Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 030003
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
656 PM CDT MON MAY 2 2016

.SHORT TERM...
215 PM CDT

THROUGH TUESDAY...

DRY AIR CONTINUES TO SLIDE SOUTH/SOUTHWEST ACROSS NORTHERN IL...AS
DEW POINTS HAVE FALLEN INTO THE MID/UPR 30S ACROSS FAR NORTHCENTRAL
IL. FURTHER SOUTH DEW POINTS ARE GENERALLY AROUND 40 THE LOWER 40S.
CLOUDS HAVE REMAINED MINIMAL ACROSS MUCH OF THE AREA...WITH SOME
DIURNAL CUMULUS WEST OF THE CHICAGO METRO AREA. JUST BEYOND PEAK
HEATING OF THE AFTERNOON THE DIURNAL CUMULUS SHOULD BEGIN TO
DISSIPATE...WITH THE NORTHEAST WINDS DIMINISHING TO AROUND 5 TO 10
MPH. HIGH PRESSURE CENTERED TO THE NORTH OF THE AREA WILL KEEP WINDS
LIGHT AND VARIABLE OVERNIGHT...WHICH COULD ALLOW TEMPERATURES TO
STEADILY RADIATE INTO THE LOWER 40S. HOWEVER AREAS THAT HAVE HAD DEW
POINTS THIS AFTERNOON FALL INTO THE MIDDLE 30S...TEMPS TONIGHT COULD
DIP INTO THE UPPER 30S BETWEEN ROCKFORD AND WAUKEGAN DOWN TO DEKALB.
HAVE INCLUDED PATCHY FROST WORDING OVERNIGHT.

TUESDAY... BROAD SFC RIDGING WILL CONSOLIDATE TO A RIDGE OVER THE
CENTRAL ROCKIES/PLAINS...WHICH WILL ALLOW A WEST/EAST GRADIENT TO
DEVELOP MIDDAY TUESDAY. WITH MINIMAL CLOUD COVER TO START THE DAY
TEMPS WILL QUICKLY WARM INTO THE 50S AND EVENTUALLY MIDDLE TO UPPER
60S BY EARLY AFTERNOON ACROSS NORTHERN IL. WEST WINDS WILL INCREASE
AS WELL...WITH THE FOCUS FOR LATE AFTERNOON/EVENING TURNING TOWARDS
A SHORTWAVE SLIDING EAST ACROSS LAKE SUPERIOR AND A TRAILING FRONTAL
BOUNDARY PROGGED TO DIVE SOUTH ACROSS THE WESTERN GREAT LAKES.
GUIDANCE HAS REMAINED RELATIVELY CONSISTENT WITH THE BEST CHANCE FOR
PRECIP ARRIVING AROUND THE EVENING HOURS FROM THE NORTH TUESDAY.

BEACHLER

&&

.LONG TERM...
248 PM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

NOAM WATER VAPOR IMAGERY SHOWS A PACIFIC JET COMING ONSHORE IN THE
WESTERN US BEING FORCED NORTHWARD INTO CANADA WITH AN UPPER LEVEL
HIGH HELPING TO CURVE THIS JET ANTI-CYCLONICALLY AROUND WESTERN
CANADA. THE LEADING EDGE OF THIS JET CONTINUES TO PUSH SOUTHWARD IN
THE CANADIAN PRAIRIES. BY TUESDAY NIGHT...NORTHERN ILLINOIS WILL BE
IN THE LEFT EXIT REGION OF THIS JET AS 500 MB HEIGHTS FALL
IMPRESSIVELY DURING CYCLOGENESIS. THE SURFACE LOW WILL PULL A COLD
FRONT ACROSS THE REGION TUESDAY NIGHT AND SPREAD RAIN SHOWERS ACROSS
THE CWA. GIVEN THE RAPID UPPER LEVEL HEIGHT FALLS...THERE IS A SMALL
CHANCE FOR THUNDERSTORMS TO OCCUR ALONG THE LINE OF SHOWERS.

HEIGHT FALLS TO NEAR 540 DAM ARE PROJECTED WITH THIS FEATURE...AND
H85 TEMPS WILL DROP INTO THE NEGATIVE SINGLE DIGITS. COLD AIR OF
THIS NATURE FALLS INTO THE 10TH PERCENTILE OF ILX/DVN SOUNDINGS
FOR THE FIRST WEEK OF MAY. GIVEN THESE ANOMALIES...DAYTIME
TEMPERATURES WILL NOT RISE MUCH ON WEDNESDAY WITH SOME LOCATIONS
ONLY HITTING THE UPPER 40S. WITH THE STEEP LAPSE RATES ACROSS THE
AREA AND THE CENTER OF THE 500 MB LOW PASSING OVER LAKE
MICHIGAN...EXPECT WEAK CONVECTIVE SHOWERS AND POSSIBLY SOME
GRAUPEL DURING THE AFTERNOON. AN ADDITIONAL SHOCK WILL COME WITH
THE NEAR FREEZING CONDITIONS FOR WEDNESDAY NIGHT. SKIES MAY CLEAR
OUT SOME...BUT SURFACE TO H85 RH REMAINS ABOVE 80 PERCENT NEAR THE
LAKE. LUCKILY THE WINDS WILL ALSO REMAIN ABOVE 5-10KT THANKS TO A
LINGERING PRESSURE GRADIENT. IF EITHER OF THESE TWO INGREDIENTS GO
AWAY IN FUTURE FORECASTS...EXPECT TEMPS TO DROP 5 DEGREES COOLER.

THE REMAINDER OF THE EXTENDED FORECAST WILL FEATURE A PSEUDO OMEGA
BLOCK PATTERN ADVANCING AND SHRINKING ACROSS THE CENTER OF THE
CONUS. EXPECT A SHARP INCREASE IN TEMPERATURES FRIDAY AND SATURDAY
AS WARM ADVECTION FROM THE WEST-SOUTHWEST WILL BE ONGOING. A COLD
FRONT LOOKS TO DROP THROUGH THE GREAT LAKES SATURDAY NIGHT AND
BECOME STATIONARY. THIS WILL DROP TEMPS ACROSS THE AREA AGAIN WHILE
KEEPING A PERSISTENT CHANCE FOR THUNDERSTORMS IN THE DAYS 6-7
FORECAST.

MM

&&

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

CONCERNS/HIGHLIGHTS FOR THE 0Z TAFS INCLUDE
-WINDS TURNING WESTERLY WITH GUSTS IN THE UPPER TEENS POSSIBLE IN
THE AFTERNOON.
-SHOWERS AT THE END OF THE 30 HR ORD TAF CYCLE...WITH A
THUNDERSTORM NOT OUT OF THE QUESTION.

VFR CIGS WITH BASES OF 7000-8000 FEET WILL ERODE QUICKLY AFTER
SUNSET. ANOTHER POCKET OF LOWER VFR CIGS ACROSS THE LAKE AND
ADJACENT CHICAGOLAND TERMINALS...WITH BASES AROUND 5000-6000 FEET
IN NE IL...AND 3000-4000 FEET IN NORTHWEST INDIANA...WILL ERODE
BUT WILL TAKE A FEW HOURS TO DO SO.

THE SURFACE RIDGE AXIS WILL BUILD OVERHEAD TONIGHT...THUS A QUICK
COLLAPSE TO THE EAST WIND IS EXPECTED WITH A PERIOD OF
LIGHT/VARIABLE WINDS TURNING LIGHT WESTERLY OVERNIGHT. AN UPPER
LEVEL DISTURBANCE WILL BUILD SOUTH LATER TUESDAY AND ESPECIALLY
TUESDAY EVENING. WINDS WILL INCREASE FROM THE WEST...THEN SHIFT TO
SOUTHWEST AHEAD OF THE DISTURBANCE. AN ISOLATED SHOWER CANNOT BE
RULED OUT IN THE AFTERNOON...BUT THERE WILL BE A PERIOD OF SHOWERS
MID TO LATE EVENING TUESDAY INTO TUESDAY NIGHT. MODEL CAPE VALUES
ARE LOW WHICH WOULD SUGGEST A NON-ZERO THUNDER THREAT...AND
FORECAST SOUNDINGS DO SHOW THE EROSION OF A CAP THROUGH THE
EVENING...BUT CONFIDENCE IS STILL TOO LOW TO INCLUDE IN THE TAF AT
THIS DISTANCE. THE THUNDER TIMING IF IT WOULD OCCUR WOULD BE MOST
FAVORED IN THE 3Z-6Z TIME FRAME.

KMD

&&

.MARINE...
248 PM CDT

WEAK UPPER LEVEL FLOW OVER THE NEXT 24 HOURS WILL KEEP CALM
CONDITIONS PRESENT OVER LAKE MICHIGAN. LITTLE DIFFERENCE IN LAKE
TO LAND TEMPERATURES WILL ASSIST IN STABILITY OVER THE LAKE AS
WELL. ON TUESDAY...SOUTHERLY WINDS WILL INCREASE AHEAD OF A COLD
FRONT BEFORE SHARPLY SHIFTING NORTHERLY BEHIND THE FRONT TUESDAY
NIGHT. COLD AIR ADVECTION AND A PRESSURE GRADIENT BEHIND THE FRONT
WILL ALLOW GUSTS IN THE UPPER 20S INTO WEDNESDAY. FOLLOWING THAT
FRONTAL FEATURE...A STABLE HIGH PRESSURE REGIME IS EXPECTED INTO
THE WEEKEND.

MM

&&

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

$$

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