Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 290814
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
414 AM EDT SUN MAR 29 2015

.SHORT TERM...TODAY AND TONIGHT

PRECIPITATION ACTIVITY PUSHING ACROSS THE NORTHERN PLAINS THIS
MORNING IS BEING FORCED BY STRONG WARM AIR ADVECTION AHEAD OF THE
VIGOROUS SHORTWAVE OVER WESTERN NODAK/SODAK. THE MAGNITUDE OF
MOISTURE TRANSPORT ON THE NOSE OF A +70 KNOT LOW LEVEL JET WHILE NOT
SURPRISING...IS NOTEWORTHY FOR TIME OF YEAR WITH PWATS OF UP TO .8
OF AN INCH. NWP DATA MAINTAINS THE STRENGTH OF THIS LLJ AXIS DURING
THE DAYLIGHT HOURS TODAY AND FORECASTS THE ARRIVAL OVER LOWER
MICHIGAN DURING THE AFTERNOON HOURS. THE TIME WINDOW FOR PRECIPATION
ACROSS SEMICH IS BETWEEN 20-03Z.

12-21Z...IMPRESSIVE DEPTH OF INFLECTION POINT IN FLOW/TROUGH IN
ADDITION TO THE RELATIVELY CLOSE PROXIMITY YET OF THE SE US
ANTICYCLONE WILL ALLOW FOR A STRONG SURFACE PRESSURE GRADIENT BY
THIS AFTERNOON. SHORTWAVE RIDGE AXIS WILL TAKE UNTIL 15Z OR SO TO
PUSH COMPLETELY THROUGH THE CENTRAL GREAT LAKES. SUSPECT IT WILL
TAKE A GROWING BOUNDARY LAYER AND THIS ADDITIONAL SOUTHWESTERLY
GEOSTROPHIC FLOW COMPONENT AT THE MIDLEVELS TO GET GUSTY
SOUTHWESTERLY FLOW TO REALLY INCREASE AT THE SURFACE. SOUTHWESTERLY
WINDS THIS AFTERNOON ARE EXPECTED TO GUST 30 TO 35 MPH. TEMPERATURES
TODAY ARE EXPECTED TO RISE INTO THE LOWER 40S...HIGHEST IN THE
SAGINAW VALLEY/NORTH OF THE GLACIAL TERRAIN.

21-05Z...THE NARRATIVE OF HIGHER CONFIDENCE FOR PRECIPATION AMOUNTS
REMAINS SOLID (.1 TO .15 OF INCH). ALSO OF HIGHER CONFIDENCE AND
NOTED EARLIER IS THIS EVENT WILL BE GOVERNED BY A VERY FAST SYSTEM
MOTION. THE FAST MOTION WILL NOT ONLY CAUSE A SHORT DURATION OF
PRECIPATION OVERHEAD...BUT IS ALSO SHOWN TO BE A DETRIMENT TO
CHARACTER/STRENGTH OF THE WARM AIR ADVECTION BY THINNING THE THETA E
RIDGE FOR WHICH THE SYSTEM CAN ACT UPON.

THE MAIN FORECAST QUESTION REMAINS CENTERED ON PRECIPITATION TYPE.
THE 29.00Z MODEL SUITE DID NOT OFFER A WHOLE LOT OF CLARITY ON THIS
SUBJECT...PROBABLY BEST SUMMED UP BY THE HUGE DIFFERENCE THAT
REMAINS IN FORECASTED AFTERNOON SURFACE DEWPOINTS PER MET/MAV. THERE
IS A STRONG MODEL CONSENSUS FOR WETBULB COOLING AT PRECIPATION
ONSET. IN FACT...RAW MODEL OUTPUT SHOWS SURFACE TEMPERATURES WARMING
MARGINALLY DURING THE MID TO LATE EVENING AFTER PRECIPATION RATES
DECREASE. CONSENSUS ON MODEL SOUNDINGS IS THAT OF A COLD
PROFILE...WITH LITTLE TO NO WARM SURGE ALOFT. SO...THIS SUGGESTS
PTYPE WILL BE LARGELY DICTATED BY THE DEPTH AND MAGNITUDE OF SURFACE
WARMING TODAY. WITH TEMPS EXPECTED TO REACH THE 40S...SUSPICION AND
GUT FEELING IS THE AREA WILL SEE MUCH MORE LIQUID. HOWEVER...GIVEN
THE THERMAL PROFILE AND THE COLD SFC DEWPONTS CANNOT RULE OUT SNOW
MIXING IN. NOT MUCH OF A CONCERN WITH LITTLE TO NO ACCUMULATION
EXPECTED. THIN NATURE OF THETA E RIDGE THEN SUPPORTS MOISTURE
STRIPPING OUT IN THE MIDLEVELS ALREADY BY 00Z. THUS...CAN VERY WELL
ENVISION A SCENARIO WHERE ICE NUCLEATION BECOMES A PROBLEM AND SEE A
MARKED TRANSITION TO DRIZZLE DURING THE EVENING.

05-12Z...SECONDARY COLD FRONT STRUCTURE SHOWN TO PUSH THROUGH THE
STATE BETWEEN 05-06Z. THE PASSAGE OF THIS FEATURE SHOULD THEN
DECREASE THE POTENTIAL FOR DRIZZLE DURING THE LATTER HALF OF THE
NIGHT DUE TO DRY AIR ADVECTION. SURFACE TEMPERATURES REMAINING ON
THE WARM SIDE OF THE FREEZING MARK WILL LIMIT THE POTENTIAL
FOR RESIDUAL MOISTURE TO FREEZE.

&&

.LONG TERM...

WEAK COLD ADVECTION TRAILING TODAY`S SYSTEM WILL BECOME NEUTRAL
DURING MONDAY MORNING. MODEL SOUNDINGS INDICATE A DEEP BOUNDARY
LAYER GROWING TO NEAR 800 MB BY MID AFTERNOON RESULTING IN NORTHWEST
WIND GUSTING TO AROUND 25 MPH BEFORE THE SURFACE RIDGE ARRIVES LATE
IN THE DAY. THIS...ALONG WITH INCREASING AMOUNTS OF SUNSHINE...WILL
HELP AFTERNOON TEMPS END UP WARMER THAN TODAY WITH HIGHS IN THE MID
TO UPPER 40S OUTSIDE OF THE NORTHERN THUMB.

THE MAIN REASON FOR THE ABBREVIATED COLD ADVECTION MONDAY IS THE
QUICK APPROACH OF THE NEXT RIPPLE OF LOW PRESSURE THROUGH THE PLAINS
AND INTO THE MIDWEST BY MONDAY EVENING. THIS SYSTEM IS DEPICTED IN
THE MODEL DATA AS A SHARD OF UPPER LEVEL ENERGY FROM THE LOW OVER
THE GULF OF ALASKA ROUNDING THE LONG WAVE RIDGE TODAY AND MOVING
THROUGH THE CANADIAN PRAIRIE MONDAY. THE SYSTEM THEN QUICKLY LATCHES
ON TO LOW LEVEL BAROCLINICITY OVER THE NORTHERN PLAINS THAT IS LEFT
OVER FROM TODAY`S SYSTEM. REMNANTS OF THE SURFACE FRONT WILL BE TO
OUR SOUTH BUT THE MID LEVELS OF THE FRONTAL ZONE WILL REMAIN WELL
ORGANIZED OVERHEAD AND TO OUR WEST THROUGH MONDAY. CONSIDERING THE
FAST NORTHWEST FLOW ALOFT...THE WAVE WILL FAVOR A TRACK ALONG THE
700 MB THETA-E GRADIENT. MODEL SOLUTIONS WITH A LOWER AMPLITUDE MID
LEVEL WAVE AND STRONGER FRONTOGENESIS LOOK BEST WHICH LEAVES THE NAM
AS AN OVERDEVELOPED OUTLIER. THE WILDCARD HERE IS THAT THE LOW LEVEL
MOISTURE BROUGHT IN BY TODAY`S SYSTEM IS NEVER REALLY SCOURED OUT
MONDAY AND REMAINS READILY AVAILABLE AT ABOUT 3 G/KG FOR THE SYSTEM
MONDAY NIGHT INTO TUESDAY. THIS EASILY SUPPORTS MODEL QPF IN THE
RANGE OF 0.25 TO 0.5 INCH BUT STILL PUTS THE NAM UNDER SUSPICION FOR
BEING OVERDEVELOPED WITH ITS SURFACE LOW FOLLOWING ITS 850-500 MB
LAYER OMEGA BULLSEYE. LEANING THE FORECAST TOWARD A MORE LIKELY
TRACK FARTHER SOUTH THEN PRESENTS PRIMARILY A RAIN EVENT FOR THE
DETROIT AREA...A RAIN/SNOW MIX FOR THE M-59 TO I-69 CORRIDOR...AND
THEN MOSTLY SNOW FOR THE SAGINAW VALLEY AND NORTHERN THUMB. SINGLE
DIGIT SNOW RATIO WILL BE A LIMITING FACTOR EVEN THAT FAR NORTH...SO
ACCUMULATION WILL BE SET AT A SLOPPY 1-2 INCHES AS A STARTING
POINT.

THE SECOND HALF OF THE WEEK WILL CONSIST OF A TRANSITION IN THE LONG
WAVE PATTERN FROM THE PERSISTENT RIDGE OUT WEST/TROUGH EAST TO MORE
OF ZONAL CONFIGURATION. THIS WILL BE SET OFF BY THE CURRENT GULF OF
ALASKA LOW MOVING INLAND AND REACHING THE NORTHERN PLAINS WEDNESDAY
INTO THURSDAY. THE LARGE SURFACE LOW PRESSURE PATTERN WILL GENERATE
DEEP SOUTHWEST FLOW EAST OF THE MISSISSIPPI AND A WARMING TREND FOR
LOWER MICHIGAN. GUIDANCE TEMPS LOOK GOOD CALLING FOR HIGHS IN THE
60S THURSDAY BEFORE THE COLD FRONT ARRIVES THURSDAY NIGHT INTO
FRIDAY. THIS FRONT WILL BRING TEMPERATURES BACK BELOW NORMAL HEADING
INTO NEXT WEEKEND.

&&

.MARINE...

A GALE WARNING IS IN EFFECT FOR SAGINAW BAY AND CENTRAL LAKE HURON
TODAY AND TONIGHT...AND THROUGH MONDAY AFTERNOON FOR THE NORTH THIRD
OF LAKE HURON. SOUTHWEST GALES WILL DEVELOP AS A LOW PRESSURE SYSTEM
MOVES THROUGH THE NORTHERN GREAT LAKES TODAY. THIS WILL BE FOLLOWED
BY NORTHWEST GALES BEHIND THE ASSOCIATED COLD FRONT OVERNIGHT
THROUGH MONDAY AFTERNOON. THE PRESENCE OF A MODEST AMOUNT OF COLD
AIR IN ADVANCE OF THE LOW...SOME OPEN WATER ON LAKE HURON...AND
FUNNELING IN SAGINAW BAY WILL SUPPORT GALE CONDITIONS. THE SECOND
ROUND OF GALES WILL BE FROM THE NORTHWEST AND WILL BEGIN DURING THE
PREDAWN HOURS MONDAY AND PERSIST THROUGH MIDDAY. TRANQUIL CONDITIONS
WILL TAKE HOLD BENEATH HIGH PRESSURE ON MONDAY NIGHT. THE NEXT LOW
PRESSURE SYSTEM IS DUE IN THE AREA LATE MONDAY NIGHT INTO TUESDAY
BUT WIND SPEED WILL BE LOWER WITH THIS SYSTEM.

&&

.AVIATION...ISSUED 1201 AM EDT SUN MAR 29 2015

VFR CONDITIONS WILL PREVAIL INTO MID SUNDAY AFTERNOON BEFORE AN
APPROACHING TROUGH BRINGS MVFR CIGS AND -SHRA OR -SHRASN BY 20Z TO
22Z OR SO. THIS ACTIVITY LOOKS TO LAST ABOUT 4-6 HOURS AS THIS
FEATURE PASSES THROUGH THE AREA. A STRENGTHENING PRESSURE GRADIENT
WILL ALSO LEAD TO STRONG SOUTHERLY FLOW BY AFTERNOON WITH GUSTS TO
NEAR 30 KNOTS. GENERALLY BREEZY CONDITIONS WILL THEN PERSIST INTO
EARLY EVENING AS WINDS VEER TO SW WITH THE PASSAGE OF THE TROUGH.
MVFR TO LOWER VFR CIGS WILL PERSIST INTO THE NIGHT WITHIN WESTERLY
FLOW BEHIND EXITING SYSTEM.

FOR DTW...VFR UNTIL 21Z-22Z OR SO SUNDAY WHEN MVFR CIGS WITH -SHRA
WILL BECOME INCREASINGLY LIKELY. SOUTHERLY WINDS FROM 190 TO 200
DEGREES WILL ALSO GUST TO 25 KNOTS OR BETTER AT TIMES AFTER 18Z
SUNDAY.

//DTW THRESHOLD PROBABILITIES...

* MEDIUM IN CEILINGS AOB 5000 FEET AFTER 21Z-22Z SUNDAY.

* MEDIUM IN WIND GUSTS TO 25 KNOTS FROM 190-200 DEGREES BY 18Z-20Z
  SUNDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...GALE WARNING FROM NOON TODAY TO MIDNIGHT EDT TONIGHT FOR LHZ363-421-
     422-441-462.

     GALE WARNING FROM NOON TODAY TO 6 PM EDT MONDAY FOR LHZ361-362.

LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

SHORT TERM...CB
LONG TERM....BT
MARINE.......BT
AVIATION.....CB


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



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