276
FXUS63 KDTX 271458
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
Issued by National Weather Service Grand Rapids MI
1058 AM EDT Sat Apr 27 2024

.KEY MESSAGES...

- Scattered showers and storms develop this morning, then some additional
  activity is possible tonight, mainly for the Tri-Cities area.

- Southwest winds gust to 35 mph this afternoon.

- Additional showers and storms are possible Sunday and Monday with
  above normal temperatures before a cold front arrives on Tuesday.

&&

.UPDATE...

Main changes were to account for a southeastward expansion of the
SPC Day1 Slight Risk area that now includes the Tri-Cities region
with this threat commencing probably late afternoon at the earliest.
For Metro Detroit and the immediate vicinity, it now appears that
precipitation will start even later than previously thought -- closer
to midnight tonight -- with low attendant chances for severe
weather. After midnight, thunderstorm chances for the Metro area grow
considerably with the approach of the cold front from the northwest.

It`s not often that southeast Lower MI experiences a tenfold
increase in atmospheric moisture over the course of 24 hours, but
that is what`s borne out by this morning`s 12Z DTX roab showing 1.25"
PWAT compared to 0.12" yesterday morning. Related to this,
precipitation chances grow considerably for the Metro after midnight
tonight. There also is a growing risk for marginally impactful rain
accumulations by late Sunday morning in the more prone areas given
the slow southward drift of the cold front and impressive boundary
parallel moist transport. The latest WPC excessive rainfall outlook
stops just west of the CWA and it will be interesting to see what
later outlooks indicate.

&&

.PREV DISCUSSION...
Issued at 805 AM EDT Sat Apr 27 2024

AVIATION...

Predominately VFR conditions this morning as rain showers move
across southeast Michigan. There have been some isolated
thunderstorms observed this morning bringing brief MVFR VSBYs. Any
chances to impact the terminals will be diminishing by 12Z and
beyond, so will leave mention out of this TAF forecast. The warm
front will continue to lift through southeast Michigan this morning
helping bring an end to the shower activity by around 14/15Z. There
may be a relatively short window for MVFR ceilings to exist early
this afternoon in the warm sector before drier air aloft and daytime
mixing will help lift ceilings quickly back to VFR for the remainder
of the day. Expect dry conditions to exist for the afternoon and
evening. Daytime mixing will support south to southwest wind gusts
approaching 30 knots during the afternoon. Shower and thunderstorm
chances return late tonight into Sunday morning.

For DTW/D21 Convection...Convection will exit within the next hour
or two of this TAF cycle. Expecting mainly dry conditions by late
morning and through the evening. Greater thunderstorm potential is
currently favored for north of the D21 airspace across KMBS late
tonight. Confidence is too low at this time to add thunder in TAFs
for the early tomorrow morning.

DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms tonight into Sunday morning.

* Moderate to high in ceilings aob 5000 feet this morning and
  afternoon.

PREV DISCUSSION...
Issued at 400 AM EDT Sat Apr 27 2024

DISCUSSION...

Surface low pressure (993 mb) affecting morning shower development
across Southeast Michigan accelerates northeastward from central
Minnesota to The Keweenaw Peninsula today as the governing wave
aloft opens up, interacting with a northern stream shortwave over
Ontario. This adjustment induces further constriction of the surface
pressure gradient as a 1034 mb surface ridge builds south across the
Mid-Atlantic. Local flow veers from SE to SW today with prevailing
speeds in excess of 15 knots. Low-level wind profiles reveal 50+
knot flow near the 5 kft AGL level, but given the warm advection
regime, mixing depths remain quite shallow for most of the diurnal
period. Still, with 25+ knot winds down to 500 ft AGL, gusts will
generally range between 25 and 35 mph by late morning.

Regarding precipitation processes, the initial band of showers tied
to isentropic ascent have moved off to the northeast while scattered
activity begins to develop with inbound frontogenesis. These showers
also benefit from substantial dynamic support as a region of
divergence moves in aloft while the main LLJ axis situates over
southern Lower Michigan. Potential exists for updraft
overachievement with UVVs capable of some lightning generation in
spite of limited instability. Opted to maintain current
Slight/Chance Thunder wording with revised PoPs. Given the barrage
of ThetaE convergence and CVA, CAM depiction varies in specifics,
but most of the morning convective activity should conclude by 16Z
while some lingering showers persist near the shoreline communities
until 18Z. Confidence continues to rise in a mainly dry afternoon
forecast as the western extend of the Atlantic anticyclone impinges
on the region. This also promotes some thinning of the cloud deck
and a late day boost to temperatures. Fully entrenched within the
warm sector marked by 850 mb temps of 12C to 13C, should easily
break into the mid (if not upper) 70s this afternoon, roughly 15F
above normal.

The anomalous warmth paired with Gulf-augmented dewpoints
approaching 60F this evening prime Lower Michigan for modest
conditional instability. Main concern is the presence of a capping
inversion around 6 kft that is represented in the NAMnest and GFS
while the feature is less prevalent via the ARW and RAP.
Additionally, RH cross-sections highlight the impact of the veered
mid-level flow which effectively dries out the column above the
inversion. Lift mechanism(s) might be non-existent during this
timeframe as the system`s cold front remains stalled over Western
Michigan. The boundary won`t release until later in the evening as
an upstream wave ejects out of the synoptic subtropical jet from the
Desert Southwest. Given this lagged frontal progression, perhaps as
late as midnight, the main threat for both broader coverage of
thunderstorms and any strong to severe activity is largely reserved
for the Tri-Cities area where MUCAPEs peak with 35-40 knots of EBS.
SPC continues to advertise a Marginal Risk for severe weather west
of a line from Adrian to Bad Axe which should stay quite isolated in
nature should storms materialize.

The front should be in the process of washing out by Sunday morning
and taking position as a bisecting stationary boundary. Not much in
the way of synoptic adjustments as the secondary shortwave takes a
slightly more westerly trajectory through the Upper Midwest than
today`s. Persistent ThetaE advection and additional warming
capitalize on the surface convergence axis for addition
showers/storms while the better forcing aloft holds off to the
northwest. Very warm conditions expected for areas south of the
front with highs breaking 80F across the southern four counties.
Additional rounds of showers and/or storms possible Sunday night.

Nuisance forecast extends into Monday with additional periods of
convective activity as the warm sector resides over the region, but
the VortMax from the secondary wave remains well off to the west.
Persistent moisture transport and confluent low-level flow maintain
unstable conditions with opportunities for both elevated and surface
based convection. A cold front arrives Monday night with
increasingly uniform westerly flow through the column. A cooler and
drier forecast stays through Wednesday morning, dependent on the
status of an extensive cold front draped from Manitoba to Texas
should wash out over the Great Lakes. Active pattern returns through
the latter half of the week with at least two speed maxes work
through the northern tier of the Lower 48 with revitalized warm
advection.

MARINE...

Strong low pressure moves across Lake Superior on today. Wind veer
southerly today with gusts touching gale force this morning before
gradually weakening through the day as much warmer air moves into the
region to stabilize flow over the cold lake water. The warm air also
fuels thunderstorm potential through tonight, and possibly even into
Sunday as the associated cold front stalls over the region. The
front awaits yet another low pressure system moving in from the
Plains Sunday into Monday.

CLIMATE...

Here are the record high temperatures for April 28th:

April 28th:
Detroit                84 (set in 1986)
Flint                  85 (set in 1990)
Saginaw/Tri-Cities     85 (set in 1990)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-422-
     441>443.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

UPDATE.......TJT
AVIATION.....AA
DISCUSSION...KGK
MARINE.......DBT/KGK
CLIMATE......KGK


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