Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 291750
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
150 PM EDT FRI MAY 29 2015


.AVIATION...

RAIN SHOWERS THAT IMPACTED SOUTHERN TAF SITES WILL CONTINUE TO
MOVE OFF TO THE NORTHEAST. CLOUDS REMAIN PERSISTENT TODAY AS
MOIST SOUTHERLY FLOW CONTINUES OVER THE AREA AHEAD OF THE COLD
FRONT SET TO MOVE THROUGH ON SATURDAY. LOW CHANCES REMAIN TIED TO
THUNDERSTORMS...WITH MBS AND FNT STILL SEEING THE BEST CHANCES
THIS AFTERNOON INTO THE EVENING. WINDS THEN GRADUALLY START TO
SHIFT FROM SOUTH TO MORE WEST/SOUTHWEST OVERNIGHT TONIGHT.

FOR DTW...UNCERTAINLY REMAINS LOW TIED WITH THUNDERSTORM AND SHOWER
DEVELOPMENT LATER TONIGHT AS PEAK HEATING IS LOST AND HAVE LEFT
MENTION OUT OF THE TAF.  CLOUDS ARE EXPECTED TO STICK AROUND AT OR
BELOW 5000 FT OVERNIGHT.  THERE WILL BE ANOTHER CHANCE FOR
RAIN/THUNDERSTORMS AGAIN ON SATURDAY AS THE COLD FRONT SLIDES
THROUGH.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM FOR CIG AOB 5KFT

* LOW FOR A TSTORM IMPACTING KDTW AIRSPACE

&&

.PREV DISCUSSION...ISSUED 1044 AM EDT FRI MAY 29 2015

UPDATE...

FORECAST REMAINS ON TRACK WITH SHOWER AND THUNDERSTORM POTENTIAL
TODAY AS MOIST SOUTHERLY FLOW INCREASES OVER THE AREA. SCATTERED
THUNDERSTORM ACTIVITY HAS PICKED UP ACROSS NORTHEASTERN LOWER
WHICH IS WHERE THE BETTER FORCING AND SHEAR IS LOCATED. THE TRI
CITIES AREA WILL SEE THE BEST CHANCES FOR STRONGER STORMS AS
INSTABILITY BUILDS THROUGH THE AFTERNOON WITH CAPE VALUES
APPROACHING 1000 J/KG. DEWPOINTS HAVE COME UP QUICKLY OVER
SOUTHERN PARTS OF THE CWA AS THE ELEVATED WARM FRONT MOVES NORTH.
ENVIRONMENT WILL REMAIN MOIST TODAY AS PRECIPITABLE WATER
APPROACHES 1.30 INCHES. ONLY CHANGE TO THE FORECAST WAS TO
INCREASE CLOUD COVER AS CLOUDS CONTINUE TO STICK AROUND WHICH
MAY KEEP TEMPS SLIGHTLY COOLER. THERE IS CONCERN WITH THE AMOUNT
OF DIMINISHING CLOUD COVER AS SEEN CURRENTLY OVER SOUTHWEST LOWER
MICHIGAN/NORTHERN INDIANA AND WHETHER THAT CAN WORK IN OVER THE
CWA.

PREV DISCUSSION...ISSUED 303 AM EDT FRI MAY 29 2015

SHORT TERM...TODAY AND TONIGHT

MOIST SW FLOW CONTINUES AS GRADIENT STRENGTHENS AHEAD OF STRONG
POLAR LOW DIGGING INTO WESTERN MANITOBA EARLY THIS MORNING.
ASSOCIATED COLD FRONT IS PROGGED TO REMAIN UPSTREAM OF THE AREA
THROUGH THE SHORT TERM PERIOD...JUST BEGINNING TO IMPINGE ON THE
SAGINAW VALLEY BY EARLY SATURDAY MORNING.

UPSTREAM HEIGHT FALLS SUPPORTING NORTHWARD ADVANCEMENT OF ELEVATED
WARM FRONT EARLY THIS MORNING. ENTIRE CWA WILL EFFECTIVELY BE IN THE
WARM SECTOR BY 12Z-14Z. HOWEVER, SLOWLY RETREATING EAST COAST
ANTICYCLONE WILL SUPPORT A COMPONENT OF SOUTHEAST FLOW AT THE
SURFACE NEAR THE GREAT LAKES THROUGH THE MORNING. THIS WILL HELP TO
SUPPRESS BOTH MIXING HEIGHTS AND TEMPERATURES A BIT FOR THE DETROIT
AREA NORTH TOWARD PORT HURON. WINDS WILL NOT VEER ENOUGH TO
ELIMINATE LAKE SHADOW EFFECTS ACROSS THE EAST, SO, WITH SUPPORT FROM
THE FULL SUITE OF 00Z GUIDANCE, LOWERED TEMPERATURES SEVERAL DEGREES
FOR THE METRO AREA . INSTEAD, EXPECT THE TEMPERATURE MAXIMUM TO
RESIDE OVER CENTRAL LOWER MICHIGAN WHERE LOCAL EFFECTS WILL BE
MINIMIZED.

YESTERDAY`S UPSTREAM DEWPOINTS CONFIRM MODEL PROGS WHICH INDICATE
TDS RISING INTO THE MID 60S BY EARLY TO MID AFTERNOON WITH SCT CU
COVERAGE, SUPPORTIVE OF MLCAPE RISING TO 1000 J/KG WITHIN THE WEAKLY
SHEARED WARM SECTOR ENVIRONMENT. LACK OF FOCUSED MESOSCALE FORCING
MECHANISM WILL RENDER UPDRAFT INITIATION CONDITIONAL ON POCKETS OF
PREFERENTIAL HEATING AND BROAD/WEAK MID-LEVEL THETA-E ADVECTION.
NOTHING BETTER THAN ISOLATED COVERAGE IS EXPECTED ACROSS THE EASTERN
2/3 OF THE AREA. FOR THE SAGINAW VALLEY AND LOCALES WEST OF U.S. 23,
GREATER INSTABILITY AND SLIGHTLY BETTER FORCING WILL INCREASE
LIKELIHOOD OF SLIGHTLY BETTER COVERAGE AS WELL AS STORM POTENTIAL TO
CAPITALIZE ON DRY MID-LEVELS & WELL-MIXED BOUNDARY LAYER TO PRODUCE
A MARGINAL SEVERE THREAT ENTIRELY DEPENDENT DIABATIC COOLING.

LOSS OF DIURNAL HEATING WILL ALLOW ANY EVENING CONVECTION TO EXPIRE
BY SUNSET, BUT NOCTURNAL ENHANCEMENT OF THE NOCTURNAL LOW-LEVEL JET
WILL EVENTUALLY REPLENISH WEAK MID-LEVEL INSTABILITY. THIS WILL
SUPPORT ANOTHER ROUND OF A LOW COVERAGE OF WEAKLY SHEARED MULTICELL
TYPE STORMS AFTER MIDNIGHT. LACK OF A DIURNAL BOUNDARY LAYER
ELIMINATES ANY NOCTURNAL SEVERE THREAT. LOWS WILL STRUGGLE TO FALL
MUCH BELOW 70 IN SOUPY WARM SECTOR AIRMASS.

LONG TERM...SATURDAY THROUGH THURSDAY

A DEEP UPPER LOW FORECAST TO TRACK FROM NRN ONTARIO INTO NRN QUEBEC
ON SATURDAY WILL DRIVE A SFC COLD FRONT ACROSS LOWER MI. A
TIGHTENING HEIGHT GRADIENT ACROSS ERN CANADA AHEAD OF THIS WAVE WILL
STRENGTHEN AN UPPER JET STREAK TO THE NORTH OF THE REGION. THIS WILL
RESULT IN DEEP LAYER FRONTOGENSIS ACROSS LOWER MI TIED TO THE
ENTRANCE REGION OF THIS UPPER JET. THERE WILL BE AMPLE DEEP LAYER
MOISTURE /PRECIPITABLE WATER APPROACHING 1.8 IN/ ALONG AND AHEAD OF
THIS FRONT. THE 00Z GFS AND CANADIAN HAVE TRENDED SLIGHTLY SLOWER IN
BRINGING THE DEEP LAYER FRONTAL CIRCULATION ACROSS SE MI ON
SATURDAY. THIS WILL PROVIDE SOME OPPORTUNITY FOR WEAK TO PERHAPS
MODEST DAYTIME DESTABILIZATION TO OCCUR OVER MOST OF SE MI. SHORT
WAVE IMPULSES LIFTING INTO THE AREA FROM THE SW ARE LIKELY TO
INITIATE CONVECTION /TIMING OF WHICH IS FAIRLY UNCERTAIN AT THIS
STAGE IN THE FCST/. THE INSTABILITY AND POTENTIAL SHORT WAVE
IMPULSES/S/ SUGGEST A REGION OF CONVECTION ON SAT WILL BE FOLLOWED
BY A PERIOD OF STRATIFORM RAIN WITHIN THE SYNOPTIC SCALE SUPPORT
WHICH ARRIVES LATER IN THE DAY INTO THE EVENING.

ANY POTENTIAL FOR STRONG TO SEVERE STORMS ON SAT WILL BE HIGHLY
DEPENDENT ON THE DEVELOPMENT OF MODERATE INSTABILITY /CAPE GREATER
THAN 1K J/KG/ AS THE STRONGER DEEP LAYER SHEAR LOOKS TO ARRIVE AFTER
THE BETTER CONVECTIVE POTENTIAL. THIS OF COURSE WILL DEPEND ON THE
DEGREE OF EARLY DAY CLOUD COVER AND TIMING OF ANY UPSTREAM SHORT
WAVE IMPULSES. THE AMOUNT OF DEEP LAYER MOISTURE AND SOME POTENTIAL
FOR REGENERATIVE CONVECTION SUGGESTS A RISK FOR SOME LOCALLY HEAVY
RAINFALL. THE 00Z NAM SOLUTION BECOMES HIGHLY SUSPECT AS IT IS MUCH
SLOWER WITH THE FRONTAL TIMING AND THUS DEVELOPS A QUASI STATIONARY
MCS OVER SRN MI. THE PROGRESSION OF THE CANADIAN UPPER WAVE SHOULD
RESULT IN A FASTER FRONTAL PUSH THAN INDICATED BY THE NAM.

MUCH DRIER AND COOLER AIR WILL FUNNEL INTO SE MI SAT NIGHT INTO SUN
MORNING IN THE WAKE OF THE SFC COLD FRONT. STRONG HIGH PRESSURE TO
THE N AND NE OF THE FORECAST AREA WILL SUSTAIN THIS COOL AND DRY AIR
AMIDST E-NE FLOW INTO THE BEGINNING OF NEXT WEEK. MID LEVEL HEIGHTS
WILL THEN REBOUND DURING THE MIDDLE TO END OF NEXT WEEK...LEADING TO
A MODEST WARMING TREND.

MARINE...

LIGHT SOUTH TO SOUTHEAST WINDS WILL OCCUR TODAY...PRECEDING THE
ARRIVAL OF A WEAK WARM FRONT. BUILDING INSTABILITY ALONG THIS WARM
FRONT WILL PROVIDE A CHANCE OF THUNDERSTORMS. THE CHANCE OF
THUNDERSTORMS WILL INCREASE ON SATURDAY AS A STRONG COLD FRONT IS
DRIVEN INTO THE GREAT LAKES REGION. THIS FRONT IS FORECAST TO TRACK
ACROSS LAKE HURON EARLY IN THE DAY SATURDAY BEFORE REACHING LAKE
ERIE SATURDAY EVENING. THE FRONT WILL BE MARKED BY A VEERING OF THE
WINDS TO THE N-NW. AN INCREASING GRADIENT ALONG WITH A PUSH OF MUCH
COOLER LOW LEVEL AIR SUGGESTS SOME GUSTY WINDS ALONG THE NEARSHORE
SATURDAY NIGHT INTO SUNDAY. WINDS WILL THEN WEAKEN LATE SUNDAY INTO
MONDAY AS HIGH PRESSURE EXPANDS ACROSS THE REGION.

&&

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

$$

AVIATION.....SS
UPDATE.......SS
SHORT TERM...JVC
LONG TERM....SC
MARINE.......SC


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


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