Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 121104
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
704 AM EDT FRI SEP 12 2014

.AVIATION...

//DISCUSSION...

METAR DATA AND RADAR IMAGERY HAS QUIETED DOWN THIS MORNING WITH
REGARDS TO THE DRIZZLE/LIGHT RAIN THAT IMPACTED ALL OF THE REGION
LAST NIGHT. LATEST SURFACE OBSERVATIONS SUGGEST THE ONLY ACTIVE AREA
REMAINING IS NEAR LAKE HURON WHERE LAKE EFFECT SHOWERS ARE SHOWING
UP ON THE KDTX AND EXETER RADARS. A BACKDOOR LIKE FRONTAL RESPONSE
IS FORECASTED TO OCCUR WHICH SHOULD PUSH MUCH OF THE DEVELOPED AND
SATURATED CLOUD ONSHORE ACROSS THE THUMB. THE NEXT SYSTEM IS SET TO
IMPACT SOUTHEASTERN MICHIGAN TONIGHT. FORCING AND MOISTURE APPEAR TO
BE WELL IN PHASE...WHICH INCREASES CONFIDENCE IN THE EVENT. TIMING
DIFFERS WITH EARLIER ONSET NORTH...LATER TIMING SOUTH.
NEVERTHELESS...EXPECTATIONS ARE FOR MVFR TO IFR CIGS/VSBYS.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FEET DURING THE TAF PERIOD.

&&

.PREV DISCUSSION...ISSUED 401 AM EDT FRI SEP 12 2014

SHORT TERM...TODAY AND TONIGHT

THE EQUATERWARD SETTLING OF THE UPPER LEVEL JET AXIS FORCED THE MAIN
BAROCLINIC ZONE WELL SOUTH OF THE OHIO RIVER OVERNIGHT. THIS HAS
PROMOTED INCREASED SURFACE RIDGING LOCALLY OVER SOUTHEASTERN
MICHIGAN WITH STOUT COLD AIR ADVECTION RESULTING IN THE LOWER
TROPOSPHERE. THE CAA HAS PROVIDED ADDITIONAL REINFORCEMENT FOR THE
SHARP INVERSION CENTERED AT 4800 FT AGL PER DTX RAOB ALONG WITH THE
ASSOCIATED THICK STRATUS DECK THAT IS IN PLACE OVER THE ENTIRE
REGION. SURFACE OBSERVATIONS AND RADAR HAS SHOWN DRIZZLE ACTIVITY
PUSHING SOUTHWARD WHICH HAS BEEN FAIRLY HEAVY AT TIMES HERE AT THE
WHITE LAKE OFFICE. A SHALLOW STEEP LAPSE RATE POCKET HAS BEEN
RESOLVED BY THE MODELS JUST UNDER THE BASE OF THE INVERSION WHICH IS
EXPECTED TO PERSIST THROUGH DAYBREAK. SEE NOTHING IN THE
OBSERVATIONS TO SUGGEST THE POTENTIAL FOR DRIZZLE WILL NOT CONTINUE
EARLY THIS MORNING.

A CENTROID OF SURFACE HIGH PRESSURE IS FORECASTED TO SPREAD EAST
ACROSS CANADA EARLY THIS MORNING...BECOMING CENTERED NNE OF THE
GEORGIAN BAY BY 18Z. WITH THE LOCALIZED SFC HIGH PRESSURE MAXIMUM
SPREADING WEST TO EAST...SURFACE WINDS ARE EXPECTED TO VEER TO THE
NORTHEAST OUT OVER THE SOUTHERN BASIN OF LAKE HURON. THIS WILL ALLOW
FOR A WEAK BACKDOOR FRONTAL RESPONSE...PUSHING A ZONE OF CONVERGENCE
INTO THE THUMB DURING THE LATE MORNING HOURS. FOR THE
FORECAST...TRANSITIONED THE LIGHT SHOWER CHANCES TO AREAS ADJACENT
TO LAKE HURON TO ACCOUNT FOR THE LOCALIZED CONVERGENCE BOUNDARIES.
FARTHER INLAND/SOUTH...DAYTIME HEATING WILL ALLOW MIXING DEPTHS TO
LIFT WHICH WILL ERODE THE PRECIPITATION GENERATING LAYER.

THE VERY POSITIVELY TILTED UPPER LEVEL TROUGH HANGING BACK ACROSS
THE DAKOTAS WILL EJECT QUICKLY EASTWARD TODAY...ENDING AT A NEUTRAL
TILT DIRECTLY OVER SOUTHEASTERN MICHIGAN BY 12Z SATURDAY. THIS WILL
BE IN RESPONSE TO STRONG UPPER LEVEL JET FORCING AS A TRAILING
STRONG JET MAXIMUM LIFTS NORTHEASTWARD TOWARD THE STATE. ACROSS THE
BOARD...DEEP COLUMN SUPPORT FOR ASCENT IS FORECASTED TO BE VERY
STRONG LATE IN THE PERIOD. GREATEST FORCING WILL COME THE LATTER
HALF OF TONIGHT IN THE FORM OF CYCLONIC VORTICITY ADVECTION. STRONG
POSITIVE TO NEUTRAL TO NEGATIVE TILTING EVENT IS SHOWN TO INCREASE
1000-500MB HEIGHT FALLS OVER THE STATE WHICH WILL CAUSE A
SUBSTANTIAL DESTABILIZATION OF THE MIDLEVELS. LOW LEVEL CONVERGENCE
IS EXPECTED TO ORGANIZE RAPIDLY WITH EVEN A CYCLOGENESIS EVENT
COMMENCING OVER WESTERN LAKE ERIE AT THE END OF THE PERIOD. THE
OMEGA PROFILE IN BUFR SOUNDINGS IS IMPRESSIVE ALONG WITH THE DEPTH
OF MOISTURE. THE POTENTIAL FOR WIDESPREAD PRECIPITATION WILL INCREASE
AFTER 21Z FOR THE SAGINAW VALLEY/TRI CITIES AS REMNANTS OF EARLIER
LOW LEVEL CONVERGENCE IS ADVECTED INLAND AWAY FROM LAKE HURON AND
THE LEAD EXTENSION OF FGEN/DEFORMATION BEGINS TO SPREAD OVER
WESTERN/CENTRAL LOWER MICHIGAN FROM THE SOUTHWEST. THE BEST OF THE
FORCING IS EXPECTED TO ALIGN THEN TONIGHT OVER THE NORTHERN 1/2 OF
THE CWA CLOSER TO THE MIDLEVEL CIRCULATION AND MIDLEVEL CONVERGENCE
AND DEFORMATION. PRECIPITATION CHANCES WILL THEN INCREASE RAPIDLY
AFTER 8Z FOR THE SOUTHERN CWA WITH THE WARM WATERS OF LAKE ERIE
SPARKING OFF THE SURFACE LOW. THIS REDISTRIBUTION OF THE HEIGHT
FALLS WILL CAUSE THE BETTER DEFORMATION TO FILL IN OVER THE
SOUTHEASTERN CWA AFTER 9Z. WENT CATEGORICALS WITH THE RAIN CHANCES
TONIGHT...WITH .1 TO .5 OF QPF POSSIBLE...HIGHEST NORTH.

LONG TERM...SATURDAY THROUGH THURSDAY

PREVAILING NORTHWESTERLIES ANCHORED ACROSS NORTHWEST CANADA WILL
LARGELY RETAIN BROAD TROUGHING ACROSS MUCH OF THE NORTH-CENTRAL
CONUS THROUGH THE MIDDLE OF NEXT WEEK.  THE PERSISTENCE OF THIS
SUPPRESSED HEIGHT FIELD AND MODESTLY ACTIVE/PROGRESSIVE FLOW WILL
ENSURE A COOLER PERIOD OF WEATHER EXISTS ACROSS THE GREAT LAKES
THROUGH THIS TIME.  THIS PATTERN WILL YIELD A COUPLE OF QUICK SHOTS
OF RAINFALL BUT GENERALLY LOOKING AT A DRY STRETCH.

STRONG MID LEVEL WAVE WORKING THROUGH THE MEAN FLOW WILL BE EXITING
TO THE EAST TO START THE PERIOD EARLY SATURDAY.  OVERALL TIMING
SUGGESTS SOME RESIDUAL FORCING AND ADEQUATE MOISTURE WILL SUPPORT A
LINGERING TAPERED POP FROM WEST TO EAST...GREATEST PROBABILITY AND
LONGER DURATION ACROSS THE EASTERN TIER THROUGHOUT THE MORNING
HOURS.  STRONG MID LEVEL SUBSIDENCE WITH STEADY DRY AIR ADVECTION IN
THE WAKE OF THIS SYSTEM BY MIDDAY.  PARTIAL LATE DAY INSOLATION WILL
NUDGE HIGHS TOWARD THE LOWER 60S...OR A GOOD 10+ DEGREES BELOW MID
SEPTEMBER NORMS.

HIGH PRESSURE TAKES FIRM RESIDENCE FOR THE REMAINDER OF THE WEEKEND
AS THE MEAN FLOW TEMPORARY FLATTENS IN ADVANCE OF THE NEXT HEIGHT
FALL CENTER.  THIS WILL YIELD PLENTY OF CLEAR SKY AS STABLE
ANTICYCLONIC FLOW RETAINS A DEEP DRY LAYER.  SIMPLE AIRMASS
MODIFICATION FOR SUNDAY GIVEN THE HIGH DEGREE OF SUN AND LIMITED
THERMAL ADVECTION...HIGHS INTO THE MIDDLE 60S.  FAVORABLE
RADIATIONAL COOLING ENVIRONMENT...PARTICULARLY SATURDAY NIGHT AS THE
HIGH SETTLES OVERHEAD.  925 MB TEMPERATURES BELOW 6C POINT TOWARD
SOME THE COLDEST LOCALES MAKING A RUN INTO THE UPPER 30S SUNDAY
MORNING.

NEXT FAST MOVING NORTHERN STREAM WAVE TRANSLATES THROUGH ON MONDAY.
DEFINED WINDOW OF MID LEVEL ASCENT ATTENDANT TO THIS WAVE AND SOME
UPPER JET SUPPORT WILL BRING THE NEXT CHANCE OF SHOWERS WITHIN THE
MONDAY AND MONDAY NIGHT PERIOD.  THE NEXT LOW LEVEL ANTICYCLONE
QUICKLY BUILDS IN BEHIND THIS WAVE FOR MIDWEEK.  RENEWED DEEPER
NORTHWEST FLOW AND A PERIOD OF MODEST COLD AIR ADVECTION WILL
REINFORCE THIS COOLER AIR MASS DURING THIS TIME...850 MB
TEMPERATURES LOCKED IN THE MID SINGLE DIGITS.

MARINE...

MODEST NORTHEAST FLOW WILL REMAIN ACROSS THE REGION TODAY.  GUSTS
MAY BRIEFLY PEAK IN THE 20 KNOT RANGE THIS AFTERNOON...PARTICULARLY
ACROSS SAGINAW BAY.  THERE REMAINS THE POTENTIAL FOR WATERSPOUTS
ACROSS SOUTHERN LAKE HURON AND SAGINAW BAY THIS MORNING GIVEN A
FAVORED ENVIRONMENT FOR PERSISTENT LAKE EFFECT SHOWERS.  WIDESPREAD
SHOWERS TONIGHT UNDER GUSTY NORTHEAST WINDS AS LOW PRESSURE TRACKS
THROUGH THE OHIO VALLEY.  DESPITE THE PERSISTENT ONSHORE
FLOW...SMALL CRAFT CONDITIONS ARE NOT EXPECTED AT THIS TIME.  WINDS
VEER TO NORTHWESTERLY AND REMAIN GUSTY IN THE WAKE OF THIS SYSTEM ON
SATURDAY.  WINDS WILL EASE SATURDAY NIGHT WITH HIGH PRESSURE
BUILDING IN.   LIGHT SOUTH TO SOUTHWEST FLOW AS HIGH PRESSURE DRIFTS
THROUGH ON SUNDAY.

&&

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

&&

$$

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

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




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