935
FXUS63 KDTX 191623
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1223 PM EDT Sun May 19 2024

.KEY MESSAGES...

- Warm and muggy conditions are expected today and during the early
part of the week with daytime highs in the 80s.

- Showers and thunderstorms are likely this afternoon from Port
Huron southwestward to Adrian including Metro Detroit. Brief heavy
downpours and gusty winds are the main concerns this afternoon.

- Chances exist for thunderstorms Monday afternoon mainly north of I
69. There will be a potential for strong to severe thunderstorms,
but low confidence exists with exactly the strong to severe threat
will occur.

- A much less humid airmass is expected for the end of the week.

&&

.AVIATION...

Higher based (6-10 kft) cloud bases this afternoon with light
southwest flow giving way to weak and variable winds/lake
breezes/outflow boundaries. Thunderstorm coverage remains
challenging, as surface based capes reach and exceed 2500 J/kg.
However, mid levels remain very dry with an upper level ridge axis
in place also attempting to hinder activity/coverage. Will be
counting on some low level convergence from the cold front and
marine influence to get additional activity going, and still have
plenty of mixed signals in hires solutions, as subtle upper level
wave currently tracks northeast through southern Lake Huron. Will
continue to monitor real time trends and continue to fine
tune/adjust inherited TAFS, which is advertising thunderstorms for
the southern taf sites late in the day. Confidence remains shaky, as
muted response with just isolated-scattered disorganized
showers/thunderstorms is in play as well, which could lingering into
early evening hours. Once diurnal activity dissipates, anticipating
mostly clear skies tonight, as the low levels attempt to dry out
with light easterly winds. Still could be some residual higher
surface dew pts over the southern tafs to support light fog/MVFR
visibility reduction late tonight.

For DTW/D21 Convection...Confidence is high clouds bases outside of
any thunderstorms/showers will be above 5000 feet this
afternoon/evening, but still seems like there is a reasonable chance
for a slow moving thunderstorm/shower to impact the terminal late
today, with potential for a strong wet micro-burst wind gust and
heavy downpours leading to IFR visibility restriction. Timing is
still uncertain, and could occur anytime between 19-01z, if at all.

DTW THRESHOLD PROBABILITIES...

*  Low-moderate for scattered thunderstorms in the airspace between
   19Z-01Z. Low for thunderstorms on Monday.

&&

.PREV DISCUSSION...
Issued at 1144 AM EDT Sun May 19 2024

UPDATE...

Brief update to the PoP forecast prior for the isolated shower and
thunderstorms activity developing within the narrow thetae plume
ahead of the frontal boundary. Increased PoPs to 20-25% from roughly
the I-94 corridor up through the Thumb through 2 pm. Greater shower
and thunderstorm coverage still anticipated towards the St Clair
County to Monroe corridor during the afternoon.

PREV DISCUSSION...
Issued at 357 AM EDT Sun May 19 2024

DISCUSSION...

A dynamic upper level jet streak is forecasted to broaden today
while lifting to Hudson Bay. The broadening will force geopotential
heights to flatten across Lower Michigan which will not only allow a
surface cold front to settle southward through northern Lower
Michigan but also result in increasing boundary layer warming
immediately ahead of the approaching cold front. A notable but
narrowing thetae plume is expected to be in place during peak
heating this afternoon with forecast soundings supporting a well
mixed boundary layer of upwards to 4.0 to 6.0 kft agl. An
interesting scenario for this afternoon as a strong consensus of
hiresolution models support convection over the southeastern 2/3rds
of the cwa. This is despite fairly convincing background
anticyclonic vorticity advection over all of the forecast area and a
resolved weak 700mb anticyclonic circulation pushing overhead. At
first glance of the environmental wind profile, cell movement would
appear to be light west to east. However, the strong consensus in
convection this afternoon is unanimous in a slow northeast to
southwest track that is in agreement with the backward propagating
Corfidi vectors.

Based on the model support, increased PoPs into the likely-numerous
category for the afternoon in southeast sections of the forecast
area. Trigger/lifting mechanisms are expected to be near the
shorelines where increased convergence is located due to
differential heating. Do not really see a true lake breeze signal
per se, but convection will likely behave similarly with the
backbuilding and convective reinforced outflow.  Very little to no
shear suggest no strong or severe thunderstorm risk. The main threat
with the convection will be heavy rainfall due to slow storm
movement. Precipitable water of 1.3 inches and flow aligned along
the axes of lift increases the concern. Will forgo any thoughts of a
Flood Watch due to an extremely small footprint to any modeled
convective cells and a favorable setup for anticyclonic vorticity
advection. Gusty winds due to pulse type-water loading and small
hail (Surface based CAPE in excess of 1000 J/kg) will be possible.

An upper level trough pushing into the Pacific Northwest will cause
downstream amplification to a ridge over the central United States
Monday and Tuesday. The cold front that approaches the area today
will quickly lift northeastward on Monday. Some uncertainty exists
with the Monday afternoon forecast as trends suggest upstream
convective activity from the Plains will approach northern Lower
Michigan Monday afternoon. Convective parameters are in the ballpark
to support a threat of severe weather. Mixed Layer CAPE is
forecasted to reach and exceed 1750 J/kg and 0-6km bulk shear will
possibly reach/exceed 35 knots. While the magnitude of the bulk
shear suggests some potential for mesocyclones, the morphology of
the cam output suggests convective line with possible forward
propagating characteristics. The severe threat will likely hinge on
the track of convective vorticity which points to northern Lower
Michigan. Will need to monitor trends in future model data as SPC
has included Southeast Michigan in a Marginal risk for severe
weather. The majority of the models are dry here for Metro Detroit
but many including the latest ECMWF are bullish on late afternoon
convective activity near Saginaw Bay and Lake Huron. Expect
revisions to the convective Outlooks. Southeast Michigan will be
well within the warm sector with an unstable air mass and highs on
Monday expected to again reach the middle 80s. The inherited
forecast included a range of slight chance to chance for the
northern forecast area.

Uncertainty continues into Tuesday as convectively augmented
vorticity maxima will have the potential to stream out of the trough
toward Southeast Michigan. A dynamic low pressure system is progged
to wrap up over the northern Mississippi River Valley Tuesday with
background forcing downstream again supporting large scale subsidence
over Lower Michigan. Confidence is not particularly high given the
favorable conditions for convection across the Plains, but there is a
signal for Tuesday morning activity then pushing out and drying for
the afternoon. Confidence is then reasonably high for a cold front
pushing through the area early Wednesday. Drying with dewpoints
falling into the 40s is expected to carry out the remainder of the
week.

MARINE...

Humid conditions persist with pockets of fog across the region this
morning. Fog should largely dissipate from Lake Huron early this
morning as southerly flow increases ahead of a cold front.
Meanwhile, fog expands across western Lake Erie and possibly into
Lake St. Clair as light southeast wind persists there. This should
mix out by midday. Today`s cold front will be weak but may produce
isolated showers or thunderstorms this afternoon and evening,
especially along the nearshore waters. An area of low pressure then
tracks in from the Midwest late Monday into Tuesday, bringing the
next chance for showers and storms with the highest likelihood
across northern Lake Huron. Winds and waves are expected to remain
below Small Craft Advisory criteria outside of any localized higher
winds within any thunderstorms. A period of stronger south wind is
increasingly likely late Tuesday night into Wednesday as a stronger
low and associated cold front lift into the region.

&&

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

$$

AVIATION.....SF
UPDATE.......AA
DISCUSSION...CB
MARINE.......TF


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