123
FXUS63 KDTX 161749
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
149 PM EDT Fri Aug 16 2024

.KEY MESSAGES...

* Another round of scattered thunderstorms may develops this
  afternoon-evening. This activity will be capable of heavy rainfall
  and an isolated storm could produce damaging wind.

* Broad coverage of low pressure stalls across Lower Michigan this
  weekend. The system supports showery and unsettled weather with
  temperatures on the cool side of normal through Sunday.

&&

.AVIATION...

Morning band of showers held longer into the afternoon complicating
the forecast for this evening. A cold front remains well to the west
over southern Lake MI and should pass over the area this evening
with a couple hours of destabilization ahead of it in a narrow warm
sector. Computer models have all backed off a bit from generating
broader coverage of showers and storms ahead of the front lowering
confidence. But it remains warm and humid with the warm front and
cold front still to pass through so will hedge away from convection
and go with a tempo for showers this evening. If/when convection can
develop, will amend the impacted airports as needed. Better support
for showers comes tonight and the ongoing tempo from 06-10Z still
looks good. Yet another round of showers and possible storms will
come Saturday afternoon as the upper low drifts overhead. Ceilings
will lower on Saturday with the low in place.

For DTW/D21 Convection...Low probability exists for thunderstorms
this afternoon/evening as early day showers held longer into the day
reducing the amount of instability that could rebuild into the area.
The cold front will pass through this evening with a couple hours to
try to reorganize ahead of it so still a chance of activity between
20-00Z. Took out thunder and left showers as confidence in
widespread thunderstorms is low. Additional rounds of showers will
exist tonight after 06Z with a trough swinging through and again on
Saturday afternoon with the upper low in place.

DTW THRESHOLD PROBABILITIES...

*  Low for thunderstorms through the evening.

*  Medium for cigs at or below 5000 ft this afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 339 AM EDT Fri Aug 16 2024

DISCUSSION...

Scattered showers and drizzle tied to the lead edge of theta-e
advection between 800-900mb starts to push east of the area by mid-
morning. This is quickly followed by remnant convection along the
surface warm front lifting out of IL/IN which tracks across SE MI
late morning-early afternoon. With only few hundred J/kg of MLCAPE
available during this window, thunder holds on the
isolated/scattered side and non-severe. Latest trends amongst the
vast majority of CAMs is for the warm front to clear the region by
~19-20Z resulting in steady theta-e advection into southern lower MI
raising surface dewpoints into the lower 70s. This looks to be
sufficient to allow instability to recover from morning activity
with 1000-1500J/kg of MLCAPE developing by late afternoon-early
evening. Overall shear is on the marginal side with 0-6km struggling
to reach 30kts, owing to a weaker overall column wind profile
likewise struggling to get much up 30kts. That said, an isolated
strong to severe storm is still in play with damaging wind gusts
being the primary hazard as DCAPE`s approach 1000 J/kg. Mid-level
lapse rates aren`t anything special, generally 6-6.5C/km at most,
precluding a large hail threat. Additionally, as is typical in these
humid airmasses, locally heavy rainfall is likely under any
thunderstorm.

Occlusion of the low over the upper Midwest offers a brief break in
rain chances early tonight behind evening convection as a mid-upper
dry slot swings through southern MI. Additional showers/remnant
upstream convection then arrive latter half of the night as the now
fully closed, stacked low drops southeast over Lake Michigan.
Daytime Saturday is marked by a transition to less organized but
numerous convective showers and scattered thunder as the low/parent
trough drift directly overhead. The loss of daytime heating will
lead to a reduction in coverage Saturday night however with the slow
speed of the low, likely only over the Ontario Peninsula by Sunday,
results in a largely persistence forecast for daytime Sunday as
diurnal heating reinvigorates scattered to numerous showers.

Dry conditions return by Monday as the low reaches the Northeast
though upper troughing remains firmly in place over the central
Great Lakes. Northerly flow in the low`s wake draws cooler Canadian
air south lowering 850mb temps to around 10-11C and results in highs
generally in the lower 70s with upper 60s possible in the Thumb.
Breezier day also looks likely Monday as increasing mixing depths
within this CAA regime supports a partial mixing down of 25-30kt
flow aloft. In general gusts between 20-25mph are favored though
stronger winds around 30mph are not out of the question,
particularly over the Thumb.

MARINE...

An upper low located over the western Great Lakes at issuance will
gradually drift eastward through the weekend, governing local
conditions until early next week. First wave of showers and
thunderstorms departs this morning, but will likely see additional
activity fill in this afternoon-evening. Thunderstorm activity later
today will have potential to become strong/severe, capable of
localized wind gusts over 35 knots, erratic waves, and lightning.
Otherwise, winds/waves subside through the morning, settling around
5-10 knots by this afternoon. Thunderstorm potential will linger
overnight and through most of the weekend under influence of the
slow-moving upper low. Winds will eventually shift from southerly to
northerly once the low passes through, which will prompt an uptick
in winds and waves that may necessitate Small Craft Advisories early
next week. The low fully departs by middle of next week, with drier
weather expected.

HYDROLOGY...

Showers and remnant thunderstorms cross the region this morning with
additional scattered thunderstorms likely developing this afternoon-
evening. The humid airmass will support locally heavy rainfall with
storms this afternoon capable of dropping a quick inch or so of
rain. A broad low pressure system then stalls over Lower Michigan
for this weekend supporting numerous showers and scattered
thunderstorms focused particularly in the daylight hours. Total
rainfall from this morning through Sunday evening is expected to be
1-1.5 inches on average, though localized totals between 2-3 inches
possible dependent on strength and frequency of thunderstorms.
Localized minor flooding of urban, low-lying, and otherwise flood
prone areas remains possible in the strong thunderstorms, but the
off and on nature of the rainfall is not expected to cause
significant flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....DRK
DISCUSSION...KDK
MARINE.......MV
HYDROLOGY....KDK


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