Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181121
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
721 AM EDT THU SEP 18 2014

.AVIATION...

//DISCUSSION...

LOW STRATUS GRADUALLY EXPANDING SOUTHWARD IN THE WAKE OF A COLD
FRONTAL PASSAGE THIS MORNING.  CEILINGS LARGELY IN MVFR...ALTHOUGH A
NARROW STRIP IFR WILL EXIST ALONG THE LEADING EDGE.  THIS IFR MAY
BRIEFLY IMPACT PTK YET THIS MORNING.  OBSERVATIONAL EVIDENCE POINTS
TOWARD MVFR CONDITIONS BEING COMMON THROUGH THE FIRST HALF OF THE
DAY AT MBS/FNT.  CEILINGS WILL GRADUALLY LIFT THIS AFTERNOON UNDER
DIURNAL HEATING.

FOR DTW...LOWER CLOUDS WILL ADVANCE INTO THE TERMINAL VICINITY JUST
AS DIURNAL HEATING TAKES A STRONGER FOOTHOLD LATE THIS MORNING.
THIS MAY INITIALLY LIMIT THE OVERALL COVERAGE OF CEILINGS AT MVFR
LEVELS.  THERE WILL BE SOME DEGREE OF DIURNAL CU DEVELOPMENT BY
MIDDAY...LIKELY IN LOWER VFR.

//DTW THRESHOLD THREATS...

* LOW CONFIDENCE IN CEILINGS BELOW 5000 FT THIS MORNING...MEDIUM
CONFIDENCE THIS AFTERNOON.

&&

.PREV DISCUSSION...ISSUED 350 AM EDT THU SEP 18 2014

SHORT TERM... TODAY AND TONIGHT

EMERGING LIGHT NORTHEAST LOW LEVEL FLOW TAKES HOLD TODAY IN THE WAKE
OF A WEAK COLD FRONT THAT EXITS TO THE SOUTH THIS MORNING.  STEADY
MOISTURE ADVECTION WITHIN THE DEVELOPING WEAK COLD AIR ADVECTION AND
TUCKED BENEATH THE ATTENDANT INVERSION WILL LEAVE A BROAD CANOPY OF
LOW STRATUS/STRATOCU IN PLACE THROUGH THE HALF OF THE DAY FOR POINTS
NORTH OF THE M-59 CORRIDOR.  LOW LEVEL MOISTURE PROFILE NOT
NEARLY AS SATURATED TOWARD THE SOUTH...WHERE DAYTIME MIXING WILL
TAKE A STRONGER FOOTHOLD EARLY ON.  THIS WILL ALLOW FOR A BIT MORE
INSOLATION UNDER A HIGHER DEGREE OF SUN.  THIS IN CONJUNCTION WITH
THE OVERALL PLACEMENT OF A RATHER TIGHT 925 MB THERMAL GRADIENT WILL
YIELD A LARGER DISTRIBUTION IN HIGHS FROM SOUTHWEST TO NORTHEAST
TODAY.  MAXIMUM TEMPERATURES WILL RANGE FRMO THE MID 60S NEAR THE
OHIO BORDER TO MID 50S IN THE THUMB.

MODEL 925/850 MB RH FIELDS AND SOUNDING DATA POINT FAVORABLY TOWARD
SEEING A CLEARING SKY WITH THE LOSS OF HEATING THIS EVENING.  IT
DOES REMAIN PLAUSIBLE FOR SOME DEGREE OF RENEWED STRATUS TO FILL IN
LATE TONIGHT UNDER STRONG NOCTURNAL COOLING AS THE FLOW SHIFTS TO
SOUTHWESTERLY AND DEWPOINT DEPRESSIONS SHRINK.  LOWER CONFIDENCE IN
THIS SCENARIO...AND WILL CONTINUE TO LEAN MORE OPTIMISTIC WITH A
LONGER DURATION OF MOSTLY CLEAR SKIES PROVIDING A FAVORABLE
RADIATIONAL COOLING ENVIRONMENT.  LOWS FROM MID 30S NORTH TO LOWER
40S SOUTH.

LONG TERM...FRIDAY THROUGH TUESDAY

THE STABLE ANTICYCLONE WILL RETREAT TO NEW ENGLAND ON FRIDAY WITH A
SURFACE RIDGE AXIS HANGING BACK ACROSS LOWER MICHIGAN. WESTERLY
RETURN FLOW WILL DEVELOP WITH TIME AS THE PRESSURE GRADIENT
INCREASES SUBSTANTIALLY OVER PORTIONS OF THE WESTERN GREAT LAKES.
HOWEVER...HERE IN SOUTHEASTERN MICHIGAN SURFACE TRAJECTORIES WILL
REMAIN DECIDEDLY SOUTHEASTERLY WHICH WILL MAINTAIN A BONE DRY
ATMOSPHERIC COLUMN. TEXTBOOK DEEP COLUMN SUBSIDENCE. THERE WILL
LIKELY BE SOME CUMULUS DEVELOPMENT FOR THE AFTERNOON...BUT
EXPECTATIONS ARE FOR SUN SPLASHED SKIES. MIXING HEIGHTS ARE SOMEWHAT
MUTED IN THE DRY AIRMASS...SQUASHED BY THE SUBSIDENCE...BUT
TEMPERATURES SHOULD BENEFIT FROM INSOLATION TO REACH THE UPPER 60S
FOR MANY AREAS.

MODEL DATA IS SUGGESTING THAT A PIECE OF UPPER LEVEL JET ENERGY WILL
BREAK OFF OF THE SOUTHWESTERN PV ANOMALY AND CREST THE RIDGE AHEAD
OF THE MAIN ENERGY THAT WILL BE CRASHING INTO THE PACIFIC NORTHWEST.
MODEL EVOLUTION HAS THIS LEAD JET ENERGY PUSHING EASTWARD AHEAD OF
THE MAIN ENERGY PLOW...UNDERGOING A DOWNSTREAM RESPONSE TO THE
HEIGHT FALLS EMERGING OVER CENTRAL CANADA. THIS JET ENERGY FALLS
INTO LOWER MICHIGAN AS A SHORTWAVE RIDGE STRUCTURE FLASHES WAY
EASTWARD. THUS...THE MODELS DO SUPPORT SOME DEEPER PACIFIC MOISTURE
MAKING INTO SOUTHEASTERN MICHIGAN TO KICK OFF THE POPS. THE PROBLEM
IS AND IT IS A BIG PROBLEM IS OVERALL DEPTH AND QUALITY OF MOISTURE.
TO PUT IT BLUNTLY THERE ARE GOING TO BE MAJOR MOISTURE ISSUES.
MODELS ARE NOW IN AGREEMENT THAT ANY TROPICAL MOISTURE FROM ODILE
WILL REMAIN BOTTLED UP OVER TEXAS AND NEW MEXICO WHILE ANY GOMEX
FEED IS COMPLETELY NON EXISTENT. SO...THE ONLY MOISTURE SOURCE IS
WHAT THE SYSTEM ITSELF WILL CARRY OVER FROM THE PACIFIC. INITIALLY
WITH THIS BREAKOFF ENERGY TO BEGIN THINGS...NOT EXPECTING MUCH OF
ANY PRECIPITATION POTENTIAL FRIDAY NIGHT AND FOR A GOOD PORTION OF THE
DAY ON SATURDAY. A FEW LOCATIONS WILL SEE SOME HYDROMETEORS GIVEN
THE OUTSTANDING WARM AIR ADVECTION SUPPORT...BUT DRY AIR IN THE
LOWEST 10 KFT TEMPERS THINGS.

THE MAIN PV ANOMALY AND UPPER LEVEL JET SURGE WILL PUSH INTO THE
GREAT LAKES BY SATURDAY AFTERNOON. THIS PUSH WILL CAUSE THE MAIN
SURGE OF THETA E ADVECTION INTO SOUTHEASTERN MICHIGAN SATURDAY
AFTERNOON. BEST CVA WILL LAG BY ROUGHLY 6 HOURS...SO BEST
PRECIPITATION POTENTIAL SHOULD LINGER WELL INTO SATURDAY NIGHT BEFORE
A COLD FRONT OR MAIN THETA E CONTENT IS PUSHED SOUTH OF THE CWA.
GIVEN PACIFIC ORIGIN WITHOUT ANY EML PUSH OR GOMEX CONNECTION LAPSE
RATES ARE FORECASTED TO BE PITIFUL. FOR NOW WILL BE LEAVING THUNDER
OUT OF THE FORECAST WHILE KEEPING POPS IN THE CHANCE CATEGORY.
SUNDAY DRIES OUT POSTFRONTALLY...ALTHOUGH TYPICAL BOUNDARY LAYER
CLOUD SHOULD PERSIST IN CAA REGIME. HIGHS ON SATURDAY SHOULD REACH
THE MIDDLE TO UPPER 70S...WHILE HIGHS SUNDAY FALL BACK INTO THE
UPPER 60S/LOW 70S.

MARINE...

WINDS HAVE RESPONDED UNIFORMLY OUT OF THE NORTH NORTHEAST IN THE
WAKE OF A COLD FRONT THAT ROCKETED SOUTHWARD THROUGH SOUTHEASTERN
MICHIGAN LAST NIGHT. SUSTAINED WINDS OF 15 TO 20 KNOTS HAVE BEEN
COMMONPLACE. SMALL CRAFT ADVISORIES REMAIN IN EFFECT THIS MORNING
FOR THE NEARSHORE WATERS OF LAKE HURON INCLUDING SAGINAW BAY.
SURFACE HIGH PRESSURE WILL CAUSE WINDS TO BECOME CALM TONIGHT WHILE
ALLOWING WAVES TO SUBSIDE. THE LULL WILL BE FAIRLY SHORTLIVED AS
SOUTHWESTERLY FLOW WILL INCREASE FRIDAY NIGHT. THIS WILL BE A GOOD
SOUTHWEST FLOW EPISODE WITH WAVE HEIGHTS OUT OVER CENTRAL LAKE HURON
EXPECTED TO RISE INTO THE 4 TO 6 FOOT RANGE. SMALL CRAFT ADVISORIES
MAY BE NEEDED FOR SAGINAW BAY FRIDAY NIGHT. SOUTHWESTERLY FLOW IS
THEN EXPECTED TO PERSIST SATURDAY AHEAD OF AN APPROACHING COLD FRONT.

&&

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

LAKE HURON...
     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT
     HURON INCLUDING SAGINAW BAY...UNTIL 10 AM THURSDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

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


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