Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 061606
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1106 AM CDT MON JUL 6 2015

.SHORT TERM...
303 AM CDT

THROUGH TUESDAY...

NEAR TERM FOCUS WILL BE ON TEMPERATURES TODAY..THEN ON CONVECTIVE
EVOLUTION LATER TODAY AND OVERNIGHT. ANOTHER QUIET MORNING IN OUR
NECK OF THE WINDS. TEMPERATURES ARE HOLDING HIGHER TONIGHT GIVEN A
LIGHT SSE WINDS AND DEWPOINTS CREEPING UP INTO THE LOW TO MID 60S.
PATCHY FOG WILL CONTINUE THROUGH DAYBREAK BUT GENERALLY NOT
EXPECTING ANYTHING DENSE EXCEPT LOCALLY WHERE WINDS DECOUPLE OR IN
RIVER VALLEYS. ATTENTION WILL BE ON THE PROGRESSION OF A COLD
FRONT CURRENTLY STRETCHED FROM NORTHERN LAKE SUPERIOR
SOUTHWESTWARD INTO THE CENTRAL PLAINS. ACTIVE CONVECTION ALONG THE
FRONT CONTINUES TO SLOWLY MARCH SOUTH AND EASTWARD...WITH AN
EXTENSIVE DEBRIS SHIELD HEADING SOUTHEASTWARD. 925 MB THERMAL
RIDGE TO OUR WEST WILL SHIFT OVERHEAD THIS AFTERNOON. MIXING TO AT
LEAST 925 MB AND LIKELY HIGHER TO 850 WHERE TEMPS ARE FORECAST TO
REACH 25/19C RESPECTIVELY WOULD SUPPORT HIGHS AROUND 90. QUESTION
HOLDS AS TO ANY LINGERING SMOKE...WHICH PER MODIS IMAGERY IS
LARGELY ALONG AND EAST OF THE AREA...AND ANY HIGH CLOUDINESS FROM
CONVECTION TO THE WEST PLAYS OUT. HAVE LARGELY HELD ONTO THE MID
TO UPPER 80S AND AM RELUCTANT TO GO HIGHER GIVEN THESE
UNCERTAINTIES AND THINK THE CLOUD COVER MAY BE MORE EXTENSIVE TO
SUGGEST THE HIGHER TEMPS WOULD BE HARDER TO REACH...WHICH COULD
EVEN SUGGEST SOME COOLER TEMPS IN OUR NORTH/WEST. STILL...HEAT
INDEX VALUES WILL GET CLOSE TO OR INTO THE 90S IN MANY AREAS WITH
THE INCREASED HUMIDITY.

MODEL CONSENSUS IS NOT EXACTLY CLEAR JUST YET AS TO HOW THINGS PLAY
OUT THROUGH TONIGHT BUT ARE COMING INTO BETTER GENERAL AGREEMENT
IN FRONTAL TIMING. MID LEVEL LAPSE RATES...WHICH ARE MORE
IMPRESSIVE CURRENTLY...WILL WEAKEN AS THE FRONT NEARS THE AREA
TONIGHT. GFS/ECMWF/SREF STILL SUGGEST FRONT CLEARS THE CHICAGO
AREA BY DAYBREAK TUESDAY...WHILE WRF-NAM AND NAM 4KM SUGGEST IT
WILL STILL BE NEAR THE MISSISSIPPI RIVER BY THIS TIME. THERE ARE
SEVERAL RIPPLES IN THE FLOW OUT AHEAD OF THE MAIN UPPER TROUGH
CURRENTLY MOVING ALONG THE CANADIAN BORDER MAY SLOW TINGS A TOUCH
AS THE UPPER JET DOES REMAIN FOCUSED TO THE NORTH...A SURFACE LOW
DOES LOOK TO TRACK ALONG FRONT FROM THE PLAINS AND NORTH INTO
WISCONSIN TONIGHT. GLOBAL MODELS HAVE BEEN CONSISTENT IN THEIR
TIMING...WHICH IS NOT A GREAT DIURNAL TIME TO MOVE THROUGH...AND
THERE IS NOTHING IN THE RAP RUNS TO SUPPORT THE WRF-NAM MODEL
SLOWER LOW PROGRESSION AND THEREFORE HOLD WITH A GFS/ECMWF BLEND
FOR FRONTAL TIMING.

THEREFORE CURRENT FEELING IS THAT THE CONVECTION CURRENTLY ONGOING
DUE TO LOW LEVEL WARM/MOIST ADVECTION IN IOWA WILL CONTINUE TO SHIFT
EAST AND RIDE ALONG THE MOISTURE TRANSPORT ACCESS NORTHEASTWARD.
SOME CONTINUED DEVELOPMENT IS EXPECTED OUT AHEAD OF THE COLD FRONT
AS THE BEST MOISTURE TRANSPORT AHEAD OF THE FRONT CONTINUES TO
PROGRESS ACROSS WISCONSIN. THE IMPLICATIONS OF THIS ARE THAT SOME
CONVECTION MAY CLIP FAR NORTH CENTRAL ILLINOIS LATE THIS MORNING
INTO THE EARLY AFTERNOON TIME FRAME AS SUGGESTED BY THE HRRR AND
SEVERAL HOPWRF-ARW ENSEMBLE MEMBERS. SEVERAL MEMBERS DO SUGGEST A
WEAKENING OF THE SOUTHERN PORTIONS OF THE CONVECTION WHICH WOULD
KEEP A QUIET MORNING PERIOD...AND THIS MAKES SENSE GIVEN THE
MOISTURE TRANSPORT WHICH IS NORTHEASTWARD DIRECTED AT THE MOMENT
WILL FOCUS NORTH THROUGH THE MORNING AND EARLY AFTERNOON.

THEN BOUNDARY LAYER HEATING/MOISTENING WOULD SUPPORT SOME
REGENERATION IN WESTERN ILLINOIS AND INTO NORTH CENTRAL ILLINOIS IN
LATER IN THE AFTERNOON...POTENTIALLY ENHANCED BY ANY OUTFLOW FROM
THE OVERNIGHT CONVECTION. DEWPOINT POOLING AHEAD OF THE FRONT WILL
ALLOW PW VALUES TO NEAR 2 INCHES...MEANING LOCALLY HEAVY DOWNPOURS
WOULD BE A POTENTIAL HAZARD. 30 KT OF DEEP LAYER SHEAR DOES STILL
SUPPORT SOME STORM ORGANIZATION AS WELL...WHICH IF THE STORMS
FORM INTO A LINE COULD ALSO POSE A WIND/MARGINAL HAIL THREAT AS
WELL. CURRENT SLIGHT/MARGINAL RISK AREAS FROM SPC HAVE CHANGED
VERY LITTLE FROM PREVIOUS FORECAST WITH THE BEST CHANCE OF TAPPING
INTO BETTER INSTABILITY COMBINED WITH THE FRONTAL FORCING IN NORTH
CENTRAL ILLINOIS AND POINTS WEST.

THEN TONIGHT...STILL SHOULD BE SOME SHOWERS AND THUNDERSTORMS
OVERNIGHT THOUGH AS DEWPOINTS HOLD STRONG IN THE SOUTHERLY FLOW
AHEAD OF THE FRONT IN THE LOWER 70S AND MAINTAIN SOME LEVEL OF
INSTABILITY...THOUGH THE BETTER ACTIVITY LOOKS TO BE WEST OF THE
AREA AND EXTENDING INTO NORTH CENTRAL ILLINOIS TIED TO THE COLD
FRONT...AND NUMEROUS SOLUTIONS SUGGEST A WEAKENING OF THE ACTIVITY
AS THE FRONT PROGRESSES THROUGH NORTHEAST ILLINOIS AND
NORTHWEST INDIANA...ESPECIALLY AFTER MIDNIGHT.

HIGH PRESSURE WILL MOVE FROM THE UPPER MIDWEST TO THE MISSISSIPPI
VALLEY ON TUESDAY WHICH WILL CONTINUE THE COLD FRONTS SOUTH AND
EASTWARD MOVEMENT. LOOKS LIKE THERE WILL BE SOME SHOWER
ACTIVITY...POSSIBLY A FEW THUNDERSTORMS TO START THE DAY TUESDAY.
WINDS TURN OFF THE LAKE AND ONSHORE...USHERING A MUCH COOLER AND
DRIER AIRMASS FOR AREAS ALONG AND NORTH OF I-80. THE FRONT WILL BE
ON THE EDGE OF OUR AREA TUESDAY AFTERNOON...MEANING A CHANCE FOR
PRECIP LINGERS FOR SOUTH AND EAST AREAS AS THINGS FIRE UP AGAIN
AHEAD OF THE FRONT...BUT THINGS COULD LARGELY BE EAST OF OUR AREA BY
THAT TIME.

KMD

&&

.LONG TERM...
303 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

LOOKS LIKE A BRIEF RESPITE TUESDAY NIGHT BEFORE THE FRONT GETS
SHIFTED BACK NORTHWARD AND BECOMES THE FOCUS FOR ADDITIONAL ROUNDS
OF PRECIPITATION THROUGH WEEKS END. THE UPPER AIR PATTERN FEATURES
HIGH PRESSURE OVER THE SE UNITED STATES EXTENDING OFFSHORE TO THE
ATLANTIC...WITH A TROUGH JUST OFF THE CALIFORNIA COAST. THE HIGH IN
THE EAST WILL SLOWLY RETROGRADE AND SHIFT INLAND TO THE WEST WHILE
THE TROUGH IN THE WEST SLOWLY MOVES EASTWARD ONSHORE INTO THE GREAT
BASIN. THIS KEEPS OUR AREA IN A SOMEWHAT MOIST WSW FLOW WITH
MULTIPLE WAVES PROPAGATING NE IN THIS FLOW PATTERN AND INTERSECTING
WITH THE STALLED OUT FRONTAL BOUNDARY. THIS PATTERN SUGGEST
OCCASIONAL PERIODS OF SHOWERS AND THUNDERSTORMS. FUTURE FORECASTS
WILL LIKELY NEED TO REFINE THE TIMING OF THESE CHANCES...WHICH
CURRENTLY LOOK TO OCCUR WEDNESDAY PM...FRIDAY...AND POSSIBLY INTO
SATURDAY. UPPER LEVEL HEIGHTS CONTINUE TO BUILD FROM THE EAST AS THE
HIGH EXPANDS OVER THE ENTIRE SOUTHERN UNITED STATES WHICH SHOULD
EVENTUALLY LIFT THE FRONTAL BOUNDARY NORTH OF THE AREA AT SOME
POINT BUT NOT UNTIL THE WEEKEND.

TEMPERATURES WILL BE MUCH COOLER THROUGH MID WEEK...WITH READINGS
BACK INTO THE 70S...WITH LAKESHORE AREAS STUCK IN THE 60S/NEAR 70
BEFORE HEIGHTS BUILD AND THE FRONT GETS LIFTED NORTHWARD.
TEMPERATURES AT THIS POINT CONTINUE TO RECOVER BACK WELL INTO THE
80S FOR THE WEEKEND.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING.

* MVFR/IFR CEILINGS EARLY TUESDAY.

* NORTHEAST WINDS OVER 10KT TUESDAY.

MM

//DISCUSSION...UPDATED 12Z...

PATCHY FOG THIS MORNING WILL QUICKLY DISSIPATE OVER THE NEXT ONE
TO TWO HOURS...WHILE DENSE HIGH LEVEL CLOUD COVER CONTINUES TO
SPREAD EAST SOUTHEAST ACROSS THE TERMINALS. VFR CONDITIONS ARE
THEN EXPECTED THROUGH MOST OF TODAY...WHILE SOUTHERLY WINDS
STEADILY INCREASE THROUGH THIS MORNING. STILL ANTICIPATING PRECIP
LATER THIS AFTERNOON AND EVENING ACROSS THE TERMINALS...DESPITE
SOME UNCERTAINTY REMAINING WITH TIMING/COVERAGE. AM A LITTLE
CONCERNED THAT THIS PRECIP COULD ARRIVE SLIGHTLY EARLIER THAN
PREVIOUSLY THOUGHT...SO MOVED UP TIMING A COUPLE OF HOURS FOR ALL
TERMINALS. A POSSIBLE EARLIER ARRIVAL SEEMS PROBABLE AS
THUNDERSTORMS CURRENTLY OVER EAST CENTRAL IOWA CONTINUE TO
STEADILY PROGRESS EAST. WITH EASTWARD EXPANDING INSTABILITY AXIS
TODAY...ITS POSSIBLE THAT THIS AREA SHOWERS/THUNDERSTORMS WILL
JUST CONTINUE TO MOVE EAST TOWARDS NORTHERN ILLINOIS. IF THIS WERE
TO OCCUR...THAN AN EVEN EARLIER ARRIVAL MIGHT BE POSSIBLE. PRECIP
LIKELY OVER THE TERMINALS BY THIS EVENING...WITH THUNDER ALSO
LIKELY SHRINKING IN COVERAGE DURING THIS TIME. THE ARRIVAL OF THE
FRONT LATER TONIGHT INTO EARLY TUESDAY MORNING WILL NOT ONLY SHIFT
THE WINDS...BUT ALLOW LOW STRATUS TO PUSH ACROSS THE TERMINALS.
HAVE NOT INCLUDED IFR IN THE TAFS...BUT WILL NEED TO MONITOR FOR
THIS POTENTIAL AS WELL THROUGH MIDDAY TUESDAY.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM HIGH THAT THUNDERSTORMS WILL OCCUR...MEDIUM ON TIMING.

* MEDIUM HIGH ON MVFR EARLY TUESDAY.

* MEDIUM HIGH ON WINDS OVER 10KT FROM NORTHEAST TUESDAY.

MM

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

TUESDAY NIGHT...VFR.

WEDNESDAY...CHANCE OF SHRA...SLIGHT CHANCE OF TSRA.

THURSDAY...CHANCE OF TSRA.

FRIDAY...CHANCE OF TSRA.

SATURDAY...CHANCE OF TSRA.

SUNDAY...CHANCE OF TSRA.

RODRIGUEZ

&&

.MARINE...
431 AM CDT

SOUTHERLY FLOW IS OCCURRING ACROSS THE ENTIRE LAKE THIS
MORNING...WITH THE HIGHEST SPEEDS CURRENTLY ACROSS THE NORTHERN
HALF OF THE LAKE. WINDS WILL REMAIN OUT OF THE SOUTH FOR MUCH OF
TODAY WITH A STEADY INCREASE IN SPEEDS ANTICIPATED THROUGH THE
AFTERNOON. WINDS TO 30KT ARE STILL LIKELY ACROSS THE NORTHERN HALF
OF THE LAKE THIS AFTERNOON INTO THE EARLY EVENING...BUT DID
SLIGHTLY LOWER SPEEDS DURING THIS TIME. ALSO...SMALL CRAFT
ADVISORY IN PLACE FOR THE ILLINOIS SHORE STILL APPEARS TO BE ON
TRACK. HOWEVER...THINK THE STRONGEST WINDS MAY OCCUR SLIGHTLY
LATER THAN THE START TIME TO THE ADVISORY. WINDS WILL VEER TO THE
NORTHWEST AND NORTH LATER THIS EVENING INTO EARLY TUESDAY MORNING
AS A FRONTAL BOUNDARY MOVES THROUGH. SOME SLIGHTLY VARIABILITY
AMONG MODEL GUIDANCE WITH EXACT TIMING OF FRONTAL PASSAGE.
NONETHELESS...INCREASING NORTHERLY WINDS OVER THE LAKE DO LOOK
LIKELY ON TUESDAY. THESE STRONGER NORTHERLY WINDS AND BUILDING
WAVES WILL LIKELY CREATE HAZARDOUS CONDITIONS FOR SMALL CRAFT ONCE
AGAIN DURING THIS TIME.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 PM MONDAY.

&&

$$

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