Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 241115
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
715 AM EDT Sun Sep 24 2017

.AVIATION...

Mostly clear sky and light wind is expected to persist through
tonight as a strong upper level ridge over the Great Lakes drifts to
the east. Slightly better southeast wind off Lake Erie tonight will
make YIP/DTW susceptible for fog late tonight, with a low chance for
LIFR conditions.

//DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 345 AM EDT Sun Sep 24 2017

DISCUSSION...

Today will likely be the fourth consecutive day of record high
temperatures at Flint and Saginaw(MBS), and Detroit also has a
chance to break the record of 89 set way back in 1891. The records
for Flint and Saginaw are 89/2007 and 90/2007 respectively.

The record early fall heat has been driven by a strongly amplified
and stable upper air pattern over North America that is producing a
591 dm ridge at 500 mb directly over lower Michigan. Satellite
imagery and model analysis fields indicate the core of the ridge is
still in place during the early morning but simulations show with
good agreement that it will drift eastward through the day. This
will still result in widespread high temperatures in the lower 90s
but likely not as many mid 90s readings compared to the last couple
of days. A light southeast wind will also return to shoreline areas
and into the Detroit metro area from Lake Erie as the surface high
follows the upper ridge slightly eastward. Mid afternoon onset of
this flow pattern was effective at preventing both DTW and DET from
reaching 90 Thursday and Friday and adds some uncertainty there
today despite full sunshine across the region.

The persistent nature of this stretch of heat keeps advisory
headlines in consideration, however there has been several hours of
relief during each of the last few nights as low temperatures
dropped into the lower to mid 60s most locations. Surface dewpoint
showed some vulnerability to boundary layer mixing yesterday and
guidance today points to readings in the lower to mid 60s which will
only produce a degree or two of heat index enhancement. These
factors suggest advisory headlines are not needed while heat
precautions remain part of other messaging.

High temperatures Monday and Tuesday are expected to come off the
weekend peak by a degree or two each day. The record at Flint is
only 86/1935 while readings will be near 91/1900 at Saginaw but are
expected to be short of 93/1891 at Detroit. This time period is the
beginning of the upper air pattern shift that has the Rockies trough
lifting into the northern Plains while eroding the ridge in the
east. This process and the added cloud cover will produce the slight
cooling trend before the associated cold front arrives. Usually
temperatures overachieve prior to a frontal passage but in this case
low level advective processes are very weak.

The latest global/long range models are settling on Tuesday night
and Wednesday timing for the front and also depicting a rather
anemic moisture pattern along it while passing through the Great
Lakes. A chance of showers and thunderstorms does seem warranted as
the front continues to show enough temperature contrast to drop
highs back into the 70s by Wednesday and then into the 60s after a
reinforcing front by Thursday into Friday. Guidance then shows high
temps possibly not warmer than the 50s to start next weekend.

MARINE...

Extended stretch of very warm and humid conditions continues today
as the region remains under the influence of strong upper ridging.
This pattern will support light winds - under 15 knots - and low
waves during this time. These conditions will persist into early
next week. A cold front crossing the Central Great Lakes Tuesday
night will bring a low chance of shower and thunderstorm activity,
along with winds shifting to the west and increasing to around 15
knots.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

AVIATION.....SF
DISCUSSION...BT
MARINE.......SF


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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