Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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 232202
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
502 PM CDT SAT MAY 23 2015

.SHORT TERM...
236 PM CDT

TONIGHT AND SUNDAY...
PRECIPITATION TIMING AND COVERAGE WILL BE THE MAIN FOCUS THROUGH THE
DAY SUNDAY. AFTERNOON WATER VAPOR IMAGERY SHOWS A LARGE UPPER LOW
SPINNING OVER UTAH/COLORADO WITH AN UPPER RIDGE AMPLIFYING OVER THE
EASTERN PLAINS AND TRANSLATING NORTHEAST. THIS CREATES A SOUTH TO
SOUTHWESTERLY UPPER FLOW FROM WEST TEXAS/NEW MEXICO INTO THE MIDWEST
WITH AN EMBEDDED UPPER WAVE MOVING NORTHEAST FROM EASTERN
KANSAS/OKLAHOMA. AT THE SURFACE...LOW PRESSURE IS OVER WEST
TEXAS/NEW MEXICO WITH A WARM FRONT DEVELOPING EASTWARD INTO
OKLAHOMA. THE LOW WILL LIFT NORTHEAST INTO THE CENTRAL HIGH PLAINS
TONIGHT AND SUNDAY MORNING. MID LEVEL WARM ADVECTION WILL INCREASE
LATE TONIGHT AS THE SYSTEM ADVANCES NORTHEAST WITH THE LOW LEVEL JET
DEVELOPING ACROSS THE MID/UPPER MISSISSIPPI RIVER VALLEY. THUS THE
BULK OF THE OVERNIGHT PRECIPITATION/CONVECTION WILL LIKELY STAY TO
THE WEST OF THE FORECAST AREA BUT SOME SCATTERED ACTIVITY WILL BE
POSSIBLE LOCALLY OVERNIGHT...MAINLY OVER WESTERN AREAS...THANKS TO
THE INCREASED WARM ADVECTION AND MOISTURE FLUX. THE THREAT REMAINS
MINIMAL SO WILL ONLY MENTION SLIGHT POPS WEST LATE TONIGHT THROUGH
DAYBREAK SUNDAY.

WARM ADVECTION STRENGTHENS ACROSS THE AREA SUNDAY...ESPECIALLY FROM
LATE MORNING THROUGH THE AFTERNOON. THE WARM FRONTAL BOUNDARY WILL
BE FOCUSED ACROSS IOWA AND LOSE DEFINITION TO THE EAST. HIGH RES
GUIDANCE RANGES FROM VERY LITTLE PRECIP ACTIVITY THROUGH THE DAY TO
WELL ORGANIZED ACTIVITY...MAINLY IN THE AFTERNOON. AM THINKING THAT
THERE MAY BE SOME LINGERING SPOTTY ACTIVITY AFTER DAYBREAK...MAINLY
NORTH/WEST...WITH A WINDOW FOR MINIMAL COVERAGE MID/LATE MORNING.
CHANCES/COVERAGE THEN INCREASE DURING THE AFTERNOON AS BETTER
FORCING SPREADS IN. STILL TOUGH TO PIN DOWN THE BEST WINDOWS FOR
PRECIP BUT PREFER THE AFTERNOON HOURS OVERALL...BUT WILL START TO
RAMP UP POPS DURING THE EARLY AFTERNOON. NORTHWEST INDIANA WILL
LIKELY HAVE THE LOWEST PRECIP CHANCE OF ANYWHERE IN THE CWA.
MORNING ACTIVITY WOULD PRIMARILY BE SHOWERS WITH THUNDER POTENTIAL
SPREADING FROM SOUTHWEST TO NORTHEAST THROUGH THE AFTERNOON. THE
MOST ABUNDANT CLOUD COVER WILL BE WEST AS WILL THE OVERALL BEST
CHANCE OF RAIN SO TEMPS WILL LIKELY BE LIMITED TO THE MID 70S THERE
...WHILE THE REST OF THE INLAND CWA SEES UPPER 70S/AROUND 80. A
SOUTHEAST WIND WILL ONCE AGAIN KEEP ILLINOIS LAKESHORE AREAS COOL
WITH COOLING EXTENDING FURTHER INLAND ACROSS EASTERN LAKE COUNTY IL.

MDB

&&

.LONG TERM...
236 PM CDT

SUNDAY NIGHT THROUGH FRIDAY...

THE EXTENDED LOOKS UNSETTLED WITH NUMEROUS CHANCES OF RAIN AND
THUNDERSTORMS. AN UPPER LEVEL RIDGE REMAINS OVER THE REGION SUNDAY
NIGHT WITH A CLOSED LOW OVER THE ROCKIES.  AS THE LOW PUSHES OVER
THE DAKOTAS MONDAY MORNING...A SERIES OF SHORTWAVE TROUGHS BEGINS TO
MARCH OVER THE REGION. EXPECTING THE SHORTWAVE TROUGH TRAIN TO
CONTINUE THROUGH THURSDAY UNTIL THE UPPER LEVEL TROUGH PUSHES EAST
OF THE REGION.

HIGH PRESSURE WILL BE OVER THE EASTERN THIRD OF THE CONUS SUNDAY
NIGHT WITH A SURFACE LOW FORMING OVER THE CENTRAL PLAINS EARLY
MONDAY MORNING.  THE LOWS WARM FRONT LIFTS NORTH THROUGH THE REGION
EARLY MONDAY MORNING AS WELL. A LOW LEVEL JET SHIFTS EAST THROUGH
THE CWA SUNDAY NIGHT AND EXPECTING TO SEE SHOWERS AND PERHAPS A FEW
THUNDERSTORMS FIRE AND THEN FESTER NORTH OF THE JET/S NOSE.
FORECASTED CAPE IS NOT OVERLY IMPRESSIVE WITH ONLY A COUPLE OF
HUNDRED OF J/KG TO WORK WITH.  WINDS WILL BE IN EXCESS OF 40 KT JUST
A COUPLE THOUSAND FEET OFF OF THE GROUND SO MY MAIN CONCERN FOR ANY
SEVERE WEATHER WOULD BE HIGHER WINDS MIXING DOWN TO THE SFC.

EXPECTING A LULL IN ACTIVITY MONDAY AFTN AS THE MAIN VORTICITY
STREAMER AND LOW LEVEL JET SHIFT EAST OF THE CWA.  SOUTHWEST WINDS
WILL BE GUSTING TO ARND 30 MPH MONDAY AFTN. HAVE LOW CONFIDENCE IN
SKY COVER AND SKY COVER WILL PLAY A BIG PART IN HOW WARM WE GET
MONDAY. DECIDED TO GO A COUPLE OF DEGREES WARMER SO ALL AREAS ARE
AROUND 80. HOWEVER LOCAL CLIMATE STUDIES SUGGEST IF WE ARE
SUNNY...WE COULD SEE MID 80S.  IN ADDITION TO WARMER TEMPS...THE
AMPLE SUNSHINE COULD KICK OFF MORE THUNDERSTORMS...BUT THINKING WE
WILL HAVE ENOUGH CLOUD COVERAGE TO KEEP CONVECTION AND TEMPS IN
CHECK.

ADDITIONAL SHOWERS AND THUNDERSTORMS ARE POSSIBLE MONDAY NIGHT BUT
THINKING THE MAJORITY OF ACTIVITY WILL BE OVER CENTRAL IL CLOSER TO
THE UPPER LEVEL VORTICITY. DID RAISE POPS SOUTH OF I-80 TO AROUND 30
PERCENT IN CASE ANY OF THE ACTIVITY TO OUR SOUTH BLEEDS INTO THE
CWA. WE REMAIN IN THE WARM SECTOR SO KEPT MIN TEMPS MILD IN THE MID
60S.

TUESDAY WILL BE ANOTHER DAY SPENT IN THE WARM SECTOR WITH
THUNDERSTORM CHANCES INCREASING THROUGH THE AFTERNOON. SOUTHWEST
WINDS WILL STILL BE GUSTY...BUT ONLY BTWN 25 AND 30 MPH. THINKING
CLOUD COVER WILL BE MORE PROMINENT TUESDAY SO LOWERED HIGHS INTO THE
UPPER 70S.  PWAT VALUES INCREASE TO OVER 1.5 INCHES TUESDAY SO COULD
SEE SOME HEAVY DOWNPOURS.

SHOWERS AND STORMS SHIFT EAST AS THE COLD FRONT SWINGS THROUGH LATE
TUESDAY NIGHT INTO WEDNESDAY MORNING.  ADDITIONAL SHOWERS AND STORMS
ARE PSBL WEDNESDAY AS THE UPPER LEVEL TROUGH FINALLY MOVES
THROUGH...BUT HAVE LOW CONFIDENCE IN OCCURRENCE AND COVERAGE SINCE WE
MAY BE STABLE.  TEMPS WILL NOT FALL MUCH BEHIND THE COLD FRONT WITH
HIGHS IN THE UPPER 70S AWAY FROM THE LAKE. SOME GUIDANCE MEMBERS
SUGGEST WINDS WILL TURN OFF OF THE LAKE SO HAVE HIGHS IN THE LOW 70S
ALONG THE LAKE SHORE. HAVE LOW CONFIDENCE IN WIND DIRECTION ALONG
THE LAKE FRONT WEDNESDAY.

LATE NEXT WEEK LOOKS WARM WITH HIGH TEMPS IN THE 80S.  COULD SEE
ISOLATED SHOWERS AND STORMS THURSDAY BUT THE BETTER CHANCE FOR
PRECIP IS FRIDAY WHEN A BOUNDARY APPROACHES FROM THE NORTHWEST.
GUIDANCE DIFFERS IN HOW QUICKLY THE BOUNDARY WILL SHIFT EAST SO
CAPPED POPS IN THE CHANCE RANGE.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* LAKE BREEZE LIKELY REACHING MIDWAY BY 23Z...POSSIBLY REACHING
  ORD AFTER 2330Z
* POSSIBLE LIGHT SHOWERS LATE TONIGHT INTO EARLY SUNDAY
* ANOTHER ROUND OF SHOWERS WITH EMBEDDED THUNDER PSBL SUNDAY AFTN

MTF/KMD

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

THE BATTLE OF THE LAKE INFLUENCE AND WARM SYNOPTIC SOUTHERLY FLOW
IS PLAYING OUT WITH THE ORD AND MDW ON THE BORDER OF THESE TWO
VARYING INFLUENCES ON WINDS. AN EARLIER LAKE BREEZE HAS STALLED
OUT CLOSER TO I-94 AND MAKING LITTLE PROGRESS AT THIS TIME. WINDS
ARE GENERALLY SSW ON THE WEST SIDE OF THE LAKE BREEZE AND ANYWHERE
FROM NE TO SE BEHIND IT. VARIABLE WINDS HAVE RESULTED AT TIMES
WITH THIS. GENERALLY EXPECT THAT WESTERN TAF SITES WILL HOLD THE
SSW WINDS THROUGH THE AFTERNOON WITH THE SE WINDS TAKING MORE
CONTROL FROM ORD EASTWARD LATE THIS AFTERNOON AND EVENING...THOUGH
TIMING ON THIS REMAINS A CHALLENGE. ALSO...WINDS BEHIND THE LAKE
BREEZE ARE NOT VERY STRONG...SO IT SHOULD BE LOW OPERATIONAL
IMPACT.

ATTENTION TURNS TO SHOWER/THUNDER POTENTIAL SUNDAY. THE LEADING
EDGE OF LOW LEVEL WARM AIR SURGES NORTHWARD LATE TONIGHT...AND
ALONG THIS BOUNDARY SOME SHOWERS ARE EXPECTED IN THE 10Z-15Z TIME
FRAME SOUTH TO NORTH. COVERAGE WILL NOT BE WIDESPREAD...THUS THE
VCSH MENTION. THEN AFTER A LULL...EXPECT THAT AS LOW LEVEL
MOISTURE ADVECTION INCREASES ANOTHER ROUND OF SHOWERS WITH
EMBEDDED THUNDERSTORMS CAN BE EXPECTED SUNDAY AFTERNOON. THOUGH
CONFIDENCE IS HIGH IN A PERIOD OF SHOWERS AND THUNDERSTORMS GUIDANCE
VARIES WITH WHETHER THIS BEGINS AT 18Z OR HOLDS OFF UNTIL CLOSER
TO 0Z THUS HAVE CARRIED A -SHRA MENTION IN THE ORD 30 HR TAF FOR
NOW TO ACCOUNT FOR UNCERTAINTY IN TIMING.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH ON LAKE BREEZE REACHING MDW AND TIMING. LOW IN IF
  LAKE BREEZE WILL REACH ORD
* MEDIUM ON SHOWER POTENTIAL AND TIMING IN THE TAFS
* HIGH IN NO THUNDER UNTIL SUNDAY AFTERNOON...BUT LOW ON IF/WHEN
  IT WILL OCCUR AT THE TERMINAL SUNDAY PM

MTF/KMD

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

SUNDAY NIGHT...CHANCE OF SHRA/TSRA. SOUTH-SOUTHEAST WINDS.

MONDAY...PERIODS OF SHRA/TSRA. GUSTY SOUTHWEST WINDS.

TUESDAY - THURSDAY...PERIODIC CHANCES FOR SHRA/TSRA. SOUTHWEST
WINDS.

FRIDAY...CHANCES OF SHRA. SOUTHWEST WINDS.

KREIN

&&

.MARINE...
236 PM CDT

HIGH PRESSURE OVER THE LOWER GREAT LAKES AND APPALACHIANS
WILL SHIFT OFF THE EAST COAST TONIGHT WHILE A SURFACE RIDGE AXIS
LINGERS ACROSS THE WESTERN LAKES. LOW PRESSURE WILL MOVE
NORTHEASTWARD FROM THE SOUTHERN HIGH PLAINS AND EVENTUALLY TO
WESTERN LAKE SUPERIOR BY MONDAY EVENING. A TROUGH OF LOW PRESSURE
MOVING ACROSS EASTERN ONTARIO THIS AFTERNOON HAS HELPED TO TIGHTEN
THE PRESSURE GRADIENT ACROSS NORTHERN LAKE MICHIGAN WHICH HAS
ALLOWED STEADY/BREEZY SOUTHWEST WINDS WHILE A WEAKER GRADIENT TO
THE SOUTH HAS ALLOWED FOR AN ONSHORE FLOW. WINDS WILL DIMINISH
TONIGHT AS THE GRADIENT WEAKENS BUT THE GRADIENT WILL TIGHTEN LATER
SUNDAY ALLOWING WINDS TO COME UP A BIT. DIRECTION WILL REMAIN
SOUTHERLY...FAVORING SOUTHWEST WINDS NORTH AND SOUTHEAST WINDS
SOUTH. WITH THE LOW PASSING WEST OF THE LAKE MONDAY SPEEDS WILL
FURTHER INCREASE AND MAY REACH SMALL CRAFT ADVISORY LEVELS FROM THE
SOUTH AND SOUTHWEST. A WARM AND MOIST AIRMASS WILL ADVECT IN WITH A
SHALLOW STABLE LAYER HOLDING IN PLACE OVER THE LAKE WHICH WILL
LIKELY RESULT IN FOG DEVELOPING...PERHAPS AS EARLY AS SUNDAY
AFTERNOON...BUT MORE SO SUNDAY NIGHT THROUGH MONDAY. ANOTHER LOW IS
FORECAST TO CROSS THE REGION TOWARD WEDNESDAY RESULTING IN NORTHERLY
WINDS TO THE NORTH OF THE TRACK AND SOUTHERLY WINDS TO THE SOUTH.
HIGH PRESSURE QUICKLY CROSSES BEHIND THE LOW LATER IN THE WEEK
BRINGING A RETURN TO SOUTHERLY WINDS AS IT MOVES OFF TO THE EAST.

MDB

&&

.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/NWSCHICAGO
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.