Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280806
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
306 AM CDT THU MAY 28 2015

.UPDATE...
916 PM CDT

FOR EVENING UPDATE...

GOING FORECAST IN GOOD SHAPE THIS EVENING...WITH ONLY A FEW
TWEAKS TO GRIDS TO MATCH HOURLY OBS TRENDS.

WEAK SURFACE COLD HAD FRONT CLEARED THE CWA BY EARLY THIS
EVENING... WITH CLEARING SKIES IN SUBSIDENCE BEHIND MID-LEVEL
SHORT WAVE PULLING AWAY TO THE EAST. ONLY A SUBTLE DROP IN DEW
POINT TEMPS INTO THE MID-50S AND FAIRLY WEAK SURFACE HIGH PRESSURE
RIDGE NOTED ACROSS AREA PER METARS...WITH LIGHT WINDS ALREADY
TURNING BACK TO THE SOUTH ACROSS IA-WI. WINDS ALONG THE LAKE
MICHIGAN SHORE THAT HAD TURNED NORTHEAST BEHIND THE FRONT WERE
ALSO COMING AROUND TO THE SOUTH FROM WAUKEGAN NORTHWARD. THUS
EFFECTS OF THE WEAK COLD FRONT TO BE MINIMAL WITH MILD LOWS NEAR
60 TONIGHT AND WARMER TEMPS EXPECTED THURSDAY.

OF SOME INTEREST IS AN AREA OF THUNDERSTORMS OVER NORTHERN WI...
WHICH HAVE BEEN MAINTAINING THEIR STRENGTH OVER THE LAST COUPLE OF
HOURS WITHIN AXIS OF HIGHER DEW POINTS TO OUR WEST/NORTH. WATER
VAPOR IMAGERY SUGGESTS A SHORT WAVE OVER NORTHERN WI MAY BE A
LITTLE SHARPER THAN MUCH OF THE AVAILABLE GUIDANCE DEPICTS...WHICH
COMBINED WITH 1700+ J/KG MLCAPE WILL PROBABLY ALLOW THESE STORMS
TO CONTINUE TO WORK SOUTHEAST FOR THE NEXT FEW HOURS. RECENT RUNS
OF THE HRRR INDICATE GRADUAL DECAY WHICH IS TO BE EXPECTED WITH
DIURNAL DECREASE IN INSTABILITY AND MORE WESTERLY FLOW ABOVE THE
SFC...THOUGH THE HRRR DOES CONTINUE TO INDICATE SOME REMNANT
ISOLATED SHOWERS AS FAR SOUTH AS THE MKE AREA OVERNIGHT. MAY ADD
SOME POPS FOR ISOLATED SHOWERS OUT OVER SOUTH/CENTRAL LAKE MI LATE
TONIGHT...THOUGH AM NOT EXPECTING PRECIP TO AFFECT WFO LOT LAND
AREAS.

RATZER

&&

.SHORT TERM...
307 PM CDT

THROUGH THURSDAY...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH SHOWER/THUNDERSTORM
TRENDS BY THE END OF THE WORK WEEK INTO THE WEEKEND...AND THEN
WITH COOLER TEMPS EXPECTED THIS WEEKEND INTO THE START OF NEXT
WEEK.

COLD FRONT WHICH PUSHED THROUGH THE CWA TODAY CONTINUES OFF TO
THE EAST THIS AFTERNOON...WHILE MID/UPPER LEVEL TROUGH OVER THE
UPPER MIDWEST AND GREAT LAKES LIFTS TO THE EAST/NORTHEAST.
MODERATE INSTABILITY WHICH WAS IN PLACE TODAY HAS WEAKENED AND
WILL FURTHER WEAKEN THIS AFTERNOON INTO THE EVENING...AS 50 DEGREE
DEWPOINT AIR MOVES ACROSS THE CWA. ANY MORE ROBUST
SHOWER/THUNDERSTORM DEVELOPMENT THIS AFTERNOON WILL REMAIN EAST OF
THE AREA...WITH ANY ISOLATED SHOWERY ACTIVITY TO DIMINISH HERE IN
THE NEAR TERM. CLOUD COVER WILL LIKEWISE DIMINISH THIS
EVENING...WITH MOSTLY CLEAR SKIES LIKELY TONIGHT.

IN THE WAKE OF THE DEPARTING MID/UPPER LEVEL TROUGH...RISING
HEIGHTS ALOFT WILL HELP SET THE STAGE FOR A DRY/SUNNY DAY WITH
WARM AND ABOVE NORMAL TEMPS IN THE LOW TO MID 80S ON THURSDAY. THE
EXCEPTION WILL BE FOR AREAS NEAR THE LAKE IN ILLINOIS WHERE
COOLER TEMPS IN THE 70S WILL BE OBSERVED WITH ONSHORE FLOW. A
LITTLE UNCERTAINTY WITH HOW HIGH THE TEMPS WILL GET IN THIS
LOCATION BEFORE THE WINDS TURN...BUT THINK TEMPS WILL HAVE A GOOD
CHANCE OF RISING QUICKLY IN THE MORNING BEFORE THIS OCCURS. SO DID
BUMP UP TEMPS AND EVEN FOR AREAS NEAR THE LAKE IN INDIANA...WHERE
SOUTHERLY FLOW SHOULD ALLOW LESS OF AN IMPACT FROM THE LAKE.

RODRIGUEZ

&&

.LONG TERM...
247 AM CDT

FRIDAY THROUGH WEDNESDAY...

FRIDAY...
MAIN CHALLENGES FOR FRI WILL BE ON PRECIP TIMING AND COVERAGE.
GUIDANCE HAS INDICATED SOME SLOWING TO THE DEPARTING SFC
RIDGE...WITH MID-LVL HEIGHTS NOT BEGINNING TO FALL UNTIL AFT
DAYBREAK FRI. THE MORE POTENT LOBE OF VORTICITY WILL BE ROUNDING THE
TROUGH AXIS EARLY FRI...THEN FORMING A SFC WAVE FEATURE ACROSS THE
SOUTHERN PLAINS. THE QUASI-STATIONARY BOUNDARY WILL BE ORIENTED FROM
THE SOUTHERN PLAINS NORTHEAST THROUGH THE UPPER MIDWEST. BUT WITH
THE MINOR DELAY IN DEPARTING RIDGE...THIS MAY PROVIDE A WEAK BUCKLE
TO THE GREATER PRECIP COVERAGE ONLY TEMPORARILY FRI MORNING. BY
MIDDAY THE BOUNDARY WILL BE DRIFTING EAST...WITH ABUNDANT LOW LEVEL
MOISTURE ADVECTING NORTH INTO THIS FEATURE. DEW POINTS WILL HOVER IN
THE LOW/MID 60S...AS PWAT VALUES APPROACH 1.5 INCHES. 850MB V-WIND
COMPONENT SUGGESTS WINDS WILL NOT BE TOO STRONG...SO AT THIS TIME
WOULD NOT SUSPECT AS THE SFC WAVE LIFTS NORTHEAST ALONG THE BOUNDARY
GROWTH IN CONVECTION TO BE VERY LARGE. HOWEVER...IT DOES APPEAR TO
BE AN IDEAL SETUP FOR EMBEDDED THUNDER. WITH THE UPSTREAM MID-LVL
VORT STRENGTHENING OVER CENTRAL CANADA...THIS WILL LIKELY ALLOW THE
QUASI-STATIONARY BOUNDARY TO FURTHER ENHANCE. THIS COULD AID IN
PRECIP PRODUCTION WITH THE BOUNDARY SLIDING OVERHEAD FRI
NIGHT.

TEMPS WILL EQUALLY BE A CHALLENGE FRI...GIVEN THE THICK SOLAR
SHIELDING POISED TO LIMIT SFC HEATING. THE ABUNDANT LOW LEVEL
MOISTURE WILL ABSORB ANY HEAT...MAKING IT DIFFICULT TO WARM AND
PERHAPS KEEPING TEMPS A FEW DEGREES LOWER THAN CURRENTLY PROGGED.
HAVE NUDGED TEMPS IN THE FAR NORTHERN CWFA DOWN A COUPLE DEGREES TO
REFLECT THIS INTO THE UPR 70S...MEANWHILE FURTHER SOUTH HAVE HELD
ONTO THE 80 TO LOW 80S RANGE.

SATURDAY THROUGH MIDDLE OF NEXT WEEK... ENSEMBLES HAVE CONTINUED TO
PROG A HIGH AMPLITUDE RIDGE ACROSS WESTERN CANADA AT THE START OF
THE WEEKEND...THEN SLOWLY WEAKENING THIS FEATURE AS THE CENTRAL
CONUS TRANSITIONS INTO A RELATIVELY FLAT WEST-EAST FLOW BY TUE/WED
OF NEXT WEEK. THE MAIN STORY FOR THE WEEKEND WILL BE ON THE TEMPS
ABRUPTLY CHANGEING FROM EARLY SUMMER TO MID-SPRING...WITH A STOUT
FRONTAL BOUNDARY SWEEPING ACROSS THE FORECAST AREA SAT MIDDAY. THIS
WILL BRING MUCH COOLER AIR AS WINDS QUICKLY VEER NORTH/NORTHEAST
AND BLEED THE MUCH COOLER MARINE AIR FROM LAKE MICHIGAN OVER
NORTHEAST IL/NORTHWEST IN SAT/SUN. HIGHS SAT MAY STRUGGLE TO WARM
BEYOND THE UPR 50S ACROSS NORTHEAST IL/NORTHWEST IN...WITH ONLY
LOW 60S ELSEWHERE.

WITH FLOW BECOMING SOMEWHAT FLAT TOWARDS MON/TUE ACROSS THE
CENTRAL CONUS...THIS WILL HELP TO FLUSH THE SFC RIDGE EAST FROM
THE GREAT LAKES REGION. THIS WILL LIKELY ALLOW TEMPS TO SLOWLY
RETURN TO SEASONAL CONDS BY MIDDLE OF NEXT WEEK...HOWEVER
CURRENTLY GUIDANCE INDICATES A DRY STRETCH AS MID-LVL HEIGHTS MAY
BEGIN TO NUDGE UP CLOSER TO TUE/WED. BUT CONFIDENCE IN THE FINAL
FEW PERIODS OF THE EXTENDED ARE CURRENTLY LOW.

BEACHLER

&&

.AVIATION...

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

* ESELY WINDS AROUND 10 KT THURSDAY AFTERNOON FOLLOWING LAKE
  BREEZE PASSAGE.

KREIN

//DISCUSSION...UPDATED 00Z...
AS WEAK HIGH PRESSURE SETTLES OVER NRN IL/IN/SRN LAKE
MICHIGAN...WINDS HAVE DROPPED OF TO CALM/LGT AND VRBL. AN AREA OF
SHOWERS IS QUICKLY DROPPING THROUGH ECNTRL WI AND CNTRL LAKE
MICHIGAN WITH AN OUTFLOW BOUNDARY RACING OUT AHEAD. LATEST RADAR
TRENDS SUGGEST THAT THE PCPN IS WEAKENING AND MOVING SELY ENOUGH
THAT IT WILL MISS THE TERMINALS...EVEN GYY. QUIET CONDITIONS
SHOULD PREVAIL THROUGH THE REMAINDER OF THE NIGHT...BUT BY EARLY
MORNING...A DEEPENING TROUGH OVER THE CNTRL/NRN PLAINS WILL HELP
TURN WINDS TO PREVAILING SELY BY DAYBREAK...WITH SPEEDS LESS THAN
10 KT. THE WEAK SELY GRADIENT WILL REMAIN IN PLACE THROUGH THE
DAY...AND SHOULD BE WEAK ENOUGH TO ALLOW FOR A LAKE BREEZE TO
DEVELOP. THE LATEST HIGH RES MODEL GUIDANCE AGREES WITH
CONVENTIONAL WISDOM THAT A LAKE BREEZE SHOULD DEVELOP UNDER THE
EXPECTED PATTERN...WITH WINDS SHIFTING TO JUST SOUTH OF EAST AND
INCREASING TO ARND 10KT.

AS THE SFC TROUGH BEGINS TO MOVE EAST ACROSS THE NORTHERN PLAINS
AND TOWARD THE UPPER MISSISSIPPI VALLEY LAKE THURSDAY
NIGHT...WINDS WILL VEER TO SOUTHERLY. WARM/MOIST ADVECTION UNDER
THE SOUTHERLY FLOW WILL BRING INCREASING LOW AND MID CLOUDS AND A
CHANCE OF SHOWERS BY THE EARLY MORNING HOURS.

KREIN

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

* MEDIUM IN LAKE BREEZE WIND SHIFT TIMING AND SPEED/DIRECTION
  FOLLOWING LAKE BREEZE PASSAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

FRIDAY...PERIODIC SHRA/TSRA. MVFR POSSIBLE. SOUTHWEST WINDS.

SATURDAY...CHANCE SHRA. MVFR POSSIBLE. STRONG NORTH-NORTHEAST
WINDS.

SUNDAY...VFR/WX NIL. NORTHEAST WINDS.

MONDAY...VFR/WX NIL. EAST WINDS.

TUESDAY...VFR/WX NIL. SOUTH WINDS.

KJB

&&

.MARINE...
247 AM CDT

WEAK SFC RIDGE OF HIGH PRESSURE CENTERED OVER EASTERN
ONTARIO...WITH SOME LINGERING INFLUENCE OF DRY AIR ACROSS LAKE
MICHIGAN FOR THE BULK OF TODAY. THE WESTERN GREAT LAKES WILL BEGIN
TO SEE THE SOUTHERLY FLOW THIS AFTERNOON/EVENING...AS WINDS
INCREASE. A SLOW MOVING FRONTAL BOUNDARY ORIENTED OVER THE
SOUTHERN PLAINS STRETCHES NORTH TO JUST WEST OF LAKE SUPERIOR.
THSI BOUNDARY WILL BEGIN TO INCH EAST TOWARDS THE NORTHERN
PORTIONS OF LAKE MICHIGAN FRI MORNING...ALLOWING THE GRADIENT TO
TIGHTEN AND SOUTHERLY WINDS TO INCREASE. THEN THE FRONTAL BOUNDARY
WILL SLIDE SOUTHEAST SLOWLY ACROSS LAKE MICHIGAN...ALONG WITH THE
GRADIENT TIGHTENING BY FRIDAY NIGHT INTO SATURDAY. A STRONG RIDGE
OF HIGH PRESSURE WILL DROP SOUTH FROM CENTRAL CANADA ALONG THE
BACK EDGE OF THE FRONT...HELPING TO INCREASE A PERIOD OF NORTH GALES
SATURDAY FOR THE CENTRAL/SOUTHERN PORTIONS OF LAKE MICHIGAN.
GUIDANCE HAS BACKED OFF A TOUCH ON THE WIND SPEEDS...HOWEVER A
GALE WATCH MAY STILL NEED TO BE ISSUED. THE STRONG WINDS COUPLED
WITH MUCH COOLER AIR WILL EASILY BUILD WAVES FOR THE SOUTHERN HALF
OF THE LAKE SATURDAY. COOL AIR AND NORTH/NORTHEAST WINDS WILL
CONTINUE TO OCCUR SAT NIGHT THRU SUN...LIKELY MAINTAINING LARGER
WAVES ALONG THE IL/IN NEARSHORE WATERS.

BEACHLER

&&

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

$$

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