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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
724 PM EDT Sat Mar 28 2015


VFR conditions will prevail tonight into much of Sunday...but
changes will come by middle/late afternoon as a fast moving low
pressure system forces a through eastward into the area. Not only
will this bring a chance of -shra...and possible mix with -shsn for
kptk will also lead to strong southerly flow as the
pressure gradient tightens in advance and along this feature. Expect
MVFR conditions to develop 20z-22z with S-south-southwest winds gusting to near
30 knots between roughly 18z-20z and 00z-02z. Conditions will then
gradually improve thereafter as this system exits to the east.

For dtw...VFR until 21z or so Sunday when MVFR ceilings with -shra will
be possible. Southerly winds...190-200 degrees...will also gust to
25 knots or better at times after 18z Sunday.

//Dtw threshold probabilities...

* medium in ceilings at or below 5000 feet after 21z Sunday.

* Medium in wind gusts to 25 knots from 190-200 degrees by 18z-20z


Previous discussion...issued 338 PM EDT Sat Mar 28 2015

Short term...through tonight

Water vapor imagery shows upper ridging beginning to Cascade down
across Michigan. This will provide dry weather...mostly clear
skies...and fairly light winds tonight as surface high pressure
becomes centered over the Ohio Valley. Good radiational cooling
conditions will set up for most of the night...inhibited only late
as high clouds the upper wave now passing through the
northern rockies approaches the Great Lakes. Warmer air will begin
to advect into the area tonight ahead of this wave...however it will
be offset by radiational cooling. This will keep min temperatures
tonight close to mins experienced this morning...well below normal
in the teens.

Long term...

Lee cyclone in southern Saskatchewan is chugging east in response to
height falls owing to the compact middle-level circulation over the
northern intermountain west. The associated pv anomaly will
translate east within progressive mean flow while additional energy
over central Canada wraps into the amplifying trough. In Southeast
Michigan, this will manifest as a quick 1-2 punch of upper forcing
with the lead wave being steered across Northern Lake Huron early
Sunday evening while trailing wave acts on residual low-level
moisture within a cooling column beginning late Sunday evening.

A strong 60kt low-level jet is forecast to develop over the northern
Great Plains tonight in advance of the lead wave. The low level jet is
expected to maintain its strength, and perhaps even broaden its
spatial footprint, by the time it reaches semi Sunday afternoon.
Fast system speed will limit moisture transport (pwats around 0.5"),
but forcing along the lead edge and within the strong moisture
transport axis will be sufficient to produce a band of light to
moderate showers moving west-east across the County Warning Area 19 through 00z. The
strengthening wind field will support wind gusts of 25 knots
areawide...potentially 30 knots in the Saginaw Valley. This will
easily drive temperatures into the 40s prior to the arrival of
precipitation. Models continue to wet-bulb the column to freezing as
showers associated with the resident low level jet track into the area,
supporting a changeover to all snow. However, suspect that the
relatively light quantitative precipitation forecast/strong warm air advection scenario may not be ideally handled
at the grid scale still prefer to lean toward rain.

Forcing associated with the trailing wave will begin spreading
across lower Michigan by 00z. Despite dry air wrapping into the column
above 700mb, sufficient low-level moisture will be in place in
advance of the cold front to support scattered rain/snow showers
during the evening. Light rates and a warm/wet ground should prevent
any accumulation.

Breezy conditions will persist Sunday night through Monday afternoon
as cold advection increases overnight. Gusts of 15 to 20 knots will
persist in spite of nocturnal stabilization courtesy of ongoing
isentropic descent. 850mb temperatures are forecast to fall to -4 to
-7c by Monday morning. 12z NAM indicates a very well-mixed
environment developing late Monday morning into the afternoon as
lapse rates approximate to dry adiabatic up to 800mb. Momentum looks
rather uniformly distributed through the layer and will be
supportive of gustiness to the tune of around 20 knots. Deep mixing
will also support a high based stratocu deck by afternoon,
especially across the north as another quick-moving embedded wave
zips by during the day. No arguments from the consensus which offers
highs solidly in the middle 40s / low 40s in The Thumb.

Building high pressure will ease the gradient by Monday evening
allowing winds to slacken as the sun sets. Isentropic ascent will
then increase overnight in advance of a fast-moving shear maximum with
origins over the northeast Pacific. This wave will bring a brief
rain or rain/snow mix late Monday night. Predictability remains low,
but a light accumulation of an inch or so will be possible over a
portion of the County Warning Area depending on the exact evolution of the low-level
thermodynamic profile.

The clipper system will quickly be moving off the the east during
the day on Tuesday. Warming temperatures throughout the day will
allow any frozen and mixed precipitation to change over entirely to
rain by middle Tuesday morning. Warmer temperatures and dry conditions
return on Wednesday and last into Thursday. Highs on Wednesday will
be in the low 50s with highs on Thursday potentially reaching into
the low 60s. The next low pressure system will track across the
northern Great Lakes dragging a cold front across lower Michigan on
Thursday evening. This system will bring the next chance of rain
showers to Southeast Michigan...possibly lasting through Saturday as
a series of weak low pressure systems follow in the wake of this
larger system.


Light southwest winds tonight will become strong by midday Sunday
and will be sustained at near-gales over Central Lake Huron by
Sunday afternoon. The presence of a modest amount of cold air and
some open water...and perhaps even some funneling in Saginaw
Bay...are enough to warrant the issuance of a gale watch for south-
southwest gales Sunday afternoon through Sunday evening for much of
Lake Huron. Winds will then subside somewhat by midnight Sunday
night and a reprieve of about 6 hours is expected before northwest
gales develop behind a passing cold front. This 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.


DTX watches/warnings/advisories...
Lake Huron...gale watch from Sunday afternoon through Sunday evening for lhz362-

Lake St Clair...none.
Michigan waters of Lake Erie...none.


short term...hlo
long term....jvc/rk

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