Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 230534
AFDMQT

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

.SHORT TERM...(This evening through Wednesday)
Issued at 243 PM EDT TUE MAY 22 2018

A surface high pressure system, light winds, and little cloud cover
have allowed for temperatures to warm nicely into the upper 60s
across the east to mid to upper 70s elsewhere this afternoon.
Lake breezes have started to work inland across the east and north
central U.P. cooling temperatures along the shores. As in the
past few days, dew point temperatures have dropped quite a bit
across north central and western interior Upper Michigan dropping
RH percentages to the 20 to 30% range (save a few upper teens in
localized areas). We continue to monitor for wildfire hotspots
given the very dry airmass and available fuels.

A quiet night is in store for the area with clear skies and lows
falling to the low to upper 40s, coldest across the east.  Given
continued light winds and surface high pressure, some very shallow
patchy fog is possible inland and along the Lake Michigan shore.
However, the dry air mass should limit the magnitude of any fog
that develops.

Wednesday looks quite similar today but slightly warmer with highs
in the mid to upper 80s across the central and west to upper 70s
across the Keweenaw Peninsula and east. Dry conditions will continue
with RH percentages falling to the 20-30% range in the north central
and interior west. Light winds will continue to prevent critical
wildfire conditions from being met, though lake breezes will once
again prevail.

.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 PM Lake Superior forecast issuance)
Issued at 243 PM EDT TUE MAY 22 2018

Winds are expected to stay below 20 knots through the entire
forecast period with the strongest winds of 15-20 kts expected
Thursday night and into Friday morning across the east.
&&

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

$$

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



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