Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 230840
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
440 AM EDT Wed May 23 2018

.SHORT TERM...(Today and tonight)
Issued at 438 AM EDT WED MAY 23 2018

Quiet start to the day with some cirrus over western Upper Michigan
and some stratus and patchy fog on Lk Michigan. Temps inland over
Upper Michigan are in the 40s. Temps near Lk Superior are staying up
in the 50s, even near 60F around Marquette, due to southerly return
flow between high pressure over southern Lk Michigan/lower MI and
weak front dropping over northern Lk Superior. Closest precip in the
form of t-storms is occurring over southwest MN into northern IA.
Storms are firing in area of focused H85 warm air advection on edge
of elevated mixed layer and higher MUCAPE. Sfc warm front is still
southwest of this elevated activity. Another area of t-storms are
over SD closer to main trough aloft and shortwaves lifting across
the northern Plains.

For Upper Michigan today, temps aloft look warmer than Tue by 1-2C
so expect highs well into the 80s inland and upper 60s/near 70F
along Lk Superior. Coolest temps today near Lk Michigan but even
there should get mid 60s. Could be some fog affecting immediate
shore of Lk Michigan east side of Garden Peninsula eastward. Looking
at another day of elevated fire weather concerns with min RH dipping
to around 20 pct inland. Winds gusting to 10-15 mph along lake
breezes this aftn look too light to justify any kind of Special
Weather Statement. This should be the last day until next week of
seeing persistent low RH blo 25 pct.

Signs of this change to a more warm, humid summerlike pattern begin
to show up tonight, though as it always seems, model forcasts of
convection show little agreement, even less than 24 hours out. Aloft
tonight we are in region of building heights as main trough aloft is
still well to the west over the Rockies and just beginning to affect
the northern Plains, but there should be significant warm and moist
advection ongoing in low levels ahead of strengthening plains sfc-
H85 trough. Similar to what is occurring this morning to the
southwest over IA and MN, expect shra/t-storms to develop on nose of
low-level jet/moisture transport and on edge of reservoir of
elevated instability with 1-6km MUCAPES of at least 1000 j/kg
forecast. Differences in the models tie into how far east this
moisture/instability gradient reach. NAM seems too aggressive with
its low-level jet and in its resulting cluster of elevated t-storms
over much of the west half of UPper Michigan by 12z Thu. Instead
like the GEM/ECMWF idea of showing similar idea to NAM but just
shifted more over mainly MN into far western Lk Superior. GFS seems
too muted with overall developing of shra/t-storms given instability
that is building over the plains currently. As always will have to
watch for convectively induced shortwaves that could trigger
activity as far east as NAM indicate, but for now will bring low
chance pops into western Upper Michigan late tonight. Effective
shear late tonight is weak under 15 kts, so maybe looking at small
hail as updrafts will not be able to persist too long.

Low temperatures tonight will be in the 40s to 50s, but given the
warmth already seen this morning, forecast lows in the low to mid
50s along Lk Superior may end up being too cool since the pressure
pattern is pretty similar with even a stronger south wind.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 243 PM EDT TUE MAY 22 2018

A much more active pattern is in store for the extended period with
multiple rounds of showers and thunderstorms expected through the
weekend. A few strong thunderstorms are possible (mainly on Friday
and Saturday) and some areas may pick up appreciable rainfall.

Wednesday night, showers and thunderstorms are expected to develop
over Wisconsin and Minnesota on the nose of an 850 mb LLJ but
weaken before reaching Upper Michigan early Thursday morning. The
overnight thunderstorms will likely generate some sort of MCV/PV
anomaly which, when combined with localized forcing along lake
breezes, will likely lead to at least isolated redevelopment over
north-central Upper Michigan Thursday afternoon. MUCAPE
approaching 1000 J/kg will be stinted by weak 0-6 km bulk shear of
20 kts or less leading to a "pulsey" storm mode.

The overall synoptic pattern will then become dominated by a
slowly-moving compact low embedded in quasi-northwesterly flow
Friday through Sunday. As the low translates eastward, several
shortwave/absolute vorticity maxima will swing through the upper
Great Lakes leading to chances for showers and thunderstorms. At
this point in time, it`s difficult to discern the exact timing of
best convective chances (especially considering the potential for
convectively-generated PV anomalies and debris cloud cover) but
generally Friday and Saturday afternoons look best for diurnal
convective redevelopment mainly west of a line from Munising to
the Stonington Peninsula. Friday, gusty southwesterly
winds/moisture transport will aid in the development of ample
instability, but once again weak shear will lead to a "pulsey"
storm mode. However, storm organization may be better on Saturday
owing to slightly stronger shear (0-6 km bulk shear in the 30-35
kt range) as the aforementioned low and an associated 500 mb
speed max move over the Great Lakes.

There is a growing signal that the upper-level low will then stall
over the upper Great Lakes Sunday and even into Monday continuing
the waves of showers and storms. However, such an evolution will
become better defined in the coming days and I am not nearly
confident enough at this point to add/remove PoPs supplied by the
model blends.

Given forecast PWAT values of 1.4-1.7" from Thursday through Sunday,
thunderstorms will have no problem producing heavy rain. In fact,
some locations across Upper Michigan may pick up several inches of
rain by early next week, especially if the upper-level low indeed
stalls over the upper Great Lakes late this weekend. Given the
western half of Upper Michigan resides in D0 - Abnormally Dry
conditions, heavy rain would certainly be welcome to encourage the
spring green-up.

Finally (as if the shower/storm chances were not enough), it
certainly looks like western parts of Upper Michigan will
experience much above average temperatures Thursday and Friday
with highs in the upper 80s. A few select numerical models throw
in the lower 90s across the Wisconsin border, but I am certainly
not confident enough to blend those in the forecast especially
considering the potential for convection and associated cloud
cover.

All in all, it looks like an active Holiday weekend across the
Upper Great Lakes. All parties planning to travel or enjoy the
warm weather outdoors are strongly encouraged to stay up to date
on the forecast, especially if planning to be out on the open
waters.
&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 133 AM EDT WED MAY 23 2018

VFR conditions are expected to prevail at all TAF sites through the
forecast period. However, patchy ground fog may affect IWD at times
through daybreak.
&&

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 438 AM EDT WED MAY 23 2018

Winds are expected to stay below 20 knots through the entire
forecast period. Expect areas of fog to develop late this week into
the weekend as humid airmass arrives over the area. Could be looking
at dense fog at times.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...JLA
LONG TERM...Borchardt
AVIATION...JLB
MARINE...JLA



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