Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 271748

Area Forecast Discussion
National Weather Service Gaylord MI
148 PM EDT Sat May 27 2017

Issued at 1005 AM EDT Sat May 27 2017

A weak wave aloft interacting with shallow, weak low level
instability has led to an increase in the stratocumulus deck
across northern Michigan this morning. Already starting to see
quick erosion kicking in as the wave pushes east and daytime
heating/mixing gets going. Otherwise no other significant changes
made to the inherited forecast. Will continue to monitor
possibility of an isolated shower or two popping up this afternoon
as lake breezes interact with some diurnal instability. Low
probability, but not completely outside the realm of possibility.


.NEAR TERM...(Today through Tonight)
Issued at 346 AM EDT Sat May 27 2017

...Warm Saturday on tap/Some showers possible by tonight...

High Impact Weather Potential: Minimal

Pattern Synopsis/Forecast: Midnight surface analysis shows an
elongated occluded front extending from low pressure over northern
Manitoba...across eastern MN/central IA/northwest MO.  Warm front
extends from northern MO across central IL/IN/OH.  Flat ridging
aloft across the Great Lakes/Ohio Valley early this morning...old
MCS that has survived from KS last night into OH early this morning
helped along by an associated MCV.  Water vapor imagery shows a weak
vorticity center along the MN/Ontario border which is pushing some
widely scattered showers across Lake Superior/Upper MI/northwest WI
also within a broad zone of difluent upper level flow (activity is
fairly high based).  00Z APX sounding shows residual moisture from
afternoon stratocumulus deck right at the inversion base just above
800mb...with a well-mixed layer below.  Axis of deeper moisture
(precipitable water values 1.00-1.25 inches) extends up into eastern
WI/Lake Michigan and spreading into western Lower MI.

Upper Mississippi Valley occluded boundary is expected to make slow
progress east today...reaching central Upper/eastern WI by late

Primary Forecast Concerns: Can we generate some convection this
afternoon at least across interior northern Lower with some skinny
instability and advancing lake breeze boundaries.

Clouds and spotty shower activity across eastern Upper and the tip
of the mitt counties early this morning should end by mid morning...
with weak short wave ridging in place across the state for today.
Given the 00Z soundings from APX/GRB expect fairly deep mixing this
afternoon...which will probably give rise to some high based cumulus
clouds and some thin instability profiles.  Some of the high
resolution guidance (and the GFS) try to paint some showers across
northern Lower away from Lakes Michigan/Huron this afternoon.  We
saw the same behavior in last night`s high resolution guidance and
that didn`t pan out...though inversion evident on 00Z APX sounding
likely will not exist this afternoon thus allow for a skinny CAPE
profile to extend above 700mb.  More likely to see showers/
thunderstorms develop along the remnant occluded boundary across
eastern WI/western and central Upper MI later this afternoon/early inclined to leave the dry forecast intact for the
forecast area through the afternoon though probably can`t rule it
out completely.  Temperatures away from the beaches expected to warm
well into the 70s this afternoon...a solidly warmer than normal

There will likely be some threat for convection across WI/western
Upper MI to spill into eastern Upper and perhaps far northwest Lower
starting this evening and continuing low level theta-
e ridge ahead of what remains of the occluded boundary will poke its
way northeast and into the forecast area.  Precipitation threat
should drop off toward Saginaw Bay.


.SHORT TERM...(Sunday through Monday)
Issued at 346 AM EDT Sat May 27 2017

...Showers and Thunderstorms Then cooler...

High Impact Weather Potential...Thunderstorms on Sunday afternoon
and Monday afternoon, although at this point they don`t look to be

Pattern Synopsis/Forecast...The pattern looks to revert back to
something cloudy and cooler after Sunday, as a 500 mb low begins to
drop in to the Upper Great Lakes from the Canadian Prairies. This
looks to put us back to normal temperatures for Sunday and then
below normal temperatures Monday as low slowly moves into place.

As the 500 mb low moves in on Sunday morning, a sharp 500 mb
shortwave trough rotates through the Upper Mississippi Valley and
into the Upper Great Lake. This spins up a sfc low in S Lower MI by
the evening, which helps to produce rain over the region for the
late afternoon and early evening hours. SREF and GEFS plumes average
around 500 j/kg for CAPE/MLCAPE with most of the members clumped
within a couple hundred joules either side of the average. However,
the both models have some members that get into the 800-1000 J/kg
range. This is also the story with the Effective shear with most of
the members clumped around the average shear <30 knots. Again, there
are some members that peak up around 40 or more knots, so it will
need to be watched, however, the peak shear on the GEFS is not
coordinated with the peak CAPE. So will have to watch if we can get
the instability and the shear during the afternoon. The ECMWF would
tend to side with the GEFS idea that the best shear is in the
morning and the best instability is in the afternoon, and neither
are strong enough to produce severe weather. So will have
thunderstorms in the forecast.

Will expect that the thunder will subside overnight, and that during
Monday afternoon as the 500 mb drops into the Upper Great Lakes,
that there will be thunder. However, with the cloud cover expected
as stratocu (more like self-destruct sunshine if there are any
breaks) would be expected in the wake of the sfc low, and out ahead
of the upper low. This will likely bring lower CAPE over the region,
which is what the GEFS and SREF both show. Overnight, any thunder
will again subside from diurnal cooling and will expect rain showers
over the region.

Primary Forecast Concerns...As outlined on Sunday`s forecast the
main concern would be if the SREF idea is right with the best shear
and instability being coordinated in Sunday afternoon and the
solutions to the a few of the members achieving shear over 40 knots
and CAPE over 800 J/kg, then there would be a severe potential. Will
go with General thunder as the SPC outlook keeps the marginal area
south of the forecast area.

.LONG TERM...(Monday night through Friday)
Issued at 346 AM EDT Sat May 27 2017

High Impact Weather Potential...None

Extended (Tuesday through Friday)...On Tuesday, we start with the
500 mb low just north of the Upper Great Lakes with spokes of energy
rotating around it. As this occurs, cool air from Canada will rotate
into the Upper Great Lakes as well. Wednesday, the low doesn`t move
too far, so that more reinforcing shots of cold air move into the
Upper Great Lakes as well. With the upper level cold pool over us,
expect that showers will be scattered about. It may be possible for
thunder at time as the 500 mb temperatures dip below -20c. Thursday
and Friday look to remain dry as the low moves east allowing dry air
to push into the Upper Great Lakes again. Temperatures will slowly
come back up Thursday to Friday allowing us to get back to normal
temperatures by the weekend. However, a sneak peak into Saturday
Looks like temperatures may drop below normal again as another 500
mb low drops in south of Hudson Bay.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 148 PM EDT Sat May 27 2017

Extensive fair weather cu field has developed across interior
northern Lower this afternoon but lake breezes are keeping coastal
areas, including most TAF sites, largely cloud free. VFR conditions
will continue through the period with light winds. Scattered showers
expected to push in from the west Sunday morning after daybreak
with increasing cloud cover.


Issued at 346 AM EDT Sat May 27 2017

Lake breeze dominance expected once again this afternoon as pressure
gradient remains weak...and probably the same on Sunday though
possibly with a stronger easterly component to the winds on Lake
Huron. Gustier southwest winds expected to develop on Monday.




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