SOUTHEAST WINDS.

MONDAY...PERIODS OF SHRA/TSRA. GUSTY SOUTHWEST WINDS.

TUESDAY - THURSDAY...PERIODIC CHANCES FOR SHRA/TSRA. SOUTHWEST
WINDS.

FRIDAY...CHANCES OF SHRA. SOUTHWEST WINDS.

KREIN

&&

.MARINE...
305 AM CDT

SURFACE HIGH PRESSURE HAS BECOME CENTERED OVER THE EASTERN GREAT
LAKES WITH A LIGHT GRADIENT OVER LAKE MICHIGAN EARLY THIS MORNING.
WINDS ARE GENERALLY SOUTHERLY. LOW PRESSURE WILL REMAIN WELL
SOUTHWEST OF THE REGION OVER THE CENTRAL ROCKIES THIS
AFTERNOON...HOWEVER THE GRADIENT IS POISED TO TIGHTEN SLIGHTLY
THIS EVENING AND ALLOW WAVES TO BUILD ACROSS THE NORTHERN PORTIONS
OF THE LAKE. WITH WARM/MOIST AIR LIFTING NORTH OVER THE LAKE FOR
THE SECOND HALF OF THE WEEKEND...THE SETUP APPEARS FAVORABLE FOR
FOG DEVELOPMENT. IT IS POSSIBLE SOME POCKETS OF DENSE FOG MAY
DEVELOP AT SOME POINT THIS HOLIDAY WEEKEND.

AS THE LOW PRESSURE BEGINS TO LIFT NORTHEAST INTO THE CENTRAL
PLAINS LATE SUN INTO EARLY MON...THIS WILL PUSH A SLIGHTLY TIGHTER
GRADIENT OVER THE SOUTHERN HALF OF LAKE MICHIGAN MON. AS A RESULT
WINDS MAY FLIRT WITH SMALL CRAFT ADVISORY CONDITIONS MON.

THROUGH NEXT WEEK WINDS WILL REMAIN SOUTHERLY OVER THE LAKE...WITH
CONTINUED PERIODS OF FOG EXPECTED.

BEACHLER

&&

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

$$

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