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 011729
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1229 PM CDT FRI AUG 1 2014

.DISCUSSION...
340 AM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH PRECIS TRENDS TODAY
THROUGH THIS WEEKEND...WITH SCATTERED SHOWERS/THUNDERSTORMS
POSSIBLE EACH DAY.

OVERALL QUIET CONDITIONS IN PLACE THIS MORNING WITH THE CAW
CURRENTLY DRY...WHILE SHOWERS SLOWLY APPROACH FROM THE
IOWA/ILLINOIS BORDER. PATCHY FOG HAS DEVELOPED
OVERNIGHT...PERIODICALLY DROPPING TO AROUND ONE MILE IN SOME
LOCATIONS. THE LOWEST VI`S REMAINS ISOLATED WITH THESE LOWER
OBSERVATIONS ONLY BEING REPORTED BRIEFLY. THIS WILL CONTINUE TO BE
LIKELY THROUGH THE MORNING HOURS ESPECIALLY AS LATEST SATELLITE
IMAGERY DEPICTING MID/HIGH LEVEL CLOUD COVER PUSHING INTO THE CAW.
SHORT WAVE TROUGH SEEN SHIFTING EAST TOWARDS WESTERN ILLINOIS THIS
MORNING WILL CONTINUE TOWARDS THE CAW...PRIMARILY BRINGING AN
INCREASE IN CLOUD COVER WITH THE SOUTHERN CAW OBSERVING THE
THICKER CLOUD COVER. ASSOCIATED SHOWER ACTIVITY WILL LIKELY HOLD
IN PLACE AS THE BETTER LARGE SCALE ASCENT REACHES THE CAW BY DAY
BREAK. THESE SCATTERED SHOWERS WILL MAINLY AFFECT AREAS SOUTH OF
INTERSTATE 80 THROUGH MID MORNING WITH PARTLY CLOUDY TO PARTLY
SUNNY SKIES IN PLACE.

AS CYCLONIC FLOW PERSISTS TODAY...SO WILL A STEADY STREAM OF WAVES
OF ENERGY TRAVERSING THIS FLOW. AS THIS ENERGY AND INCREASING
LARGE SCALE ASCENT MOVE OVERHEAD TODAY...IT WILL DO SO AS LOW
LEVEL LAPSE RATES STEEPEN. FORECAST SOUNDINGS ARE SHOWING THAT
THE ENVIRONMENT OVER NORTHERN ILLINOIS AND NORTHWEST INDIANA WILL
BE WELL MIXED AS EARLY AS 15-16Z. THIS COINCIDING WITH SLIGHTLY
INCREASING MID LEVEL LAPSE RATES AND DEW POINTS AROUND 60...WILL
YIELD WEAK TO MODERATE INSTABILITY AND NO CAP AS SOON AS MID DAY.
ALTHOUGH COVERAGE STILL APPEARS TO BE SCATTERED WITH MOST AREAS
LIKELY OBSERVING MORE PERIODS OF DRIER CONDITIONS...MOST GUIDANCE
IN FAIR IN AGREEMENT WITH BETTER COVERAGE THAN HAS BEEN SEEN OVER
THE LAST COUPLE OF DAYS. DO HAVE INCREASING POPS INTO THE
AFTERNOON WITH LOW CHANCE POPS IN PLACE BY 18Z. THE ENTIRE CAW
WILL OBSERVE THIS SCATTERED DEVELOPMENT TODAY BUT DO FEEL THAT THE
SOUTHERN THIRD OF THE CAW...ALONG AND SOUTH OF INTERSTATE
80...COULD OBSERVE BETTER COVERAGE. THIS WILL BE DUE TO BETTER
LARGE SCALE ASCENT WITH THE PASSING MID LEVEL FEATURES. WIDESPREAD
ORGANIZED/STRONG DEVELOPMENT IS NOT ANTICIPATED TODAY BUT ISOLATED
STRONGER WIND GUSTS AND SMALL HAIL COULD BE OBSERVED WITH THE
STRONGER THUNDERSTORMS. THE STEEP LOW LEVEL LAPSE RATES COULD
SUPPORT BETTER DOWNWARD MOMENTUM OF HIGHER WIND GUSTS DESPITE
GENERALLY WEAK FLOW WITHIN THE COLUMN...AS AXIS OF HIGHER PW ATS
SHIFTING THROUGH THE CAW COULD POSSIBLY SUPPLEMENT THIS LACK OF
FLOW WITH PRECIS LOADING. EXPECT COVERAGE/INTENSITY TO COME DOWN
LATER THIS EVENING...BUT WITH SOME POSSIBLE LINGERING SHOWERS
ACROSS NORTHERN ILLINOIS AS ANOTHER SHORT WAVE TROUGH APPROACHES
FROM THE NORTHWEST.

EXPECT LOW 80S ONCE AGAIN TODAY...BUT POSSIBLY NOT QUITE AS HIGH
AS THURSDAY DUE TO INCREASING CLOUD COVER/PRECIS. SATURDAY AND
SUNDAY WILL OBSERVE SIMILAR TEMP TRENDS...WITH SCATTERED
SHOWER/THUNDERSTORM ACTIVITY POSSIBLE ONCE AGAIN SATURDAY
AFTERNOON.

RODRIGUEZ

&&

.AVIATION...

//OED AND MD CONCERNS...UPDATED 18Z...

* SCATTERED SHRA/TSRA THIS AFTERNOON.
* LAKE BREEZE LIKELY BY MID-LATE AFTERNOON.
* WIND DIRECTION MAY BE BRIEFLY COMPLICATED BY TSRA OUTFLOW WITH
  HIGHER SPEEDS UP TO 30 KT POSSIBLE.

KJB

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

SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP ACROSS THE AREA
THIS AFTERNOON AS AN UPPER LEVEL DISTURBANCE MOVES ACROSS THE AREA.
A LAKE BREEZE IS EVIDENT CURRENTLY RIGHT ALONG THE LAKE SHORE AND
THE EXPECTATION IS THAT THE LIGHT WIND REGIME WILL ALLOW THIS
BOUNDARY TO PUSH INLAND OVER THE EASTERN TERMINALS BY MID TO LATE
THIS AFTERNOON. UNFORTUNATELY...HOWEVER...THE TIMING OF THIS BOUNDARY
MOVING OVER THE TERMINALS THIS AFTERNOON HAS DIMINISHED SOME...AS IT
APPEARS SOME OF THE OUTFLOW FROM THE STORM CURRENTLY MOVING OVER MDW
COULD DELAY OR PUSH THE LAKE BREEZE BOUNDARY BACK OVER THE LAKE FOR
A PERIOD. ONCE THIS BOUNDARY DOES MOVE OVER THE TERMINALS...THE MAIN
THREAT FOR SCATTERED CONVECTIVE ACTIVE SHOULD SHIFT TO THE WEST AND
SOUTH OF THE MAIN EASTERN TERMINALS WITH AN EASTERLY WIND SHIFT.

KJB


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

* MEDIUM WITH TSRA NEAR THE TERMINALS THROUGH AROUND 21 UTC THIS
  AFTERNOON.
* LOW-MEDIUM WITH LAKE BREEZE TIMING THIS AFTERNOON.
* LOW CONFIDENCE IN WIND DIRECTION IF AFFECTED BY TSRA OUTFLOW.

KJB

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

SATURDAY NIGHT...DRY/VFR.

SUNDAY...SLGT CHC AFTN/EVE TSRA...OTHERWISE VFR.

MONDAY THROUGH THURSDAY...CHANCE OF SHRA/TSRA.

RATZER

&&

.MARINE...
230 AM CDT

NO MAJOR MARINE FORECAST CONCERNS THIS MORNING AS WEAK SURFACE
PRESSURE GRADIENT DOMINATES THE REGION. AN AREA OF LOW PRESSURE JUST
SOUTHEAST OF JAMES BAY WILL LIFT NORTHEAST TODAY...WITH A WEAK
SURFACE TROUGH WASHING OUT ACROSS NORTHERN LAKE MICHIGAN. WEAK HIGH
PRESSURE RIDGING WILL DEVELOP AS THE TROUGH DISSIPATES...COMBINING
WITH EXISTING HIGH PRESSURE OVER THE OHIO VALLEY TO MAINTAIN WEAK
PRESSURE GRADIENT AND GENERALLY LIGHT WIND CONDITIONS ACROSS THE
LAKE WITH DAILY LAKE BREEZE DEVELOPMENT INTO SUNDAY. AN AREA OF LOW
PRESSURE WILL PASS NORTH OF THE LAKES SUNDAY AND SUNDAY NIGHT AND
WILL TRAIL A WEAK COLD FRONT ACROSS THE NORTHERN AND CENTRAL PARTS
OF THE LAKE. THE GRADIENT WILL TIGHTEN A BIT SUNDAY INTO SUNDAY
EVENING ACROSS THE NORTHERN PART OF THE LAKE IN ASSOCIATION WITH THE
PASSAGE OF THIS LOW AND WEAK FRONT...WITH SOUTH WINDS INCREASING
TO A MORE SOLID 15 KT OR SO. THE FRONT WILL THEN DISSIPATE WITH THE
GRADIENT AGAIN BECOMING RATHER WEAK SUNDAY NIGHT INTO MONDAY.
LONGER RANGE GUIDANCE INDICATES ANOTHER SOMEWHAT STRONGER LOW
DEVELOPING OVER THE PLAINS AND APPROACHING THE WESTERN LAKES
REGION LATE NEXT WEEK.

RATZER

&&

.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.