Area Forecast Discussion
Issued by NWS Marquette, MI
FXUS63 KMQT 261719
Area Forecast Discussion
National Weather Service Marquette MI
119 PM EDT TUE JUL 26 2016
.SHORT TERM...(Today and tonight)
Issued at 512 AM EDT TUE JUL 26 2016
Water vapor imagery and RAP analysis show a vigorous shortwave
moving across far northern Ontario. At the sfc, associated cold
front runs from northern Ontario to ND. Ahead of the front, nose of
35-40kt low-level jet and 850mb theta-e advection are producing a
small area of shra/tsra in far northern MN early this morning.
Closer to home, it`s been a clear more comfortable night for
sleeping. The traditional interior cold spots have dropped down into
the low/mid 50s. Meanwhile, along the Great Lakes, temps are in the
60s with some locations along Lake Superior still around 70F.
First issue today will be the ongoing convection in far northern MN.
As low-level jet translates eastward a bit this morning, shra/tsra
should spread out over western Lake Superior before tending to
weaken or dissipate as low-jet weakens. 03z experimental HRRR had a
a very good handle on this scenario, and it maintained pcpn long
enough to reach the Keweenaw mid/late morning. Attention then turns
to new development expected this aftn. While there are no obvious
shortwaves upstream, subtle height falls, approaching cold front,
lake breeze development and building instability will support new
shra/tsra this aftn. GFS shows mlcapes increasing to 750-1300j/kg
today, and as is typical, the NAM is higher with upwards of
2000j/kg. Deep layer shear is on the order of 25kt across roughly
the sw half of the fcst area and 35-45kt across the ne half of the
fcst area, indicating the better potential of organized storms and a
svr risk will be over the ne half. However, the greater instability
will likely be where the shear is less over the sw. Overall, at this
point, it appears isold svr storms will be possible across the area
today. The best potential may end up across central Upper MI, where
there is an overlap of stronger shear and better instability.
Initiation area of new convection this aftn will likely be in north
central Upper MI where developing lake breeze off Lake Superior will
provide a focusing of low-level convergence. Development would then
expand mostly s and e from there. High temps should reach the
mid/upper 80s over most of the area. Will be locally cooler along
Lake Superior and Lake Michigan.
Cold front will drop s across Upper MI tonight and may clear
Menominee by 12z Wed. As instability fades from n to s thru the
night, expect shra/tsra to diminish/end. However, some shra/tsra may
linger thru the night near the MI/WI border as a shortwave
approaches late with the frontal boundary in the vcnty.
.LONG TERM...(Wednesday through Monday)
Issued at 357 AM EDT TUE JUL 26 2016
Wednesday and Wednesday night: A cold front is progged to continue
sagging southward through the area Wednesday before stalling to the
south of the U.P. Wednesday night. A shortwave is progged to slide
through the Upper Great Lakes region Wednesday afternoon and evening
before sliding south and east of the area Wednesday night.
Steeper lapse rates associated with the shortwave along with
increased forcing across the southern U.P. will help to increase
chances for showers and thunderstorms. Again, the southern areas of
the U.P., in closer proximity to the slowing cold front, will have
the better chances due to increased forcing. MUCAPE values are
progged to be between 1000-2000 J/kg Wednesday afternoon/evening
south of the front. The severe weather potential looks low at this
point, through this time period as shear values are only expected to
be around or below 25-35 knots, oriented along the forcing
mechanism. Some of the storms during the afternoon/evening may pulse
up and become strong to severe, on a very isolated basis, but
organized/widespread severe weather is not expected. Storm motion
would most likely be from the west at or around 30 to 35 mph. The
main threat from any of the stronger storms would be small hail and
Thursday through Friday night: High pressure and dry air is still
progged to slide into the area from Canada by Thursday morning and
then linger through this time period. Aloft, the Upper Great Lakes
region will be under a slight troughing pattern to near zonal flow.
This flow along with fairly dry air in place will keep the bulk of
the precipitation to the south of the U.P., while also helping to
keep temperatures closer to or slightly below normal for this time
of year. For reference, normal highs are right around 77 while
normal lows are around 55. The coolest night is expected to be
Thursday night as the surface ridge is centered overhead. This will
allow skies to clear and wind to become light and variable. The
combination of light winds, clear skies and precipitable water
values around 50 percent of normal will provide ideal radiational
cooling conditions. Inland locations may drop down into the low to
mid 40s for Thursday night.
Saturday and Saturday night: The aforementioned high pressure system
will slide to the east of the area through this time period.
As this happens, warmer and more moist, southerly flow will return
to the Upper Great Lakes region. Aloft, it looks as if there may be
a shortwave that slides across the area late Saturday, bringing
small chances for showers and thunderstorms. Details will be fine-
tuned as the weekend approaches as the exact timing will be key for
increased chances of showers and thunderstorms.
Sunday through Tuesday: An upper-level 500mb ridge is expected to
build across the Upper Great Lakes region allowing temperatures to
warm above normal once again and reducing the chances for showers
and thunderstorms through Monday night. Models then hint at an
approaching cold front for Tuesday, but there are differences in
timing of the front for Tuesday; therefore, have gone with a
consensus of the models. This will keep a chance of showers and
thunderstorms in the forecast for Tuesday.
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 118 PM EDT TUE JUL 26 2016
VFR conditions should prevail at KIWD/KCMX/KSAW thru this fcst
period. Building instability this aftn along with approaching cold
front and lake breeze development will trigger sct shra/tsra. These
shra/tsra are most likely to occur around KSAW, and possibly around
KIWD as well. Only included a VCTS mention with uncertainty in
coverage of pcpn and uncertainty in whether either terminal will
actually be impacted. If pcpn does occur, mvfr conditions will be
possible with brief ifr not out of the question.
.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 512 AM EDT TUE JUL 26 2016
Winds across Lake Superior for the remainder of the week should be
mostly 15kt or less as pres gradient remains on the weak side
across the Upper Great Lakes.