Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 171920
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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