233
FXUS63 KDTX 111839
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
239 PM EDT Sat May 11 2024

.KEY MESSAGES...

- Above normal temperautures are expected Sunday into Monday.

- Showers and thunderstorms return late Sunday night and Monday as a
cold front drops through the region. This front will then stall
overhead leading to persistent rain chances into early Tuesday.

- The potential for heavy rainfall will exist for a portion of
Southeast Michigan Monday and Tuesday.

- Cooler than average temperatures are expected Tuesday and
Wednesday.

&&

.DISCUSSION...

Cold core aloft has extensive cumulus/stratocumulus deck in place
across Southeast Michigan this afternoon. Spokes of absolute
vorticity and corresponding axes of convergence have provided for
waves of ascent to result in loosely organized, scattered to
numerous rain showers over Southeast Michigan. Satellite imagery and
radar reflectivity trends support a very shallow convective response
with a struggle to get much above 8.0-11.0 kft agl where dry air and
a slightly stable environmental temperature lapse rate profile
exists. Given the absolute vorticity center and support for cyclonic
flow, expectations are for a persistence of rain showers for the
remainder of the afternoon. There is a potential for the showers to
wane for some areas while focusing more across the Thumb. There
still remains a potential for some thunder particularly if a few
breaks can develop due to increasing convective depths and
convective scale subsidence. No strong or severe weather with CAPES
of only 100-200 J/kg.

For tonight, the popular question again centers on whether or not
the Aurora Borealis will be visible across Southeast Michigan with a
G5 Severe Geomagnetic Storm Watch in effect from the NWS Space
Weather Prediction Center. A difference scenario today with the
extensive lower tropospheric cloud due to the vorticity maximum.
Will most likely see some thinning out of the cloud as the boundary
layer cools, however, cannot not envision a total clearing out.
Therefore, sky coverage is expected to vary on a local basis,
particularly earlier in the evening. It behooves one to err on a
more pessimistic/cloudier outlook this evening/tonight for two
reasons. The forecast area will be in a zone conducive for
persistent weak stretching deformation and a lowering subsidence
inversion could hold/trap saturation at its base. Possible for some
clearing, but will be carrying a mostly cloudy forecast early.

Rising geopotential heights and confluence aloft will allow for
another shortwave ridge feature for the Central Great Lakes on
Sunday. A sharp, distinct absolute anticyclonic vorticity maximum is
progged to to push directly through the cwa between 12-18Z. Forecast
soundings depict active subsidence occuring in the midlevels by the
mid morning hours, then lowering down in the column around midday.
Pleasant and comfortable conditions are anticipated for much of the
day. By afternoon, its only natural Southeast Michigan will be
influenced by differential cyclonic vorticity advection as the AVA
moves eastward away from the region. Therefore, increasing clouds
are expected as warm advection precipitation spreads across the U.P.
and northern Lower Michigan. Temperatures are expected to be near 70
Sunday afternoon, but have kept it lower by a degree or two.

Two PV anomalies are then forecasted to move eastward over portions
of North America in tandem from Sunday night through Tuesday.
Locally, the first wave is expected to drop a cold front into
Southeast Michigan on Monday while it stalls and becomes stationary.
Difficult to pinpoint duration of rain shower and/or thunderstorm
activity. High confidence in an unsettled period with relatively
higher certainty there will be showers and thunderstorms Monday
afternoon. Will need to monitor model trends as very weak flow will
bring the potential for slow moving convection and heavy rain.
Potential for severe weather is on the low side with 0-6km bulk
shear of 20 knots and Mixed Layer Cape of less than 1000 J/kg. Wet
weather to continue on Tuesday with Southeast Michigan possibly
getting clipped by the northern periphery of the southern wave as it
passes through. Concern there is if the same area could get heavy
rainfall both days. Way too early to try and hammer out details on
convection.

&&

.MARINE...

Northwesterly gusts to 25 knots in the wake of cold frontal passage
will subside late this evening into the overnight. Until then, will
maintain current Small Craft Advisories for Saginaw Bay and Lake St
Clair/Western Lake Erie. While an isolated thunderstorm cannot be
ruled out into early evening, generally just expect rain showers
(which will taper off quickly this evening). High pressure briefly
builds into the area Sunday morning providing favorable marine
conditions before a secondary low approaches later on Sunday. This
second system offers potential for enhanced southwest flow over
Saginaw Bay, and possibly Small Craft Advisory criteria gusts.
Showers and storms arrive late Sunday evening and overnight. A
stationary front then settles over the Great Lake early next week
offering additional opportunities for thunderstorms.

&&

.HYDROLOGY...

A cold front will settle southward into Southeast Michigan Monday
night before stalling across the area on Tuesday. Showers and
thunderstorms will be possible along this boundary. Rainfall may
exceed 0.50 inch for portions of Southeast Michigan. Forecast
confidence is low at this time and impacts to rivers next week is
unknown.

&&

.PREV DISCUSSION...
Issued at 126 PM EDT Sat May 11 2024

AVIATION...

Widely scattered to numerous rain showers will continue through the
afternoon and early evening hours in response to the departing low
pressure system presently located over the Thumb. A rumble of
thunder is possible but coverage and duration remains too limited
for inclusion in the forecast. Cloud ceilings will attempt to lift
towards low-end vfr through the afternoon, however periods of mvfr
cigs are favored with the rain chances.

The cloud shield will gradually shift northeast tonight as low
pressure continues to travel east. This persistent cloud shield will
linger through the late evening to early morning hours over the
Thumb, and it will be a close call if the western edge of the shield
holds on across the terminals beyond Midnight. Most model guidance
supports the cloud coverage shifting just northeast of all terminals,
which is represented on the outgoing TAFS. Otherwise, breezy
westerly flow with gusts around 25 knots are expected during daylight
hours.

For DTW/D21 Convection...  Another round of showers are expected
with peak heating this afternoon into early evening. Thunderstorm
chances remain very limited.

DTW THRESHOLD PROBABILITIES...

* Very low for an isolated thunderstorm this afternoon into the early
  evening.

* High for ceiling 5000 ft or less today and tonight.

* Medium confidence in reaching westerly crosswind threshold this
  afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

Lake St Clair...Small Craft Advisory until 8 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 8 PM EDT this evening for LEZ444.

&&

$$

DISCUSSION...CB
MARINE.......DG
HYDROLOGY....CB
AVIATION.....AM


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.