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FXUS63 KDTX 181053
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
553 AM EST Fri Jan 18 2019


.AVIATION...

Just enough lingering low level moisture expected this morning to
promote MVFR cigs, but drier west-northwest flow is eventually
expected to win out and produce VFR conditions this
afternoon into the evening hours. Light snow then expected to
develop around midnight across southern TAF sites, spreading north
overnight.

For DTW...Low level dry air will take a while to take hold, and low
clouds are not expected to dissipate until late afternoon hours.
Snow looks to develop around midnight, and pick up in intensity,
with peak snow rates/reductions in visibilities expected 13-17Z
Saturday.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less through early afternoon, low
late this afternoon and evening, then high tonight.


* High for snow as precipitation type.

&&

.PREV DISCUSSION...
Issued at 311 AM EST Fri Jan 18 2019

DISCUSSION...

Lingering flurries will come to an end shortly after forecast
issuance this morning. Some semblance of sfc ridging will expand
across Lower Michigan today amidst mid level confluent flow,
possibly allowing some dissipation of the stratus deck overhead. Low
level cold air advection today will be offset to a degree by a
deepening daytime mixed layer, supporting daytime highs ranging from
the upper 20s to low 30s.

Mid level trough amplification will be underway today in the lee of
the central/southern Rockies. This wave will then traverse the
southern Mississippi Valley Saturday before lifting into the central
Appalachians late Sat night. The strongest ascent, aided by some
modest instability, will be confined to the surface low track across
KY/TN. The amplitude of the long wave trough will still result in
some mid level height falls across srn Mi late tonight into Sat
morning. The lift across Se Mi will just be much more elevated this
far north of the sfc low. Model solutions are in good agreement in
showing an initial band of light snow tracking across srn Mi
overnight tonight, aided by mid level frontal forcing within the
entrance region of an upper jet. This upper jet is forecast to
intensify to the northeast of the region Saturday morning, resulting
in some strengthening of the mid level front over Se Mi which will
also accelerate the moisture transport from the TN/OH Vallyes into
the elevated front. Trends over the last few model cycles have been
toward a little faster exit of this forcing to the east Sat
afternoon as a northern stream positive PV anomaly quickly drops
into the nrn Great Lakes.

Low level northeast winds will be on the increase tonight, resulting
in some dry air advection in the low levels. This along with the
less than impressive isentropic ascent and unfavorable snowflake
size will pose some limiting factor for good snowfall rates tonight.
A little better and deeper lift with some potential for a period of
more favorable snow microphysics will support a little better
accumulation potential Saturday morning before the forcing exits in
the afternoon. The array of model liquid QPF fields suggest less
than a tenth of inch north of the I-69 corridor and up to 4 tenths
near the Ohio Border (where forcing and moisture quality will be
better). Taking into consideration that low level dry air and less
than favorable snow microphysics for at least a good portion of the
event, a conservative forecast for total snow seems in order (3-5
inches near the Ohio Border tapering to less than an inch north of I-
69). Hi res solutions actually suggest some meso scale influence off
Lake Huron under the northeast flow on Saturday, with a potential
lake plume pushing inland off Saginaw Bay. This may lead to some
locally higher snowfall amounts in the Saginaw Valley.

As the system exits to the east Sat afternoon/evening, the low level
flow will back toward the north-northeast. Despite a surge of dry
arctic air and subsidence keeping the over-lake mixed layer
relatively shallow, the long fetch over Lake Huron and favorable
snow microphysics will provide a chance for some minor accumulations
(of dry fluffy snow) along the eastern thumb into the Port Huron
area Sat night through Sunday. Otherwise, the cold air that will
advance into the area during the latter half of the weekend will be
the coldest thus far this winter (850mb temps dropping to -20 to
-23C by Sunday). This will keep Sun high temps only in the teens.
Wind chill readings will range from zero to 15 below Sat night into
Mon morning.

Arctic high pressure overhead will keep conditions dry and cold on
Monday. A fast moving mid level wave is then forecast to lift out of
the central plains across the Great Lakes on Tuesday. The 00Z model
suite have trended a little less amplified and faster with this
feature. They continue to suggest a strong theta e surge ahead of
this wave that will not only bring a good shot of precipitation, it
will also drive some warm air into Se Mi, possibly changing snow
over to rain. Colder air is then expected to quickly follow in the
wake of this system for the remainder of the week.

MARINE...

Weakening northwest winds today will give way to increasing
northeast winds this evening as low pressure tracks well south of
the Great Lakes region on Saturday. Snow, along with northeast winds
of 20 to 30 knots are expected during the day, as much colder air
filters into the region over the weekend. Brief gusts to
marginal gales are possible over western Lake Erie and southern Lake
Huron. Winds will remain strong into Sunday as they back around to
the north, with heavy freezing spray likely over open waters of Lake
Huron. Cold airmass will persist on Monday, but winds will become
much lighter and shift to the southeast.

&&

.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


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