Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 021033
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
633 AM EDT SUN AUG 2 2015


.AVIATION...

STRENGTHENING SWLY WINDS WILL GUST TO AROUND 25 KTS LATE THIS
MORNING INTO AFTN IN ADVANCE OF AN APPROACHING TROUGH AND COLD
FRONT. INCREASING INSTABILITY WILL SUPPORT POTENTIAL FOR TSTORMS TO
IMPACT MAINLY KMBS/KFNT THIS AFTERNOON WHILE REMAINING TERMINALS
SHOULD REMAIN CAPPED WITH NOTHING MORE THAN HIGH BASED CU. MORE
SIGNIFICANT TSTORM EPISODE POSSIBLE 00Z-06Z TONIGHT AS UPSTREAM
CONVECTION ORGANIZES AND MOVES DOWNSTREAM CARRYING AN ELEVATED
SEVERE THREAT...PARTICULARLY FOR NW AREAS. UNCERTAINTY IS HIGHER IN
DETROIT AREA GIVEN EXPECTED TSTORM ARRIVAL WELL AFTER SUNSET AND
LOSS OF DIURNAL HEATING.

FOR DTW...VERY LOW CHANCE FOR A TSTORM INVOF KDTW 18-00Z WITH
CAPPING EXPECTED TO PREVAIL WARRANTING REMOVAL OF PRIOR PROB30
GROUP. MOST PROBABLE TIME FOR TSTORMS WILL BE 03-06Z IN ADVANCE OF
THE COLD FRONT.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR TSTORMS THIS AFTN. MEDIUM AFTER 03Z TONIGHT.

&&

.PREV DISCUSSION...ISSUED 526 AM EDT SUN AUG 2 2015

UPDATE...

A REFINEMENT OF THOUGHTS AFTER PERUSING FRESH ARRIVING HIGH
RESOLUTION GUIDANCE, PARTICULARLY THE RAP, HRRR AND 00Z 3KM
EXPERIMENTAL NAM WHICH APPEAR TO BE SHEDDING SOME LIGHT ON THIS
AFTERNOON AND EVENING`S SEVERE POTENTIAL. ALTHOUGH OVERALL FORECAST
REASONING HAS NOT CHANGED, NEW INFORMATION IS INCREASING CONFIDENCE
THAT AFTERNOON CONVECTION WILL REMAIN CONFINED TO NORTHERN AREAS
ALONG THE NOSE OF THE DEVELOPING LOW-LEVEL JET WHILE AREAS SOUTH OF
M59 REMAIN CAPPED THUS INHIBITING PREMATURE OVERTURNING.

IN ADDITION TO THE PRIMARY THREAT OF UPSCALE GROWTH OF CONVECTION
INTO AN ORGANIZED MCS, A FEW STORMS COULD ALSO DEVELOP IN ADVANCE OF
THIS LINE WITHIN THE CORRIDOR PRECEDING WARM ADVECTION. THIS
PREFRONTAL CONVECTION WILL HAVE STEEP LAPSE RATES AND AN APPRECIABLE
RESERVOIR OF INSTABILITY WITH WHICH TO WORK. THE OFT CONSERVATIVE
07Z RAP INDICATING 0-1KM MLCAPE APPROACHING 2500 J/KG IN MIDLAND/BAY
COUNTY BY 22Z. IN ADDITION, STRENGTHENING SWLY FLOW WILL SUPPORT
ELEVATED BULK SHEAR DURING THIS TIME THUS POTENTIALLY SUPPORTING A
FEW SUPERCELLS AS UPSTREAM CONVECTION ORGANIZES OVER WISCONSIN, LAKE
MICHIGAN, AND NORTHERN LOWER MICHIGAN. GIVEN WELL MIXED/DEEP
BOUNDARY LAYER INDICATED ON FORECAST SOUNDINGS, IT APPEARS THAT A
POTENTIALLY SIGNIFICANT/70MPH, IF RELATIVELY ISOLATED, WIND THREAT
MAY EXIST MAINLY INVOF THE SAGINAW VALLEY IN ADVANCE OF THE MAIN
LINE AS EARLY AS 21/22Z. FOR THE SAME REASON, TORNADO THREAT WOULD
APPEAR LIMITED DUE TO HIGH LCLS. THOUGH THIS AFTN/EVENING`S
CONVECTIVE TRENDS WILL STILL BE CRITICAL, LATEST GUIDANCE DOES
SUPPORT THE OFFICIAL FORECAST STRONGLY ENOUGH TO CONSIDER
ADVERTISING A THREAT FOR 70 MPH WIND GUSTS CONDITIONAL ON MCS
ORGANIZATION. WILL ALLOW TIME FOR UPDATED SPC DAY 1 AND FOR DAY CREW
TO EVALUATE LATEST TRENDS AND HIGH RES GUIDANCE BEFORE ELEVATING
WORDING IN THE HWO AND OTHER PRODUCTS.

FINALLY, AS NOTED IN THE ORIGINAL MORNING FORECAST PACKAGE, A
LIMITED SEVERE THREAT WILL EXIST WITH ANY CONVECTION THAT TRAVERSES
LAND ACROSS THE NORTH DURING THE AFTERNOON HOURS. IF LATEST RAP RUNS
ARE ANY INDICATION, THE THERMODYNAMIC ENVIRONMENT MAY EVOLVE A BIT
FASTER THAN PREVIOUSLY FORECAST YIELDING INCREASED CONFIDENCE IN
SEVERE WIND POTENTIAL AT LEAST OVER THE THUMB PERHAPS AS EARLY AS
18Z SHOULD UPSTREAM CONVECTION DEVELOP WITHIN FAVORABLE WAA/STEEP
LAPSE RATE ENVIRONMENT.

PREV DISCUSSION...ISSUED 252 AM EDT SUN AUG 2 2015

SHORT TERM...TODAY AND TONIGHT

SHOWERS AND THUNDERSTORMS HAVE DEVELOPED OVER MN AND WI DURING THE
PREDAWN HOURS AS A FAST-MOVING LEAD SHORTWAVE PROVIDES FORCING
WITHIN THE STEEP LAPSE RATE ENVIRONMENT BEING DRAWN EAST BY BROAD
CYCLONIC WNW FLOW. THIS ENVIRONMENT WILL RACE EAST THROUGH THE
AFTERNOON FOCUSING A CORRIDOR OF CONVECTION ACROSS PRIMARILY ACROSS
LAKE HURON AND NORTHERN LOWER MICHIGAN. SOUTHEASTERN PORTIONS OF THE
CWA WILL REMAIN LARGELY CAPPED THROUGH PEAK HEATING AS H85
TEMPERATURES RISE WELL INTO THE UPPER TEENS SUPPORTING HIGHS
APPROACHING 90F. HOWEVER, SLIGHTLY WEAKER CAPPING/BETTER FORCING
ACROSS THE NORTH WARRANT AT LEAST A HIGH CHC POP FROM THE SAGINAW
VALLEY INTO THE THUMB, INCREASING TO LIKELY BY LATE THIS AFTN. THIS
ACTIVITY WILL CARRY AT LEAST A LOW END SEVERE RISK 18-00Z NORTH OF
THE I-69 CORRIDOR AS IT WILL RESIDE ALONG THE EASTERN PERIPHERY MORE
STRONGLY SHEARED SWLY FLOW AND AS SURFACE TDS RISE INTO THE MID AND
UPPER 60S SUPPORTING MODERATE DESTABILIZATION. LATEST HRRR RUNS HAVE
A DEPICTION SIMILAR TO EXPECTATIONS, PARTICULARLY WRT TO EXPECTED
SOUTHWARD EXTENT. MEANWHILE 4KM SPC RUN APPEARS ENTIRELY TOO
GENEROUS WITH CONVECTIVE COVERAGE/EVOLUTION WITHIN STRONGLY CAPPED
AREAS.

SECOND AND POTENTIALLY GREATER SEVERE THREAT MAY EXIST TONIGHT,
LARGELY CONDITIONAL ON EXTENT OF PRECEDING AFTERNOON CONVECTION AND
QUALITY OF RECOVERY. DEVELOPING STRONG SWLY FLOW IN ADVANCE OF
PRIMARY TROUGH AXIS WILL CERTAINLY GIVE THE EXPECTED GENESIS AREA
OVER NORTHERN LOWER OR CENTRAL MI A DECENT SHOT AT RECOVERY BY 00Z.
BETWEEN 00-06Z, STRONG HEIGHT FALLS WILL SPREAD ACROSS THE GREAT
LAKES ELICITING A STRONG LLJ RESPONSE AND IMPRESSIVE MEAN WIND
THROUGH THE LOWER ATMOSPHERE. ASSUMING THE ABSENCE OF STABILIZING
EFFECTS OF EARLIER ACTIVITY, CONVECTIVE INITIATION ALONG THE
INTENSIFYING SURFACE TROUGH WOULD HAVE POTENTIAL TO GROW UPSCALE AND
PROPAGATE INTO AN ENVIRONMENT CHARACTERIZED BY 0-1KM BULK SHEAR
AROUND 40KTS, H7-H5 LAPSE RATES IN EXCESS OF 7.5C/KM, AND 0-1KM
MLCAPE OF 1500 TO 2000 J/KG. THREAT WOULD THEN DIMINISH FROM TOWARD
THE FAR SOUTHEAST AS CONVECTION ENCOUNTERS COMBINATION OF
INCREASINGLY CAPPED MID-LEVELS AND NOCTURNAL STABILIZATION.

LONG TERM...

UPPER LEVEL TROUGH AXIS (EXTENDING FROM LARGE UPPER LEVEL LOW
CENTERED OVER NORTHERN ONTARIO) WILL BE IN PLACE ON MONDAY OVER THE
CENTRAL GREAT LAKES...WITH COLD 500 MB TEMPS AROUND -14 C. THE MAIN
SURFACE COLD FRONT SHOULD CLEAR SOUTHERN MICHIGAN SHORTLY AFTER
12Z...AND SOUTHEAST MICHIGAN WILL BEGIN TO DRY OUT WITH SLOWLY
FALLING DEW PTS. HOWEVER...THERE STILL COULD BE JUST ENOUGH RESIDUAL
LOW LEVEL MOISTURE AROUND TO GENERATE SUFFICIENT INSTABILITY TO POP
ISOLATED-SCATTERED SHOWERS AND MAYBE A THUNDERSTORM...AS THERE IS
ALSO A SECONDARILY COLD FRONT WHICH LOOKS TO BE DROPPING SOUTH FROM
NORTHERN LOWER MICHIGAN...PROVIDING THE BETTER FOCUS. 850 MB TEMPS
STILL IN THE LOWER TEENS ON MONDAY...ALLOWING FOR MAXES AROUND 80
DEGREES...WILL FALL INTO THE UPPER SINGLE NUMBERS TO AROUND 10 C BY
TUESDAY...WHICH SHOULD RESULT IN MAXES HOLDING IN THE MID/UPPER 70S.
A SPOKE OF UPPER LEVEL ENERGY IS FORECASTED TO SWING THROUGH
NORTHERN LOWER MICHIGAN DURING TUESDAY..COUPLED WITH THE DAYTIME
INSTABILITY COULD TOUCH OF A FEW SHOWERS NORTH OF I-69...OTHERWISE
UPPER LEVEL NORTHWEST CONFLUENT FLOW/GENERAL SUBSIDENCE REGIME LOOKS
TO PERSIST AT LEAST INTO WEDNESDAY...SUPPORTING SLOWLY STRENGTHENING
HIGH PRESSURE OVER LOWER MICHIGAN...PROVIDING FAVORABLE RADIATING
NIGHTTIME CONDITIONS ALLOWING MINS TO FALL INTO THE LOW/MID
50S...WITH HIGHS STILL STUCK IN THE 70S FOR WEDNESDAY.

MARINE...

SOUTHWEST WINDS WILL BE INCREASING TODAY AHEAD OF A COLD
FRONT...WITH 25 KNOT GUSTS EXPECTED ACROSS ALL NEARSHORE
WATERS...AND SMALL CRAFT ADVISORIES WILL CONTINUE. COLD FRONT
ARRIVING TONIGHT LOOKS TO TRIGGER THUNDERSTORMS...WHICH COULD BE
SEVERE...PRODUCING WINDS OF 50 KNOTS.  WINDS WILL TURN WEST AND THEN
NORTHWEST BEHIND THE FRONT DURING MONDAY. WIND SPEEDS MONDAY LOOK TO
BE GREATEST OVER NORTHERN LAKE HURON...WHERE THEY WILL REACH BETWEEN
15 TO 25 KNOTS MONDAY NIGHT THROUGH TUESDAY NIGHT AS COOLER AIR
SETTLES OVER THE CENTRAL GREAT LAKES REGION. THERE WILL BE A CHANCE
OF SHOWERS AND ISOLATED THUNDERSTORMS OVER LAKE HURON DURING THIS
TIME FRAME AS WELL.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...BEACH HAZARDS STATEMENT FROM NOON EDT TODAY THROUGH THIS EVENING
     FOR MIZ049.

LAKE HURON...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 4 AM EDT MONDAY FOR
     LHZ421-422-441>443.

LAKE ST CLAIR...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 4 AM EDT MONDAY FOR
     LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 4 AM EDT MONDAY FOR
     LEZ444.

&&

$$

AVIATION.....JVC
UPDATE.......JVC
SHORT TERM...JVC
LONG TERM....SF
MARINE.......SF


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


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