Area Forecast Discussion
Issued by NWS Gaylord, MI

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506
FXUS63 KAPX 260345
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1145 PM EDT Tue Apr 25 2017

.UPDATE...
Issued at 1006 PM EDT Tue Apr 25 2017

Marine layer from Lake Huron getting pushed up into eastern upper
and far ne lower MI, initially with increasing stratus and now
with increasing drizzle. Expect this to expand into a touch more
of ne lower, but the sse sub-850mb fetch should prevent rapid
growth into a large part of northern lower MI.

Meanwhile, band of warm-advection forced virga is pushing ne-
ward over nw lower MI. Dry layer centered on 700mb (per 00z APX
sounding) is thinner in eastern upper MI, and some showers have a
better shot of getting thru to the surface. Of course, drizzle
is already occurring there, so this is largely of only academic
interest.

Otherwise, high clouds will tend to thicken tonight. Tweaked some
temps down near Lake Huron.

&&

.NEAR TERM...(Tonight through Wednesday)
Issued at 300 PM EDT Tue Apr 25 2017

High impact weather potential: Stratus and fog potential downwind
of Lake Huron and a chance for thunderstorms Wednesday afternoon.

Pattern synopsis and forecast:

Not a complicated synoptic pattern, but certainly some difficulty on
how the weather will evolve. One area of low pressure was in far nrn
Wisconsin, with another in Oklahoma. Both of these were connected by
a cold front. Inverted trough extends from the nrn Wisconsin low
into Ontario. Southeast winds that were still gusty in most places,
continued to gradually advect higher sfc based moisture into the
area from a closed off system in the SE states. There really isn`t
any high dew points across the Great Lakes and in the plains for
that matter, with readings in the 40s and low 50s. However, the Gulf
of Mexico has been increasingly tapped by stronger southerly winds
ahead of the sfc low in Oklahoma, and we are starting to see 60s dew
points surging northward through Texas. We have higher level clouds
passing by, along with developing cumulus, with another day of warm
temperatures in the 60s and 70s. This is away from the cooling
effects of the gusty SE wind coming off cold Lake Huron.

Several waves of weak shortwaves buried within stronger SW flow
aloft from the south central plains to the nrn Mississippi
valley. This will bring periods of thicker clouds and slowly
increasing chances of precipitation to nrn Michigan. Of course,
trying to time these is always the difficult thing. The first one to
roll through seems easiest however. That`s the wave in Iowa with an
elevated warm front producing a band of showers. This will roll into
nrn Michigan later in the evening, but likely dissipate as it will
be unable to sustain itself as it plows into the drier air
here. It will serve to help moisten things up, before another wave
is expected late tonight into Wednesday morning, which will have
much stronger low level winds feeding better moisture from above the
sfc, over an impressive H8 frontal zone. This will primarily evolve
across eastern upper and areas north. Kept likely chances for rain,
but the stronger forcing and high QPF will remain well west of us.
Also tonight, there are indications that the moisture advected from
the SE will cross over cold Lake Huron and result stratus and fog
for areas eastern upper and portions of the NE lower coastline. This
certainly has merit, as a few observations downwind of Lake Huron
are already seeing pockets of stratus. Do not believe that this will
impact any other areas overnight leading into Wednesday morning.
Lows in the mid 40s north and NE, with readings as warm as the
middle 50s in the GTV Bay region.

While stratus and fog take time to erode out in eastern upper and
the NE lower coastal areas while staying rather cool in the flow
off Lake Huron, it appears that any clouds from the departing wave
in the morning, will start to thin out. This will help warm things
right back up again, with highs reaching the lower to middle 70s.
Just when some of the stronger mid level flow and shortwaves would
be arriving, a parent longwave trough starts to negatively tilt.
This will pull that stronger shortwave energy back westward, with
better moisture, forcing and resultant QPF through Wisconsin and
Lake Michigan ahead of the system cold front. Nrn Michigan will
continue to see sfc moisture increasing with time, as dew points
climb into the lower to middle 50s and 500 J/kg of MLCAPE.
However, when it comes to chances for precipitation, we are held in
check since we will just have fairly minimal forcing and no boundary
to focus precipitation on. Low level winds will be too strong for
lake breezes and the cold front remains out west through the day.
Have just gone with a fairly low end 30 percent chance for showers
and thunderstorms for Wednesday afternoon.

&&

.SHORT TERM...(Wednesday night through Friday)
Issued at 300 PM EDT Tue Apr 25 2017

...Rain/thunderstorm chances continue through Thursday...

High impact weather potential: Chance of thunderstorms continue
Wednesday night - Thursday, some of which may include heavier
downpours. Small threat for a severe storm or two Wednesday evening
and again Thursday.

Pattern Forecast: Sharp troughing is expected to be evident by
Wednesday evening across the central plains with an elongated area
of low pressure centered from the western Upper Peninsula
southwestward into the mid-Mississippi Valley. As mid-level energy
progresses northeastward Wednesday night, the wave gradually becomes
negatively tilted with an open tap to Gulf of Mexico moisture
allowing for continued increasing deep layer moisture through
Thursday. PWATs progged to rise range from 1-1.25+ inches across the
Midwest/western Great Lakes...thus an inherent threat for some
embedded heavier downpours in any showers/thunderstorms as better
mid-level dynamics/support arrives Wednesday night through early
Thursday. Surface cold front crosses the area Thursday ushering in
drier conditions for Thursday night-Friday.

Primary Forecast Concerns: Focus lies from Wednesday night through
Thursday and revolves around PoPs, thunder chances, and any
potential for severe weather and heavier downpours.

Scattered showers expected to be ongoing across portions of northern
Michigan Wednesday evening, most widespread across northwest
Lower/eastern Upper. Thunder chances continue across the entire area
with a plume of 300-800 J/kg of MLCAPE nosing into northern Lower
before diminishing from west to east after midnight. Again, question
marks lie within how much cloudiness during the day Wednesday
prevents (or doesn`t prevent) instability from being realized.
However, even with rather low CAPE values, 0-6 km bulk shear values
ahead of Thursday`s front progged between 45-55 kts so any updraft
able to develop and tap into that may have the potential to become
strong-severe. However, rather low confidence on any deep convection
being able to develop during the evening due to a lack of forcing as
any appreciable forcing is still well off to our west. The overall
threat is quite low, but worth monitoring over the next 24 hours.

As was mentioned prior, low pressure gradually shifts northeastward
into southern Ontario late Wednesday night into Thursday, eventually
dragging a cold front across the area. Rain potential ahead of and
along the front progressively shifts eastward, perhaps falling
heavily at times in some locales thanks to a tight baroclinic zone
and better forcing focused just ahead of the front. Still some
guidance differences in terms of overall coverage of heavy rain
potential and duration, but the transient nature to the front should
prevent flooding issues. In terms of any additional severe weather
chances...SPC`s Day 3 outlook depicts most of the Great Lakes and
Ohio Valley in a marginal risk for severe storms Thursday. High bulk
shear values continue to warrant at least the mention again, but
limited instability (even more so than Wednesday?), despite stronger
dynamics may limit Thursday`s overall severe weather threat. Falling
afternoon temperatures will be the rule along with much drier
conditions expected to prevail by Thursday night into Friday.

Above normal early day high temps on Thursday...ranging from the
upper 50s north to the low 70s east of I-75. Back to near-normal
readings for Friday from near 50 north to the low 60s toward Saginaw
Bay.

.LONG TERM...(Friday night through Tuesday)
Issued at 300 PM EDT Tue Apr 25 2017

The general theme in the extended period is a continued active
weather pattern...with some shots of cooler air.  A couple separate
systems will impact the great lakes during this time...but models
have not yet congealed enough to draw any confident conclusions. The
Euro is talking generally dry for Friday into Saturday...with a
significant system lifting from the southern plains into the great
lakes Sunday through Tuesday. The GFS is also dry for Friday, but a
bit more bullish on the Sunday system, by bringing pops into the
forecast area on Saturday. Both solutions are selling
significantly cooler air behind this system for Monday and
Tuesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1145 PM EDT Tue Apr 25 2017

LIFR at APN into Wed morning.

Persistent e to se low-level flow continues, in advance of low
pressure in eastern Iowa. Humidity levels are slowly increasing,
contributing to marine fog/stratus when that muggier air crosses
the chilly waters of Lake Huron. Fog/stratus has already pushed
into APN, with prevailing LIFR conditions. Only question is when
it lifts; suspect it will take until early/mid afternoon (when
winds veer a bit more southerly). Some portion of the stratus
could eventually make it into PLN; haven`t hit that TAF too hard
just yet, but will be monitoring. Elsewhere, VFR into Wed morning,
becoming MVFR with some showers Wed afternoon/evening.

E to se winds tonight, backing more southerly and becoming gusty
again on Wednesday.

&&

.MARINE...
Issued at 300 PM EDT Tue Apr 25 2017

Gusty east to southeast advisory level winds will continue tonight,
while trying to kick more south on Wednesday, in advance of a low
pressure system and cold front. While these winds will weaken into
tonight, they pick right back up on Wednesday, and thus the advisory
has been extended. The low pressure and a cold front advance into
the region later Wednesday night and Thursday morning with a weaker
gradient, but likely showers and potentially a few storms.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 8 PM EDT Wednesday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 8 PM EDT Wednesday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 8 PM EDT Wednesday for LSZ321-322.
&&

$$

UPDATE...JZ
NEAR TERM...SMD
SHORT TERM...MJG
LONG TERM...KAB
AVIATION...JZ
MARINE...SMD



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