Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 131650
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1250 PM EDT SAT SEP 13 2014

.AVIATION...

//DISCUSSION...

PERSISTENT MVFR CEILINGS WILL CONTINUE TO SLOWLY LIFT. PLENTY OF
CLOUD RE-ENFORCEMENTS UPSTREAM ACROSS NORTHERN LOWER MICHIGAN WILL
HELP MAINTAIN COVERAGE THROUGH THE BALANCE OF THE AFTERNOON...
HOWEVER CEILINGS WILL CONTINUE TO DRIFT UPWARD. EXPECTATIONS ARE FOR
THE CLOUDS TO THIN THROUGH THE EVENING HOURS...BUT CONFIDENCE IN
COMPLETE DISSIPATION IS LESS THAN PREVIOUSLY ADVERTISED. LOOKING
LIKE DIURNAL CLOUD DEVELOPMENT WILL HAPPEN SUNDAY...COMMENCING BY
LATE MORNING. OTHERWISE...MARGINALLY GUSTY NORTHWEST WINDS WILL
TEMPER THROUGH THE AFTERNOON ONCE TEMPERATURES STABILIZE AROUND
DAYTIME MAXES. WINDS WILL RELAX SUBSTANTIALLY AFTER SUNSET.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET THROUGH THIS AFTERNOON.
* MODERATE CONFIDENCE IN CEILINGS BELOW 5000 FEET SUNDAY AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 401 AM EDT SAT SEP 13 2014

SHORT TERM...TODAY AND TONIGHT

08-12Z SAT...THE VIGOROUS VORTICITY MAXIMUM AS OF 7Z IS CENTERED
DIRECTLY OVER NORTHEASTERN WISCONSIN. IMPRESSIVE DRY SLOT FEATURE IS
CURRENTLY UNDERCUTTING THE CIRCULATION ALREADY PUNCHING ONSHORE OF
WESTERN LOWER MICHIGAN. TDTW Z LOOP THIS MORNING IS AWESOME IN
SHOWING NEAR SURFACE LAKE ERIE MOISTURE BEING VAULTED NORTHWESTWARD
AHEAD OF THE INBOUND LOW...WITH RAPID SATURATION OF MOISTURE DOWN
LOW. KDET OBSERVATIONS LINES UP PREFECT TO RECENT Z IMAGE WITH
CEILINGS DOWN TO 800 FT WITH RAIN. THE NAM SOLUTION HAS BEEN SPOT ON
SO FAR...AND SHOWS THIS MOISTURE ADVECTING STRAIGHT NORTHWARD DURING
THE NEXT FEW HOURS EVENTUALLY CONTRIBUTING TO A RAPIDLY ORGANIZING
TROWAL STRUCTURE. EXPECT RAIN TO NOW FILL IN OVER ALL AREAS
ESPECIALLY FROM THE DETROIT METRO AREA STRAIGHT NORTHWARD THROUGH
THE THUMB. LESSER AMOUNTS ARE ANTICIPATED FOR LOCATIONS SOUTH OF
M59. QPF IS STILL EXPECTED TO RANGE FROM .1 SOUTH TO .75 OF AN INCH
FOR THE TRI CITIES WHERE .5 HAS ALREADY FALLEN.

12-18Z SAT...SHORT RADIUS OF CYCLONIC CIRCULATION WILL LEAD TO
ALMOST INSTANTANEOUS SYSTEM RELATIVE ISENTROPIC DESCENT FOR ALL
AREAS EXCEPT THE EASTERN THUMB AND SOUTHERN LAKE HURON BASIN. MODELS
ARE PROGGING VERY STRONG SUBSIDENCE IN THE WAKE OF THE CYCLONIC
CIRCULATION WITH THE SIGNALS VERY CLEAR...300K ISENTROPIC
DOWNGLIDE...SUBSIDENCE INVERSION STRUCTURE...MEAN RH. CLOUDS MAY
SCATTER OUT FOR A TIME...BUT THE RESPONSIBLE FORECAST IS TO KEEP
THEM HANGING TOUGH DURING THE MORNING...WITH MOISTURE SUB 3500 FT
DIFFICULT TO SCOUR OUT BELOW A DEVELOPING INVERSION.

18-00Z SAT...HIGH AMBIENT MOISTURE AND DAYTIME HEATING WILL ALLOW
CLOUDS TO EITHER REDEVELOP OR TRANSITION INTO CUMULOFORM. WITH
MATURITY OF THE PBL LATE SUSPECT THAT DEEPENING CLOUD SCALE
SUBSIDENCE INTRODUCED BY CONVECTIVE CIRCULATIONS WILL LEAD TO
GROWING HOLES IN THE DECK LATE. THE ADDED SUBSIDENCE AND DRY AIR
ENTRAINMENT WILL THEN AID A SETTING SUN IN CLEARING OUT SKIES.

00-12Z...THE CENTER OF SURFACE HIGH PRESSURE WILL PUSH RAPIDLY
EASTWARD ACROSS THE STATE. CLEAR SKIES...LIGHT WINDS AND A STABLE
AIRMASS WILL LEAD TO IDEAL RADIATIONAL COOLING CONDITIONS. MOS
GUIDANCE CAME IN QUITE COLD FOR TONIGHT WITH LOWS (13 TO 17 DEGREES
BELOW NORMAL) AND HAD NO QUALMS PUSHING THE FORECAST IN THIS
DIRECTION. LOWS OUTSIDE OF THE HEAT ISLAND ARE EXPECTED TO DROP INTO
THE 30S WITH MID 30S LIKELY IN THE THUMB. ADDED A PATCHY FROST
MENTION BUT WILL LEAVE THE DAYSHIFT FLEXIBILITY WITH REGARDS TO ANY
POSSIBLE FROST HEADLINES.

LONG TERM...SUNDAY THROUGH FRIDAY

1028 MB SURFACE HIGH CENTERED JUST TO THE EAST SUNDAY MORNING WILL
DRIFT TOWARD THE EAST COAST THROUGH THE LATTER HALF OF THE WEEKEND.
LIGHT SOUTHWEST RETURN FLOW WILL EMERGE ALONG THE BACKSIDE DURING
THE DAY...PROVIDING JUST A SLIGHT BOOST TO OUR SLOWLY MODERATING
RESIDENT SEASONABLY COOL AIR MASS.   STEADY MID LEVEL SUBSIDENCE AND
A DEEP DRY LAYER WILL ENSURE PLENTY OF SUN...ALLOWING HIGHS TO TAKE
AN INCREMENTAL JUMP INTO THE LOWER/MIDDLE 60S.  THICKENING CIRRUS
SHIELD WILL SPILL INTO THE REGION SUNDAY NIGHT DOWNSTREAM OF THE
NEXT INBOUND NORTHERN STREAM SHORTWAVE.  THIS COMBINED WITH THE
PERSISTENT LOW LEVEL SOUTHWEST GRADIENT WILL CONTAIN LOWS IN THE MID
TO UPPER 40S...LOWER 50S WITHIN THE DETROIT HEAT ISLAND.

MID LEVEL WAVE WILL SWEEP ACROSS SOUTHEAST MICHIGAN MONDAY EVENING.
FORCING WILL STRENGTHEN WITH TIME THROUGHOUT MONDAY AS FAVORABLE
UPPER JET FORCING AUGMENTS THE UPTICK IN CYCLONIC VORTICITY
ADVECTION AND LOW LEVEL FRONTAL CONVERGENCE.  GREATEST WINDOW FOR
SHOWER DEVELOPMENT WILL CENTER ON THE AFTERNOON AND EVENING HOURS.
ASSUMING A PERIOD OF MODEST THERMAL RECOVERY IN ADVANCE OF THIS
MOISTURE...HIGHS WILL AGAIN ARRIVE IN THE LOWER AND MIDDLE 60S.

A COOL AND STABLE PATTERN EVOLVES IN THE WAKE OF THIS SYSTEM FOR
THE MIDWEEK PERIOD.  HIGH PRESSURE WILL STEADILY BUILD INTO THE
REGION ON TUESDAY...ALONG THE EDGE OF THE MAIN CORRIDOR OF MID LEVEL
HEIGHT FALLS STREAMING ACROSS SOUTHERN CANADA.  A PERIOD OF COLD AIR
ADVECTION MONDAY NIGHT AND EARLY TUESDAY WILL SHAVE 2-3 DEGREES OFF
THE LOW LEVEL THERMAL PROFILE.  THIS WILL AGAIN CONTAIN HIGHS IN THE
LOWER AND MIDDLE 60S DESPITE THE HIGH DEGREE OF INSOLATION.  WEAK
COLD FRONT ATTENDANT TO THE AFOREMENTIONED HEIGHT FALLS WILL SETTLE
ACROSS THE REGION TUESDAY NIGHT.  LIMITED AVAILABLE MOISTURE AND
WEAK FRONTAL FORCING WILL LEAVE JUST A PERIOD OF THICKER MID CLOUD
WITH THE PASSAGE OF THIS FEATURE.  THIS FRONTAL PASSAGE WILL AGAIN
REINFORCE THIS COOLER AIR MASS AS ANOTHER STRONG LOW LEVEL
ANTICYCLONE TAKES HOLD.  THIS CONTINUES TO POINT TOWARD A
PERPETUATION OF BELOW NORMAL TEMPERATURES RIGHT THROUGH THE END
OF THE WORK WEEK.

MARINE...

A NORTH TO NORTHEAST WIND THIS MORNING WILL SHIFT TO
NORTHWESTERLY TODAY AS DEVELOPING LOW PRESSURE LIFTS FROM LAKE
ERIE TOWARD SOUTHERN QUEBEC.  THIS WILL RESULT IN MARGINAL SMALL
CRAFT CONDITIONS FOR GUSTY WINDS ACROSS THE SOUTHERN LAKE HURON
BASIN THROUGH THIS AFTERNOON.   EXTENSIVE AREA OF SHOWERS TRACKING
ACROSS THE REGION THIS MORNING WILL BRING A CHANCE FOR WATER
SPOUTS.  STRONG HIGH PRESSURE BUILDING IN FROM THE WEST WILL RAPIDLY
REDUCE WINDS AND WAVES ON THE LAKES BY EARLY THIS EVENING. THIS
HIGH WILL MAINTAIN LIGHT WINDS THROUGH SUNDAY. A WEAK COLD FRONT
TRACKING ACROSS THE REGION ON MONDAY WILL BRING THE NEXT CHANCE OF
SHOWERS. HIGH PRESSURE TAKES CONTROL AGAIN BY MIDWEEK.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING OUTER SAGINAW BAY...UNTIL 4 PM SATURDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...
     SMALL CRAFT ADVISORY...UNTIL 4 PM SATURDAY.

&&

$$

AVIATION.....MANN
SHORT TERM...CB
LONG TERM....MR
MARINE.......MR


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