Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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367
FXUS63 KDTX 182230
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
630 PM EDT Fri Aug 18 2017


.AVIATION...

MVFR/lower VFR ceilings within unsettled westerly flow around low
pressure to the north will scatter out during the course of the
evening as daytime heating is lost. Remaining wind gusts on the
order of 20 knots will also subside with loss of BL mixing. Just as
clouds decrease, another shortwave will pivot into existing upper
trough and bring lower VFR to potential MVFR cigs as well as rain
showers late tonight into Saturday morning, generally 10-11z thru 14-
15z. While diurnal cumulus will remain on cusp of SCT-BKN in the
wake of this wave, a generally clearing trend is expected Saturday
afternoon/evening as drier northwest flow ensues in wake of trough.

For DTW...Cigs aob 5kft will scatter out around 02z, but return in
the 09z-11z time frame with the arrival of another disturbance. Will
maintain the PROB30 for shras attm given Hires model trend late this
afternoon. This system will race through quickly so a return to SCT
conditions will begin by afternoon.


//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft through 02z and again roughly in the 09z-
  17z time frame.

* Low for thunderstorms impacting terminal 11z-14z Saturday am.

&&

.PREV DISCUSSION...
Issued at 336 PM EDT Fri Aug 18 2017

DISCUSSION...

Gusty westerly winds topping out around 30 mph this afternoon, with
dew pts settling toward 60 degrees under cloudy/mostly cloudy skies.

Upper level trough/wave over the upper Mississippi River valley to
arrive early Saturday morning. Narrow/short lived 850-700 MB theta-e
Ridge will attempt to slide in overnight, with PW values around 1.5
inches along the southern Michigan border, but the 850 mb jet/winds
fail to back a whole lot over the Ohio Valley, and thinking just
chance pops are justified with marginally unstable showalter indices
around. In fact, local probabilistic SREF guidance argues for just
low chance right along the border, with slight chance farther north.
Fairly cold 500 mb temps of -13 to -15 C Saturday morning will lead
to a brief opportunity for a thunderstorm or two to develop before
trough/thermal axis slides east.

Upper level northwest confluent flow becoming established Saturday
afternoon will allow high pressure to build into the southern Great
Lakes, with dry and pleasantly warm conditions around for the rest
of the weekend. 850 MB temps reaching 15 C Sunday afternoon should
allow maxes to reach into mid 80s.

Pseudo upper level zonal flow setting up on Monday, and although we
should still be under the influence of the departing high, with warm
advection pattern and warm front set up over the midwest, there is
concern for increasing mid/high clouds during Monday afternoon, with
could hinder viewing of the eclipse. Airmass looks capable of
supporting upper 80s to around 90 degrees for highs, but with high
clouds and eclipse leading to less insolation, prefer to be a bit
more conservative.

Otherwise, cloud cover will certainly ramp up throughout Tuesday as
troughing builds in across the Great Lakes aloft. Warm, humid air
with dewpoints in the upper 60s along with embedded short-waves aloft
will bring the likely chance for rain showers and thunderstorms
throughout Tuesday, before a cold front acts to bring in cool, dry
air early Wednesday. The cold front will be quite impactful in terms
of temperature change, where forecasted highs are only expected to
cap in low to mid 70s both Thursday and Friday. A broad, surface high
pressure system will then move in place across Michigan late next
week into the weekend, which will look to bring an extended period of
dry weather.

MARINE...
Small craft advisories will continue into the evening as
strong and gusty westerly winds continue. These winds will
gradually weaken overnight and continue to weaken Saturday as high
pressure builds in from the west.  A weak disturbance may bring some
light showers across western Lake Erie Saturday morning.  Light
westerly winds Saturday will back to the south southwest on Sunday
and continue into the beginning of next week.  The next chance for
showers and thunderstorms will start across Lake Huron Monday then
spread across all of the water Monday night and continue through
Tuesday. Winds will finally veer back northwest Tuesday night.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ049.

Lake Huron...Small Craft Advisory until 8 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....DG
DISCUSSION...SF/AM
MARINE.......DRC


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at www.weather.gov/detroit.



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