Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 211552

Area Forecast Discussion
National Weather Service Marquette MI
1152 AM 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 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 12Z TAFS through 12Z Friday morning)
Issued at 642 AM EDT THU JUL 21 2016

MVFR conditions will continue through the morning at all sites as a
bow echo/derecho mcs moves through the area this morning. After this
moves by, we will wait for the next round of convection which would
be this afternoon and will affect KSAW mainly and have vcts to cover
this. VFR conditions will move in first at KIWD and last at KSAW
this morning and then last through tonight at all sites.

.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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