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Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
317 am EDT Mon may 28 2018


Near term / today through tonight

As of 315 am EDT...a mild and muggy night continues across Southeast
Michigan as upper ridging remains firmly in place. In the lower
levels, a weak frontal boundary remains draped across the north-
central Great Lakes and is expected to drift slightly southward
through the course of the day. Elevated dewpoints well into the 60s,
light low-level winds, and mainly clear skies have promoted an
environment again favorable for patchy, perhaps locally dense fog.
Best coverage of fog will be north of the M-59 corridor, where low
temperatures settling in the mid 60s will result in closer to near 0
dewpoint depressions. Further south, lows will only fall into the
upper 60s, with near 70 readings in the Detroit Metro.

After any morning fog dissipates by 8-9 am, the forecast then shifts
to the two main concerns of the day. The first will be the hottest
Memorial Day since 2012. Slightly higher thicknesses and rising
heights aloft will yield the hottest day of the long Holiday
weekend, with widespread lower 90s expected across inland areas.
Closer to the lake coastlines, temperatures will be slightly marine-
modified, but still warming into the 80s. With dewpoints continuing
in the mid 60s, it will feel quite muggy, and heat indices are
expected to reach into the mid 90s for most areas in Southeast
Michigan. For everyone out enjoying their outdoor activities today,
make sure to keep heat safety in mind, such as taking frequent
breaks and staying hydrated. Record high temperatures will again be
in play today (see the climate section below for more information).

The second weather concern for the day will be the potential for
thunderstorms, especially this afternoon and this evening. Early
this morning, a weak shortwave riding the top of the ridge axis has
helped spawn a mesoscale convective system across northern Minnesota, northern Wisconsin,
and parts of the up. Continue to monitor the eastward progression of
this system, and possible associated mesoscale convective vortex. Hi-res guidance does not
expect it to hold together much past Lake Michigan as it continues
moving southeastward.

As the day progresses, compressional warming in the low/midlevels
will help limit cloud cover again today, with boundary layer cumulus
suppressed. Heading into the afternoon and evening, the big question
will be coverage of potential thunderstorms. Ambient thermodynamic
environment remains similar to the past few days, with 1000-2000
j/kg MLCAPE likely with dcape in excess of 1000 j/kg. 700 hpa temps
do increase slightly to more in the 6-8 c range, warmest towards
central lower Michigan. This warming will act as a cap to possible
convection, with a fair amount of cin that will also need to be
eroded with daytime heating. Lapse rates will be favorable, with
steep low-level lapse rates in a well-mixed boundary layer, and
steeper midlevel lapse rates on the order of 7-7.5 c/km helping to
fatten the cape column.

The more noticeable change for today, albeit subtle, resides in the
kinematic field. Hi-res guidance and nam12 depict slightly better 0-
6km and effective bulk shear profiles increasing to around 30 knots,
aided in part by the aforementioned subtle shortwave that will be
riding the northwest flow regime aloft. The European model (ecmwf) and GFS also
depict this shortwave, which may be locally enhanced by the mesoscale convective system
mentioned above. With the slightly better kinematics in place, and
looking back at persistence of storm activity/intensity the past 2
days in the virtually similar thermodynamic environment, any storms
that develop today will be capable of becoming severe with brief
gusty winds and hail 1 inch or greater in diameter. Have coordinated
with spc, and portions of the Tri-Cities east into The Thumb will be
added into a marginal risk for severe storms for today. Locally
heavy rainfall, gusty winds, and hail are the primary threats with
the strongest storms that develop.

Timing of convective initiation is still in question, but cams seem
to be in general agreement that the best window for activity will be
in the 20z-04z timeframe, with coverage only isolated to widely
scattered. Will carry chance pops in the areas mentioned above, with
slight chance down towards Flint and southeast into the eastern
thumb and portions of the northern Detroit Metro.

Any lingering thunderstorm activity wanes by midnight with the loss
of daytime heating. It will be another muggy night with low
temperatures only falling into the 60s for most areas and dewpoints
staying in the 60s. Building high pressure from Hudson Bay will help
shift winds tonight to the northeast, and a light enough persistent
flow should help to keep any fog concerns at Bay.

Short term / Tuesday through Thursday night

The aforementioned high will continue to attempt to ridge
southwestward into Southeast Michigan on Tuesday, and will bring in
slightly drier and cooler air. Still though, high temperatures will
warm well into the 80s and it will feel muggy again as dewpoints
remain in the 60s and heat indices flirt with lower 90s. The
slightly drier air and the approach of the ridge axis from the west,
which will be folding in on itself with the approach of the remnants
of subtropical storm Alberto, will help keep most areas dry. The
exception may be towards central lower Michigan with any convection
that can fire downstream of Lake Michigan. Lows Tuesday night will
range from the upper 50s to mid 60s.

The remnants of Alberto will continue to approach the region
Wednesday, with cloud cover rapidly increasing early in the day. A
wet stretch of weather is then expected beginning the second half of
Wednesday and continuing into Thursday. A surge in tropical moisture
will naturally accompany the remnants of Alberto, with pwats surging
over 2 inches; likely record values for late may. The remnant
central low pressure itself looks to track west of Southeast
Michigan based on the latest NHC forecast, which will allow for some
elevated instability to accompany the tropical moisture. Widespread
periods of rain with embedded thunder will be likely, with heavier
rain segments also occurring. Currently not expecting a flooding
threat with this system, but will continue to watch over the next
few days.

Temperatures Wednesday and Thursday will feature daytime highs in
the lower 80s with continued mild nights with lows in the 60s.

Long term / Friday through Sunday

Inbound northern stream energy from the northern plains will act to
absorb the remnants of Alberto heading into the weekend. Still a
decent amount of uncertainty in the forecast evolution during the
long term as these two features interact, but consensus at this time
favors a general drying trend heading into the weekend with
temperatures returning closer to average to start the month of June.



The wind pattern will be light and variable across marine areas
today as a weak frontal boundary lingers over northern lower
Michigan and Central Lake Huron. Warm and humid air over the cold
open waters of Lake Huron maintains some fog and haze and the front
continues to support a chance of thunderstorms during the afternoon.
The frontal boundary accelerates south of Lake Erie by Tuesday
morning as high pressure builds north of Georgian Bay and produces a
more uniform light to moderate easterly wind across the lakes
through Tuesday night. There will be a measured wave response to the
wind pattern mainly over Central Lake Huron and Saginaw Bay before
the wind direction turns southeast Wednesday. The remnants of
Tropical Storm Alberto will then enter the Great Lakes near the
south end of Lake Michigan on a track toward The Straits Wednesday
night. It is expected to produce a large area of rain and increase
southerly wind to around 25 knots over the open waters of Lake Huron
through Thursday.



Here is a list of record high temperatures for today.

Monday, may 28th:

Detroit 95 (set in 2012)
Flint 93 (set in 2012)
Saginaw/Tri-Cities 92 (set in 1977)


Previous discussion...
issued at 1154 PM EDT sun may 27 2018


Ridging will maintain VFR conditions and light winds throughout the
upcoming forecast with just a small chance at shallow, patchy MVFR
fog for a few hours early Monday morning.

Dtw threshold probabilities...

* none.


DTX watches/warnings/advisories...
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.



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