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afddtx

Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
357 am EST Sat Dec 7 2019

Discussion...

Cool northwest flow aloft will usher in a minor shortwave across the
northern Great Lakes with little consequence to Southeast Michigan
this morning. Expecting a quiet day today under the influence of a
surface high pressure and an overall dry airmass. Low stratus from
yesterday have relinquished their hold over the area, but mid/high
clouds are now moving in association with warm air advection aloft.
Southerly return flow will kick in as the surface high moves into
the eastern Ohio Valley towards the late afternoon. This may bring
some breaks in clouds later today as flow tries to draw them to the
north. Low level warm advection will commence too late in the day to
see a response in daytime highs which will hold in the 30s.

Strengthening low level 40-50 knot jet will help advect warm/moist
air into the area on Sunday. An increase in 850 mb temperatures to
around 2c by 12z Sunday morning that will support high temperatures
in the 40s. Tightening pressure gradient between high pressure off
the East Coast and troughing across Ontario will bring an uptick in
southerly winds with gusts to around 20-30 mph by late Sunday
morning and afternoon. A frontal boundary will be sagging southward
and and eventually become stationary. This will become the focus for
convection later in the day Sunday into Monday when a low pressure
system develops near the left exit region of the 130 kt southern
stream jet and moves northeastward along this frontal and through
Michigan. The track of the low keeps Southeast Michigan on the warm
side with another day of mostly 40s to possibly 50 degrees towards
the Michigan/Ohio border for mondays high temperatures. This means that low
level thermal profiles will be warm enough for p-type to fall as rain
through most of Monday. Chances for lighter precipitation will start
Sunday evening with bulk of precipitation falling early Monday
morning and afternoon.

Cold air will begin filtering into Michigan Monday night as the low
lifts into Quebec bringing potential for a transition from rain to
snow with any lingering precipitation on the back side of the system
or from lake enhanced precipitation under cold low level northwest
flow. Thermal trough then sets up for the mid-week period bringing
Arctic air to the Great Lakes along with opportunities for lake
effect snow. Temperatures at 850 mb will drop to around -20c by
Wednesday afternoon bringing high temperatures down into the teens
and low 20s. The coldest morning of the week will be Thursday
morning with lows in the lower teens and wind chills dropping into
the single digits.

High pressure will be passing through the Michigan and to the east
during the day on Thursday turning low level winds to the southwest.
This will help drive the Arctic airmass out of the region towards
the end of the work week. This will then bring gradual warmup back
into the 30s by Friday. Conditions remain mostly dry until the
weekend when the next low pressure system lifts out of the Gulf and
across the eastern Ohio Valley potentially bringing the next chance
at impactful weather to Southeast Michigan.

&&

Marine...

High pressure builds into the southern Great Lakes early this
morning. The high will be quick to depart to the east by Sunday
evening while a cold front begins to sink into the northwestern
Great Lakes. The result will be a strengthening southwesterly
gradient over the region today. Developing low pressure over
southern Ontario will lead to increased warm advection which will
result in a stable profile over the cool water, but a strong low-
level jet and long southwesterly fetch will bring the potential for
gusts to gale force over northern and Central Lake Huron for much of
Sunday. A gale watch has been issued for this area. Another low
pressure system then tracks through the region on Monday evening,
bringing widespread rain for most of the area and snow for Northern
Lake Huron. This system will usher in a much cooler air mass and
unsettled conditions for the early part of next week.

&&

Hydrology...

Next chance for an extended period of rainfall will start Sunday
evening and continue through Monday. Increased moisture transport
will bring precipitable water values nearing 0.8 inches into Southeast Michigan as
a low pressure system moves across Michigan. Rainfall totals will
range mostly between a quarter of an inch to a half inch. Higher
totals will be possible if any training of heavier rainfall occurs
over any location. A transition to wintry mix will be possible if
any precipitation lingers long enough after the system passes off to
the northeast. Rainfall may lead to ponding of water in low-lying
areas and small rises on area rivers.

&&

Previous discussion...
issued at 1153 PM EST Fri Dec 6 2019

Aviation...

Cold cyclonic flow will remain over lower Michigan through tonight
with composite longwave trough in place over far eastern North
America. Differential anticyclonic vorticity advection with rising
geopotential heights supports increasing high pressure over the
region. Satellite trends show steady erosion of lower cloud stratus
through the course of the evening. High cloud will move into the
state on Saturday in response to increasing warm air advection aloft
and remnant shortwave passing from the Dakotas down through the Great
Lakes. VFR conditions. Low confidence in any MVFR boundary layer
cloud for Saturday.

Dtw threshold probabilities...

* low for cigs aob 5000 feet tonight and Saturday.



&&

DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...Small Craft Advisory from 4 am to 4 PM EST Sunday for lhz421-422-
441-442.

Gale watch from late tonight through Sunday afternoon for lhz362-
363.

Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&

$$

Discussion...aa
marine.......tf
hydrology....aa

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