Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 251613

Area Forecast Discussion
National Weather Service Gaylord MI
1213 PM EDT Fri May 25 2018

Issued at 1212 PM EDT Fri May 25 2018

Water vapor imagery and upper air maps reveal short-wave ridging
across Michigan with upstream short-wave troughing advancing
slowly through the Midwest. Closed but weak-ish surface and upper
level low pressure is across south-central Canada with surface
troughing extending down through the Upper Midwest into the
Central Plains and some semblance of a warm front stretching
eastward through the northern Great Lakes. Plume of deeper
moisture and best instability still resides from the Central
Plains into the Upper Midwest and far western Great Lakes. But a
corridor of steeper mid level lapse rates/EML does stretch
eastward through northern Michigan. Hence the elevated
showers/storms that continue to pop. Also some surface based
instability developing across the CWA today with juicier dewpoints
and some congested CU taking off across northern lower MI.

Rest of today, convective development and trends remain the main
forecast challenge. Ongoing spotty showers moving through the
Straits region as well as NW lower MI appear tied to gravity wave
ripples emanating from convection in Wisconsin (can see the
ripples on satellite imagery). With ongoing heating and modest
instability, we may continue to see additional pop-up showers
through the afternoon particularly across NE lower Michigan where
the SW/W flow will be running into the Lake Huron marine layer.
Meanwhile, remnants of convection over Wisconsin and what appears
to be a convectively induced MCV will roll up through central and
eventually eastern upper MI and will likely produce some
additional showers/storms up that way. Nothing severe anticipated
as we just don`t have the winds aloft/shear to support severe. But
some brief small hail is possible.


.NEAR TERM...(Today through Tonight)
Issued at 342 AM EDT Fri May 25 2018

Impactful weather: Shower and thunderstorm chances increasing.
Severe weather not expected. Possible reduced visibility due to
fog in some areas tonight.

Pattern synopsis and forecast:

Early this morning, shallow mid level ridging was seen over nrn
Michigan, with shortwave troughing slowly working across the central
and nrn plains. The shortwave was ejecting several weak pieces of
energy/vorticity into, and over the ridging aloft and elevated warm
front, and through a channel of relatively higher moisture (PWATS
1.25" to 1.50") from srn Canada where a sfc low resides, through the
nrn Great Lakes. While overall forcing mechanisms are weak, pockets
of showers were roaming around the upper Mississippi valley and much
of the western Great Lakes, due primarily to DPVA, and LLJ forcing.
Some of these showers and rumbles of thunder continued to impact
eastern upper Michigan (MUCAPES roughly 300-600 j/kg). Elsewhere in
nrn Michigan, there was just some increasing higher level cloud.
Temperatures were largely mild in the 60s.

Some of these showers across eastern upper may continue past daybreak
as there is evidence of continued weak vorticity advection, but would
have to believe that chances will lower due to less coverage from a
decaying LLJ and associated forcing. There should be enough residual
cloudiness in this pattern to result in a mostly cloudy sky and
suppressed temperatures today for eastern upper. Highs generally in
the mid to upper 70s, while less clouds and greater incoming solar
heating in nrn lower will bring in another warm day in the 80s.
Chances for showers and what is expected to be, non-severe
thunderstorms, increase again for this afternoon and tonight for
primarily NW lower Michigan and eastern upper Michigan into far
nrn Lake Huron. This due to the arrival of the shortwave trough
and associated warm front. The higher chances for showers and
storms in these areas are due to the sfc based warm front getting
held up across nrn lower due to the cold and more dense air mass
over the cold Great Lakes, as well as what appears to be a
localized enhancement of the LLJ coming off Lake Michigan ahead of
a steeper lapse rate gradient aloft. The resulting greater
moisture and wind convergence maximizes in these areas, possibly
including far NE lower. Elsewhere, the lower chances for getting
rain are the overall weakly forced regime of the system as a
whole. Also tonight, low level stratus and fog wants to make a
reappearance in eastern upper, nrn Lake Michigan and the Straits
region, as sfc dew points increase further via weak SW winds
(which leads to a more humid day Saturday). Gotta believe that
this whole setup will bring scattered to numerous showers and
thunderstorms late today and mainly tonight (again, with highest
chances in the aforementioned areas). MUCAPES late today into
tonight are mainly below 1000j/kg, largest across far western
sections of Chippewa and Mackinac counties of eastern upper. If
there could be a risk of a severe storm, it would be there, per
SPC marginal risk. However, 0-6km bulk shear of less than 30kts
suggest much to be desired for storm organization. A mild night
again tonight with lows in the mid 50s to lower 60s.


.SHORT TERM...(Saturday through Sunday)
Issued at 332 AM EDT Fri May 25 2018

...Warm with scattered showers and storms...

High Impact Weather Potential...Scattered thunderstorms possible
across all of northern Michigan Saturday and mainly northeast Lower
Michigan on Sunday.

Pattern Synopsis/Forecast...A broad, low-amplitude shortwave trough
will push across the Upper Great Lakes region on Saturday. This will
be followed by a second, more concentrated shortwave diving into
northern Michigan on Sunday. Combined with ample moisture across the
region (PWATs roughly around 1.3"), these mid level features will
lead to an unsettled holiday weekend with showers and storms at

Primary Forecast Concerns...PoPs and thunderstorm chances through
the weekend.

Increasing moisture on Saturday is expected to push dewpoints into
the lower 60s (approaching 65F in spots) across northern Michigan.
Raw model dewpoints getting into the upper 60s are likely overdone
(leading to inflated diurnal instability), but SREF probs of at
least 60F are quite high across northern Lower on Saturday. Did cut
down numbers a bit to account for diurnal mixing. Similar numbers
expected Sunday, though perhaps a tad lower in the afternoon.
Combined with temperatures climbing into the mid 70s to mid 80s both
afternoons, MLCAPE may exceed 1000 J/kg in some areas. Low and mid
level lapse rates look decent enough, but the question will be how
much cloud cover from the mid level shortwaves may limit insolation.
Ingredients certainly favorable for scattered showers and storms,
particularly on Saturday. Low level wind fields not particularly
impressive for storm organization, though, with 0-6km bulk shear
below 30 knots on Saturday, and 30-40 knots in some localized areas
Saturday night into Sunday. Given somewhat lower freezing levels on
Saturday, suppose any stronger storm may be capable of producing
some small hail. As has been mentioned by previous forecasters, this
setup by no means looks to be a washout for the holiday weekend
(PoPs generally 50% or less). However, those with outdoor activities
planned will want to be prepared for the possibility of some
thunderstorms developing in the area, particularly during the
afternoon/evening hours.

.LONG TERM...(Sunday night through Thursday)
Issued at 332 AM EDT Fri May 25 2018

High Impact Weather Potential...Possibly a few thunderstorms
developing at times, mainly during the afternoon hours Tuesday
through Thursday.

Another warm day on tap for Memorial Day with highs progged to range
from the mid/upper 70s eastern Upper to near 90 across interior
northern Lower. Rising heights behind the departing shortwave and
building surface high pressure should generally limit any additional
rain chances. However, weak passing disturbances will continue to
traverse a building mid-level ridge overhead through midweek. This
will allow for periodic small chances for showers and perhaps a few
storms at times through Thursday, particularly during peak heating
hours. Temperatures look to remain above normal, with highs
generally in the 70s to mid 80s.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 612 AM EDT Fri May 25 2018

...Increased chances for showers and non-severe storms, with areas
of stratus and fog development tonight mainly threatening PLN...

Conditions will largely be VFR over the TAF period. A few showers
and rumbles of thunder will roll through PLN over the next hour or
so due to a disturbance aloft crossing an elevated warm front in
the area. Otherwise, low pressure in srn Canada will be
responsible for pockets of showers/storms west of us to advect in
periods of higher level clouds. The main chance for showers and
scattered expected non-severe storms arrives late this afternoon,
and mainly tonight, as the sfc low slowly comes closer, and as
it`s associated sfc based warm front drapes itself across the
region. The best chances will be for the NW lower airports, but
CIGS/VSBYS will largely be VFR unless in a shower or storm. The
more impactful weather may turn out to be potential stratus and
fog development due to increased sfc based moisture rolling into
NW lower via WSW/SW weak winds. Confidence not entirely high on
this, but the potential is surely there. CIGS can go IFR/LIFR with
reduced VSBYS. Low end LLWS to continue until mid morning or so,
and will lead to some gustiness today.


Issued at 332 AM EDT Fri May 25 2018

The pressure gradient finally tightens a bit today with the approach
of low pressure and a warm front from srn Canada. Low end advisory
gusts are expected along many of the nearshores of Lake Michigan due
to a helping boost by coastal convergence. The gradient relaxes
again tonight as the low pressure nears us, and remains rather loose
well into next work week. Scattered showers and non-severe
thunderstorms are expected late this afternoon and tonight for most
of the nearshore waters, and again at various times over the holiday
weekend as the low pressure and weak frontal boundary lingers around
the region.


LM...SMALL CRAFT ADVISORY until 5 PM EDT this afternoon for


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