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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 151454
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1054 AM EDT SAT JUN 15 2013

.UPDATE...

-- Changed Discussion --
THE INHERITED FORECAST IS IN GOOD SHAPE WITH LITTLE REFINEMENT
NEEDED IN THE UPDATE. DEFINITIVE MCV FROM YESTERDAYS UPSTREAM
CONVECTION IS CHURNING EASTWARD. THIS FEATURE IS EMBEDDED WITHIN
A MERIDIONAL 700-850MB THETA E GRADIENT ON THE BACK EDGE OF THE
MIDLEVEL GEOPOTENTIAL HEIGHT RIDGE IN PLACE OVER THE WESTERN GREAT
LAKES. TWO SPOKES OF ENHANCED MOISTURE HAVE DEVELOPED DUE TO THE
ORGANIZATION OF THE MESOSCALE CIRCULATION...THE FIRST OF WHICH IS
WASHING ASHORE OF FAR WESTERN LOWER MICHIGAN THIS MORNING...THE
SECOND MORE COMPACT WITH THE CONVECTIVE VORT ITSELF. THE LEAD
ACTIVITY HERE IN LOWER MICHIGAN IS WEAKENING WITH TIME AS IT
OUTPACES THE AFOREMENTIONED THETA E GRADIENT. NWP SUGGESTS SOME
DIURNAL BOUNDARY LAYER GROWTH MAY CONNECT WITH THIS MIDLEVEL
MOISTURE CAUSING SOME LATE AFTERNOON REVIVAL AFTER 20Z OVER
SOUTHEASTERN MICHIGAN. CONFIDENCE IS FAIRLY HIGH THAT AFTERNOON
ACTIVITY WILL REMAIN SCATTERED WITH QPF AMOUNTS LIGHT. GENERAL
CHANCE POPS THIS AFTERNOON HAVE THIS IN HAND. WARM MIDLEVELS DUE
TO RESIDUAL LATENT HEATING WILL KEEP CAPE DENSITIES AT A
MINIMUM...NO SEVERE WEATHER RISK ANTICIPATED.

THE DEEPER THETA E IS EXPECTED TO WASH ACROSS SOUTHEASTERN
MICHIGAN THIS EVENING. LINEAR EXTRAPOLATION OF UPSTREAM RADAR
MOSAIC TIMES THIS ACTIVITY LARGELY AFTER 01Z. THIS SUPPORTS THE
LIKELY TO NUMEROUS POP FORECAST.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
ISSUED 722 AM EDT SAT JUN 15 2013

//DISCUSSION...

VFR CONDITIONS WILL HOLD FIRM AS LIGHT SOUTHWEST WINDS PERSIST
BEHIND DEPARTING HIGH PRESSURE. A PASSING CIRRUS CANOPY WILL GIVE
WAY TO A LOWERING CLOUD DECK AND DEVELOPING CEILINGS AROUND 4KFT BY
LATE AFTERNOON AS MOISTURE TRANSPORT INCREASES INTO THE AREA. A
PASSING SHOWER OR TWO WILL BE POSSIBLE FROM MID-AFTERNOON ONWARD AS
THE MOIST AIRMASS PUSHES INTO SOUTHEAST MICHIGAN, BUT WIDESPREAD
RAINFALL STILL APPEARS MOST LIKELY TO OCCUR AFTER MIDNIGHT.
SCATTERED THUNDERSTORMS WILL ALSO BE POSSIBLE THROUGH THE OVERNIGHT
PERIOD AS A DEVELOPING LOW-LEVEL JET PROVIDES MARGINAL NOCTURNAL
INSTABILITY.


//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5KFT AFTER 20Z

* LOW CONFIDENCE THAT A THUNDERSTORM WILL IMPACT KDTW AIRSPACE
-- End Changed Discussion --

&&

.PREV DISCUSSION...ISSUED 355 AM EDT SAT JUN 15 2013

SHORT TERM...TODAY AND TONIGHT

EXPANSIVE FIELD OF DEEP SUBTROPICAL MOISTURE STRETCHING FROM THE
GULF COAST TO SOUTH-CENTRAL CANADA IS IN PLACE ALONG THE WESTERN
PERIPHERY OF THE CENTRAL CONUS LONGWAVE RIDGE THIS MORNING. MULTIPLE
FOCI OF CONVECTIVE ACTIVITY ARE ONGOING WITHIN THIS GENERAL REGION,
MOST NOTABLY THE IOWA/MISSOURI CONVECTIVE COMPLEX THAT WILL
CONTRIBUTE TO APPRECIABLE CLOUD DEBRIS ENVELOPING THE CWA THROUGH
THE EARLY PORTION OF THE DAY. MEANWHILE, THE CONVERGENT EASTERN
FLANK OF THIS PROMINENT MOISTURE FIELD IS NOTED ON REGIONAL RADAR
IMAGERY AS AN ACTIVE REGION OF SHOWERS/TSTORMS EXTENDING FROM THE
WESTERN GREAT LAKES INTO WESTERN ONTARIO.

AN EASTWARD SURGE OF THIS WARM MOIST AIRMASS CAN BE EXPECTED BY LATE
THIS AFTERNOON AS THE LARGE CLOSED LOW OVER MANITOBA FORCES A RAPID
DEAMPLIFICATION OF THE FLOW ACROSS THE NORTHERN STATES. AS A RESULT,
MID AND HIGH CLOUDS/DEBRIS WILL EVENTUALLY GIVE WAY TO AN INCREASING
COVERAGE OF DIURNALLY-ENHANCED CU AS MID-LEVEL MOISTURE TRANSPORT
INTO THE LOWER PENINSULA RAMPS UP AROUND 20Z. BLANKET CHANCE POPS
ARE IN PLACE DURING THE EARLY EVENING PERIOD TO ACCOUNT FOR AT LEAST
SCATTERED COVERAGE OF SHOWERS ALONG THE H7 THETA-E GRADIENT IN
ADDITION TO ANY DIURNALLY FORCED ACTIVITY THAT MAY BE ABLE TO GET
GOING BEFORE LOSS OF SURFACE HEATING. WARM MID-LEVELS AND A WEAK
AMBIENT WIND FIELD REALLY LIMIT ANY CONCERNS FOR SEVERE POTENTIAL
HERE.

THE CONVECTIVELY ENHANCED SHORTWAVE OVER THE TX PANDHANDLE AT 08Z
THIS MORNING WILL THEN PROVIDE THE MAIN OPPORTUNITY FOR SHOWERS AND
THUNDERSTORMS FOR THE AREA AS IT SHEARS TOWARD SOUTHEAST MICHIGAN
WITHIN THE DEAMPLIFYING LARGE SCALE FLOW OVERNIGHT. THE
STRENGTHENING UPPER MASS GRADIENT OVER THE NORTHERN GREAT LAKES WILL
ELICIT RAPID JET STREAK DEVELOPMENT THAT WILL PROVIDE RIGHT ENTRANCE
SUPPORT OVER SEMI IN THE 06-12Z PERIOD WHILE A DEVELOPING 40KT LLJ
PROVIDES AMPLE MOISTURE TRANSPORT, LOW-LEVEL FORCING, AND SUFFICIENT
INSTABILITY FOR WHAT SHOULD BE A RESPECTABLE COVERAGE OF SHOWERS AND
THUNDERSTORMS. ALTHOUGH WARM MID-LEVELS LOOK TO ONCE AGAIN LIMIT THE
MOST UNSTABLE PARCELS TO AROUND 500 J/KG CAPE, 0-3KM SHEAR PUSHING
45KTS BY EARLY SUNDAY MORNING IS ENOUGH TO WARRANT MONITORING OF ANY
ONGOING CONVECTION FOR POTENTIAL ORGANIZATION AND A VERY LOW-END
SEVERE THREAT.

LONG TERM...SUNDAY THROUGH FRIDAY

SOUTHEAST MICHIGAN FIRMLY POSITIONED WITHIN A ZONAL MID LEVEL FLOW
AT 12Z SUNDAY MORNING...WITH THE PROGRESSIVE HEIGHT FALLS EMANATING
OFF THE CLOSED LOW WOBBLING ACROSS SOUTHERN SASKATCHEWAN EFFECTIVELY
SUPPRESSING THE MAIN UPPER RIDGE AXIS WELL TO THE SOUTH.  SHORTWAVE
ENERGY WORKING THROUGH THIS FLOW WILL SHIFT TO THE EAST DURING THE
MORNING HOURS ON SUNDAY.  PROXIMITY OF THE AREA TO THE BACK EDGE OF
THE EXITING MID LEVEL FORCING AND ATTENDANT HIGHER THETA-E/MOISTURE
GRADIENT WILL MAINTAIN A CHANCE OF SHOWERS/ELEVATED THUNDER DURING
THE MORNING PERIOD.  TRAILING FRONTAL BOUNDARY TIED TO THE SOUTHERN
EXTENSION OF THE BROADER HEIGHT FALLS WORKING ACROSS SOUTHERN
ONTARIO WILL QUICKLY FOLLOW BY MIDDAY.  THIS WILL PROMPT A STEADY
DRYING OF THE COLUMN WITHIN DEVELOPING AND DEEPENING WEST-NORTHWEST
FLOW FOR THE LATTER HALF OF THE DAY.  NAM THE SLOWEST WITH THIS
PROCESS...ALLOWING TIME FOR A MODULATING THERMODYNAMIC PROFILE TO
YIELDS SBCAPE VALUES UPWARDS OF 1500-1800 J/KG WITH STEEP LOW LEVEL
LAPSE RATES AND MINIMAL CAPPING ISSUES...MAINLY ACROSS THE
SOUTHEASTERN HALF.  REGARDLESS...LACK OF ANY IDENTIFIABLE FORCING
MECHANISMS REMAINS PROBLEMATIC...SUGGESTING A LOW COVERAGE/ISOLATED
POP SCENARIO /IF ANY/ CONDITIONAL ON PROPERLY CAPITALIZING ON A
DECREASINGLY SUPPORTIVE MOISTURE FIELD.  A WELL MIXED VEERING LOW
LEVEL GRADIENT AND A PERIOD OF GOOD INSOLATION WILL BRING HIGHS INTO
THE LOWER 80S.

ANOTHER ROUND OF HEIGHT FALLS WORKING DOWNSTREAM OF THE
AFOREMENTIONED LOW WILL EASE THE NEXT COLD FRONT SOUTHWARD INTO
LOWER MICHIGAN SUNDAY NIGHT AND MONDAY.  SUBTLE TIMING DIFFERENCES
YET AS TO WHETHER THE BOUNDARY ACTUALLY REACHES THE SAGINAW VALLEY
PRIOR TO MONDAY...BUT THE OVERALL NET EFFECT WILL BE FOR THE LOW
LEVEL FRONTAL ZONE TO EVENTUALLY ALIGN WITHIN THE MEAN WESTERLY FLOW
DRAPED ACROSS THE REGION DURING THE DAY ON MONDAY.  A RATHER
DISORGANIZED LOOKING FORCING FIELD...SOME SEMBLANCE OF WEAK
CONVERGENCE/FGEN ATTEMPTS TO EMERGE ALONG THE FRONTAL SLOPE BENEATH
THE UPPER JET CORE AND WITHIN A WEAKLY CYCLONIC MID LEVEL FLOW.
THIS WILL CONTINUE TO SUPPORT A GENERAL CHANCE POP MENTION WITH THE
AID OF MODERATE LOW TO MID LEVEL DAYTIME DESTABILIZATION.
PROGRESSIVE DETERIORATION OF THE THERMODYNAMIC FIELD FROM NORTH TO
SOUTH THROUGH THE EVENING HOURS AS COOLER/DRIER AIR WORKS IN BEHIND
THE FRONT.  THIS WILL BE ONGOING COINCIDENT WITH THE ARRIVAL OF THE
MAIN MID LEVEL TROUGH AXIS.  ANY LEGITIMATE SPIKE IN LARGE SCALE
ASCENT WILL ARRIVE AS BOTH THE MOISTURE QUALITY AND DEGREE OF
INSTABILITY IS ON THE DOWNTURN.  THIS WILL SEEMINGLY CONTAIN BOTH
THE OVERALL COVERAGE AND STRENGTH OF ANY ADDITIONAL PRECIPITATION
DEVELOPMENT.

STRETCH OF BENIGN WEATHER CONDITIONS WITH HIGH PRESSURE TAKING AN
EXTENDED RESIDENCE TUESDAY AND WEDNESDAY.  THIS WILL PROVIDE A
PERIOD OF COOLER AND LESS HUMID CONDITIONS UNDER CLEAR/SUNNY SKIES.
NORTHEAST FLOW OFF THE COOLER LAKE WATERS WILL CONTRIBUTE TO DAYTIME
READINGS STRUGGLING TO CLIMB MUCH ABOVE OF THE LOW/MID 60S ACROSS
THE THUMB ON TUESDAY.  ELSEWHERE HIGHS GENERALLY LOWER 70S APPEAR
ATTAINABLE GIVEN THE PROJECTED STRENGTH OF THIS AIRMASS.  GRADUAL
WARMING TREND THROUGH THE LATTER HALF OF THE WEEK.

MARINE...

LIGHT AND VARIABLE WIND WILL PERSIST INTO THE MORNING FOLLOWED BY A
RETURN TO SOUTHERLY WINDS DURING THE DAY TODAY. SOME DISRUPTION OF
MARINE CONDITIONS IS POSSIBLE DUE TO SHOWERS AND THUNDERSTORMS, BUT
THIS SHOULD BE MOSTLY SATURDAY NIGHT AS THE NEXT LOW PRESSURE SYSTEM
MOVES THROUGH NORTHERN ONTARIO. WIND AND WAVE CONDITIONS WILL
OTHERWISE BE FAVORABLE OVER THE NEXT SEVERAL DAYS UNTIL PERHAPS LATE
MONDAY WHEN THE NEXT COLD FRONT IS DUE THROUGH THE REGION.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

UPDATE.......CB
AVIATION.....JVC
SHORT TERM...JVC
LONG TERM....MR
MARINE.......JVC


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