Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 032027
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
327 PM CDT FRI JUL 3 2015

.SHORT TERM...
200 PM CDT

THROUGH SATURDAY NIGHT...

SHARP UPPER TROUGHING IN NORTHERN ONTARIO...WITH BROAD TROUGHING
EXTENDING SOUTHWEST THROUGH NORTHERN ILLINOIS AND INTO THE ARKLATEX
REGION. A MORE WELL DEFINED COLD FRONTAL BOUNDARY WILL SINK
SOUTHEAST THROUGH THE NORTHERN GREAT LAKES TONIGHT ASSOCIATED WITH
THE TROUGH AXIS IN CANADA. MEANWHILE... SHORTWAVE ENERGY IS
TRACKING TO THE SOUTH OF THE SOUTHERN EXTENSION OF THE 500 MB
HEIGHT DEPRESSION OVER CENTRAL ILLINOIS...CLOSER TO THE LOW LEVEL
SURFACE FRONT IN SOUTHERN ILLINOIS. ADDITIONALLY...SMOKE ALOFT
FROM FIRES IN CANADA CONTINUE TO DRIFT TOWARD THE AREA UNDER NW
FLOW ALOFT. UPSTREAM OBSERVATIONS IN NORTH DAKOTA/WESTERN
MINNESOTA DEPICTING HAZE...WITH SMOKE REPORTED IN OBSERVATIONS IN
SOUTHERN MANITOBA. THIS FLOW DIRECTION WILL CONTINUE TO DRIFT THIS
SMOKE/HAZE TOWARD THE GREAT LAKES THROUGH AT LEAST EARLY SATURDAY
BEFORE THE UPPER FLOW BACKS TO A WSW DIRECTION. MORE ON THIS ON
OUR SOCIAL MEDIA OUTLETS.

BACK TO THE SENSIBLE WX FORECAST...THE BROAD UPPER TROUGH SLOWLY SHIFTS
EASTWARD THROUGH TONIGHT...TAKING THE MORE EXTENSIVE CLOUDINESS
WITH IT AS UPPER LEVEL HEIGHT RISES/NEGATIVE VORTICITY ADVECTION
SHIFTS THROUGH THE GREAT LAKES REGION. LIGHT PRECIP MAINLY SOUTH
OF OUR FAR SOUTHERN ZONES WILL TAPER THIS AFTERNOON AND EVENING AS
WELL. FARTHER NORTH...THE COLD FRONT WILL DRIVE AN AREA OF
PRECIPITATION...BUT THIS SHOULD LARGELY REMAIN CONFINED INTO
WISCONSIN AND OVER NORTHERN AND CENTRAL LAKE MICHIGAN TONIGHT AS
LOW LEVEL RH PROFILES ARE DRY.

WE WILL LIKELY SEE SOME DISSIPATING CLOUDS WITH THIS FRONT IN THE
MORNING...OTHERWISE DAYTIME HEATING LOOKS TO LEAD TO DECENT WARMING
ON THE INDEPENDENCE DAY ALONG WITH SOME AFTERNOON CUMULUS CLOUDS OUT
AHEAD OF THE WEAKENING FRONT. MOST GUIDANCE DECAYS THE FORCING WITH
THIS FRONT BEFORE EXITING SOUTHERN WISCONSIN...BUT THERE IS A SMALL
CHANCE THAT A SHALLOW POP-UP SHOWER SNEAKS INTO FAR NORTHERN
ILLINOIS GIVEN SOME WEAK INSTABILITY PRESENT AS SUGGESTED BY THE GFS
AND SPC WRF...LIKELY OVERDONE ON THE GFS GIVEN HIGH DEWPOINTS IN THE
RAW MODEL FORECAST. LOW LEVEL WIND FIELDS ARE GENERALLY 10 KT OR
LESS...SUGGESTING A SE LAKE BREEZE IS STILL A LIKELY SCENARIO IN THE
AFTERNOON...THOUGH WITH MUCH LESS OF A MAGNITUDE OF LAKE COOLING AND
INLAND PROGRESSION ANTICIPATED GIVEN THE PREDOMINANT WESTERLY FLOW.
THE UPPER FORCING IS BENIGN...SO WILL BE RELYING ON ANY SURFACE
CONVERGENCE...POSSIBLY AIDED BY THE LAKE BREEZE...TO TRIGGER ANY
SHOWERS. IF ANYTHING OCCURS...IT WOULD BE ISOLATED IN NATURE...WITH
THE MORE LIKELY SCENARIO JUST AFTERNOON CUMULUS CLOUDS...AND HAVE
CONTINUED WITH A DRY FORECAST GIVEN THE WRF-NAM/4KM NAM HAS HIGH
DEWPOINTS AND HAS NO PRECIP. WOULD NOT BE SURPRISED IF SOME LOW POPS
ARE INTRODUCED IN THE NORTH GIVEN A SIGNAL IN THE GFS/SREF/CANADIAN
AND SOME HI-RES GUIDANCE. OTHERWISE A SPLENDID FORECAST WITH
READINGS IN THE 80S INLAND...70S NEAR THE LAKE...AND MODEST HUMIDITY
LEVELS. BENIGN CONDITIONS WILL RULE THE EVENING PERIOD WITH
TEMPERATURES FALLING THROUGH THE 70S AND CLEARING SKIES.

KMD

&&

.LONG TERM...
325 PM CDT

SUNDAY THROUGH FRIDAY...

PRIMARY CONCERN IS WITH COLD FRONT PASSAGE MONDAY NIGHT AND
ASSOCIATED THUNDERSTORM POTENTIAL. ALSO FOCUSED ON WARM TEMPERATURES
FOR SUNDAY AND MONDAY.

AFTER DAYS OF NORTHWEST FLOW ALOFT...TREND OF RISING HEIGHTS ON
INDEPENDENCE DAY WILL CONTINUE INTO SUNDAY AS WE BECOME POSITIONED
UNDER SHORTWAVE RIDGING. A WEAK UPPER LOW WILL DEVELOP OVER THE TN
AND LOWER OH VALLEY...WITH ITS FORCING WELL REMOVED FROM OUR AREA.
OUTSIDE OF GFS...WHICH APPEARS TO BE AN OUTLIER WITH STRONGER
DISTURBANCE IN WEAK FLOW ALOFT KICKING OFF CONVECTION IN EASTERN
CWA ON SUNDAY...CONTINUE TO FAVOR A DRY FORECAST. BIG STORY WILL
BE MUCH WARMER TEMPERATURES IN THE UPPER 80S DUE TO 925 MB TEMPS
RISING TO THE LOWER 20S CELSIUS. EXPECTING A FEW SPOTS OF
90...INCLUDING INLAND PORTIONS OF CHICAGO HEAT ISLAND. WEAK
SOUTHERLY LOW LEVEL FLOW AND STRONG WARMING OF LAND WILL LIKELY
ENABLE LAKE BREEZE TO PUSH INLAND INTO NORTHEAST IL...CAPPING
HIGHS AROUND 80 NEAR THE IL SHORE...BUT INLAND PUSH WILL BE
LIMITED DUE TO FAIRLY DEEP MIXING OVER LAND. ITS UNCERTAIN WHETHER
LAKE BREEZE WILL PUSH INTO NW INDIANA SHORE AREAS.

SURFACE HIGH PRESSURE RIDGE WILL SLIDE EAST SUNDAY NIGHT AND
FRONTAL TROUGH TRAILING LOW PRESSURE MOVING INTO UPPER MIDWEST
WILL APPROACH...RESULTING IN SOUTHERLY WINDS INCREASING TOWARD
DAYBREAK MONDAY AND THEN BECOMING GUSTY DURING THE DAY ON
MONDAY...WITH GUST SPEEDS UP TO 30 MPH AT TIMES. SEASONABLY WARM
LOWS OF ~65-70 SUNDAY NIGHT WILL SET THE STAGE FOR TEMPS PERHAPS
EVEN WARMER THAN SUNDAY ON MONDAY AS 850/925 MB TEMPS WARM A FEW
MORE DEGREES. MODEL CONSENSUS HAS ALSO BEEN FOR SLOWER APPROACH OF
COLD FRONT TO WEST...ALSO SUPPORTIVE OF WARMER TEMPS. DID BUMP UP
MAX T TO UPPER 80S TO AROUND 90...BUT IF DAYLIGHT HOURS END UP DRY
AND SUNNIER AS ITS STARTING TO APPEAR THEY MIGHT...LOWER 90S TEMPS
WILL LIKELY BE MORE WIDESPREAD ESPECIALLY FOR EASTERN HALF OF CWA.
DEWPOINTS RISING INTO THE UPPER 60S TO LOWER 70S WILL YIELD HEAT
INDEX VALUES IN THE MID TO UPPER 90S. REGARDING CONVECTION AHEAD
OF AND ALONG THE FRONT...KEPT POPS IN SLIGHT TO CHANCE RANGE
MAINLY NW 1/3 OF CWA MONDAY AFTERNOON...WITH LIKELY TO CATEGORICAL
POPS MONDAY NIGHT.

MIDLEVEL LAPSE RATES LOOK TO BE FAIRLY MEAGER...WHICH COULD LIMIT
INSTABILITY SOME...AND THERE ARE QUESTIONS ON INTENSITY OF
CONVECTION IF FRONT SLOWS EVEN MORE GIVEN WHAT WOULD BE
UNFAVORABLE DIURNAL TIMING. DESPITE THESE ISSUES...SLIGHTLY BETTER
MIDLEVEL FLOW AND A STRONG LOW LEVEL JET COULD SUPPORT AT LEAST
SOME POTENTIAL FOR STRONG/SEVERE STORMS MONDAY EVENING AS WELL AS
HEAVY DOWNPOURS GIVEN PWAT VALUES POSSIBLY IN EXCESS OF 2 INCHES.
WINDS WILL FLIP NORTHERLY TUESDAY BEHIND COLD FRONT...BUT
SHOWER/TSRA CHANCES COULD CONTINUE TUESDAY MORNING INTO AFTERNOON
ESPECIALLY IN SOUTHEAST CWA CLOSER TO WAVE OF LOW PRESSURE ALONG
FRONTAL TROUGH. TEMPS WILL COOL DOWN INTO 70S TUESDAY...AND MAY
NOT GET OUT OF THE 60S LAKESIDE. FOR THE REST OF THE
PERIOD...GUIDANCE VARIES ON JUST HOW COOL AIRMASS WILL BE...WITH
LATEST ECMWF QUITE CHILLY UNTIL RECOVERY TO CLOSER TO NORMAL BY
THE END OF THE WORK WEEK. HAVE LOW POPS DAILY WEDS-FRIDAY...BUT
THESE MAY BE OVERDONE IF MORE AMPLIFIED GREAT LAKES TROUGHING
OCCURS AND KEEPS STORM TRACK SOUTH OF THE AREA.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* EAST TO NORTHEAST WINDS SPORADICALLY REACHING 10-11 KT BUT
  PRIMARILY LESS THAN 10 KT THIS AFTERNOON.

* LIGHT WESTERLY WINDS SATURDAY BUT POSSIBLE SHIFT TO EAST OR
  SOUTHEAST LATER SATURDAY AFTERNOON WITH LAKE BREEZE.

MDB

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE ACROSS THE REGION CONTINUES TO RESULT IN LIGHT AND
VARIABLE WINDS...WITH AN EASTERLY DIRECTION FAVORED. LAKE
INFLUENCE MAY REINFORCE EAST TO NORTHEAST WINDS AT ORD/MDW BY MID
AFTERNOON SO A SLIGHT UPTICK IN WIND SPEEDS MAY OCCUR BUT SPEEDS
LOOK TO BE UNDER 10 KT THE MAJORITY OF THE TIME. GYY SHOULD SEE A
STEADIER NORTHEAST WIND THROUGH THE AFTERNOON. WINDS WILL DIMINISH
AND TURN SOUTHEASTERLY EARLY THIS EVENING THEN TREND TO THE WEST
AND SOUTHWEST LATE TONIGHT. LIGHT WEST WINDS ARE EXPECTED SATURDAY
AND A LAKE BREEZE IS EXPECTED TO DEVELOP. THERE IS SOME
INDICATION IT MAY BE MORE OF A SOUTHEASTERLY LAKE BREEZE WHICH
WOULD HAVE A TOUGHER TIME REACHING ORD/MDW BUT WITH SUCH A WEAK
FLOW REGIME A MORE TYPICAL EASTERLY LAKE BREEZE WITH A FURTHER
INLAND PUSH MAY RESULT. WILL KEEP A LIGHT WESTERLY WIND AT ORD FOR
SATURDAY AFTERNOON FOR NOW BUT THERE IS POTENTIAL FOR AN EAST TO
SOUTHEAST SHIFT...THOUGH SPEEDS WOULD PROBABLY BE UNDER 10 KT.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WINDS REACHING 10-11 KT THIS AFTERNOON AND
  MEDIUM- HIGH CONFIDENCE THAT IT WILL BE SPORADIC WITH SPEEDS
  MAINLY UNDER 10 KT.

* LOW CONFIDENCE THAT LAKE BREEZE WIND SHIFT WILL ARRIVE AT
  ORD/MDW SATURDAY AFTERNOON.

MDB

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

SATURDAY NIGHT...DRY. VFR. S WINDS.
SUNDAY...DRY. VFR. S WINDS. LAKE BREEZE PSBL.
MONDAY...TSRA LIKELY LATE. SW WINDS.
TUESDAY...CHC TSRA. NW WINDS BECOMING NE.
WEDNESDAY...DRY. VFR. E WINDS.
THURSDAY...CHC TSRA. NW WINDS.

BMD

&&

.MARINE...
240 AM CDT

A RIDGE STRETCHES FROM WISCONSIN ACROSS SOUTHERN LAKE MICHIGAN
INTO MICHIGAN THIS MORNING RESULTING IN LIGHT AND VARIABLE WINDS
ACROSS THE SOUTH HALF OF THE LAKE...AND SOUTHWEST WINDS ACROSS THE
NORTH. THE NORTHERN HALF OF THE LAKE WILL SEE WINDS INCREASING
INTO THE 15 TO 25 KT RANGE THIS AFTERNOON AND EVENING AHEAD OF AN
APPROACHING FRONT. MEANWHILE...THE SOUTH HALF WILL CONTINUE TO
SEE LIGHT WINDS WITH LAKE BREEZES RESULTING IN ONSHORE FLOW THIS
AFTERNOON. THE FRONT WILL BEGIN TO SAG ACROSS THE NORTH HALF OF
LAKE MICHIGAN LATE TONIGHT...DROPPING TO AROUND MIDLAKE
SATURDAY...THEN LIFTING NORTH AGAIN. SOUTH WINDS FRESHEN UP ACROSS
THE LAKE AGAIN SUNDAY NIGHT INTO MONDAY AHEAD OF A STRONGER COLD
FRONT PROGGED TO SWEEP ACROSS THE LAKE MONDAY NIGHT.

BMD

&&

.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/NWSCHICAGO
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.