Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 270828

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
328 AM EST Mon Feb 27 2017


A relatively tranquil start to the work week, before turning more
active for the midweek period.  Weak impulse cruising through a
prevailing lower amplitude westerly flow to remain south of the
region today, yielding little more than perhaps a brief glancing
shot of mid cloud across the far south.  This will leave a high
degree of insolation potential under developing light southwest flow
in the wake of exiting surface ridging.  This will occur within the
background of gradually increasing upper heights as the mean flow
slowly backs.  Resident air mass will moderate accordingly to this
pattern, with afternoon temperatures likely arriving roughly 5 to 7
degrees warmer than readings noted yesterday.  Highs of mid-upper
40s...or ballpark 10 degrees above normal.

Branch of an elongated central pacific upper jet now entering the
US/Mexican border will break off and shear downstream within the
existing west-southwesterlies.  The effective increase in deep layer
flow will organize a region of heightened isentropic ascent with an
accompanying surge of higher theta-e. Flow trajectories direct this
arc of waa/forcing into lower Michigan mid-late morning Tuesday.
Onset timing for the resulting precipitation shield likely within a
couple hours either side of 12z.  Temperatures to dip into the mid
30s tonight, but a sufficiently deep warm layer with increasing
freezing levels continues to support an all liquid ptype at arrival.
Degree of mid level theta-e advection likely destabilizes the
profile enough to allow for elevated thunder.

Solid period of warm air advection throughout Tuesday, with 850 mb
temperatures approaching 10C by late afternoon.  This will shift
highs back into the 50s across most locales.  Brief period of
subsidence would favor a lull in activity for the latter half of the
day.  Attention then turns to the inbound surface wave/frontal zone
tied to a sizable eastward expanding height fall gradient and 150
knot upper jet core.   Strong deep layer ascent to accompany these
features, pointing to another wet period Tuesday night.  Convective
potential again contingent on moving meaningful instability
northward enough to support greater updraft strength.  Latest model
projections would suggest SE Michigan will reside just outside of
the greater instability axis, but could see a localized greater
convective response along the immediate east/southeast flank of the
surface low as it tracks across the region overnight.  SPC Day 2
outlook holds far southeast Michigan under a marginal risk for
severe wx.

The Wednesday and Wednesday night periods carry a greater level of
uncertainty. Trailing surface cold front eases across the region
early in the day.  Potential does exist for a more sizable low-mid
level response to emerge as favorable upper jet positioning and
strong inbound cva intersect the frontal slope.  00z NAM arriving
with a much more dynamic solution, providing an expansive long
duration deformation/fgen driven period of precipitation
/particularly north/.  This solution would yield a large south to
north temperature gradient, with the potential for several inches of
accumulating snow over the Tri-cities and convection across the far
south. GFS/ECMWF not nearly as dynamic, but generally provide a
similar setup but with differing positioning/strength and timing of
the key large scale features.  Forecast remains largely skewed
toward the latter solution at this stage, presenting higher end pops
with a general late day/evening transition in ptype from rain to
snow before moisture strips out.



High pressure will build over Lower Michigan and Lake Huron today
and bring favorable marine conditions that will last through
tonight. Light south wind will become moderate over the open waters
by Tuesday with gusts mostly around 25 knots. The south direction
will minimize wave concerns on nearshore waters while reinforcing
another round of mild air and rain showers into Tuesday night. This
will precede the next low pressure system that is projected to move
over the northern Great Lakes Tuesday night through Wednesday
morning. Stronger north wind will develop as this system exits with
gusts around 30 knots projected to bring colder air back into the
region Wednesday night. This will be the next time period for
potential marine headlines, most likely small craft advisories for
high waves. The wind will diminish by Thursday while the colder air
lasts through Friday.



Temperatures will moderate today while even milder air arrives late
tonight into Tuesday and lasts through Wednesday. Several waves of
rain showers will occur in this pattern with generous rainfall
totals expected through mid week. Showers and possibly a
thunderstorm Tuesday morning will be followed by a break during the
afternoon and then another round of activity Tuesday night as a warm
front moves into Lower Michigan, together producing totals around a
half inch. Rain is then expected to continue through Wednesday as
the next low pressure system moves through the central Great Lakes.
Additional rainfall amounts around a quarter inch will be possible
before rain changes to snow Wednesday night. The long duration of
this event will minimize flooding potential, although a new round of
rises could result in area rivers and streams.


Issued at 1150 PM EST Sun Feb 26 2017


Southwest winds 10 to 12 knots will ease further overnight as
surface ridge builds across area. Winds will then remain under 10
knots Monday as they back to south and then southeast by evening.
With northern/southern streams currently split, concentration of
clouds will be north/south of area with just sct-bkn 5-10kft deck in
between. This will change somewhat Monday afternoon/evening as the
northern edge of southern shortwave traversing the Ohio Valley leads
to increased moisture and possibly a more persist bkn-ovc deck in
the 4-5kft area.

For DTW...SSW winds of 10 to 12 knots will decrease overnight and
remain light Monday, backing to the S and then SE. Scattered vfr
clouds will be the rule into Monday afternoon with an increasing
chance of lower vfr bkn cigs on the order of 4-5kft after ~22z.


* Low in ceilings aob 5000 feet after 22z Monday.


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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