Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 101921

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
321 PM EDT Thu Aug 10 2017

Mostly sunny skies today and for the rest of the afternoon due in
part to very dry low and mid levels as seen on 12z dtx sounding with
pws 0.75 and dewpoint spreads over 20 degrees at surface.  This and
800mb cap limiting much cu development.  There is a bit more thin
high clouds crossing the northern counties from dissipated showers
earlier to the west.  Temperatures most locations in the 80s and
will have pretty much a repeat of last evening.

Tonight and Friday, weak mid level wave and surface low centered
over northern Wisconsin and an attendant cold front will drift
eastward across Michigan and exit to the east early Friday night.
Moisture, decent instability and shear is all lacking with this whole
system. Showers and thunderstorms are finally developing this
afternoon aided by diurnal heating across Wisconsin. As this activity
moves eastward it will weaken/dissipate by the time it reaches the
far western portion of the forecast area around or after midnight.
Will slowly spread small chance for showers tonight across the entire
area by morning as a few showers may continue with increasing theta-e
and weak isentropic forcing.

The front and wave axis will take the whole day Friday and maybe
early Friday night to cross and exit to the east.  As diurnal
heating commences, shower coverage will gradually increase
throughout the day with enough instability achieved in the afternoon
to over come weak mid level cap and produce some thunderstorms. Any
storms will not be severe as mentioned earlier, instability and shear
are very weak and moisture limited with pws around 1.0 inch. Any
shower activity Friday night will occur along the far eastern
forecast area and end by midnight followed by plenty of cloud cover.

Saturday low level moisture will lead to plenty of diurnal cu.  A
secondary cold front will drop southward in the afternoon triggering
some scattered showers down to about the Detroit Metro Area before
daytime heating wanes. Highs Saturday will only make it to the ;ow
70s in the Thumb with earlier passage of the front to nr 80 along
the Ohio border. High pressure building in will bring clear skies
Saturday night and cool temperatures again in the 50s.

High pressure is projected to be more firmly in control of weather
conditions around SE Michigan during Sunday. This will ensure a dry
finish to the weekend with temperatures near normal values in the
mid 70s to around 80. Otherwise, global model solutions remain
locked in on the large scale blocking pattern in the upper level
flow over North America for the first half of next week. A short
wave system embedded in the large scale upper trough over eastern
Canada is shown to move through the Great Lakes during Monday. The
feature could generate some high based light rain showers over Lower
Michigan while the bulk of significant rainfall will be to our south
where the primary surface low pressure reflection and frontal zone
will reside. Model agreement is better on the location, strength,
and timing of this system in the latest NWP cycle moving it east of
the region by Tuesday. The upper level ridge within the omega block
is then expected to drift into the Midwest and support a prolonged
period of dry weather with temperatures on the warm side of normal
for the mid week period.



Weak low pressure will slowly track across northern Michigan tonight
and Friday. Showers and a few thunderstorms will be possible
tonight, mostly over Lake Huron, with scattered to numerous showers
and thunderstorms then developing on Friday as a cold front works
across the region. Winds will be southerly ahead of the system
tonight into Friday, then flip to the northwest behind the cold
front late during the evening and overnight. Sustained wind speeds
should remain at 15 knots or less through Friday night.


Issued at 130 PM EDT Thu Aug 10 2017


Light southerly flow in advance of approaching low pressure will
maintain quiet weather with a SCT-BKN cu field this afternoon, in
addition to some mid/high level clouds that will mainly stream over
FNT and MBS. Loss of heating will allow cu field to scatter out this
evening. Leading band of moisture working into the area ahead of the
low will arrive overnight, roughly in the 5-9Z window, bringing a
small chance for showers and increasing cloud cover between 4000-
6000 feet. Chances for showers are too low to include a mention in
TAFs however, but the best potential late tonight will be towards
MBS. The low will track across northern Michigan Friday, with
southerly flow advecting high dewpoints into the area and
maintaining smaller chances for showers through the morning. Best
chance for showers and thunderstorms looks to hold off until after
18Z with better instability from daytime heating and closer to an
approaching cold front.

For DTW...Ceilings look to remain just above 5000 feet overnight as
lower level moisture begins to work in ahead of approaching low
pressure. Best chance for ceilings to drop below 5000 feet looks to
be about 15Z Friday as increasing moisture combines with daytime
heating. Showers will be possible early Friday, but best chance
holds off until after 18Z.


* Low for ceilings at or below 5000 feet late tonight through early
  Friday morning. Medium after 15Z.

* Low for thunderstorms after 18Z Friday.


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



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