Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 301538
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1138 AM EDT TUE JUN 30 2015

.UPDATE...

SHOWER COVERAGE BEGINNING TO INCREASE ALONG THE LEAD EDGE OF THE
TROUGH AXIS OVER WESTERN LOWER MICHIGAN. THIS CORRIDOR OF ENHANCED
FORCING WILL WORK ACROSS THE NORTHERN HALF OF THE CWA 18-00Z WITH
SOME ADDITIONAL DIURNAL ENHANCEMENT TO INTENSITY/COVERAGE STILL
EXPECTED. FURTHER SOUTH, COVERAGE APPEARS MORE DEPENDENT ON
INSTABILITY WHERE ANYWHERE FROM 200-500 J/KG MLCAPE IS FORECAST.
NEXT 90 MINUTES SHOULD BE TELLING WITH REGARD TO CONVECTIVE
POTENTIAL, BUT ADDITIONAL CLOUD ENHANCEMENT DUE TO MCV OVER NORTHERN
IN/OH IS SURE TO LIMIT TSTORM POTENTIAL. MINOR UPDATE TO THE GRIDS
HAS BEEN MADE TO SIGNIFICANTLY TEMPER EXPECTATIONS FOR THUNDER,
ESPECIALLY NORTH OF M59, AND LOWER TEMPS A COUPLE DEGREES DUE TO
EXTENSIVE CLOUDS.

&&

.AVIATION...ISSUED 723 AM EDT TUE JUN 30 2015

MOISTURE ORPHANED OFF OF THE WEAK SURFACE REFLECTION NEAR LAKE ERIE
HAS STREAMED NORTHWESTWARD THIS MORNING IN DEVELOPING SOUTHERLY
FLOW. CIGS HEIGHTS ACROSS THE TERMINAL HAVE PREDOMINATELY REMAINED
IN THE MVFR RANGE. THIS MOISTURE WILL WORK NORTHWARD TO KMBS LATE
THIS MORNING AND MAY CONTRIBUTE TO DEVELOPING SHOWER ACTIVITY DURING
THE LATE MORNING HOURS. A SHORTWAVE AND MIDLEVEL TROUGH AXIS WILL
THEN TRACK THROUGH THE CWA DURING THE LATE AFTERNOON CONTRIBUTING
DEEPER MOISTURE AND A NUMEROUS/LIKELY COVERAGE OF SHOWERS AND
THUNDERSTORMS. THE DEEPER MOISTURE IS EXPECTED TO STALL OUT OVER
LOWER MICHIGAN WITH NO TANGIBLE DRY AIR ADVECTION. THIS IS EXPECTED
TO LEAD TO ANOTHER ROUND OF LOWERING CIGS AND VSBYS TONIGHT...WITH
CURRENT PROGS SUGGESTING IFR CONDITIONS BY SUNRISE WEDNESDAY.

FOR DTW...MVFR CIGS WILL PERSIST THE FIRST 3 HOURS OF THE TAF PERIOD
BEFORE LIFTING TO VFR. LOW POTENTIAL FOR PRECIPATION WILL EXIST IN
THE TAF PERIOD BEFORE INCREASING SIGNIFICANTLY DURING THE LATE
AFTERNOON. LACK OF A FOCUSING MECHANISM BRINGS A DIFFICULTY IN
PINPOINTING PRECIPATION CHANCES. DEEPER MOISTURE PERSISTING
THROUGHOUT THE OVERNIGHT IS EXPECTED TO LEAD TO IFR CIGS BY 10Z
WEDNESDAY MORNING.

//DTW THRESHOLD PROBABILITIES...

* HIGH IN CIGS BELOW 5000 FT THROUGHOUT THE TAF PERIOD.

* MEDIUM IN THUNDERSTORMS TUESDAY AFTERNOON AND EVENING.

&&

.PREV DISCUSSION...ISSUED 354 AM EDT TUE JUN 30 2015

SHORT TERM...TODAY AND TONIGHT

AN IMPRESSIVE +100 KNOT UPPER LEVEL JETLET CASCADING DOWN THE
FORWARD FACE OF THE WESTERN NOAM RIDGE INTO NORTHERN MINNESOTA THIS
MORNING WILL CAUSE A RAPID REINFORCEMENT OF THE DOWNSTREAM TROUGH
DURING THE NEXT 6 TO 9 HOURS. THE MODELS CLEARLY DEFINE A TIGHT
SHEAR GRADIENT ON THE DOWNSTREAM FLANK OF U/L JET MAXIMUM OVER
PORTIONS OF WI AND IL BY 18Z. EMBEDDED SHORTWAVE ENERGY WITHIN THE
REPOSITIONING TROUGH AXIS...INCLUDING THE STRONGER LAKE
SUPERIOR/U.P. SHORTWAVE WILL SWEEP ACROSS LOWER MICHIGAN DURING THE
AFTERNOON AND EARLY EVENING HOURS TONIGHT.

A WEAKER AND LESS PROGRESSIVE SURFACE REFLECTION OVER WESTERN LAKE
ERIE THIS PAST EVENING HAS LARGELY BEEN OVERWHELMED BY DEVELOPING
SOUTHERLY FLOW IN ADVANCE OF THE APPROACHING SHORTWAVE. THIS HAS
ALLOWED AN OLD NEAR SURFACE OCCLUSION OR FRONTAL BOUNDARY TO LIFT
NORTHWESTWARD INTO THE DETROIT AREA. THERE HAS BEEN SOME
DRIZZLE/SPRINKLES/LIGHT RAIN WITHIN THIS THETA E RIBBON IN ADDITION
TO LOW CLOUD STRATUS. RADAR EVOLUTION THIS MORNING SUGGESTS THIS
SHOULD CONTINUE TO IMPACT THE AREA DURING THE NEXT 3 HOURS BEFORE
ADVECTING FARTHER NORTHWARD.

THE ENHANCED MOISTURE PLUME IS EXPECTED TO TRACK TO THE NORTHERN CWA
BY THE LATE MORNING...POST 15Z. SIGNAL WITHIN THE CAM DATSETS IN
ADDITION TO FCST SOUNDING ANALSYIS SUGGESTS AT SOME POTENTIAL FOR
SCATTERED SHOWERS TO INITIATE OFF OF THIS MOISTURE WITH DAYTIME
HEATING. THESE INTIAL SHOWERS APPEAR TO BE SHALLOW...WITH TOPS AT 15
KFT AGL.

UPSTREAM SHORTWAVE ENERGY COLLECTED ALONG THE AFOREMENTIONED SHEAR
GRADIENT WILL THEN BE KICKED EASTWARD FAIRLY QUICKLY DURING THE
AFTERNOON HOURS DUE TO A NUMBER OF FACTORS. THE INCREASE IN
MAGNITUDE OF DIFFERENTIAL CYCLONIC VORTICITY ADVECTION WILL THEN ADD
A SIGNIFICANT COMPOMENT OF SYNOPTIC SCALE SUPPORT FOR ASCENT. IT
REMAINS DIFFICULT TO ADD MUCH DETAIL UNDER LITTLE TO NO CAPPING AND
FAVORABLE LARGE SCALE ASCENT. LOOKING AT MODEL DATA...THERE APPEARS
TO BE A STRONG DEPENDENCE FOR CONVECTION BASED ON SFC DEWPOINTS.
THIS SUGGESTS THAT AREAS IN THE WESTERN CWA AND THE TRI CITIES STAND
THE BEST POTENTIAL TO WITNESS HIGHER QPF AMOUNTS. A MORE PERSISTENT
LIGHT EASTERLY FLOW OVER THE THUMB DOWN INTO THE DETROIT METRO AREA
WILL LIKELY TEMPER THE DEWPOINT RESPONSE THERE. AN INCREASE IN THE
MEAN 600-400MB MOISTURE CONINCIDENT TO THE DEEP TROUGH AXIS SUPPORTS
GOING WITH A LIKELY/NUMEROUS POP THIS AFTERNOON. TALL SKINNY CAPE
WITH SUB 400 J/KG SBCAPE SUPPORTS NO ORGANIZED SEVERE WEATHER RISK.
AN ISOLATED HEAVY RAIN THREAT IS AGAIN IN PLAY...WITH VERY SLOW
STORM MOTION PREDICTED. COLUMN MEAN WIND SUGGESTS ANY CONVECTIVE
CELLS THIS AFTERNOON WILL TRACK SW TO NE AT APPROXIMATELY 15 MPH.
WITH SUCH WEAK FLOW THERE IS POTENTIAL FOR STORM MOTION TO BECOME
MODULATED BY SHORTWAVE/VORTICITY CENTERS. IN FACT...COULD ACTUALLY
SEEM SOME MINOR BACKBUILDING AND TRAINING OF SHOWER OR THUNDERSTORM
CELLS TOWARDS EVENING. ATTM...THE BEST POTENTIAL FOR THIS TO OCCUR
IS OVER CENTRAL SECTION OF THE CWA...AWAY FROM THE RAISN RIVER BASIN.

SYNOPTIC SCALE FORCING IS EXPECTED TO CARRY A RAIN CHANCE INTO THE
EVENING HOURS BEFORE THE LOSS OF DIURNAL HEATING ENDS THE POTENTIAL
AFTER MIDNIGHT.

LONG TERM...WEDNESDAY THROUGH MONDAY

SURFACE LOW PRESSURE WILL CONTINUE TO EXIT THE AREA ON
WEDNESDAY...WHILE HIGH PRESSURE BEGINS TO EXPAND INTO THE NORTHERN
AND WESTERN GREAT LAKES. UPPER SHORTWAVE WILL DROP THROUGH THE U.P.
AND INTO ONTARIO LATE WEDNESDAY INTO WEDNESDAY NIGHT. THIS MAY
TRIGGER A FEW SHOWERS OR THUNDERSTORMS IN THE AFTERNOON/EVENING AS A
COLD FRONT IN THE PROCESS OF WASHING OUT DROPS DOWN INTO THE AREA
AND DAYTIME HEATING ALLOWS SOME SURFACE-BASED INSTABILITY TO BUILD.
BEST CHANCES FOR ANY ACTIVITY LOOK BEST OVER THE SAGINAW VALLEY AND
THUMB...AND EVEN THEN CHANCES DO NOT LOOK HIGH WITH LIMITED MOISTURE
AVAILABLE AND POTENTIAL FOR A MID-LEVEL CAP TO REMAIN IN PLACE.

SURFACE HIGH WILL SHIFT DOWN INTO THE CENTRAL GREAT LAKES ON
THURSDAY AND THURSDAY NIGHT. THIS WILL PROVIDE QUIET WEATHER AND
MOSTLY SUNNY SKIES FOR THE AFTERNOON. ONE MORE PIECE OF ENERGY IS
THEN EXPECTED TO DROP THROUGH THE LONGWAVE TROUGH THAT HAS BEEN
STUCK OVER THE GREAT LAKES AND NEW ENGLAND ON FRIDAY BEFORE THE
PATTERN SHIFTS. THE PROBLEM IS THAT MODELS ALL SEEM TO HANDLE THIS
ENERGY DIFFERENTLY...00Z GFS SLIDES IT THROUGH ONTARIO...12Z EURO
DROPS IT ACROSS MICHIGAN...AND THE 00Z GEM DROPS IT THROUGH THE
MIDWEST AND ACROSS THE OHIO VALLEY. EURO SOLUTION WOULD BE THE MORE
FAVORABLE ONE FOR SHOWERS/TSTORMS...BUT WITH POOR MODEL
CONTINUITY...WILL KEEP THE FORECAST DRY.

MODEL SOLUTIONS CONTINUE TO SHOW UPPER RIDGING SLIDING OVERHEAD FOR
THE HOLIDAY WEEKEND. THIS WOULD SUPPORT A DRY FORECAST AND A WARMING
TREND WITH MAX TEMPERATURES NUDGING TOWARDS 80 DEGREES. GFS/EURO
BOTH ARE KEYING IN ON AN UPPER LOW TRACKING THROUGH ONTARIO EARLY
NEXT WEEK BUT SHOW INCONSISTENCIES WITH TIMING. THIS WILL PROVIDE A
PERIOD OF SHOWERS/TSTORMS IN THE MONDAY OR TUESDAY TIMEFRAME.

MARINE...

LOW PRESSURE SLOWLY PASSING OVERHEAD WILL BRING RELATIVELY LIGHT
WINDS TODAY...OUTSIDE OF A PUSH OF 15 KNOT WEST WINDS LATE THIS
AFTERNOON AND EVENING OVER WESTERN LAKE ERIE. WINDS WILL THEN TURN
NORTHWESTERLY BEHIND A WEAK FRONT TONIGHT...BUT REMAIN 15 KNOTS OR
LESS. HIGH PRESSURE BUILDING INTO THE GREAT LAKES WILL THEN PROVIDE
QUIET WEATHER AND LIGHT WINDS WEDNESDAY THROUGH THURSDAY NIGHT.

&&

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

$$

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


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).


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