National Weather Service United States Department of Commerce


000
FXUS63 KDTX 231130
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
730 AM EDT Thu Sep 23 2021


.AVIATION...

Surface low pressure center is now located invof northern Macomb
County. Occluded low is expected to keep IFR ceilings in place over
all of Southeast Michigan today. Some dry air advection this evening
may allow cigs to rise into MVFR flight category before nocturnal
cooling will try to lower again to high IFR. Periods of light rain
showers and/or drizzle will remain possible throughout the day.
Track of surface low overhead does bring some challenges to the wind
direction forecast during the first 6 hours.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less through the period.

&&

.PREV DISCUSSION...
Issued at 333 AM EDT Thu Sep 23 2021

DISCUSSION...

Surface low pressure currently over western Ontario/Lake Erie
retrogrades back over SE MI early this morning while becoming more
or less vertically stacked. The system has already undergone
occlusion drawing mid-level air into the circulation, which helped
give the region a lull in shower activity late last evening. Drier
air helps to decrease rainfall rates bringing an end to the heaviest
rain/flooding risk for the area. As a result, the Flood Watch has
been cancelled a few hours early. That said, shower activity is not
over yet due to the low wobbling back over the area. Guidance has a
fair consensus on the center of the track touching the Metro Detroit
area before moving north over the Thumb this afternoon. Given this
track, the eastern CWA, who have seen the most rain, would see only
scattered light showers and drizzle with the main western
deformation axis and heavier rain (currently over northeastern
IN/southwestern MI at time of writing) generally staying to our west
over west MI. Westernmost counties of the CWA (particularly the Tri-
Cities area) could be clipped by this axis but as these areas have
seen significantly less overall rainfall, areal flood potential is
low (worth noting here, there is a Flood Warning still in effect for
the Saginaw River which additional rainfall will likely prolong). On
the other side of the coin for this system, winds will weaken over
the course of the morning and afternoon due to the low reaching
peaking maturity and weakening as it moves into the area.

Low pressure finally clears the area late tonight into Friday
morning as it slides into the upper Great Lakes and northern
Ontario. A few scattered showers could linger on the backside of the
low over the northern Thumb/Saginaw Valley tonight but these should
depart by Friday morning. Brief ridging influence takes hold over
the region daytime Friday bringing back sunny skies and temperatures
closer to normal. This will be shortlived as another upper trough
digs south into the western Great Lakes with an associated surface
cold front swinging across lower MI Saturday morning. Light to
moderate showers will be possible ahead of this front but given its
progressive nature, there are no concerns for heavy rain/flooding.
Lake Michigan helps to blunt the coldest air behind the front
allowing our highs to still reach into the mid 60s.

Upper level ridging then develops over the central US Monday and
looks to amplify as the week progresses as a downstream response to
a large Pacific NW longwave moving onshore. This ridge will
influence our weather for a good chunk of next week keeping the area
dry with temperatures around or slightly above normal.

MARINE...

Strong low pressure system starts turning northeastward this morning
to begin a departure that will take most of the day. Last evening
pressure gradient was impressive with a broad area of on-shore
sustained gales, plus some storm-force gusts mixing down from the
925 mb level. A Storm Warning was issued in response to
observational trends for the Port Austin to Port Huron nearshores
and will expire with the remaining Gale Warning at 8 AM EDT. Waves
have already reached their peak and winds began trending lower.
Speeds drop-off quicker by mid-morning, but residual wave energy has
warranted a back-end Small Craft Advisory for the southern Huron
nearshores until the afternoon. Weaker yet modest W/SW winds
expected behind the low through much of the weekend.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory until 8 AM EDT this morning for MIZ048-054.

Lakeshore Flood Advisory until noon EDT today for MIZ048-049-054-
055.

High Wind Warning until 8 AM EDT this morning for MIZ049-055-063.

Lake Huron...Gale Warning until 8 AM EDT this morning for LHZ361>363-421-422-
441>443-462>464.

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

Small Craft Advisory until 4 PM EDT this afternoon for LHZ422.

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

$$

AVIATION.....CB
DISCUSSION...KDK
MARINE.......KK


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