Commentary on the forecast - afternoon and Tonight

Se 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 mid 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 mid 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.

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Remaining Forecast discussion -

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 forecast
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.

. . posted at 352 PM EST Monday January 26 2015


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