Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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799
FXUS63 KDTX 251744
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
144 PM EDT Fri May 25 2018


.AVIATION...

Dry southwest winds are well established over southeast Michigan
this afternoon as the area remains positioned to the northwest of
strong Mid Atlantic high pressure. Midlevel anticyclonic flow
trajectories and antecedent dry air to hold through this evening and
into tonight. Weak remnant jet axis aloft will push into the area
allowing moisture return to commence by sunrise Saturday. High cloud
associated with passing Indiana midlevel low and diurnal heating
will bring an increase in mixed boundary layer cumulus Saturday
afternoon.

For DTW...Latest indications that wind directions will subtly back
to around 170 degrees at/around 00Z this evening in response to
a Lake Erie lake breeze.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 355 AM EDT Fri May 25 2018

DISCUSSION...

A mid summer weather pattern continues taking shape across the Great
Lakes today and lasts through the upcoming holiday weekend. It will
consist of warm and increasingly humid conditions with a few time
windows of thunderstorm potential. The coverage/timing of storms and
associated cloudiness play an important role in daytime high
temperatures that will be increasingly capable of reaching or
exceeding 90 as the weekend progresses, especially as southwest low
level wind is projected to be just strong enough to limit the
inland lake breeze extent.

For today, surface high pressure centered off the mid Atlantic coast
holds primary influence over the southern Great Lakes for one more
day. The main result is maintenance of surface dewpoint in the less
humid range of the 50s. The position of the upper level ridge also
directs most of the high clouds from upstream convection through the
northern Great Lakes. Mostly sunny sky will then help lift high
temperatures into the mid and upper 80s as model soundings indicate
the boundary layer mixing well into 850 mb temps around 15C.

Initiation of afternoon thunderstorms is a little closer to our west
during peak heating today which slightly increases the chance of
some activity surviving through Lower Michigan tonight. Model
indications suggest intensity will be strongly dependent on diurnal
surface based instability while coverage may linger due to the
central Plains/upper Midwest short wave moving over the Great Lakes.
The primary negative factor for maintenance is the lack of nocturnal
surface based or elevated instability downstream of initiation,
including over SE Michigan. However, the moisture profile remains
deep judging by PW around 1.2 inches from model soundings by 12Z
Saturday. This, along with the weakly forced larger scale pattern
suggests a few stray showers will be possible late tonight through
Saturday morning based on timing of the weak upper wave.

The potential for surface based convection developing over SE
Michigan is much improved by Saturday afternoon mainly due to
surface dewpoint rising into the lower to mid 60s. This leads to
model projections of MLCAPE around 1500 J/kg and MUCAPE near 2000
J/kg during peak heating subject to lower adjustments due to cloud
cover. There is also reasonable model agreement on timing of the
upper wave that is slow enough to still provide some weak support
both surface and aloft. Trends for severe storm potential from the
last few forecast cycles still hold with the primary limiting factor
being a wind profile with speed less than 30 knots below 500 mb and
more like around 15 knots below 700 mb. Chance POPs are maintained
again due to the presence of the upper wave and weak surface
reflection during peak heating.

Model consensus for Sunday offers a short wave farther north over
Ontario and a weaker or nonexistent frontal passage Sunday night.
The exception is the NAM solution which is stronger with the wave
and surface front and thus more active with another potential round
of thunderstorms Sunday afternoon. This part of the forecast has
below average predictability due to the small scale of the wave at a
longer time range. The subject circulation is shown over the
Canadian Rockies today and is initialized better with closed 500 mb
contours by the GFS, ECMWF, and Canadian which all still keep the
wave mainly to our north during Sunday and warm air in place through
Memorial Day. Thunderstorm potential then remains tied to daytime
heating near the lake breeze convergence zone in an otherwise
uncapped thermal profile. Scattered coverage with afternoon timing
to finish the holiday weekend.

MARINE...

High pressure will continue sliding to the east towards the Mid-
Atlantic region today. Light to moderate southwest return flow will
develop as the day progresses, with winds generally 10-20 knots. A
cold front will slowly drift southward from Lake Superior this
weekend bring increasing chances for scattered showers and
thunderstorms. The front will wash out over the region Sunday with
high pressure building in its wake for early next week.

&&

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

$$

AVIATION.....CB
DISCUSSION...BT
MARINE.......IRL


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at www.weather.gov/detroit.



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