FXUS63 KAPX 160154

Area Forecast Discussion
National Weather Service Gaylord MI
954 PM EDT Wed Jul 15 2020

Issued at 955 PM EDT Wed Jul 15 2020

It`s a soggy evening, along a relatively broad axis extending from
MBL to APN and Drummond Isl. Been well over an hour since any
thunderstorm was particularly strong, and with instability waning
thanks to loss of diurnal heating, that trend should continue.
But some heavier downpours and solid rainfall rates are still seen
in lingering convection. At APX proper, we are just above 1.5" of
rainfall since about 4 pm. Another slug of solid rain is pushing
into nw lower MI presently. All of this is occurring behind a cold
front that has reached far se sections of the forecast area.

Showers and a few thunderstorms will continue in the above areas
for several more hours. Precip coverage will start to wane in nw
lower MI between 2 and 4 am, as an initial shortwave moves across
the area. Showers will become spottier in ne and n central lower
MI after 4 am, but they should not come to a total end thru at
least 8 am.

Min temps from mid-upper 50s in eastern upper MI to the low-mid
60s near Saginaw Bay.


.NEAR TERM...(Through Thursday)
Issued at 419 PM EDT Wed Jul 15 2020

...Showers and thunderstorms tonight...

High Impact Weather Potential: Marginal risk for a severe storm
this evening. Locally heavy rainfall also possible.

Pattern Synopsis/Forecast: Afternoon composite analysis reveals
broad scale troughing through central Canada and down into the
Midwest with an upper level jet streak stretching from Wisconsin
into SE Ontario. Convectively induced short-wave is near Chicago
this afternoon, along with a decaying area of showers/storms...
pivoting northeastward toward Lower Michigan. Nearly stationary
surface boundary stretches from Eastern Upper Michigan and just
into NW Lower Michigan, before continuing on through Chicago and
surface low pressure over western Illinois. Only modest surface
heating/low level instability along and ahead of the front, with
MLCAPE values just topping 500 J/Kg per latest SPC mesoanalysis.
Nonetheless, with increasing dynamic support/approach of upper
level trough and jet entrance region along with MUCAPE values
pushing 1000 J/Kg, axis of largely post-frontal showers/storms
have been filling/expanding northeastward into the forecast area
over the last several hours.

Convective trends and severe weather possibilities remain the
primary forecast concern with the latest SPC Day One maintaining
a narrow axis of "marginal" severe storms up through Northern
Lower Michigan.

Larger scale troughing and upper jet axis will continue to swing
into and across the region tonight while convectively induced
short-wave pivots across Lower Michigan. And based on regional
radar trends, that will likely be enough bring fairly widespread
showers and storms across the forecast area through tonight. As
far as severe storms are concerned; as mentioned, only modest low
level instability out there there this afternoon while strongest
mid level flow/higher 0-6Km bulk shear values are further
west/north at the moment. SPC mesoanalysis does suggest a period
of increased effective bulk shear over the next few hours which
may lead to a few strong storms and marginal severe storm threat.
We will also have to keep an eye on heavy rainfall potential
through tonight with the convective potential and PWAT values
climbing to over 1.75". Heaviest rainfall potential appears to be
setting up a little further northward than previous forecast and
I`ve shifted the heaviest QPF forecast toward the northern half of
the CWA.

Widespread precip ends overnight into Thursday morning. A few
pop-up showers and perhaps a thunderstorm is possible across
Northeast Lower Michigan Thursday afternoon.


.SHORT TERM...(Thursday night through Saturday)
Issued at 419 PM EDT Wed Jul 15 2020

High Impact Weather Potential: Thunderstorm chances and high heat
index Saturday.

Pattern Synopsis: Fairly zonal upper pattern over the Great Lakes
going into the weekend. However, a good /sometimes gusty/ SW flow
develops over the area ahead of an approaching cold front. The SW
flow will bring in increasing moisture/instability and an increase
in precipitation chances Saturday.

Forecast/Details: SW flow persists over the region Friday and
Saturday. 850mb temps rise from around 14C to 19C during the period
as well with temperatures making another run for 90F both days. With
dewpoints approaching 70F, heat index values could reach the mid to
upper 90s.

Precipitation-wise, there is the possibility of a decaying MCS-
type area of precipitation dropping into the U.P. early Saturday.
Otherwise, the increase in moisture and heat will push CAPE values
up to around 1500J/kg by Saturday afternoon. Showers and
thunderstorms are at least possible Saturday especially in the
afternoon due to instability and weak areas of shortwave energy
moving through northern MI.

.LONG TERM...(Saturday night through Wednesday)
Issued at 419 PM EDT Wed Jul 15 2020

High Impact Weather Potential: Thunderstorm/severe weather potential
Sunday. High heat index expected Sunday as well.

Moisture continues to increase over the region Saturday night and
Sunday with temperatures making another run at 90F and heat index
values possibly reaching the mid to upper 90s again. CAPE values are
forecast to reach close to 3000J/kg before a cold front moves
through the area Sunday afternoon. Descent amount of shear in place
as well as westerly winds around 850mb increase and SW flow at the
surface continues. Timing of frontal passage Sunday will make a big
difference as to the amount of thunderstorm development.

The rest of next week looks cooler /but still above normal/ as broad
troughing over S Canada drops briefly over the Great Lakes.
Precipitation chances will be best Monday with decreasing chances
through mid week.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 742 PM EDT Wed Jul 15 2020

Showers and some embedded thunderstorms will continue tonight,
diminishing late as a cold front slides a bit further east. Brief
IFR cigs/vsbys possible tonight, especially early. VFR on

Winds will be somewhat variable this evening, settling in from
the n or e and light by Thursday.


Issued at 303 AM EDT Wed Jul 15 2020

A cold front will work into nrn Michigan today, before dropping SE
of the region tonight. This front will bring a broken band of
showers this morning, before showers and thunderstorms become more
numerous/likely this afternoon/evening with daytime heating and
subsequent destabilization. A few storms may be severe for the Lake
Huron nearshore, mainly Alpena south. Large hail and damaging winds
are the primary threats. Showers remain likely behind the front
through tonight, a few of which may linger in Lake Huron into
Thursday morning. Portions of Lake Huron, especially south of
Alpena, could see a few more showers and storms Thursday afternoon,
before relative high pressure moves in Thursday night.

Light southerly winds will become highly variable with the front,
and with lake breezes this afternoon. Light winds with a good degree
of variability continue through Thursday, before winds back more out
of the W/SW Thursday night. No significant winds/waves.





NWS APX Office Area Forecast Discussion