Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 170844
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
344 AM CDT FRI APR 17 2015

.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/IROQUIS/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
ELSEHWERE...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.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

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

SATURDAY...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.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

LM...NONE.
&&

$$

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