Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 310745
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
345 AM EDT SUN JUL 31 2016

.DISCUSSION...

The low pressure system that has affected lower Michigan since
Friday continues to evolve slowly over the region early this
morning. Satellite imagery indicates the primary wave aloft moving
to our east into southern Ontario while supporting a sizable area of
showers/storms on its NW flank over central and SE Michigan. This is
where the mid level theta-e axis is wrapping around the circulation
in a mature deformation/occlusion process that is feeding elevated
convection with numerous to widespread overage. The northeastward
drift of the upper wave will help confine the pattern mainly along
and north of the I-69 corridor through the morning and maintain
similar coverage. Heavy rainfall remains problematic in this
scenario due to the slow evolution of the large scale pattern,
slow cell motion, and near tropical moisture characteristics
highlighted by PW peaking near 1.8 inches with 700 mb dewpoint
near 4C. So far, early morning activity has shown rainfall rates
exceeding 1 inch per hour only over small areas as cell clusters
undergo relatively quick cycling of intensity. This will be
monitored as potential remains for evolution favorable to produce
excessive rainfall warranting at least urban and small stream
flood advisories before the moisture axis shrinks eastward during
the afternoon.

To the south of the main rainfall area during the morning, mid level
isentropic descent will keep coverage minimal over even dry until
afternoon when surface based instability will develop. Scattered
thunderstorms will again be possible across the area during peak
heating from late afternoon into early evening. Consensus of CAM and
synoptic scale model output indicates surface based CAPE reaching
1500-2000 J/kg mainly south of the M-59 corridor resulting in
scattered storms of pulse/multicell mode with locally heavy
rainfall similar to the last couple days. Coverage will be
modulated by available surface convergence which the NAM is most
aggressive in producing inland from the lakes in a combination of
trailing inverted trough and differential heating. This surface
solution does fit the larger scale scenario of lingering cyclonic
flow aloft after the primary wave exits to the east but both the
4km NAM and NAM12 even then suggest no more than scattered
coverage.

A short round of high pressure finally settles into the Great Lakes
by Monday. The 00Z models indicate a short wave ridge aloft building
overhead between the exiting trough and the next round of stronger
jet energy moving through the Rockies. Temperature guidance points
to a warm high pressure air mass that will allow high temps to
easily reach the lower to mid 80s Monday afternoon into Tuesday
afternoon. That upstream jet energy is then expected to spread
clouds into the region and possibly even some dying convection by
Tuesday night. The latest model solutions are trending toward deep
enough lee trough development over the plains for moderate low level
jet formation and return flow into the Midwest. There is enough
agreement across the NAM, GFS, ECMWF, and GEM for support of chance
POPs in this scenario. This would be followed by another round of
warm high pressure for the second half of the week in advance of
the next cold front still targeted for Friday. Medium range models
still do not indicate any big temperature falls even behind this
front for next weekend.

&&

.MARINE...

Northeast winds persisting today, but generally in the 10 to 15 knot
range, with waves under 4 feet. winds will become even lighter
tonight into monday, with light and variable winds on Tuesday.
Modest southerly breeze kicking in by Wednesday. Scattered
thunderstorms around today, with next chance arriving during the
middle of next week.

&&

.HYDROLOGY...

Additional showers and thunderstorms are expected today, but with
less coverage compared to yesterday. None-the-less, any
thunderstorms that develop will be capable of producing torrential
rainfall, with amounts exceeding 1 inch within an hour due to slow
movement. Localized urban and small stream flooding remains
possible.

&&

.PREV DISCUSSION...
Issued at 1156 PM EDT Sat Jul 30 2016

AVIATION...

Showers/embedded thunder have become more numerous north of KPTK
late this evening within deformation axis of shortwave that is
moving through the area. This activity will most likely affect
KMBS/KFNT overnight. Activity further south will remain isolated as
mid level dry slot overspreads far southern Michigan. Will maintain
some fog overnight given degree of moisture left over from recent
rain. Another weak shortwave digs into area behind the current
system, so additional sct shras/tsras will be possible...most likely
focus north before deformation fades and then sinking south during
afternoon/early evening as trough settles through area.

For DTW...While terminals missed out of convection today, coverage
was much more extensive. Do not expect quite a repeat on Sunday, but
PROB30 group is probably warranted as surface trough settles into
area and helps focus activity. Otherwise, will maintain light fog
overnight given degree of low level moisture and light winds. After
mid level dry slot leads to some additional clearing, radiation fog
should become more likely.

//DTW Threshold Probabilities...

* Low for ceilings aob 5kft overnight.

* Low for tstorms impacting KDTW Sunday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.

&&

$$

DISCUSSION...BT
MARINE.......SF
HYDROLOGY....SF
AVIATION.....DG


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