Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 201359

Area Forecast Discussion
National Weather Service Gaylord MI
959 AM EDT Tue Jun 20 2017

Issued at 1000 AM EDT Tue Jun 20 2017

Troughing and -20C 500mb cold pool across the Great Lakes region
this afternoon will keep the area cooler than normal and bring
showers and a few thunderstorms. Showers upstream from MN
Arrowhead to the Straits and another area over C and S WI both
associated with shortwaves moving through the trough. Both swing
through MI exiting this afternoon. Descent lift with adequate
moisture ahead of the shortwaves will bring good shower chances to
much of the region late this morning and this afternoon. Shower
chances will be best in areas that do see breaks in the clouds.

As for thunderstorm chances, cold pool overhead but will still need
some afternoon heating to get thunderstorms to develop. Little
afternoon heating expected north due to cloud cover, but some
breaks mainly south of M-32. CAPE values in those areas could
reach 500 J/kg and "skinny" so not expecting severe
thunderstorms. However, low freezing level /6700 ft/ and wet bulb
zero /5900 ft/ will make small hail possible in any thunderstorms
that do develop.

Winds should get a bit gustier this afternoon with mixing in the
lower levels, so some gusts to around 20kts possible mainly in
the lower Peninsula. Will keep an eye on this for possible SCAs on
the nearshores.


.NEAR TERM...(Today through Tonight)
Issued at 242 AM EDT Tue Jun 20 2017

...A few thunderstorms yet again today...

High impact weather potential...Nothing too significant. May see
some brief gusty winds and small hail with any thunderstorm activity.

Pattern synopsis/forecast...Rather amplified (for summer at least)
NOAM pattern continues, with well developed and continuing to mature
Great Lakes centered troughing bookended by equally robust western
NOAM and far west Atlantic ridge axes. Cool, shortwave filled deep
northwest flow is the result across our area, which when combined
with the diurnally driven instability cycle, resulted in another
round of showers and embedded thunderstorms this past afternoon and
evening. That has largely dissipated with loss of solar insolation,
waiting on arrival of next shortwave trough/vort max (currently
rotating southeast across northern Minnesota) and surface based
instability development today to kick off more convection.

Primary forecast concerns/challenges...Shower and thunderstorm
evolution and intensity today into this evening.

Details...Upstream wave arrives this morning, largely exiting our
area by later this afternoon. Primary forcing actually passes just
south of our area. Won`t matter however, with attendant surge of
subtle cooling aloft (H5 temps at ~-20C) working over surface rooted
destabilization processes to drive more scattered/numerous showers
with embedded thunderstorm today. Surface flow remains primarily
westerly, supporting Lake Michigan stabilization/shadowing across
northwest lower and focus for best shower coverage across northeast
lower. Pattern recognition with typical synoptic driven west flow
patterns supports enhanced surface based convergence/attendant
showers across interior eastern upper Michigan...sliding slowly
south with time as Lake Superior flexes its muscle on the low level
wind environment. Definitely not much going for any widespread
severe storms, with mean layer cape remaining well below 1k
Joules/kg and core of deep layer shear passing by to our south.
Skinny cape profiles also noted up through the favored hail growth
region, although simple low wet bulb freezing levels (sub 7kft) sure
supports some small hail potential. Of course, storm cell merger or
localized enhanced convergence via storm scale cold pools could
enhance updraft speed and lead to an isolated severe storm.
Definitely don`t think this will be the case, and will refrain from
such wording in all our hazardous weather products. A cool day for
sure, with highs running a good 10 to 15 degrees below normal.

Slow height rises/subtle warming aloft behind departing wave and
loss of solar insolation looks to bring a quick demise to any
lingering showers this evening, setting the stage for a mostly dry
overnight. Clouds look to also depart, and when combined with light
winds via arrival of surface high pressure, sets the stage for a
rather cool mid-June night, with lows by morning mostly in the mid
and upper 40s.


.SHORT TERM...(Wednesday through Thursday)
Issued at 242 AM EDT Tue Jun 20 2017

...A brief break then more showers...

High impact weather potential...None expected.

Weak surface high pressure and slowly rising heights aloft should
bring a break from the showery condtions Wednesday. This should be
short lived however, as a surface warm front moves through the
region late Wednesday night into Thursday yielding more showers and
possible storms. Temperatures are expected to moderate to close to
seasonal averages.

.LONG TERM...(Thursday night through Monday)
Issued at 242 AM EDT Tue Jun 20 2017

A cold front is expected to lead to additional chances for showers
and storms Thursday night. Perhaps a morning shower Friday,
otherwise windy and turning slightly cooler most spots (except for
in southeast zones due to downsloping). A broad upper trough
centered to our north over the weekend into early next week is then
expected to bring cooler temperatures and possibly a few instability
driven showers.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 634 AM EDT Tue Jun 20 2017

More of the same today, with another round of diurnally driven
cumulus producing showers and perhaps a rumble of thunder or two,
especially at KAPN. Otherwise, bases of cu should remain high
enough to keep conditions VFR, although any heavier showers will
likely drop conditions briefly. Moisture pulls off to the east
tonight, resulting in gradually decreasing clouds. West winds, at
times a bit gusty today, become light tonight.


Issued at 242 AM EDT Tue Jun 20 2017

West winds to continue today through Wednesday, with localized
development of onshore flow Wednesday afternoon as lake breezes
develop. Winds just a bit gusty today, but look to remain mostly
below small craft advisory levels. Winds become increasingly light
tonight and Wednesday as high pressure settles overhead. Winds
become south to southwest Wednesday night and Thursday, picking up
speed in the process. May see advisory level winds on some
nearshore waters by Thursday morning.




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