Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240857
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
457 AM EDT Thu May 24 2018

.SHORT TERM...(This evening through Thursday)
Issued at 354 PM EDT WED MAY 23 2018

Benign conditions currently will give way to a more active pattern
as the Upper Peninsula sits underneath the ring of fire through
tomorrow. Mid-to upper-level ridging centered over the
Mississippi River Valley is allowing for the local forecast area
to sit on its periphery. Weak shortwave traversing through early
tomorrow, coupled with just enough of an increase in atmospheric
moisture, should allow for showers to trigger first thing in the
morning across the western portions of the U.P., progressing
eastward throughout the day. An uptick of instability by tomorrow
afternoon could allow for thunderstorms to develop, although they
currently look to remain of the garden variety type.

Unseasonably warm temperatures will continue tonight into tomorrow
with highs reaching the mid to upper 80s in the interior. Lows
tonight will struggle to drop below the upper 40s, with most
locations staying in the 50s.

.LONG TERM...(Friday through Wednesday)
Issued at 456 AM EDT THU MAY 24 2018

No meaningful changes in medium range guidance is noted from 24hrs
ago. Mean western Canada ridge/eastern Canada trof pattern that has
dominated for some time will be progressing downstream and breaking
down over the next several days as mean troffing tends to become
established from the Gulf of AK into western Canada/Pacific NW.
Southern stream trof that was over the western CONUS has been kicked
ne into the northern Rockies by a sharp trof approaching the W
Coast. Remnants of this trof now over the northern Rockies and the
associated shortwaves will shift eastward along the U.S./Canada
border region over the next few days, bringing an unsettled period
of weather to Upper MI thru at least the first half of the Memorial
Day weekend. With large portions of west and central Upper MI only
receiving less than 25pct of normal rainfall over the last 30 days,
widespread, decent rainfall is needed. While that probably won`t
happen, there is at least the potential for some areas to receive
much needed rainfall as sct showers and thunderstorms roam Upper MI
today thru Sun. With shortwaves slipping e of the area Sun, dry
weather should return for Memorial Day. Back to the w, the trof
currently approaching the W Coast will split with the southern
portion establishing a new western CONUS trof/mid-level low this
weekend. With the aforementioned troffing setting up off the Gulf of
AK into western N America next week, this western CONUS trof/mid-
level low will eventually get forced ne/weaken like its predecessor,
providing Upper MI with another opportunity of shra/tsra at some
point during the last half of next week. As for temps, with the
departure of the eastern Canada trof, the mechanism for sending any
strong surges of cooler air into the Upper Lakes will be gone.
Overall, the upcoming 7-10 day period looks solidly above normal,
though the typical cooler by the lake will occur frequently. Many
days will see more summerlike dwpts readings as well.

Assessing the model fcst of shortwave progression in addition to the
uncertain spin-up of waves by convection over the Plains will make
for a complicated and uncertain fcst with regard to timing better
opportunities of shra/tsra Fri/Sat. However, surprisingly, there is
reasonable agreement for a pair of shortwaves to affect Upper MI
Fri, one roughly in the morning hrs and the second late
aftn/evening. In a broad sense, model qpf guidance aligns with the
timing of these waves. 30-35kt low-level jet in response to the
first wave should support more organized convection spreading across
the area in the morning, weakening as it reaches the eastern fcst
area. Air mass/instability recovery behind the morning convection
will then occur for the next shortwave to take advantage of late
aftn/evening. Convection in the morning will be elevated, and models
show a wide range of mucape values for parcels lifted from an
elevated sfc. Best estimate is that 500-1000j/kg will be avbl. With
effective shear under 20kt, not anticipating any svr storms during
the morning. With precipitable water up around 1.5 inches, 250pct of
normal, locally hvy rainfall is certainly possible. Late
aftn/evening mlcapes are fcst into the 1500 to around 2000j/kg
range. With deep layer shear under 25kt, organized svr storms are
not expected with the late aftn/evening convection. However, given
the instability, can`t rule out pulse type isold svr storms. Delta
theta-e from the sfc to mid-levels is over 20K, supporting a risk of
strong winds while WBZ heights btwn 9 and 10.5kft over the w half
supports a risk of larger hail. Shra/tsra will wind down during Fri
night.

On Sat, another shortwave, is fcst to approach. Weak pres gradient
over the area will support lake breeze development which will likely
become the focusing mechanism for convection. Thus, pops will be
highest in the interior on Sat. With mlcape increasing to 1000j/kg
or so and deep layer shear increasing to around 30kt, there is some
potential of organized storms and a svr risk, but potential is
still low unless instability is greater.

Shortwave trof will be shifting e of the area on Sun, and so there
should be a trend toward drier weather. Will maintain schc/low chc
pops in the morning which will then become confined to s central
Upper MI in the aftn where lingering moisture/lake breeze
convergence and a little instability may still support some shra.

Memorial Day should be dry, but there are some hints that there may
be sufficient instability in the aftn to generate isold shra along
lake breezes. Will retain a dry fcst for now.

Tue thru Thu, attention turns to the ejection of the trof/mid-level
low becoming established over the western CONUS this weekend. Ahead
of this feature, guidance has trended toward a less amplified/weaker
mid-level ridge moving across the western Great Lakes on Tue.
Whether this will allow shortwave energy ejecting from the trof to
bring some shra/tsra into the area as early as Tue remains to be
seen, but there are trends to support that potential. Wed/Thu look
more unsettled with shra/tsra possible as the remants of the western
CONUS trof lift ne across the area.
&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 139 AM EDT THU MAY 24 2018

VFR conditions are expected to prevail at all TAF sites through the
forecast period. There could be some showers and thunderstorms at
all TAF sites during the day on Thu. Coverage should be limited
due to lingering dry air. Covered with a VCSH for now and will
refine as we get farther into the morning.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 347 PM EDT WED MAY 23 2018

Fog currently engulfing northern Lake Michigan has continued to
advect northward, pooling along the Schoolcraft/Mackinac County
land/water boundaries. This fog is anticipated to persist through
the overnight hours into early tomorrow morning before finally
dissipating. Otherwise, no significant marine hazards are expected
for the next couple of days with winds topping out at around 10-15
knots through tomorrow, briefly becoming stronger across eastern
Lake Superior and Lake Michigan/Bay of Green bay overnight
tomorrow.
&&

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

$$

SHORT TERM...lg
LONG TERM...Rolfson
AVIATION...JLA
MARINE...lg


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