Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 211737
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
137 PM EDT Fri Apr 21 2017
Moisture lingering behind exiting low pressure remains trapped under
an inversion this afternoon. Meanwhile, cold air advection filtering
into the area if offsetting daytime heating, and will help to keep
ceiling heights in the 2500-3500 range for the remainder of the
afternoon and evening. Skies will start to clear over the western
part of Michigan this evening, affecting MBS first. The remainder of
the TAF sites will take a little longer for stratus deck to scatter
out as moisture under the inversion is reinforced by north and then
northeast flow off Lake Huron. This adds some uncertainty with
timing the breakup of the stratus deck from FNT south. Gusty west-
northwest winds (270-290) will gradually turn more northwesterly by
late afternoon (290-330). The mixed layer does not look to support
gusts over 25 knots. Gusts will subside this evening as sustained
speeds also fall to less than 10 knots overnight.
For DTW...Stratus deck below 5000 feet is likely to hold through the
evening before scattering out overnight. Timing of the stratus break-
up is a little uncertain due to reinforcement as flow turns north-
northeast off Lake Huron. Most likely time still looks to be around
07Z. West-northwest gusts, just over 20 knots at best, should stay
below crosswind thresholds.
MVFR stratus will likely hold through the afternoon before
possibly lifting above 3kft. CIGS below 5kft should then scatter out
around 06z as high pressure builds into the region.
//DTW THRESHOLD PROBABILITIES...
* High in ceilings below 5000 ft through this evening then low late
* Low for reaching crosswind threshold this afternoon.
Issued at 403 AM EDT Fri Apr 21 2017
Split flow is in place over North America this morning with the
southern branch bisecting the center of the contiguous United
States. This will generally hold for the next 48 hours or so before
a vigorous jet streak and associated shortwave try to impinge upon
the northern Great Lakes. The next couple of days will be
characterized by strongly anticylonic flow in the lower troposphere
with daytime temperatures running about 3 to 7 degrees below normal.
A shift in the pattern will eventually occur as flow trajectories
transition more uniformly out of the south on late Monday. The net
result is a wonderful stretch of springtime weather through the
early next week period before moisture return brings precipitation
chances by the middle of next week.
Latest MSAS analysis places the center of surface low pressure at
1006 mb over Georgian Bay. A well developed upper level jet maximum
has been working northeastward through the southern stream and is
now in place directly over southeastern Michigan. Forecasted theta e
plan view supports and surface observations confirm that richest of
near surface theta e has been shoved well eastward. What remains is
a secondary midlevel deformation axis that aligns well to the
northern edge of the aforementioned jet axis. It is this secondary
deformation axis that has remained some what axis with regards to
light shower and or drizzle activity. Various observation sites have
been reporting intermittent light hydrometeors all night. Per radar,
and forecasted lapse rates in the 1.5 to 5.0 kft agl layer decided
to carry a chance for a light shower north of I 69 through daybreak.
850mb theta e support some drying out just after daybreak across the
northern cwa which should strip out the light shower potential. Will
maintain the relative pessimistic cloud forecast for today given 700-
600mb convergence axis that will only slowly shear out across the
area. Clouds and the lower tropospheric cold advection will keep
temperatures in the lower to middle 50s. Gradient flow today will
become a small issue, with high confidence in west to northwest
winds today in the 25 to 30 mph range.
An anchoring of the entrance region to the upper level jet streak
appears it will really slow down the arrival of the surface ridge
axis tonight. As a result, expecting more of a gradient flow
component to hold on, which will limit the radiational cooling
potential. Lows tonight are expected to dip into the middle to upper
30 for areas outside of the urban heat island, around 40 degrees for
Geopotential height rebound on Saturday will support a lake aggregate
ridge directly over the central Great Lakes on Saturday. This will
support a fantastic spring day with sunny skies. Classic lake breeze
response is in order late afternoon and early evening keeping
shoreline areas cool. Outstanding spring weather will carry forward
both Sunday and Monday with temperatures moderating into the middle
60s each day. Model sounding show the subsidence inversion
collapsing down into the surface Sunday night. Any other time of the
year and one would be concerned about fog, but given the depth and
amount of drying of the boundary layer feel the potential is low.
Rather, it will serve in keeping clouds out of the picture until
late Monday night.
Low pressure will continue exiting east of Lake Huron this morning
with high pressure building into the region in it`s wake. The
gradient created in between these systems with west/northwest flow
ushering in cooler air, will result in elevated wind speeds through
the afternoon. Wind gusts are expected to peak near 25 knots within
the cool, unstable airmass thus will be issuing small craft
advisories for all the nearshore waters until this evening. The high
pressure system will remain over the Great Lakes through the weekend
providing favorable boating conditions.
Lake Huron...Small Craft Advisory until 8 PM EDT this evening for LHZ421-422-
Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.
Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.
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