Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 030637
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
137 AM CDT SUN MAY 3 2015

.UPDATE...
914 PM CDT

FOR EVENING UPDATE...

NO CHANGES TO GOING FORECAST THIS EVENING...BEYOND SOME MINOR TWEAKS
TO HOURLY TEMPS EARLIER ACCOUNT LAKE BREEZE. PRETTY DECENT LOOKING
SHORT WAVE TRACKING EASTWARD ACROSS EASTERN IOWA AT THIS HOUR PER
WATER VAPOR...THOUGH ITS MOVING INTO INCREASINGLY DRIER AIR AS IT
CONTINUES ITS EASTWARD TREK WITH RADAR RETURNS DEPICTING EROSION OF
LIGHT SHOWERS ALONG THE NORTHEAST FLANK THROUGH THE EARLY EVENING
HOURS. THIS MID-LEVEL WAVE WILL MOVE ACROSS THE FORECAST AREA DURING
THE OVERNIGHT HOURS...THOUGH GUIDANCE INDICATES THE BETTER MOISTURE
AND MOISTURE TRANSPORT WILL REMAIN ACROSS EASTERN IOWA INTO
SOUTHWEST WI. WHILE SOME EXPANSION IN COVERAGE IS POSSIBLE OVERNIGHT
INTO THE LOT CWA...IT APPEARS THE NEAR-TERM FOCUS WILL REMAIN
SOUTH/WEST OF THE FORECAST AREA WHERE GREATER MOISTURE AND WEAK
INSTABILITY ARE FOCUSED. OTHERWISE...HARD TO IMPROVE TOO MUCH ON THE
SLIGHT CHANCE SHOWER POPS LATE TONIGHT INTO SUNDAY MORNING.

RATZER

&&

.SHORT TERM...

TONIGHT THROUGH MONDAY NIGHT...

300 PM...FORECAST CONCERNS INCLUDE A CHANCE OF SHOWERS OVERNIGHT
INTO SUNDAY MORNING...THEN SHOWERS AND THUNDERSTORMS SUNDAY NIGHT
THRU MONDAY NIGHT.

IN THE SHORT TERM...A LAKE BREEZE HAS DEVELOPED WITH WINDS TURNING
ONSHORE IN NORTHWEST INDIANA...AND THEN SOUTHEASTERLY FROM
DOWNTOWN TO THE WI BORDER. SHORT TERM/HI RES GUIDANCE SUGGESTS
THIS BOUNDARY MAY CONTINUE MOVING INLAND THIS AFTERNOON BUT LOW
CONFIDENCE WITH 10+ MPH WINDS SPEEDS. COULD SEE THE LAKE BREEZE
REMAIN NEAR THE SHORE FOR THE NEXT FEW HRS THEN PUSH FURTHER
INLAND LATE THIS AFTERNOON/EARLY THIS EVENING AS WIND SPEEDS
DIMINISH SOME DIURNALLY.

UPPER WAVE OVER SOUTH CENTRAL IA/NORTHERN MO WILL MOVE NORTHEAST
TONIGHT AS IT SLOWLY WEAKENS. MODELS DIFFER ON HOW MUCH PRECIP
WILL REACH THE AREA. HAVE CONTINUED WITH SLIGHT CHANCE POPS FOR
MUCH OF THE AREA OVERNIGHT...DIMINISHING SUNDAY MORNING ACROSS
THE NORTH. ALSO REMOVED THUNDER AS INSTABILITY LOOKS RATHER LOW.
INCREASING MID/HIGH CLOUDS WITH THIS WAVE WILL ALSO HELP KEEP LOW
TEMPS RATHER MILD TONIGHT...GENERALLY IN THE 50S. AFTER ANY
MORNING SHOWERS...EXPECT AT LEAST PARTLY CLOUDY IF NOT MOSTLY
SUNNY SKIES SUNDAY AFTERNOON AND AFTER A WARMER START...HIGHS
SHOULD MAKE A RUN FOR THE LOWER 80S MOST AREAS. BREEZY SOUTHWEST
WINDS SHOULD PREVENT ANY LAKE COOLING WITH NO LAKE BREEZE
EXPECTED.

A FRONTAL BOUNDARY WILL MOVE ACROSS THE NORTHERN GREAT LAKES
SUNDAY EVENING...THEN SETTLE ACROSS AREA MONDAY. TIMING APPEARS TO
BE JUST A TAD SLOWER AND TRIMMED POPS SOME SUNDAY EVENING...WHICH
MAY END UP MAINLY DRY. SET UP STILL FAVORS THE POTENTIAL FOR HEAVY
RAIN BUT TRYING TO TIME INDIVIDUAL WAVES FOR BEST PRECIP TIMING IS
A BIT DIFFICULT. CONSENSUS SEEMS TO FOCUS ON MONDAY NIGHT AS THE
BEST TIME FOR WIDESPREAD SHOWERS/THUNDERSTORMS. MAINTAINED LIKELY
POPS SUNDAY NIGHT THRU MONDAY NIGHT...BUT THESE WILL LIKELY NEED
REFINEMENT WITH LATER FORECASTS.

PRECIP TIMING AND ASSOCIATED CLOUD COVER ALONG WITH FRONTAL
POSITION WILL ALL AFFECT HIGH TEMPS ON MONDAY...WHICH AT THIS
POINT IS SHAPING UP TO BE A BIT WARMER...WITH TEMPS IN THE 70S...
THOUGH CLOUD COVER AND EASTERLY WINDS COULD SIGNIFICANTLY LOWER
TEMPS ACROSS NORTHEAST IL AND THE LAKESHORE. CMS

&&

.LONG TERM...

TUESDAY THROUGH SATURDAY...

300 PM...MAIN FORECAST CONCERN ARE PRECIP CHANCES AND HIGH TEMPS.

WITH THE EXPECTATION THAT THE BEST CHANCE FOR PRECIP MAY END UP
BEING MONDAY NIGHT...POSSIBLY LINGERING INTO TUESDAY MORNING...
LOWERED POPS TUESDAY AND THESE MAY STILL BE TOO HIGH AS THE FOCUS
SHIFTS NORTH OF THE AREA. DECENT AGREEMENT THAT THE FRONTAL
BOUNDARY WILL STILL BE LOCATED ACROSS THE AREA TUESDAY AND THIS
WILL MAINTAIN COOLER EASTERLY FLOW OFF THE LAKE...BUT SOUTH OF
WHEREVER THIS BOUNDARY LIES...TEMPS WILL BE WELL INTO THE 70S. THE
FRONT WILL MOVE NORTH AS A WARM FRONT TUESDAY NIGHT INTO
WEDNESDAY. NOT MUCH TO FOCUS PRECIP DEVELOPMENT BUT MAINTAINED LOW
CHANCE POPS THRU WEDNESDAY MORNING. BY THE TIME THE FRONT LIFTS
NORTH...PRECIP CHANCES SHOULD END WITH GENERALLY DRY CONDITIONS
THRU THURSDAY. PRECIP CHANCES BEGIN TO INCREASE LATE IN THE WEEK
WITH PERHAPS THE BEST CHANCES FRIDAY NIGHT INTO SATURDAY.

HIGH TEMPS SHOULD CLIMB BACK INTO THE LOWER 80S SOUTH OF THE WARM
FRONT WED/THURS/FRI...WITH PERHAPS SOME ONSHORE WINDS/COOLER TEMPS
WEDNESDAY AS THE FRONT LIFTS BACK NORTH. CMS

&&

.AVIATION...

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

* SOUTH-SOUTHWEST WINDS GUSTING 20-25 KT THIS AFTERNOON.
* CHANCE FOR SHRA/TSRA LATE SUNDAY NIGHT.

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

RETURNING MOIST AIR ON A LOW-LEVEL JET WILL CONTINUE TO SPRING
STORMS ACROSS IA THROUGH DAYBREAK. WITH LESS MOISTURE AND NAMELY
INSTABILITY FURTHER EAST...ISOLATED SHOWERS ARE EXPECTED ACROSS
NORTH CENTRAL AND NORTHEAST IL...WITH A LITTLE MORE COVERAGE
POSSIBLE ACROSS NORTHWEST IL DURING AND JUST AFTER DAYBREAK AS
STORMS FROM IA WEAKEN. ALL IN ALL LITTLE PRECIPITATION CONCERNS
FOR THE CHICAGO AREA TAF SITES THROUGH MOST IF NOT THIS ENTIRE
TAF...AS DRY ENOUGH AIR WILL PREVAIL TODAY. SOUTH-SOUTHWEST WINDS
WILL INCREASE TODAY WITH A TIGHTER PRESSURE GRADIENT...YIELDING
OCCASIONAL GUSTS OF 20-25 KT LATE THIS MORNING AND MORE SO THIS
AFTERNOON. THE LOW-LEVEL JET AXIS WILL BE POSITIONED MORE OVER
THE AREA SUNDAY NIGHT PROVIDING 40-45 KT WINDS SPEEDS ABOVE 1000
FT. THE NEAR-SURFACE SPEEDS SHOULD BE ENOUGH /12 KT OR SO/ NOT TO
CREATE TRUE LOW-LEVEL WIND SHEAR.

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

* MEDIUM-HIGH IN WINDS.
* LOW ON TIMING OF SHRA/TSRA LATE SUNDAY NIGHT OR JUST BEYOND TAF
  PERIOD.

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

MONDAY THROUGH TUESDAY...PERIODIC SHRA/TSRA WITH MVFR AND BRIEF
IFR POSSIBLE.

WEDNESDAY THROUGH FRIDAY...PRIMARILY VFR.

MTF/IZZI

&&

.MARINE...
135 AM CDT

SOUTH-SOUTHWEST WINDS WILL INCREASE ACROSS THE GREAT LAKES REGION
TODAY AS THE PRESSURE GRADIENT TIGHTENS IN ADVANCE OF AN
APPROACHING COLD FRONT. THE OFFSHORE COMPONENT ALONG THE WESTERN
SHORE OF THE LAKE WILL BE ENOUGH TO WARRANT A SMALL CRAFT
ADVISORY FROM LATE MORNING THROUGH THE AFTERNOON.

LOW PRESSURE FAR TO THE NORTH OF THE GREAT LAKES WILL USHER THE
COLD FRONT INTO THE WESTERN LAKES REGION LATER TONIGHT. THIS FRONT
WILL EASE ITS WAY SOUTHEASTWARD ACROSS LAKE MICHIGAN BY EARLY
AFTERNOON MONDAY TURNING WINDS TO THE NORTH IN ITS WAKE. WITH THE
FRONT FORECAST TO STALL JUST SOUTH OF LAKE MICHIGAN...WINDS ACROSS
THE LAKE WILL TURN EASTERLY LATER MONDAY NIGHT AND THROUGH
TUESDAY. THE FRONT WILL THEN RETURN NORTHWARD AS A WARM FRONT
TUESDAY NIGHT AND WEDNESDAY. SOUTHERLY WINDS ARE THEN EXPECTED FOR
MUCH OF THE REST OF THE WEEK.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...10 AM SUNDAY TO 7
     PM SUNDAY.

&&

$$

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