Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240724
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 105 AM EDT Fri Mar 24 2017

AVIATION...

Elevated convection associated with approaching warm front will
spread into terminals by 06z and persist for several hours. Cigs
will be around 3500 feet with this activity. The warm front will
lift into the northern forecast area, but guidance suggests MVFR to
lower VFR cigs will generally persist even as SSW flow gusts to 25
knots or a bit more as far north as KPTK. The front stalls and then
settles back south late Friday, bringing lowering cigs and light
rain/fog as low pressure encroaches from the southwest.

For DTW...Ceilings are expected to drop to 3-4 kft through about 09z
with some modest improvement in the wake of passing shower activity.
Guidance, however, suggest MVFR/lower VFR stratus on Friday with
cigs lowering further by evening. Wind gusts within the tightening
pressure gradient in the wake of warm frontal passage will increase
to 25 knots or so and perhaps as high as 30 knots.

//DTW THRESHOLD PROBABILITIES...

* High for cigs below 5000 ft through 09z tonight.

* Medium for cigs falling back below 5000 ft after 15z Friday and
  high after 00z Friday evening.

* Low for a thunderstorm impacting terminal overnight.

* High for gusts exceeding 25 knots Friday.


&&

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

$$

DISCUSSION...SC
MARINE.......DRK
HYDROLOGY....DRK
AVIATION.....DG


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