Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 300344
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1144 PM EDT SAT AUG 29 2015


.AVIATION...

CONDITIONS STILL EXPECTED TO STEADILY DETERIORATE THROUGH TONIGHT
INTO EARLY SUNDAY MORNING BY WHICH TIME ALL LOCATIONS WILL BE LOW
MVFR AT BEST WITH A GOOD COVERAGE OF IFR EXPECTED NW OF DETROIT
METRO. LOWEST CIGS/VSBYS WILL BE FOUND ALONG THE SURFACE LOW TRACK
INVOF KMBS/KFNT WHERE CONDITIONS WILL TAKE LONGER TO RECOVER DURING
THE MORNING. BY LATE MORNING, CONCERTED TREND TOWARD MVFR LIFTING TO
VFR CEILING SHOULD BE UNDERWAY. WINDS WILL REMAIN LIGHT THROUGH THE
PERIOD.

FOR DTW...CONDITIONS WILL IMPROVE MOST QUICKLY IN THE DETROIT AREA
FURTHER FROM THE LOW AND WHERE MOISTURE QUALITY IS SLIGHTLY LESS.
CONFIDENCE IN IFR CEILING IS NOT HIGH HERE...BUT SHOULD ONE DEVELOP,
WOULD EXPECT IMPROVEMENT TO MVFR BEFORE NOON.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CIG AOB 5KFT AFTER 08Z.

&&

.PREV DISCUSSION...ISSUED 514 PM EDT SAT AUG 29 2015

UPDATE...

QUICK UPDATE TO GIVE POPS A GENEROUS BUMP UPWARD TO CATEGORICAL
SOUTH OF M59. SHOWERS HAVE SHOWN A MARKED INCREASE IN COVERAGE
OVER THE LAST 60 MINUTES ALONG A LINE FROM CHICAGO TO LANSING
WITHIN THE CORRIDOR OF INCREASED FORCED ASCENT IN THE MID- LEVELS.
QPF WAS GIVEN A CORRESPONDING NUDGE UPWARD TO ANYWHERE FROM A
TENTH TO A QUARTER OF AN INCH THROUGH 2AM. THIS UPDATE IS PURELY
COSEMETIC AS THE INCREASE IN POPS SIMPLY REFLECTS A CONFIRMATION
OF DAY SHIFT REASONING. UPDATED GRIDS/ZONES FORTHCOMING.

PREV DISCUSSION...ISSUED 357 PM EDT SAT AUG 29 2015

SHORT TERM... AFTERNOON AND TONIGHT

SCATTERED TO NUMEROUS COVERAGE OF SHOWERS WILL CONTINUE DURING THE
AFTERNOON AND EVENING. THIS WILL BE THE RESULT OF A WELL ORGANIZED
LARGE SCALE PATTERN SUPPLYING MODERATE FORCING IN A MOIST BUT WEAKLY
UNSTABLE ENVIRONMENT. IR AND WV SATELLITE IMAGERY CONTINUE TO SHOW A
GOOD COMBINATION OF SUPPORT FROM THE RIGHT ENTRANCE REGION OF THE
UPPER JET AND DOWNSTREAM OF THE TROUGH AXIS...INCLUDING AN INFUSION
OF DCVA MOVING THROUGH THE TROUGH FROM IOWA/ILLINOIS/WISCONSIN.
THESE LARGE SCALE FEATURES WILL CONTINUE TO DRIVE LOW TO MID LEVEL
MOISTURE TRANSPORT/ISENTROPIC LIFT WITHIN THE SURFACE TO 850 MB ZONE
OF THE WARM FRONT. MID AFTERNOON RADAR TRENDS DEPICT A CHANCE POP
SCENARIO REFLECTED IN THE FORECAST TOWARD EARLY EVENING. AN INCREASE
IN COVERAGE OF SHOWERS IS THEN EXPECTED FOR THE BULK OF THE EVENING
AS THE UPSTREAM VORTICITY MAX MOVES THROUGH THE TROUGH AXIS...MORE
DUE TO THE EXTRA FORCING THAN ANY ADDED INSTABILITY. THE CLOUDS...
PRE-EXISTING SHOWERS...AND MEAGER MID LEVEL LAPSE RATES WILL ENSURE
EVEN MUCAPE STAYS NEAR OR EVEN UNDER 500 J/KG. THE FORECAST DOES
CARRY AN ISOLATED THUNDERSTORM FOR ANY ELEVATED ACTIVITY THAT
REMAINS POSSIBLE WITHIN THE SURFACE TO 850 MB FRONTAL ZONE BEFORE
THE UPPER TROUGH AXIS SLIDES EASTWARD AFTER MIDNIGHT AND SHOWER
CHANCES DIMINISH.

THE REMAINS OF THE SURFACE WARM FRONT JUST SOUTH OF THE INDIANA/OHIO
BORDER DURING THE EVENING WILL DRIFT NORTHWARD OVERNIGHT. THE FRONT
WILL WEAKEN WITH TIME BUT STILL BE ABLE TO TAP BOUNDARY LAYER
MOISTURE SUPPLYING LOW STRATUS OVER MUCH OF SOUTHERN WISCONSIN/IOWA
AND NORTHERN ILLINOIS. EXPECT AREAS OF FOG WILL ALSO BE LIKELY BY
SUNRISE AS MIN TEMPS SETTLE MOSTLY INTO THE LOWER 60S MATCHING MID
AFTERNOON OBSERVED DEWPOINT ACROSS THE AREA.

LONG TERM...SUNDAY THROUGH FRIDAY

A WEAKNESS IN THE UPPER LEVEL HEIGHT FIELD OR SUBTLE TROUGH AXIS
WILL GRADUALLY EASE EASTWARD OUT OF LOWER MICHIGAN DURING THE FIRST
HALF OF THE DAY ON SUNDAY. THE ABSOLUTE VORTICITY MAXIMUM IS PROGGED
TO BE DIRECTLY OVER PORTIONS OF THE FAR EASTERN CWA AT 12Z WITH
DECREASING DIFFERENTIAL CYCLONIC VORTICITY ADVECTION THEN SET FOR
THE DAYLIGHT HOURS. THE KINEMATIC FIELD OVERHEAD WILL BE WEAK...WITH
LITTLE TO NO TANGIBLE ADVECTION. AS A RESULT...LOOKING AT A WEAK
THETA E DISCONTINUITY OR FRONTAL BOUNDARY TO REMAIN PARKED OVER THE
CENTRAL TO NORTHERN PORTIONS OF THE CWA. THE THETA E RIDGE AXIS IS
FORECASTED TO BECOME SHEARED EASTWARD DURING THE AFTERNOON WITH
DEAMPLIFICATION OF THE FEATURE. THE SUM OF THE PARTS POINTS TO SOME
VERY WEAK FORCING FOR ASCENT OCCURRING IN THE LOW LEVELS ALONG
THIS BOUNDARY WITH A LACK OF FAVORABLE SYNOPTIC SCALE FORCING FOR
ASCENT ALOFT. MODELED THERMODYNAMICS ARE VERY MARGINAL WITH
INSTABILITY OF A FEW HUNDRED J/KG POSSIBLE BY THE AFTERNOON HOURS.

CAMS AND DETERMINISTIC OFFER A SOLUTION THAT ANY WARM AIR
ADVECTION/MOISTURE ADVECTION PRECIPITATION WILL BE SOUTH AND EAST OF
THE CWA AT 12Z. THIS LIMITS THE PRECIPITATION POTENTIAL TOMORROW TO
A ISO-SCT SHOWER DEVELOPMENT THAT MAY GENERATE ALONG THE
AFOREMENTIONED WEAK THETA E DISCONTINUITY. REMOVED PRECIPITATION
MENTION DURING THE MORNING AND WANTED TO COMMUNICATE THE POTENTIAL
FOR THE AFTERNOON. WILL MAINTAIN A MENTION OF THUNDER GIVEN A
SLIGHTLY UNSTABLE COLUMN AND MOISTURE....BUT NO STRONG WEATHER IS
ANTICIPATED. GIVEN HEART OF THETA E RIDGE OVERHEAD...LOOKING AT
HIGHS TOPPING OUT AROUND 80 DEGREES WITH SOME PEAKS OF SUNSHINE
DEVELOPING AS THE DAY PROGRESSES.

AN EXPANDING AND EASTWARD PROGRESSING UPPER LEVEL RIDGE AXIS WILL
THEN ALLOW HEIGHTS TO INCREMENT UPWARD OVER SOUTHEASTERN MICHIGAN
FOR THE BEGINNING OF THIS WEEK. A STRONG UPPER LEVEL RIDGE IS
FORECASTED WITH 500 MB HEIGHTS OF 590 DAM BY MONDAY EVENING. IT IS
APPEARING WITH MORE AND MORE LIKELIHOOD THAT AN EXTENDED RUN OF
ABOVE NORMAL TEMPERATURES WILL BEGIN MONDAY WITH DAYTIME HIGHS
RISING EASILY INTO THE MID TO UPPER 80S.

EXTENDED...ABOVE NORMAL TEMPERATURES WILL BE COMING BACK TO THE
AREA NEXT WEEK AS BROAD UPPER LEVEL RIDGING TAKES HOLD.  MAINLY DRY
CONDITIONS ARE EXPECTED DURING THIS TIME EXCEPT ON WEDNESDAY AS
MODELS ARE ADVERTISING A WEAK WAVE MOVE THROUGH.

MARINE...

BENIGN MARINE WEATHER WILL CONTINUE ACROSS THE GREAT LAKES REGION
THROUGH MUCH OF THE UPCOMING WEEK. A STRONG RIDGE OF UPPER LEVEL
HIGH PRESSURE WILL MAINTAIN LIGHT FLOW AND A GENERAL SOUTHWEST WIND
DIRECTION.

&&

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

$$

AVIATION.....JVC
UPDATE.......BT
SHORT TERM...BT
LONG TERM....CB/SS
MARINE.......CB


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


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