Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 240505
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 302 PM EDT Thu Mar 23 2017

DISCUSSION...

Upper ridge axis over Michigan will flatten tonight as shortwave
energy arrives, first from MN/IA this evening and then as additional
energy ejects out of the upper low over the Desert Southwest. Strong
60kt low-level jet will surge up into Michigan late as the Desert
Southwest low moves towards the Plains. This will send a warm front
up through Lower Michigan this evening and tonight. Min temps in the
30s should be reached in the evening and early overnight before
beginning to rise. Band of isentropic ascent (290-300K) and strong
theta-e advection, supported by upper diffluence, will bring a
chance for rain showers after 10 PM. Will keep pops higher north of
I-69, where the nose of the low-level jet will push in as the front
lifts northward. Very dry air will initially allow for some cooling
in the low-levels due to wet-bulb effects at precipitation onset.
Quick arrival of warmer air and will make the chance for
snow/sleet/freezing rain brief and low. Enough warm air will arrive
with the low-level jet to increase elevated instability, and would
not be surprised to hear a few rumbles of thunder, but potential is
low overall.

Frontal boundary will stall over the area late tonight, with
convergence increasing along this boundary as the upper low moves
through the Plains and as upper energy moves through Canada around
another low over Hudson Bay. The front will only sink slightly south
Friday and Friday night as both these features move east. Strong and
moist southwest flow will meanwhile ride over the frontal boundary,
and combined with right entrance region forcing from a strong upper
jet streak, will yield a high chance for rain over Northern Lower
Michigan Friday, and then across Central Michigan Friday night as
the front sinks south. Well-mixed but shallow boundary layer in the
warm sector combined with abundant cloud cover lends some
uncertainty to the temperature forecast tomorrow. With 925-850mb
temps only rising to 9-12C, kept max temps in the 50s over the
northern Thumb and Saginaw Valley, and low to mid 60s elsewhere.

The front, and rain along it, will sink into Southern Lower Michigan
Saturday as strong high pressure develops over Ontario and Quebec.
It will make little progress beyond that however as the upper low
tracking into the Ohio Valley and Southern Great Lakes stalls the
front or slides it back slightly northward Saturday night into
Sunday. Max temperatures will vary widely across the area on
Saturday, ranging from the low 40s north of Saginaw to around 60
near the Ohio border.

Overall, the quasi-stationary frontal boundary is expected
to remain over Southeast Michigan through the weekend, leading to a
prolonged period of wet weather.

As weakening low pressure approaches Southeast Michigan on Sunday
rain will continue throughout the day as southerly flow advects
mild, moist air into the region. Following the passage of the low
across central Lower Michigan on Sunday night a brief interlude in
rain will occur on Monday. Temperatures during this period will
remain mild with highs in the mid 50s to low 60s both Sunday and
Monday. Rain chances then return Monday night and Tuesday as another
wave crosses the Great Lakes. High pressure builds in during the
middle of next week bringing drier conditions with temperatures near
normal for late March with highs in the lower 50s and lows in the
30s.

MARINE...

Modest southeasterly flow will veer to southwesterly by Friday
morning as a weak warm front lifts across the region. Highest speeds
will be across west Lake Erie and Lake St Clair, where gusts will
approach 25 kts. Given the offshore nature of the flow, waves are
expected to remain in the 2-3 foot range. A stronger surface low
will approach the Lakes region Saturday, flipping the flow to the
northeast and freshening across Lake Huron. Winds will maintain a
southerly component over Erie and St Clair early Saturday before
slowly transitioning to easterly flow.

HYDROLOGY...

Widespread rainfall is expected across Southeast Michigan for most
of the upcoming weekend. Rainfall totals from Saturday through
Sunday are expected to approach or exceed an inch across the region.
Specifically totals in the 1-1.25 inch range are possible across the
Saginaw Valley with slightly lesser amounts elsewhere. 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.....DG
DISCUSSION...HLO/JD
MARINE.......Mann
HYDROLOGY....Mann


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at www.weather.gov/detroit.



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