Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 221714

Area Forecast Discussion
National Weather Service Marquette MI
114 PM EDT Tue May 22 2018

.SHORT TERM...(Today and tonight)
Issued at 431 AM EDT TUE MAY 22 2018

Water vapor imagery and RAP analysis show shortwave that was over
the central Plains 24hrs ago now shearing e across the western Great
Lakes in the more confluent flow regime over the area between a deep
trof over ne Canada and low amplitude ridging from the southern
Plains e into the Atlantic. Very little shra activity remains with
this wave. Only isolated -shra/sprinkles are noted in ne WI.

Not out of the question that there could be a few sprinkles over far
s central Upper MI over the next few hrs. Otherwise, weak nw low to
mid-level flow developing in the wake of the shortwave will advect
drier air into Upper MI today, leading to clearing skies. This will
allow temps to rise well into the 70s in the interior, perhaps
reaching 80F at a few spots. Under a weak gradient wind regime
today, lake breezes will rule the aftn, leading to cooler conditions
lakeside. There is some question as to how far sfc dwpts may fall
this aftn under drying air mass. Utilizing mixing heights, RAP
suggests dwpts will fall most over nw into n central Upper MI. The
NAM is similar, but much more muted with the dwpt drop. The GFS
favors the central and eastern fcst area for a sharp drop in dwpts.
In the end, combined some of the mix down potential from the RAP and
GFS with bias corrected guidance to arrive at aftn dwpts. Result is
min RH falling to 25-30pct over a wide portion of central Upper MI
inland from the Great Lakes. With sustained winds light in the 5-
10mph range at most locations, fire wx concerns will not be further
aggravated today.

Quiet night is on the way tonight under clear skies and calm/near
calm wind. Expect mins in the 40s, though a few of the traditional
cold spots over the interior e may slip blo 40F. Some guidance is
suggestive of at least patchy fog development tonight. Given the dry
conditions that have dominated in recent weeks and the drying
expected this aftn under building mixed layer, fog seems unlikely
tonight unless the expected drying of the boundary layer fails to
occur today.

.LONG TERM...(Wednesday through Monday)
Issued at 452 AM EDT TUE MAY 22 2018

After a couple more days of elevated fire weather concerns, expect a
change to a more summerlike active weather pattern by late week as
warm and more humid airmass advects across the Upper Great Lakes
ahead of troughing aloft from scntrl Canada to the northern Plains
and associated sfc low tracking from scntrl Canada to the Upper
Great Lakes.

Continue to favor lower Td/RH on Wed as high pressure/dry airmass
persists at least one more day. High temps into the mid 80s inland
west with RH values blo 25 pct point to another elevated fire
weather day. Winds will be light, but could see 10-15 mph gusts
where lake breezes are strongest. Thu will serve as transition day
toward switch to the summerlike weather. Could see weaker convective
shortwave on edge of building elevated mixed layer lead to shra and
t-storms moving over west U.P. through the day. Also possible could
be additional shra/t-storm development along lake breeze convergence
zone from west to north central. Will depend on how high sfc dwpnts
and sfc based CAPES. Going to go with persistence for lower Td, so
resulting instability and associated t-storm chances would be lower.
As long as intitial clouds are not too thick, much of west half of
Upper Michigan should see temps reach well into the 80s.

Fri into Sat, we should be fully into this warm and somewhat humid
airmass, at least for May. Sfc low over southern Manitoba and sfc
ridge over southeast CONUS will lead to warm/moist return flow into
the Upper Great Lakes. Some hint that Upper Michigan will be on nose
of southwest low-level jet and moisture transport. If that is true
then will likely be a period of widespread showers/t-storms early in
the day. Some convectivly induced shortwaves will likely be in the
mix as well since there should be decent coverage of shra and t-
storms Thu aftn/evening upstream, but cannot pin those down right
now. MLCAPES building over 1000j/kg will also lead to chances of
shra/t-storm more in the aftn. Attm forecast 0-6km shear of 20-30
kts is pretty marginal for organized/severe storms, but given
steeper lapse rates and MLCAPES checking in over 1000j/kg, there
could be some stronger storms. Will carry high chances for shra t-
storms on Fri. Similar to Thu, if cloud cover is not too persistent
or thick, temps should rise well into the 80s. Unlike Thu, Td could
be pushing 60F. Quite the change from the persistent low-level dry
airmass we have been dealing with for most of May.

More unsettled weather for Fri night and Sat as sfc low and warm
front slide across Upper Michigan. Chances for shra/t-storms
continue, but by Sat aftn with front dropping across northern Upper
Michigan, the focus may shift over WI/MI border into scntrl Upper
Michigan where steeper lapse rates persist and MLCAPES may rise to
1500-2000j/kg. Shear may be slightly higher than Fri. More strong
storms seem possible. Heavy rain also possible with PWATS over 1.5
inches and K-index values up to 35. Warmest temps well into the 80s
again on Sat toward WI border while cooler conditions develop with
the fropa near Lk Superior. Unsettled weather now looks to linger
through Sun and even into Memorial Day as upper level trough is
slower to exit. No big focus for widepsread shra/t-storms but could
be pop-up activity due to lake breezes and lingering instability.
Overall late this week into the holiday weekend looks like our first
taste of summer type weather.

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 113 PM EDT TUE MAY 22 2018

VFR conditions are expected to prevail at all TAF sites through the
forecast period. Patchy fog may develop near KIWD and KSAW
overnight and into Wednesday, but confidence is not high enough to
include in the TAFs at this point in time.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 431 AM EDT TUE MAY 22 2018

A weak pres gradient will dominate for the next few days, resulting
in winds of 5-15kt across Lake Superior today through Thu. A low
pres system or trough moving across the western Great Lakes on Sat
may lead to somewhat stronger winds at some point Fri/Sat.

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


SHORT TERM...Rolfson
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