Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 301119

Area Forecast Discussion
National Weather Service Gaylord MI
719 AM EDT SAT JUL 30 2016

.SHORT TERM...(Today and tonight)
Issued at 344 AM EDT Sat Jul 30 2016

Overview...There is an area of low pressure in the Ohio Valley and
high pressure over the Upper Great Lakes, James Bay, and the
Northern Plains. At 500 mb, there is a series of troughs and ridges
in the vicinity of the Upper Lakes, which have allowed the moisture
to remain in S Lower and portions of S Lake Michigan, leading to
showers and thunderstorms. It is the weak flow/sfc low that will be
the main concern through the next several periods as this system
looks to throw more moisture back north today and tonight.

Today...Models have a pretty distinct dry slot at the sfc and up
through 700 mb, that is moving mainly west along and south of the M-
55 corridor. While the analysis from the RAP13 has this, the radar
as of 07z is still showing that the rain is moving north. However,
the rain is staying out of the SE counties at the moment, so maybe
the rain will stop short of the US-10 corridor. If that is the case,
and I have that in my grids this morning, areas west of I-75 and
along M-55 will have minimal chances for rain showers through 18z,
and probably 00z. Boundary layer CAPEs are only a couple hundred
J/kg at most through the day, and most of the other traditional
convective indices keep the numbers low enough for rain showers,
with maybe a thunderstorm.

Tonight...After 00z, the expectation is for the deformation rain
showers to redevelop on the east side of the state with the Hi-Res
models suggesting as far north as the M-32 corridor through 06z. The
NMM suggests almost to the Straits by 12z. However, with the GFS and
ECMWF in the ARW camp and will be keeping the rain south of M-32 and
mainly east of I-75.

.LONG TERM...(Sunday through Friday)
Issued at 344 AM EDT Sat Jul 30 2016

...Some showers northern Lower Sunday/Warmer next week...

High Impact Weather Potential: Minimal through the weekend.

Pattern Synopsis/Forecast: Long wave trough axis lies across the
Great Lakes/Ohio Valley with a bit of a split flow pattern across
the Midwest/Great Lakes with Michigan within weak upper level flow
between the two streams.  Short wave trough in the southern branch
of this split over the Mississippi Valley will pass south of the
forecast area and into the lower Great Lakes this weekend (actually
a pair of short wave troughs).  A new round of height falls moves
into western Canada this weekend...and eventually pushes short wave
ridging into the Midwest and Great Lakes during the first part
of next week.

Broad/weak high pressure centered over northern Ontario/upper Great
Lakes/upper Midwest early this morning...wavy frontal boundary
stretches from the mid Atlantic west into the central/northern High
Plains.  Frontal wave expected to pass south of Michigan Saturday
along with the short wave troughing...with a general weak pressure
gradient across the forecast area expected through the weekend
and the first part of next week.

Primary Forecast Concerns: A farther north trend with short wave
energy moving through southern Michigan is threatening to bring some
showers to at least northeast Lower...along with some potential
along Lake Michigan breeze across northwest Lower.

Sunday...Some mixed signals with regard to precip chances for
Sunday. NAM-WRF is most aggressive in pulling a weak mid level
circulation into central Lower and subsequently a decent swath of
rainfall for a good chunk of northeast/north central Lower. Some
hints in other guidance that enough deep moisture will spread into
northeast Lower at least during the first half of the day to justify
some PoPs. During the afternoon...weak gradient will allow for lake
breeze development with some signals for scattered shower
development west of the I-75 corridor.  Probably not unreasonable
though GFS really likes this idea along with its upper 60s dew
points along and west of the US-131 corridor which appears to be a
bit excessive. Shower chances expected to wane with loss of heating
Sunday evening. Meanwhile...a nice day expected across eastern Upper
with temperatures warming to around 80 degrees across the interior.

Monday...Short wave ridging builds into the upper Midwest Monday
with some height rises pushing into Michigan.  Surface pressure
gradient remains pretty flat which should allow for another round of
lake breeze development.  But anticipating a drier boundary layer
Monday afternoon...with a commensurate decrease in shower chances
along said lake boundaries.  More sunshine across northern Lower
(and continued sun across the Upper Peninsula) will push
temperatures into the lower-mid 80s Monday afternoon.

Extended forecast (Tuesday through Friday)...Expecting a warming
trend heading into midweek...and looks to be mainly dry through
midweek though with warm air returning always wary of some upstream
convective remnants wreaking havoc with a sunny/warm forecast
(Tuesday?).  Temperatures both Tuesday and Wednesday likely to flirt
with 90 degrees over northern Lower...and should start to get a bit
more sultry especially by Wednesday/Thursday.  Approaching height
falls and an associated cold front will arrive Thursday night/Friday
morning which will likely be the best chance for rain next week.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 709 AM EDT Sat Jul 30 2016

Main concern this morning is this wandering boundary to the south
that keeps generating showers and thunderstorms to the south of
the forecast area, and occasionally, showers at or near one of the
aerodromes. Models are showing a wedge of dry air from the sfc to
about 15,000 feet over N Lower this morning, that is keeping the
rain to the south. This is due to the sfc high forcing the dry air
south into the forecast area. It is beginning to look like that
while the rain will stay south of the TAF sites for most of the
day, the high will weaken a bit as a weak mid level trough of low
pressure moves into the Upper Great Lakes, and pushes the
moisture up the east side of the state to around APN. There is a
small chance for showers after 06z tonight as the trough and
moisture move through the forecast area. Have decided to keep it
out of the forecast, for now, as it is looking like a low chance
event. It is more likely rain showers will form south of APN and
the rest of the TAF sites through 12z Sunday morning.


Issued at 344 AM EDT Sat Jul 30 2016

Today Through Sunday night...Winds briefly this afternoon may just
get to small craft in Lake Michigan as the pressure gradient briefly
tightens up, and with some coastal convergence it is possible, but
for the time that it would be there looks rather short(about an hour
or two) and would expect a rapid drop off as the gradient relaxes by
00z. Winds for Tonight through Sunday night, continue as we have
seen the last few days, winds generally out of the east at 5 to 10
knots with occasional gusts to 15 knots through the day, and
variable winds at 10 knots or less overnight.


.APX Watches/Warnings/Advisories...


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