666
FXUS63 KDTX 202040
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
440 PM EDT Mon May 20 2024

.KEY MESSAGES...

- Another round of showers and thunderstorms is expected this evening
  as activity develops and moves in from western Lower Mi.

- An isolated thunderstorm could approach severe intensity with
  damaging wind the primary hazard. Large hail is also possible but
  tornado potential is low.

- Additional storms are possible Tuesday afternoon followed by a line
  of strong to severe storms late Tuesday night. Damaging wind is the
  greatest threat Tuesday night.

- Warm and muggy conditions with high temperatures in the mid to
  upper 80s continue through mid week until a cold front moves
  through the region Wednesday.

- There is one more chance for showers/storms Wednesday before a
  cooler and less humid air mass follows the front for the late week
  period

&&

.DISCUSSION...

The early afternoon convective cluster followed the warm front
supported instability gradient along and north of the I-69 corridor
this afternoon. Hourly mesoanalysis showed 0-6 km bulk shear
sneaking up to around 30 knots as the storms increased coverage,
just enough for some forward propagation and sporadic wind damage as
the storms matured. The southward moving outflow then became the
focus of a secondary development capable of its own sporadic wind
damage and large hail before exiting into Ontario at press time.

Yet another round of storms is on schedule to affect Lower/SE Mi
this evening as upstream activity develops eastward. Mid afternoon
satellite imagery clearly shows the outflow reinforced warm front
beginning to recover northward or at least hold a position near the
M-59 to I-96 corridors for the late afternoon. Surface pressure
falls associated with the inbound MCV will be sufficient to draw
instability northward into SW Lower Mi late in the diurnal cycle
while the mid level circulation further supports organized
convection. Maintenance of instability then becomes more
questionable after midnight as the surface low slips through central
Lower Mi. The surface low is a tracer for MCV support that carries
the remaining convective clusters into Lake Huron before sunrise.

The MCV subsidence wake appears as a substantial short wave ridge in
model data to start off Tuesday. The effective frontal boundary
sinks back south as well to leave conditions dry for the morning
before a transition to return flow moisture transport occurs in the
afternoon. Scattered showers and a stray thunderstorm are possible
through the evening as the surface warm front sharpens up ahead of
the next Midwest low pressure system. The southern stream
circulation in today`s Pacific coast trough has good model agreement
on a track into the Midwest where it deepens substantially by
Tuesday night. The leading cold front becomes the subject of the
next round of severe thunderstorm potential for our area, although
the latest model trends exhibit a strong nocturnal limiting factor
for eastward longevity. The 12Z HREF hi-res members show good
agreement on a convincing weakening trend across Lower Mi late
Tuesday night. This is a surprising solution given how strongly
forced the pattern is on the background of the larger scale low
pressure system. The SPC Slight/Marginal risk combo nicely depicts
the decreasing potential for severe intensity into Wednesday
morning.

&&

.MARINE...

A stalled boundary extends from southern Lake Huron to southern Lake
Michigan with a mid level system rippling along it. This helped
touch off a afternoon round of storms.  Additional mid level support
this evening will lead to another round of storms reaching the
eastern lakes around midnight. The front will linger Tuesday which
could help another round of storms in the afternoon. A stronger
surface low will then lift northeast through northern Michigan
Tuesday night into Wednesday, pulling a cold front through the
region leading to yet another round of storms Wednesday. Conditions
are expected to remain below Small Craft Advisory criteria tonight
through Tuesday, though locally higher winds and waves will be
possible within any thunderstorms. Winds increase out of the south
to 20 to 30 knots ahead of the associated cold front Wednesday, then
veer to the west Wednesday night into Thursday while remaining gusty
to around 25 knots. Less humid air settles in for the late week as
high pressure builds in.

&&

.CLIMATE...

Here are the record high temperatures for May 20th through
May 22nd:

May 20th:
Detroit                91 (set in 1977)
Flint                  92 (set in 1934)
Saginaw/Tri-Cities     93 (set in 1977)

May 21st:
Detroit                92 (set in 1977)
Flint                  93 (set in 1921)
Saginaw/Tri-Cities     94 (set in 1977)

May 22nd:
Detroit                90 (set in 1994)
Flint                  91 (set in 1934)
Saginaw/Tri-Cities     89 (set in 1992)

Here are the record high low temperatures for May 20th
through May 22nd:

May 20th:
Detroit                68 (set in 1934)
Flint                  65 (set in 1939)
Saginaw/Tri-Cities     70 (set in 1975)

May 21st:
Detroit                71 (set in 2013)
Flint                  67 (set in 1934)
Saginaw/Tri-Cities     66 (set in 2021)

May 22nd:
Detroit                67 (set in 1941)
Flint                  65 (set in 1977)
Saginaw/Tri-Cities     68 (set in 1977)

&&

.PREV DISCUSSION...
Issued at 1204 PM EDT Mon May 20 2024

AVIATION...

High based (6-10 kft), mostly scattered CU field developing with
diurnal heating/instability, with potential for scattered strong
thunderstorm development. Much higher confidence across Tri-Cities
region (MBS) and Flint vicinity as circulation/shortwave trough
tracking out of the Midwest lifts through northern Lower Michigan
this evening. Still, warm advection arm/instability gradient lifting
through southeast Michigan still presents a low chance for southern
areas, especially as activity becomes more surface based later
today. The 500 MB trough axis will be slow to move through the
Central Great Lakes, and with strong low level jet, scattered rain
showers/thunderstorms tonight, which will also tend to help lower
cloud bases more in the 2-6 kft range, mainly northern taf sites,
closest to the departing circulation.  Southwest winds today around
10 knots becoming weak westerly or variable tonight.

For DTW/D21 Convection...

Low chance of thunderstorms this afternoon into tonight, with
the bulk of storms expected to be north of the terminal. With timing
very difficult to pin down and the low chances of the airport being
directly impacted, preference is to leave out of the taf and monitor
trends for possible inclusion if confidence increases. Otherwise,
cloud ceilings look hard to come by, and any bkn-ovc layers above
5000 feet. Best chance for cloud bases aob 5000 feet looks to be
Tuesday morning.

DTW THRESHOLD PROBABILITIES...

*  Low for thunderstorms this afternoon through tonight.

*  Low for aob 5000 feet Tuesday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.

&&

$$

DISCUSSION...BT
MARINE.......DRK
CLIMATE......BT
AVIATION.....SF


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