Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 020010
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
710 PM CDT WED JUL 1 2015

.UPDATE...644 PM CDT

HAVE ADDED SCATTERED SPRINKLES THROUGH MID-EVENING FOR NORTH
CENTRAL AND PARTS OF NORTHEAST IL...THOUGH THE EXPECTATION IS FOR
THIS PRECIP TO DECREASE IN COVERAGE AS IT MOVES EAST.

WEAK MID-LEVEL SHORT WAVE PROPAGATING EAST-SOUTHEAST ACROSS
NORTHEASTERN IA EARLY THIS EVENING...WITH AN AREA OF LIGHT RAIN
ASSOCIATED WITH THIS FEATURE. 12Z RAOB SOUNDINGS...AND CURRENT
RAP/ARW FORECAST SOUNDINGS INDICATE DRY LOW LEVELS FARTHER TO THE
EAST ACROSS NORTHERN IL...WITH TEMP-DEW POINT DEPRESSIONS OF
NEARLY 20 DEG C IN THE 850-650 MB LAYER. SURFACE OBS INDICATE MAIN
CLOUD BASE UP IN THE 080-120 KFT RANGE...WITH SOME EVAPORATION
LIKELY IN DRY AIR BELOW. PRECIP HAS MADE IT FARTHER EAST THAN
HIGH-RES MODELS INDICATED...THOUGH WOULD STILL EXPECT A GRADUAL
DISSIPATING TREND AS THE SYSTEM ENCOUNTERS DEEPER LOW LEVEL DRY
AIR TO THE EAST.

UPDATED HOURLY POP/WX/SKY GRIDS...AND UPDATED ZFP/LFP/NOW AND
GRAPHICAST AVAILABLE.

RATZER

&&

.SHORT TERM...
327 PM CDT

THROUGH SATURDAY...

GENERALLY QUIET CONDITIONS EXPECTED THROUGH THE PERIOD AS
STEERING FLOW WILL TEND TO KEEP BEST FORCING TO THE SOUTH OF THE
CWA. IN THE NEAR TERM...HAVE MAINTAINED A DRY FORECAST FOR MOST
AREAS THIS EVENING THROUGH MIDNIGHT OUTSIDE OF LOW CHANCE POPS FOR
THE FAR SOUTHERN CWA OWING TO POTENTIAL SLIGHT EXPANSION OF
SHOWERS CURRENTLY TO THE WEST/SOUTHWEST. ALSO MONITORING SMALL
AREA OF PRECIP DROPPING SOUTHEAST THROUGH EASTERN IOWA.
EXTRAPOLATING THIS ALONG SOUTHEASTWARD MEAN FLOW ALOFT...IT WOULD
CLIP AREAS ACROSS NORTH CENTRAL ILLINOIS. HOWEVER...AT THIS
TIME...LITTLE PRECIP IS ACTUALLY MAKING IT TO THE GROUND. WITH
RATHER DRY CONDITIONS IN PLACE OVER THE CWA...WOULD EXPECT FURTHER
EROSION OF THIS PRECIP WITH EVEN LESS OF IT MAKING IT TO THE
GROUND. SO...IF ANYTHING WERE TO OCCUR...IT WOULD BE A BRIEF
SPRINKLE. CLOUD COVER TONIGHT MAY BE A LITTLE CHALLENGING...BUT
WENT MORE AGGRESSIVE WITH CLOUD COVER IN THE NEAR TERM AND LATER
TONIGHT. MID/HIGH CLOUDS APPROACHING WILL PROVIDE CONTINUED CLOUDY
CONDITIONS THIS EVENING...AND THEN LOW STRATUS OVER THE SOUTHERN
HALF OF THE LAKE AND SOUTHWEST MICHIGAN LOOKS TO WORK ITS WAY BACK
SOUTHWEST MORE TOWARDS EARLY THURSDAY MORNING.

A CONTINUED SOUTHERLY TREND WITH APPROACHING SYSTEMS THURSDAY
THROUGH SATURDAY HAS OCCURRED...AND HAVE LOWERED POPS THROUGH THE
PERIOD WITH DRY CONDITIONS EXPECTED FOR THE CWA. ALTHOUGH TEMPS
WILL CONTINUE TO BE BELOW NORMAL THROUGH THE END OF THE
WORK...TEMPS WILL BEGIN TO REBOUND BY SATURDAY WITH HIGHS AROUND
80 FORECAST. HOWEVER...PERSISTENT ONSHORE FLOW WILL KEEP TEMPS
LOWER NEAR THE LAKE.

RODRIGUEZ

&&

.LONG TERM...
327 PM CDT

SATURDAY NIGHT THROUGH WEDNESDAY...

SATURDAY EVENING IS LOOKING LIKE IT WILL REMAIN DRY FOR 4TH OF
JULY FIREWORKS IN THE ABSENCE OF ANY REAL FORCING OR INSTABILITY.
THIS PATTERN LOOKS TO CONTINUE INTO SUNDAY AND SUNDAY
EVENING...THOUGH A FEW STRAY SHOWERS/POP-UP TSTORMS CANNOT BE
RULED OUT ACROSS THE SOUTHERN PORTION OF THE CWA. ATTENTION THEN
TURNS TO MONDAY AS MODEL GUIDENCE CONTINUES TO ADVERTISE THE
SOUTHWARD MOVEMENT OF A LOW AMPLITUDE TROUGH WELL TO THE NORTHWEST
WITH A CORRESPONDING COLD FRONT. WAA LOOKS TO RAMP UP DURING THE
DAY ON MONDAY...THOUGH MOST OF THE DAY WILL LIKELY REMAIN DRY AS
THE BEST FORCING STAYS NORTH OF THE AREA. MODEL GUIDANCE HAS
STARTED TO AGREE THAT THE COLD FRONT WILL PASS THROUGH THE CWA
LATE MONDAY NIGHT INTO EARLY TUESDAY MORNING. HOWEVER...RUN-TO-RUN
INCONSISTENCY HAS LED TO LOW CONFIDENCE ON THE EXACT TIMING OF THE
FROPA...AS WELL AS THE STRENGTH OR COVERAGE OF ANY ASSOCIATED
CONVECTION. AREA-WIDE SLIGHT POPS MAY HAVE TO BE ADJUSTED IN
FUTURE FORECASTS AS MODEL GUIDANCE CONSISTENCY INCREASES. THERE
ARE ALSO QUESTIONS ON WHETHER THE FRONT WILL PASS RIGHT ALONG OR
STALL INTO THE TUESDAY AND WEDNESDAY TIMEFRAME...WHICH WOULD HAVE
IMPLICATIONS ON AREAWIDE POPS...CLOUD COVER...AND TEMPS.

BATZEK/BORCHARDT/NIXON

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* POTENTIAL FOR IFR/LIFR CIGS LATE TONIGHT INTO THURSDAY MORNING.

* LOW POTENTIAL FOR FOG LATE TONIGHT INTO THURSDAY MORNING.

* NORTHEAST WINDS 10 TO 15 KT ON THURSDAY.

RC

//DISCUSSION...UPDATED 00Z...

COOL HIGH PRESSURE WILL REMAIN LOCKED OVER THE GREAT LAKES REGION
THROUGH THURSDAY. THIS WILL KEEP WINDS IN A GENERALLY NORTHEAST
DIRECTION...WITH SPEEDS PICKING UP TO THE 10-15 KT RANGE BY MID
THURSDAY MORNING AFTER DIMINISHING THIS EVENING. SOME GUIDANCE
IS INDICATING THE FORMATION OF IFR/LIFR CIGS AND FOG LATE TONIGHT
NEAR LAKE MICHIGAN AND THEN SPREADING INLAND. DRY CONDITIONS AND
SOME SUN FOR THE TAF SITES TODAY MAKE FOG DEVELOPMENT SEEM FAIRLY
UNLIKELY...WITH LOW CLOUDS A MORE PROBABLE SCENARIO IF THEY OCCUR.
CONFIDENCE IS LOW ON COVERAGE AND DURATION OF POTENTIAL LOWER
CLOUDS...SO HAVE MAINTAINED A SCT IFR MENTION IN THE TAFS FOR NOW.
CLOUD BASES WILL LIFT BY MID THURSDAY MORNING...AND CANNOT RULE
OUT MVFR CIGS UNTIL ABOUT MID DAY BEFORE FURTHER SCATTERING
OCCURS...ESPECIALLY FOR GYY.

RC


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM-HIGH IN WIND FORECAST.

* LOW IN IFR/LIFR CIGS LATE TONIGHT INTO THURSDAY MORNING.

* LOW IN FOG LATE TONIGHT INTO THURSDAY MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY THROUGH SUNDAY...VFR.

MONDAY AND TUESDAY...CHANCE FOR SHRA/TSRA AND ASSOCIATED VSBY
IMPACTS.

RC

&&

.MARINE...
356 PM CDT

ON THE EDGE OF HIGH PRESSURE TO THE NORTH/NORTHWEST...NORTHERLY
FLOW IS PERSISTING OVER THE LAKE. SPEEDS HAVE GENERALLY STAYED IN
THE 10 TO 20 KT RANGE OVER THE OPEN WATERS...WHILE 10 TO 15 KT HAS
BEEN OBSERVED ALONG THE NEARSHORE IN ILLINOIS/INDIANA.
HOWEVER...VEERING FLOW HAS ALLOWED FOR THE HIGHER WAVES TO REACH
PORTIONS OF THE INDIANA SHORE WITH WAVES OF 3 TO 6 FT BEING
REPORTED THIS AFTERNOON. THESE HIGHER WAVES SHOULD DIMINISH THIS
EVENING AND OVERNIGHT...WITH THE SMALL CRAFT ADVISORY GOING
THROUGH THIS EVENING. NORTHERLY FLOW WILL ONCE AGAIN BE OBSERVED
ON THURSDAY AND AS THE SURFACE PATTERN TIGHTENS UP...SPEEDS WILL
LIKELY RETURN BACK TO THE 10 TO 20 KT RANGE FOR BOTH THE OPEN
WATERS AND NEARSHORE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...BEACH HAZARDS STATEMENT...INZ002 UNTIL 8 PM WEDNESDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 8 PM WEDNESDAY.

&&

$$

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