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 300733
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 AM CDT THU JUL 30 2015

.UPDATE...

858 PM CDT

A QUIET EVENING ACROSS THE FORECAST AREA WITH DEW POINTS ABOUT 15
DEGREES LOWER THAN 24 HOURS AGO AND PWATS OVER ONE INCH LOWER.
GOING FORECAST IS IN GOOD SHAPE WITH TEMPERATURES INCHING THEIR
WAY DOWN. THURSDAY LOOKS LIKE A VERY SIMILAR DAY TO TODAY EXCEPT
THE CLEAR CONDITIONS AND LOW DEW POINTS WILL BE THE RULE FROM THE
GET GO. THIS SHOULD PROVIDE SUFFICIENT MIXING WITHIN AN ALREADY
MODEST PRESSURE GRADIENT TO SUPPORT WESTERLY WIND GUSTS ONCE
AGAIN IN THE 20 TO 27 MPH RANGE AND SO HAVE INCHED THOSE UP IN THE
FORECAST SOME.

MTF

&&

.SHORT TERM...
221 PM CDT

TONIGHT THROUGH FRIDAY...

COLD FRONT MOVING EAST OF THE FORECAST AREA THIS AFTERNOON...WITH
SURFACE HIGH PRESSURE RIDGE EXPANDING FROM THE CENTRAL PLAINS INTO
CENTRAL IL/IN. SOUTHERN PERIPHERY OF MID-LEVEL TROUGH ASSOCIATED
WITH CLOSED UPPER LOW OVER ONTARIO WILL SWEEP ACROSS THE REGION
TONIGHT...THOUGH GENERALLY DRY ATMOSPHERE UPSTREAM PER OAX 12Z
RAOB AND EXPECT ONLY A FEW PATCHY MID-HIGH CLOUDS WITH WEAK HEIGHT
FALLS AHEAD OF TROUGH AND BENEATH RIGHT ENTRANCE TO UPPER LEVEL
JET STREAK LIFTING THROUGH THE NORTHERN LAKES. SURFACE DEW POINTS
CONTINUE TO DROP OFF INTO THE 50S ON BREEZY WEST-NORTHWEST
WINDS...SETTING THE STAGE FOR A LESS HUMID NIGHT WITH LOWS NEAR
AVERAGE IN THE LOW-MID 60S.

UPPER PATTERN SETTLES INTO A RIDGE IN THE WEST/TROUGH IN THE EAST
CONFIGURATION THROUGH THE END OF THE WEEK...WITH A COUPLE OF MINOR
AMPLITUDE SHORT WAVES DEPICTED IN GUIDANCE FOR THURSDAY AND
FRIDAY. MODELS INDICATE A RATHER WEAK SURFACE TROUGH REFLECTION
WITH THE WAVE TOMORROW...WITH A LITTLE MORE OF A WEAK COLD FRONTAL
TROUGH INDICATED FRIDAY. GFS IS MORE BULLISH WITH DEVELOPING
CONVECTION ALONG THE FRONT FRIDAY AFTERNOON...THOUGH AM A LITTLE
SUSPICIOUS GIVEN OVERALL DRYNESS OF SOUNDINGS AND WEAK LOW-LEVEL
CONVERGENCE IN WESTERLY WINDS ALONG SOUTHWEST-NORTHEAST ORIENTED
BOUNDARY. SURFACE RIDGE TO OUR SOUTH PREVENTS ANY SIGNIFICANT
MOISTURE RETURN...WITH CURRENT UPSTREAM DEW POINTS OVER THE PLAINS
IN THE 30S AND 40S ACROSS NEBRASKA. THE WRF...WHICH OFTEN OVERDOES
LOW LEVEL MOISTURE/CAPES IS DRY WITH NO CAPE AND FOR NOW AM
MAINTAINING A DRY FORECAST. IT DOES LOOK FAIRLY BREEZY...WITH
WINDS IN THE 25 KT RANGE WITHIN THE MIXED LAYER FOR
FRIDAY...LIKELY GOOD FOR GUSTS 20+ MPH. 850 MB TEMPS RANGE FROM
+16/18 C THURSDAY TO AROUND +18 C FRIDAY...MIXING DOWN TO MID-
UPPER 80S FOR HIGHS BOTH DAYS AND A GOOD DEAL OF SUNSHINE.

RATZER

&&

.LONG TERM...
303 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

HOLDING ONTO THE IDEA THAT THE FRIDAY AFTERNOON ACTIVITY WILL BE
LIMITED AND HAVE CONTINUED A DRY FORECAST WITH THE COLD
FRONT/TROUGH PASSAGE FRIDAY EVENING...HOLDING SIMILAR REASONING TO
THE SHORT TERM DISCUSSION. SEVERAL PIECES OF GUIDANCE...INCLUDING
THE GFS AND GEM...ARE A BIT MORE AGGRESSIVE WITH PRECIPITATION ON
THE FRONT.

FOLLOWING THE FRONTAL PASSAGE...THE PATTERN CHANGES VERY LITTLE ON
SATURDAY WITH NORTHWEST FLOW ALOFT...SURFACE HIGH PRESSURE IN THE
PLAINS..AND LOW PRESSURE OVER HUDSON BAY. VERY SUBTLE DROP IN LOW
LEVEL THERMAL FIELDS SUGGEST A SLIGHTLY COOLER DAY THOUGH
TEMPERATURES HOLD AROUND NORMAL. ALSO A BIT HIGHER POTENTIAL FOR
ONSHORE WINDS/SOME LAKE BREEZE...MAINLY NEAR THE LAKESHORE. HIGHS IN
THE LOW TO MIDDLE 80S SEEM REASONABLE.

THE SURFACE HIGH PRESSURE AXIS SHIFTS EASTWARD SATURDAY NIGHT.
MEANWHILE...THE FLOW ALOFT AMPLIFIES WITH THE WESTERN CONUS RIDGE
BUILDING...AND THE HUDSON BAY TROUGH DIGGING DEEPER INTO THE EASTERN
CONUS. THIS PATTERN SUPPORTS OCCASIONAL WAVES PROPAGATING SW THROUGH
THE AREA AT TIMES...MOST NOTABLY LATE SATURDAY NIGHT INTO EARLY
SUNDAY...WITH MAYBE A SLIGHTLY STRONGER FRONT INTO EARLY MONDAY. EACH OF
THESE BRINGS A CHANCE OF SHOWERS AND THUNDERSTORMS. TEMPERATURES
HOLD AROUND NORMAL THROUGH THIS TIME AS WELL. AFTER THE FRONT ON
MONDAY...COOLER HIGH PRESSURE BUILDS IN FOR TUESDAY. THE
BAROCLINIC ZONE ASSOCIATED WITH THE FRONT GETS HUNG UP IN/OR MORES
LIKELY SOUTH OF OUR SOUTHERN ZONES TUESDAY BEFORE LIFTING BACK
NORTH INTO WEDNESDAY.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG/GUSTY WESTERLY WINDS MID MORNING THRU EARLY EVENING. CMS

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

WITH LOW PRESSURE WELL NORTH OF THE AREA ACROSS HUDSON BAY AND
HIGH PRESSURE OVER THE CENTRAL PLAINS BUILDING ACROSS THE OHIO
TONIGHT AND FRIDAY...A WESTERLY GRADIENT WILL REMAIN ACROSS THE
TERMINALS TODAY. AS THE LOW LEVELS BEGIN MIX LATER THIS MORNING...
WINDS WILL INCREASE INTO THE 14-18KT RANGE WITH GUSTS INTO THE MID
20KT RANGE. ITS POSSIBLE SPEEDS AND GUSTS MAY BE A BIT HIGHER THAN
ADVERTISED IN THE EARLY/MID AFTERNOON DEPENDING ON HOW DEEP THE
MIXING BECOMES SO A FEW GUSTS APPROACHING 30KTS ARE POSSIBLE BUT
NOT CONFIDENT THESE WILL BECOME PREVAILING. WINDS WILL DIMINISH
WITH SUNSET THIS EVENING. GENERALLY SKC EXPECTED THRU THE PERIOD
WITH HIGH BASED FEW CU POSSIBLE TODAY. CMS

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR WINDS THRU THE PERIOD. CMS

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

FRIDAY...PRIMARILY VFR BUT AN ISOLATED AFTERNOON-EVENING
SHRA/TSRA CANNOT BE COMPLETELY RULED OUT. GUSTY WEST WINDS.

SATURDAY...VFR THEN SLIGHT CHANCE FOR SHRA/TSRA SATURDAY NIGHT.
MAINLY NORTHWEST WINDS...BUT LAKE BREEZE WIND SHIFT POSSIBLE.

SUNDAY THROUGH TUESDAY...PRIMARILY VFR WITH PERIODIC CHANCE FOR
SHRA/TSRA. LAKE BREEZE WIND SHIFT POSSIBLE DURING
DAYTIME...ESPECIALLY ON TUESDAY.

RC

&&

.MARINE...

233 AM...STRONG LOW PRESSURE OVER HUDSON BAY WILL REMAIN GENERALLY
STATIONARY INTO THIS WEEKEND AS IT SLOWLY WEAKENS. HIGH PRESSURE
OVER THE CENTRAL PLAINS WILL SLOWLY SPREAD EAST ACROSS THE OHIO
VALLEY TONIGHT AND FRIDAY. THIS WILL ALLOW A WESTERLY GRADIENT TO
PERSIST OVER THE LAKES REGION THROUGH FRIDAY. A WEAK COLD FRONT
WILL MOVE SOUTH ACROSS THE LAKE FRIDAY AFTERNOON/EVENING.

THE GRADIENT WILL BE STRONGEST ACROSS NORTHERN PORTIONS OF THE LAKE
THIS MORNING WITH SOME GUSTS TO 30KTS POSSIBLE. AS TEMPERATURES WARM
AND WINDS INCREASE OVER LAND THIS AFTERNOON...STRONGER WINDS WILL
LIKELY BE CONFINED TO THE WESTERN SHORE OF LAKE MICHIGAN WITH SPEEDS
DIMINISHING SOME OVER THE CENTRAL AND EASTERN PORTIONS OF THE LAKE
AND POSSIBLY TURNING MORE SOUTHWEST WITH LOW CONFIDENCE FOR SPECIFIC
SPEEDS/DIRECTIONS THIS AFTERNOON. SPEEDS/GUSTS THEN INCREASE A BIT
LATE TONIGHT INTO FRIDAY MORNING AHEAD OF THE FRONT. CMS

&&

.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.