Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 211927

Area Forecast Discussion
National Weather Service Marquette MI
327 PM EDT THU JUL 21 2016

Issued at 1151 AM EDT THU JUL 21 2016

MCS/Squall line that produced widespread wind damage over especially
northwest Upper Michigan earlier this morning continues to march
east and southeast attm out of the cwa. Skies are already clearing
over west half and soupy airmass with dwpnts near 70 remains in
place. Though the cool front with lower dwpnts in the 50s moves in
this evening, mid to upper levels may be too subsident and dry for
significant redvelopment of shra/tsra. 12z INL sounding was capped
to sfc based convection with convective temp in upper 90s. WV loop
shows a lot of drying from southern Manitoba into northwest Lk
Superior behind the wave that turned into the squall line that
crossed the U.P. WV loop also shows subtle wave sliding over
northwest MN with another wave producing lightning strikes across
central MN. Timing out these waves the southern wave should stay
mainly over WI, but the northern one would arrive over central U.P.
aft 20z during peak heating. Kept small/isold chances in despite
limited low-level convergence as the wave could be enough to kick
off isold shra/tsra. If they occur they would be strong with MLCAPES
over 2000j/kg and effective shear 30-40 kts. Main change to previous
forecast was to lower pops but cannot take them out completely
though majority of high res guidance such as latest HRRR runs and
NCAR ensemble WRF would suggest that scenario is more probable.

As skies clear and limited cu is expected until mid-late aftn, H85
temps up to 21-22c point to another day with max temps into low 90s
over parts of west and central U.P. Dwpnts thus far are into upr 60s
to low 70s. Though these values may be slightly lower than readings
on Wed aftn in the mid 70s, expect heat index values once again to
top out in the upper 90s to near 100 degrees.

.SHORT TERM...(Today and tonight)
Issued at 434 AM EDT THU JUL 21 2016

Forecast continues to be tricky, with a large portion of time
dedicated to keeping up with current trends and conditions over the
next several hours.

The large complex of thunderstorms, spanning from the international
border north of DLH into central MN, continues to push east, with
the strongest portion on the northern half of that line where the
cap is weakest. Short term models continue to do a poor job
initializing with this convection, so model forecasts are not a big
help. Think that the complex will shift east through the CWA while
gradually diminishing. Certainly will see potential for convection
along that line to be severe, particularly over the west where
instability/DCAPE is greatest. Significantly uncertain with how this
morning convection will play out toward the eastern side of the CWA.

Next question is how the ongoing convection will impact conditions
this afternoon/evening. A shortwave northeast of the CWA will drop a
cold front into western U.P. late this afternoon, which should be
able to develop at least scattered convection. The best convective
potential looks to be over north central Upper MI closer to the
larger scale ascent with the shortwave, but can`t rule out precip
chances across the rest of the area. It does appear that ongoing
convection will clear in time for instability to rebuild, possibly
in the 2,000-4,000 J/kg range (large range given the uncertainty
involved). With around 40kts of effective shear, storms should have
no problem becoming organized. Large hail and damaging winds are the
primary hazards expected. Storms will clear out late this evening,
leaving a dry forecast by late tonight.

.LONG TERM...(Friday night through Thursday)
Issued at 325 PM EDT THU JUL 21 2016

A mean upr rdg wl bring above normal temps to the area thru this
weekend. Expec a sfc Hudson Bay hi pres rdg to cause dry wx for Upr
MI Fri ngt thru Sat. But then a strong upr disturbance pushing ewd
thru Ontario is then likely to bring more showers/TS Sat ngt into
Sun, and some of the storms could be severe. Drier and somewhat
cooler air wl follow this disturbance early next week before
disturbances moving E thru a WNW flow aloft bring a chc for some
showers/TS mid next week along with near normal temps.

Fri ngt/Sat...Sfc Hudson Bay hi pres rdg ahead of upr rdg axis in MN
is fcst to dominate this fcst period and bring generally dry wx.
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. A strong shrtwv is fcst to push into the nrn plains on
Sat, supporting deepening lo pres in the nrn plains/SCentral Canada.
In general, models have tended to slow down the ewd progression of
this disturbance, so most of the guidance shows Upr MI remaining dry
the entire day even though some hi/mid clds wl drift into the area
ahead of the accompanying lo pres/warm fnt in the Upper MS River
Valley. Although these clds wl tend to cap max temps a bit, h85 temps
rising toward 18-20C over the W in the aftn wl still support max
temps well into the 80s. Locations near the Great Lks wl be cooler
with relatively weak pres gradient allowing lk breeze formation.

Sat ngt/Sun...This period looks like the best chc for some showers/
TS as potent shrtwv moves to the E along the Cndn border,
accompanied by sfc lo pres in Ontario/attendant occluded fnt/warm
conveyor belt with axis of pwat 1.5-2.0 inches. Most of the models
generate some moderate qpf during this period. The 12Z GFS is a bit
of an outlier among the guidance by showing less qpf because this
model fcsts more of the convection wl remain to the S on Sat ngt/Sun
and thus distrupt mstr inflow into Upr MI. While this scenario is
plausible, wl trend the fcst toward hier likely pops until more of
the models move in this direction. Numerous showers and elevated TS
wl arrive over the W half on Sat ngt and then overspread the E
half on Sun mrng. Considering the strength of the disturbance and
ribbon of strong mid lvl winds/h5 winds fcst up to 40-50kts/as well
as plentiful mstr and some instability with SSI fcst up to -3C to
-5C, some of the stronger storms could be severe with large hail
especially over the srn counties even if they are elevated to the N
of warm fnt/triple pt lo that may remain to the S of Upr MI. Vigorous
dry slotting under the jet surge region of the shrtwv wl diminish
pops W-E on Sun following the occluded/cold fropa, but more sfc based
showers/TS may dvlp in the aftn especially over the W and central if
there is sufficient clrg of lingering lo clds and the mid lvl drying/
capping are not overwhelming. If sfc based storms do dvlp, these
could be severe under axis of strong mid lvl winds/drying. Temps wl
fall no lower than the 60s on Sat ngt. Depending on the degree of
clrg on Sun aftn, some places especially over the W half could see
temps rebound well into the 80s.

Sun ngt thru Tue...Arrival of dnva/deep lyr qvector dvgc with more
dry advection in the wake of exiting shrtwv as well as nocturnal
cooling on Sun ngt should diminish any lingering showers/TS over
mainly the E half. A cooler and drier airmass with h85 temps 12-14C
in NW flow ahead of trailing sfc hi pres wl then dominate on Mon.
Tue should be mosunny and a bit warmer under lingering sfc hi pres/
h85 temps rebounding close to 16-17C.

Wed/Thu...As is typical in the summer, explicit model output shows
quite a bit of variability on timing of shrtwvs fcst to impact the
Upper Great Lks under WNW flow aloft mid next week. Wl carry some
chc pops on Wed/Thu to account for this variability.  Temps wl
probably be close to normal as h85 temps are fcst not far fm 15C.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 142 PM EDT THU JUL 21 2016

Conditions have cleared out behind the strong thunderstorms that
moved through earlier this morning. VFR conditions should prevail
through Friday as drier air moves into the region. Only issue will
be gusty westerly winds this aftn and again on Friday especially at
the more exposed CMX location.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 434 AM EDT THU JUL 21 2016

Aside from the strong convection moving into western Lake Superior
early this morning (see marine warnings/statements for more
details), 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 today,
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.

Upper Michigan...
Lake Superior...
Lake Michigan...


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