Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 210527
Area Forecast Discussion
National Weather Service Marquette MI
127 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...(Thursday night through Wednesday)
Issued at 333 PM EDT WED JUL 20 2016
A mean upr rdg wl bring above normal temps to the area thru this
weekend. After lingering showers/TS end on Thu evng, a sfc hi pres
wl bring dry wx to Upr MI late Thu ngt thru most of Sat. A strong
upr disturbance pushing ewd thru the Upr Lks is then likely to bring
more showers/TS Sat ngt into Sun, and some of these storms could be
severe. Cooler and drier air wl follow this disturbance early next
Thu ngt...Expect lingering showers/TS over mainly the SE half of the
CWA to diminish in the evng with passage of weak cold fnt, arrival
of mid lvl drying, dnva, deep lyr qvector dvgc and nocturnal
cooling. PWAT is fcst to dip as lo as 0.5 inch late at ngt, so skies
should turn clr with the aprch of sfc hi pres/acyc llvl flow. Min
temps may bottom out as lo as 60 over the interior W.
Fri/Fri ngt...Warm but relatively dry airmass/sfc hi pres are fcst
to dominate this period just to the E of upr rdg axis over MN. H85
temps are fcst to be 18-20C on Fri aftn, supporting max temps at
least close to 90 away fm lk moderation that wl be favored near Lk
Sup with llvl WNW flow. This downslope flow wl accentuate the wrmg
over the scentral, where max temps may reach close to 95.
Fortunately, dry airmass wl support sfc dewpts mixing out into the
50s where the temps wl be warmest. Although models hint some hi clds
may return over the W on Fri ngt, some interior locations could see
temps fall into the upr 50s with lgt winds.
Sat...A strong shrtwv is fcst to push into the nrn plains on Sat,
supporting deepening lo pres in the nrn plains. In general, models
have tended to slow down the ewd progression of this disturbance, so
most of the guidance hints the day on Sat wl be dominated by sfc hi
pres shifting slowly to the E and thus remain dry despite more
hi/mid clds drifting into the area ahead of the lo pres/warm fnt.
Did retain some chc pops over the W to account for the faster
guidance. Although these clds wl tend to cap max temps a bit, most
places wl see temps rising well into the 80s and a trend toward more
humidity with strengthening SSE flow. Locations downwind of Lk MI
should be a bit cooler with the llvl SSE wind.
Sat ngt/Sun...This period looks like the best chc for some
showers/TS as potent shrtwv moves to the E, accompanied by sfc lo
pres in Ontario/attended occluded fnt/axis of pwat aoa 2 inches.
Considering the strength of the disturbance and ribbon of strong mid
lvl winds/h5 winds fcst up to 60kts/ as well as plentiful mstr and
instability with SSI fcst aob -5C, some of the stronger storms could
be severe even if they are elevated in nature to the N of warm fnt
that may remain to the S of Upr MI. Pops should diminish over the W
beginning in the aftn with arrival of drier air behind the occluded/
cold fropa. Temps wl run above normal during this time.
Extended...After lingering showers/TS end over the E on Sun evng, a
cooler airmass wl dominate on Mon/Tue with h85 temps falling as lo
as 12C. Although some of the medium range guidance hints there could
be at least some bkn clds and even a few showers on Mon under a
sharper cyc NW llvl flow left in the wake of the departing sfc lo
pres, most of this time should be dry. Depending on how quickly
another disturbance aprchs fm the W toward mid week, more showers/TS
could arrive Tue ngt/Wed.
.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.