244
FXUS63 KAPX 200758
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
358 AM EDT Mon May 20 2024

.KEY MESSAGES...

- Strong to severe storms possible this afternoon through this
evening.

- Another round of strong to severe storms will be possible
 Tuesday night as a cold front passes through and brings a
 potential squall line passage through the region.

- Cooler and occasionally unsettled Wednesday into early
  Thursday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 355 AM EDT Mon May 20 2024

Southwesterly flow beginning to dominate the central CONUS...with
bulk of convective activity crossing the central Plains into the Mid
MS Valley early this morning in advance of a couple PV niblets
deepening as they cross the central Plains...along a lingering BCZ
stretching from central Quebec down through the OH Valley...and back
into the central Plains...where anomalous moisture (pwats 1.5 inch
or greater) looms in the vicinity of this boundary. Warm over the
Great Lakes region...with 850mb Ts in the low to mid teens...and
highs yesterday reaching well into the 70s over even northern Lower,
with low and mid 80s from NE Lower down into central Lower where
better downsloping aided in maxing out temps under the primary ridge
axis. Dry here in northern MI though...with pwats on the very low
end of climo at 0.25in from our 0z/20 sounding. Upstream convection
over WI has been weak...but appears things are trying to hold
together a little better as of 6z with IR satellite denoting a
better showing of cooling cloud tops to our west in the last couple
hours.

Anticipating leftover PV max from the central Plains/mid MS Valley
to continue to trek NEward into the Upper Midwest/Great Lakes
through today...ultimately dragging the boundary back northward
toward central Lower with time today. Signals currently point toward
an MCS/line of storms crossing central Lower MI during the late
afternoon/evening during peak heating, with north central Lower most
likely on the north end of this. However, it may be possible to
develop some storms across NE Lower toward Saginaw Bay this
afternoon, out ahead of the primary line from WI. Primary focus
should be south of the Mighty Mac...and particularly toward M-72/M-
55 this afternoon into tonight, depending on how far north the
boundary ends up getting today...though will expect rain and general
thunderstorms to overspread the area tonight as well...most likely
exiting the Sunrise Side toward daybreak Tuesday or later. Not a
clear cut forecast by any means, though.

Primary Forecast Concerns:

Bottom line up front: potential severe threats today/tonight, if
they materialize, will be damaging winds, large hail, heavy
rain...and a tornado can`t be ruled out. Primary focus for strong to
severe convection will most likely be 1pm-midnight EDT from west to
east...though not impossible we will deal with lingering rain/storms
into the bulk of the night.

Strong to severe storms possible this afternoon into this evening...
Initial concern is how quickly precip will get into the area, given
current dry air mass in the low-levels. Noting satellite imagery
upstream is still trying to hold things together back over IA, and
even into parts of SW WI...think it`s not impossible this
activity/convective debris holds together and gets in here to
moisten up the atmosphere across NW Lower. There is also some
suggestion that a lobe of moist air from the dying convection over
the OH Valley may try to make it up into our SE (Saginaw Bay) area
early in the day. Both of these ideas, if they verify, could suggest
a greater potential for destabilization during the afternoon as
deeper moisture and better forcing work in from the west with the
niblet. Otherwise...it will take longer for convection to make it
here and/or develop in the first place...with less instability to
work with if it remains dry in the low-levels. However...noting that
attm I`m struggling to find dewpoint guidance moist enough for
what`s actually going on right now...I`m becoming a little more
suspicious that things could get beefy this afternoon.

Primary background flow in the low-levels could become south to
southwesterly, which, if differential heating allows for lake
breezes to develop, could suggest we may have to watch for pop-ups
over NE Lower ahead of the primary line of storms coming out of WI
which could produce some marginal hail. Given low-level veering flow
potential along the Lake Huron lake breeze...anything that develops
out this way could have a little spin with it. Additionally...will
have to see how the incoming line of storms from WI interacts with
any lingering boundaries from NE Lower, as this could produce
anything from embedded spin-ups to very focused training convection
and flash flooding. Given pwats are expected to approach the high
end of climo, won`t be shocked to see some areas get overly
soaked...particularly noting a majority of the CWA may very well end
up in the stratiform rain on the north end of the line, where storm
motions would more likely end up being slow.

One thing that may work in our favor with regard to lowering severe
potential today...is that wind fields aren`t overly impressive with
this system...noting deep-layer shear may run around 30kts...which
tends to be just sufficient enough for storm organization. There
currently appears to be a fairly narrow area of better shear,
though, which could end up further north than where we currently
expect the primary MCS to develop. This could either reduce severe
potential...or shift it further north than currently expected
(primary focus attm is along and south of M-72...but could end up as
far north as the Bridge or the southern UP).

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 355 AM EDT Mon May 20 2024

Pattern Synopsis / Forecast:

Potent 500mb wave ejecting from the Rockies into the central Plains
set to utilize favorable jet streak dynamics to generate surface
cyclogenesis. This wave and surface low will continue to deepen as it
moves northeast into the western end of Lake Superior (likely sub
990mb), where it will largely become occluded / vertically stacked
and eventually closed off by Wednesday. In response to this system
developing and deepening considerably, southerly flow looks to force
a warm frontal boundary northward across northern Michigan through
the day Tuesday, settling somewhere near or just north of the north
shore of Lake Superior. The passage of this frontal boundary will
lead to lessened shower coverage (especially farther south in the
CWA) Tuesday morning. Deep convective response anticipated across
the heart of the Corn Belt region, and with potent SW flow aloft,
should steer this area of strong to severe storms into the upper
Great Lakes region later Tuesday night in conjunction with the cold
frontal boundary. As the occlusion of the cyclone manifests and the
cyclone itself slowly drifts eastward across Lake Superior on
Wednesday, this should support additional showers (perhaps thunder?)
into Wednesday before the drier and cooler air behind the system
finally makes its way into the Northwoods Thursday. Quick turnaround
to milder temperatures Friday into Saturday as shortwave ridging
ahead of another 500mb wave in the Canadian prairies moves overhead
before another trough axis is forced eastward into the Great Lakes
for the weekend, bringing more potential showers and perhaps some
thunder too.

Primary Forecast Concerns:

Tuesday: Sub 990mb low moves into the west end of Lake Superior,
which, based off of severe climo for APX, is in a favorable spot.
This system will be pumping a deeply moist airmass into the region
in the wake of the northward surging warm frontal boundary. Diurnal
heating may suffer a bit with high clouds, but instability is still
progged to make an appearance, albeit with a capping inversion.
Deeper convection upstream likely becomes more of a linear mode
(squall line / MCS) along the cold front as it moves through
Wisconsin into Lake Michigan, and eventually, the Northwoods. Most
CAMs are loaded with high amounts of CIN (+100J/kg), but the cold
front will provide the necessary forcing to break through that cap
as this activity progresses into the area, likely after midnight
Tuesday night. Given the proximity of the surface low, atmospheric
dynamics look to be pretty primed for activity if something can make
it here (latest CAMs suggest that is well within possibility).

With the linear mode expected, probably looking at more of a wind
threat as this feature passes through. The presence of the low
pressure casts some wild cards into this setup, as shear will be
rapidly increasing in conjunction with strengthening LLJ dynamics
(850mb winds increase to 45-55kts, maybe higher?) and a 500mb wind
max really acting to stretch out hodographs (Bulk shear up to 55-
60kts, as high as 30-40kts from 0-1km and SRHs potentially well over
400m^2/s^2). This opens the door for some embedded hailers in the
stronger updrafts within the line, and even a quick spinup tornado
along the line as it surges northeastward into northern Michigan.
WHILE UNLIKELY, any "renegade" updrafts that succeed in forcing
through the capping inversion ahead of the main line could have a
volatile environment to feast from (i.e. supercellular mode with all
hazards on the table). Overall, latest CAM guidance hint at the best
instability fading the farther north and east one goes across the
APX footprint, which matches the latest SPC Day 2 outlook putting a
Slight Risk (2/5) across much of northern lower Michigan and
Marginal Risk (1/5) elsewhere. One final note- will have to monitor
any convective trends downstate and points south during the day
Tuesday, as any disruptions to the moisture advection regime may
wipe out any instability across the region, and thus erodes severe
potential as well.

Wednesday and Beyond: Following the passage of the cold front, the
occluded nature and slow progression of the system will lead to the
cooler air behind the system to be a bit slow to return to the
region. Presence of the low pressure system over Lake Superior
should help any diurnal instability to materialize into additional
showers and perhaps some thunder too Wednesday. Drier air finally
moves in behind the system, leaving cooler air overhead, with the
area holding dry Thursday and Friday (outside of some lingering
showers in the eastern Yoop Thursday owing to their proximity to the
departing system).

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1145 PM EDT Sun May 19 2024

High pressure centered over the Western Great Lakes region will
slide east overnight...replaced by low pressure and an
approaching warm front on Monday. Dry wx will persist overnight...
before chances of showers and thunderstorms begin to increase
late Monday morning thru Monday night as moisture and instability
increase along and ahead of this system. Prevailing conditions
will remain VFR thru Monday...but may occasionally drop to
MVFR/IFR within heavier showers/storms. Prevailing conditions
will deteriorate to MVFR Monday night as an organized area of
convection pushes thru our region. Light/variable surface winds
overnight will become SE at around 10 kts on Monday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

SHORT TERM...FEF
LONG TERM...HAD
AVIATION...MLR