Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 260920
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
520 AM EDT Tue Mar 26 2024

.KEY MESSAGES...

- Widespread rain will affect the area this morning.

- Gusty winds are expected today, with a few gusts up to 40 MPH
  possible.

- Scattered thunderstorms are possible late this afternoon and
  evening. A few storms may produce damaging wind gusts.

- Cooler and drier weather returns Wednesday.

&&

.AVIATION...

Main area of showers will be working out of the terminal corridor
around the start of the new forecast period. Generally drier
conditions expected to follow for the latter half of the
morning/afternoon however lingering low level moisture still offers
a low chance for a few light showers, which is supported by a
portion of the model guidance. As such, not enough confidence to
completely remove inherited rain mention for the first half of the
day, though impacts will be minimal should a shower pass overhead.
This lingering moisture does support continued MVFR ceilings through
the day however. Approaching cold front leads to the generation of a
secondary round of showers as well as a few thunderstorms late this
afternoon into the evening (~20-02Z). IFR ceilings possible with
this activity as well as stronger wind gusts.

For DTW... MVFR ceilings are already in place early in this morning
and will remain so through the bulk of the day today. Main surge of
rain will be vacating around forecast start offering a drier late
morning/afternoon before another round of showers and storms develop
to the west. This line will cross the airport roughly between 21-01Z
this evening bringing with it potential IFR ceilings and stronger
wind gusts.

.DTW THRESHOLD PROBABILITIES...

* High for ceilings at or below 5000 feet today.

* Moderate for wind gusts at or above 30kts from ~160 degrees
  Tuesday morning.

* Low to moderate for thunder between ~21-01Z this evening.

&&

.PREV DISCUSSION...
Issued at 300 AM EDT Tue Mar 26 2024

DISCUSSION...

Upstream VAD Wind Profile data are nicely showcasing the ongoing
momentum surge via the strengthening low level jet. This is
responsible for the excellent northward moisture transport (inbound
precipitable water values nearing one inch) driving the widespread
rain across western Lower Michigan attm. Model 296k isentropic
analysis indicates the low level jet strengthening to 70-80 knots
over nrn Indiana by 09-10Z this morning, with max theta e
convergence focused over Se Mi. Widespread rain will thus result
during the early morning. The low level jet is shown to quickly
translate north and east of Se Mi between 12Z and 15Z. This will
result in a significant decrease in the coverage and intensity of
the rain. Low level wind fields will be quite strong this morning,
with RAP soundings indicating 2-3k foot level winds of 55-60 knots.
Given that the boundary layer is drier across Se Mi, the expectation
is that there will be enough evaporative cooling near the surface to
limit the degree of convective mixing and thus keep morning wind
gusts below advisory criteria (45 MPH).

The morning rainfall is occurring within the warm conveyor
associated with the sfc low lifting across Wisconsin this morning.
Mid level height falls from the associated upper wave are expanding
across Lower Mi, helping to drive the warm conveyor eastward. There
remains strong model agreement that the secondary short wave
emerging from northern Missouri this morning will lift across nrn
Illinois this afternoon and into northern Michigan this evening.
This wave is forecast to develop a negative tilt as it works
eastward, driving a narrow region of forced ascent along/in advance
of a sfc cold front. This front is forecast to track across Se Mi in
the 21Z to 02Z time frame. Steep mid level lapse rates will maintain
at least weak elevated instability, supportive of numerous showers
and scattered thunderstorms along the front in light of the forced
ascent. Se MI remains within a marginal risk of severe weather (with
Slight just brushing the western CWA) which is predicated on the
amount of available surface based instability that is able to advect
ahead of the sfc front. In light of the strong low level wind fields
(50 knots at 2-3k feet), even weak convective updrafts may be able to
bring some localized damaging wind gusts to the surface. If SBCAPE
is able to maintain several hundred J/kg into Se Mi to balance the
80+ knot bulk shear values, then a little more organized severe
potential will be possible. Given the high 0-1km helicity values, a
brief weak tornado can not be ruled out in this instance.

The mid level wave and surface low pressure system will be driven
northward out of the area tonight as the northern stream upper low
now diving into the Dakotas tracks across Lake Superior and northern
Ontario Wed afternoon/evening. The southern lakes will remain within
the base of the longer wave trough into Thursday night as the upper
low lifts northward to Hudson Bay. Seasonally cool conditions will
result. Very dry air across the region will keep precip out of the
forecast.

MARINE...

A very strong low level jet (winds at 1 kft of 55-60 knots) will
continue to surge over the Great Lakes, just ahead of the arrival of
widespread rainfall, which is now filling in. Soundings display an
extremely stable over-lake environment with the antecedent warm air
above the cooler waters, which will likely keep the wind maxima just
above the surface. However, gradient winds will ramp as a response
to momentum flux, increasing around 30 knots through the morning and
afternoon. As widespread rainfall builds in, the stable marine layer
will weaken, bringing increased chances to see sustained winds and
gusts to gales. Still, soundings are quite stable even with
rainfall, so it is unlikely gusts will be able to tap into the
strongest winds aloft. Gust to gales up to 40 knots are favored at
this time, favored across north-central to south-central Lake Huron.
A Gale Warning remains in place for a greater portion of Lake Huron,
the Saginaw Bay, and the Lake Huron shoreline down to Port Sanilac.
Small Craft Advisories are in place for locations south for wind
gust potential just shy of gales. A short-fused upgrade to a Gale
Warning cannot be ruled out as we continue to monitor upstream
observations.

Otherwise, a secondary line of showers with possible embedded
thunderstorms are expected to move the Great Lakes late this evening
along a cold front. Some localized stronger wind gusts to 40 knots
will be possible with any thunderstorm activity. High pressure
builds in behind the front, bringing quieter marine weather to the
Great Lakes.

HYDROLOGY...

Precipitation will largely occur in two periods today. The first
will be this morning, mainly prior to 9 AM. The second round will be
this evening. While there will be some lingering showers and/or
drizzle between these two time periods, the rainfall amounts will be
very light. The combined total precipitation from these two rounds
of rain is expected to fall into the quarter to three quarter inch
range. The second round of showers this evening will occur along a
cold front. The passage of this front will usher in cooler and drier
conditions for Wednesday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ443.

     Gale Warning until 10 PM EDT this evening for LHZ362-363-421-422-
     441-442-462-463.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....KDK
DISCUSSION...SC
MARINE.......AM
HYDROLOGY....SC


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