Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 211558

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1158 AM EDT Sat Oct 21 2017


Clear skies below 10kft through the period as dry air and subsidence
dominate. Steady S to SSE flow near 10 kts will persist today before
backing and diminishing somewhat with nocturnal decoupling tonight.
S wind increases again Sunday morning.


* None.


Issued at 1011 AM EDT Sat Oct 21 2017

As of 1010 AM EDT...Quick update to the forecast to account for the
latest trends in observations from across the region, and ongoing and
upstream satellite trends for sky cover. Another great weather day
for late October is expected, with partly cloudy skies and dry
weather. It will be another mild day, with temperatures 15-20 degrees
above normal with highs reaching into the mid and upper 70s for most
areas. Rest of forecast is in good shape and previous discussion
highlights well below.

Issued at 309 AM EDT Sat Oct 21 2017


Return flow within the low level anticyclone over the eastern
seaboard will persist across Se Mi through the weekend. A region of
very dry air in the low to mid levels circulating around this high
will continue to advect across Lower Mi today. The result will be a
continuation of warm and dry weather. Although high level clouds
will be more plentiful today, good southerly flow with similar
mixing depths as yesterday and a slightly warmer airmass will
support highs mainly in the mid to upper 70s (15 to 20 deg above
late Oct norms). A slow moving sfc cold front will move into the
western Great Lakes tonight into Sunday, increasing the southerly
gradient across Se Mi. This will lead to another relatively mild
night (lows in the 50s). A later frontal timing will support dry
conditions for most if not all of the day Sunday. The gradient flow
will lead to breezy conditions and a little better mixing depths,
supporting forecast highs near 80.

The aforementioned cold front will be driven into Lower Mi ahead of
a long wave mid level trough axis. The 00Z model solutions continue
to suggest a split flow evolving as the trough moves into the
central US, with a cut off low developing over the srn Ms Valley and
the northern branch of the trough lifting into nrn Ontario by the
end of the weekend. A plume of deep layer moisture will still
accompany the front as it crosses Lower Mi late Sun/Sun night, with
some degree of upper jet support sustaining some low level fgen.
This will warrant a good chance of showers as it works into the

Northern stream trough amplification is forecast to take hold across
the nrn plains and upper Ms Valley on Mon downstream of a 150 knot
upper jet crossing the Canadian Rockies. Differences persist among
the various model suite in timing of the southern stream upper low
lifting northward and phasing with this amplifying northern stream
trough. The differences have large impacts on the forecast across Se
Mi Mon into Tues. The GFS solution continues to suggest a deeper and
slower southern stream low, phasing with the northern stream east of
the forecast area. This suggest the better rainfall potential will
be from the upper Ohio Valley into upstate New York. The ECMWF
remains faster with this phasing, thereby placing the better
dynamics and thus rainfall across Lower Mi with rapid sfc
cyclogenesis taking hold across the ern Great Lakes. The Canadian
solution is more in line with the ECMWF. There is quite a bit of
spread among GFS ensemble members, leading to a good deal of
forecast uncertainty. In maintaining continuity, the forecast will
remain a little favored toward the wetter Euro/Canadian solutions
Mon into Tues. Despite the model differences, there will a good deal
of cold Canadian air driven into the region in the wake of this


Southerly winds 10 to 20 knots today will increase into the 20 to 25
knot range tomorrow afternoon ahead of a cold front. This front will
bring showers late Sunday into Sunday night, along with a wind shift
to the west by Monday morning. Wind direction and magnitude will
then become uncertain early next week, as a deepening low pressure
system tracks into the Central or Eastern Great Lakes. The strength
of the low remains somewhat uncertain, but there does appear the
potential for Gale force winds by Tuesday.


A cold front will attempt to move through southeast Michigan Sunday
night, producing rain showers Sunday evening and Sunday night.
Rainfall totals around a quarter of an inch are expected. A
deepening low pressure system is the forecasted to move up from the
Ohio Valley early next, and this system will have the potential to
produce rainfall amounts in excess of one inch during the Monday-
Tuesday time frame. However, the exact track and strength of the low
remains uncertain at this time, which will determine where the swath
of heavy rain occurs.


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



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