Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 280232
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1032 PM EDT SAT AUG 27 2016

.UPDATE...

The earlier convective complex exited SE Michigan during late
afternoon and left behind enough mesoscale subsidence to produce a
quiet evening. Upstream observations now show renewed development
of showers and thunderstorms as this subsidence wanes and as
larger scale elements come together over the western Great Lakes.
The new activity is supported mainly by the entrance region of the
upper jet and associated weak frontogenesis in the 850 to 700 mb
layer, judging by the change in theta-e gradient in this layer
colocated with the surface trough. Surface mesoanalysis also shows
surface based cape of 1000-1500 J/kg over SW lower Michigan but
with a considerable gradient to the north and east into our area.
This will keep showers scattered and storms ordinary as there is
not much potential for the greater instability to work eastward.
Instead, expect nocturnal convection to be increasingly dependent
on the pocket of elevated instability that the NAM shows move
overhead with the surface trough later tonight through Sunday
morning. Plan to hold with the chance/scattered POPs in the going
forecast and monitor later adjustments.

&&

.PREV DISCUSSION...
Issued at 713 PM EDT Sat AUG 27 2016

AVIATION...

Weak low pressure over the Midwest during early evening will move
toward Lake Superior during the night and pull a warm front north of
lower Michigan. This will place SE Michigan in the relative warm
sector before a surface trough slides into the region toward
sunrise. Light wind within these features, combined with wet ground
from earlier widespread rainfall, will make IFR restriction
increasingly likely. There remains some uncertainty on the
distribution between fog and stratus as the surface trough moves
into the region and brings a renewed chance of showers or an
isolated thunderstorm. Rain-cooled evening temperatures favor MVFR
fog by mid evening, dropping to IFR, and then transitioning to IFR
stratus along and behind the trough where the wind field will be
slightly stronger through Sunday morning. Westerly flow leading weak
high pressure into the region will bring improvement to VFR early to
mid Sunday afternoon.

For DTW... A fairly rapid reduction to IFR restriction in fog is
possible during late evening/overnight after heavy rainfall during
the day. Light wind and humid conditions will contribute and help
maintain fog transitioning to IFR stratus through Sunday morning.

//DTW Threshold Probabilities...

* High for ceiling 5000 feet or less overnight through Sunday
  morning.

* Low for ceiling/visibility below 200 ft or 1/2 sm.

PREV DISCUSSION...
Issued at 334 PM EDT Sat AUG 27 2016

DISCUSSION...

Strong corridor of southwest flow will remain over the area through
the near term, funneling additional mid-level energy across the area
tonight. Fairly strong right entrance support will remain over the
Central Great Lakes during this time as the height gradient
contracts in response to the shortwave entering Minnesota this
afternoon. High moisture content will ensure low levels of
instability persist tonight and this should be sufficient for
regeneration of a few showers along the developing nocturnal LLJ
axis. Maintained a 40 pop roughly north/west of I-69 with just a low
schc elsewhere as theta-e advection could still kick off a few
isolated showers or storms.

Sunday will feature building high pressure as the Minnesota
shortwave tracks north of Lake Superior and upstream height rises
commence. Flow will veer to the northwest as the surface high takes
hold over the Northern and Western Great Lakes, forcing the moisture
axis and instability gradient south. 12z progs hang up this boundary
right along the Ohio border, so have introduced a low chance pop
there as solenoidal component of forcing during peak heating could
certainly ignite a few thunderstorms. Severe concerns remain low at
this time owing to marginal shear, although an isolated wind gust to
60 mph in Lenawee or Monroe County is not out of the question.

Flow continues to gradually veer into Sunday night, setting the
stage for a marine inversion to advect from northeast to southwest
across the CWA. NAM12 soundings appear quite favorable for a very
shallow inversion and the potential for marine stratus development
for the latter half of Sunday night. Bumped up sky cover and
overnight lows accordingly. Suppression of the instability gradient
and zonal flow aloft will sustain dry conditions through monday with
highs slightly above average values as H5 heights rise into the low
590s. Any marine stratus that forms will clear early and give way to
just passing high clouds embedded within flat flow aloft.

Surface cold front will move through the area on Tuesday and
Wednesday. A fairly moist airmass ahead of the front will allow for
scattered showers and thunderstorms to develop over portions of
southeast Michigan. As the cold front passes through on Wednesday,
above average temperatures should drop near to slightly below normal
for the remainder of the period. High pressure is expected to build
over the area Thursday and continue through the weekend.

MARINE...

Rapidly diminishing potential for thunderstorms through the evening,
leading to a quiet overnight period.  Modest southeast winds
shifting to southwest through this time.  Winds then becoming
northwesterly on Sunday as a front lifts through.  Strongest winds
expected across northern Lake Huron, but still at or below 20 knots.
High pressure will then bring a light and somewhat variable flow for
early next week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

UPDATE.......BT
AVIATION.....BT
DISCUSSION...JVC/DE
MARINE.......MR


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