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000
FXUS63 KDTX 231715
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
115 PM 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...

Light rain my work back into the I-94 corridor this afternoon, but
trends suggest most of this will be a bit further south. Will adjust
forecast to limit duration and increase cig/vsby restrictions. To
the north of this, scattered showers will develop by early evening
within pocket of marginal instability between light rain to the
south and cold front to the north. A few thunderstorms will even be
possible along front as it drops south through the area later in the
evening. MVFR cigs should occur in the wake of the front. Southwest
winds will gust to 25-30 kts this afternoon and then veer to north
06z-10z from north to south.

For DTW/D21 Convection...Confidence is low on occurrence of thunder
this evening as a cold front encroaches on the region. Any activity
would be isolated and likely weakening as it tracks into the more
stable sector KPTK south after initially developing within an area
of marginal instability from KFNT north.

DTW THRESHOLD PROBABILITIES...

* Medium confidence in ceilings aob 5 kft after 21z today, high late
  tonight into Wednesday morning.

* Low in thunderstorms impacting the terminal late this evening.

&&

.PREV DISCUSSION...
Issued at 1026 AM EDT Tue Apr 23 2024

UPDATE...

12z KDTX RAOB this morning shows a prominent dry layer in the lowest
8.5 kft agl, which is supported by large T/Td spread of 15-20 F
across southeast MI. Local scattered radar returns, likely just
virga or light showers attm, are tied to a broader frontal
slope/theta-e gradient that has contributed to expanding shower and
thunderstorm coverage from northern Missouri to central Illinois.
Continued northeast expansion of the precipitation shield is
expected through early afternoon toward southern portions of the
cwa. No adjustments were made to the categorical PoPs south of M-59
for this afternoon, and thunder potential still looks low as mid
level lapse rates decrease and equilibrium levels drop toward -10 C
this afternoon.

Other component of the short-term forecast is the Marginal Risk for
northern portions of the cwa this afternoon-evening. Mid-level WV
loop shows the vort max currently ~120 miles northwest of
Minneapolis, with the wave actively taking on a more neutral tilt.
Lapse rates invof this wave are in excess of 7 C/km, per morning
RAOBs at INL and MPX. As the wave pivots toward SE MI, it will drive
a ribbon of DPVA and steep lapse rates atop low level moisture
advection (observed dewpoints upper 40s-low 50s upstream), with the
interface of these two features to produce a narrow ribbon of
enhanced instability between roughly I-94 and I-69. A band of
broken, shallow convection forms in its wake after 4 PM or so
followed by some trailing convection across the Tri Cities and Thumb
along the front. 12z model suite so far is consistent with earlier
guidance suggesting the environment will be favorable for a stronger
updraft or two to produce hail up to an inch in diameter and/or wind
gusts of 40-60 mph. A main limiting factor to this setup is a large
imbalance between shear and instability, with forecast maximum
MUCAPE of only ~500 J/kg invof a strong 65-75 mid level jet that
produces 0-6km shear values of up to 80 knots in the more bullish
solutions.

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 LHZ421-422-
     441>443.

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.....DG
UPDATE.......MV
DISCUSSION...CB
MARINE.......KGK


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