Rain Chances

If we didn’t have the Great Lakes to talk about in our area our weather predictions would have been a boring matter this summer.  I suppose in summation one would have to say “sunny and warm” as a wrapup for the past three months.  Dry would also factor into the report – the last time we had over a quarter-inch of rain was back on the 11th.  We did manage to get .13 of an inch on the 17th which did little more than wet the ground.  Our total for the month stays at 1.93 inches (these are Otsego totals).

Today we have a new feature to add to the sunny predictions and that is some haze caused by the smoke from the fires out west.

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The SPC is giving us a marginal chance of storms for tonight into early tomorrow morning.  The NWS is giving us a 60% chance of rain during that period though most point forecasts are showing around a tenth of an inch we could see higher amounts under any storms which may pass through.

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Forecast Discussion North

Impactful weather: Chance for more thunderstorms again today.
There`s a marginal risk for severe storms, with damaging winds and
to a lesser degree, large hail, as the main threats.

Pattern synopsis and forecast:

One shortwave trough has exited east, along with the decayed showers
and storms from yesterday. There is another shortwave seen crossing
Manitoba, with an associated low pressure in western Ontario. A cold
front drapes back SE from this low pressure through nrn MN and into
far SE ND, which then connects to a more stationary boundary that
heads westward across far nrn SD. While the greatest DPVA is well
north into Ontario, a 30-35kt LLJ and bulls-eye of moderate to
strong theta-e convergence north of the front, and some assistance
with some upper divergence, was producing some strong showers and
thunderstorms across srn ND into western MN, along a tight lapse
rate gradient. Some severe thunderstorm warnings have been issued in
this area. Ahead of this activity, there was a pre-frontal trough
from south central upper Michigan down through a good chunk of
eastern WI, which, with the assistance of a weak shortwave/vort max,
has resulted in in some scattered showers and occasional thunder in
an environment of growing MUCAPE. This activity was working slowly
eastward. In nrn Michigan, there`s been clearing with areas of fog
that have developed, primarily along and south of M-32, where most
of the convection occurred yesterday.

Per hi-res sfc wind guidance, the pre-frontal trough works it`s way
into nrn Michigan early to mid morning, while the apparent
associated weak shortwave/vort max weakens dramatically. All
guidance reflects little to no QPF for the morning, despite growing
MUCAPES seen in fcst soundings. Doubt this is a zero chance
scenario, so will have some slight chance of showers in the best low
level convergence this morning across eastern upper, maybe into far
nrn Lake Michigan.

Focus then shifts to this afternoon. There are hints of lake breeze
convergence across Mackinac county in eastern upper and in far NE
lower Michigan starting early this afternoon. The initial vorticity
advection and cold front come in later in the afternoon, while
MLCAPES grow to 1500-2000j/kg. Again based on latest guidance, the
only QPF output in those lake breeze convergence areas (there is no
observable sfc based convergence outside of these areas, even back
west in south central upper and NE WI, even with an analyzed front
coming in), so will make some somewhat big changes in the current
pops that are all over nrn Michigan.

Now tonight, sigh. This could turn out to be the more impressive
convection. The front dives through the srn CWA in the evening
(although at this point, it doesn`t appear to be a player). Rather,
the focus will be on two things. One, the convection in south
central upper and NE WI, will be sustained by additional vorticity
coming through (which exactly where this will be has a level of
uncertainty to it). This could drive that convection into far nrn/NE
lower/Straits region through the evening. Also, there is some level
of LLJ theta-e convergence seen to the SW of there, closer to the
GTV Bay region/south of M-32 in nrn lower, where MUCAPES still run
in the 1500-2000j/kg range and effective shear increases to more
impressive 30-35kts or so. There is just way too much uncertainty to
have too high of pops anywhere in the CWA, but as far as a severe
chance, seems like this evening into past midnight is the best time.
The combination of instability and shear in best across the GTV Bay
region over toward Saginaw Bay. If there are some severe storms,
damaging winds and large hail are the main threats.

Highs today will range from around 80F in eastern upper, to the
middle and upper 80s along and south of M-72 in nrn lower. Lows
tonight will largely be in the low to mid 60s.

Forecast Discussion South

-- A few chances for a storm through Wed morning --

There`s some moisture at 850 mb this morning which is touching
off some isolated showers in southwest Michigan, but they aren`t
amounting to much. By this afternoon, a weak surface trough down
the middle of the Lower Peninsula coinciding with diurnal heating
and little capping may be enough for isolated showers or a
thunderstorm to develop east of US-131. Deep-layer shear will only
be 10 to 20 knots, so generally hit-or-miss non-severe storms are
expected.

While there`s no substantial upper-level wave to help support
convection from above Monday night other than a speed max, some
moisture transport convergence at the nose of a low-level jet
should force convection to develop over Wisconsin during the
evening. At least the forward part of this convection may organize
in the increasingly sheared environment, and given the lingering
MUCAPE provided that moisture transport around 850 mb is
sustained, it`s possible that storms could cross Lake Michigan and
bring a marginal potential for strong wind gusts and/or hail.
This does not look like a soaker for most, however.

May be a repeat of convection at the nose of the nocturnal low-
level jet Tuesday night. This would again give us a marginal
potential for strong winds.

-- Warm through Thursday, smoky skies --

850 mb temperatures in the upper teens to lower 20s (Celsius)
will continue to favor high temperatures in the upper 80s to lower
90s through Thursday. The ECMWF ensembles are pinning Wednesday
as the hottest day this week. A large amount of smoke from western
U.S. wildfires has accumulated within an anticyclone over the
past several days. Now that the anticyclone is starting to weaken
and sprawl out under more zonal flow, relatively dense upper-
tropospheric smoke plumes are set to arrive over our area on
Monday. Vertically integrated smoke content greater than 50 mg/m2
is progged in the experimental HRRR-Smoke. The size and magnitude
of this plume over Michigan is reminiscent of mid-August 2018.
Fortunately, relatively little smoke is expected to mix down to
the surface. Given the flow pattern, wouldn`t be surprised to see
hazy/smoky skies through Wednesday or Thursday.

-- Rain chance late this week, cooler weekend --

The recurving path of tropical cyclone Laura after its expected
Gulf coast landfall mid-week remains unclear, however it appears
more probable that the circulation will stay south of Michigan.
But depending on the evolution of a Rossby wave trough advancing
toward the Great Lakes on Friday, some moisture contribution from
Laura would help increase the potential for needed rain in our
area, prior to a cold front providing relief from the heat over
the weekend.