Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 042017

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
417 PM EDT Mon Jul 4 2022


Modest warm advection from the southwest continues over the area the
rest of this afternoon with highs peaking in the upper 80s to near
90 beneath a healthy coverage of convective debris cirrus. Upstream
radar mosaic features a line of showers and storms across WI and N
IL this afternoon that mark the leading edge of moisture transport
associated with a negatively tilted shortwave impulse over the
region. The lead activity should continue to weaken heading into
this evening as it moves into a progressively less favorable
environment, but do expect the LLJ to strengthen and veer tonight
over WI and redirect the moisture plume eastward. As it does so, it
will engage the warm frontal boundary in place and lead to a flare-
up of convection over eastern WI. This convection is favored to
propagate mainly SSE-ward along the instability gradient that will
likely hold to our west. Still expect scattered showers and storms
to spread in later this evening and overnight as the LLJ and
moisture feed move overhead, but the better severe threat does
appear to stay off to our west tied to the better instability. PWATs
are expected to rise to near 2 inches with soundings showing a deep
warm cloud layer and at least a brief period where Corfidi vectors
offer some backbuilding potential early Tuesday morning. This spells
a threat for localized heavy rain, but limited instability overnight
will preclude a widespread flooding threat. A marginal risk of
excessive rainfall is highlighted in WPC`s day 1 outlook.

The wave departs the region by mid-morning Tuesday with subsidence
in its wake and strong mid-level warm advection likely leaving a cap
in place across the area for much of the day Tuesday. Did shift PoPs
downward significantly as this scenario looks like the most likely
scenario at this point based on the latest suite of hi-res guidance.
There will however remain a slight chance that convection triggers
along the southward-sagging frontal boundary during the late
afternoon or evening. If this activity materializes, it would be
capable of producing isolated damaging wind gusts and large hail as
MLCAPE on the order of 1000-2000 J/kg and bulk 0-6km wind shear on
the order of 35-40 kt will be in place.

Dew points will likely trend up into the mid 70s tomorrow and result
in a very muggy day as high temps reach the upper 80s to lower 90s
away from the lakeshore. This would result in heat index values in
the upper 90s to near 100 for a few hours during the late afternoon.
Decided to hold off on a heat advisory with this forecast package as
there remains some concern for convective debris to linger overhead
as well as the potential for afternoon convection to spoil peak
heating, especially across the southern two tiers of counties where
an advisory would be most probable. Prefer to let tonight`s forecast
play out and reassess with a later forecast update.

The southward advancing front reaches the MI state line late
tomorrow evening while ample instability exists just to the south -
this looks to set off another flare-up of convection along the
frontal zone/instability gradient. Most of this activity should
remain to the south, but could see some strong to severe storms
develop south of I-94 late Tuesday night. Any of these storms would
have an attendant heavy rain threat as well with a very moist
environment to feed off.

High pressure will build in from the north on Wednesday, promoting a
light east/northeasterly wind and stable conditions through the day
- highs in the lower 80s inland and mid 70s immediately downwind of
Lake Huron. The frontal boundary will remain active just south of
the Michigan state line, so there will likely be some degree of
cloudiness originating from that convection. Another more vigorous
wave in the flow looks to emerge Wednesday night then track across
the region and bring the next chance of showers and storms on
Thursday. Medium range guidance shows the upper ridge
restrengthening over the northern Rockies late in the week. As this
feature translates eastward, its broad surface high pressure
reflection is modeled to spread across the Great Lakes which
suggests mainly dry and seasonable conditions for the coming weekend.



Light S-SE winds persist this afternoon with generally dry weather
anticipated through sunset, aside from a stray shower or
thunderstorm. Upstream thunderstorm complex to then track eastward
into the Great Lakes after midnight, in which strong to severe
thunderstorms will be possible. Mariners should be prepared for
frequent lightning, gusty winds, and brief periods of enhanced waves
through the morning hours tomorrow, especially across the southern
marine zones. Slight chance for additional showers/storms daytime
tomorrow along a warm front oriented west-east across central Lake
Huron. Otherwise, building high pressure keeps the wind field light
and thus marine conditions favorable aside from aforementioned
thunderstorm impacts. Similar setup persists through mid week as mid
level disturbances dive southeast, keeping shower/storm chances in
play mainly for the southern marine areas.



Scattered showers and storms are forecast to track through the
region late this evening through Tuesday morning as a warm front
moves in from the west. With abundant moisture arriving with the
warm front, there will be potential for these storms to produce
heavy rainfall rates. However, the best instability/fuel for these
storms is expected to stay to the west tonight and should limit the
overall flooding threat. Latest model guidance suggests basin-
average rainfall amounts ranging from a quarter inch to three
quarters of an inch will be most likely, but localized pockets in
excess of 1 inch can be expected where any stronger or training
storms track through. These amounts are not expected to lead to
widespread flooding given the antecedent dry conditions.


Issued at 122 PM EDT Mon Jul 4 2022


VFR conditions prevail as cirrus continues to stream into the region
tied to ongoing convection over WI/IL with some diurnal still
expected to develop late afternoon-evening. Main area of focus for
the forecast is potential for convection late tonight into early
Tuesday morning. Trends among the hi-res models this morning have
been for the line of convection that is expected to move across
southern WI/Lake MI to track further south than prior forecasts with
the bulk of storms missing SE MI to the west/south. That said, there
still is enough potential for the terminal corridor to be clipped by
the northern edge of this line to maintain inherited TEMPO groups.


* Moderate for thunderstorms Monday night/Tuesday morning.


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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