Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 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...
307 PM CDT

THURSDAY NIGHT THROUGH WEDNESDAY...

WITH STEERING FLOW KEEPING MOST OF THE ENERGY WELL NORTH OF THE
CWA THURSDAY NIGHT...EXPECT DRY CONDITIONS THURSDAY EVENING.
HOWEVER...NORTHEASTWARD MOVING SHORT WAVE ENERGY AND VEERING LLJ
COULD ALLOW FOR SOME PRECIP TO MOVE ACROSS NORTHERN ILLINOIS. WITH
THIS POSSIBILITY DID LEAVE CHANCE POPS ACROSS NORTH CENTRAL
ILLINOIS...BUT WITH MOST AREAS LIKELY REMAINING DRY DURING THIS
PERIOD. INSTABILITY DOES NOT LOOK TO BE OVERLY GREAT DURING THIS
PERIOD AND AM NOT TOO CONCERNED WITH THUNDER...BUT WITH AT LEAST
WEAK INSTABILITY AND A DECENT LLJ...DID LEAVE MENTION OF THUNDER
IN THE GRIDS. UPPER LEVEL TROUGH TO THE WEST/NORTHWEST WILL DIP
ACROSS THE REGION ON FRIDAY AND ALLOW FOR THIS MORE ENERGETIC FLOW
TO DRAW CLOSER TO THE CWA. ALTHOUGH BETTER LOW/MID LEVEL
CONVERGENCE SHOULD REMAIN TO THE NORTH IN WISCONSIN THROUGH THE
DAY FRIDAY...INCREASING INSTABILITY WITH LITTLE CIN IN THE
PRESENCE OF 60 DEGREE DEWPOINTS ALONG WITH INCREASING LARGE SCALE
LIFT SHOULD ALLOW FOR SCATTERED SHOWER/THUNDERSTORM DEVELOPMENT.
INITIALLY THIS WILL BE FOR AREAS ACROSS NORTH CENTRAL
ILLINOIS...BUT DO THINK THAT AT LEAST ISOLATED TO WIDELY SCATTERED
DEVELOPMENT WILL BE POSSIBLE FOR REMAINING AREAS IN THE AFTERNOON.
WEAKER MID AND UPPER LEVEL FLOW SHOULD LIMIT INTENSITY OF ANY
DEVELOPMENT...ALTHOUGH CANNOT RULE OUT ISOLATED STRONGER STORM
WITH STRONG GUSTS THE MAIN HAZARD. ALSO...INCREASING MOISTURE WILL
ONCE AGAIN HELP FOR HEAVIER DOWNPOURS DURING THIS TIME.

FRIDAY NIGHT INTO SATURDAY MORNING APPEAR TO BE THE BEST PERIODS
FOR WIDESPREAD PRECIP DEVELOPMENT AND HAVE INCREASED TO
CATEGORICAL POPS DURING THIS PERIOD. THIS WILL OCCUR AS THE MID
LEVEL TROUGH AND ASSOCIATED SURFACE LOW AND FRONT PUSH THROUGH.
WITH FLOW STILL REMAINING WEAK AND WITH DIMINISHING INSTABILITY
THROUGHOUT THE NIGHT...NOT OVERLY CONCERNED WITH WIDESPREAD SEVERE
STORMS. HOWEVER...STRONGER FORCING COULD STILL ALLOW FOR ISOLATED
STRONG DEVELOPMENT. WITH AN ABUNDANCE OF MOISTURE STILL IN
PLACE...HEAVIER RAIN WOULD LIKELY BE THE MAIN HAZARD. PRECIP WILL
LIKELY LINGER SATURDAY MORNING BUT PUSHING SOUTH DURING THIS TIME.
ON THE BACKSIDE OF THIS FRONT/PRECIP...STRONGER NORTHERLY WINDS
WILL ALLOW MUCH COOLER AIR TO MOVE OVER THE REGION...WITH TEMPS
LIKELY FALLING THROUGHOUT THE DAY.

RODRIGUEZ

&&

.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...
225 PM CDT

GENERALLY LIGHT TO MODERATE SOUTHERLY FLOW EXPECTED THROUGH TOMORROW
NIGHT WITH SOUTHERLY WINDS INCREASING SOME FRIDAY IN ADVANCE OF
APPROACHING COLD FRONT. COLD FRONT WILL DROP DOWN THE LAKE FRIDAY
NIGHT WITH AN UNSEASONABLY STRONG CANADIAN HIGH BUILDING INTO THE
REGION IN ITS WAKE. A HEALTHY LATE SEASON SHOT OF CHILLY AIR ALONG
WITH THE TIGHT GRADIENT SHOULD SET THE STAGE FOR A PERIOD OF STRONG
FULL FETCH NORTH WINDS DOWN THE LAKE SATURDAY INTO SATURDAY NIGHT.
FORECAST SOUNDINGS SUGGEST THE MIXED LAYER WILL BE SHALLOW BUT DO
SHOW GALE FORCE WINDS WITHIN THE MIXED LAYER THAT SHOULD BE
TRANSPORTED TO THE SURFACE...ESPECIALLY CLOSE TO THE SHORE WHERE
WATER TEMPS ARE WARMER AND CONDITIONS LIKELY TO BE MORE UNSTABLE.
WHILE WIND AND GUST GRIDS DONT REFLECT THIS...THE STRONGEST WINDS
SHOULD OCCUR WITHIN ABOUT 5-8MI OF THE SHORE OVER SOUTHERN THIRD OF
THE LAKE. A LITTLE EARLY TO HOIST A GALE WATCH AT THIS POINT...BUT
CERTAINLY SOMETHING THAT MAY NEED TO BE CONSIDERED SOON.

&&

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

$$

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