Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211852

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
252 PM EDT Sat Jul 21 2018


Showers with a few embedded thunderstorms will remain prevalent into
early evening as low pressure settles southeast from southwest lower
Michigan into the northern Ohio Valley and moisture continues to
funnel northwest into the area within broad southeastery flow around
this cyclonic circulation. While the chance of showers (and isolated
thunder) persists into the overnight hours, coverage and generally
intensity will decrease substantially with the loss of diurnal late
day heating. With the continued influx of moist low level air during
the overnight, low temperatures will remain mild in the mid to upper

Shower chances will have to be increased to some degree on Sunday as
secondary low pressure wraps back west northwest towards the region
from the DELMARVA to near Lake Huron as the circulation of the
current low pressure center settles southeast of the Ohio River.
Model solutions remain widely divergent as to the exact amount of
moisture that will make it back this far west, but scattered shower
with isolated thunder seems a pretty good bet, particularly over the
northern half of the forecast area where lift/forcing from this
system will be strongest. Will also decrease temperatures given the
expectation of more overcast conditions.

Isolated showers will be possible again on Monday as this second low
stalls and dissipates in the vicinity. Temperatures will remain very
pleasant for late July given the mostly cloudy skies that should
remain in place with this system. Highs will range in the upper 70s
to lower 80s across the forecast area.

The extended forecast still remains in low confidence in chance of
precipitation terms.   Weak ridging still looks to hang around,
however a trough axis is also forecasted to be close by.  The area
is forecasted to stay mostly dry through the week, with only some
slight chances for showers.  Tuesday through Thursday are expected
to be the warmest as highs warm up into the mid to upper 80s.



Broad low pressure will drift southeastward into the northern Ohio
River Valley from tonight into Sunday. Unsettled conditions will
continue into tonight across most of the local waters with periodic
showers and isolated thunderstorms. However, coverage will decrease
with the loss of daytime heating. A second low pressure system will
track back northwest to near Lake Huron on Sunday, renewing the
chance of showers

Meanwhile, will cancel Small Craft Advisories for the Lake Huron
nearshore waters with the afternoon update as gusts have dropped to
20 knots or less and waves remain below advisory criterion. There is
a chance that wind gusts and waves will warrant a Small Craft
Advisory over western Lake Erie on Sunday. However, the forecast
remains just shy so will forgo an advisory at this time, especially
given the short duration of even marginal advisory conditions.


Issued at 107 PM EDT Sat Jul 21 2018


An expansive area of low presure drifting southeast through northern
Indiana will maintain southeasterly flow and intermittent showers
through tonight. An isolated risk for thunderstorms will occur
during peak daytime heating from 18-22Z, mainly for the northern
sites PTK, FNT, and MBS where better forcing resides. Otherwise
after a diurnal uptick in showers, coverage is expected to decrease
slightly after sunset. Plentiful low-level moisture will maintain
MVFR ceilings with a trend towards more variable MVFR to VFR
ceilings by this evening. Winds will gradually back to the east
tonight as the low continues pushing southeast into the Ohio Valley.
A few high-res model solutions then indicate the possibility for
another low pressure retrograding west from the Mid Atlantic to
bring another round of light rain on Sunday. Opted to leave light
rain out of the TAFs for Sunday morning due to low probability at
this time.

For DTW...MVFR ceilings are expected to continue through the
afternoon with a trend towards VFR by evening. Brief IFR conditions
will be possible in heavier showers. Risk for thunderstorms is low
with better chance to the north. Northeast runway operations become
increasingly likely on Sunday with flow backing to the northeast at
or above 7 knots.


* High in ceilings at or below 5000 ft through late afternoon.
  Moderate this evening. High late tonight through Sunday.

* Low in thunderstorm occurrence and timing.


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



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