Forecast opinion

Early indications, based on radar trends and initial 12z model guidance suggest that the light snow
event expected over the forecast area will be delayed slightly. While flurries and light snow
showers are still expected to spread into the area this afternoon, a wedge of very dry air, noted
from 850-600mb on the 12z KDTX sounding will limit precipitation with this initial push of moisture
within broad isentropic lift pattern under left exit region of 100-120Kft h3 jet streak. As noted,
radar trends support this idea as activity to this point has faded steadily in its transit acrosses
Lower Michigan. Better fgen forcing aided by the jet streak will eventually overcome this and allow
for some light accumulations during the late afternoon, particuarly from the Saginaw valley on east
along the I 69 corridor.

This does not mean that overall snow amounts are expected to be less than originally expected. The
aforementioned jet streak has a slight anti-cyclonic shape to it as it archs across the area. This,
in general, should support a better pocket of lift within the right entrance region, which will
cross the area overnight.

12z model solutions seem to pick up on this and bring the most persistent light snow to the area
from evening into the overnight hours as strong warm air advection pattern continues to provide
additional lift/moisture coincident with this jet support. Between struggling eastward expansion
from initial evaporation, and the second area of lift overnight, the event is essentailly pushed
forward in time by 2-4 hours, with 1-2 inches still expected through a fair portion of the forecast
area with local amounts perhaps approaching 3 inches within strongest fgen banding over the mid cwa,
roughly the I 69 to M-59 corridors. Conversely, would expect the areas south of I 94 and also over
the northern Thumb to receive the least amount of snow, likely less than an inch in some instances.

Will be issuing an update by noon to better align the forecast to these expectations. Timing will be
adjusted most, but location will also be refined ever so slightly.

. . posted at 1133 AM EST Friday November 28 2014

Remaining Forecast thoughts - Saturday through Thursday

Warm air advection will work its way to the surface on Saturday as a surface warm front lifts north
through the central Great Lakes as mid level heights continue to rise across the region. 850 mb
temperatures are forecast to rise to around +10 celsius across the southern Great Lakes. Despite the
passage of the surface warm front daytime temperatures are only expected to get to around 40 degrees
as a strong inversion traps low level moisture in the lowest few thousand feet of the column. This
will lead to an extended period of light rain or drizzle during the weekend. Low temperatures on
Saturday night will be close to Saturdays highs with abundant cloud cover and continued drizzle
preventing much in the way of radiational cooling. Temperatures on Sunday will range from the mid
40s across the north to the mid 50s towards the Ohio border ahead of an approaching cold front
progged to track through the area late Sunday afternoon into Sunday evening. Although this front
will bring a strong push of cold air through the area, it will not have much in the way of
precipitation as the low will be of Pacific origins and unable to tap into deeper gulf moisture well
to the south.

Behind the cold front daytime highs will come back down into the 30s during the early part of the
work week as strong high pressure of 1040+ mb tracks through the Great Lakes region. Modest warm air
advection will boost temperatures a few degrees Wednesday and Thursday on the back side of the high
as a mid level trough with a weak surface reflection brings a slight chance for snow showers to the
area during the middle part of next week.

. . posted at 342 AM EST Friday November 28 2014


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.