FXUS63 KMQT 171136

Area Forecast Discussion
National Weather Service Marquette MI
736 AM EDT Wed Jul 17 2019

.SHORT TERM...(Today and tonight)
Issued at 409 AM EDT WED JUL 17 2019

Weak surface trough is now located south of the forecast area
across northern Lower Michigan into north central Wisconsin. With
weak surface high pressure skirting by along he north shore of Lake
Superior...low level northeasterly and easterly flow should help
keep dewpoints in check...mid 50s to around 60...through the early
afternoon hours. High will still be in the low to mid 80s for most
today away from the cooling influence of the easterly flow off Lake
Superior. With the lower dewpoints it will be the most comfortable
day of the week thus far.

Yesterday it appeared models were converging on how convection would
evolve ahead of next shortwave traversing along south central
Canada. However...the spread in the model guidance is now even
greater. There is pretty low confidence in how convection will
evolve this afternoon and evening. Ongoing convection in South
Dakota will play a role in the evolution of shras/tsras through the
day. With better instability southwest of the area over MN and
western WI anticipate one convective complex to be focused
there...especially as LLJ cranks up this evening in that area.
There could be another area of more organized showers and storms
over northern MN tied to the better forcing with the shortwave. If
things develop this way...it will leave most of the U.P. in a QPF min
through the overnight hours with more scattered shras/tsras vs. a
MCS which could bring more widespread rains. As said
earlier...confidence is pretty low in how things will evolve across
the U.P. tonight into early Thursday.

As low level winds turn southerly later today and this
evening...dewpoints will spike back into the mid and upper 60s
making it feel uncomfortable again. Lows tonight will stay in the

.LONG TERM...(Thursday through Tuesday)
Issued at 517 AM EDT WED JUL 17 2019

After a warm week (above normal temps) this week under a more
zonally oriented flow in which the westerlies have shifted n, a more
amplified pattern will again develop over N America, and it will be
a familiar pattern that has mostly prevailed since late Apr/early
May. Troffing is fcst to amplify over eastern N America early next
week in response to a building ridge and expansive positive height
anomalies developing over western N America. GEFS was picking up on
this trof development for late July several days ago, but over the
last few days, trend has been for the trof to develop sooner. CFSv2
has been consistently showing this cooler pattern holding thru late
July and into early Aug. So, expectation is for above normal temps
to continue this week with Fri being the warmest day. Cooling will
get underway over the weekend. Then, next week and the following
week should feature temps generally around normal overall, but
probably tilted to the cool side of normal more often than the warm
side. As for pcpn, zonally oriented flow for the remainder of the
week will send one more stronger shortwave across northern
Ontario/northern Great Lakes tonight/Thu, bringing the potential of
shra/tsra. Another weaker wave may bring an opportunity of shra/tsra
late Fri, and then shortwave going on to become part of the eastern
N America trof amplification will offer another chc of pcpn at some
point over the weekend. Thereafter, the development of the eastern N
America trof will be a below normal pcpn signal for Upper MI. Pcpn
when it occurs next week will be more on the isold/sct side as the
pattern won't be favorable for widespread and/or significant pcpn
events. Hopefully, areas that are still in need of additional good
rainfall will see it over the next several days.

Beginning Thu, shortwave will be moving across Northern
Ontario/northern Great Lakes. How associated convection plays out
across the Upper Great Lakes tonight will have some bearing on what
happens on Thu, and what happens tonight is much more uncertain than
it was 24hrs ago. Best course of action is probably to maintain
decent continuity from previous fcsts rather than incorporating too
much of the guidance that has changed. In that regard, it's quite
possible heavier pcpn will split Upper MI heading thru Thu morning
as one area of heavier pcpn passes by to the s along the instability
gradient and another area passes by to the n in association with
stronger shortwave dynamics. For now, fcst will retain flavor of
previous fcsts and show shra/tsra chc diminishing from w to e during
the morning hrs. With departure of large scale forcing from
shortwave during the aftn, new convective development will depend on
lingering cloud cover, affecting instability, and whether there will
be any boundaries around for low-level forcing. A general s to sw
wind that is strong enough to prevent a Lake Superior lake breeze
suggests there may not be a good boundary for convection. Remains to
be seen if there will be any outflow boundaries from convection
tonight/Thu morning. Opted to just retain schc/low chc pops in the
aftn. Will be very warm/uncomfortably humid day with high temps in
the mid 80s for much of the area along with dwpts in the 65-70F
range. Temps could reach 90F if there is more sun. Coolest
conditions will be along Lake MI east of Escanaba.

Another shortwave approaches Fri/Fri night. While fcst soundings
indicate a cap that needs to be overcome, most erode it for
convection to develop either late in the day or evening. Low chc
pops were included in the fcst during this time. However, it is
noted that models suggest that there will be a boundary to the s of
Upper MI, so that may keep convection that develops mostly s of the
fcst area or at least more likely to just affect southern Upper MI.
With deep layer shear in excess of 40kt and MLCAPES of at least a
couple thousand j/kg, there will be the potential of svr storms
should convection develop. Fri will be the warmest day of the week
as 850mb thermal ridge (around 20C) moves over the area. Most of the
guidance has trended down slightly with temps. Still, upper 80s/lwr
90s should be common for max temps, and dwpts of 65 to around 70F
will make it very uncomfortable. Gradient wind may be weak enough to
allow a lake breeze to develop off Lake Superior in the aftn to
provide some cooling. Gradient s-sw wind will keep conditions cooler
along Lake MI e of Escanaba. With the heat, limit outdoor activity
and stay hydrated.

There is plenty of uncertainty with the final shortwave that goes on
to become part of the eastern N America trof amplification. Last few
days of model runs have not shown much consistency in whether this
shortwave will force a sfc low pres wave far enough n to bring
shra/possible tsra to Upper MI at some point over the weekend. For
now, fcst reflects low chc pops due to the uncertainty. Drier/cooler
weather will then take hold early next week.

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 736 AM EDT WED JUL 17 2019

VFR conditions will prevail at KIWD/KCMX/KSAW through much of the
period. After 00Z tonight...scattered showers and thunderstorms will
begin to move west to east across the U.P. Due to high model
uncertainty...confidence remains low in the extent of the aerial
coverage of these showers. Any showers or storms that approach the
TAF sites overnight will have the potential to reduce ceilings and
visibilities to IFR for brief time periods. Will just mention VCSH
in the TAFs until the convective evolution becomes more clear through
the day.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 409 AM EDT WED JUL 17 2019

Winds will be under 20 knots over most of Lake Superior
today except over the far west where northeasterly winds
will be funneled and may gust up to 25 knots. As a surface
trough approaches tonight...southerly winds will increase over
the eastern Lake and may gust over 25 knots through Thursday
morning. Beyond that winds will remain below 20 knots into
early next week. Patchy fog will remain across Lake Superior

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


LONG TERM...Rolfson
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