Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 102014
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CDT THU JUL 10 2014

.DISCUSSION...
313 PM CDT

MAIN FORECAST CONCERNS FOCUS ON TIMING OF THE RETURN OF SHOWERS AND
THUNDERSTORMS TO THE REGION LATE FRIDAY...WITH THE POTENTIAL FOR
SOME STRONGER STORMS AND LOCALLY HEAVY RAINFALL DURING THE OVERNIGHT
HOURS FRIDAY NIGHT. SCATTERED THUNDERSTORMS REMAIN POSSIBLE THROUGH
THE WEEKEND AS WEAK SURFACE COLD FRONT SLOWLY MOVES THROUGH THE
REGION WITHIN INCREASINGLY MOIST AIR MASS. FORECAST THEN TRENDS
TOWARD COOLER WEATHER EARLY NEXT WEEK...AS CLOSED UPPER LOW NOW OVER
NORTHERN ALBERTA EVOLVES EAST-SOUTHEASTWARD INTO THE GREAT LAKES
REGION.

IN THE NEAR TERM...SURFACE HIGH PRESSURE OVER THE GREAT LAKES REGION
WAS PRODUCING DRY/SUNNY CONDITIONS ACROSS THE AREA THIS AFTERNOON.
SURFACE WINDS WILL GRADUALLY BECOME MORE SOUTH-SOUTHEAST TONIGHT AS
THE HIGH DRIFTS TO THE EAST...AND RETURN FLOW DEVELOPS INTO THE
MISSISSIPPI VALLEY AHEAD OF WEAK TROUGH DEVELOPING ACROSS THE
PLAINS. A SERIES OF MID-LEVEL SHORT WAVES ARE PROGGED TO TRAVERSE
WESTERLY FLOW ACROSS THE NORTHERN TIER OF THE CONUS FRIDAY THROUGH
THE WEEKEND...THOUGH THE INITIAL WAVE CURRENTLY PROPAGATING THROUGH
THE DAKOTAS WILL BE WORKING AGAINST VERY DRY THERMODYNAMIC PROFILES
AS NOTED IN 12Z GREAT LAKES/OHIO VALLEY RAOBS. PRECIP CHANCES WILL
INCREASE BY LATE FRIDAY HOWEVER...AS LOW LEVEL MOISTURE ADVECTS INTO
THE REGION WITH WINDS BECOMING MORE SOUTH-SOUTHWEST AND AS SOUTHERN
PERIPHERY OF 100+ KT UPPER JET CORE TRANSLATES ACROSS THE UPPER
MIDWEST. WITH THE DRY AIR INITIALLY IN PLACE...MODEL GUIDANCE
CONTINUES TO TREND SLOWER WITH THE ADVANCE OF PRECIP INTO THE CWA
FRIDAY...WITH MUCH OF THE AREA EXPECTED TO REMAIN DRY THROUGH THE
DAY. HAVE BACKED POPS OFF TO SLGT CHANCE FAR WEST IN THE AFTERNOON
BASED ON THIS CONSISTENT TREND...WITH POPS THEN INCREASING FROM WEST
TO EAST FRIDAY EVENING/NIGHT. FORECAST SOUNDINGS DEPICT MID-LEVEL
LAPSE RATES ARE FAIRLY UNIMPRESSIVE DURING THE AFTERNOON/EARLY
EVENING HOURS FOR MUCH IN THE WAY OF THUNDER...THOUGH THUNDERSTORM
POTENTIAL DOES LOOK TO INCREASE FRIDAY NIGHT AS DEEP MOISTURE
SPREADS INTO THE REGION ALONG WITH WARM ADVECTION IN THE 900-800 HPA
WHICH COMBINE TO PRODUCE SOME TALL/SKINNY CAPE PROFILES. DEEP LAYER
BULK SHEAR (0-6 KM) INCREASES QUICKLY TO 30-40 KT FRIDAY NIGHT WITH
INCREASE IN BOTH UPPER JET AND LOW LEVEL JET SPEEDS...AND SPC HAS
PULLED THE 5% SEVERE RISK INTO NORTH CENTRAL ILLINOIS FOR FRIDAY
NIGHT...THOUGH GIVEN THE RELATIVELY THIN CAPE PROFILES...SUSPECT
LOCALLY HEAVY RAINFALL MAY BE MORE AF A WEATHER THREAT AS FORECAST
PRECIPITABLE WATER VALUES CLIMB INTO THE 2.0+ INCH RANGE.

MCS WILL LIKELY BE EXITING THE CWA STAGE RIGHT (INDIANA) SATURDAY
MORNING...WITH THE FORECAST BECOMING SOMEWHAT MESSY IN ITS WAKE. LOW
LEVEL THETA-E RIDGE AND WARM/MOIST ADVECTION AXIS REMAINS AIMED INTO
THE FORECAST AREA ON SOUTHWEST WINDS...WITH OUTFLOW FROM
OVERNIGHT/MORNING ACTIVITY AND APPROACH OF WEAK SURFACE TROUGH FROM
THE WEST/NORTHWEST LIKELY BECOMING FOCUS FOR CONTINUED CONVECTIVE
FESTERING OR NEW INITIATION THROUGH THE AFTERNOON. WHILE CONFIDENCE
IN DETAILS OF TIMING AND LOCATION OF THUNDERSTORM CLUSTERS BECOMING
LOWER INTO SATURDAY AFTERNOON/NIGHT...HAVE MAINTAINED LIKELY POPS AS
CONFIDENCE IS FAIRLY HIGH THAT PERIODS OF SCATTERED STORMS ARE A
PRETTY GOOD BET. POTENTIAL FOR LOCALLY HEAVY RAINFALL WILL REMAIN
INTO SUNDAY AS WELL...BEFORE DEEP MOIST AXIS SHIFTS SOUTHEAST.
THUNDERSTORM CHANCES CONTINUE THROUGH SUNDAY AND INTO MONDAY TOO AS
THE SURFACE COLD FRONT EVENTUALLY MOVES SLOWLY ACROSS THE FORECAST
AREA...BEFORE THE FOCUS FOR ORGANIZED SHOWERS AND STORMS MOVES OFF
TO THE SOUTHEAST.

TEMPS DURING THE FRIDAY-MONDAY PERIOD WILL BE WARMING...WITH AROUND
80/LOWER 80S FRIDAY AND LOW-MID 80S FOR THE MOST PART SUNDAY BEFORE
SLIGHT POST-FRONTAL COOLING MONDAY. COULD EVEN BE A FEW UPPER 80S
SATURDAY AND SUNDAY ACROSS THE SOUTHERN PARTS OF THE CWA...THOUGH
POTENTIAL FOR EXTENSIVE CLOUDS/PRECIP/OUTFLOW LENDS LOWER CONFIDENCE
TO REALIZING THAT POTENTIAL.

AS HINTED AT IN THE FIRST PARAGRAPH...WEATHER THEN TAKES A TURN
TOWARD THE COOL/SHOWERS SIDE HEADING INTO TUESDAY AS THE
AFOREMENTIONED UPPER LOW DIGS SOUTHEAST AND DEEPENS ACROSS THE GREAT
LAKES REGION TUESDAY. AFTER A SERIES OF WARM AND HUMID DAYS THROUGH
THE WEEKEND...TEMPS MAY NOT RISE ABOVE 70 IN A FEW SPOTS TUESDAY AS
STRONG COLD ADVECTION TAKES HOLD ON BREEZY NORTHWEST WINDS. GRADUAL
IMPROVEMENT IS EXPECTED HOWEVER...AS THE UPPER LOW SLOWLY LIFTS OUT
TO THE NORTHEAST THROUGH THE END OF NEXT WEEK...WITH DRY WEATHER AND
TEMPERATURES MODERATING BACK THROUGH THE 70S EXPECTED
WEDNESDAY-THURSDAY.

RATZER

&&

.AVIATION...

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

* INCREASE IN EASTERLY WIND SPEEDS TO AROUND 10 KT THIS AFTERNOON.

RODRIGUEZ

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

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER ONCE
AGAIN THIS AFTERNOON...WITH QUIET AND VFR CONDITIONS EXPECTED TO
PERSIST. DEVELOPING THUNDERSTORMS WELL WEST OF THE TERMINALS
FRIDAY WILL REMAIN WEST OF THE TERMINALS THROUGH THE END OF THE
FORECAST PERIOD. CURRENT EASTERLY WINDS WILL OBSERVE AN INCREASE
IN SPEEDS THROUGH THE AFTERNOON...WITH SPEEDS AROUND 10 KT
BECOMING LIKELY BY MID AFTERNOON.

RODRIGUEZ

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

* HIGH CONFIDENCE WITH VFR CONDITIONS.

* HIGH CONFIDENCE OF AN INCREASE IN WIND SPEEDS...MEDIUM HIGH
  CONFIDENCE OF TIMING.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRIDAY NIGHT...CHC TSRA

SATURDAY THROUGH MONDAY...PERIODIC CHANCES FOR TSRA. MAINLY VFR.

TUESDAY THROUGH WEDNESDAY...SLIGHT CHC SHRA.

KMD

&&

.MARINE...
229 PM CDT

HIGH PRESSURE IS OVER THE EASTERN GREAT LAKES BUT LIGHT AND VARIABLE
WINDS REMAIN OVER THE LAKE. WINDS WILL BECOME SOUTH AS THE HIGH
SHIFTS FURTHER EAST TONIGHT.  SOUTH WINDS INCREASE TO 15 TO 25 KT
OVER THE NORTHERN HALF OF THE LAKE TOMORROW WHILE THE SOUTH HALF
WILL SEE S TO SE WINDS AT 10-20 KT.  WINDS DIMINISH SATURDAY AS A
TROUGH OF LOW PRESSURE MOVES OVERHEAD AND BECOME SOUTHWEST SATURDAY
NIGHT.

A LOW PASSES WELL NORTH OF THE LAKE SATURDAY NIGHT AND SUNDAY AND
ITS COLD FRONT SWINGS OVER THE LAKE SUNDAY MORNING. WINDS BECOME
WEST BEHIND THE FRONT AND THEN A SECOND FRONT PUSHES DOWN THE LAKE
SUNDAY NIGHT INTO MONDAY.  WINDS WILL BECOME NORTH TO NORTHWEST
10-20 KT BEHIND THE FRONT.  WINDS DIMINISH TUESDAY NIGHT AND THEN
HIGH PRESSURE MOVES OVER THE LAKE WEDNESDAY NIGHT.

JEE

&&

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

$$

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