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 291912
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
212 PM 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 18Z...

* 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.

* LAKE BREEZE POSSIBLE AGAIN ON WEDNESDAY AFTERNOON.

KJB

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

OBSERVATIONS NEAR THE SHORES OF LAKE MICHIGAN ARE SHOWING SIGNS OF A
LAKE BREEZE DEVELOPING. THIS BOUNDARY WILL LIKELY PUSH INLAND A
LITTLE THIS AFTERNOON...IMPACTING KGYY AND POSSIBLY KMDW LATER IN
THE AFTERNOON. HOWEVER...I HAVE SOME DOUBTS THAT IT WILL MAKE IT TO
MDW GIVEN THE 12-15 KT OF 925 MB WEST-NORTHWESTERLY FLOW THAT IT
WILL BE WORKING AGAINST. FOR NOW...I WILL CONTINUE TO MONITOR THE
TRENDS OF THIS LAKE BREEZE AND MAKE A DECISION LATER OF WHETHER OR
NOT TO REMOVE THE WIND SHIFT FROM THE MDW TAF.

OTHERWISE...THE OTHER CONCERN LATER THIS AFTERNOON AND EVENING IS
THE THREAT FOR SCATTERED SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE
AREA. IT STILL APPEARS THE BEST TIMING FOR ANY ACTIVITY WOULD BE
AFTER 21 UTC THROUGH AROUND 02 UTC THIS EVENING. DUE TO THE
SCATTERED NATURE EXPECTED...I HAVE CONTINUED TO HANDLE THIS CHANCE
WITH A VCSH.

WINDS LOOK TO CONTINUE OUT OF WEST-NORTHWESTERLY DIRECTION INTO
WEDNESDAY. HOWEVER...ANOTHER LAKE BREEZE MAY DEVELOP WEDNESDAY
AFTERNOON...AND DUE TO WEAKER WESTERLY FLOW AROUND 925 MB...THE
BOUNDARY COULD THREATEN THE EASTERN TERMINALS WITH AN EASTERLY WIND
SHIFT LATER IN THE AFTERNOON. CONFIDENCE IS A BIT LOW THIS FAR
OUT...SO I HAVE LEFT THIS MENTION OUT OF THE 30 HOUR ORD TAF.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW 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.

KJB

//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...
210 PM CDT

HIGH PRESSURE IN THE NORTHERN AND CENTRAL PLAINS IS EXPECTED TO
WEAKEN SOME OVER THE COMING DAYS BUT GENERALLY REMAIN STATIONARY FOR
MOST OF THE WEEK AS AN UPPER LEVEL LOW PRESSURE SYSTEMS REMAINS
PARKED OVER JAMES BAY THROUGH SATURDAY. IN THIS PATTERN WEAK LOW
PRESSURE SYSTEMS WILL GLIDE SOUTHEAST DOWN THE LAKE AT TIMES...WITH
THE FIRST EXPECTED LATER TONIGHT INTO EARLY WEDNESDAY.

IN THIS STAGNANT PATTERN THE PRESSURE GRADIENT WILL REMAIN ON THE
LIGHTER SIDE AND WILL PROMOTE THE DEVELOPMENT OF LAKE BREEZES FOR
THE NEARSHORE WATERS AND VARIABLE WINDS OVER MUCH OF THE OPEN LAKE
AND WINDS GENERALLY 15 KT OR LESS.  KMD

KMD

&&

.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.