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area forecast discussion
national weather service detroit/pontiac mi
733 pm edt thu jul 9 2020


limited window yet late this evening for an isolated thunderstorm in
the vicnity of fnt and mbs based on recent radar trends. otherwise,
simply some lingering high based cloud cover within a light south or
variable wind into the mid morning hours. a greater potential for
thunderstorms will exist friday afternoon and early evening as a
frontal boundary tracks through the region. an initial round of
convection may arrive as early as 15-16z, with more widespread
activity anticipated for mid-late afternoon. confidence remains high
enough to outlook these periods for all southeast michigan

dtw threshold probabilities...

* medium for thunderstorms friday afternoon and early evening.


.prev discussion...
issued at 356 pm edt thu jul 9 2020


another hot and muggy afternoon and evening to get through on this
heat advisory stretch across southeast michigan before a little
relief arrives tomorrow. southwest flow into the area has maintained
high moisture with dewpoints in the upper 60s to low 70s. this is
both increasing heat indices to near 100 and supporting the
continued chances for diurnally driven convection. the main trigger
for these showers and thunderstorms are lake boundaries and minor
waves rolling through the area. any initial activity will then kick
out outflow boundaries, which could then triggering additional
showers and thunderstorms. environment today is characterized by
mlcape values of 1000-2000 j/kg, steep low level lapse rates of at
least 8-9 c/km with flow below 20 knots up to around 10 km. in this
weakly sheared environment, disorganized pulse type showers and
thunderstorms will be the main storm mode. high moisture and steep
low level lapse rates will support downburst potential from water
loading of the more robust updrafts.

the heat advisory will remain in effect through this evening as warm
and muggy conditions persist with overnight lows remaining in the
70s. the good news is a brief pattern shift takes place tomorrow as
a shortwave is forecast to track across the great lakes. timing of
this shortwave will bring increasing cloud cover early in the day
with scattered convection possible during the late morning/early
afternoon. this will mitigate further warming and hold high
temperatures in the upper 80s to low 90s. high moisture with
dewpoints in the upper 60s to low 70s will remain in place tomorrow,
so it will still feel pretty muggy. continued higher moisture will
bring heat indices into the low to mid 90s with only localized spots
capable of reaching the upper 90s in the urban heat island of
detroit. this moisture will again fuel convection with the best
forcing for more widespread activity after 18z with the approaching
cold front and larger scale ascent. clouds and any earlier activity
puts into question the degree of instability that can develop with
slightly better shear promoting better organization than previous
days. it still appears to be a low severe threat at this time, but it
will be something to keep an eye on tomorrow as the day evolves.

northwest post frontal winds bring a much needed break from the
highs in the 90s this weekend. humidity will drop as well with the
70s dewpoints being pushed south of the state with high temperatures
forecast to fall back into the 80s. the synoptic pattern over the
weekend will have troughing/lower heights over the great lakes as a
few pacific shortwaves move through the northern periphery of the
four corners ridge. this leaves open the possibility for some
scattered showers and thunderstorms over the weekend with the
stronger shortwave on sunday bringing the best chance for more
widespread activity. unfortunately, the respite from heat will begin
to release through early next week as ridging builds into the great
lakes and allows southwest flow to bring a return of heat and
humidity. by wednesday, models forecast 850mb temperatures climbing
back above 20c helping high temperatures rise back into the low/mid
90s range.


a weak pressure gradient across the region will persist through
tonight while providing light and variable winds across the region.
afternoon thunderstorm chances will once again exist today but most
storm activity will remain over land areas where instability will be
a little greater. a weak area of low pressure will then move across
lower michigan on friday. this system will bring a much better
chance for thunderstorms to the marine areas. this system will also
result in light south-southeast winds across the marine areas friday
with winds backing toward the northwest by saturday as the low
pressure system moves east of the region. light offshore winds will
keep marine conditions favorable outside of thunderstorm activity.


.dtx watches/warnings/advisories...
mi...heat advisory until midnight edt tonight for miz047-048-053-060>062-

lake huron...none.
lake st clair...none.
michigan waters of lake erie...none.


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