Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 271125
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
725 AM EDT SUN JUL 27 2014

.AVIATION...

//DISCUSSION...

THE FIRST CONCERN FOR AVIATION INTERESTS WILL BE THE FOG AND LOW
CEILING DURING THE EARLY MORNING...FOLLOWED BY THUNDERSTORM
POTENTIAL DURING THE AFTERNOON AND EARLY EVENING...AND THEN THE
PASSAGE OF A STRONG COLD FRONT TONIGHT.

VLIFR/LIFR RESTRICTION IN FOG/STRATUS IS THE RESULT OF LOW LEVEL
MOISTURE RETURNING NORTHWARD AHEAD OF THE LOW PRESSURE SYSTEM THAT
WILL SWEEP THROUGH THE REGION DURING THE AFTERNOON. EXPECT A TYPICAL
PACE OF IMPROVEMENT ON THE FOG/STRATUS AS LATE JULY SURFACE HEATING
GETS UNDERWAY. CONDITIONS WILL THEN QUICKLY DESTABILIZE BY EARLY
AFTERNOON AND STORMS WILL DEVELOP IN CLUSTERS THAT WILL LIKELY
AFFECT MBS FIRST AND THEN QUICKLY PROGRESS TO THE SOUTHEAST AND EXIT
THE TERMINAL CORRIDOR BY 00Z THIS EVENING.

THE PASSAGE OF THE COLD FRONT WILL BRING COOLER AIR AND MVFR STRATUS
FROM NORTH TO SOUTH OVER SE MICHIGAN AFTER MIDNIGHT. THE WIND WILL
STAY UP FROM THE NORTH AND THEN GUST NEAR 20 KNOTS MONDAY MORNING
INTO EARLY AFTERNOON.

FOR DTW... VISIBILITY WILL FOLLOW A TYPICAL UPWARD IMPROVEMENT CYCLE
AS FOG LIFTS TO LOW STRATUS AND THEN MIXES OUT TOWARD NOON. THERE IS
HIGH CONFIDENCE IN THUNDERSTORM OCCURRENCE DURING THE AFTERNOON BUT
NOT AS MUCH ON TIMING OF STRONGEST ACTIVITY/POTENTIAL SEVERITY. THE
LATE AFTERNOON WINDOW OFFERED IN THIS FORECAST PACKAGE WILL BE
REFINED AS THE EVENT UNFOLDS.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE ON VISIBILITY LESS THAN 1/2 MILE AND CEILING LESS
  THAN 200 FEET.

* HIGH CONFIDENCE IN THUNDERSTORM DEVELOPMENT DURING THE AFTERNOON.

* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FEET LATE TONIGHT THROUGH
  MONDAY MORNING.

&&

.PREV DISCUSSION...ISSUED 358 AM EDT SUN JUL 27 2014

SHORT TERM...TODAY AND TONIGHT

UPPER LOW DROPPING FROM CANADA INTO MINNESOTA THIS MORNING WILL
CONTINUE TO TRACK SOUTHEAST AND INTO MICHIGAN BY 00Z/8PM TODAY.
SURFACE LOW TRACKING AHEAD OF THIS FEATURE WILL SLIDE ACROSS
MICHIGAN AHEAD OF THE UPPER CIRCULATION. BY 15Z/10AM...EXPECT THE
LOW TO BE CENTERED OVER LAKE MICHIGAN WITH AN ELEVATED WARM FRONT
SITUATED FROM NORTH-CENTRAL LOWER MICHIGAN DOWN ACROSS THE
THUMB...AND THE SURFACE COLD FRONT STILL BACK OVER WISCONSIN. BOTH
FRONTAL FEATURES WILL BE THE FOCUS FOR ACTIVITY EARLY TODAY...WITH
SHOWERS/TSTORMS FIRST EXPECTED TO DEVELOP ACROSS THE TRI-CITIES AND
THUMB DURING THE LATE MORNING/EARLY AFTERNOON AS CONVERGENCE
INCREASES ALONG THE ELEVATED FRONT. THE WHOLE SYSTEM WILL THEN DROP
SOUTH AND EAST TOWARDS LAKE ERIE...PULLING A WEDGE OF COLDER AIR
DOWN INTO SOUTHEAST MICHIGAN BEHIND IT...AND LIKELY BRINGING
SHOWERS/TSTORMS TO THE WHOLE AREA.

MOSTLY CLEAR SKIES TO START TODAY WILL AID IN DESTABILIZATION BEFORE
UPPER HEIGHT FALLS RAMP UP DURING THE AFTERNOON AND THE COLD FRONT
APPROACHES. MODEL FORECASTS FOR ML/SB CAPE LOOK TO REACH BETWEEN
1500-2500 J/KG BY THE TIME THE CAP ERODES BETWEEN 14-15Z (PER NAM
SOUNDINGS). THERE WILL ALSO BE A FAIRLY STRONG UPPER JET...100
KNOTS...THAT DIVES SOUTH INTO THE OHIO VALLEY DURING THE AFTERNOON
AND EVENING...PLACING SOUTHEAST MICHIGAN WITHIN LEFT EXIT REGION
FORCING BEFORE IT SLIDES SOUTH THROUGH THE EVENING. A STRONGER CORE
OF MID-LEVEL WINDS WILL ALSO DIVE INTO THE OHIO VALLEY. THE AXIS OF
STRONGER WINDS WILL REMAIN TO OUR SOUTH...BUT WILL STILL INCREASE
SHEAR OVER THE SOUTHERN PORTION OF THE FORECAST AREA TODAY AS IT
BRUSHES BY. ALTHOUGH 0-1KM SHEAR WILL BE QUITE LOW...UNDER 10
KNOTS...0-6KM SHEAR WILL RUN FAIRLY HIGH AT 40-45 KNOTS. THE
COMBINATION OF INSTABILITY AND SHEAR WILL BRING THE THREAT FOR
SEVERE WEATHER TODAY. THE THREAT WILL HOWEVER DECREASE FROM NORTH TO
SOUTH FROM MID/LATE-AFTERNOON THROUGH THIS EVENING AS
SHEAR/INSTABILITY SHOW SIMILAR TRENDS. THE OVERALL SEVERE THREAT FOR
ALL OF SOUTHEAST MICHIGAN LOOKS TO TAPER OFF BY 8 PM...WITH THE
THREAT NORTH OF I-69 LOOKING TO TAPER OFF BY 5 PM. FORECAST
SOUNDINGS INITIALLY SUPPORT A LARGE HAIL THREAT WITH FAT CAPE AND
LOW FREEZING LEVELS...AS WELL AS A DAMAGING WIND THREAT WITH A DRY
SUB-CLOUD LAYER AND HIGH 0-6KM SHEAR. SOUNDINGS THEN SHOW A N-S
TRANSITION TO TALL AND SKINNY CAPE AS COOLER AIR WORKS IN AT THE
LOWER-LEVELS DURING THE LATE AFTERNOON/EVENING...THEN SUPPORTING A
HEAVY RAIN THREAT AS PW VALUES REMAIN UP NEAR 1.5 INCHES. WHILE
SEVERE WEATHER WILL BE POSSIBLE ACROSS ALL OF SOUTHEAST MICHIGAN
TODAY...BETTER POTENTIAL WILL BE LOCATED SOUTH OF THE I-69 CORRIDOR
AS THIS AREA WILL HAVE MORE TIME TO DESTABILIZE BEFORE THE COLD
FRONT WORKS ACROSS.

MOISTURE WILL CONTINUE TO WRAP AROUND THE LOW AS IT DROPS SOUTHEAST
OF THE AREA TONIGHT. WE SHOULD ALSO SEE SOME RAIN (WITH A FEW
EMBEDDED THUNDERSTORMS) CONTINUE IN THE DEFORMATION AREA ON THE
NORTH SIDE OF THE SYSTEM THROUGH THE EVENING AND INTO THE OVERNIGHT
HOURS. DRIER AIR WILL WORK IN AT THE MID-LEVELS LATE
TONIGHT...ALLOWING RAIN TO TAPER OFF. FOG THREAT SHOULD BE MITIGATED
AS NORTHERLY WINDS CONTINUE BEHIND THE FRONT AT AROUND 10 MPH
TONIGHT.

TEMPERATURES THIS AFTERNOON SHOULD WARM UP AROUND 80...WHICH WILL
FEEL MUGGY WHEN COMBINED WITH DEWPOINTS IN THE MID/UPPER 60S. LOWS
TONIGHT WILL BE HELD UP BY SATURATED SOILS AND LINGERING
CLOUDS/RAIN...DESPITE H850 TEMPS FALLING TO BELOW 10C. THIS SHOULD
PROVIDE MIN TEMPS IN THE MID 50S TO LOW 60S.

LONG TERM...

A RETURN TO BELOW NORMAL TEMPERATURES WILL HIGHLIGHT WEATHER
CONDITIONS THROUGHOUT THE UPCOMING WEEK. MONDAY WILL BE THE COOLEST
DAY AS HIGHS STRUGGLE TO REACH 70 FOLLOWED BY ABOUT A CATEGORY OF
MODERATION EACH DAY THROUGH WEDNESDAY AND THEN HOLDING IN THE MID TO
UPPER 70S ALL THE WAY INTO NEXT WEEKEND. THE TEMPERATURE MODERATION
WILL BE VULNERABLE TO THE EVENTUAL COVERAGE OF SHOWERS WHICH WILL BE
POSSIBLE EACH DAY AS LATE JULY SURFACE HEATING MAINTAINS INSTABILITY
IN THE COOL AIR MASS.

THE LOW PRESSURE SYSTEM AFFECTING THE AREA TODAY AND TONIGHT WILL
EXIT EAST BY SUNRISE MONDAY FOLLOWED BY MODERATE NORTHERLY FLOW AND
COLD ADVECTION THROUGH THE DAY. MODEL SOUNDINGS INDICATE ENOUGH
SUBSIDENCE WARMING AROUND 700 MB TO CONFINE CONVECTION TO ABOUT 800
MB OF BOUNDARY LAYER THROUGHOUT THE DAY...GOOD FOR GENEROUS COVERAGE
CUMULUS BUT NO RAIN. FORECASTS OF 850 MB TEMPS EITHER SIDE OF 7C
SUPPORT THE GOING FORECAST HIGHS MOSTLY IN THE UPPER 60S...POSSIBLY
70 IN THE DETROIT AREA TO OHIO BORDER...FAVORING BELOW GUIDANCE
VALUES. FOR SOME PERSPECTIVE...THE RECORDS FOR COOLEST MAX TEMPS ON
JULY 28TH: DTW 68/1926...FNT 64/1981...MBS 60/1981.

THE NEARLY MERIDIONAL HEIGHT GRADIENT ALOFT WILL MAINTAIN SURFACE
HIGH PRESSURE OVER THE PLAINS AND LIGHT NORTHWEST SURFACE WIND OVER
LOWER MICHIGAN MONDAY NIGHT. THE TENDENCY FOR DECOUPLING WILL BE
REDUCED BY THE NEXT SURGE OF UPPER LEVEL ENERGY IN THE NW FLOW
ALOFT...WELL AGREED UPON IN THE 00Z MODEL CYCLE...WHICH WILL SHARPEN
THE SURFACE PRESSURE GRADIENT DURING THE NIGHT AND BRING CLOUDS INTO
THE REGION LATE IN THE NIGHT. GUIDANCE MIN TEMPS IN THE UPPER 40S
LOOK REASONABLE IN THIS SCENARIO FOR THE TYPICALLY COOLER LOCATIONS
BUT MAY BE SLIGHTLY TOO COOL FOR THE REST OF THE REGION. THAT BEING
SAID...THE RECORD LOW FOR THE 29TH FOR MBS LOOKS REACHABLE AT
48/1965 AND EVEN FOR DTW 50/1971 BUT NOT FNT AT 42/1928.

CONTINUED SOUTHWARD MOVEMENT OF THE UPPER LEVEL HEIGHT FALL CENTER
TUESDAY WILL COMBINE WITH SURFACE HEATING FOR A CHANCE OF SHOWERS IN
BETWEEN POCKETS OF SUNSHINE. LOW LEVEL MOISTURE WILL BE ADEQUATE FOR
A RUMBLE OF THUNDER AS 850 MB DEWPOINT IS SHOWN TO HOVER IN THE
UPPER SINGLE DIGITS(C). MODEL SOUNDINGS INDICATE SKINNY CAPE
EXTENDING ABOVE -20C BUT ARE OTHERWISE UNIMPRESSIVE. GIVEN THE
POTENTIAL FOR CLOUDS AND SCATTERED SHOWERS...MAX TEMPS IN THE LOWER
70S WOULD SEEM LIKE A STRETCH IF NOT FOR THE EQUAL POTENTIAL FOR
SUNSHINE AND SURFACE HEATING.

THE LARGE UPPER LOW/TROUGH WILL REMAIN IN PLACE OVER THE EASTERN
THIRD OF NORTH AMERICA WEDNESDAY THROUGH THE END OF THE WEEK...BUT
PREDICTABILITY DROPS OFF ON THE DETAILS OF THE UPPER AIR PATTERN IN
THE MODEL SOLUTIONS. THE GENERAL PATTERN OF DAYTIME INSTABILITY
SUPPORTING SCATTERED SHOWERS LOOKS SOLID UNDER THE UPPER LEVEL COLD
POOL THAT WILL PERSIST EACH DAY...BUT WITH SLUGS OF DRY AIR AND
NEUTRAL FLOW MODULATING ACTIVITY.

MARINE...

EXPECT THUNDERSTORM ACTIVITY TO STEADILY INCREASE COVERAGE AND
INTENSITY AS THE DAY PROGRESSES. SEVERE WEATHER POTENTIAL REMAINS
MAINLY OVER THE SOUTH HALF OF LAKE HURON THROUGH WESTERN LAKE ERIE
DURING THE MID AFTERNOON HOURS. WIND AND WAVE ACTION WILL OTHERWISE
BE FAVORABLE THROUGH TODAY BEFORE A COLD FRONT MOVES THROUGH THE
REGION TONIGHT. NORTHERLY WINDS WILL RAMP UP BEHIND THE FRONT...
PEAKING WITH 30 KNOT GUSTS OVER SOUTHERN LAKE HURON MONDAY. A SMALL
CRAFT ADVISORY IS IN EFFECT MONDAY MORNING THROUGH MIDNIGHT MONDAY
NIGHT AS THE LONG NORTH FETCH WILL BE FAVORABLE FOR BUILDING LARGE
WAVES THAT WILL IMPACT THE SOUTH HALF OF LAKE HURON AND NEARSHORE
MARINE ZONES. COOL HIGH PRESSURE WILL THEN BUILD INTO THE NORTHERN
PLAINS AND GREAT LAKES AND RETURN BENIGN MARINE WEATHER FOR THE MID
WEEK PERIOD.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...DENSE FOG ADVISORY...MIZ068-MIZ069-MIZ075-MIZ076-MIZ082-
     MIZ083...UNTIL 11 AM SUNDAY.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY AND THE NEARSHORE WATERS FROM
     PORT AUSTIN TO HARBOR BEACH...FROM 5 AM MONDAY TO MIDNIGHT
     TUESDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM HARBOR BEACH TO PORT
     HURON...FROM 8 AM MONDAY TO MIDNIGHT TUESDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....BT
SHORT TERM...HLO
LONG TERM....BT
MARINE.......BT


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






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