Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221642
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1242 PM EDT Sat Jul 22 2017


.AVIATION...

The region of showers which tracked across the terminals this
morning will continue exiting to the east of Se Mi early this
afternoon. While there is a region of mid level subsidence behind
this feature, very high low level moisture and daytime heating will
support some degree of scattered showers this afternoon. Some late
morning clearing over portions of srn Mi will continue to rapidly
fill in with diurnal cu given the abundance of low level moisture.
The expectation is that bases will gradually rise to MVFR with
persistent daytime heating. There is however some concern that lower
based clouds may hold on through the evening from time to time. Sfc
troughing will hold across Se Mi through the night. Given the ample
low level moisture and some flux off the lakes under light easterly
flow, there is a good potential for fog and/or low stratus
development tonight. For this reason, some IFR conditions have been
added to the terminals.

For DTW...Recent satellite data suggests a better mixing potential
across metro Detroit this afternoon. Thus, cloud bases should
undergo a steady rising trend heading into the evening.

//DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms Sunday afternoon.

* High in ceilings at or below 5000 feet this afternoon through
  Sunday morning.

&&

.PREV DISCUSSION...
Issued at 243 AM EDT Sat Jul 22 2017

DISCUSSION...

While the heaviest concentration of thunderstorm activity continues
to propagate into highest theta-e airmass from Indiana back west to
northern Illinois/eastern Iowa, gradually veering low level jet
associated with surface troughing/warm front snaking into area from
upper level low pressure poised just north of North Dakota will act
to feed some of the higher theta-e air into lower Michigan late
tonight into much of Saturday.

This will maintain a muddled area of convection north of the main
storm clusters, especially this morning as last of lift within
entrance region of exiting jet streak helps invigorate the activity
within broad area of weak ascent. While severe weather potential is
very low with this activity, the passage of warm front/trough will
bring PWAT values in excess of 2.00 inches, so locally heavy rain
remains a possibly (mainly south of the M-59 corridor).

While convective activity will lessen from mid morning into the
afternoon, models suggest weak low level convergence will remain as
weak cyclogenesis occurs due to jet energy slight height falls
associated with the aforementioned upper system over the southern
Canadian prairie provinces.

The upper system then tracks along US/Canadian border and digs into
the northern/central Great Lakes Sunday/Sunday night. Region of
height falls in advance of this upper low will expand and result in
a surface low meandering near the area into Sunday night. All this
will lead to a continue chance of scattered showers/thunderstorms,
especially Sunday afternoon/evening as cold front pivots southeast
into area.

Between the low level forcing provided by this front, and upper
support from digging shortwave, expect coverage of convection to
expand (especially given favorable diurnal timing from mid/late
afternoon into early evening). While mid/upper level wind fields
will be more conducive to severe wind gusts with storms, low level
forcing/convergence is very much in question and will ultimately be
determined by the location of the weak low pressure locked to the
increasing height falls associated with the approaching shortwave.

Warm and humid conditions can be expected today and to some degree
into Sunday as this system encroaches on the region. Thereafter,
high pressure will build into area early in the week in the wake of
late Sunday cold front. This will lead to cooler and less humid
conditions in the Monday/Tuesday time frame.

A second upper low is then expected to cross southern Canada and
push another cold front into area by roughly Wednesday night. Some
increase in temperatures and humid can be expected within southwest
flow in advance of this front with a round of showers/thunderstorms
also possible during this time frame. In its wake, another Canadian
high pressure system will bring a slightly cooler and less humid
airmass back to the area through the remainder of the week. During
this Thursday/Friday period, any shower activity will be minimal and
most likely subdued to the south/southwest of the area around the
periphery of the high pressure.

MARINE...

Winds will turn south to southeast today ahead of low pressure
moving into the area. Wind speeds will remain below 15 knots for
most areas, but gusts may occasionally top 20 knots over western
Lake Erie where the gradient will be a little stronger. Winds will
then weaken overnight and Sunday for most locations as the low
tracks overhead, while increasing to 15 to 20 knots on the north
side of the system over the northern half of Lake Huron. Winds will
back to the north Sunday night and Monday behind a cold front as as
high pressure builds in from the west.

The best potential to see showers and thunderstorms this weekend
will be this morning (mainly over Lakes Erie and St Clair), and
Sunday afternoon and evening.

HYDROLOGY...

Round of showers, with a few embedded thunderstorms, working across
Lower Michigan early today should mainly impact areas along and
south of the I-69 corridor. Potential exists for these areas to see
greater than 0.25 inches of rainfall, with locations along and south
of I-94 possibly picking up just under an inch of rain by late
morning.

&&

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

$$

AVIATION.....SC
DISCUSSION...DG
MARINE.......HLO
HYDROLOGY....HLO


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at www.weather.gov/detroit.



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