951
FXUS63 KDTX 032310
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
710 PM EDT Thu Apr 3 2025

.KEY MESSAGES...

- Detroit area flooding continues to improve as several river flood
  warnings continue across portions of southeast Michigan.

- The next round of widespread rain arrives Friday evening into
  Saturday. This rain may become briefly heavy south of M-59 with a
  30- 40% probability for over 1 inch of rainfall.

- Cooler conditions ensue early next week with rain/snow showers
  likely on Monday before high pressure settles in mid-week.

&&

.AVIATION...

Westerly wind diminishes with sunset as high pressure builds into
Lower Mi from the Midwest tonight. This also limits clouds to broken
high level varieties and helps keep rain showers south of the Ohio
border tonight and through the bulk of Friday. High pressure slides
from northern Lower Mi and Lake Huron into Ontario by Friday
afternoon resulting in a veering wind trend toward the NE across the
terminals. A slight uptick in speed occurs into Friday evening as
the next low pressure system reaches the Ohio valley, from which
rain moves into Lower Mi later Friday night.

.DTW THRESHOLD PROBABILITIES...

* None

&&

.PREV DISCUSSION...
Issued at 329 PM EDT Thu Apr 3 2025

DISCUSSION...

Mild and windy this afternoon behind the strong low now moving
through Central Quebec. Temps have reached into the upper 50s to mid
60s, with gusts of 40-45 mph. Winds will quickly diminish this
evening and become light tonight as high pressure builds into the
area. Increase in mid-high clouds tonight will mitigate any fog
threat due to the soaked ground as min temps dip into the 30s.
Slight chance of high based light showers/sprinkles near the
southern Michigan border this evening before the 700 MB winds back to
the west.

Longwave trough over the Rockies of North America with summer-like
ridge (~595 DAM at 500 MB) building off the Southeast Coast on
Friday. Sprawling surface high pressure (1030 MB) over the Central
Great Lakes will allow for further drying during the day on Friday,
before the next wave of moisture and rain arrives Friday Evening.

The positively tilted northern stream trough tracking through
Central Canada will be the dominate player, which will keep the
surface wave/reflection steady/relatively flat as it tracks through
the northern Ohio Valley and into the Eastern Great Lakes Saturday
morning. None-the-less, good baroclinic zone and mid level FGEN with
the strong southwest low level jet reaching the southern Michigan
border supporting moderate to potentially brief heavy rain as
showalter index lowers into the low single numbers/approaching zero
toward the southern Michigan border. As such, a rumble of thunder
not out of the question south of M-59. With 850 MB dew pts pushing 10
C up to near the M-59 border and PW values up around 1.25 inches,
rainfall totals of half an inch to one inch appear likely south of
I-69, with a 30-40 percent chance to exceed 1 inch south of M-59,
per Euro ensembles.

For the rest of Saturday, it looks to be a close call, but it
appears the main moisture axis will slide just far enough east for
the second wave tracking through eastern Ohio Valley to have minimal
impacts/glancing blow with with the rain shield as pronounced mid
level dry slot takes hold.

Upper level westerly confluent flow for the second half of the
weekend before a strong clipper system is progged to move through on
Monday. Despite what looks to be an unfavorable timing in the
afternoon, with 850 MB temps lowering to around -10 C, should be
cold enough to support snow on the back side of the low, but surface
temps holding above freezing through 00z Tuesday should lead to snow
melt on main roads. Still could be adjustments in timing of the
system however, which could improve the prospects of accumulating
snow. A pretty good wind pop with the surge of cold advection is
anticipated, with gusts above 40 mph in play.

MARINE...

The low pressure system now over Quebec will quickly lose its grip
on the Great Lakes as high pressure has begun to build into the
region. Our current Gale Warning for the Straits will be allowed to
expire at 4 PM as winds should come down pretty quickly over the
next couple hours. The Small Craft Advisories around the Thumb will
continue through this evening as winds also come down noting a few
gusts to gales will be possible over the next couple hours. High
pressure will keep the area dry with light winds through Friday
before the next low pressure system approaches from the southwest
Friday night into Saturday. Though it is tracking along the stalled
front located over Ohio, there is a northern trough dropping down
through the region at the same time which will help spread rain and
thunderstorms up throughout the entire area. The front drops back
south for Sunday leading to quieter conditions again.

HYDROLOGY...

Will allow the areal flood warning for Macomb, Oakland, Washtenaw
and Wayne counties to expire at 4 PM as rain waters continue to
slowly recede. Localized pockets of flooding will still take
additional time to improve, as there also are several river flood
warnings continuing across portions of southeast Michigan as well.

The next round of widespread rainfall is expected Friday evening and
Friday night, with some lighter activity on Saturday as a low
pressure system tracks up the Ohio Valley. Rain will be moderate to
potentially briefly heavy south of M-59, where rainfall amounts of
half an inch to one inch are expected. Any embedded thunderstorms
could enhance activity, pushing rainfall totals in excess of 1 inch.
However, confidence is currently low on this scenario. This rainfall
will likely cause additional rises on area streams and rivers this
weekend with the potential for additional minor flooding.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...None.

Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...None.

Michigan waters of Lake Erie...None.

&&

$$

AVIATION.....BT
DISCUSSION...SF
MARINE.......DRK
HYDROLOGY....SF


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at www.weather.gov/detroit.