National Weather Service United States Department of Commerce

Forecast commentary -

Strong Canadian high pressure ( 1030+ mb ) will remain anchored along/near Ontario/Quebec border
over the next several days.

12z DTX indicated a very dry airmass in place over southeast Michigan today, as 850 mb dew pt
depression checked in at 32 C, with a pw value of 0.14 inches.

Brisk northeast winds will continue through tonight ( holding min temperatures in the low/mid 20s ),
shifting to the north-northeast early tomorrow morning. Strengthening low-mid level circulation
tracking through southern Ohio will send 850-700 mb theta-e gradient over Lenawee/monroe counties
overnight. But with continued low level feed of dry air, still looking at the snow shield holding
near the southern Michigan border. 12z regional GEM would even argue for light accumulations south
of I-94 as 700 mb specific humidity rises to 2.5 g/kg. Preference is more toward the slightly drier
rap solution, but low chance pops for light snow late tonight still seems warranted south of I-94,
especially if that flow becomes a bit more easterly off Lake Erie.

Upper level shortwave ridging to become established on Wednesday. With northerly flow off cold
waters of Lake Huron, looks like good temp gradient setting up during the day, as 925 mb temps
advertised to range from -8 C over northern tip of the Thumb to -2 C along the southern Michigan
border, translating to highs in lower 30s to lower 40s.

Dry airmass and skies becoming clear Wednesday night will lead to a favorable radiating night,
sending temps into the lower 20s. Could even see mins sneak into the teens in the normally colder
locations if winds fully decouple.

Thursday and beyond...

Confluent nw flow still forcing all meaningful precip south of the area while ensuring mostly sunny
skies with dominant high pressure at the surface. The third week of spring will see temperatures
creeping ever-closer to average values as ridging builds over the central Contiguous U.S. for the
remainder of the forecast period.

. . posted at 309 PM EDT Tue Mar 20 2018

Dry and cool week ahead as the main jet axis to the south of the region with split flow aloft and a
thermal trough locked overhead. In addition, broad surface high is now anchored over northern
Ontario where it will remain more or less through the coming weekend. This high will usher in cool
and dry air through the coming days as flow wavers from northeasterly to northerly. High
temperatures will hover around 10 degrees below normal through the week.

Though it will be dry, the storm track just to our south will bring a couple storms near the mi/oh
border. First storm is coming together right now over Tennessee as a compact vort max tracking east
spins up a surface low beneath it. This pairing of lows will continue toward the east coast today
while a stronger wave surges into it from the west. Difluent flow aloft and developing area of
pressure falls will stretch and enhance the trailing trough through the Ohio Valley. Most of the
short range and hires models are keeping the precip shield to our south, while the ec/GFS/gem still
want to nudge it into southern Michigan. Soundings are very dry with deep layer of dry air from
900-600mb ( some even deeper ), meaning snow will have a very difficult time reaching the ground.
Will remove the chance pops for extreme southern Michigan tonight in favor of the drier suite of

For the latter half of the week, upper level ridge will begin to build into the midwest, but
persistent trough will hold over the Great Lakes. Slight moderation to the airmass as the flow
becomes more north/northwesterly and highs start to increase slightly. This will bring highs into
the low 40s.

Our next chance of rain will come this Saturday night as a low skirts the region to the south yet
again. Model trends have been drier over se Michigan as they again split the flow over the region
with the southern stream drawing the system southward. Surface high over Ontario and Quebec is
forecast to be even stronger than the current high thus it should also help shunt the activity
southward. Will keep a chance PoP going for now while we monitor trends further.

Amplified ridge aloft and at the surface should lead to favorable and warmer conditions Sunday thru
Monday before the next trough swings through the region bringing the next chance of precip either
Tuesday or Wednesday.

. . posted at 337 AM EDT Tue Mar 20 2018