Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 140825
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
425 AM EDT Thu Mar 14 2024

.KEY MESSAGES...

- Showers develop periodically today with few thunderstorms possible.

- Marginally severe storms are possible near the Michigan-Ohio
border this afternoon and early evening where hail could approach an
inch in diameter.

- Seasonably colder temperatures arrive Sunday and Monday.

&&

.DISCUSSION...

Competing upper level features surrounding the Great Lakes are set
to influence weather conditions over the next 24 hours. Quasi-
stationary northern stream jet is absorbing the exiting shortwave
ridge over Lower Michigan that maintained dry conditions locally
through midnight. This ridge has been forced out by inbound height
falls tied to an elongating jet streak releasing across The Plains,
downstream of a retrograding parent upper low over the Desert
Southwest. Ageostrophic exit region response aloft from the central
CONUS speed max has already resulted in a closed cyclonic
circulation at/below 700 mb atop the Missouri River basin that has
strengthened the LLJ across Illinois and Indiana. 00Z data offers
some conflicting takes on the evolution of ThetaE advection and
shower activity today as a surface warm front extending well east of
the primary low struggles to translate northward into southern Lower
Michigan. This lends low confidence for the boundary to interface
with a stalled cold front stretched across central Lower.
Ultimately, expect differing convective timing and character between
rainfall over the northern CWA (anchored to the cold front) and
thundershowers generated off the elevated warm frontal zone.

Current obs reveal minimal movement of the surface boundaries, but
early morning convective activity did crop up once low-mid level
dewpoints responded to the uptick in confluent lower tropospheric
southwesterly flow. Elevated narrow-diameter updrafts converted the
shallow CAPE profiles to isolated single cell thundershowers as the
initial moisture plume was shoved up the isentropic surface. This
lends low confidence in the overall handing of both CAM and
hydrostatic solutions of various showers/storms through the midday
hours. The complex environmental structure is further impacted by
perpetual ThetaE advection which combines with an increasing
frequency of CVA packets that offer direct moist ascent. The dynamic
inbound wave also provides a robust wind field as 0-6 km bulk shear
climbs into the 50 knot range given weak easterly gradient flow at
the surface. Ultimately, it`s impossible to specifically rule out
precipitation at any one location before 06Z tonight since mid-level
lapse rates steepen, PWATs rise into the 0.8-1.2 inch range, and
FGEN enhancements occur between both frontal zones.

Latest thinking generally differentiates activity from north to
south with longer duration showers along/north of I-69, a midday
lull south of I-69 to I-96/696, and then a low-chance for strong to
marginally severe storms between I-96/696 and the state-line. For
northern locations, the colder airmass offers deeper column
saturation that can capitalize on modest ascent resulting in
prolonged/organized rain showers of light to moderate intensity
which are largely focused along the retreating vicinity cold front
zone. For the middle portion of the CWA, models are mixed regarding
the progressiveness of morning showers and the degree to which the
airmass diurnally recovers before any afternoon/evening
precipitation. Main concern with the more organized thunderstorm
potential exists across the southern four counties where MUCAPEs
could exceed 500 J/kg. Forecast soundings are now more definitive in
keeping instability elevated as opposed to some brief transition to
surface- based instability. This limits severe hazards to mainly a
marginal hail threat should any more robust updrafts develop within
the warm sector between 21Z and 01Z. Ill defined surface low then
tracks east- northeasterly along I-94 this evening before exiting
into Ontario. Trailing shower activity appears brief tonight as
northerly flow spills in offering a more subsident column.

Drier and cooler environment arises Friday as low-level anticyclonic
flow builds out of the High Plains. Stratus will linger throughout
the midday hours while the 925 mb thermal gradient fights to make
southward progress. Northerly gradient winds offer better cooling
potential for The Thumb region off Lake Huron where temperatures
hold in the 40s. Elsewhere, readings will be sensitive to the rate
of clearing and 925 mb temperatures, therefore highs above 50F are
most likely for Metro Detroit. Broader clearing trend arrives Friday
night until a positively tilted trough digs into the Upper Midwest.
This draws an initial mid-high cloud veil into the Great Lakes by
Saturday morning. A more seasonable airmass then settles in while
thermal troughing spills downstate Sunday and Monday. Potential
exists for some scattered light showers with arcing upper level
energy Saturday and Sunday afternoon. Some snowflakes could mix in
briefly, especially for the Tri-Cities and Thumb regions Sunday.
Upstream longwave amplification commences mid-week, eventually
spreading a warmer and drier airmass into Michigan.

&&

.MARINE...

A stalled front across the southern Great Lakes will remain through
the day while the first of a pair of low pressure systems track up
along it and through the region tonight. This low will bring showers
and thunderstorms to the region today and tonight. On Friday, a
second low pressure systems will then track along the front, which
will be a little further southeast over the Ohio Valley. Rain
showers may clip portions of Lake Erie early Friday morning but the
bulk of the rain will be south of the area. In addition to
precipitation, as high pressure builds in from the north the
gradient will tighten which will increase the northeasterly winds to
around 20 to 25 knots and the onshore flow will build wave heights
along the shoreline of the Thumb and into Saginaw Bay. A Small Craft
Advisory has been issued to account for this period of elevated wind
and waves Thursday afternoon through Friday afternoon.

&&

.HYDROLOGY...

Rain showers and some afternoon thunderstorms increase in coverage
today as a low pressure system approaches from the southwest. An
elevated warm front will drive much of this activity for the
southern half of the forecast area while the influence of a cold front
further north maintains longer duration of showers north of I-69.
Locally heavy downpours can be expected with total rainfall amounts
averaging around half an inch. Locally higher amounts in excess of
an inch will be possible near the Michigan/Ohio state-line where
thunderstorm coverage will be greatest. While flooding is not
expected today or early tonight, ponding of water on roadways and in
poor drainage areas may occur.

&&

.PREV DISCUSSION...
Issued at 1049 PM EDT Wed Mar 13 2024

AVIATION...

During the course of the morning, there will be a robust transport
of low to mid level moisture into Se Mi in advance of an upper short
wave and associated sfc low lifting from the Mid Mississippi Valley
into the southern Great Lakes/northern Ohio Valley. The initial
moisture surge will result in increasing clouds and decreasing
ceiling heights this morning. Although there will be some weak
elevated instability with the initial moisture surge in the morning,
probabilistic guidance suggests thunderstorm chances will remain
low. The warm sector and thus instability axis will nudge into
southern Michigan Thursday afternoon. This will result in much
higher thunderstorm chances, particularly from PTK south. Given the
amount of moisture being transported north of the sfc warm front,
which is likely to stall around or just south of the I-94 corridor,
much of Se Mi will be within IFR and/or LIFR conditions with
persistent showers and/or drizzle through the day Thursday.

For DTW...The most probable time for thunderstorms to affect metro
will be in the mid to late afternoon hours on Thursday. This will
the time period when the elevated instability axis expands across
metro Detroit.

DTW THRESHOLD PROBABILITIES...

* High in ceilings aob 5000 feet Thursday.

* Moderate in thunderstorms Thursday afternoon.

* Low in ceilings and/or visibilities aob 1/2SM or 200 Feet.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 4 PM this afternoon to 4 PM EDT Friday
     for LHZ421-422.

     Small Craft Advisory from 10 PM this evening to 4 PM EDT Friday for
     LHZ441-442.

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

$$

DISCUSSION...KGK
MARINE.......DRC
HYDROLOGY....KGK
AVIATION.....SC


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