Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 060853
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
353 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 09Z...

* SHOWERS WITH POSSIBLE THUNDER LATER THIS EVENING.

RODRIGUEZ

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

QUIET AND DRY CONDITIONS EXPECTED THIS MORNING WITH ANY PRECIP
ACTIVITY STAYING WELL WEST OF THE TERMINALS AT THIS TIME. PATCHY
FOG WITH INCREASING HIGH LEVEL CLOUD COVER IS LIKELY THIS
MORNING...WITH SOUTHERLY WINDS OBSERVING A STEADY INCREASE THROUGH
MIDDAY. MAIN FORECAST CHALLENGE FOR THE TERMINALS IS PRECIP TRENDS
AND TIMING. AM MONITORING SHOWERS/THUNDERSTORMS ACROSS MINNESOTA
AND FAR WESTERN IOWA...WHICH COULD FIRST IMPACT RFD BY LATE
MORNING. THIS DEVELOPMENT WILL LIKELY DRIFT EASTWARD THROUGH
MIDDAY AND POSSIBLY REACH RFD...BUT SHOULD ALSO OBSERVE A
WEAKENING TREND AS IT APPROACHES. BEST FOCUS THIS FORECAST PERIOD
FOR ALL TERMINALS WILL ARRIVE LATER THIS AFTERNOON AND EVENING
ALONG AN APPROACHING SURFACE TROUGH AND FRONTAL BOUNDARY.
HOWEVER...GUIDANCE VARIES TO THE EXTENT OF COVERAGE AND INTENSITY
OF ANY PRECIP AS WELL AS TIMING AND DURATION. BASED ON LATEST
TRENDS HAVE INCLUDED PRECIP IN THE TAFS WITH RFD HAVING THE BETTER
CHANCE TO OBSERVE IT EARLIER IN THE AFTERNOON...AND THEN THE
REMAINING TERMINALS NOT UNTIL LATER IN THE EVENING. CONFIDENCE IS
LOWER AT THIS TIME...AS SOME GUIDANCE IS BRINGING THIS PRECIP IN
EARLIER. OTHER CHALLENGES WILL ARRIVE VERY LATE IN THE FORECAST
PERIOD...WITH LOW CEILINGS AND WIND SPEED/DIRECTION LIKELY
BECOMING PROBLEMATIC.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE WITH VFR CONDITIONS THIS MORNING/TODAY.

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION TODAY.

* LOW MEDIUM CONFIDENCE WITH SHOWERS/THUNDER AND TIMING/DURATION
  LATER THIS EVENING.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...CHC MORNING TSRA AND POSSIBLE MVFR CIGS...TRENDING
TOWARDS VFR CONDS BY AFTN.

WEDNESDAY...SLIGHT CHANCE OF SHRA LATE.

THURSDAY THROUGH SATURDAY...CHANCE OF TSRA.

BEACHLER

&&

.MARINE...
220 PM CDT

WITH HIGH PRESSURE DEPARTING THE LAKES REGION AND A LOW PRESSURE
TAKING SHAPE IN THE HIGH PLAINS...SOUTHERLY WINDS WILL CONTINUE TO
STRENGTHEN ACROSS THE LAKE. ON THESE WINDS WILL COME HIGHER DEW
POINT AIR. WEBCAM IMAGERY FROM AROUND THE LAKE INDICATES HAZE THAT
MAY BE A LITTLE MORE THICKER ALREADY OVER THE WATER. CONCERNS WITH
DENSE FOG WILL INCREASE DURING THE DAY AND EVENING ON MONDAY WHEN
DEW POINTS OF 10-20 DEGREES HIGHER THAN THE LAKE WATER TEMPERATURES
MOVE OVER THE LAKE.

THE OFFSHORE SOUTHWESTERLY WINDS ON MONDAY AFTERNOON AND EVENING
LOOK TO REACH SMALL CRAFT ADVISORY CRITERIA ALONG THE ILLINOIS SHORE
AND IT IS POSSIBLE ALONG THE INDIANA SHORE. WILL GO AHEAD AND ISSUE
A SMALL CRAFT ADVISORY ON THIS SHIFT FOR THE ILLINOIS SHORE. AS FOR
THE OPEN WATERS...THE STABILITY WILL KEEP GUSTS FAR BELOW WHAT THEY
COULD BE MONDAY AFTERNOON...AS WINDS JUST OFF THE DECK /WITHIN
700 FT/ ACROSS THE NORTHERN PART OF THE LAKE ARE FORECAST TO BE
40-50 KT. WILL MENTION A FEW GALE FORCE GUSTS POSSIBLE ACROSS THE
NORTH AND THAT WILL BE PARTICULARLY TRUE FROM THE AREA OF THE
NORTH BUOY TO THE U.P. SHORE.

THE SYSTEM COLD FRONT WILL MOVE SOUTHWARD DOWN THE LAKE OVERNIGHT
MONDAY NIGHT. THE ONSHORE FLOW FROM THIS ON TUESDAY...IF A LITTLE
STRONGER THAN FORECAST...COULD BRING WAVES TO NEAR SMALL CRAFT
ADVISORY CRITERIA ALONG MAINLY THE INDIANA SHORE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...NOON MONDAY TO 10
     PM MONDAY.

&&

$$

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