Area Forecast Discussion
Issued by NWS Chicago, IL

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591
FXUS63 KLOT 050857
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
357 AM CDT THU MAY 5 2016

.SHORT TERM...
323 AM CDT

TODAY THROUGH FRIDAY...

DEEP UPPER TROUGH/CLOSED LOW OVER THE OHIO VALLEY WILL LOSE ITS
GRIP ON THE REGION TODAY...MOVING TO THE EAST COAST/MID-ATLANTIC
BY THIS EVENING. SURFACE HIGH PRESSURE RIDGE OVER THE UPPER
MISSISSIPPI VALLEY AND NORTHERN LAKES THIS MORNING WILL SPREAD
ACROSS THE FORECAST AREA FROM THE NORTHWEST LATER TODAY...BENEATH
SUBSIDENCE ASSOCIATED WITH RISING HEIGHTS IN THE WAKE OF THE
DEPARTING TROUGH. THIS SUBSIDENCE AND ADVECTION OF DRIER AIR FROM
THE NORTH WILL WORK TO ERODE LINGERING CLOUD COVER OVER THE
EASTERN PARTS OF THE FORECAST AREA TODAY. TEMPERATURES WILL
MODERATE A BIT TODAY THOUGH STRONGER WARM ADVECTION HOLDS OFF
UNTIL TONIGHT. AFTERNOON HIGHS FROM THE MID 60S WEST TO THE UPPER
50S/AROUND 60 FAR EAST ARE EXPECTED...THOUGH NORTH-NORTHEAST LAKE
BREEZE WINDS WILL KEEP AREAS NEAR LAKE MICHIGAN IN THE 50S.

LOW-LEVEL WARM ADVECTION BEGINS IN EARNEST FROM THE NORTHWEST
TONIGHT AS UPPER RIDGE BUILDS ACROSS THE UPPER MISSISSIPPI VALLEY
AND NORTHERN GREAT LAKES. VARIOUS MODELS INDICATE POTENTIAL FOR
SOME LIGHT PRECIP UPSTREAM ACROSS WI...THOUGH 00Z SOUNDINGS FROM
THE SOURCE REGION OF THE NORTHERN PLAINS AND FAR UPPER MIDWEST
APPEAR PRETTY DRY...AND MODEL FORECASTS OF THE 300-305 K
ISENTROPIC SURFACES DEPICT UNIMPRESSIVE CONDENSATION PRESSURE
DEFICITS WHICH ADDS CONFIDENCE TO KEEPING A DRY FORECAST.

BY FRIDAY MORNING...SURFACE RIDGE AXIS IS OFF TO THE
SOUTH/SOUTHEAST OF THE CWA. WESTERLY LOW LEVEL FLOW...DRY PROFILES
AND 925 MB TEMPS OF +20 TO AROUND +23 C BY AFTERNOON SUPPORT MUCH
WARMER SURFACE TEMPS RANGING FROM THE UPPER 70S ACROSS THE FAR
EASTERN CWA...AND 83-84 F FOR MAXES ACROSS OUR WEST/NORTHWEST
COUNTIES. THE SURFACE PRESSURE GRADIENT SHOULD BE WEAK ENOUGH TO
ALLOW A LAKE BREEZE TO DEVELOP BY FRIDAY AFTERNOON...THOUGH WITH
ENOUGH WEST WIND COMPONENT TO PREVENT IT FROM PUSHING TOO FAR
INLAND OVER NORTHEAST IL. LAKE BREEZE MAY BE A BIT STRONGER INTO
NORTHWEST INDIANA WHERE GRADIENT WILL BE A BIT WEAKER.

RATZER

&&

.LONG TERM...
323 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE REMAINS STEADFAST IN AMPLIFYING A SHORT WAVE TROUGH
WHICH MOVES ACROSS SOUTHERN CANADA FRIDAY...THEN DIGS SOUTHEAST
AND BREAKS DOWN THE UPPER RIDGE ACROSS THE WESTERN GREAT LAKES
REGION OVER THE WEEKEND. AT THE SURFACE...THIS MANIFESTS AS A
SOUTHEASTWARD MOVING SURFACE LOW AND COLD FRONT WHICH MOVES INTO
THE CWA EARLY SATURDAY MORNING. DESPITE STEEP MID-LEVEL LAPSE
RATES...FORECAST SOUNDINGS INDICATE A LACK OF DEEP SATURATION
COINCIDENT WITH THE FRONT PUSHING ACROSS NORTHERN PARTS OF THE CWA
EARLY SATURDAY. THIS...ALONG WITH DIURNAL MINIMUM FOR NEAR-SURFACE
BASED INSTABILITY SUGGESTS LIMITED POPS INITIALLY ACROSS THE
NORTHERN HALF OF THE CWA. CONVECTION POTENTIAL LOOKS A LITTLE
BETTER ACROSS THE SOUTHERN COUNTIES OF THE FORECAST AREA LATE
MORNING/EARLY AFTERNOON WHERE DIURNALLY WARMING BOUNDARY LAYER
SHOULD SUPPORT GREATER NEAR-SURFACE BASED CAPES. ELEVATED CAPE IS
INDICATED FARTHER NORTH ON THE COOL SIDE OF THE BOUNDARY INTO THE
AFTERNOON ATOP COOL BOUNDARY LAYER WHICH MAY SUPPORT RAIN/EMBEDDED
THUNDER POTENTIAL AS LARGE SCALE FORCING INCREASES. TEMPERATURES
WILL BE TRICKY ON SATURDAY WITH FRONT MOVING THROUGH DURING THE
MORNING/MIDDAY. MILD START TO THE DAY WILL LIKELY ALLOW MOST
LOCATIONS TO WARM INTO THE 60S BEFORE STRONGER NORTHERLY COOL PUSH
DEVELOPS BEHIND THE FRONT...AND SOUTHERN COUNTIES LIKELY TAPPING
THE LOW-MID 70S. FALLING TEMPS ARE EXPECTED NEAR LAKE MICHIGAN
HOWEVER...WHERE READINGS WILL LIKELY DIP INTO THE 50S.

THE FRONT THEN PUSHES WELL SOUTH OF THE CWA INTO THE OHIO VALLEY
SATURDAY NIGHT...WITH WEAK SURFACE HIGH PRESSURE SPREADING ACROSS
THE REGION. THIS SHOULD TAKE PRECIP CHANCES SOUTH OF THE FORECAST
AREA SATURDAY NIGHT AND SUNDAY WHILE DRY...MODESTLY COOL WEATHER
LINGERS LOCALLY.

DAYS 5-7 SEE A CONTINUATION OF SPLIT FLOW ALOFT...WITH A CLOSED
UPPER LOW OVER THE WESTERN CONUS EVENTUALLY WEAKENING AND LIFTING
NORTHEAST ACROSS THE MIDWEST THROUGH WEDNESDAY. DIFFERENCES IN
GUIDANCE ABOUND THOUGH THERE IS GENERAL CONSENSUS THAT THE FRONT
TO OUR SOUTH LIFTS BACK INTO THE AREA AS A WARM FRONT SUNDAY NIGHT
INTO MONDAY... BECOMING NEARLY STATIONARY AS THE ASSOCIATED
SURFACE LOW MOVES INTO OUR AREA LATE TUESDAY/WEDNESDAY. THIS SETS
UP THE POTENTIAL FOR A POTENTIALLY WET EARLY-MID WEEK PERIOD WITH
TEMPS NEAR NORMAL IN THE 60S/LOW 70S...AND ALSO SOME DAILY LAKE
COOLING.

RATZER

&&

.AVIATION...
FOR THE 06Z TAFS...

HIGH PRESSURE STRETCHES FROM LAKE SUPERIOR INTO THE CENTRAL PLAINS
AND WILL INCH TOWARDS NORTHERN ILLINOIS OVERNIGHT AND THROUGH THE
DAY THURSDAY. A MODEST NORTHERLY GRADIENT PERSISTS ACROSS NORTHERN
ILLINOIS LATE THIS EVENING AHEAD OF THE RIDGE AXIS...WHICH WILL
ALLOW A NORTHERLY BREEZE WITH GUSTS TO AROUND 20 KT AT TIMES TO
CONTINUE THROUGH MUCH OF THE OVERNIGHT HOURS. IN ADDITION...AN UPPER
LOW OVER INDIANA LATE THIS EVENING WILL CONTINUE TO RESULT IN SOME
SHOWERS ACROSS NORTHERN INDIANA AND LAKE MICHIGAN. GYY SHOULD BE THE
ONLY TERMINAL THAT SEES PRECIP...THOUGH MDW IN PARTICULAR MAY BE
CLOSE AND CANNOT RULE OUT A FEW SPRINKLES AND/OR SOME MVFR CIGS
SNEAKING THAT FAR WEST...WITH FEW018 ALREADY SHOWING UP IN THE
MDW OB.

VFR CONDITIONS AND MODEST NORTH WINDS WILL CONTINUE THROUGH THE DAY
THURSDAY...THOUGH SHOULD SEE GUSTS TAPERING THROUGH THE DAY AS THE
RIDGE GETS CLOSER AND THE GRADIENT TO RELAXES. ANTICIPATE A LAKE
BREEZE WILL FORM DURING THE AFTERNOON TURNING WINDS TO THE
NORTHEAST. AROUND SUNSET THURSDAY EVENING...WINDS ARE EXPECTED TO
BECOME LIGHT AND VARIABLE AS THE HIGH MOVES OVERHEAD...THEN
EVENTUALLY BECOME WESTERLY BY EARLY FRIDAY AS THE RIDGE SINKS TO
OUR SOUTH.

BMD

&&

.MARINE...
356 AM CDT

LAKE MICHIGAN REMAINS UNDER A MODERATE NORTHERLY GRADIENT EARLY
THIS MORNING BEHIND DEPARTING LOW PRESSURE CENTERED ALONG THE MID
ATLANTIC COAST AND HIGH PRESSURE BUILDING INTO THE UPPER MIDWEST.
THE HIGH WILL CONTINUE TO BUILD SOUTHEAST ACROSS LAKE MICHIGAN
TODAY ALLOWING WINDS TO DIMINISH. THE GALE WARNING WILL BE ALLOWED
TO EXPIRE EARLY THIS MORNING...HOWEVER A SMALL CRAFT ADVISORY
WILL REMAIN IN EFFECT FOR HAZARDOUS WINDS AND WAVES THROUGH MID
MORNING FOR THE ILLINOIS NEARSHORE WATERS...AND THROUGH LATE THIS
AFTERNOON FOR THE INDIANA NEARSHORE WATERS. THE RIDGE AXIS WILL
SETTLE SOUTHEAST OF LAKE MICHIGAN LATE THIS EVENING AND TONIGHT
ALLOWING SOUTHWEST TO SOUTH WINDS TO OVERSPREAD THE LAKE...
INCREASING INTO THE 15 TO 25 KT RANGE BY MIDDAY FRIDAY. ANOTHER
AREA OF LOW PRESSURE IS EXPECTED TO MOVE ACROSS ONTARIO INTO
QUEBEC ON FRIDAY WITH A TRAILING COLD FRONT PUSHING SOUTH ACROSS
LAKE MICHIGAN FRIDAY NIGHT INTO EARLY SATURDAY WITH NORTHERLY
WINDS TO AROUND 30 KT EXPECTED BEHIND THE FRONT.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ743-LMZ744-LMZ745-LMZ777-LMZ779 UNTIL 4 AM
     THURSDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 7 PM THURSDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 AM THURSDAY.

&&

$$

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