Area Forecast Discussion
Issued by NWS Chicago, IL

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779
FXUS63 KLOT 290747
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
247 AM CDT FRI APR 29 2016

.UPDATE...
901 PM CDT

SCATTERED LIGHT RAIN SHOWERS/DRIZZLE WILL CONTINUE INTO THE
OVERNIGHT HOURS AS AN UPPER LEVEL SHORTWAVE OVER NORTHERN
IOWA/SOUTHERN MINNESOTA MOVES EASTWARD. OTHERWISE COOL AND CLOUDY
CONDITIONS ARE EXPECTED WITH LOWERING CEILINGS AND
FOG...CONDITIONS THAT WILL LINGER INTO FRIDAY MORNING. THE
SHORTWAVE WILL EAST OF THE AREA FRIDAY RESULTING IN A DRY
DAY...BUT EXPECT A SLOW CLEARING TO CLOUDS WITH SOME SUN PEAKS
POSSIBLE LATE IN THE DAY.

KMD

&&

.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 DRAPED 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 ECMWF KEEPS THE COOLER AIR MASS TO OUR EAST.

KJB

&&

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

LOW CEILINGS WILL PRESENT THE MAIN FORECAST CHALLENGE OVERNIGHT
THROUGH MIDDAY FRIDAY. CEILINGS HAVE ALREADY DROPPED TO 005-009
LATE THIS EVENING AND SHOULD CONTINUE TO SLOWLY TREND DOWN
OVERNIGHT ALONG WITH SOME FOG/BR REDUCING VISIBILITY TO 2-4 SM.
CONDITIONS SHOULD STEADILY IMPROVE AFTER SUNRISE FRIDAY MORNING
WITH CEILINGS LIFTING BACK TO MVFR MID TO LATE IN THE MORNING AND
EVENTUALLY SCATTERING OUT DURING THE AFTERNOON...THOUGH CONFIDENCE
IN SPECIFIC TIMING IS ONLY LOW TO MEDIUM AT THIS TIME. WINDS ARE
EXPECTED TO VEER TO THE NORTHEAST FRIDAY MORNING WITH WIND SPEEDS
PICKING UP TO AROUND 10 KT...THEN FURTHER INCREASING FRIDAY NIGHT
AS LOW PRESSURE DEEPENS ACROSS THE PLAINS.

BMD

&&

.MARINE...
246 AM CDT

HIGH PRESSURE WILL REMAIN JUST NORTH OF LAKE MICHIGAN TODAY
ALLOWING LIGHT FLOW ONCE AGAIN AND AFTERNOON LAKE BREEZES TO
DEVELOP. LOW PRESSURE IS PROGGED TO DEEPEN OVER THE PLAINS TONIGHT
INTO SATURDAY ALLOWING NORTHEAST WINDS TO PICK BACK UP INTO THE 15
TO 25 KT RANGE BY SATURDAY EVENING...WITH 30 KT WINDS NOT OUT OF
THE REALM OF POSSIBILITY. THE STRONG NORTHEAST BREEZE WILL PERSIST
INTO SUNDAY...THEN SHOULD DIMINISH AGAIN SUNDAY NIGHT INTO MONDAY
AS THE LOW DEPARTS EAST AND HIGH PRESSURE BUILDS BACK ACROSS THE
REGION. THE RIDGE AXIS WILL MOVE EAST OF LAKE MICHIGAN MONDAY
NIGHT AS ANOTHER LOW PRESSURE SYSTEM DEVELOPS OVER HUDSON BAY
ALLOWING WINDS TO TURN SOUTH TO SOUTHWESTERLY. THE LOW WILL DRIVE
A COLD FRONT ACROSS LAKE MICHIGAN AROUND MIDWEEK.

BMD

&&

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

$$

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