National Weather Service United States Department of Commerce

Forecast commentary -

The forecast remains on target as a cold and rainy day unfolds across Southeast Michigan with a
gusty northeast wind adding some harshness to conditions. The exception is across the Tri Cities and
portions of the northern Thumb where breaks of sun provide much improvement over points south.
Clouds are expected to increase toward that area but incoming data and observations support a halt
to the westward progression of the rain band around mid afternoon. It is expected to become centered
roughly along a line from Bad Axe to Flint which offers a chance of light showers brushing
Shiawassee and southern Saginaw counties. This was the primary check in the morning update along
with extension of the lakeshore flood advisory through the afternoon for Monroe county.


. . posted at 1153 AM EDT Sat Apr 20 2019



Southeast Michigan holding position early this morning within the expansive northern periphery of a
mid level circulation centered over the lower Ohio Valley. This circulation is forecast to gradually
lift northeast over the next 24 hours, reaching the central Appalachians by Sunday morning. This
movement will draw the attendant mid level deformation axis and an accompanying plume of higher
moisture westward into southeast Michigan during the daylight period. Ongoing light rainfall fixated
along far eastern areas sustained via weak isentropic ascent within the background of a
backing/cyclonic flow above 850 mb. While this forcing will tend to fade through the morning,
renewed deep layer ascent tied to the inbound deformation will work to expand the coverage of
rainfall westward and into a good portion of the forecast area late morning into the afternoon. This
will present a high likelihood for a several hour period of rainfall generally along and southeast
of a Howell to Flint to Bad Axe line. Diminishing potential northwest of this line, with mainly dry
conditions now favored over the Saginaw valley today. The cool resident airmass contained within the
prevailing low level north- northeast gradient will again see limited diurnal temperature recovery
today, owing to the extensive cloud cover and increasing shower potential. Warmest readings likely
noted outside the expected precipitation axis over northwest sections /northwest of Saginaw/, where
highs may push well into the 50s. Elsewhere, afternoon readings will be limited primarily to the mid
and upper 40s. Gusty conditions will contribute to this raw environment, broadly reaching 25 mph at
times with a localized higher response of 30 to 35 mph expected immediately downwind of Saginaw Bay.



A contracting axis of deeper moisture may tend to persist well into the evening hours as the
deformation only slowly unravels upon exit of the parent circulation. This will maintain a window
for light rain prior to midnight over a small areal footprint. Otherwise, conditions tonight will
become marked by strengthening deep layer stability as upper heights increase above weak low level
ridging. Despite a reduction in inversion heights and a corresponding decrease in moisture depth,
narrow region of moisture still tucked beneath the inversion favors a lingering stratus deck well
into the night. Clearing potential will increase from northwest to southeast Sunday morning as the
low level thermal trough pulls east and deep layer drying takes a greater hold.


Dry conditions hold during the latter half of the weekend as upper ridging takes control. Assuming
any lingering early day stratus vacates prior to midday, the high degree of insolation into an
increasing thickness field will translate into a noteworthy warming trend Sunday. The 850-925 mb
thermal layer will net roughly 6-8 degrees from that noted Saturday, yielding afternoon temperatures
well into the 60s.


Moderating trend continues into Monday, aided by developing warm air advection within increasing
southerly flow along the backside of the departing ridge axis. The overall temperature response
still carries some uncertainty Monday, owing to the possibility that thicker high cloud arrives in
advance of an approaching mid level wave. Potential certainly exists for highs to eclipse 70
degrees, particularly if the area manages to witness a period of sunshine within the warm sector.
Greater potential for showers/elevated thunder initially focuses to the north and west during the
daylight period, but with increasing potential Monday night into Tuesday as the main vorticity max
and associated surface reflection/cold front lift through the Great Lakes.


. . posted at 350 AM EDT Sat Apr 20 2019