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000
FXUS63 KLOT 171405
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
905 AM CDT FRI MAY 17 2013

.DISCUSSION...
428 AM CDT

EARLY THIS MORNING A STATIONARY FRONT RAN FROM NE IA...FAR NW AND
NE IL...AND NORTHERN IND. ND...NORTHEAST AND FAR NORTHWEST IL.
BOUNDARY POSITION IS WELL DEFINED BY BOTH WIND PATTERN AND LARGE
DIFFERENCE IN DEW POINTS ON OPPOSITE SIDES OF THE FRONT. AN UPPER
LOW WAS OVER THE EASTERN PORTION OF THE MO-AR BOARDER WHILE
A FEW DISTURBANCES...LIKELY CONVECTIVELY INDUCED...WERE JUST
UPSTREAM OF THE LOCAL FORECAST AREA.

THE FIRST DISTURBANCE WAS MOVING ACROSS FAR NW AND N CENTRAL IL
WITH A SECOND ALONG THE MN-IA BORDER AND A THIRD MOVING OVER THE
MID MO VALLEY FROM NEB E OVER FAR WESTERN IA. THESE DISTURBANCES
PRECEDED AN UPPER LOW MOVING E ALONG THE SD-NEB BOARDER.

THE FIRST DISTURBANCE DID PRODUCE A FEW SHOWERS AND THUNDERSTORMS
AS FAR E AS OVER THE FAR SW PORTION OF THE FA LAST EVENING AND
EARLIER THIS MORNING BUT HAD DISSIPATED AS THEY MOVED E INTO A
CAPPED AREA. THE SECOND DISTURBANCE. THE MAIN AREA OF CONVECTION
THAT HAD BEEN MOVING ACROSS IA HAD ALSO DISSIPATED AS IT MOVED
AWAY FROM THE BETTER ISENTROPIC LIFT RESULTING FROM MODERATELY
STRONG MID LEVEL WAA. THE THIRD DISTURBANCE HAS GENERATED AN
ELONGATED AREA OF THUNDERSTORMS ALONG THE MN-IA BORDER WHERE 30-35
KT SOUTHERLY FLOW IN THE 1.5 TO 3 KM AGL LAYER WAS MAXIMIZING LIFT
IN AN AREA OF RELATIVELY LARGE ELEVATED CAPE N OF THE STATIONARY
FRONT.

LATER TODAY THE CAP IS PROGGED TO BE REMOVED THOUGH FORECAST
TEMPERATURE PROFILES ARE NOT INDICATING AND SIGNIFICANT CAPE
AVAILABLE TO BE REALIZED. IN ADDITION...THE BEST ISENTROPIC LIFT
IS PROGGED TO MOVE ACROSS WI DURING THE DAY. STILL...THERE WILL BE
INCREASING CHANCES OF SHOWERS AND THUNDERSTORMS SPREADING W TO E
ACROSS THE LOCAL AREA DURING THE MORNING AS PERSISTING THROUGH THE
AFTERNOON AND EARLY EVENING AS THE SD-NEB UPPER LOW AND THE MO-AR
UPPER LOW MERGE AND MOVE TO OR SLIGHTLY E OF THE MID MS VALLEY BY
00Z. BEYOND THE FIRST PART OF THIS EVENING CHANCES OF PRECIP ARE
SMALL EXCEPT FOR THE FAR SE PORTION OF THE FA WHICH WILL STILL BE
UNDER THE INFLUENCE OF THE SLOW MOVING UPPER LOW WHICH IS PROGGED
TO BE OVER/NEAR THE LOWER OH VALLEY AT 12Z SAT.

THE UPPER PATTERN WILL BECOME MORE AMPLIFIED OVERNIGHT AND SAT
BEFORE BECOMING ZONAL E OF THE ROCKIES MID NEXT WEEK. WHILE THE
FLOW WILL BE AMPLIFIED THE FLOW WILL BE SLUGGISH AS AN UPPER
TROUGH MOVING OVER THE PACIFIC COAST EARLY THIS MORNING REACHES
THE ROCKIES LATE SAT-SAT NIGHT WHILE ANOTHER UPPER TROUGH OVER THE
N PACIFIC OFF THE B.C. COAST MOVES OVER PAC NW COAST. BY LATE SUN-
SUN NIGHT THE PAIR OF TROUGHS ARE PROGGED TO FORM AN UPPER LOW
OVER THE NORTHERN HIGH PLAINS. THIS UPPER LOW IS TO THEN VERY
SLOWLY MOVE E TO THE UPPER MIDWEST BY WED EVENING WHILE ALSO
GRADUALLY WEAKENING. HOWEVER...A FAIRLY STRONG SURFACE LOW IS
PROGGED TO MOVE E ACROSS THE NORTHERN PLAINS AND UPPER MS VALLEY
BEFORE THE UPPER SYSTEM WEAKENS AS DOES THE SURFACE REFLECTION.
DUE TO THE VERY SLOW EASTWARD PROGRESS OF THE SYSTEM A PROLONGED
PERIOD OF PERSISTENT RELATIVELY STRONG S TO SW LOWER LEVEL FLOW
WILL BE TRANSPORTING A CONTINUOUS STREAM OF MOISTURE FROM THE
WESTERN GULF UP ACROSS THE MID MS VALLEY AND TO THE UPPER MIDWEST
AND WESTERN GREAT LAKES.

WHILE THE MOST LIKELY TIME FRAME FOR RAIN IS LATER MON AND TUE AS
THIS IS WHEN SIGNIFICANT WARM AIR ADVECTION AND RESULTING UVV
ALONG WITH THE ARRIVAL OF ABUNDANT MOISTURE OCCURS...THERE WILL BE
CHANCES OF RAIN IN THE FORECAST FROM SUNDAY NIGHT RIGHT THROUGH
END OF NEXT WEEK...FIRST AS THE UPPER LOW APPROACHES THERE LIKELY
WILL BE SMALLER SCALE SHORT WAVES ROTATING AROUND TO AFFECT THE
LOCAL AREA EARLY IN THE WEEK BEFORE THE UPPER LOW IN OVER THE
AREA...AND THEN AS AN UPPER TROUGH TAKES UP SEMI PERMANENT
RESIDENCE OVER THE GREAT LAKES LATE WEEK.

STRONG WAA OCCURS AHEAD OF THE UPPER LOW DURING SAT AND SUN AND
WITH THE CORE OF THE WARM AIR OVER THE REGION ON SUN. WITH PARTLY
TO MOSTLY SUNNY SKIES TEMPERATURES ARE EXPECTED TO BE INTO THE
MID AND UPPER 80S. INCREASED CLOUDINESS WILL LIMIT HIGH
TEMPERATURES MON TO THE LOWER AND MID 80S. MIDWEEK AS THE UPPER
LOW/TROUGH MOVE OVER AND PAST THE AREA COOLER AIR WILL SPREAD S
AND SE OVER THE AREA. CONSIDERABLE CLOUDINESS AND SHOWERS WILL
KEEP AFTERNOON TEMPERATURES LIMITED TO LOWER AND MID 70S BY WED
AND UPPER 60S AND LOWER 70S ON THU.

TRS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* ISOLATED SHOWERS/THUNDERSTORMS SOUTHWEST OF TERMINALS DEVELOPING
  TOWARD MIDDAY. PSBL VCTS THIS AFTERNOON.

* VARIABLE EASTERLY WINDS WINDS ARND 8-10KT...OCCASIONAL GUSTS TO
  16-18KT MIDDAY THRU AFTN.

* CIGS REMAIN VFR...PATCHY MVFR CIGS WITH THUNDERSTORMS WEST OF
  ORD/MDW.

MDB

//DISCUSSION...UPDATED 12Z...

COMPLEX OF THUNDERSTORMS ACROSS NORTHEAST IOWA/WEST CENTRAL
WISCONSIN CONTINUE TO DRIFT NORTHEAST THIS MORNING...AND NOT
EXPECTED TO IMPACT DIRECTLY ANY OF THE NORTHERN IL/NORTHWEST IN
AIRFIELDS. STALLED FRONTAL BOUNDARY REMAINS SOUTHWEST OF THE TAF
SITES THIS MORNING...AND SHOULD ONLY LIFT NORTH SLIGHTLY
THROUGHOUT THE DAY TODAY. CIGS REMAIN VFR WITH BASES GENERALLY
AROUND 8-10KFT AGL. GUIDANCE CONTINUES TO SUGGEST VFR CONDS WILL
PREVAIL FOR MUCH OF THE DAY...PSBLY INTO TONIGHT. WITH THE
BOUNDARY REMAINING SOUTH OF THE TAF SITES...WINDS ARE NOT EXPECTED
TO CHANGE MUCH THROUGHOUT THE DAY/AFTN. WILL REMAIN ARND A 060-090
DEG RANGE WITH SPEEDS SHOWING SOME INCREASE THIS AFTN. IT APPEARS
SOME OCCASIONAL GUSTS MAY OCCUR THIS AFTN...TO 18KT. OTHERWISE
SPEEDS WILL BE ARND 8 TO 12 KT.

THE BEST CHC FOR PRECIP WILL OCCUR SOUTHWEST OF THE TAF SITES THRU
MUCH OF THE MORNING...WITH MINIMAL COVERAGE. BY MIDDAY COVERAGE
SHUD BEGIN TO INCREASE IN SHOWERS/THUNDERSTORMS...HOWEVER IT STILL
APPEARS THE BEST INSTABILITY WILL BE FOCUSED WITH THE BOUNDARY AND
THIS WILL BE JUST WEST/SOUTHWEST OF THE TAF SITES. HOWEVER...HAVE
INCLUDED A MENTION OF VCTS AS SOME STORMS COULD BE RATHER CLOSE TO
THE AIRFIELDS. THEN IT APPEARS ANY PRECIP WILL PUSH BACK TO THE
WEST/SOUTHWEST OF THE AIRFIELDS...WITH A SMALL CHC OF PRECIP
CONTINUING THROUGH THE EVENING HOURS. WINDS WILL EVENTUALLY BEGIN
TO TURN SOUTHEASTERLY ONCE THE BOUNDARY LIFTS OVERHEAD AND TO THE
NORTH OF THE TAF SITES...HOWEVER THIS DOES NOT APPEAR TO OCCUR
UNTIL AFT 05Z SAT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM-HIGH CONFIDENCE IN WIND SPEED/DIRECTION TRENDS.

* LOW CONFIDENCE IN SHRA/TSRA TIMING/COVERAGE.

* HIGH CONFIDENCE IN PREVAILING VFR CIGS WITH BRIEF MVFR CIGS
  POSSIBLE IN TSRA.

MDB

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

SATURDAY NIGHT...VFR.
SUNDAY THROUGH WEDNESDAY...VFR. PERIODIC CHANCES FOR SHRA/TSRA.
THURSDAY...VFR. PSBL MVFR WITH CHANCE FOR SHRA.

BEACHLER

&&

.MARINE...
341 AM CDT

RIDGE OF HIGH PRESSURE HAS BECOME CENTERED NEAR JAMES BAY EARLY THIS
MORNING...EXPECTED TO DRIFT SOUTHEAST AND BECOME CENTERED NEAR
WESTERN QUEBEC TONIGHT. SOUTH OF THIS HIGH PRESSURE WAS A STALLED
FRONTAL BOUNDARY THAT STRETCHING ACROSS THE CENTRAL PLAINS INTO THE
OHIO VALLEY. ACROSS THE CENTRAL PLAINS AN AREA OF LOW PRESSURE IS
EXPECTED TO DEVELOP...THIS LOW PRESSURE WILL DRIFT NORTH AND BEGIN
TO LIFT THE STALLED FRONTAL BOUNDARY TO THE NORTH. THE GRADIENT
REMAINS RELATIVELY WEAK ACROSS THE LAKE...AND THIS APPEARS TO REMAIN
THROUGH THIS EVENING AS THE BOUNDARY BEGINS TO APPROACH THE SOUTHERN
PORTION OF THE LAKE. WINDS WILL GENERALLY BE NORTH/NORTHEAST OVER
THE LAKE...FURTHER SOUTH WINDS MAY START EASTERLY THEN BECOME
NORTHEASTERLY. THEN AS THE BOUNDARY SLIDES NORTH ACROSS THE SOUTHERN
PORTION OF THE LAKE...WINDS WILL BECOME EASTERLY. THE GRADIENT DOES
INCREASE MARGINALLY...AND MAY PRODUCE SPEEDS BETWEEN 10 TO 20 KT
SAT. LOW PRESSURE ACROSS THE CENTRAL PLAINS WILL DRIFT NORTH OVER
THE WEEKEND...AND THIS WILL ALLOW THE BOUNDARY TO STEADILY LIFT
NORTH ACROSS THE LAKE. AS THIS OCCURS...WINDS TO THE SOUTH OF THE
BOUNDARY WILL TURN SOUTHEASTERLY. MEANWHILE THE FAR NORTHERN
PORTIONS OF THE LAKE WILL BE NORTHEAST/EAST. EVENTUALLY THE NORTHERN
PORTIONS OF THE LAKE WILL BECOME SOUTHEAST WINDS...BUT THIS DOES NOT
OCCUR UNTIL CLOSER TO SUNDAY MORNING. THE SLOW MOVING LOW PRESSURE
SYSTEM WILL EVENTUALLY REACH THE WESTERN GREAT LAKES...HOWEVER THIS
DOES NOT APPEAR TO OCCUR UNTIL CLOSER TO WED OF NEXT WEEK. AS THE
LOW FINALLY LIFTS NORTHEAST OF LAKE MICHIGAN MID-WEEK...THE FRONTAL
BOUNDARY WILL PUSH SOUTH ACROSS THE LAKE. THIS WILL ALLOW WINDS TO
BECOME NORTHWEST TO NORTH.

BEACHLER

&&

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

$$

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