National Weather Service - Area Forecast Discussion

FXUS63 KAPX 290905

Area Forecast Discussion
National Weather Service Gaylord MI
505 AM EDT Thu Jul 29 2021

.NEAR TERM...(Today through Tonight)
Issued at 220 AM EDT Thu Jul 29 2021

Impactful weather: Showers and embedded thunderstorms ending
quickly, then becoming gusty with the start of cooling and less

Pattern synopsis and forecast:

Upper level troughing was sliding out over the Atlantic ocean early
this morning, while broad ridging continues to engulf most of the
western half of the conus. Nrn Michigan remains in between, still,
with upper level NW flow in place. A shortwave trough was barreling
through the region attm, with latest RUC analysis suggesting, and is
well-verified based on latest satellite/regional reflectivity loops,
that one vort max and associated sfc trough was pushing through
eastern upper attm. This vort/MCV produced the late evening into the
overnight hours stratiform rain/showers with occasional rumbles of
thunder. The main action has been out west, where the shortwave`s
deep layer -divQ was creating more magic, along and just north of a
warm front, extending from sfc low pressure in NW/nrn WI back
through mid Lake Michigan and across areas in and around M-55. While
our night has been rather uneventful, out west in WI, LLJ and upper
jet dynamics and DPVA have been working with a much more favorable
environment conducive for strong convection, which has been
resulting in discrete supercells and developing QLCS signatures with
bowing segments/mesovortices, owing to 0-3km shear vectors a bit
more orthogonal to reflectivity structures. Hence, tornadoes and
damaging winds were much more common out there. Much of this
convection was propagating SE/S along the main theta-e and
instability gradient. This led to more and more confidence in a much
less severe weather/flooding threat for in these here parts.
However, another MCV has been suggested to cross mid Lake Michigan
prior to daybreak, which could still lead to some convective
initiation over the next few hours along and just north of the
frontal zone, possibly allowing for additional convective activity.
Gotta believe our chance for severe weather and potential flooding
are more than on a downturn, maybe more a free-fall, but we`re
obviously watching latest radar trends closely.

The above sentiments result in the thinking of a more rapid eastward
push of showers and mostly non-severe storms into today, with the
"bulk" of the action and main forcing being done by daybreak or
shortly thereafter, while the sfc low crosses srn lower Michigan. We
then enter an an increasingly intrusive thermal/moisture advection
process that can be more aptly characterized as "drier" and "more
stable", with zero synoptic forcing settling in for today and
tonight. We will however, have a tighter pressure gradient settling
in through the day, with winds turning gusty out of the NW, which
will also serve to feed in cooler and less humid air. The gusty
winds may continue into a good chunk of this evening, with partly
cloudy to mostly clear skies and no significant chance for fog due
to wind being strong enough in the BL.

High temperatures will largely be in the middle to upper 70s, with
lower 80s in downsloping areas of NE lower. Lows tonight will
largely be lower to middle 50s.


.SHORT TERM...(Friday through Saturday)
Issued at 353 AM EDT Thu Jul 29 2021

High Impact Weather Potential: Minimal attm...

Pattern Synopsis/Forecast:

Welcome to the weekend forecast! ...Or nearly so...does Friday
count? Anywho, similar pattern looks to continue into the weekend,
with ridging west, anomalous troughing east...and the Great Lakes
under the upper level expressway, as it were, between the two major
upper level features. Weak ridging and associated subsidence will be
in place Friday with cool, Canadian dry air in the area...but
rain/storm chances increase going into late Friday night and
Saturday as the next niblet of shortwave energy gets on the
expressway to vacation "down south" in Michigan for the weekend.

Primary Forecast Concerns: Low humidity Friday
afternoon...rain/storm chances late Friday night into Saturday

As mentioned above...mid-level subsidence should be firmly in
control of the region Friday...with a slight bit of ridging dropping
in from the north. This will leave surface high pressure just to our
west...bringing along with it some continental Canadian air...such
that it should be cool and dry...both precip-wise, and humidity-
wise...noting that model guidance Pwats in the 0.5" range are
anomalously dry, running on the dry side of climo for a change. With
afternoon dewpoints potentially as low as the 30s under decent
mixing, with highs in the upper 60s to lower 70s in most spots...
may have to keep an eye on this for near critical afternoon
humidities Friday afternoon for fire weather purposes. It is
typically more difficult to get critical humidities this time of
year, especially with somewhat recent rain...though this is a pretty
dry airmass moving in. From a general public standpoint...looks like
it could be a cool night again across the south, depending on how
quickly upstream cloud cover moves in ahead of the next system.
Probably a nice sweater and campfire evening Friday evening...just
be sure to fully extinguish the campfire when you`re done!! (And
enjoy some s`mores!)

As mentioned in last night`s discussion...still not convinced that
precip will move in terribly quickly Friday night, given antecedent
anomalously dry conditions in place over the area from departing
Canadian high pressure. Guidance does seem to have slowed up a
little from earlier runs...though it does seem to want to key in on
precip moving into E. Upper after midnight/2am Friday night into
Saturday better moisture does move into the area along
a weak boundary/warm front...with surface flow turning more
westerly/southwesterly behind the departing high...and some mid-
level WAA taking place. Could be enough instability associated with
the system to toss in some rumbles of thunder Friday night...though
do not foresee anything even remotely like what is being experienced
to our west in Wisconsin we should be dry/cool enough here
in the Great Lakes to minimize much surface based instability,
especially during the overnight hours. Might be able to eke out some
elevated instability with potential for mid-levels to warm a tad as
the shortwave and some minor CAA aloft moves in. We`ll see. Better
chances for thunder exist Saturday...ahead of the cold front and
strengthening vort max dropping in from the north. Do note we are
now under a Day 3 marginal risk of severe storms Saturday...mainly
for some strong gusty winds...which does make some sense given the
cold front coming in...potential for some instability (maybe around
1000j/kg CAPE?) ahead of it...and shear in the 30-35kt range.
Something to keep an eye on in the coming days...and something to be
sure to remind folks it will be the weekend, and this is
Northern people will be out and about in our beautiful
Great Outdoors.

Going into Saturday night...will be watching for the vort max to
wind up a little more...spinning up a surface low to our
east...though there is some uncertainty in where and how deep this
vort max gets Saturday night into Sunday morning. That could play a
role in perpetuating shower chances in Saturday night/Sunday morning
as additional moisture drops into the base of the trough...though do
suspect some models may be overdoing the mid-level has
been the case off and on the last couple weeks.

.LONG TERM...(Saturday night through Wednesday)
Issued at 353 AM EDT Thu Jul 29 2021

High Impact Weather Potential: Minimal attm...

As mentioned at the end of the short term...will be looking for the
short term to start off with that shortwave energy deepening up in
the base of the trough...which could lead to lingering/additional
shower chances as cold air aloft settles in Sunday. As mentioned
above as well, however...there is some uncertainty in exactly where
and how deep the shortwave and associated vort max ends up Sunday
morning...which will ultimately play a starring role in the
persisting shower idea. Going into the remainder of the long
term...additional niblets of energy swirling down through the flow
may lead to potential precipitation chances...though there is still
some uncertainty in timing and positioning of upper level features
that will ultimately result in changes in this portion of the
forecast in the coming days. Despite this...looks like troughing-
east, ridging-west idea (both potentially anomalous) will persist
into the middle of next week. A bit of a blocky-looking setup,
though there may be signals for changes towards the middle of next
week and beyond...noting CPC guidance for the 5th to the 11th of
August is trending warmer again.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 503 AM EDT Thu Jul 29 2021

Low pressure will pass to our south through this morning, ending any
further rain chances for the TAF period. Increasing sunshine is now
expected through the day, while a tighter pressure gradient brings
gusty NW winds, primarily for the NW lower airports. As the cooler
air arrives, MVFR CIGS are expected for a period this morning,
before daytime heating/mixing into increasingly drier air returns
conditions back to VFR. Too much wind in the BL for any fog
development tonight, and partly cloudy/mostly clear skies are for
continued VFR.


Issued at 220 AM EDT Thu Jul 29 2021

Low pressure will pass to our south through this morning, allowing
any light rain/showers to end this morning for most of the region. A
tighter pressure gradient settles in through the day, with gusty NW
winds and slightly unstable overlake conditions leading to needed
advisories most all areas into tonight. Higher pressure and lighter
winds work in over the region for Friday and Friday night.


LH...SMALL CRAFT ADVISORY from 2 PM this afternoon to 4 AM EDT Friday
     for LHZ345-347>349.
LM...SMALL CRAFT ADVISORY from noon today to 4 AM EDT Friday for
LS...SMALL CRAFT ADVISORY from noon today to midnight EDT tonight for



NWS APX Office Area Forecast Discussion