National Weather Service United States Department of Commerce

Forecast commentary -

12z DTX sounding revealed stout low level inversion at 900 mb, which has been able to sustain clouds
thus far with the low level northeast flow coming off Lake Huron. However, afternoon mixing and
lowering inversion heights is supporting a north-south clearing tread over the central Great Lakes,
which should continue into the early evening hours. Weak shortwave trough passing through the
northern Great Lakes early this evening, with cold air filtering in overnight ( 925/850 mb temps
lowering into negative low to mid numbers over Lake Huron ), which looks to support a redevelopment
of Lake Huron stratus ( although significant differences noted in 925 mb relative humidity fields
between NAM/GFS/hiresarw/Euro ), pushing inland during the day on Wednesday, as differential heating
leads to increasing northeast flow, and potential low/circulation developing ( see regional GEM ).

Between clouds and northeast flow off Lake Huron, looks like there will be a significant range in
max temps, from mid 40s across the far north, to low-mid 50s across the far southwest, farthest
removed from Lake Huron. Once again, afternoon mixing/boundary layer depths increasing expected to
dissipate low clouds late, but warm advection mid/high clouds should then be on the increase ahead
of our next storm system. Low level thermal profiles will be borderline as precipitation overspreads
southeast Michigan Wednesday night- Thursday morning, as it looks like a narrow/700 mb fgen band
could break out/develop as good surge of moisture takes place, with 700 mb specific humidity
climbing to 5 g/kg by Thursday morning. Interestingly, the 12z NAM is one of the driest solutions
with the low level dry air holding into Thursday for most of southeast Michigan. Meanwhile, 12z Euro
is one of the more aggressive solutions in terms of QPF, but 1000-850 mb thicknesses all above 1305
M-along and south of I-69 corridor, suggesting all rain. Bottom line, expecting mainly a rain event
as surface temps in the 30s Wednesday night climb into the 40s on Thursday, but a brief period of
snow is possible late Wednesday night-Thursday morning, mainly north of M-59 if precipitation rates
are sufficiently high enough to wet bulb/saturate the initially above freezing warm layer ( 2-6 kft
per NAM soundings ). If that narrow but potentially intense 700 mb fgen materializes, a narrow swath
of wet snow accumulation is possible for Thursday morning commute, best shot along and north of I-69
corrdidor, but local SREF weighted probablistic guidance suggests rain, with low chance of snow
north of I-69.

Low pressure pushing east across northern Ohio will bring the continued chance for rain on Friday as
it pushes east into New England. The chance for rain is expected to diminish through the late
morning and afternoon hours, as a surface high starts to edge in from the west. The weekend looks to
be shaping up to be a nice one, as cloud cover gradually diminishes and temperatures warm-up
slightly into the mid- 50s for a high. Temperatures are expected to climb into the upper 50s to
lower 60s for the early half of next week as se winds usher in milder air.

Low pressure pushing ne from Texas into the Ohio Valley Monday into Tuesday will bring the next
chance for rain. There are slight variations regarding the track of the low, however, long-range
models are showing convergence regarding precipitation Monday night into Tuesday. Additional rain
showers will be possible as a second low develops from the Central Plains into Michigan Tuesday into
Wednesday. Confidence is much lower regarding this system as the GEM holds off on this potential
system until late next week.

. . posted at 314 PM EDT Tue Mar 28 2017

Quiet forecast through the midweek period as high pressure aloft and at the surface build into the
region. The last of whatever light showers can develop over the far southern forecast area will move
off early this morning but only a slow improvement in cloud cover will be realized. The surface high
currently over Manitoba, will track across Ontario and Quebec through the week which will place us
in the southern periphery of the ridge resulting in drier and cooler easterly flow. Expect a cooling
trend through Thursday in response to this sustained easterly flow. Stronger subsidence aloft due to
an amplifying ridge ahead of the next southern stream trough will dry the column out from the top
down. Basically we'll end up with a low stratus deck around 2-3Kft by this afternoon that should
scour out from north to south allowing some sun by nightfall.

Will keep with the cool easterly flow in the low levels on Wednesday but a drier airmass will result
in plenty of sun through the day. Could see some cirrus debris ahead of the next system and also a
few diurnal cu early in the diurnal cycle before scattering out. The next system will be over the
Southern Plains Wednesday, pinching off from the northern jet. Southern jet tries to absorb it but
some energy in the trough remains tied to the northern jet which isn't doing the models any favors.
Overall they are pretty well in sync but the setup could turn one way or the other pretty quick. As
for now will go with persistence forecasting with the steady model output.

The low will lift northeast Wednesday night with good warm air advection centered around 5-10Kft
ahead of it into the region. Low level easterly flow from the surface high will hold through the
day. Looks like the initial rain will stay to our west late Wednesday night and Thursday morning as
the 850mb jet surges northward over Wisconsin. This would all be elevated showers on the lead
isentropic leaf but gets a little complicated by the right entrance region of the northern stream
jet max over northern lower. Models are trying to light up this eastward extension of the elevated
front Thursday morning from about Flint northward. Dry air in the lowest ~8Kft will make it tough
for this to reach the ground but will be something to watch. Better precip chances come Thursday
afternoon as the 850mb jet slides over lower Michigan bringing a surge of better theta-e into the
area. This in conjunction with upper level diffluence and isentropic ascent looks to produce a broad
coverage of showers across the area. There does remain a chance of some mix precip at the lead edge
if it can get going early enough Thursday morning as dry, cool surface layer will wet bulb, but
overall think best precip chances will come after diurnal heating commences.

Rain will taper off overnight as the system progresses eastward with the last of the showers exiting
the area Friday morning. Ridging will build back into the region Friday for the weekend. This will
bring quiet weather and a slight warming trend back to the mid 50s.

. . posted at 322 AM EDT Tue Mar 28 2017