Scientific Forecaster Discussion
fxus63 kdtx 201944
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
344 PM EDT sun Oct 20 2019
Quiet conditions for the remainder of today as downstream shortwave
ridge pushes to the east ahead of the next impactful system
developing across the plains. A strong upper level jet streaming out
of the pac northwest and over the central rockies with an associated pv Max
is supporting Lee cyclogenesis this afternoon. Throughout the day
tomorrow, the reintensification of the upper jet rounding the base
of the trough will trigger the deepening of this surface low to
around 985 mb as it drifts across the upper Mississippi Valley and
into the Western Lake Superior basin by the evening. Warm/moist air
advection within increasing southerly flow will push across
Southeast Michigan allowing for high temperatures in the 60s tomorrow
afternoon. Moisture transport in conjunction with isentropic ascent
and upper jet support will bring widespread likely chances for
precipitation. Showers and thunderstorms along the prefrontal trough
will be followed by a cold front before the mid level dry slot
spreads across the state. The environmental set up as convection
rolls through will be one of high shear and low instability. This
will bring a non zero chance for strong to potentially severe storms
given the overall wind environment. Low topped discrete cells
embedded within a broken line of activity will be moving generally
from southwest to northeast through the County Warning Area.
The increasing gradient flow tomorrow will also allow for a rather
gusty day as southeast winds begin ramping up by late morning/early
afternoon and into the evening. Gusts of 30-40 mph will be possible
during this time. The increasing onshore flow will result in
Lakeshore flooding concerns across portions of the Great Lakes. Post
frontal winds out of the south/southwest will weaken slightly late
Monday night into Tuesday morning.
Cold air advection starting late Monday night will bring
temperatures back down into the 50s for Tuesday. Winds begin ramping
back up again by Tuesday afternoon out of the southwest as mixing
depths increase into 30+ knot flow associated with the occluded low
that is still hanging around in southern Ontario. Gusts of around 30
mph will again be possible on Tuesday. Lingering trough with
associated shortwave energy will bring lingering precipitation
chances mainly across the Saginaw Valley.
Wednesday looks to be cool and dry as the upper level trough axis
exits east and lower Michigan resides underneath the upper level
northwest confluent flow. Pretty good moisture (pw values aoa 0.75
inches) surge returns Wednesday night into Thursday however, as
weakening wave comes out of the Midwest. The 850-750 mb Theta-E axis
looks to crest over Southeast Michigan late in the day/Thursday
evening, presenting the highest chance for rain showers with low
level fgen/frontal boundary in place. Positive tilted upper level
trough axis/respectable cold pool (850 mb temps of -4 to -8 c) to
pass through the central Great Lakes on Friday... per 12z Euro.
Large surface high to then move in for Saturday providing a pleasant
and dry day before rain potentially arrives on Sunday as Euro and
Canadian models indicate a Gulf Coast system tracking north, at
least reaching into the Ohio Valley. Outgoing forecast pops may be
too low for Sunday, but the 12z GFS does off up support for a dry
forecast as the upper level energy diving into the base of the
trough across Texas on Friday is not as strong and we are
potentially dealing with just a progress longwave trough axis coming
through Friday/Friday night. Majority of the GFS ensemble members
gives credence to the operational run, so will be interesting to
follow the next couple runs out of the Euro & GFS.
Deepening low pressure to the west will lead to a transition to
moderate easterly flow tonight. This low is forecast to deepen
throughout the day Monday supporting a transition to uniformly
strong southeast flow with gusts to gale force expected Monday
afternoon through Monday evening. This will be especially true over
Northern Lake Huron where gusts to 40 knots or more seem plausible
by Monday evening.
Further south, the relatively stable southeast fetch will initially
limit wind gust potential with gale force gusts then expanding over
much of the lake as cold air infiltrates by Monday evening. Winds
will veer to the southwest late Monday night into Tuesday with gale
or near gale force gusts expected again after a relative lull during
the morning hours. Gale warnings and small craft advisories will be
issued with this forecast package with the cutoff between the two
hazard falling roughly through far Southern Lake Huron.
Strong low pressure will track into the northern Great Lakes on
Monday with a trailing cold front then pivoting east/northeast
through the region Monday night. Widespread rainfall is expected
from Monday afternoon into Monday night as this system encroaches on
and then passes through the area. At this time, basin-averaged
rainfall amounts of around one half of an inch are forecast with
localized amounts up to three quarters of an inch possible. Hence,
flooding is not expected. However, ponding on susceptible roads and
other prone areas is expected.
issued at 126 PM EDT sun Oct 20 2019
VFR conditions are expected throughout all/much of the forecast with
rain showers and possible MVFR conditions moving in at or shortly
after 18z Monday as occluding frontal boundary encroaches on the
region. Light/variable winds this afternoon will become northeast
this evening/overnight and then veer to southeast and increase by
midday Monday with gusts nearing 20 knots by 16z-18z.
For dtw...light northeast winds will become southeast late tonight
into Monday and increase by midday. Rain showers will hold off until
18z-20z Monday afternoon with eventual MVFR conditions possible with
this activity late Monday.
Dtw threshold probabilities...
* low for cigs aob 5kft after 16z Monday, moderate by 20z Monday.
Michigan...Lakeshore flood advisory from 11 am Monday to midnight EDT Monday
night for miz049-055-063.
Lake Huron...Gale Warning from 2 PM Monday to 4 am EDT Tuesday for lhz363-421-
Gale Warning from 11 am Monday to 4 am EDT Tuesday for lhz361-362.
Lake St Clair...Small Craft Advisory from 11 am Monday to 4 am EDT Tuesday for
Michigan waters of Lake Erie...Small Craft Advisory from 11 am Monday to 4 am EDT Tuesday for