Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLOT 020721
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 AM CDT TUE SEP 2 2014

.DISCUSSION...
842 PM CDT

THUNDER HAS CEASED IN THE SHOWER ACTIVITY NORTH OF INTERSTATE 88.
EXPECT THESE SHOWERS TO SLOWLY DRIFT SOUTHEAST AND WEAKEN EVEN MORE WITH
THE LOSS OF DAYTIME HEATING. THERE ARE SOME SHOWERS MOVING
NORTHEAST THROUGH IOWA THIS EVENING AHEAD OF AN UPPER TROUGH AXIS
THAT MAY DRIFT THROUGH LATER TONIGHT...AND ADDED A SLIGHT CHANCE
OF SHOWERS TO ACCOUNT FOR THIS...BUT AT THIS TIME IT DOES NOT LOOK
TO BE TOO BIG OF A DEAL GIVEN THE LACK OF MOISTURE. MODELS
STILL SUGGEST THE THUNDERSTORM ACTIVITY FARTHER WEST IN SOUTH
DAKOTA AND NEBRASKA WILL ALSO WEAKEN WITH TIME AND GENERALLY PASS
BY INTO WISCONSIN TUESDAY.

THE BIGGER SHOW IS TAKING PLACE IN THOUGH MISSOURI AND EXTENDING
INTO SOUTHWEST ILLINOIS. THIS AREA IS SOUTH AND EAST OF A
STRENGTHENING UPPER JET AND WITH BETTER AXIS TO DEEPER MOISTURE.
STILL LOOKS LIKE SOME OF THIS WILL PROGRESS INTO OUR SOUTHEASTERN
ZONES AFTER MIDNIGHT. CURRENT GRIDS HAVE A DECENT HANDLE ON THIS
EVOLUTION.

KMD

//PREV DISCUSSION...
323 PM CDT

MAIN FORECAST CONCERNS ARE GENERALLY PRECIP CHANCES TONIGHT...AND
AGAIN LATE WEDNESDAY INTO FRIDAY WITH RETURN OF WARM/MORE HUMID AIR.
ATTENTION THEN TURNS TO MUCH COOLER AND DRIER WEATHER NEXT WEEKEND
INTO EARLY NEXT WEEK.

OUTFLOW FROM OVERNIGHT IOWA MCS AND PRE-FRONTAL TROUGH MOVING INTO
INDIANA THIS AFTERNOON HAS ALL BUT ENDED SIGNIFICANT THUNDERSTORM
THREAT FOR THE FORECAST AREA THIS AFTERNOON...WITH THE POTENTIAL FOR
ONLY A FEW ISOLATED SHOWERS AND THUNDERSTORMS MAINLY EAST OF A
PONTIAC TO VALPARAISO LINE. ADDITIONAL SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS OVER NORTHEAST IOWA/WESTERN WISCONSIN ARE
ASSOCIATED WITH UPPER LEVEL TROUGH AND TRUE SURFACE COLD FRONT...
THOUGH THIS ACTIVITY SHOULD BE AT ITS DIURNAL PEAK THIS AFTERNOON
AND HIGH-RES GUIDANCE INDICATE A WEAKENING/DISSIPATING TREND AS IT
APPROACHES AND MOVES INTO NORTHERN IL THIS EVENING. BASED ON THIS
HAVE BACKED OFF LATE AFTERNOON AND EVENING POPS EVEN FURTHER...WITH
ONLY A SLIGHT CHANCE MENTION OF A FEW SHOWERS MAINLY NORTH OF I-88
IN FAR NORTHERN IL INTO EARLY EVENING. ILX 18Z SOUNDING SHOWS DRY
RELATIVELY DRY COLUMN...WITH A FAIRLY STRONG CAPPING INVERSION NOTED
BETWEEN 800-850 HPA. NO WONDER CONVECTION ALONG PRE-FRONTAL TROUGH
IN OUR EASTERN CWA HAS STRUGGLED THIS AFTERNOON. PRECIP POTENTIAL
DOES STILL APPEAR TO INCREASE LATER TONIGHT ACROSS CENTRAL IL...AND
ACROSS OUR FAR SOUTHEASTERN CWA...AS DEEP LAYER FORCING INCREASES
WITH APPROACH OF MAIN UPPER TROUGH AXIS AND LOW LEVEL WINDS BACK
ALONG COLD FRONTAL BAROCLINIC ZONE. GUIDANCE HAS CONTINUED TO TREND
FARTHER SOUTH WITH THE AXIS OF PRECIP HOWEVER...AND HAVE FOLLOWED
SUIT OVERNIGHT WITH POPS AGAIN MAINLY SOUTH OF ROUGHLY A
PONTIAC-VALPO LINE. COLD FRONT CLEARS SOUTHEAST CWA EARLY TUESDAY
MORNING...WITH ANY LINGERING PRECIP IN OUR FAR SOUTHEAST BY
MID-MORNING.

FLOW BECOMES FAIRLY ZONAL ALOFT IN THE WAKE OF THE DEPARTING TROUGH
TUESDAY...WITH WEAK SURFACE HIGH PRESSURE MOVING ACROSS THE AREA.
MILD/DRY WEATHER EXPECTED FOR THE MOST PART TUES-WED.

A SHOT OF VERY WARM AND HUMID AIR THEN IS SET TO RETURN LATER
WEDNESDAY NIGHT INTO FRIDAY. STRONG SHORT WAVE MOVES ACROSS THE
PACIFIC NORTHWEST AND ACROSS THE CANADIAN BORDER DURING THE PERIOD
AND INDUCES SURFACE LOW PRESSURE DEVELOPMENT ACROSS THE NORTHERN
PLAINS. SOUTHERLY RETURN FLOW STRENGTHENS AS GRADIENT TIGHTENS
SOUTHEAST OF THE LOW...WITH SURFACE WARM FRONT LIFTING NORTHEAST
ACROSS THE FORECAST AREA LATE WEDNESDAY NIGHT INTO THURSDAY. SHOWER
AND THUNDERSTORM POTENTIAL INCREASES WITH THE WARM FRONT...THOUGH
THE BEST FORCING IS GENERALLY NORTH OF THE FORECAST AREA. GREATER
THUNDERSTORM POTENTIAL APPEARS TO BE WITH THE APPROACH/PASSAGE OF
THE COLD FRONT WHICH TRAILS THE LOW ON FRIDAY. DEPENDING ON CLOUD
COVER AND EFFECTS OF ANY PRECIP...THURSDAY LOOKS TO BE VERY WARM AND
HUMID...WITH DEW POINT TEMPS CLIMBING INTO THE 70S AND AFTERNOON
HIGH TEMPS IN THE UPPER 80S-LOW 90S. FRIDAY ALSO HAS THE POTENTIAL
TO BE SIMILARLY WARM...THOUGH SOME COOLING BEHIND THE FRONT ACROSS
FAR NORTHERN IL AND CLOUDS/PRECIP MAY BE LIMITING FACTORS.

A SPRAWLING AREA OF HIGH PRESSURE BUILDS IN BEHIND THE COLD FRONT
SATURDAY AND TAKES UP RESIDENCE INTO EARLY NEXT WEEK. DRY AND MUCH
COOLER WEATHER...HIGHS LOW-MID 70S AND LOWS IN THE
50S...CHARACTERIZE THE FORECAST FOR THE EXTENDED PERIOD
SATURDAY-MONDAY.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE.

KJB

//DISCUSSION...UPDATED 06Z...

WIDELY SCATTERED SHOWERS ARE DEVELOPING AGAIN ACROSS NORTHERN
ILLINOIS IN ASSOCIATION WITH THE APPROACHING SURFACE COLD FRONT AND
UPPER LEVEL DISTURBANCE. OVERALL THIS ACTIVITY LOOKS TO BE
LIGHT...AND SHOULD ONLY PERSIST ACROSS THE AREA FOR A COUPLE
HOURS. THEREAFTER...A QUIET WEATHER DAY IS EXPECTED ACROSS THE
REGION. LIGHT WESTERLY FLOW DURING THE DAY WILL LIKELY ALLOW A
LAKE BREEZE TO DEVELOP. HOWEVER...AT THIS TIME IT APPEARS THAT IT
MAY STRUGGLE TO REACH KORD AND KMDW...WITH KGYY THE MOST LIKELY
CANDIDATE TO EXPERIENCE A WIND SHIFT THIS AFTERNOON.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR ALL ELEMENTS.

KJB

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

WEDNESDAY AND THURSDAY...PREDOMINANTLY VFR...THOUGH THERE IS A
SLIGHT CHANCE OF A THUNDERSTORM.

FRIDAY...PRETTY GOOD CHANCE OF A PERIOD OR TWO OF TSRA.

SATURDAY AND SUNDAY...VFR. NORTHEAST WINDS LIKELY.

IZZI

&&

.MARINE...
220 AM CDT

A COLD FRONT WHICH CLEARED THE LAKE EARLY THIS MORNING HAS SHIFTED
WINDS WESTERLY. THE WINDS WILL RETURN TO SOUTHERLY BY AFTERNOON AS
HIGH PRESSURE TRANSLATES EAST ACROSS THE OHIO RIVER VALLEY. WIND
SPEEDS IN NEARSHORE AREAS OF ILLINOIS AND INDIANA ARE
EXPECTED TO BE LIGHT ENOUGH THIS AFTERNOON TO ALLOW FOR AT LEAST
SOME TEMPORARY ONSHORE COMPONENT OF WIND.

THE NEXT FEATURE OF INTEREST FOR THE LAKE IS STRONG...ALMOST
EARLY-AUTUMN-LIKE...LOW PRESSURE DEVELOPING ACROSS THE HIGH PLAINS
REGION ON THURSDAY MORNING. THIS LOW WILL TRANSLATE TO NORTH OF THE
GREAT LAKES BY LATE THURSDAY NIGHT. AHEAD OF THIS FEATURE WILL BE
GUSTY SOUTHERLY WINDS OVER LAND. THE OFFSHORE COMPONENT OF THIS WILL
LIKELY ALLOW FOR A WINDOW OF SMALL CRAFT ADVISORY WINDS IN THE
ILLINOIS AND POSSIBLY THE INDIANA NEARSHORE AREAS. AN ASSOCIATED
STRONG COLD FRONT TO THE LOW WILL MOVE DOWN THE LAKE SOMETIME DURING
THE DAY FRIDAY...TURNING WINDS NORTHERLY. THIS WILL BUILD
WAVES...PRESENTLY FORECAST OVER THE SOUTHERLY PART OF THE LAKE TO
REACH 4 TO 6 FEET FRIDAY NIGHT INTO THE DAY SATURDAY. IF THIS
FORECAST WERE TO HOLD...IT WOULD LEAD TO SMALL CRAFT ADVISORIES
AND BEACH HAZARD STATEMENT ISSUANCES FOR ILLINOIS AND INDIANA
SHORE AREAS.

MTF

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.