Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211937
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
337 PM EDT Mon Aug 21 2017

.DISCUSSION...
A mid level trough extending from a closed low over Hudson Bay into
the upper Plains will sweep through the Great Lakes Tuesday. This
will spinup a surface low over Wisconsin tonigh that will lift
northeast while driving a cold front through southeast Michigan from
Late morning through the late Afternoon. In the meantime, warm moist
air continues to advect into lower Michigan increasing instability
and the chance for showers and thunderstorms. A few thunderstorms
have developed across northern Washtenaw County along an elevated
boundary from early convection to the south that has drifted
northward. With no real dynamics this afternoon and tonight, it will
take smaller mesoscale features to initiate any convection. Will
carry lower pops for most of the area through the night but do expect
that there will be some activity, just not everyone will see it.
Best shot will be to the west and north where a bit more moisture and
forcing will begin occurring late tonight as the front approaches.
Band of showers and thunderstorms will work its way southeast
Tuesday with the front with the bulk of the activity confined across
the northern half of the CWA which will be more influenced by the
entrance region of the upper jet and stronger pva. Further south
will still likely to have showers and thunderstorms with the front
but not as much concentration. The atmosphere will be tropically
moist so there will be a threat for heavy downpours and strong gusts
from precip load shedding along with some hail until frontal passage
but widespread severe weather is not expected.


Skies will begin clearing early afternoon Midalnd and Bay and work
its way through the rest of the forecast area by sunset.  It will be
warm and muggy tonight and Tuesday as dewpoints remain nr 70.  The
much cooler drier air will begin advecting in Tuesday night as high
pressure builds in and remains in control for several days bringing
below average temps for Wednesday and especially Thursday.

An upper level trough will remain in place over the region through
the end of the week keeping a prolonged period of cooler conditions
in place. A shortwave pivoting through the trough will bring a
chance for isolated showers and scattered clouds on Thursday as
highs struggle to top 70 across Southeast Michigan. High pressure
will then build into the region through the end of the week keeping
dry conditions in place. Temperatures will remain slightly below
average with highs in the 70s and lows in the upper 40s to mid 50s
through the weekend.

&&

.MARINE...

The next low pressure system and associated cold front will be
advancing toward the Great Lakes tonight and then passing through
the region on Tuesday. Light southerly wind will continue this
evening but will increasing from the southwest later tonight as low
pressure deepens while moving into the Straits region. Wind and
waves will remain below SCA thresholds leaving widespread showers
and thunderstorms along and ahead of the front as the primary marine
weather impact before the frontal passage. Strong northwest wind
behind the front will have gusts reaching 30 knots over the open
waters of Lake Huron late Tuesday afternoon and Tuesday night as
colder air spills into the region. As it stands now, the wind
pattern will be from the northwest direction enough to keep the
highest waves offshore of the southern Lake Huron nearshore zones
before veering toward the north and weakening during Wednesday. The
incoming air mass will be cold enough to produce enough instability
over the water for marginal waterspout potential Wednesday into
Thursday.

&&

.HYDROLOGY...

A low pressure system over the Plains states will reach the Straits
region by Tuesday morning and pull a strong cold front through Lower
Michigan. Moisture/humidity will increase considerably ahead of the
front and provide fuel for numerous showers and thunderstorms late
tonight through Tuesday. Basin average 24 hour rainfall totals are
expected to be in the 0.25 to 0.50 inch range with locally higher
amounts near 1 inch possible where multiple thunderstorms occur. The
potential for flooding is expected to be limited by the fast
movement of the associated cold front which is projected to exit
eastward by Tuesday evening.

&&

.PREV DISCUSSION...
Issued at 134 PM EDT Mon Aug 21 2017

AVIATION...

Mostly cirrus debris from all the upstream convection to deal with
today but there will be some afternoon cu developing which may
impact the Detroit area terminals for a bit this afternoon. Could
see some isolated showers this afternoon but coverage will be too
low to include in a taf at this time. Better chances for showers and
thunderstorms come Tuesday morning as a low pressure system tracks
northeast along a stalled boundary through northern MI. A trailing
cold front will then swing through Tuesday afternoon. Looks like the
best chance for showers and maybe thunderstorms will come in the 10-
14Z window tomorrow. MVFR/IFR conditions will be possible with
heavier storms. Winds will get gusty out of the southwest ahead of
the cold front.

For DTW... VFR will consist of ceiling above 5000 ft during the
morning with some scattered cumulus during the afternoon. There
remains low potential for an isolated shower or storm during the
afternoon as a few small isolated showers are already developing
upstream. Best chance for storms will come Tuesday morning with a
secondary chance along the cold front in the afternoon.

//DTW THRESHOLD PROBABILITIES...

* Low for a thunderstorm during the afternoon. Medium Tuesday
  morning.


&&

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

$$

DISCUSSION...DRC/JD
MARINE.......RBP
HYDROLOGY....RBP
AVIATION.....RBP


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.


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