Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 301115
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
715 AM EDT MON MAR 30 2015

.AVIATION...

THERE WILL BE A FEW HOURS OF CLEAR SKY OVER THE TERMINAL CORRIDOR
DURING THE MORNING BEFORE DAYTIME HEATING GENERATES ADDITIONAL HIGH
BASED STRATOCU BY LATE MORNING THROUGH THE AFTERNOON. THE CLOUD
COVER WILL BE GREATER TOWARD MBS AND FNT BUT ALL AREAS WILL
EXPERIENCE ANOTHER WINDY DAY AS GUSTS PUSH 30 KNOTS FROM THE
NORTHWEST THROUGH MOST OF THE AFTERNOON.

THE NEXT LOW PRESSURE SYSTEM WILL APPROACH FROM THE WEST DURING THE
EVENING. THE SMALL BUT INTENSE SYSTEM IS EXPECTED TO TRACK ALONG THE
SOUTHERN MICHIGAN BORDER DURING THE NIGHT. ASSUMING THIS TRACK
HOLDS...THEN PRECIPITATION WILL BE MOSTLY RAIN IN THE DTW AREA...A
MIX OF RAIN AND SNOW AT PTK AND FNT...AND MOSTLY SNOW IN THE MBS
AREA. THE GREATEST POTENTIAL FOR A WET SNOW ACCUMULATION IS IN THE
FNT AND PTK AREA BUT IFR CONDITIONS IN TERMS OF BOTH CEILING AND
VISIBILITY ARE LIKELY ALL AREAS THROUGH SUNRISE TUESDAY BEFORE THE
SYSTEM EXITS EASTWARD.

FOR DTW... WITH VFR IN PLACE...THE MAIN CONCERN TODAY WILL BE
NORTHWEST WIND GUSTING NEAR 30 KNOTS DURING THE LATE MORNING AND
AFTERNOON. AFTER THAT...THE PRECIPITATION FORECAST TONIGHT WILL BE
VERY SENSITIVE TO THE TRACK OF LOW PRESSURE NEAR THE OHIO BORDER
WHICH KEEPS ALL RAIN AND DRIZZLE AT DTW THROUGH SUNRISE TUESDAY.

//DTW THRESHOLD PROBABILITIES...

* HIGH FOR CEILING AOB 5000 FEET TONIGHT AND TUESDAY MORNING.

* MODERATE FOR CROSS WIND THRESHOLD FROM 300 GUSTING 25-30 KTS TODAY.

* MODERATE FOR RAIN AND DRIZZLE AS PRECIPITATION TYPE TONIGHT.

&&

.PREV DISCUSSION...ISSUED 408 AM EDT MON MAR 30 2015

SHORT TERM... TODAY AND TONIGHT

GUSTY NORTHWEST WIND WILL CONTINUE TODAY ON THE HEELS OF YESTERDAY`S
LOW PRESSURE SYSTEM AND COLD FRONT. THE FRONT AND INCOMING SURFACE
HIGH PRESSURE HAVE PACIFIC ORIGIN AND SO EXPECT TEMPERATURES TO
RECOVER EASILY INTO THE 40S ACROSS SE MICHIGAN DURING THE AFTERNOON
WITH A FEW LOWER 50S POSSIBLE NEAR THE OHIO BORDER. THE TEMPERATURE
REBOUND WILL BE AIDED BY DEEP BOUNDARY LAYER MIXING WITHIN THE
RELATIVELY MILD PACIFIC AIR MASS ALONG WITH SOME LATE MARCH
SUNSHINE...AGAIN ESPECIALLY NEAR THE OHIO BORDER.

THE MAIN FORECAST CHALLENGE FOR THE SHORT TERM REMAINS WITH THE NEXT
UPPER WAVE ENTERING THE NORTHERN PLAINS TODAY AND ARRIVING IN THE
GREAT LAKES THIS EVENING. EXPECT THE BASIC SCENARIO TO UNFOLD WITH
THE PACIFIC FRONT CONTINUING EASTWARD THIS MORNING WHILE THE POLAR
FRONT SETTLES THROUGH THE NORTHERN GREAT LAKES DURING THE REST OF
THE DAY. THE NORTHERN PLAINS WAVE WILL THEN LATCH ON TO THE TRAILING
PORTION POLAR FRONT OVER THE UPPER MIDWEST DURING THE AFTERNOON AND
EVENING AND FLARE UP A PATTERN OF PRECIPITATION OVER SOUTHERN LOWER
MICHIGAN AS IT SLIDES ALONG THE SOUTHERN MICHIGAN BORDER THROUGH
TONIGHT. EXPECT THIS TO RESULT IN A SHARP RAIN/SNOW LINE IN OUR AREA
ROUGHLY ALONG THE M-59 CORRIDOR WITH A WET 1-2 INCH ACCUMULATION TO
THE NORTH AND ALL RAIN TO THE SOUTH EXCEPT FOR A MIX IN THE
DETROIT AREA JUST BEFORE TAPERING OFF AFTER SUNRISE.

THE PRECIP TYPE AND AMOUNT FORECAST WILL BE VERY SENSITIVE TO THE
PRECISE TRACK OF THE SYSTEM ON WHICH THE LATEST MODEL CYCLE
CONTINUES TO OFFER A WIDE SPREAD. THE BEST ASSESSMENT AT THIS POINT
SUGGESTS THE ECMWF IS TOO FAR SOUTH CONSIDERING HOW MUCH WARM AIR
WILL BE IN PLACE AHEAD OF THE SYSTEM AND THE APPARENT DEPENDENCE ON
THE POLAR BAROCLINIC ZONE FOR THE WAVE TO INTENSIFY. AT THE SAME
TIME...THE NAM CONTINUES TO EXHIBIT TOO STRONG A CORRELATION BETWEEN
THE TRACK OF THE SURFACE LOW AND THE MEAN LAYER VERTICAL MOTION
FIELD AHEAD OF THE WAVE. THERE WILL...NO DOUBT...BE A STRONG
VERTICAL MOTION RESPONSE DUE TO OUTSTANDING FRONTOGENESIS AND
DYNAMIC SUPPORT. THE GFS MAY HAVE THE BEST IDEA IN MAINTAINING A
MORE LINEAR VERTICAL MOTION FIELD WHICH BOTH THE MID LEVEL FGEN AND
FAST NW FLOW ALOFT WILL HAVE A HAND IN SHAPING...AS OPPOSED TO
GREATER AMPLIFICATION OF THE WAVE ITSELF. THE SHARPENING OF THE
FRONTAL ZONE SHOULD ALSO ALLOW COLDER AIR TO LEAK SOUTHWARD INTO
THE AREA AFTER MIDNIGHT JUST AS THE STRONGEST LIFT MOVES OVERHEAD.
A GFS CROSS SECTION AT 06Z TONIGHT SHOWS ALL OF THE INGREDIENTS
FOR A BURST OF SNOW WITHIN A BAND OF 0.25 INCH 6 HR QPF. MOST
IMPRESSIVE IS AN OMEGA MAX OF 20 UB/S CENTERED AROUND 700 MB
WITHIN A DEEP LAYER OF LOW STABILITY/NEAR INSTABILITY ABOVE THE
FRONTAL ZONE. EXPECT SNOW RATIO TO BE LESS THAN 10:1 GIVEN HOW
MILD THE BOUNDARY LAYER WILL BE TO START...BUT THE PEAK
PRECIPITATION RATE AFTER MIDNIGHT IS EXPECTED TO COOL THE
TEMPERATURE PROFILE ENOUGH FOR A SOLID CHANGE OVER TO SNOW
FOLLOWING THE 1300M 1000-850 MB THICKNESS BEFORE THE SYSTEM EXITS
EASTWARD TOWARD SUNRISE.

LONG TERM...

THE COMPACT...DEEPENING LOW PRESSURE CENTER WILL EXIT THE FAR
EASTERN SECTIONS OF THE CWA AT/AROUND 12Z TUESDAY. WHILE THERE IS
SOME DISAGREEMENT ON THE END TIMING OF THE PRECIPITATION FOR TUESDAY
MORNING (SPECIFICALLY THE SLOWER NAM SOLUTION)...THE OVERWHELMING
CONSENSUS CALLS FOR THE END OF PRECIPITATION ACROSS THE FAR EASTERN
SECTIONS OF THE CWA BY 14Z.

FIRST ITEM OF NOTE FOR THE TUESDAY PERIOD WILL BE STOUT
NORTHEASTERLY FLOW IN THE WAKE OF THE LOW PASSAGE. MODEL DATA
SUGGESTS BREEZY CONDITIONS WITH WINDSPEEDS SOLIDLY IN THE MID 20S
MPH DURING THE MIDDAY TIMEFRAME. MEANWHILE...A SHORT WAVELENGTH 1000-
500MB HEIGHT RISE FEATURE COMPLETING THE DYNAMIC RESPONSE COUPLET
WILL THEN PUSH DIRECTLY INTO LOWER MICHIGAN FROM THE WEST NORTHWEST
DURING THE LATE MORNING AND EARLY AFTERNOON. ASSOCIATED SURFACE
RIDGING IS FORECASTED TO EXPAND EASTWARD INTO THE CENTRAL GREAT
LAKES. NAM/ECMWF SHOW A GOOD AMOUNT OF LOW LEVEL CONVERGENCE
DEVELOPING IN RESPONSE TO THE OPPOSING WIND TRAJECTORIES WITH A
QUASI STATIONARY FRONT SETTING UP IMMEDIATELY TO THE WEST OF THE
CWA. INTERESTINGLY ENOUGH...THERE APPEARS TO BE ENOUGH GOING ON
ALONG THE BOUNDARY WITH ADEQUATE LOW LEVEL UVV/S AND STEEP LAPSE
RATES RESIDING IN THE 3 TO 6 KFT AGL LAYER TO KEEP A LOW CHANCE OF A
SHOWER IN THE FORECAST TUESDAY AFTERNOON FOR AREAS SOUTH AND WEST OF
DETROIT/ANN ARBOR. NOCTURNAL COOLING AND ANTICYCLONIC VORTICITY
ADVECTION WILL THEN ALLOW SURFACE HIGH PRESSURE TO TAKE ROOT OVER
THE CENTRAL GREAT LAKES TUESDAY NIGHT. A STABLE...LAKE AGGREGATE
HIGH SETTING WILL BRING QUIET AND COLD CONDITIONS TUESDAY NIGHT.

LACK OF A PRESSURE GRADIENT AND RESIDUAL SURFACE HIGH PRESSURE
WEDNESDAY BRINGS ANOTHER QUIET DAY. FULL SUN AND SLUGGISH WARM AIR
ADVECTION SHOULD ALLOW TEMPERATURES TO RISE INTO THE UPPER 40S TO
AROUND 50 DEGREES.

A PROGRESSIVE UPPER LEVEL RIDGE AXIS IS EXPECTED TO PUSH ACROSS
MUCH OF NORTH AMERICA WEDNESDAY NIGHT. PRECIPITATION OVER THE
NORTHERN GREAT LAKES IN A RIDGE RUNNER FASHION WILL APPROACH THE
AREA...BUT SHOULD REMAIN TO THE NORTH OF THE CWA. THE NOCTURNAL LOW
LEVEL JET IS EXPECTED TO ORGANIZE THE WARM FRONT WELL NORTHEAST OF
THE STATE FOR THURSDAY MORNING WITH SOUTHEASTERN MICHIGAN BECOMING
POSITIONED UNDERNEATH A MILD WARM SECTOR. A FOCAL POINT OF THIS
WEEKS FORECAST WILL BE DAYTIME HIGHS ON THURSDAY. THERE EXISTS
TIMING UNCERTAINTY REGARDING THE EVENTUAL COLD FRONT PASSAGE THAT
WILL COME AS MIDLEVEL TROUGH/PV ANOMALIES COLLECT ON THE BACKSIDE OF
THE RIDGE. FOR NOW...WENT OPTIMISTIC WITH HIGHS IN THE MIDDLE 60S.
ECMWF GUIDANCE IS SUGGESTING THAT 70 DEGREES PLUS COULD EVEN BE IN
PLAY.

MARINE...

A GALE WARNING REMAINS IN EFFECT FOR NORTHERN LAKE HURON TODAY AS
NORTHWESTERLY FLOW WILL ALLOW COLDER AIR TO SPREAD ACROSS THE
NORTHERN LAKES. UNSTABLE CONDITIONS ARE EXPECTED TO SUPPORT
WINDSPEEDS IN THE 35 TO 40 KNOT RANGE. A DYNAMIC...FAST MOVING LOW
PRESSURE SYSTEM WILL THEN TRACK ACROSS LAKE MICHIGAN AND THE
SOUTHERN PENINSULA TONIGHT. SURFACE WIND TRAJECTORIES ARE EXPECTED
TO DEVELOP AND STRENGTHEN OUT OF THE NORTHEAST TOWARDS DAYBREAK ON
TUESDAY. WINDSPEEDS ARE FORECASTED TO REACH 30S KNOTS ACROSS THE
SOUTHERN BASIN OF LAKE HURON BY MIDDAY. SMALL CRAFT ADVISORIES FOR
THE NEARSHORE WATERS WILL LIKELY BE NEEDED.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...GALE WARNING UNTIL 6 PM EDT THIS EVENING FOR LHZ361-362.

     SMALL CRAFT ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR LHZ421-441.

LAKE ST CLAIR...NONE.

MICHIGAN WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....BT
SHORT TERM...BT
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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