Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300523
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1223 AM CDT SAT APR 30 2016

.UPDATE...
932 PM CDT

CURRENT FORECAST IS IN FAIRLY GOOD SHAPE FOR TONIGHT INTO EARLY
SATURDAY. CLOUDY CONDITIONS WILL DOMINATE TONIGHT WITH
TEMPERATURES ONLY DIPPING SLIGHTLY FROM WHERE THEY ARE
CURRENTLY...WHICH FOR MOST PLACES IS THE 40S. WATER VAPOR
SATELLITE AND REGIONAL RADAR ANALYSIS DEPICTS THE DYNAMIC
SYSTEM...WITH ITS UPPER LEVEL CENTER IN LEE OF THE ROCKIES. WARM
ADVECTION AHEAD OF THE LOW CONTINUES TO PRODUCE THUNDERSTORMS
ACROSS THE PLAINS AND MID MISSOURI REGION...WITH SNOW ON ITS BACK
SIDE IN COLORADO. THE WARM ADVECTION WING OF THE STORM WILL LIFT
NORTHEAST THROUGH THE AREA TOMORROW. IT WILL INDEED BE
WET...BREEZY...AND COOL...THOUGH FOR AREAS NORTH THE BULK OF THE
STEADIER RAIN WILL BE IN THE AFTERNOON.

KMD

&&

.SHORT TERM...
204 PM CDT

THROUGH SATURDAY...

COOL CLOUDY CONDITIONS HAVE PERSISTED AGAIN THIS AFTERNOON...WITH
THE LACK OF FORCING TO SCOUR THE CLOUDS FROM THE WEAK MID-LVL
HEIGHT RISES AND LACK OF PRESSURE GRADIENT. THIS HAS KEPT CLOUD
IMPROVEMENTS TO A MINIMUM AS WELL...AND THE NORTH/NORTHEAST SFC
FLOW HELD TEMPS ALONG THE IMMEDIATE LAKESHORE IN THE MID/UPR 40S.
FURTHER INLAND TEMPS HAVE SLOWLY WARMED INTO THE LOW/MID 50S.

THROUGH THIS EVENING AND MUCH OF THE OVERNIGHT HOURS MID-LVL
HEIGHTS WILL REMAIN SLIGHTLY ELEVATED...WHICH SHOULD MAINTAIN THE
DRY FORECAST THROUGH AT LEAST 9Z. LOW LEVEL MOISTURE WILL BE
STEADILY ADVECTING NORTH AS A FRONTAL BOUNDARY DRIFTS NORTH AHEAD
OF THE SHORTWAVE PRESENTLY POSITIONED OVER THE CENTRAL PLAINS. THE
CONTINUED NORTHEAST/EAST SFC WINDS WILL HELP TO DELAY THE ONSET
OF PRECIP ALONG AND NORTH OF I-80 UNTIL JUST AFTER DAYBREAK...BUT
EXPECT STEADY MOISTENING THROUGH THE COLUMN TO OCCUR WITH POPS
APPROACHING CATEGORICAL BY EARLY AFTERNOON.

VERY MOIST SAT AFTN IS IN STORE...AS PWAT VALUES ARE PROGGED TO
APPROACH 1 INCH AND PERHAPS ALONG THE SOUTHERN HALF OF THE
FORECAST AREA NEARLY 1.2 INCHES. WITH THE MOIST AXIS OVERHEAD SAT
AFTN AND ISENTROPIC ASCENT TO PARCELS COUPLED WITH A LOW LEVEL JET
AROUND 30-40KT...THE POTENTIAL FOR MODERATE RAIN TO OCCUR
THROUGHOUT THE AFTERNOON APPEARS FAVORABLE...ALONG WITH SOME
EMBEDDED THUNDER FROM MODEST INSTABILITY IN THE SOUTHERN CWFA.
TEMPS SAT WILL SLOWLY WARM INTO THE LOW/MID 50S...HOWEVER FOR
AREAS ADJACENT TO LAKE MICHIGAN IN FAR NORTHEAST IL THE NORTHEAST
WINDS WILL LIKELY KEEP TEMPS IN THE UPR 40S.

BEACHLER

&&

.LONG TERM...
256 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN CONCERN GOING INTO THE LONGER TERM FORECAST PERIOD WILL BE WITH
THE CONTINUATION OF WIDESPREAD PCPN INTO SATURDAY EVENING.  THE
VARIOUS MODELS ARE IN GOOD AGREEMENT ON TRACKING A BAND OF MODERATE
RAIN THROUGH THE CWA INTO THE EVENING HOURS AS A WEAK NRN STREAM
SHORTWAVE PHASES WITH THE MAIN SYNOPTIC WAVE TRACKING ACROSS THE
UPPER MISSISSIPPI VALLEY.  THE EXTENDED PERIOD OF WARM ADVECTION
THROUGH A DEEP LAYER AHEAD OF THE SYNOPTIC UPPER LOW...REFLECTED IN
FORECAST PWATS IN EXCESS OF 1 INCH THROUGH THE EVENING BACKS UP THE
SCENARIO FOR MODERATE RAIN.  INSTABILITY WILL LARGELY BE CONFINED TO
THE SRN PORTIONS OF THE CWA...SO...THE GREATEST CHANCES FOR THUNDER
SHOULD STILL BE SOUTH OF THE I-80 CORRIDOR.  INSTABILITY IS EXPECTED
TO BE RELATIVELY WEAK...OFF-SETTING MODERATE MID AND UPPER LEVEL
FORCING.  THEREFORE THE SEVERE THREAT IS MINIMAL AND TS COVERAGE
WILL LIKELY BE MORE ISOLD/EMBEDDED.  PCPN SHOULD BEGIN TO DIMINISH
THROUGH THE OVERNIGHT HOURS AS THE UPPER TROUGH CONTINUES TO DIG TO
THE SOUTH AND EAST...CUTTING OFF THE ISENTROPIC LIFT.  THE
PERSISTENT CANADIAN HIGH PARKED NORTH OF THE GREAT LAKES WILL
GRADUALLY BEGIN TO MOVE TO THE EAST...WITH RIDGING EXTENDING INTO
THE NRN/CNTRL PLAINS.  UNSEASONABLY LOW TEMPS WILL PERSIST THROUGH
THE WEEKEND AND INTO EARLY NEXT WEEK AS NELY FLOW CONTINUES TO DRAW
COOLER AIR FROM LAKE MICHIGAN.

FROM TUESDAY AND THROUGH THE REMAINDER OF THE EXTENDED PERIOD...
FORECAST CONFIDENCE DIMINISHES AS THE LONGER RANGE MODELS CONTINUE TO
HAVE DIFFICULTY IN AGREEING ON A SOLUTION IN HANDLING THE NRN STREAM
OF THE UPPER LEVEL PATTERN.  THERE IS SOME CONTINUITY ON KEEPING THE
SRN STREAM JET SHUNTED WELL TO THE SOUTH...BUT THE GFS/ECMWF DIVERGE
QUICKLY ON THEIR DEPICTION OF THE NRN STREAM...PRACTICALLY BECOMING
180 DEGREES OUT OF PHASE.  SO...HAVE TRENDED CLOSE TO A BLENDED
SOLUTION WITH LITTLE CHANGE TO THE GOING FORECAST. ULTIMATELY...THIS
TRENDS THE FORECAST TO NEAR NORMAL TEMPERATURES WITH PERIODIC
CHANCES FOR PCPN.  GIVEN THAT PCPN CHANCES WILL BE TIED TO NRN
STREAM SHORTWAVE ENERGY...WILL KEEP POPS GENERALLY IN THE SLIGHT
CHANCE RANGE.

KREIN

&&

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

PRIMARY AVIATION CONCERNS WILL BE RAIN DEVELOPING BY LATE MORNING
SATURDAY AND PERSISTING THROUGH THE EVENING...AND LEADING TO
LOWERING MVFR CIGS AND EVENTUALLY IFR. GUSTY EAST-NORTHEAST WINDS
ARE ALSO A FORECAST CONCERN.

LOW PRESSURE OVER THE SOUTHERN PLAINS WILL DEEPEN AND LIFT
NORTHEAST INTO THE MID-MISSISSIPPI VALLEY THIS AFTERNOON. RAIN
ASSOCIATED WITH THIS SYSTEM WILL SPREAD ACROSS THE TERMINALS
DURING THE LATE MORNING HOURS...WITH STEADY LIGHT/MODERATE RAIN
EXPECTED THROUGH THE AFTERNOON. WHILE MVFR CIGS MAY SCATTER OUT
DURING THE REMAINDER OF THE OVERNIGHT AND EARLY MORNING HOURS...
THIS RAIN SHOULD RESULT IN REDEVELOPMENT OF MVFR CIGS BY MID-DAY
AND THESE LIKELY WILL LOWER FURTHER TO IFR BY EVENING. DRYING IN
THE MID-LEVELS DEVELOPS LATER THIS EVENING WHICH WILL ALLOW RAIN
TO DIMINISH TO LIGHT RAIN/DRIZZLE INTO THE OVERNIGHT HOURS OF
SATURDAY NIGHT. DRY LOW LEVEL EAST/NORTHEAST FLOW MAY RESULT IN
MORE SHOWERY START TO PRECIP LATE THIS MORNING...THOUGH CONFIDENCE
IS FAIRLY HIGH IN TIMING AND THAT COLUMN WILL SATURATE BY EARLY
AFTERNOON. MOST OF THE STATISTICAL GUIDANCE SUPPORTS IFR OR LIFR
CIGS OVERNIGHT...SO FAIRLY HIGH CONFIDENCE IN CONDITIONS
DETERIORATING TO IFR.

CURRENT NORTHEAST WINDS WILL VEER MORE EASTERLY BY MORNING...AND
WILL INCREASE AS THE LOW MOVES TOWARD THE REGION AND THE GRADIENT
TIGHTENS. GUSTS BY MID-DAY OR EARLY AFTERNOON MAY EXCEED 25 KT AT
TIMES. WINDS WILL EASE A BIT SATURDAY NIGHT AND BACK MORE NORTH-
NORTHEAST.

RATZER

&&

.MARINE...
256 PM CDT

WITH STRONG HIGH PRESSURE PARKED NORTH OF THE GREAT LAKES AND LOW
PRESSURE DEVELOPING OVER THE SRN PLAINS...GENERALLY NELY FLOW WILL
CONTINUE OVER LAKE MICHIGAN.  INITIALLY...THE PRESSURE GRADIENT IS
RELATIVELY WEEK...BUT AS THE SFC LOW TRACKS NORTH INTO THE MISSOURI
VALLEY BY SATURDAY EVENING...THE GRADIENT ACROSS THE STRENGTHEN WITH
PREVAILING WIND DIRECTION BECOMING MORE ENELY AT ARND 20-25 KT. THIS
FETCH AND WIND SPEED SHOULD SET UP SMALL CRAFT ADVISORY CONDITIONS
FOR THE ILLINOIS NEARSHORE WATERS BY LATE SATURDAY MORNING OR EARLY
SATURDAY AFTERNOON AND INTO SATURDAY EVENING.  THE LATEST GUIDANCE
SUGGESTS THAT THERE COULD BE A BRIEF LULL IN WIND SPEEDS SATURDAY
NIGHT...BUT THERE IS A CHANCE THAT THE SMALL CRAFT ADVISORY MAY NEED
TO BE EXTENDED INTO SUNDAY AS THE ENELY FETCH COULD KEEP WAVES
AROUND 4 FEET INTO SUNDAY AFTERNOON.  AS THE SFC LOW MOVES OFF TO
THE EAST TO THE MID ATLANTIC REGION SUNDAY NIGHT OR MONDAY
MORNING...HIGH PRESSURE WILL BUILD SOUTH ACROSS THE GREAT LAKES WITH
A RELATIVELY WEAK GRADIENT SETTING UP MONDAY AND PERSISTING THROUGH
MIDWEEK.

KREIN

&&

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

&&

$$

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