National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLOT 291555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1055 AM CDT TUE JUL 29 2014

.DISCUSSION...
323 AM CDT

SYNOPSIS...BELOW NORMAL TEMPERATURES CONTINUE THIS WEEK WITH
TEMPERATURES EVER SO SLOWLY MODERATING. THERE IS A CHANCE FOR
AFTERNOON SHOWERS AND THUNDERSTORMS THROUGH SATURDAY WITH THE
BEST CHANCES OF SHOWERS TODAY AND THEN IT APPEARS AGAIN LATE IN
THE WEEK...FRIDAY OR POSSIBLY SATURDAY. WITH THE WINDS CONTINUING
TO EASE OVER THE LAKE...THE BEACH HAZARD STATEMENT WILL END AT
4AM CDT AS PLANNED.

TODAY AND TONIGHT...
THE UPPER LEVEL LOW IS OVER JAMES BAY WHILE A SURFACE HIGH IS OVER
THE GREAT PLAINS. WITH A WEAK PRESSURE GRADIENT...WINDS WILL WILL
BE LIGHT THIS MORNING. THEY WILL PICK UP AS MIXING GETS GOING BUT
A LAKE BREEZE IS EXPECTED THIS AFTERNOON. HAVE MEDIUM CONFIDENCE
ON HOW FAR INLAND THE LAKE BREEZE PUSHES...BUT EXPECTING
TEMPERATURES TO FALL TO AROUND 70 BEHIND THE LAKE BREEZE. CANNOT
RULE OUT COOLING INTO THE 60S DUE TO UPWELLING OF COOLER LAKE MI
TEMPERATURES FROM THE RECENT STRONG NORTHERLY WINDS. ALL OTHER
LOCATIONS SHOULD SEE HIGHS IN THE MID TO UPPER 70S.

WE WILL HAVE MULTIPLE SOURCES OF FORCING TODAY BETWEEN THE LAKE
BREEZE AND AN UPPER LEVEL VORTICITY STREAMER SWINGING THROUGH THE
REGION. A FEW ISOLATED SHOWERS ARE CURRENTLY OVER CENTRAL WI AND
CENTRAL LAKE MICHIGAN AHEAD OF THAT WAVE. ALL AREAS HAVE A CHANCE
TO SEE ISOLATED TO SCATTERED SHOWERS THIS AFTERNOON. THE BEST
CHANCE AND COVERAGE WILL BE EAST OF A MCHENRY TO FOWLER INDIANA LINE
ALONG THE LAKE BREEZE. ALSO THINKING THE BEST CHANCE FOR
THUNDERSTORMS WILL BE ALONG THE LAKE BREEZE DUE TO THE ADDED
FORCING. THAT BEING SAID...ONLY EXPECTING ISOLATED THUNDERSTORMS
AS CAPE SHOULD BE LIMITED TODAY. MODELS SEEM TO BE OVER DOING
DEWPOINTS A BIT WHICH IS RESULTING IN OVER FORECASTED CAPE VALUES.
NO SEVERE STORMS ARE EXPECTED.

AN UPPER LEVEL WAVE AND COLD FRONT WILL PUSH SOUTH TONIGHT INTO
WEDNESDAY AND LOWS WILL BE IN THE UPPER 50S IN THE OUTLYING AREAS.
DOWNTOWN WILL HAVE A LOW IN THE LOWER 60S.

JEE

WEDNESDAY...
THE AFOREMENTIONED COLD FRONT LOOKS TO LOSE STEAM AS IT MOVES INTO
OUR SOUTHERN FORECAST AREA DUE TO THE UPPER WAVE AND SUPPORT
MOVING MORE EAST THAN SOUTH. THE SLOWER MOVEMENT WILL KEEP THIS
FOCUS...ALBEIT WEAK...IN THE EASTERN FORECAST AREA INTO THE
AFTERNOON. THAT AND ANOTHER LAKE BREEZE COULD PROVIDE FOR A
HANDFUL OF AFTERNOON SHOWERS/STORMS. AGAIN CHANCES ARE LIKELY NOT
AS HIGH AS SOME GUIDANCE IS INDICATING AND THAT LOOKS TO BE
ESPECIALLY TRUE NORTH AND WEST OF I-55. TEMPERATURES ARE EXPECTED
TO BE VERY SIMILAR TO TODAY.

THURSDAY THROUGH THE WEEKEND...
LITTLE PROGRESSION IN THE AMPLIFIED UPPER LEVEL PATTERN IS
FORECAST THROUGH SATURDAY. AS AN ILLUSTRATION OF THIS...FORECAST
SEA LEVEL PRESSURES RANGE FROM 1016MB TO 1019MB FROM THURSDAY
THROUGH SATURDAY NIGHT...I.E. NO CHANGE AND DAILY LAKE BREEZES.
THERE IS ONE FINAL UPPER LEVEL SHORT WAVE ON THE BACKSIDE OF THE
LONG WAVE TROUGH THAT HAS SURPRISINGLY GOOD CONSISTENCY ON THE
EC...GFS...AND GFS ENSEMBLE THAT COULD BRING HIGHER REGIONAL
COVERAGE TO AFTERNOON SHOWERS/STORMS ON FRI AND POSSIBLY ON SAT
DEPENDING ON FEATURE TIMING. ITS A PRETTY SUBTLE FEATURE TO KEY IN
ON AND WITH LITTLE IN THE WAY OF LOW-LEVEL FOCUS HAVE UNDERCUT
MODEL BLEND POPS WHICH ARE BIASED BY WHAT SEEMS TO BE A TOO WET
GFS. DRY WEATHER LOOKS TO OCCUR IN ITS WAKE WITH HIGHER CONFIDENCE
DURING THE LATTER HALF OF THE WEEKEND.

MTF

&&

.AVIATION...

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

* LAKE BREEZE MAY IMPACT MDW LATER THIS AFTN WITH WINDS SHIFTING
  TO NE OR E BEHIND IT. BREEZE SHOULD STALL BEFORE REACHING ORD.

* ISOL TO SCT SHRA DEVELOP THIS AFTN INTO THE EARLY EVENING. MAY
  SEE A FEW THUNDERSTORMS AS WELL.

JEE/KB

//DISCUSSION...UPDATED 14Z...
HAD TO DROP THE PROB 30 FOR THUNDER DUE TO THE RESTRICTIONS OF
HAVING IT WITHIN THE FIRST 9 HOURS OF THE FORECAST. AT THIS TIME I
HAVE OPTED TO KEEP A TEMPO GROUP FOR THUNDER OUT OF THE FORECAST
DUE TO UNCERTAINTIES ON THE EXTENT OF THUNDER IN THIS AFTERNOONS
DEVELOPMENT. THERE IS STILL CERTAINLY STILL A LOW END THREAT OF
THUNDER IMPACTING THE AIRFIELDS LATER THIS AFTERNOON AFTER THE
21-22 UTC HOUR.

KB

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

LIGHT AND VARIABLE WINDS WILL BECOME NORTHWEST AROUND 8 KT BY MID
MORNING. A LAKE BREEZE IS EXPECTED AND SHOULD PUSH THROUGH MDW AND
GYY. WINDS WILL TURN EAST AT MDW BEHIND THE LAKE BREEZE AND
NORTHEAST AT GYY. THE BEST CHANCE FOR SHOWERS AND THUNDERSTORMS WILL
BE AROUND THE LAKE BREEZE DUE TO EXTRA FORCING ALONG IT. STILL
HAVE LIMITED CONFIDENCE ON HOW MANY STORMS WILL OCCUR...BUT HAVE
GREATER CONFIDENCE IN SCATTERED SHOWERS AROUND THE TERMINALS.

WINDS SLOWLY BECOME WEST NORTHWEST OVERNIGHT AND THEN NORTHWEST
WEDNESDAY MORNING. VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

JEE

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

* LOW-MEDIUM CONFIDENCE IN LAKE BREEZE IMPACTING THE TERMINALS
  LATER THIS AFTERNOON.

* MEDIUM CONFIDENCE IN SCT SHRA DEVELOPMENT ACROSS THE AREA THIS AFTERNOON.

* LOW CONFIDENCE IN ISOLATED TS IMPACTING THE TERMINALS THIS AFTERNOON.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE/KB

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

WEDNESDAY NIGHT...VFR.

THURSDAY THROUGH SATURDAY...PREDOMINANTLY VFR...WITH A CHANCE OF
TSRA IN MAINLY THE AFTERNOON & EARLY EVENING.

SUNDAY...VFR.

MONDAY...SCHC TSRA.

JEE

&&

.MARINE...
323 AM CDT

WILL END THE SMALL CRAFT ADVISORY AT 4AM CDT AS PLANNED. WINDS AND
WAVES CONTINUE TO RAPIDLY DIMINISH.

HIGH PRESSURE IS TO OUR WEST WITH AN UPPER LEVEL LOW OVER JAMES BAY.
WINDS WILL BE WEAK AND VARY ACROSS THE LAKE TODAY WITH A LAKE BREEZE
EXPECTED ALONG THE IL SHORE.  A COLD FRONT/UPPER LEVEL WAVE PUSHES
SOUTH DOWN THE LAKE TONIGHT THROUGH TOMORROW MORNING. WINDS BECOME
NORTH BEHIND THE FRONT BUT WINDS WILL REMAIN LIGHT AT AROUND 10 KT
DUE TO THE WEAK PRESSURE GRADIENT. AS THE BROAD UPPER TROUGH
ACROSS EASTERN CANADA ROTATES SLOWLY EASTWARD...THE PRESSURE
GRADIENT WILL CONTINUE TO BE LIGHT ACROSS THE LAKE WITH LITTLE IN
THE WAY TO DRIVE WINDS OVER 15 KT INTO THE WEEKEND. AFTERNOON
LAKE BREEZES WILL BE FAVORED IN NEAR SHORE AREAS WITH VARIABLE
WINDS IN THE EVENING OVER A FAIR AMOUNT OF THE LAKE ON MANY
NIGHTS.

JEE/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