Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 281923
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
323 PM EDT Fri Oct 28 2016
Upper level energy will continue to race across the southern tier of
the central Canadian provinces tonight, steering surface low
pressure across the Northern Great Lakes. Strong 50-60kt low-level
jet will develop in response, passing over Southeast Michigan this
evening and tonight. The low-level jet will push an influx of warm
air and low-level moisture into the area overnight. Very dry air
will be pre-existing below 500mb per KDTX raob, and there does not
look to be much lift to work with 10-12C dewpoints at H850 that will
surge into the area behind the warm front. Will include just a few
showers over the northern portion of the forecast area where forcing
will be slightly stronger near the weak surface trough axis.
Remainder of the area will fill in with low clouds late as lower-
levels (roughly 800-900mb) saturate. Some question as to how well
the shallow boundary layer will moisten given good mixing within.
Forecast soundings keep the very lowest levels dry, and will forego
a mention of fog or drizzle during the overnight and early morning
hours at this time. Concern is the warmer surface temps and
dewpoints that will ride over the cold ground (soil temps measured
in the 40s this morning across SE Mich). NAM model is hitting this
the hardest (saturated boundary layer), but sometimes has a moist
low-level bias in these situations. Min temps will be reached in the
mid to late evening, then rise overnight with strong warm air
Next concern overnight will be with the winds. Warm air advection
will initially occur above about 950mb, forming a strong inversion
and limiting mixing depths. Boundary layer will then deepen later in
the night, however, as low-level warm front arrives. Forecast
soundings suggest gusts to 30 or even 35 mph developing.
Cold front trailing the low will drop into Central Michigan late
Saturday and then sink very slowly through Southeast Michigan
Saturday night. Little upper forcing will be around to support the
frontal circulation tomorrow and will only retain low chances for a
shower. Improved mixing tomorrow will realize warming aloft, and
combined with warm start to the day, should boost temps to well
above normal despite mostly cloudy skies. Guidance offers reasonable
max temps in the mid 60s north to around 70 near/south of Detroit.
Frontal boundary looks to sink slowly southward through southern
Michigan Saturday night and Sunday. FGEN forcing looks to ramp up
late Saturday night into Sunday as an upper trough works through the
area and right entrance region forcing slides in overhead. Healthy
theta-e plume surging into the area ahead of the trough (PW 1.2-1.3
inches) should work with forcing to provide widespread rain across
the area. Timing looks a little slower in latest model runs, with
most of the rainfall now expected between 2AM and 11AM Sunday (12
NAM even slower). Nature of FGEN forcing makes placement of heaviest
rainfall hard to predict this far out, but expecting at least one
good band. Great consensus with broad high pressure building into
the area by Sunday night, allowing the area to dry out.
High pressure moving away from the region on Monday will bring mild
and dry conditions. Low pressure passing to the north of Michigan
Monday night into Tuesday will bring a southwesterly flow that will
yield unseasonably mild conditions on Tuesday. An increased chance
for precipitation will occur midweek as low pressure develops along
a frontal boundary.
Southerly winds will continue to increase from this afternoon into
tonight as low pressure tracks to the north of Lake Superior. A Gale
Warning is now in effect for the open waters of northern Lake Huron
from this evening into the overnight hours as sustained winds near
gale force and gusts reach gale force for a time before stable
conditions develop within this warming south flow. Small Craft
Advisories also continue for the nearshore waters from late today
into Saturday morning in anticipation of these gusty south winds.
Gusty, fresh northwest winds will then build across northern Lake
Huron on Saturday in the wake of a passing frontal boundary. High
pressure will then bring more tranquil conditions late this weekend
into early next week.
An upper level disturbance will progress into the central/southern
Great Lakes Saturday night along an west to east boundary which will
be settling slowly southward through the area during that time
frame. This will produce a period of rain overnight into Sunday
morning. While rainfall amounts are not expected to be heavy enough
to produce flooding, expect a band of one quarter to perhaps one
half an inch of rainfall before rain ends Sunday morning. These
higher totals will be particularly likely along and south of the
Issued at 1230 PM EDT Fri Oct 28 2016
Remaining area of MVFR stratus affecting KMBS/KFNT will mix out/lift
north of terminals as the forecast period begins with VFR conditions
area-wide this afternoon/this evening. SSW winds will reach 10 knots
or so in best mixing early in forecast, back to S/SSE this evening,
and increase from SSW again in tightening gradient flow overnight.
Even with 10m flow in 12-16 knot range, SW low level jet of 50+ kts
will bring period of LLWS into Saturday morning. This jet will bring
increasing low level moisture/stratus late tonight into Saturday as
it veers to the west in advance of frontal boundary sagging south
into area. Lowest ceilings will affect KPTK north initially before
expanding into I-94 terminals as front settles southward with time.
//DTW Threshold Probabilities...
* Medium in ceilings aob 5kft after 10z Saturday morning, high after
Lake Huron...Gale Warning from 8 PM this evening to 4 AM EDT Saturday FOR LHZ362-
Small Craft Advisory until 10 AM EDT Saturday FOR LHZ421-422-
Lake St Clair...Small Craft Advisory until 10 AM EDT Saturday FOR LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 10 AM EDT Saturday FOR LEZ444.
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