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Area forecast discussion 
National Weather Service Detroit/Pontiac Michigan
658 PM EST Monday Jan 26 2015


Weak surface ridging anchored over the region will sustain a
dry/stable low level environment through at least the early portion
of the night. VFR conditions with simply some pockets of thicker
middle/high cloud through this time. The ridge positioning will
retain a light east to northeast flow tonight. This pattern will
introduce the potential for some degree of stratus expansion off
lakes Huron/Erie into Southeast Michigan through the early-middle
morning period. Latest observations provide Little Signal yet on
possible coverage or timing. Will continue to highlight this
potential across the Detroit corridor. A backing wind field
will eventually settle to northerly into Tuesday. This process
may allow for a brief period of VFR diurnal stratocu early in
the day before a drying northerly flow takes a greater foothold.

//Dtw threshold probabilities...

* moderate for ceiling below 5000 feet tonight into Tuesday morning.


Previous discussion...issued 352 PM EST Monday Jan 26 2015

Short term... afternoon and tonight

Southeast Michigan is in the quiet weather area between a weak wave of low
pressure over the Midwest and the developing East Coast snowstorm.
The Midwest wave will leave some middle and high clouds over our area
tonight as it shears apart and transfers its upper level energy to
the powerful cyclogenesis occurring offshore of the New England
states. The remnant middle and high clouds over our area will then be
complemented overnight by clouds from the western fringe of the East
Coast system. The amount and extent of these clouds remain in
question and will be strongly dependent on a boost from Lake Ontario
and Lake Erie while the low level flow remains easterly...and then
from Lake Huron as the flow backs toward the north later in the
night. Afternoon satellite imagery indicates that Lake Huron remains
active with easterly flow carrying most of the clouds into northern
lower...and this suggests Lake Erie and Ontario should be able to
contribute as much tonight...especially once the nocturnal inversion
sets up after sunset. Coverage may not be solid but enough to make a
difference in the temperature forecast when combined with a Lake
Huron component as the wind turns toward the northeast after
midnight. Expect lows will be a few degrees warmer at all locations
compared to this morning but still capable of single digits interior
thumb and Saginaw Valley. Cloud cover should then respond with a
decreasing trend into Tuesday morning as the mean low level flow
turns more northerly and shortens or eliminates lake trajectories
and draws in increasing amounts of dry air building behind the East
Coast system.

Long term...

A number of factors will align to produce a localized surface high
pressure center over southeastern Michigan Tuesday through Wednesday
night. The ingredients include...very strong synoptic scale
subsidence along the periphery of the deepening Atlantic coastal low
pressure system...confluence aloft...and building geopotential
heights due to the Stout shortwave ridging pushing across the
western Great Lakes. Very little changes were needed to the
inherited forecast. Agree with the aforementioned discussion on a
less aggressive cloud forecast for Tuesday given overall magnitude
of the subsidence that is expected. Typically see very dry airmasses
in these wrap around surface ridges. The Wednesday morning low
temperature forecast is an interesting one because of the
potential for favorable radiative cooling conditions. However...a
lack of a fresh snowpack limits the certainty...current forecast
of upper single digits above zero to ten degrees is reasonable.
The eastward migration of the surface ridge axis and reemergence
of westerly return flow during the afternoon hours on
Wednesday...brings a good likelihood that temperatures could
moderate by as much as a category for Wednesday. Current forecast
calls for temperatures in the upper 20s to around 30 degrees.

Thursday will start out active as another clipper system moves
through the Great Lakes region. Center of the low will be tracking
across northern Illinois and Southern Lower Michigan through the day
on Thursday before exiting by early Friday morning. Previous
discussion mentioned a warmer thermal profile with a general 1 to 3
inches of snow over a 12 hour period still looking on target with
the latest model runs. Higher amounts will likely be seen over
northern areas of the County Warning Area with amounts tapering off closer to the
Ohio border. High pressure then builds in behind the departing
clipper...bringing with it much colder air to the region this
upcoming weekend.


Light to moderate winds will persist through Thursday as the
gradient relaxes due to resident high pressure. An approaching weak
low pressure Wednesday night through Thursday will cause an uptick
in southerly winds, but gustiness will be limited due to warm stable
flow from the south. Cold air moving into the Great Lakes in the
wake of this system will mark the beginning of a renewed stretch of
active marine weather Thursday night into next week as multiple
bouts of Arctic air traverse the waters.


DTX watches/warnings/advisories...
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.


long term....cb/ss

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