Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 102321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
621 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 00Z...

* POTENTIAL FOR A LAKE BREEZE FRIDAY AFTERNOON/EVENING.

BMD

//DISCUSSION...UPDATED 00Z...

FAIR WEATHER WILL CONTINUE FOR ANOTHER DAY OR SO BEFORE CHANCES FOR
SHOWERS AND THUNDERSTORMS INCREASE ACROSS THE AREA FRIDAY
EVENING/NIGHT. IN THE MEANTIME...VFR CONDITIONS WILL PREVAIL AT THE
TERMINALS WITH HIGH PRESSURE INCHING EAST AWAY FROM THE REGION.
EAST/EAST SOUTHEAST WINDS WILL DROP OFF AS WE DECOUPLE AFTER SUNSET
THIS EVENING...AND DIRECTION SHOULD GENERALLY VEER TOWARDS THE SOUTH
OVERNIGHT. WINDS WILL PICK UP OUT OF THE SOUTH AROUND 10 KT OR SO
DURING THE DAY FRIDAY. A LAKE BREEZE IS EXPECTED TO FORM...HOWEVER
IT IS UNSURE AT THIS POINT WHETHER OR NOT IT WILL HAVE A STRONG
ENOUGH PUSH TO MAKE IT ACROSS THE TERMINALS. WITH A SSW WIND AROUND
OR SLIGHTLY ABOVE 10 KT...A LAKE BREEZE WOULD LIKELY SLOWLY PUSH
INTO NORTHERN COOK COUNTY TOWARDS ORD...BUT MAY BE STOPPED SHY OF
THE TERMINAL. WILL GO WITH THIS THOUGHT FOR NOW BUT OBVIOUSLY THIS
IS A SITUATION THAT WILL HAVE TO BE MONITORED...AND THE PICTURE MAY
BECOME MORE CLEAR AS IT STARTS TO COME IN RANGE OF MORE OF THE
HIGHER-RES MODEL SOLUTIONS OVERNIGHT AND EARLY TOMORROW.

BMD


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW CONFIDENCE IN LAKE BREEZE REACHING TERMINALS FRIDAY.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

SATURDAY...TSRA. MVFR/IFR PSBL.
SUNDAY THROUGH TUESDAY...PERIODIC CHANCES FOR TSRA/SHRA. PRIMARILY VFR.
WEDNESDAY...VFR.

BMD

&&

.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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