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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS63 KDTX 121810
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
210 PM EDT Fri Apr 12 2024

.KEY MESSAGES...

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- A Wind Advisory is in effect until midnight tonight. Northwest
  wind gusts peak at 45-50 mph with localized 55 mph gusts possible
  early this evening in the Thumb.

- Widespread rain continues today with highest rainfall amounts
  toward the Tri Cities and Thumb where up to an additional inch of rainfall
  is possible. Elsewhere, additional rainfall amounts will be a half
  inch or less.

- Wind diminishes overnight with a gradual warming trend through the
 weekend into next week.

- Thunderstorms are possible Sunday as a weak low pressure system
 and cold front track through the area.
-- End Changed Discussion --

&&

.AVIATION...

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MVFR conditions will prevail for much of the afternoon with
southeast Michigan experiencing overcast skies, rain, and gusty
winds on the western end of the departing low pressure. W-NW wind
gust potential peaks around 21Z with gusts to around 40 knots that
last until about 8-9 pm this evening. Gusts to around 40 knots
result from slightly better mixing that develops. VFR conditions
will develop this evening as dry air begins to push in and scatters
out the rain and low clouds. Expect gusts to hold at around 25-30
knots tonight and persist out of the W-NW.

For DTW... High confidence in west to northwest wind gusts reaching
at least into the 35-40 knot range this afternoon. Light showers and
MVFR ceilings will linger. Ceilings expected to lift towards lower
VFR this evening.

.DTW THRESHOLD PROBABILITIES...

* High for cigs at or below 5k ft through this afternoon. Low to Moderate
  this evening.

* High for west-northwest wind gusts reaching cross wind thresholds
  this afternoon.
-- End Changed Discussion --

&&

.PREV DISCUSSION...
-- Changed Discussion --
Issued at 932 AM EDT Fri Apr 12 2024

UPDATE...

Rapid deepening of low pressure has commenced over the past 12-24
hours characterized by a 1000-500mb 12 hr height change down to 13
dam, where a 982 mb low now sits over western Ontario. An
uncharacteristically strong low level jet will continue to increase
in intensity along the western flank of the departing low pressure
system, which will coincide with peak diurnal heating. Although
mixing depths remain on the shallower side, generally between 2kft-
4kft, this will still be sufficient enough to tap into the shallow
jet aloft, tapping into 45-55 kts. Accounting for momentum transfer
to the surface, the forecast remains on track to see 45-50 mph wind
gusts through the afternoon and evening. Expect wind gusts to ramp
up through the remaining morning hours, with peak gusts expected
between 3-9PM EDT. Some isolated peak gusts to 55 mph cannot be
ruled out across SE MI, but this is more favorable across the Thumb
and especially along the shoreline given the peak jet maxima
location resides across this area, with the west-northwest flow off
the lake.

PREV DISCUSSION...
Issued at 413 AM EDT Fri Apr 12 2024

DISCUSSION...

Mid-level wind maximum digging into the Ohio Valley this morning has
initiated rapid strengthening of the locally dominant surface low
(now 987 mb), with occlusion ongoing over southern Ontario.
Continued deepening of the low amongst strengthening mid-level height
falls, closed upper level circulation, and substantial moisture
depth create an environment favorable for broad coverage of rain
showers especially during the first half of the day.

Current radar mosaic shows a mix of disorganized rain showers and a
persistent deformation band extending from roughly Alma to Ann Arbor.
Shallow northwest flow around the surface low is still overcome by
southerly flow aloft, hence the continued SW-NE storm motion. This
will change over the next several hours however as the deformation
axis progresses, pivoting storm motion to become northwest to
southeast (see over SW lower MI). The expectation is for the bulk of
rain showers to be east of I-75 by this point, where they will likely
stall before releasing southeast toward Ontario. Reinvigoration of
shower intensity is also expected in this vicinity once flow
reorients, owing to a backdrop of low level convergence ahead of a
strengthening low level jet. Rainfall amounts will thus be highest
in the Thumb region, ranging from a half inch to locally up to an
inch by this evening. Elsewhere, forcing and moisture depth will
gradually wane supporting a transition from steady rain this morning to
light showers or mist this afternoon, with overall rainfall amounts
under a half inch.

Deepening northwest flow has already initiated strong cold advection
across the forecast area, with H8 temperatures dropping toward 0 C
this morning. This corresponds to high temperatures today in the 50s
but enough boundary layer growth to access the strong low level jet
mentioned above. Rapid strengthening and occlusion of the low will
lead to a jet max of 60+ knots centered around 850mb. The limiting
factor here will be relatively shallow boundary layer depths,
somewhere between 2.0 to 4.0 kft agl. Winds at the top of the
boundary layer (per forecast soundings) generally hold at or below
50 knots, with just occasional peaks above that in a time window
between 21z-00z this evening. Once momentum transfer processes are
considered, this still corresponds to frequent gusts between 45 to 55
mph which is in line with the current Wind Advisory. Will continue
to acknowledge the need for close monitoring of observations,
especially between 5pm-sunset/toward the Thumb, for short-fused
upgrade potential. Wind gusts will subside overnight as the nocturnal
inversion settles and the background wind field diminishes.

Saturday`s weather will be in stark contrast to today with plenty of
sunshine as mid-level heights climb and surface ridging builds in.
The quieter weather will be brief, as a glancing low amplitude wave
drives a weak surface low through the region on Sunday. The
accompanying mid-level height falls will be strong enough to draw in
50+ degree dewpoints and modest mid-level flow around 40 to 45 knots.
A leading round of elevated convection will be possible Sunday
morning if remnants from the Upper Midwest can hold together,
otherwise there is a chance for surface-based convection to
revitalize along the cold front as it drops across the forecast area
early Sunday afternoon. With the background wind field, steep lapse
rates, and focused forcing mechanism, some organized cells will be
possible.

Otherwise, the inbound thermal ridge initiates a period of strong
thickness advection which eventually brings H8 temperatures back
above +10 C by Sunday morning. This kicks off a period of high
temperatures in the upper 60s to 70s, which continues through middle
of next week.

MARINE...

Deepening low pressure continues to lift through the central Great
Lakes early this morning maintaining widespread rain. This low is
expected to reach its minimum pressure late this morning over the
Georgian Bay/northern Ontario resulting in rapid strengthening of
northwesterly winds across the region as colder air is pulled south.
High-end gales likely develop over the northern two-thirds of Lake
Huron this afternoon and persist into early tonight. Storm force
gust potential carries some uncertainty as its dependent on the
exact overlake thermal profile to support mixing depths that could
tap into 55+kt winds at/above 925mb. For now, have continued to opt
to hold the current Gale Warning with sporadic gusts touching storms
however a short-fused upgrade to a Storm Warning may be needed later
today if model data and/or obs supports this stronger flow reaching
the surface. For the rest of the region, gusts between 35-45kts are
expected through tonight into Saturday morning.

Gradient gradually loosens over the course of Saturday as the low
slides into Quebec with weak surface high pressure building in its
wake. While winds likewise slowly weaken, gale potential lingers
over northern/central Lake Huron into early Saturday afternoon.
Calmer conditions take hold by Saturday night before a much weaker
low drops out of Canada into the central Great Lakes Sunday. System
brings chances for additional light showers and a few thunderstorms
daytime Sunday. No wind headlines expected with this system as gusts
generally top out aob 20kts.

HYDROLOGY...

A strong low pressure system will bring additional rainfall to
southeast Michigan again today. Rainfall amounts since Thursday
morning range from a half inch in the Tri Cities and Thumb to 1 to
localized 2 inches around metro Detroit. Steady rain this morning
will transition to lighter showers across metro Detroit this
afternoon with under a half inch of additional rainfall expected. The
highest rainfall totals will be focused near the Thumb with a half
inch to locally 1 inch of rain expected through this evening. Storm
totals will end up being around 1 to 2 inches for the entire system,
which will lead to rises on area rivers and ponding on roadways.
Widespread flooding is not anticipated, but minor flooding of prone
urban and poor drainage areas remains possible. Rain will exit the
region late this evening.
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&&

.DTX WATCHES/WARNINGS/ADVISORIES...
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MI...Wind Advisory until midnight EDT tonight for MIZ047>049-053>055-
     060>063-068>070-075-076-082-083.

Lake Huron...Gale Warning until 10 AM EDT Saturday for LHZ421-422-441>443-
     462>464.

     Gale Warning until 4 PM EDT Saturday for LHZ361>363.

Lake St Clair...Gale Warning until 10 AM EDT Saturday for LCZ460.

Michigan waters of Lake Erie...Gale Warning until 4 AM EDT Saturday for LEZ444.

     Low Water Advisory until 10 PM EDT this evening for LEZ444.
-- End Changed Discussion --

&&

$$

AVIATION.....AA
UPDATE.......AM
DISCUSSION...MV
MARINE.......KDK
HYDROLOGY....MV


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