Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241713
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
113 PM EDT Fri Mar 24 2017

.AVIATION...

Just mid clouds around early this afternoon as majority of southeast
Michigan resides solidly in the warm sector, promoting strong
southwest wind gusts of 25 to 30 knots across southern TAF sites.
The frontal boundary over northern Lower Michigan will be on the move
to the south by early this evening, helped out by sunset and the
cold flow off Lake Huron.

Modest surface based instability has built up toward the Ohio border
this afternoon, and there is a very low risk of a thunderstorm early
this evening as front drops south.

Low clouds should easily develop and lower this Evening/Tonight as
low level front produces showers, and expected to reach IFR
conditions, with Likely LIFR conditions at all TAF sites late
Tonight, with little to no improvement Saturday morning as the front
remains stalled and showers and drizzle persists.

For DTW...SOUTHWEST winds near 20 knots sustained, gusting to 30+
knots early this afternoon will subside toward sunset, becoming
light during the evening hours, with wind shift to the northeast
occuring by midnight. Easterly winds (around 10 knots) then look to
prevail overnight into Saturday. High confidence in borderline
IFR/LIFR conditions developing Tonight, and moderate for LIFR
conditations.


//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5000 FT after 00z this evening.

* Low confidence in cigs/vsby aob 200 FT or 1/2SM late tonight into
  early Saturday morning.

* High guidance in southwest gusts exceeding 25 knots this afternoon.

* Very low risk of a thunderstorm early this evening

&&

.PREV DISCUSSION...
Issued at 1139 AM EDT Fri Mar 24 2017

UPDATE...

Front will settle into south-central Michigan by late this afternoon
before beginning to slide back southward in response to strong high
pressure building into Ontario and Quebec. High-res models have been
keen on developing a band of showers ahead of the surface front this
evening, roughly along and south of the M-59 corridor. Digging
deeper, this is where they place the strongest convergence as the
front encounters stronger southerly flow and a weak low-level theta-e
surge in the warm sector. This surge is already evident on upstream
satellite imagery from the Mississippi River Valley up into southern
Illinois, where observation sites are reporting lower clouds working
in. Will add a mention of showers to the forecast for this evening
between roughly the M-59 and I-94 corridors. Stability indices
indicate a risk for thunder, but forecast soundings still indicate
enough of a cap to leave out a mention for now.

PREV DISCUSSION...
Issued at 324 AM EDT Fri Mar 24 2017

DISCUSSION...

A region of showers and thunderstorms developed over the wrn Great
Lakes last evening along the lead edge of the low level jet. A
convectively induced mid level short wave feature sustained the
widespread rain across the southern sections of Se Mi during the
overnight. The strong low level inflow overnight, 45-60 knots in the
900-850mb layer, has rapidly advected a much warmer and more
moisture laden atmosphere into Se Mi. As the mid level short wave
slides east of the area early this morning, the resultant mid level
subsidence will support an end to most if not all of the showers by
12Z.

The southerly flow into the region has been a result of the deep
upper low now rotating into the srn plains and strong low level
anticyclone off the Mid Atlantic coast. While somewhat diffuse at
the moment, the sfc warm front now over far nrn Indiana will lift
northward into Central Michigan by afternoon. This will place Se Mi
within the warm sector today, resulting in highs well into the 60s
(with some low 70s possible). The exception will be closer to the
sfc front over the nrn Saginaw Valley and Thumb. Rain chances
through the day will largely be confined to the mid level portions
of the frontal boundary, north of the forecast area. The frontal
boundary will make a push to the south late today and especially
tonight as strong high pressure expands across Lake Superior and
Upper Mi. An increase in the upper jet max to the northeast of Lower
Mi will result in a strengthening of the mid level frontal forcing
as it slides south into the Saginaw Valley and Thumb region tonight,
resulting in widespread rain. Farther south, higher sub 900mb
moisture will lift into the region from the south, warranting at
least a chance of showers.

The upper jet max to the northeast will slide to the Canadian
Maritimes on Saturday. Meanwhile the aforementioned upper low will
rotate across Missouri. The 00Z model suite suggest these features
will sustain some degree of mid level deformation forcing across srn
MI. Given the deep layer moisture which will be present, high
probabilities of rain will result. The main uncertainty at this
point is where over Lower Mi the forcing will be more persistent as
this will be the location which experiences the most prolonged
rainfall. The sfc front will continue to push south on Saturday. To
the north of this front, the marine modified air under northeast sfc
winds will support a cold shallow stable layer, with temps holding
in the 30s and low 40s. Note that in some instances these temps are
considerably lower than MOS given its poor handling in these
situations. In fact, rather gusty northeast winds off Lake Huron
will lead to a rather brisk day across the tri cities and thumb
regions. The front is expected to push south of I-94 during the
first half of the day, so some of these locals may remain in the
warm sector long enough to see temps approach 60 before the passage
of the cold front.

The main upper low is forecast to rotate across Lower Mi late Sunday
into Sunday night. While the low will generally begin to fill,
residual deep layer moisture across the area and the associated mid
level height falls will remain supportive of a good chance rain
through the latter half of the weekend. The 00Z model suite suggest
sfc based instability lifting toward the MI/OH border on Sunday,
supporting a chance of thunderstorms south of 696 corridor. Mid
level short wave ridgeing in the wake of this upper wave will
overspread the area on Monday providing a dry day before a short
wave trough tracks across the area Mon night into Tuesday. Ample
deep layer moisture and the potential for some enhanced mid level
frontal forcing will warrant a good chance for rain during this time
frame. High pressure will then dominate the region during the mid
week period, supporting dry conditions with temps near late March
averages.

MARINE...

A low pressure system over the Central Plains and the associated
warm front will control the forecast through the weekend. The warm
front is already lifting north through the Great Lakes, currently
draped across the Saginaw Bay. As this continues north,
southwesterly winds will spread across the eastern lakes, with the
strongest winds over Lake St Clair and Lake Erie deeper into the
warm sector. Strong area of high pressure digging into the northern
lakes tonight will force the front back southward which will switch
the winds over Northern Huron to the northeast. The surface low will
then approach on Saturday which will help strengthen the winds.
Though winds appear to stay below 25 knots, we could see small craft
advisory conditions for waves piling up along the shoreline of the
Thumb Saturday morning. Winds will become easterly on Saturday night
as the low weakens overhead.

HYDROLOGY...

A lengthy stretch of wet weather has begun for southern Michigan
with periods of showers persisting through Sunday night. Rainfall
totals will approach 1 inch across much of the area with locally
higher amounts possible due to isolated thunderstorms. In addition,
a warm front may drape itself across Mid Michigan which could lead
to higher totals across that region as well, nearing 1.25 inches.
Runoff from the rainfall will increase flow rates and water levels
in local streams and rivers. However, widespread flooding is not
expected.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SF
UPDATE.......HLO
DISCUSSION...SC
MARINE.......DRK
HYDROLOGY....DRK


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