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000
FXUS63 KDTX 202354
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
754 PM EDT Sat Apr 20 2024

.KEY MESSAGES...

- Areas of frost are possible late tonight and Sunday night.

- Warming trend occurs Sunday and into Monday with dry and sunnier
conditions.

- Showers and thunderstorms arrive Tuesday with gustier winds.

&&

.AVIATION...

VFR conditions will prevail through this TAF period. The clouds at
around 6kft will likely linger through much of the night. Even with
the loss of daytime heating, the degree of clouds west of Lake
Michigan supports at least FEW to SCT coverage into tomorrow
morning. Winds are expected to lighten to around 5 knots for tonight.
May see a period of clear skies across the north tomorrow morning as
winds begin to pick back up to around 10 knots. Think there will be
some sort of diurnal cumulus response given the low level lapse
rates. Will have a SCT VFR clouds for tomorrow afternoon as mixing
supports gusts out of the west to around 25 knots by around 17-18Z.

DTW THRESHOLD PROBABILITIES...

* Low in ceilings aob 5000 feet tonight and tomorrow.

&&

.PREV DISCUSSION...
Issued at 308 PM EDT Sat Apr 20 2024

DISCUSSION...

Cloudy and chilly conditions persist through the rest of the today
amidst thermal troughing marked by an 850 mb temp of minus 8C per
20.12Z KDTX RAOB. Some additional sprinkles driven by persistent
weak cyclonic flow aloft and deep mixing are still possible, but
diurnal increases in dewpoint depressions indicate a higher
likelihood for virga than actual precipitation. Gustiness decreases
through the late afternoon hours as wind speeds wane within the
lowest 6 kft. Modest pressure gradient keeps speeds relatively
elevated until the overnight hours.

Main concern for tonight is the potential for frost/freeze
conditions. Recent model trends depict a longer duration for clouds
and less radiation cooling (RAP/NAM) which is reflected in slight
upward revisions to overnight lows and sky grids. While the
expectation is that many locations should reach the freezing mark,
temperatures will struggle to get much colder than 32F.
Additionally, the duration of freezing conditions appears rather
brief, perhaps an hour or two near sunrise. This follows a
coordinated effort with surrounding offices to address the
anticipated conditions through non-headline means. Should the
aforementioned cloud deck materialize, the back-edge would start to
exit from the northwest after 08Z. Note that temperatures across
Metro Detroit only minimize in the mid 30s tonight.

A ridge axis across the Intermountain West gets shoved downstream
Sunday by an inbound Pacific trough. This also causes the ridge to
shear into the energetic western periphery of the stalled Hudson Bay
low. The deflection effectively displaces the strongest jet winds
northwest of southern Lower Michigan offering a more subsident
column, locally. Although wind direction generally remains westerly
(if not northwesterly), flow trajectories take on a more
anticyclonic orientation supporting subtle warm advection and an
eventual increase in temperatures. This helps shrink the magnitude
of below normal readings to just a few degrees with afternoon MaxTs
expected to lift into the mid (if not upper) 50s. Boundary-layer
mixing supports afternoon gusts to around 25 mph, especially
along/north of I-69. The milder airmass should offset freeze
concerns Sunday night as temperatures only fall into the mid 30s, in
spite of mostly clear skies. Did add a Patch Frost mention for a
couple hours.

1025 mb surface high pressure centers over the Lower Mississippi
Valley Monday as warmer air within the composite ridge spills into
the Great Lakes. Southwesterly flow and moderating thermodynamic
profiles are indicative of highs AOA 60F. Dry weather persist as
PWATs remain below 0.50 inches until Monday night.

A closed low over Saskatchewan opens up and phases with a jet streak
as it crosses the High Plains and settles into the Upper Midwest on
Tuesday. The GFS, NAM, and ECMWF are all in decent agreement with
the low-level circulation tracking across north Lake Superior
Tuesday with a confluent LLJ. Plume of ThetaE accelerates
aggressively northeastward across Lower Michigan facilitating a
rapid saturation process. Numerous showers develop within the warm
sector Tuesday with enhanced divergence aloft dynamically augmenting
UVVs that may suffice to initiate some thunderstorm activity. Lapse-
rates are not particularly impressive, but a few hundred J/kg of
MUCAPE and decent effective shear should suffice. Afternoon non-
convective winds will be gusty with peak speeds in the 30-40 mph
range. A secondary trough/front trailing in close succession brings
another period of showers late on Tuesday until the main cold front
works through. Model spread increases Wednesday with how a pair of
PV anomalies interact which has ramifications on the southward
progress for another bout of unseasonably cool air.

MARINE...

Largely a persistence forecast this evening into Sunday as the
overall pattern remains unchanged for the central Great Lakes.
Moderate west to northwest winds this evening only marginally weaken
overnight (dropping ~5kts) before restrengthening daytime Sunday as
low pressure dropping south over eastern Ontario re-tightens the
gradient. This system draws a cold front through the area setting up
more uniform northwesterly by the latter half of Sunday- little to
no precip expected with this fropa. Strongest winds behind this
front occur over the central and northern portions of Lake Huron
where peak gusts reach 25-30kts. Small craft advisories likely will
need to be reissued for the Saginaw Bay as a result. Gusts closer to
15-20kts favored over the southern portions of the region. High
pressure dropping out of northern Canada then quickly tracks across
the region Sunday night through the first half of Monday bringing a
brief period of more favorable marine conditions.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....AA
DISCUSSION...KGK
MARINE.......KDK


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