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000
FXUS63 KDTX 231003
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
603 AM EDT Tue Apr 23 2024

.KEY MESSAGES...

- Rain today with possible thunderstorms this afternoon and evening.
The potential for hail exists with any thunderstorm activity.

- Strong winds of 30 mph will be possible in the Thumb late tonight.

- Dry weather with below normal temperatures is expected Wednesday
and Thursday

- Periodic rain and/or thunderstorm chances will impact the region
late Friday through the upcoming weekend as a series of low pressure
systems lift into the central part of the country. Low confidence
exists in the timing of rain activity.

&&

.AVIATION...

A band of light showers is tracking across the area this morning as
a low pressure system moves from Lake Superior into northern MI.
Regional observations suggest quite a bit of dry air exists near the
surface, so expect VFR conditions to prevail through the morning. As
the low continues to progress southeast today, a mid-level cold
front develops overhead across southern Lower MI and produces a band
of rain midday that mainly affects the Metro Detroit TAF sites but
may clip FNT as well. Some rainfall rates may be heavier with this
round of rain, and expect reduction in flight category to MVFR.
Finally, a strong surface cold front drops southward out of northern
MI this evening into tonight, producing another round of showers and
possible thunderstorms. With steep environmental lapse rates in
place, an isolated storm may produce large hail or a strong wind
gust. Did introduce a TEMPO TSRA for MBS where confidence is the
highest. Winds will be predominantly SW today at 15 to 20 knots with
gusts in excess of 25 knots. Winds then shift N tonight into
Wednesday morning behind the cold front. High confidence in MVFR
ceilings overnight as the frontal inversion traps sufficient
moisture in place.

For DTW/D21 Convection...Early morning showers will be light as they
arrive from the west around 12z, maintaining VFR. Rain associated
with the mid-level front will spread over the airspace mainly
between 16z and 02z with MVFR likely. Conditions improve slightly
this evening but there remains potential for a cluster of additional
showers around midnight. Confidence is low on occurrence of thunder.
Overnight FROPA timing also carries a fair amount of uncertainty,
but latest data suggests 08-10z Wed will be the target for a wind
shift to N.

DTW THRESHOLD PROBABILITIES...

* High confidence in ceilings aob 5 kft after 18z today.

* Low in thunderstorms late this evening.

&&

.PREV DISCUSSION...
Issued at 352 AM EDT Tue Apr 23 2024

DISCUSSION...

A positively tilted upper level trough will deamplify with opening
geopotential heights as it swings progressively from the Dakotas to
the Eastern Great Lakes during the next 30 hours or so. The first of
three phases is arriving now as arrival of 115 knot upper level jet
will support warm advection across all of Lower Michigan. Regional
radar mosaic supports a fairly thin band of light shower/sprinkles
from Lake Superior clear down to the northern Illinois. Modeled RH
fields pinpoint the better moisture/saturation north of I 69 between
09-12Z this morning. For the southern cwa including Metro Detroit,
there are some serious reservations on how widespread/how much
rainfall will occur early with a significant amount of dry air
holding in the lowest 5000 ft agl. Given the trends, preference is
to have PoPs at less than 50 percent early this morning. After 12Z,
tail of midlevel moisture strings out overhead while system relative
isentropic ascent becomes neutral. Lower column moisture remains
subsaturated and the setup appears to support a period of dry
weather over much, if not all of the forecast area.

The second phase of the event today will occur as a subtle right
entrance region to an internal jet impulse slides overhead of
Southeast Michigan. Models have been consistent in recent days of
depicting an area frontogenesis lifting through the region as a
frontal wave. The model trends over the past 24 hours have coalesced
around the older ECMWF solution which does bring the best 1000-850mb
fgen along and south of M59 and I 69 corridors between 17-01Z today.
Was very aggressive in trying to time/locate categorical PoPs for
widespread precipitation during the afternoon period. There is some
uncertainty with regards to the northern extent, whether or not the
precipitation will fill in north of M59. Given the extensive cloud,
and precipitation cooler high temps are expected across the southern
CWA today.

The third phase of the event today will coincide with the arrival of
the height falls/midlevel cold advection that will occur immediately
in advance of the deep trough axis. Steepening lapse rates are
progged after across western and northern Lower Michigan. Decent
model UVV signal in convective shower/tstorm initiation upstream that
will then track towards the northern cwa between 21-03Z. There is
some question on what the coverage of activity will be here across
Southeast Michigan as model soundings are holding onto a residual
subsidence bubble between 1.3 and 5.0 kft agl. It is this dry air
that will really impact the setup, limiting MUCAPES to 250 J/kg
if/when it develops and ensuring that it will remain elevated. There
is also the potential for some thunder late along the northern
fringe of fgen that could sneak into northern portions of Metro
Detroit. That will be dependent on how pervasive and opaque the low
cloud will be during the afternoon. Marginal instability with very
low freezing heights bring a potential for hail. The latest Swody1
has a Marginal designation for severe weather for the far northern
portion of the cwa, and this is for any thunderstorm activity in the
aforementioned 21-03Z time window.

The potential exists for a brief period of gusty north winds late
tonight in the Thumb, along the Lake Huron shoreline as wind
directions abruptly turn northerly. Latest model trends have backed
off a bit on the strength of the winds as the low is depicted to be
more of en elongated surface trough structure. Overall, the
magnitude of the gradient flow is not expected to be as strong as
previously expected, but surface wind gusts of 30 to 35 mph are
expected.

Differential cold air advection in the lowest 5.0 kft of the
atmosphere and rising geopotential heights will support a
prototypical stable spring anticyclone over Southeast Michigan
Wednesday through much of the daytime Friday. Wind trajectories will
classically begin out of the north Wednesday then veer to the
southeast for both Thursday and Friday. Very low to nil sky fraction
anticipated through the middle of the day Friday. Favorable
radiative cooling conditions are expected both Thursday and Friday
mornings. Frost and Freeze warnings will likely be needed. The
coldest will be Thursday morning with temperatures down into the
middle to upper 20s areawide.

An anomalously deep upper level trough with a southern stream
connection will remain very progressive as it pushes into the upper
Midwest for the weekend. Model trends are holding that a double
barrel low pressure system will plague the region from late Friday
throughout the upcoming weekend. The first of the low centers is
expected to be impacted by the stable blocking ridge here locally
which should force the strong potential vorticity anomaly well to the
west of Lower Michigan. As a result, there is a thought the initial
precipitation activity to fall across Lower Michigan will remain
elevated, forced by a strong low level jet primarily Friday night
and early Saturday. There has been a consistent signal that flow
trajectories will remain overwhelmingly anticyclonic Saturday and
into Sunday as short wavelength ridging amplifies downstream of the
main upper level trough energy.

MARINE...

Surface low pressure associated with an upper level disturbance
crosses central Ontario and northern Lake Superior today driving an
uptick in gradient flow. A Small Craft Advisory remains in effect
until 4 pm today as 25+ knot gusts and 4+ feet waves spread from
Saginaw Bay to the rest of the nearshore zones by sunrise. The
system also provides some rounds of showers which include potential
for a few thunderstorms later in the day, particularly ahead of an
evening frontal boundary. Colder post-frontal air filters in tonight
leading to brisk northerly flow. Some low-end potential for gusts to
gales exists while lapse rates remain steep and forecast soundings
are well-mixed while the stronger LLJ winds clip central Lake Huron.
More favorable marine conditions are expected Thursday with high
pressure in control, at least until midday Friday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ441>443.

     Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422.

Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444.

&&

$$

AVIATION.....TF
DISCUSSION...CB
MARINE.......KGK


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