Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 020652
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
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.

&&

.AVIATION...ISSUED 1147 PM EDT SAT AUG 1 2015

SW WINDS WILL INCREASE LATE SUN MORNING INTO SUN AFTERNOON DUE BOTH
TO DIURNAL MIXING AND A STRENGTHENING WSW GRADIENT IN ADVANCE OF AN
APPROACHING COLD FRONT. AN INFLUX OF INSTABILITY DURING THE DAY WILL
LEAD TO INCREASING CHANCES FOR THUNDERSTORMS...TIMING OF WHICH
CARRIES A GOOD DEAL OF UNCERTAINTY AT THIS EARLY STAGE IN THE
FORECAST.

FOR DTW...THE TWO MOST PROBABLE TIME PERIOD FOR THUNDERSTORM
IMPACTING METRO WILL BE SUN AFTERNOON WITH THE INFLUX OF INSTABILITY
AND LATE SUN EVENING/NIGHT AHEAD OF A COLD FRONT.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN THUNDERSTORMS SUNDAY AFTERNOON AND NIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
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.

&&

$$

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


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



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