744
FXUS63 KDTX 281949
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
349 PM EDT Fri Jun 28 2024

.KEY MESSAGES...

- Widespread showers and some embedded thunderstorms expected late tonight
  through early Saturday morning.

- Strong to severe thunderstorms are possible Saturday afternoon-evening
  with damaging wind gusts and locally heavy rainfall as the main
  threats.

- High pressure fills in behind a cold frontal passage on Sunday to bring
  cooler and drier weather for early next week.

&&

.DISCUSSION...

SE MI resides on the western periphery of a surface high pressure
system which is now centered just off of New England, and a broad
area of low pressure with a trailing compact shortwave, which
resides just west of the Great Lakes into the Dakotas. Influence of
return flow from the departing high pressure and increasing
proximity to the aforementioned low has and will continue to direct
and expansive plume of deep layer theta-e into the Great Lakes
through tomorrow morning. This has initially resulted in expansive
coverage of mid and high level clouds along with mostly dry
conditions as top down saturation must initially erode the expansive
dry layer up through h600, as observed in the 12Z DTX RAOB. Arrival
of the shortwave into Lake Superior late tonight into tomorrow
morning will drive a prolific amount of deep layer moisture between
06Z-12Z, resulting in peak PW values between 2.10-2.15 inches
(99.5th percentile w.r.t climatology). For the remainder of today,
the expectation is to see a fair amount of virga with pockets of
drizzle or light rain as moisture builds into the region. The
overnight period will see expansive coverage of rain, including
periods of heavy rain given the PW, deeper warm cloud layer, deep
mean RH, and magnitude of the LLJ. Elevated instability will very
gradually build in with the widespread coverage, but only a few
hundred J/kg to start. Some thunderstorms cannot be ruled out
overnight, favored over the Metro area. Please see the hydrology
section for additional information on rainfall totals.

The moisture axis will move out of SE MI through the afternoon
hours. There will be a window though approximately 21Z where
building diurnal instability will coincide with the tail-end ridge
of the moisture axis, ahead of a weak surface cold front, that can
provide more isolated to scattered shower or storm activity. There
is high uncertainty regarding CI and hi-res output is not all that
impressive regarding storm potential, but chance PoPs will remain in
the forecast given the warm and moist airmass in place with dew
points in the lower 70s. If thunderstorms are observed, kinematics
are favorable for some strong to severe storm development. 0-6 km
bulk shear values will reside between 35-40 knots through the
afternoon. A quick look at storm-relative hodographs display a
greater portion of hodograph is dominated through 0-1 km. Main
hazards with any afternoon or evening development would be an
isolated tornado or damaging wind gusts to 60 mph. But again this is
highly conditional on CI development which is low confidence. SWODY2
has a marginal risk in place as a result. A final window for shower
or storms will reside in the evening with a shortwave, favored along
or north of M59. Otherwise, breezy conditions are expected through
tomorrow afternoon and evening, with peak gust potential between 30-
35 mph.

A strong and dry cold front will move in Sunday morning and will
bring relief of temperatures as highs peak in the low 70s, 60s
across the Thumb. An expansive high pressure system with dry
Canadian air will fill in through Monday, pulling in h850 values
down to 8C. Overnight lows leading into Monday will have the
potential to drop into the upper 40s given the boost in subsidence
and clear skies. Monday will remain temperate with highs again in
the 70s. Dry weather and sunny skies are expected Monday, with the
next chance for showers and storms by the midweek periods once the
departure of high pressure advects back in Gulf moisture.

&&

.MARINE...

High pressure departs to the east making way for a low pressure
system to move in. Pressure gradient tightens allowing for winds of
15-20 knots on Saturday ahead of the next low pressure system, which
will also bring chances for showers and storms Saturday. Winds
slowly veer southwesterly through the afternoon and evening Saturday
and flow direction will line up with the maximum fetch length over
Saginaw Bay during the daytime hours. Lower-level winds will also
have an easy time mixing down with little to no temperature
inversion aloft in place. Wind gusts of 30 knots or greater may be
able to mix down under this environment. Gust potential and flow
direction has lead to a Small Craft Advisory being issued for
Saginaw Bay from 12pm to 10pm Saturday.

Winds veer to the north-northwest on Sunday behind the cold front,
maintaining speeds over 20 knots around the nearshore areas of the
Thumb and over central Lake Huron. Gusts to 25 knots or greater are
also possible. Due to fetch direction and length, the potential for
waves to meet Small Craft Criteria exists on Sunday in addition to
hazardous wind conditions.

&&

.HYDROLOGY...

Widespread rain, with a chance for embedded thunderstorms, is
expected to increase in coverage overnight, especially between 06Z-
12Z (2AM-8AM). Periods of heavy downpours will be likely given the
warm and humid airmass in place. Basin averaged mean precipitation
amounts will likely vary between a quarter to three-quarters of an
inch, however, highly localized rainfall totals between 1-2 inches
will be possible with heavy downpours, especially with any
thunderstorm activity.

The most likely location to see rainfall totals in excess of one
inch will by along or south of the I-94 corridor, but overall,
confidence in any exact location of highly localized rainfall totals
remains low. Thus will preclude the issuance of any flood watch
products at this time.

&&

.PREV DISCUSSION...
Issued at 120 PM EDT Fri Jun 28 2024

AVIATION...

Strong 700-650mb thetae advection has led to an abundance of virga
on regional radar mosaic this afternoon. A dry southeasterly feed
will persist throughout the afternoon and into the early evening
hours. There is some model signal that a sprinkle will be possible
beginning after 00Z. Confidence is too low to include this issuance.
Organized deep cyclonic flow will then push into the area after 08Z
tonight. A secondary thetae surge will then bring the chance for
showers and thunderstorms at the Detroit terminals after 08Z. Did
time out a 2 hour tempo for thunderstorm activity between 09-11Z
Saturday. Well mixed westerly flow is forecasted to develop behind a
cold front Saturday afternoon with wind speeds of 15 to 25 knots.

For DTW/D21 Convection...The potential exists for thunderstorm
activity between 09-11Z Saturday morning.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling aob 5000 ft Saturday morning.

* Moderate for thunderstorms Saturday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from noon to 10 PM EDT Saturday for LHZ421-422.

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

$$

DISCUSSION...AM
MARINE.......BC
HYDROLOGY....AM
AVIATION.....CB


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at www.weather.gov/detroit.