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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 232244
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
644 PM EDT Tue Apr 23 2024

.KEY MESSAGES...

- Shower and thunderstorm chances increase this evening ahead of a
  cold front. There is potential for hail with any thunderstorm
  activity.

- Breezy late tonight with gusts up to 30 mph in the Thumb.

- A Freeze Watch is in effect for all of southeast MI late Wednesday
  night through early Thursday morning as overnight lows dip into
  the upper 20s.

- Rain chances increase Friday night as a series of lows lift into
  the upper Midwest. There is low confidence in shower and
  thunderstorm potential Saturday and Sunday.

&&

.AVIATION...

-- Changed Discussion --
An upper level short wave will track across Se Mi this evening. Weak
elevated instability will present the chance for showers and a few
thunderstorms with this system. Overall, the degree of elevated
instability will weaken during the evening. Therefore, the better
chances for thunderstorms, if any, will remain at FNT and MBS. The
upper wave will drive front across Se Mi from late evening into the
overnight. There will be a veering of the winds to the north-
northeast with the passage of this front. Post frontal cold air
advection and ample low level moisture will sustain widespread MVFR
based stratus well into Wed morning. A little bit of post frontal
moisture and flux off Lake Huron will contribute to some light
rain/snow showers from PTK northward Wed morning.

For DTW/D21 Convection...Remnant weak elevated instability will
advance across the metro airspace between 03Z and 06Z. There is
expected to be scattered to numerous coverage of showers during this
period. Just isolated coverage of thunderstorms is expected. A push
of colder air will arrive within strengthening north winds after 12Z
Wed morning. Wind gusts will top 20 knots.

DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings aob 5000 feet this evening. High overnight
  into early Wed afternoon.

* Low in thunderstorms impacting the terminal tonight.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
-- Changed Discussion --
Issued at 349 PM EDT Tue Apr 23 2024

DISCUSSION...

Frontal forcing has lifted into southern lower Michigan, with a band
of steady rain filling into Lenawee and Monroe Counties as of
issuance. This band is expected to hold along/south of I-94 before
shearing southeast late this evening. Attention then turns to the
cumulus field upstream across northern lower MI-WI-MN where
convective cells have been developing over the past couple hours
invof the mid-level wave and trailing cold front. Expectation is for
these showers and thunderstorms to move into the Tri Cities and
Thumb region between 22-00z (6-8pm local) and track southeast across
the rest of the cwa tonight. Steep mid level lapse rates approach 8
C/km upstream, which will advect into northern portions of the cwa
and be the main catalyst for a stronger updraft or two this evening.
Widespread strong storms are not expected, however, as low
instability will struggle to maintain updrafts in such high shear.

The upper level trough and surface front will slide southeast into
Lake Erie by daybreak Wednesday, ushering out any lingering showers.
Breezy conditions linger through the morning, especially around the
Thumb region where gusts may approach 30 mph. Morning lows will
reflect post-frontal cold advection, as some spots around the Tri
Cities and Thumb will see temperatures near freezing and wind chills
in the teens. Standard subsidence inversion settles between 3.0-5.0
kft agl, initially trapping leftover moisture and maintaining a
thick stratus deck for the morning. A much drier low level airmass
then advects south Wednesday afternoon, dropping PWAT values below
0.25" (below the 10th percentile per SPC climo) and quickly mixing
out clouds by afternoon. H8 temperatures dropping into the single
digits during the day leads to a range of temperatures from near 40
degrees in the Thumb to low 50s for inland and urban locations.

Dry weather persists through mid-day Friday as heights build and a
roughly 1030 mb surface high stalls overhead. Opportunities for
cloud cover remain limited, with just a glancing stream of high
cloud moving in Thursday invof a low amplitude wave. Main concern
during this time window is sub-freezing temperatures (upper 20s)
Thursday morning, in which a Freeze Watch has been issued overnight
Wednesday through Thursday morning.

Benign conditions come to an end Friday afternoon as the next storm
system ejects out of the Plains and into the Upper Midwest. The
primary circulation will stay well to our west, but will push the
warm conveyor and associated moist isentropic upglide right overhead
by Friday evening. A strong low level jet, 40-45 knots at 850 mb,
contributes to substantial warm advection and moisture transport
into the area at this point, increasing confidence in a period of
widespread rain Friday night and a gradual warm up through the
weekend. Temperatures Saturday and Sunday look to climb comfortably
into the 70s.

Precipitation prospects for the weekend offer much less certainty,
beginning with a mid-level dry slot that arrives Saturday morning.
This creates a highly conditional convective setup in which
available long-range guidance struggles with depth and magnitude of
static stability within the dry slot. If the atmosphere is dry and
capped (e.g. 00z Euro), convection would struggle to initiate and be
reliant on a warm/moist boundary layer that may not come to
fruition. On the other hand, favorable return flow and opportunity
for the SE CONUS ridge to direct embedded shortwaves toward lower MI
(e.g. 12z GFS) Saturday and Sunday will warrant monitoring for
thunderstorm potential.

MARINE...

A Small Craft Advisory will expire at 4 PM today as gusty winds and
heightened waves diminish into the evening hours. Surface low
pressure associated with an upper level disturbance crossing the
Midwest has shifted south, becoming more diffuse over The Straits as
a secondary surface low emerges further west. Expect some additional
rounds of showers this evening, including the potential for a few
thunderstorms that could result in locally higher winds/waves. Most
of the convective activity should develop ahead of the system`s cold
front through before colder post-frontal air filters overnight. This
leads to brisk northerly flow and low-end potential for gusts to
gales while lapse rates steepen and forecast soundings are well-
mixed once stronger LLJ winds clip central Lake Huron. Will likely
issue another Small Craft Advisory for Saginaw Bay and The Thumb
with the evening marine update. Gradient winds trend lower midday
Wednesday before high pressure starts building into the Great Lakes.
More favorable marine conditions are expected Thursday with
sustained ridging until Friday. Unsettled weather returns Saturday,
dependent on trajectory of a large low pressure system ejecting from
The Plains.
-- End Changed Discussion --

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
MI...Freeze Watch from late Wednesday night through Thursday morning for
     MIZ047>049-053>055-060>063-068>070-075-076-082-083.

Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
-- End Changed Discussion --
&&

$$

AVIATION.....SC
DISCUSSION...MV
MARINE.......KGK


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