Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 282220
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
620 PM EDT FRI AUG 28 2015


.AVIATION...

DISSIPATION OF DIURNAL CU WILL GIVE WAY TO OVC MAINLY ABOVE 10KFT AS
PART OF A WEAK WAVE SHEARS ACROSS NORTHERN LOWER MICHIGAN. SOUTHEAST
PERIPHERY OF THE PRECIP SHIELD, THE PART THAT CONCERNS SE MICHIGAN
THROUGH TONIGHT, IS NEARLY ALL VIRGA. A VERY LIGHT HIGH BASED SHOWER
OR BRIEF DRIZZLE IS NOT OUT OF THE QUESTION FROM KFNT SOUTH, BUT THE
KMBS WILL HAVE THE HIGHEST PROBABILITY OF SEEING LIGHT RAIN. VFR
WILL THEREFORE PERSIST AT ALL AIRFIELDS THROUGH AT LEAST MOST OF
SATURDAY. POTENTIAL FOR ANOTHER ROUND OF DIURNAL LOW VFR CU TO
DEVELOP ON SAT, BUT EXTENSIVE MID-LEVEL CLOUDS WARRANT A CAUTIOUS
APPROACH DUE TO DIMINISHED SURFACE HEATING. ISO-SCT SHOWERS POSSIBLE
SAT AFTN, BUT CONFIDENCE COVERAGE IS SUFFICIENTLY LOW ATTM TO
WARRANT EXCLUSION FROM THE TAFS. LIGHT SOUTHERLY WIND THROUGH THE
PERIOD.

//DTW THRESHOLD PROBABILITIES...

* LOW IN CIGS AOB 5KFT SATURDAY AFTN.

&&

.PREV DISCUSSION...ISSUED 357 PM EDT FRI AUG 28 2015

SHORT TERM...THIS EVENING AND TONIGHT

LOW AMPLITUDE SHORTWAVE RIDGING COMPONENT IS ROLLING THROUGH THE
CENTRAL GREAT LAKES REGION THIS AFTERNOON. THIS IN COMBINATION WITH
RESIDUAL HIGH STABILITY IN THE LOWER ATMOSPHERIC COLUMN IS KEEPING
SURFACE HIGH PRESSURE FIRMLY IN CONTROL OF THE WEATHER ACROSS THE
CWA. SFC OBSERVATIONS ARE REPORTING SOUTHEASTERLY SURFACE WINDS AT
MANY OF THE SITES.

MODEL DATA CONTINUES TO SUPPORT LOW LEVEL DRY AIR HOLDING THROUGH
TONIGHT. A LEAD WING OF ELEVATED WARM AIR ADVECTION IS FORECASTED TO
DEVELOP IN A SHEARING DEFORMATION AXIS OVER PORTIONS OF MID MICHIGAN
AND INTO THE SAGINAW BAY REGION. OVERALL INTEGRITY OF THETA E RIDGE
IN ADVANCE OF SHORTWAVE IS MODELED TO BE VERY POOR TO POOR. THIS
LENDS CONFIDENCE THAT COVERAGE OF DEVELOPING ACTIVITY TONIGHT SHOULD
REMAIN SCATTERED IN NATURE. CAMS AND DETERMINSITIC SOLUTIONS SUGGEST
THE TIME WINDOW TO 09-12Z NEAR SAGINAW. A LIGHT QPF POTENTIAL AS ANY
HIGH BASED SHOWER ACTIVITY SHOULD FALL OUT OF 7 KFT TO PERHAPS AS
HIGH AS 10 KFT AGL BASES. CLOUD COVER TONIGHT WITH WARMER DAYTIME
TEMPS TODAY SUPPORTS WARMER LOWS TONIGHT...AROUND 60 DEGREES.

LONG TERM...SATURDAY THROUGH NEXT FRIDAY

THE 12Z MODEL MODEL SUITE CONTINUE TO SHOW THE CLOSED MID LEVEL
CIRCULATION NOW OVER IOWA LIFTING INTO LOWER MI AND WEAKENING TO
MORE OF AN OPEN WAVE ON SATURDAY. THERE ARE MODEL DIFFERENCES AS TO
HOW PROGRESSIVE THIS SYSTEM WILL BE AS IT ROTATES ACROSS THE
STATE...WITH MODEL SOLUTIONS SEEMING TO STRUGGLE WITH THE DEGREE OF
PHASING WITH A NORTHERN STREAM WAVE CURRENTLY ROTATING INTO SRN
MANITOBA. THIS NRN STREAM WAVE APPEARS DEEPER THAN SUGGESTED BY MOST
OF THE 12Z SUITE...WHICH MAY KEEP MORE WAVE SEPARATION BETWEEN IT
AND THE WAVE OVER IOWA. THE 12Z ECMWF SOLUTION LEANS MORE IN THIS
DIRECTION...WHICH IS ACTUALLY FAIRLY WELL ALIGNED WITH THE CURRENT
SET OF FORECAST GRIDS.

MID LEVEL FRONTAL ASCENT WILL BE SUSTAINED ALONG THE LEAD EDGE OF
THE MID LEVEL TROUGH AXIS ON SATURDAY VIA DYNAMICS WITHIN THE
ENTRANCE REGION OF A 60-70KT UPPER JET MAX SLIDING FROM LAKE HURON
INTO NRN QUEBEC. THE ISENTROPIC ASCENT AND RIBBON OF MID LEVEL
MOISTURE IS FORECAST TO SLOWLY ADVANCE FROM THE SAGINAW VALLEY
REGION TO METRO DETROIT AND POINTS SOUTH DURING THE COURSE OF THE
DAY SATURDAY. THIS SUPPORTS THE CURRENT CHANCE OF SHOWERS IN THE
FORECAST. MODEL SOUNDINGS SUGGEST LITTLE IF ANY SURFACE BASED
INSTABILITY /ESPECIALLY ACROSS THE NRN HALF OF THE AREA WHERE THE
DAY WILL START OFF WITH MORE CLOUD COVER/. THUS THE CHANCES FOR
THUNDERSTORMS CONTINUE TO LOOK LOW. EARLY DAY CLOUD COVER AND
POTENTIAL SHOWERS WILL LIMIT AFTERNOON HIGHS TO THE 70S OVER MOST OF
THE AREA...EXCEPT METRO DETROIT/ANN ARBOR AND PTS WHERE HIGHS MAY
TOUCH 80.

THE NORTHERN STREAM TROUGH IS THEN FORECAST TO DROP INTO LOWER MI
LATE SAT AFTERNOON/SAT EVENING. FORCED ASCENT ASSOCIATED WITH THIS
WAVE WILL SUPPORT A CONTINUED CHANCE OF SHOWERS SAT NIGHT. THE BROAD
NATURE OF THE UPPER TROUGH /AT LEAST PER ECMWF SOLUTION/ COMBINED
WITH A LITTLE BETTER HEATING ON SUNDAY /SFC TEMPS IN THE LOW 80S AND
DWPTS IN THE MID TO UPPER 60S/ WILL WARRANT A CHANCE OF CONVECTION
DURING THE DAY SUNDAY. A LITTLE LESS MOISTURE DEPTH WILL SUPPORT
BETTER INSOLATION COMPARED TO SATURDAY...ALLOWING WEAK SURFACE BASED
DESTABILIZATION AND THUS BETTER POTENTIAL FOR THUNDERSTORMS.

EXTENDED...A MOSTLY QUIET STRETCH OF WEATHER IS IN STORE FOR
SOUTHEAST MICHIGAN NEXT WEEK.  UPPER LEVEL RIDING ALONG WITH RISING
HEIGHTS WILL KEEP THE AREA MAINLY DRY AS TEMPERATURES WARM INTO THE
MID 80S FOR THE WEEK.  SOME DIURNAL DRIVEN SHOWER ACTIVITY MAY
DEVELOP EARLY IN THE WEEK AS THE TROUGH FROM THE WEEKEND PUSHES
EAST.

MARINE...

LOW PRESSURE OVER THE PLAINS TODAY WILL WEAKEN CONSIDERABLY AS IT
APPROACHES THE WESTERN GREAT LAKES TONIGHT INTO SATURDAY. THE RESULT
WILL BE A CONTINUED WEAK SFC GRADIENT OVER THE EASTERN GREAT LAKES
THIS WEEKEND AND THUS GENERALLY LIGHT WINDS. HIGH PRESSURE WILL THEN
BUILD OVER THE REGION NEXT WEEK...LEADING TO CONTINUED LIGHT WINDS
AND IDEAL BOATING CONDITIONS.

&&

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

$$

AVIATION.....JVC
SHORT TERM...CB
LONG TERM....SC/SS
MARINE.......SC


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


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