Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 041724
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
124 PM EDT TUE AUG 4 2015


.AVIATION...

AN AGITATED CU FIELD IS DEVELOPING AHEAD OF THE NEXT WEAK FRONTAL
BOUNDARY CURRENTLY DROPPING THROUGH CENTRAL MI. VFR CONDITIONS
SHOULD PREVAIL THROUGH MUCH OF THE FORECAST WITH HIGH BASED CEILINGS
STAYING UP AROUND 5-6KFT. SOME ISOLATED SHOWER/THUNDERSTORM ACTIVITY
WILL PASS THROUGH THE AREA DURING PEAK HEATING THIS AFTERNOON BUT
MAINLY ONLY AFFECT FNT AND MBS...POSSIBLY BRUSHING PTK. WESTERLY
FLOW WILL REMAIN ELEVATED THIS AFTERNOON WITH GUSTS TO 20 KNOTS.
WINDS WILL RELAX TONIGHT WHILE BECOMING NORTHWEST UNDER CLEARING
SKIES.

FOR DTW...DAYTIME HEATING...COUPLED WITH A WEAK FRONTAL BOUNDARY
SWINGING SOUTH THROUGH LOWER MICHIGAN...IS EXPECTED TO RESULT AN
ENHANCED CU FIELD BUT CEILINGS SHOULD REMAIN VFR...GENERALLY ABOVE
5000 FEET. SHOWER/THUNDERSTORMS ACTIVITY IS EXPECTED TO REMAIN NORTH
OF THE AIRPORT.

//DTW THRESHOLD PROBABILITIES...

* LOW FOR CIGS BELOW 5000 FT AGL THIS AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 334 AM EDT TUE AUG 4 2015

SHORT TERM...TODAY AND TONIGHT

DRIER LOW LEVEL AIR IN PLACE ACROSS SOUTHEAST MICHIGAN AS INDICATED
BY THE SURFACE DEW PTS IN THE 50S. HOWEVER...THE MID LEVELS ARE
SIGNIFICANTLY COLDER...WITH THE 00Z RAOB OUT OF GREEN BAY REPORTING
A 500 MB TEMP OF -17 C. THUS...WITH SOME SEMBLANCE OF SURFACE
TROUGH/COLD FRONT MOVING THROUGH CENTRAL LOWER MICHIGAN DURING PEAK
HEATING...ENOUGH INSTABILITY AND CAPE (UP TO 500 J/KG) TO GENERATE
SCATTERED SHOWERS TODAY...WITH EQL LEVELS EVEN POTENTIALLY SLIPPING
BY 20000 FEET TO GENERATE ISOLATED THUNDERSTORMS...WITH GREATEST
CONCENTRATION OF ACTIVITY ACROSS THE NORTHERN THUMB REGION. FARTHER
SOUTH TOWARD THE OHIO BORDER...MID LEVEL DRY AIR SEEN IN THE WATER
VAPOR IMAGERY AND 700 MB RH FIELDS SHOULD BE SUFFICIENT TO CAP
ACTIVITY...AND SUBSEQUENTLY SHOULD SEE HIGHS SNEAK BACK INTO THE
LOWER 80S FROM DETROIT SOUTH WITH 850 MB TEMPS UP AROUND 12 C.
COOLER 850 MB TEMPS FARTHER NORTH...COUPLED WITH THE ADDITIONAL
CLOUD COVERAGE AND SHOWERS SHOULD HOLD LOCATIONS NORTH OF M-59 IN
THE UPPER 70S. PRETTY GOOD LOW LEVEL COLD ADVECTION THIS
EVENING/TONIGHT WITH 925 MB TEMPS LOWERING INTO THE LOWER
TEENS...AND WITH SURFACE WINDS TRENDING TOWARD CALM...GOOD RADIATORS
SHOULD MAKE A RUN TOWARD 50 DEGREES...ASSUMING THERE IS LITTLE IN
THE WAY OF 5000-6000 KFT CLOUDS LINGERING WITH WEAK 850 MB
FGEN/BAROCLINIC ZONE...OTHERWISE MINS HOLDING IN THE 50S.

LONG TERM...

STRONG ANTICYCLONIC VORTICITY ADVECTION BACKED BY GEOPOTENTIAL
HEIGHT REBOUND WILL PROVIDE A PERFECT SETUP FOR STRONG SURFACE HIGH
PRESSURE OVER THE GREAT LAKES REGION ON WEDNESDAY. MODEL DATA
SUPPORTS THIS NOTION DEPICTING THE CENTER OF THE ANTICYCLONE
SHIFTING FROM THE LAKE MICHIGAN-SUPERIOR AGGREGATE TO THE LAKE
SUPERIOR-HURON AGGREGATE BY 00Z THURSDAY. EVEN THE MOIST-BIASED NAM
IS SHOWING A STRONGLY STABLE COLUMN WITH STRONG STABILITY BETWEEN 5
AND 20 KFT AGL. EXPECTING A HIGH AMOUNT OF INSOLATION AND
THUS...RAISED HIGHS SLIGHTLY WITH MID TO UPPER 70S LIKELY ACROSS
MUCH OF SEMICH. THE EXCEPTION...LOWER 70S...WILL IN BE THE NORTHERN
THUMB WHERE LOCALIZED WINDS OFF OF LAKE HURON WILL LIKELY CAUSE SOME
INLAND PENETRATION OF THE MARINE LAYER.

DAMPENING MIDLEVEL RIDGE AXIS WILL THEN WORK ACROSS SOUTHEASTERN
MICHIGAN WEDNESDAY NIGHT AND THROUGH MUCH OF THE DAY ON THURSDAY.
THE ASSOCIATED ANTICYCLONIC VORTICITY BUBBLE IS SHOWN TO BE OVERHEAD
12Z THURSDAY BEFORE PASSING EASTWARD DURING THE MIDDAY PERIOD. THIS
WILL CAUSE THE REMNANT SURFACE RIDGING TO BEGIN RETREATING EASTWARD
BUT ALL SIGNS ARE IT WILL MAINTAIN CONTROL LOCALLY. IMPRESSIVE
SHORTWAVE IS FORECASTED TO SLIDE ALONG THE OHIO RIVER ON THURSDAY.
MODELS ARE UNAMINOUS IN KEEPING MEASURABLE PRECIPATION WELL SOUTH OF
THE OHIO-MICHIGAN STATELINE. ATTM...MODELS ARE ALSO SHOWING IT TO BE
A REAL STRUGGLE IN BRINGING THE HIGH CLOUD CANOPY THIS FAR
NORTHWARD. THERE IS A BIG DIFFERENCE BETWEEN THE NAM AND OTHER
SOLUTIONS...WITH THE NAM DEVELOPING A WEAK LOWER TROPOSPHERIC
FRONTAL BOUNDARY OVER THE NORTHERN CWA AS DIFFERENTIAL FLOW DEVELOPS
WITH A SECONDARY SURFACE HIGH NOSING SOUTHWARD DOWN NORTHERN LAKE
HURON. WITH ENHANCED CONVERGENCE ALONG THIS BOUNDARY THE NAM IS MORE
THAN WILLING TO PRODUCE PRECIPIATION ALONG IT BY THE AFTERNOON
HOURS. THERE IS A NON-ZERO POTENTIAL WITH SOME SUPPORT FROM VERY
WEAK BROAD MID TO UPPER LEVEL DEFORMATION FORCING. HOWEVER...
CONFIDENCE IS WAY TOO LOW TO JUMP ON THIS SOLUTION AND WILL MAINTAIN
A DRY FORECAST. ANY SATURATION WITHIN THE NAM BUFR SOUNDINGS IS FAR
FROM IMPRESSIVE. BUMPED HIGHS AGAIN UPWARD INTO THE UPPER 70S MOST
AREAS...COOLER AGAIN NEAR THE LAKESHORE.

MARINE...

WHILE HEADLINES ARE NOT EXPECTED OVER THE NEXT FEW DAYS OVER LAKE
HURON...A RATHER STRONG UPPER LOW FOR THIS TIME OF YEAR WILL REMAIN
DISPLACED SOUTH OF HUDSON BAY ALLOWING SEVERAL SHOTS OF COOLER AIR
WITH ACCOMPANYING GUSTY NORTH TO NORTHWEST WINDS IN THE WAKE OF THE
PASSING COLD FRONTS. THIS SETUP WILL YIELD SCATTERED SHOWERS AND A
FEW THUNDERSTORMS AGAIN TO MAINLY LAKE HURON THIS AFTERNOON AND
EVENING. A SECONDARY COLD FRONT WILL BRING SLIGHTLY STRONGER WINDS
WITH GUSTS IN THE 25 KNOT RANGE TODAY. WHILE THIS SYSTEM MAY BRING
CONDITIONS APPROACHING SMALL CRAFT ADVISORIES...THE DUE WESTERLY
TRAJECTORY WILL KEEP THE FETCH UNFAVORABLE FOR THE NEARSHORE AREAS
ALONG SOUTHEASTERN MICHIGAN. WINDS WILL THEN SLOWLY DECREASE ON
WEDNESDAY AS A HIGH PRESSURE SYSTEM APPROACHES WITH A LIGHT AND
VARIABLE WIND FIELD ON THURSDAY AS THIS HIGH BUILDS OVER THE REGION.

&&

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

$$

AVIATION.....DRK
SHORT TERM...SF
LONG TERM....CB
MARINE.......CB


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


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