Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 190901
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 AM CDT SAT APR 19 2014

.DISCUSSION...
314 AM CDT

MAIN FORECAST CHALLENGES/CONCERNS ARE WITH A WARMING TREND TODAY
THROUGH EARLY NEXT WEEK WITH SHOWER CHANCES INCREASING LATE SUNDAY
NIGHT INTO MONDAY...AND WITH A SLIGHT CHANCE OF THUNDERSTORMS FOR
THE SOUTHERN CWA MONDAY AFTERNOON/EARLY EVENING.

UPPER LEVEL RIDGING ONGOING ACROSS THE REGION THIS MORNING AS A
FAIRLY VIGOROUS VORT MAX QUICKLY PUSHES EAST ACROSS THE NORTHERN
CONUS/SOUTHERN CANADA...AND WITH A LARGE UPPER LEVEL TROUGH
PUSHING THROUGH THE SOUTHWEST CONUS. AT THE SURFACE...LARGE HIGH
PRESSURE SPANNING FROM CANADA SOUTH THROUGH THE CENTRAL GREAT
LAKES AND MID MISSISSIPPI VALLEY SOUTHWARD TO THE SOUTHERN GULF
STATES...WHILE A TROUGH OF LOW PRESSURE IS SITUATED OVER THE
NORTHERN PLAINS. WITH THIS HIGH OVERHEAD...A QUIET BUT COOL
MORNING ACROSS THE CWA WITH TEMPS CURRENTLY IN THE 30S WITH
GENERALLY CLEAR SKIES IN PLACE OUTSIDE OF SOME FEW/SCT HIGH LEVEL
CIRRUS. WITH SOME ONGOING WEAK WAA EXPECTED TO CONTINUE DO EXPECT
TEMPS TO FALL 1-2 MORE DEGREES IN SOME SPOTS BUT WITH A TREND MORE
TOWARDS STEADY TEMPS OVER THE NEXT SEVERAL MORE LIKELY. LATEST
SATELLITE IMAGERY DEPICTING A SUBSTANTIAL AMOUNT OF MID/HIGH LEVEL
CLOUD COVER OVER THE CENTRAL CONUS STREAMING OUT AHEAD OF THE
PREVIOUSLY MENTIONED MID/UPPER LEVEL FEATURES. ALTHOUGH AS HAS
BEEN THE TREND...WOULD ANTICIPATE THIS MOISTURE TO DIMINISH OR AT
LEAST THIN AS IT DRIFTS EAST/SOUTHEAST ACROSS THE UPPER LEVEL
RIDGE AND WOULD EXPECT THE CLEAR SKIES TO PERSIST THIS MORNING
MAKING WAY FOR SUNSHINE TODAY ACROSS THE CWA. CONTINUED WARMING AS
WELL AS A RETURN TO MORE SOUTHERLY FLOW AS SURFACE RIDGE DEPARTS
TO THE EAST...DO EXPECT TEMPS TO RISE INTO THE 60S AND EVEN 70S IN
SOME LOCATIONS OUTSIDE OF THE COOLER AREAS NEAR THE LAKE AS
ONSHORE FLOW WILL BE PRESENT ONCE AGAIN. HIGH CONFIDENCE WITH LAKE
COOLING FOR THE ILLINOIS SIDE BUT LOWER CONFIDENCE ON THE INDIANA
SIDE. WINDS WILL TURN MORE EAST/SOUTHEAST SYNOPTICALLY BUT WITH
LIGHTER FLOW STILL IN PLACE...COULD EASILY SEE AREAS NEAR GYY TURN
BACK MORE NORTHEAST...ESPECIALLY BEFORE 925MB FLOW RAMPS UP LATER
THIS AFTERNOON.

GUIDANCE IN GOOD AGREEMENT WITH TAKING THE VORT MAX AND ATTENDANT
SURFACE TROUGH CURRENTLY NORTHWEST OF THE REGION NORTH INTO CANADA
TODAY INTO TONIGHT. AS THIS OCCURS...EXPECT ASSOCIATED BAROCLINIC
ZONE TO STALL NORTHWEST OF THE CWA TONIGHT INTO SUNDAY MORNING
WHILE UPPER LEVEL TROUGH ACROSS THE SOUTHWEST CONUS SLOWLY LIFTS
TO THE NORTHEAST TOWARDS THE CENTRAL PLAINS. WHAT THIS MEANS FOR
THE CWA IS CONTINUED DRY CONDITIONS AS ANY SHOWER/THUNDERSTORM
DEVELOPMENT STAYS WELL WEST/NORTHWEST OF THE CWA...WITH A RATHER
MILD DAY IN STORE ON SUNDAY. THE BULK OF THE CLOUD COVER SHOULD
LIKEWISE STAY TO THE NORTHWEST AND WITH THERMAL AXIS INCHING
TOWARDS THE CWA...EXPECT TEMPS TO RISE TO THE MID AND UPPER 70S
INCLUDING AREAS NEAR THE LAKE.

GUIDANCE BEGINS TO DIVERGE WITH REGARDS TO THE EVOLUTION OF THE
APPROACHING UPPER LEVEL TROUGH SUNDAY NIGHT INTO MONDAY AS WELL AS
ANOTHER VORT MAX DROPPING SOUTHEAST OUT OF CANADA DURING THIS
TIME. LIKELY SCENARIO IS FOR ANY PRECIP TO REMAIN NORTHWEST OF THE
CWA FOR MOST OF SUNDAY NIGHT...BUT DID INCLUDE SLIGHT CHANCE POPS
FOR SHOWERS AFTER MIDNIGHT TO ACCOUNT FOR A POSSIBILITY FOR THESE
SHOWERS TO DRIFT SOUTHEAST. NONETHELESS...PRECIP CHANCES WILL
INCREASE THROUGHOUT THE DAY MONDAY AS UPPER LEVEL SYSTEMS SHIFT
EAST THROUGH THE MID AND UPPER MISSISSIPPI VALLEYS. THIS WILL HELP
STEER DEVELOPING SURFACE TROUGH AND FRONTAL BOUNDARY EAST TOWARDS
THE CWA WITH SHOWERS LIKELY FOR THE ENTIRE CWA MONDAY AFTERNOON.
CONFIDENCE IS LOW WITH REGARDS TO THE AMOUNT OF MOISTURE RETURN
OUT AHEAD OF THIS SYSTEM MONDAY...BUT IT DOES APPEAR AS IF A
NARROW RIBBON OF HIGHER DEWPOINTS DOES TRY TO ADVECT NORTH ACROSS
THE SOUTHERN CWA. INSTABILITY AXIS LIKEWISE DOING THE SAME DURING
THIS TIME AND SO HAVE INCLUDED A SLIGHT CHANCE FOR THUNDER MAINLY
FOR THE SOUTHERN HALF OF THE CWA DURING THIS TIME. EXPECT SHOWERS
TO PERSIST INTO THE EVENING WITH SOME POSSIBILITY FOR THUNDER AT
LEAST INTO A PART OF THE EVENING...BEFORE COLDER/DRIER AIR REALLY
WORKS ITS WAY SOUTH ACROSS THE REGION AND PRECIP SHIELD EXITS BY
EARLY TUESDAY.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE.

RATZER

//DISCUSSION...UPDATED 06Z...

SURFACE HIGH PRESSURE RIDGE OVER LAKE MICHIGAN AND NORTHEAST
ILLINOIS EARLY THIS AM WILL MOVE EAST TODAY...WITH WINDS GRADUALLY
VEERING MORE EAST-SOUTHEAST DURING THE MORNING HOURS. LAKE BREEZE
IS EXPECTED TO DEVELOP AND MAY RESULT IN A WIND SHIFT MORE TO THE
EAST ACROSS ORD AND POSSIBLY MDW/GYY. WHILE EXACT DIRECTION
SOMEWHAT UNCERTAIN...SOME EASTERLY OR EAST-SOUTHEAST COMPONENT IS
EXPECTED. OTHERWISE...VERY DRY CONDITIONS WITH VFR CONDITIONS
THROUGH THE PERIOD.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* LOW CONFIDENCE IN EXACT WIND DIRECTION SATURDAY AFTERNOON...BUT
  HIGH CONFIDENCE IT WILL BE GENERALLY EAST-SOUTHEAST.
* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

RATZER

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

SUNDAY...VFR.

MONDAY...SCT`D SHRA...MAINLY IN AFTERNOON.

TUESDAY THROUGH THURSDAY...VFR.

IZZI

&&

.MARINE...
251 AM CDT

HIGH PRESSURE RIDGE OVER THE WESTERN LAKES EARLY THIS MORNING WILL
DRIFT OFF TO THE EAST TODAY...WHILE A PAIR OF SURFACE LOW PRESSURE
CENTERS OVER THE NORTHERN PLAINS AND CANADIAN PRAIRIES CONSOLIDATE
INTO A SINGLE LOW NORTH OF THE BORDER. SOUTH-SOUTHEAST WINDS WILL
GRADUALLY INCREASE TODAY INTO TONIGHT AS THE LOW MOVES EAST INTO
ONTARIO AND THE GRADIENT TIGHTENS IN ADVANCE OF A COLD FRONT WHICH
WILL TRAIL THIS LOW INTO THE CENTRAL AND SOUTHERN PLAINS. SOUTHERLY
WINDS MAY APPROACH 30 KT ON THE NORTHERN PORTION OF THE LAKE TONIGHT
AS THE LOW PASSES BY TO THE NORTH. THE GRADIENT WILL THEN WEAKEN
SUNDAY AS THE LOW CONTINUES TO TRACK EAST TOWARDS JAMES BAY... AND
THE FRONT SAGS SOUTHEAST ACROSS THE LAKE. THE COLD FRONT WILL NOT
COMPLETE ITS TRANSIT OF THE LAKE AT THAT TIME HOWEVER...AS ANOTHER
WEAKER AREA OF LOW PRESSURE DEVELOPS OVER THE SOUTHERN PLAINS SUNDAY
AND LIFTS NORTHEAST ALONG THE FRONT INTO THE GREAT LAKES REGION ON
MONDAY. THIS LOW WILL PULL THE COLD FRONT SOUTHEAST OF THE LAKE BY
MONDAY EVENING. NORTHERLY WINDS WILL THEN INCREASE AS THE GRADIENT
TIGHTENS AHEAD OF AN AREA OF HIGH PRESSURE BUILDING EAST ACROSS THE
PLAINS AND UPPER MIDWEST INTO TUESDAY. THE HIGH PRESSURE RIDGE WILL
MOVE ACROSS THE WESTERN LAKES WEDNESDAY MORNING...WHILE ANOTHER DEEP
LOW TAKES SHAPE TO THE WEST ACROSS THE NORTHERN HIGH PLAINS. STRONG
SOUTH WINDS ARE ANTICIPATED AGAIN THURSDAY AS THIS LOW ALSO MOVES
EAST.

RATZER

&&

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

$$

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