Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 221030
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
630 AM EDT Sun Oct 22 2017


.AVIATION...

Low levels will remain dry for one more day (ceiling free below 12
kft), but increasing southerly flow ahead of a cold front will allow
for quickly lowering ceilings near and just after sunset, with MVFR
showers likely making it into MBS and FNT toward midnight. Showers
will gradually continue to spread eastward overnight into Monday
morning.

Southerly winds expected to reach around 15 knots sustained this
afternoon, and still holding around 10 knots this evening.

//DTW THRESHOLD PROBABILITIES...

* Medium confidence in cigs aob 5000 4-12z Monday, high confidence
  after.

&&

.PREV DISCUSSION...
Issued at 328 AM EDT Sun Oct 22 2017

DISCUSSION...

Mild and breezy conditions will end the weekend across Se Mi as deep
southerly flow will be in place today ahead of a slow moving cold
front tracking across the wrn Great Lakes. Despite some occasional
mid/high level clouds today, the southerly flow should boost mixing
depths slightly, supporting high temps from the mid 70s to near 80
(15 to 20 deg above late October norms). An evolving split flow
within an approaching long wave mid level trough will support a
deceleration of the approaching sfc cold front as it tracks into Se
Mi tonight into the day Monday. While mid level moisture advection
late this afternoon through tonight may lead to some sprinkles/light
showers out ahead of the sfc front, the main forcing for precip will
be post frontal lower tropospheric fgen. Based on 00Z model
guidance, timing of this forcing will focus the better rainfall
chances across the western half of the forecast area tonight.

Mid level trough amplification across the nrn plains/upper midwest
is shown by the entire 00Z model suite. There does however remain
differences in handling of the southern stream wave set to amplify
over the srn Ms Valley today and its interaction with the deepening
northern stream trough. The GFS/NAM solutions dampen the srn stream
wave more rapidly as it lifts into the Upper Ohio Valley Mon night
and keep a good deal of phase separation with the northern stream
wave. This results in the better large scale dynamics developing
over the ern half of the forecast area into srn Ontario Mon/Mon
night. The ECMWF/Canadian however indicate the srn stream wave
lifting across Se Mi Monday night, rapidly phasing into the nrn
stream. The result is a region of persistent mid level forcing over
Lower Mi with a rapidly deepening sfc low over Lake Huron Mon night.
This solution suggests the possibility of several inches of rain
across Se Mi Mon/Mon night (whereas the GFS camp is more in the one
to two inch range). There remains a fair amount of ensemble spread
with the ECMWF members in the handling of this system. There is also
concern that the ECMWF may be over deepening this system (a trend
noted in several systems last cool season). Perhaps better sampling
of the northern stream energy now entering the Pacific Northwest
today will lead to a convergence in model solutions over the next
couple forecast cycles.

The aforementioned concerns with the ECMWF solution will steer the
forecast toward the GFS camp this forecast cycle, with the main
impact being a little lower forecast rain totals and slightly lower
wind speeds on Tues. As the southern stream wave enters the TN/OH
Valleys Mon/Mon night, mid level deformation will intensify across
the slow moving front over Se Mi. Tightening of the mid level theta
e surfaces within good upper level divergence and conditional mid
level instability will lead to robust mid level ascent over Se Mi.
This combined with a good influx of moisture into the frontal slope
(pwats around 1.5 inches) will support high chances for rain,
especially Mon afternoon and evening.

A deep upper low is forecast to develop over the Great Lakes by
Tuesday. Cold Canadian air will be driven into the region by this
system, with 850mb temps expected to drop into the negative digits.
Diverging model solutions and poor run to run continuity lead to
high forecast uncertainty mid week into next weekend. The expected
persistence of mid level troughing over the region through mid week
with periodic mid level waves will support occasional showers
Tues and Wed.

MARINE...

Southerly winds in the 15 to 20 knot range today ahead of a cold
front, which will slowly work into southeast Michigan tonight. Wind
gusts up around 25 knots over southern Lake Huron this evening will
diminish as we head into Monday as the frontal boundary stalls over
the area. Low pressure coming up from the south on Monday will be
deepening, but it appears the track will be too close to the Central
Great Lakes to generate Gale Force winds, and the Gale Watch will be
dropped. Although, there still is a less than 30 percent chance the
low could deepen greater than advertised to produce gales, but would
not be until late Tuesday as colder air wraps into the system.

HYDROLOGY...

A cold front carrying a band of showers will work into the area late
this evening into early Monday morning before a rapidly
strengthening low develops along it causing it to become nearly
stationary over Lower Michigan. Although the strength and track of
the low remain uncertain at this time, there is potential for more
than 2 inches of rain over a portion of the area Monday into Monday
night as strong deformation forcing lifts through the peninsula.
Urban and small stream flooding will be a possibility during this
time.

&&

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

$$

AVIATION.....SF
DISCUSSION...SC
MARINE.......SF
HYDROLOGY....SF


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