Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 010755
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
255 AM CDT SUN MAY 1 2016

.SHORT TERM...
248 AM CDT

THROUGH TONIGHT...

A CLOUDY AND DREARY DAY IS ON TAP TODAY ACROSS NORTHERN ILLINOIS
AND NORTHWEST INDIANA. AN ELONGATED AREA OF LOW PRESSURE IS
DRAPED ACROSS CENTRAL ILLINOIS AND INDIANA WITH LOW
CLOUDS...PATCHY FOG...AND DRIZZLE IN PLACE ACROSS THE LOCAL
FORECAST AREA EARLY THIS MORNING. MEANWHILE...AN UPPER LOW OVER
NEBRASKA EARLY THIS MORNING IS PROGGED TO MOVE EAST ACROSS IOWA
THIS AFTERNOON AND INTO NORTHERN ILLINOIS THIS EVENING. SCATTERED
SHOWERS ARE EXPECTED TO REDEVELOP OUT AHEAD OF THIS LOW MAINLY
DURING THE AFTERNOON AND EVENING HOURS FOR NORTHERN ILLINOIS AND
NORTHWEST INDIANA. MODELS CONTINUE TO INDICATE MODEST ELEVATED
INSTABILITY...SO CANNOT RULE OUT AN ISOLATED THUNDERSTORM MAINLY
SOUTH OF I-80 NEAR THE SURFACE FRONT...BUT THE OVERALL LIKELIHOOD
OF THUNDER IS LOW. THE UPPER LOW WILL EXIT TO OUR EAST AROUND
MIDNIGHT OR SO WITH PRECIP CHANCES QUICKLY TAPERING THEREAFTER.
BUMPED DOWN TEMPERATURES SOME FOR TODAY AND EXPECT FAIRLY SIMILAR
CONDITIONS TO YESTERDAY WITH NO REAL CHANGE IN AIRMASS. LESS
PRECIP TODAY MIGHT HELP US WARM A LITTLE MORE BUT OVERCAST SKIES
AND MORNING FOG WILL INHIBIT INSOLATION AND MODELS HAVE BEEN TOO
WARM THE LAST COUPLE OF DAYS. THE FAR SOUTHERN TIER OF COUNTIES
WOULD HAVE THE BEST CHANCE FOR BREAKING OUT OF THE LOW CLOUDS AND
SEEING A LITTLE SUNSHINE THUS EXCEEDING TEMPERATURE PROJECTIONS
BUT LEANING AGAINST THAT SCENARIO FOR NOW.

DEUBELBEISS

&&

.LONG TERM...
248 AM CDT

MONDAY THROUGH SATURDAY...

STRONG BLOCKING RIDGE WILL BE IN PLACE ACROSS MUCH OF THE WESTERN
HALF OF THE CONTINENT TO START NEXT WEEK...WHILE A DEEP TROUGH
CONTINUES ACROSS THE MIDWEST AND GREAT LAKES. SOUTHERN STREAM
SHORT WAVES WILL BRING A SLIGHT CHANCE FOR A FEW LIGHT SHOWERS OR
SPRINKLES SOUTH OF I-80 ON MONDAY...FAVORED DIURNALLY IN THE
AFTERNOON AND EARLY EVENING. FORECAST SOUNDINGS SHOW AN
INVERSION/ISOTHERMAL LAYER BASED AROUND 800 MB MONDAY SO THERE
ISNT MUCH OPPORTUNITY FOR DEEP CONVECTIVE GROWTH...AND SUSPECT GFS
IS OVERPRODUCING QPF. WILL MAINTAIN 20 POPS FOR THE FAR SOUTHERN
FORECAST AREA. EXPECT HIGH TEMPS AROUND 60.

ON TUESDAY...WILL SEE A LITTLE MORE SUNSHINE AS TRANSIENT MID
LEVEL RIDGING PUSHES ACROSS THE AREA. FORECAST SOUNDINGS TUESDAY
INDICATE STEEP LOW/MID LEVEL LAPSE RATES DEVELOPING DURING THE
AFTERNOON WHICH SHOULD SUPPORT AT LEAST SOME DIURNAL CU
GROWTH...THOUGH WITH NO SIGNIFICANT FORCING OVER THE AREA WILL NOT
MENTION ANY POPS AT THIS TIME EVEN THOUGH THERMODYNAMICALLY
TUESDAY LOOKS BETTER FOR PRODUCING PRECIP THAN MONDAY. MODELS ARE
BACKING OFF ON TEMPERATURES TUESDAY AFTERNOON...DESPITE DEEP
MIXING STILL EXPECTED. TEMPS ALOFT NOW APPEAR TO ONLY SUPPORT LOW
TO MID 60S SO HAVE TRIMMED BACK TEMPS A FEW DEGREES.

TUESDAY NIGHT INTO WEDNESDAY WILL BRING MORE UNSETTLED AND COOLER
CONDITIONS BACK TO THE REGION. GUIDANCE CONTINUES TO INDICATE A
WAVE TOPPING THE STRONG WEST COAST RIDGE NEAR THE ARCTIC CIRCLE
EARLY IN THE WEEK WILL DISLODGE A COLD AIRMASS SET TO ARRIVE INTO
PORTIONS OF THE GREAT LAKES TUESDAY NIGHT INTO WEDNESDAY. GFS
CONTINUES TO RUN SLIGHTLY COOLER THAN THE ECMWF THOUGH BOTH MODELS
WOULD SUPPORT HIGHS ONLY IN THE LOW TO MID 50S WEDNESDAY AND
THURSDAY...WITH TEMPS NEAR THE LAKE ONLY IN THE 40S. WILL CONTINUE
TO NUDGE DOWNWARD FROM THE STARTING POINT OF OUR GENERAL MODEL
CONSENSUS BLEND WHICH STILL APPEARS TOO WARM...HOWEVER ANTICIPATE
FURTHER DOWNWARD REVISIONS TO TEMPS IF TRENDS OVER THE PAST COUPLE
DAYS HOLD. THERE REMAIN SOME MODEST TIMING AND TRACK
DIFFERENCES...BUT SHOWERS ARE POSSIBLE WITH THE COLD FRONT AND
ADDITIONAL SHOWERS ARE POSSIBLE WEDNESDAY AFTERNOON/EVENING AS
DIURNAL INSTABILITY DEVELOPS ONCE AGAIN.

FOR THOSE HOPING FOR MORE SUMMER-LIKE CONDITIONS TO RETURN...
GUIDANCE CONTINUES TO INDICATE THE WEST COAST RIDGE WILL INCH
EASTWARD THROUGH THE WEEK...AND SHOULD BEGIN TO EXERT ITS
INFLUENCE OVER THE WESTERN GREAT LAKES REGION BY LATE IN THE
WEEK AND INTO NEXT WEEKEND. THIS WILL BRING A WARMING TREND FRIDAY
AND SATURDAY ALONG WITH DRY CONDITIONS AND PLENTY OF SUNSHINE. IF
ECMWF/GFS PROJECTIONS HOLD...WE WILL BE WARMING WELL INTO THE 70S
SATURDAY POSSIBLY PUSHING THE 80 MARK IN SOME AREAS.

DEUBELBEISS

&&

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

06Z TAF CONCERNS ARE PRIMARILY
-PROLONGED PERIOD OF LIFR CIGS OVERNIGHT.
-IFR VSBY IN DZ/BR AT TIMES INTO SUNDAY MORNING.
-PERIOD OF SHRA SUNDAY EVENING WITH LOWER CIGS.

EXTENSIVE AREA OF IFR/LIFR CIGS OF 300-700 FT HAVE DEVELOPED
ACROSS ALL OF NORTHERN IL AND NORTHWEST INDIANA LATE THIS EVENING.
OBS TRENDS INDICATE FURTHER LOWERING INTO SOLID LIFR 300-400 FT
LIKELY FOR ALL TAF SITES NEXT FEW HOURS WITH PERSISTENT DRIZZLE
INTO SATURATED AIR MASS NORTH OF LOW PRESSURE TRACKING ACROSS
CENTRAL IL. GUIDANCE SUGGESTS THERE WILL BE SOME MARGINAL
IMPROVEMENT TO IFR/LOW MVFR CIGS LATE SUNDAY MORNING...THOUGH
ANOTHER ROUND OF SHOWERS IS EXPECTED LATE IN THE AFTERNOON AND
EVENING HOURS WHICH WILL LIKELY SERVE TO LOWER CIGS TO
IFR/POSSIBLY LIFR AGAIN. LOW PROBABILITY OF ISOLATED TSRA EXISTS
EARLY SUNDAY EVENING AS WELL...THOUGH GREATEST POTENTIAL SHOULD
REMAIN SOUTH/SOUTHEAST OF TERMINAL SITES. SOLID IMPROVEMENT IN CIG
CONDITIONS/LOW LEVEL DRYING IS NOT EXPECTED UNTIL LATE SUNDAY
NIGHT/EARLY MONDAY MORNING.

WITH SURFACE LOW PRESSURE TRACKING SOUTH OF THE TERMINALS...
NORTHEAST WINDS OF GENERALLY 10-15 KTS ARE EXPECTED THROUGH THE
TAF PERIOD.

RATZER

&&

.MARINE...
253 AM CDT

A PERIOD OF MODERATELY STRONG NORTHEAST WINDS GUSTING 20-25 KT
WILL PERSIST ACROSS LAKE MICHIGAN TODAY...EVENTUALLY BACKING MORE
NORTHERLY AND DIMINISHING AS LOW PRESSURE MOVES EAST ACROSS
ILLINOIS AND INDIANA AND REACHES THE UPPER OHIO VALLEY EARLY
MONDAY. WEAK HIGH PRESSURE RIDGING WILL THEN SETTLE SOUTH ACROSS
THE GREAT LAKES REGION MONDAY AND MONDAY EVENING...BEFORE AN AREA
OF LOW PRESSURE APPROACHES FROM ONTARIO. THIS LOW...AND ITS
ACCOMPANYING COLD FRONTAL TROUGH... WILL PUSH SOUTHEAST ACROSS
THE LAKE TUESDAY AND TUESDAY NIGHT. LIGHT WINDS WILL SHIFT TO THE
SOUTHWEST AND INCREASE TO 15-25 KTS INITIALLY AS THE TROUGH AND
LOW APPROACH TUESDAY...SHIFTING NORTH-NORTHWEST BEHIND THE FRONT
EARLY WEDNESDAY WITH SPEEDS 25-30 KT AND PERSISTING INTO THURSDAY
BEFORE DIMINISHING THURSDAY NIGHT/EARLY FRIDAY AS HIGH PRESSURE
RIDGING BUILDS IN FROM THE NORTHWEST. ON THE SOUTH END OF THE
LAKE...MARGINAL SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED TO
CONTINUE THROUGH THE DAY. WILL MONITOR AS WE MAY BE ABLE TO CANCEL
EARLIER THAN CURRENT EXPIRATION THROUGH THIS EVENING.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 1 AM
     MONDAY.

&&

$$

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