Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 210853
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
453 AM EDT THU AUG 21 2014

.SYNOPSIS...
A WARM FRONT WILL GRADUALLY LIFT NORTHEAST INTO THE GREAT LAKES
THROUGH SATURDAY...THEN CONTINUE TO WAVER ACROSS THE REGION
THROUGH THE BEGINNING OF NEXT WEEK. DISTURBANCES IN NORTHWEST FLOW
ALOFT WILL INTERACT WITH A VERY WARM AND MOIST AIRMASS TO PRODUCE
SHOWERS AND THUNDERSTORMS AT TIMES THROUGH THE PERIOD.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A VERY COMPLEX CONVECTIVE FORECAST TODAY. EARLY THIS MORNING
SHOWERS AND EMBEDDED THUNDERSTORMS DEVELOPED IN MOIST ASCENT
ASSOCIATED WITH A WEAK LOW LEVEL JET ACROSS NORTHERN INDIANA.
THESE WILL DRIFT INTO WEST CENTRAL OHIO THROUGH THE EARLY MORNING.
MEANWHILE A WEAK DISTURBANCE OVER NORTHERN ILLINOIS WILL MOVE
SOUTHEAST IN NORTHWEST FLOW ALOFT. THERE IS A CONSISTENT SIGNAL
IN THE SUITE OF CONVECTIVE ALLOWING MODELS THAT THUNDERSTORMS WILL
BLOSSOM OVER INDIANA THIS MORNING...ORGANIZING IN MODERATE WIND
FIELDS...THEN SURGING SOUTHEAST ACROSS OUR AREA THROUGH MIDDAY.
THIS MAY BE STARTING TO SHOW ITS HAND ACROSS NORTHWEST
INDIANA...ALTHOUGH MANY OF THE MODELS DID NOT HANDLE THE DECAYING
STORMS OVER SOUTHWEST INDIANA VERY WELL. THERE IS ALSO GENERAL
AGREEMENT FROM THE SYNOPTIC MODELS ON THIS SCENARIO...ALTHOUGH
PLACEMENT OF THE TRACK OF THE STORMS VARIES. MAINTAINED THE LIKELY
POPS AND BROADENED THEM A BIT. DO NOT THINK THERE MUCH OF A SEVERE
THREAT WITH THIS AND THAT THE SPC DAY 1 OUTLOOK IS MORE GEARED
TOWARD AN OVERNIGHT SYSTEM (SEE BELOW). AFTER THIS COMPLEX MOVES
OUT...THE CAMS HAVE THE REGION GENERALLY DRY FOR THE REST OF THE
AFTERNOON AND EVENING...AND THIS SEEMS REASONABLE IF A LARGE
COMPLEX OCCURS. QPF GENERATED IN THE SYNOPTIC MODELS MAY BE A
RESULT OF PARAMETERIZATION...BUT MAINTAINED SOME CHANCE POPS INTO
THE EVENING JUST IN CASE. HAVE A SLIGHTLY GREATER CHANCE IN THE
NORTH SINCE THE EARLIER CONVECTION MAY TAKE A MORE SOUTHEASTWARD
TRAJECTORY. HIGH TEMPERATURES WILL BE TRICKY AND POSSIBLY LIMITED
BY CLOUDS AND PRECIPITATION. FORECAST FALLS IN BETWEEN THE WARM MAV
AND COOL MET...BUT ANY SUN THIS AFTERNOON COULD LEAD TO A JUMP IN
TEMPERATURES.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
NEXT DISTURBANCE IN THE NORTHWEST FLOW ALOFT WILL AFFECT THE AREA
TONIGHT. THERE ARE INDICATIONS A LARGE COMPLEX OF STORMS/MCS WILL
FORM OVER MINNESOTA AND WISCONSIN AND DIVE SOUTHEASTWARD. SOME
TIMING AND PLACEMENT DISCREPANCIES EXIST...BUT THE MOST LIKELY
TRAJECTORY APPEARS TO BE TOWARD THE NORTHERN HALF OF THE CWA...SO
HAVE ALIGNED POPS ACCORDINGLY. IF AN ORGANIZED MCS
DEVELOPS...THERE MAY BE AN ATTENDANT RISK FOR STRONG TO DAMAGING
WINDS. HOWEVER THE DIURNALLY UNFAVORABLE TIMING MAY LEAD TO A
WEAKENING TREND. SPC HAS PLACED THE WESTERN HALF OF THE CWA IN A
SLIGHT RISK. ALSO...WPC HAS PLACED THE AREA IN A SLIGHT RISK OF
EXCESSIVE RAINFALL DUE TO THE MULTIPLE CLUSTERS OF THUNDERSTORMS
WITH HEAVY RAIN. WITH A MOIST AIRMASS AND CLOUD COVER...LOWS WILL
ONLY DROP INTO THE LOWER 70S IN MANY SPOTS.

MORE STORMS WILL BE POSSIBLE ON FRIDAY...BUT COVERAGE IS IN
QUESTION AS CONFIDENCE DECREASES ON INDIVIDUAL FEATURES IN THE
NORTHWEST FLOW. HOWEVER...HIGH PRECIPITABLE WATER VALUES AND THE
LINGERING BOUNDARY ACROSS THE REGION WILL ACT IN FAVOR OF
THUNDERSTORM DEVELOPMENT DURING PEAK HEATING. A SIMILAR SCENARIO
APPLIES TO SATURDAY. COMPLICATING MATTERS IS A SLIGHT CHANGE IN
THE PATTERN ORIENTATION FROM SATURDAY INTO SUNDAY. THE CENTRAL
CONUS RIDGE IS EXPECTED TO CONTINUE TO BUILD...AS A TROUGH DIGS
OVER THE WESTERN ATLANTIC. THERE ARE NOW INDICATIONS THAT HIGH
PRESSURE OVER THE ST. LAWRENCE VALLEY WILL NOSE
SOUTHWESTWARD...SERVING TO BACK DOOR FRONT THE LOW LEVEL BOUNDARY.
THIS MAY SHIFT THE FOCUS OF ANY STORMS THAT DEVELOP. BY SUNDAY THE
LOW LEVEL BAROCLINIC ZONE BECOMES MORE DIFFUSE...LOW LEVEL FLOW
WEAKENS...AND ATMOSPHERIC MOISTURE LESSENS...SO STORM CHANCES MAY
BE PRETTY LOW.

FRIDAY AND SATURDAY WILL LIKELY BE THE WARMEST DAYS OF THE SHORT
TERM PERIOD WITH HIGHS IN THE UPPER 80S TO LOWER 90S. HEAT INDICES
IN THE SOUTHWEST WILL BE NEAR 100. BY SUNDAY...THE NORTHEAST
SURFACE FLOW MAY HELP LIMIT TEMPERATURES A BIT. WITH HIGH DEW
POINTS...OVERNIGHT LOWS WILL CONTINUE TO RESIDE ON EITHER SIDE OF 70.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
GETTING INTO MONDAY-TUESDAY...THE RIDGE CONTINUES TO BUILD WITH
HEAT/HUMIDITY. FLOW BECOMES VERY LIGHT THROUGH THE BULK OF THE
TROPOSPHERE AND IT BECOMES QUESTIONABLE IF COVERAGE OF DAYTIME/EVE
STORMS WARRANTS MENTION. RIGHT NOW HAVE RUN 15-25% RAIN CHANCES
BOTH OF THESE DAYS...AND THAT MAY BE TOO HIGH. INTO
WEDNESDAY...SOME HINTS OF HEIGHT FALLS WHICH MAY ALLOW A LITTLE
STRONGER FLOW OR A WEAK SHORTWAVE TROUGH TO CROSS THE GREAT LAKES.
SO A BETTER STORM THREAT THEN...HOWEVER AT THIS TIME RANGE THIS IS
A VERY LOW CONFIDENCE FORECAST GIVEN CONDITIONAL NATURE OF THE
RIDGE BUCKLING.

SO ALL IN ALL...HAVE TENDED TO FOCUS RAIN CHANCES NEAR PEAK HEATING
INTO THE EVENING AND ALLOW FOR SOME DRY NIGHTS/EARLY MORNINGS. FLY
IN OINTMENT WILL BE ANY FORWARD PROPAGATING MCS THAT SURVIVES
THROUGH THE NIGHT...ORIGINATING TO OUR NORTHWEST  AND FALLING DOWN
NNWLY FLOW EITHER SATURDAY MORNING OR SUNDAY MORNING. LOW CONFIDENCE
STORM CHANCE...BUT HIGH CONFIDENCE WARM/HUMID PATTERN IS THE STORY
FOR THE SAT-WED TIMEFRAME.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
THE REGION WILL BE WEDGED BETWEEN TWO SYNOPTIC SCALE SYSTEMS OVER
THE NEXT 24 HOURS. A MID LEVEL CLOSED LOW SLOWLY MOVING FROM THE
EASTERN GREAT LAKES TO NEW ENGLAND AREA. MEANWHILE...A MID LEVEL
RIDGE WILL TRY TO NUDGE ITS WAY NORTHWARD INTO THE MIDDLE
MISSISSIPPI VALLEY. OUR AREA WILL BE INFLUENCED BY THE NORTHWEST
FLOW ALOFT BETWEEN THESE TWO SYSTEMS ALONG WITH EMBEDDED
DISTURBANCES RIDING SOUTHEAST ON THE EAST SIDE OF THE RIDGE AXIS
FROM TIME TO TIME. AT THE SAME TIME...A WEAK TO MODEST LOW LEVEL
JET WILL BRING SOME LOW LEVEL MOIST ASCENT. MANY MODEL
SOLUTIONS...INCLUDING THE CONVECTION ALLOWING MODELS...CONTINUE TO
STRUGGLE WITH TIMING AND PLACEMENT OF CONVECTION OVER THE NEXT 24
HOURS. THERE IS SOME CONSENSUS IN AT LEAST THE FIRST 12 HOURS. A
WEAK DISTURBANCE OVER NRN INDIANA IS EXPECTED TO MOVE SOUTHEAST
ACROSS NRN OHIO THIS MORNING. ALSO...A LOW LEVEL JET IS FORECAST
TO IMPINGE ON THE REGION FROM THE WEST. WE SHOULD SEE AN INCREASE
IN SHOWERS AND THUNDERSTORMS THIS MORNING...ESPECIALLY BETWEEN 12Z
AND 18Z. HAVE PLACED TEMPO MVFR CONDITIONS AT ALL THE TAF SITES.
FOR THIS AFTERNOON...SOME MODELS SUGGEST WE COULD BE IN A
RELATIVE LULL AS THE LOW LEVEL JET DIURNALLY WEAKENS AND THE
DISTURBANCE MOVES AWAY. HAVE LEFT A VCSH DESCRIPTOR AT THE TAF
SITES FOR LOW CHANCES FOR SHOWERS OR A STORM.

FOR TONIGHT...ANOTHER EMBEDDED DISTURBANCE IS FORECAST TO ROTATE
SOUTHEAST INTO THE REGION. THERE CONTINUES TO BE DIFFERENCES IN
THE EVOLUTION OF NOCTURNAL CONVECTION. RIGHT NOW..THE BEST CHANCE
FOR SHOWERS/STORMS SHOULD OCCUR AFTER 06Z AND BE MORE WEIGHTED
TOWARDS THE NORTHERN TAF SITES OF KDAY...KCMH...AND KLCK.
HOWEVER...IT SHOULD BE NOTED THAT SOME MODELS HAVE CONVECTION
AFFECTING THE ENTIRE REGION IN THE FORM OF A MESOSCALE CONVECTIVE
SYSTEM. WILL CONTINUE TO MONITOR MODEL TRENDS FOR TIMING AND
SPATIAL COVERAGE.

OUTLOOK...THUNDERSTORMS POSSIBLE FRIDAY EVENING THROUGH SUNDAY.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...NONE.
KY...NONE.
IN...NONE.

&&

$$
SYNOPSIS...SNYDER
NEAR TERM...SNYDER
SHORT TERM...SNYDER
LONG TERM...BINAU
AVIATION...HICKMAN






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