Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 290003
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
703 PM CDT THU APR 28 2016

.SHORT TERM...
140 PM CDT

THROUGH FRIDAY...

ANOTHER COOL/CLOUDY AFTERNOON ACROSS THE REGION...WITH NORTHEAST
WINDS USHERING IN MUCH COOLER TEMPERATURES INTO NORTHEAST
ILLINOIS WITH TEMPS LOCKED IN THE MID/UPR 40S. FURTHER INLAND AWAY
FROM LAKE MICHIGAN TEMPS HAVE WARMED INTO THE MID/UPR
50S...ESPECIALLY ACROSS THE SOUTHWEST CWFA. THERE IS SOME BREAKS
IN THE THICK STRATUS ALONG THE SOUTHERN CWFA...AND WITH A WARM
FRONTAL BOUNDARY DRAPPED ACROSS CENTRAL ILLINOIS SLOWLY LIFTING
NORTH...IT IS POSSIBLE SOME OF THE SOUTHERN PORTIONS OF THE
FORECAST AREA COULD TOUCH THE LOW/MID 60S BEFORE SUNSET THIS
EVENING.

THE LACK OF MECHANICAL MIXING THIS AFTERNOON/EVENING WILL ALLOW
CLOUDS TO REMAIN...WITH MINIMAL SCOURING OF THE STRATUS LAYER
PROGGED THROUGH THIS EVENING/OVERNIGHT. SOME OF THE GUIDANCE
CONTINUES TO PROG SCATTERED SHOWERS LIFTING NORTHEAST AHEAD OF THE
FRONTAL BOUNDARY THIS EVENING/OVERNIGHT...HOWEVER FEEL THAT
COVERAGE WILL REMAIN MINIMAL. IN ADDITION WITH THE LACK OF A LIFT
COMPONENT...EXPECT DROPLET SIZE TO BE MINIMAL WHICH COULD RESULT
IN PRECIP BEING MORE IN THE FORM OF DRIZZLE WITH PERHAPS SOME
LIGHT RAIN. AS THE OVERNIGHT PROGRESSES AND THE UPPER LEVEL SYSTEM
DRIFTS EAST...THE COVERAGE AND PROBABILITIES FOR PRECIP WILL
STEADILY DWINDLE FROM SOUTHWEST TO NORTHEAST. TEMPS OVERNIGHT WILL
ONLY COOL INTO THE LOW/MID 40S.

SHORTLY AFTER DAYBREAK FRI MID-LVL HEIGHTS WILL BE ON THE
RISE...WHICH WILL USHER IN DRIER AIR...HOWEVER WITH THE CONTINUED
LACK OF MIXING THE CHALLENGE IS HOW QUICKLY DO WE ERODE THE THICK
STRATUS LAYER. GUIDANCE HAS SLOWED THE RATE OF IMPROVEMENT UNTIL
MIDDAY...TO PERHAPS LATE AFTERNOON. THIS WILL END UP CONTROLLING
HIGHS FOR FRI...SO HAVE HELD ONTO THE TEMPS GENERALLY IN THE
MID/UPR 50S WITH PERHAPS SOME LOW 60S IN THE FAR SOUTHERN CWFA.
ELSEWHERE THE NORTHEAST FLOW OFF OF LAKE MICHIGAN WILL CONTINUE TO
SEE TEMPS REMAIN IN THE MID/UPR 40S AGAIN FRI.

BEACHLER

&&

.LONG TERM...
334 PM CDT

FRIDAY NIGHT THROUGH THURSDAY...

THE MAIN FORECAST CONCERN DURING THE EXTENDED PERIOD WILL BE WITH
THE INCREASING RAIN POTENTIAL AND THE CONTINUING UNSEASONABLY COOL
CONDITIONS THIS WEEKEND.

AN UPPER LEVEL TROUGH...CURRENTLY NOTED IN WATER VAPOR IMAGERY
SPINNING OVER THE SOUTHWESTERN CONUS...WILL SHIFT EAST-NORTHWARD
ACROSS THE CENTRAL HIGH PLAINS ON FRIDAY...WHILE INDUCING SURFACE
LOW PRESSURE ACROSS THE SOUTHERN AND CENTRAL PLAINS. THIS SYSTEM
WILL THEN SHIFT EASTWARD OVER THE CENTRAL STATES THROUGH THE
WEEKEND. MEANWHILE...A LARGE AND EXPANSIVE AREA OF SURFACE HIGH
PRESSURE WILL CONTINUE TO DOMINATE OVER SOUTHERN CANADA AND THE
UPPER MIDWEST AND GREAT LAKES REGION.

EAST TO NORTHEASTERLY SURFACE FLOW WILL CONTINUE FOR THE NEXT
SEVERAL DAYS...AND WILL LIKELY INCREASE BY SATURDAY AS THE SURFACE
LOW CONTINUES TO APPROACH MISSOURI. THIS WILL RESULT IN CONTINUED
CLOUD COVER AND UNSEASONABLE COOL CONDITIONS IN THE 40S TO 50S.
RAIN CHANCES LOOK TO INCREASE DURING THE DAY ON SATURDAY. THERE
CONTINUES TO BE TIMING DIFFERENCES AMONGST THE LATEST MODEL
GUIDANCE AS TO WHEN THE RAIN WILL DEVELOP OVER THE AREA ON
SATURDAY. HOWEVER...THE CHANCES OF RAIN BY SUNDAY AFTERNOON IS
QUITE HIGH AREA-WIDE AS A BAND OF FGEN LOOKS TO SET UP OVER THE
AREA IN ASSOCIATION WITH THE DEVELOPING 850 MB WARM FRONT. THIS
LOOKS TO SET UP A DECENT RAIN EVENT OVER THE AREA INTO SATURDAY
EVENING. IT APPEARS THE THREAT OF THUNDERSTORMS WILL REMAIN SOUTH
OF THE AREA...SO I CONTINUED TO LEAVE THE MENTION OUT OF THE
FORECAST. HOWEVER...WITH THE PROXIMITY WITH THE 850 FRONT TO MY
SOUTHERN CWA...I CANT RULE OUT THE POSSIBILITY OF AN EMBEDDED
STORM THERE SATURDAY AFTERNOON/EVENING. OTHERWISE...SOME LINGERING
SHOWERS LOOK TO CONTINUE AT TIMES INTO SUNDAY BEFORE ENDING...BUT
AT THIS TIME THE BEST WIDESPREAD RAIN POTENTIAL IS LOOKING TO BE
FROM SATURDAY AFTERNOON THROUGH SATURDAY EVENING.

TEMPERATURES DO LOOK TO BE ON A SLOW WARMING TREND EARLY NEXT
WEEK...WITH MAINLY DRY WEATHER EXPECTED. HOWEVER...THE UPPER LEVEL
WEATHER PATTERN NEXT WEEK DOES LOOK TO FAVOR BUILDING HEIGHTS OVER
THE PLAINS STATES...WHICH SHOULD FAVOR FALLING HEIGHTS AND
TROUGHING OVER THE EASTERN CONUS AND POSSIBLY PARTS OF THE GREAT
LAKES REGION AS WELL. THIS COULD RESULT IN SOME COOLER WEATHER
POSSIBLY DROPPING OVER THE REGION MID TO LATE WEEK.
HOWEVER...THERE IS A GOOD AMOUNT OF ENSEMBLE SPREAD WITH THE
EASTWARD EXTENT OF THE UPPER RIDGING AND WARMER ATMOSPHERE LATER
IN THE WEEK. THE CURRENT GFS IS MORE BULLISH IN BRING COOLER AIR
OVER THE REGION BEHIND A COLD FRONT LATER IN THE WEEK.
HOWEVER...THE LATEST ECWMF KEEPS THE COOLER AIR MASS TO OUR EAST.

KJB

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN CONCERNS:
* CIGS DETERIORATING FROM IFR AND LOW MVFR TO LIFR TONIGHT AND
  TIMING OF IMPROVEMENT ON FRIDAY
* LOW MVFR TO IFR VSBY IN -RA/DZ AND BR TONIGHT INTO EARLY FRI AND
  TIMING OF IMPROVEMENT FRIDAY MORNING

POOR AVIATION CONDITIONS WILL BE THE RULE TONIGHT AND LIKELY
THROUGH FRIDAY MORNING BEFORE SLOW IMPROVEMENT ENSUES. A EXPANSIVE
AREA OF STRATUS COVERS THE MIDWEST AND WEAK GRADIENT ALONG WITH
LITTLE IN THE WAY OF DRY ADVECTION SHOULD MAKE THE STRATUS SLOW TO
ERODE INTO FRIDAY. IFR AND LIFR CIGS OVER SOUTHERN WI AND
NORTHEAST IL WILL SPREAD SOUTHWARD OR CURRENT CIGS WILL SIMPLY
BUILD DOWNWARD AS INVERSION STRENGTHENS. THERE IS A STRONG
CONSENSUS IN LIFR CIGS IN NEAR TERM GUIDANCE AND WITH SITES IN SE
WI AND FAR NE IL ALREADY LIFR...HAVE PRETTY GOOD CONFIDENCE THAT
IT WILL DEVELOP AT ALL THE TERMINALS OVERNIGHT AND PERSIST THROUGH
THE MORNING RUSH AT ORD/MDW. CIGS WILL THEN GRADUALLY LIFT THE
REST OF THE DAY AND THEN POSSIBLY SCATTER BY LATE AFTERNOON...SO
HAVE PUSHED BACKED SCATTERING IN THE TAFS.

A DISTURBANCE ASSOCIATED WITH UPPER LEVEL LOW PRESSURE OVER THE
REGION HAS RESULTED IN AN AREA OF -RA/DZ EXPANDING NORTHEASTWARD
LATE THIS AFTERNOON. VSBY HAS FALLEN TO IFR AND MVFR WITH THIS
PRECIPITATION AND EXPECT THIS TO OCCUR AT THE EASTERN TERMINALS
THIS EVENING...WITH THE -RA/DZ POSSIBLY LINGERING UNTIL EARLY
FRIDAY MORNING. IFR TO LOW MVFR VSBY COULD THEN LINGER UNTIL MID
MORNING BEFORE IMPROVEMENT OCCURS. CONFIDENCE IS A BIT LOWER IN
VSBY TRENDS GIVEN VARIABILITY ACROSS THE REGION.

WINDS WILL REMAIN GENERALLY NORTH AND NORTHEAST...WITH DIMINISHING
SPEEDS TONIGHT...FOLLOWED BY SPEEDS AROUND 10 KT FROM MID TO LATE
FRIDAY MORNING THROUGH THE AFTERNOON.

RC

&&

.MARINE...
351 PM CDT

ANOTHER STORM SYSTEM IS EXPECTED TO DEVELOP OVER THE PLAINS ON
FRIDAY...THEN SHIFT EASTWARD OVER THE MID MISSISSIPPI VALLEY TO THE
OHIO VALLEY...WHILE WEAKENING...THROUGH SUNDAY MORNING. OVERALL...A
PERSISTENT EAST-NORTHEASTERLY FLOW PATTERN IS EXPECTED OVER THE LAKE
THROUGH AT LEAST EARLY NEXT WEEK. ALTHOUGH THE FLOW WILL BE FAIRLY
LIGHT...THERE WILL BE PERIODS OF HIGH WIND SPEEDS. AS THE LOW
APPROACHES THE REGION ON SATURDAY...THE EAST-NORTHEASTERLY WINDS
WILL LIKELY INCREASE INTO THE 15 TO 25 KT RANGE LATE SATURDAY INTO
SUNDAY. THIS COULD AGAIN RESULT IN HIGH WAVES OVER THE SOUTHERN AND
WESTERN SHORES OF LAKE MICHIGAN...WHICH COULD SUPPORT ANOTHER SMALL
CRAFT ADVISORY.

KJB

&&

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

$$

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