National Weather Service United States Department of Commerce


000
FXUS63 KDTX 110957
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
557 AM EDT Sun Apr 11 2021


.AVIATION...

Showers have cleared the terminals (sans KMBS) this morning with VFR
in place across the region. Conditions this afternoon will be
governed by the northward progression of additional shower activity
as an occluded low migrates into Lower Michigan. Model trends favor
scattered showers for the Metro terminals this afternoon and evening
while from KPTK north, rain will be more isolated or hold off
altogether. MVFR cigs are expected with this activity into the
overnight hours. Also monitoring potential fog development as winds
become nearly calm late tonight within a moisture laden lower
atmosphere and a lowering trend in cigs to accompany IFR vsbys for
the Metro airfields until nearly the end of the TAF cycle.

For DTW... Another round of scattered showers will evolve Sunday
afternoon and tapper off late evening. Mainly MVFR concerns until
late tonight when IFR vsby/cig becomes possible.

.DTW THRESHOLD PROBABILITIES...

* Medium for ceiling at or below 5000 ft this afternoon and high
Sunday evening/night.

&&

.PREV DISCUSSION...
Issued at 357 AM EDT Sun Apr 11 2021

DISCUSSION...

The closed low pressure circulation centered near the south end of
Lake Michigan presents impressively in satellite and radar imagery
during the early morning. The band of rain associated with this
mature system exits the Saginaw valley and northern Thumb toward
sunrise followed by a pronounced dry slot that takes over the
weather for SE MI for the remainder of the morning. Locations along
and south of the I-69 corridor have the best chance of sunshine with
any staying power before the core of the upper low pivots into the
area. Despite the morning sun, impressive occlusion of the surface
front displaced the thermal ridge eastward leaving a rare case of
April south flow low level cold advection to progress through the
day. Model projections take 850 mb temps down to about 2C within the
cold core of the low pressure system which leads to near steady
temperatures or a couple degree rise for highs in the 50s. Any
temperature rebound is further hindered by rain showers that expand
coverage within the upper low circulation. About the only result of
diurnal effects will be the increase in coverage and intensity of
showers into the likely POP range mainly along and south of the
I-96/696 corridor. Freezing level drops to around 5000 ft this
afternoon but thunderstorm potential remains limited in this scenario
due average relative lapse rate within the thermal profile and which
was unable to generate any lightning upstream yesterday.

The daytime heating influence on the pattern fades and leads to a
decrease in showers more into scattered coverage for the rest of
tonight. There may even be periods of time with no coverage judging
by trends in hi-res model solutions, however chance POPs remain
warranted as the upper low pivots slowly overhead and is still near
the west end of Lake Erie by Monday morning. The rex block in the
500 mb flow positioned over Labrador ensures the Great Lakes
circulation stalls for much of the day. This allows the current
Canadian Rockies trough to catch up and merge over Lower MI
resulting in a rare coast-to-coast zonal deformation pattern that
features easterly flow aloft all across southern Canada. Likely POPs
are maintained in the forecast for showers during the merging process
but then drops off Monday night into Tuesday. The consensus of
solutions from the 00Z model run suggest POPs remain more in the
chance category as long as the upper level deformation axis remains
positioned overhead which then keeps the surface trough located to
our north where showers are more likely to be concentrated.

The general trend in model solutions has the upper air pattern
shifting toward a more standard omega block off the Pacific coast
resulting in the deformation zone pulling apart over the Great Lakes
during the late week period. There is a lot of moving parts in this
process which likely leads to adjustments in upcoming forecasts. As
of this model cycle, the trend is toward increased influence of high
pressure and a modest warming trend in the Great Lakes to finish the
week.

MARINE...

Low pressure will continue tracking northeast toward lower Michigan
today bringing a period of unsettled weather that will last through
at least Monday. Rounds of showers will accompany the low pressure
system, especially during the daytime hours today and Monday.
Moderate south to southeasterly winds will prevail today and into
tonight, with gusts generally holding below 20 knots. The low
pressure system will begin to slowly weaken late Monday into Tuesday
as it stalls over the central Great Lakes, as winds become lighter
and veer more southwesterly early next week. Drier weather and winds
shifting to the north will then prevail by the middle of the week as
weak surface high pressure attempts to build across the central Great
Lakes.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....KK
DISCUSSION...BT
MARINE.......IRL


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