Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 210712
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
312 AM EDT THU JUL 21 2016

.SHORT TERM...(This evening through Thursday)
Issued at 416 PM EDT WED JUL 20 2016

A very tricky forecast through this forecast period in respect to
high temperatures and convection potential. Two areas of convection
look possible, one early in the morning with the second in the
afternoon. If enough of a break in the cloud cover occurs, near
record temperatures will be possible Thursday with heat index values
approaching 100 degrees over the west half.

Satellite imagery this afternoon is showing a decent CU field across
western Upper Michigan late this afternoon. Radar imagery is showing
very little across the U.P. as of 19Z while the main focus for
showers and thunderstorms has been across central WI. This is closer
to the stationary front or warm front, stretching northwest to
southeast across that area, providing the necessary forcing. Water
vapor imagery is showing several waves can be seen sliding around
the periphery of the ridge.

Tonight into Thursday morning: The broad scale features include the
dominate ridging in place across the central U.S. including the
Upper Great Lakes region. At the surface, the Upper Great Lakes will
be influenced very warm moist southerly flow on the west side of a
surface high over the eastern U.S. The first issue for this time
period will be the timing and intensity of a shortwave progged to
slide into the western U.P. overnight tonight. The shortwave can be
seen on WV imagery over southern Saskatchewan this afternoon. This
wave is progged to slide into the western U.P. by 9Z/21 and across
the rest of the area by 15Z. Many of the Hi-Res model have a complex
of showers and thundestorms sliding across the U.P. during that time
period. MUCAPE values are progged to be around 2000-3000 J/KG during
that time period with deep layer shear values with the wave around
30 to 40 knots. If the complex makes it into the U.P. severe weather
is a possibility late tonight into early Thursday morning. Again,
there is still a lot of uncertainty with this shortwave.

Thursday afternoon: The best chance for showers and thunderstorms
will slide into the U.P. Thursday afternoon as a stronger shortwave
and weak cold front slides into the area. Instability is progged to
be around 2500 to 3500 J/KG during the afternoon hours along with
effective shear values around 35 to 45 knots orthogonal to the
front. The combination of these two ingredients, during peak
heating, along with cold front forcing and potential forcing from
early day outflow boundaries, will create conditions favorable for
severe thunderstorms thursday afternoon. The main threats will be
large hail and damaging winds.  Hi-Res models suggest development
along the front to occur between 18Z and 21Z before sliding south
and east of the area around 00Z/22.

Outside of the severe weather potential, temperatures may also
become an issue Thursday afternoon. This is largely dependent upon
the amount of cloud cover that lingers over the U.P. If the first
area of convection slides out quick enough that skies clear,
temperatures will warm into the upper 80s to low 90s across portions
of the south central and western U.P. This, coupled with very high RH
values would create heat indices between 95 and 100 degrees. Again,
the extreme values would be dependent upon the amount of cloud cover
in the afternoon; however, even with a lower temperature, it will be
very muggy and uncomfortable outside Thursday afternoon.

.LONG TERM...(Friday through Wednesday)
Issued at 312 AM EDT THU JUL 21 2016

Nam shows a strong 500 mb ridge over the plains 12z Fri with a
shortwave north of Lake Superior that move east. A shortwave trough
over the Pacific NW will move over the top of the ridge into the
northern Rockies 12z Sat and head to the northern plains late Sat
night into Sun morning. Isentropic lift and moisture on I310K
surfaces appear across the cwa 12z Sun. Have Friday dry and slowed
pops on Sat down until late Sat afternoon in the west. Have the east
dry for Sat evening and then have pops in after midnight for all of
the cwa with likely pops across the west half of the cwa. Friday
looks really warm and bumped temperatures up a few degrees in some
places due to downslope winds and other change is have dew points
higher earlier in the morning...then bring dry air in slowly.
Otherwise, did not make too many changes to the going forecast.

In the extended, GFS and ECMWF show a 500 mb trough across south
central Canada into the northern Plains 12z Sun that moves a front
through the area on Sun. This trough remains into Mon. Sfc high
pressure is over the area on Tue with the front well south of the
area. Another trough moves into the northern MS river valley 12z Wed
and into the upper Great Lakes. Temperatures will be near normal for
this forecast period.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 123 AM EDT THU JUL 21 2016

VFR to high end MVFR conditions are expected through much of the TAF
period. Details for this TAF issuance are difficult to pin down with
exact timing of any showers and thunderstorms as model agreement on
evolution of convection over the Plains is poor. Overall confidence
in any one solution is fairly low, but will include -SHRA and VCTS at
KIWD and KCMX for chances of showers and thunderstorms sliding in
from the west late tonight into Thu morning. VCSH for convection
possibly developing in the afternoon as a weak cold front passes
through the area.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 333 PM EDT WED JUL 20 2016

Expect winds to hold below 20 kts through the forecast period under
a relatively weak pressure gradient and high overwater stability.
Warm and humid air will flow across Lake Superior on tonight through
Thu, which will allow fog to form, locally dense at times. More fog
is likely late in the weekend as another humid airmass moves over
the Upper Lakes.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...KEC
LONG TERM...07
AVIATION...Voss
MARINE...KC


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