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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 171747

Area Forecast Discussion
National Weather Service Marquette MI
147 PM 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 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 18Z TAFS through 18Z Thursday afternoon)
Issued at 139 PM EDT WED JUL 17 2019

Although VFR conditions are currently prevailing at the terminals,
conditions will deteriorate later this evening through the
overnight hours as a large cluster of showers and thunderstorms
moves through. Confidence is increasing that all three terminals
will likely be directly impacted, but low confidence remains on
timing, given that several more hours are needed to watch its
evolution, currently in MN. Once these storms move through 
overnight, indications point toward LL stratus potentially 
lingering around into tomorrow morning, but have held off on 
reducing categories for this issuance. Conditions will decidedly 
improve from mid-morning Thursday through the remainder of this 
TAF period, with southerly winds today becoming more S-SW 


.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