215
FXUS63 KMQT 171949
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
349 PM EDT Fri May 17 2024

.KEY MESSAGES...

- There is a 20 percent chance of thunderstorms across the
  western U.P. late this afternoon/early evening and then a
  20-30 percent chance across the Keweenaw later this evening
  into the overnight. None of the storms will be strong.

- Breezy south winds and very warm temps in the 70s and 80s
  Saturday ahead of a cold front that will bring scattered
  afternoon/evening thunderstorms. The strongest storms may
  contain small hail.

- Elevated fire weather possible on Saturday then very dry with
  light winds on Sunday.

- More rain chances early to middle of next week as a series of
  disturbances moves across the area in a developing warm and
  moist southerly flow.

&&


.SHORT TERM /THROUGH TONIGHT/...
Issued at 346 PM EDT Fri May 17 2024

Water vapor imagery and RAP analysis show that the shortwave trof
that brought shra to the area yesterday thru last evening has lifted
across northern Ontario. In the wake of that wave, westerly flow
prevails into Upper MI. An area of sct -shra has been moving out
across western Lake Superior to the Keweenaw in an area of
waa/isentropic ascent. The -shra that have reached the Keweenaw are
really not much more than sprinkles. Elsewhere, skies cleared out
quickly in the morning, but daytime heating led to a blossoming of
cu. Stabilizing marine layer off of Lake MI and Lake Superior are
evident, preventing cu. Temps have risen into the low/mid 70s F in
the interior. Closer to the Lakes, temps range down into the 50s
with some 40s F at lakeside locations along Lake Superior.

Aforementioned waa/isentropic ascent will continue to support some
-shra/sprinkles across the Keweenaw over the next few hrs. MLCAPE
has increased to 100-200j/kg into far western Upper MI. This limited
instability may support development of a few shra/tsra late
aftn/early evening, less than 25pct chc. During the night, vigorous
shortwave that is now over nw MT will swing out to ND. While the
main low-level jet in response to this wave will develop ne thru MN
during the night, there will be a modest increase in 850mb winds
further ne across western Lake Superior this evening. The resulting
increase in waa/isentropic ascent should yield some shra/tsra later
this evening across northern portions of western Lake Superior and
possibly also nw Upper MI, mainly the Keweenaw where fcst reflects
30pct chc. Shra/tsra associated with the main 40-50kt low-level jet
developing across MN would reach western Lake Superior late tonight.
Expect min temps tonight ranging from the lower 40s on the east side
of the Keweenaw and near Lake MI to 55-60F in the southerly wind
downslope areas far w (Ontonagon/Gogebic counties).

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 320 AM EDT Fri May 17 2024

Highlights of the extended forecast include very warm conditions
this weekend with the potential for elevated fire weather conditions
at times, then more opportunities for possible widespread rain next
week.

Beginning Saturday, the UP will be squarely in the warm sector of a
surface low near Lake Winnipeg with 850 mb temps of 14-16C spreading
across the UP. This unseasonably warm air mass will support high
temps most locations in the lower to mid 80s with the highest
readings most likely for downsloping areas along Lake Superior west
and central where breezy south winds in the tightening gradient
ahead of the approaching frontal boundary could gust as high as 30-
35 mph at times per model soundings. However, south flow off Lake MI
will keep the eastern UP mostly in the 70s to perhaps even 60s
readings along the shorelines. ECMWF EFI highlights the unseasonably
warm temps well, and like the model soundings, also hint at the
possibility of unseasonably strong wind gusts across the far west.
The combination of hot temps and gusty winds suggests potential for
elevated fire wx conditions, but the main limiting factor is RH
values as dew points surge to around 50F.

Elevated dew points could also result in late afternoon/evening
thunder chances as the system`s cold front presses across the
area. SPC has placed the west half of the UP in a marginal risk
of severe storms on Saturday. However, believe there is some
question on the degree of fcst instability across the area. The
NAM soundings depict a drier airmass with limited CAPE
(generally 500 j/kg or less) and more capping at mid-levels
while the GFS shows MLCAPE values increasing near 1000 J/kg
range in the west with almost no capping during the afternoon
based on more aggressive ramp up of sfc dew points rising well
into the 50s. If the more moist and unstable GFS verifies then
bulk shear values forecast in the 30-40kt range could possibly
generate a few stronger storms with marginally severe hail or
gusty winds. Ultimately, the threat of storms or severe
potential will hinge on how much sfc dew points mix out during
the day on Saturday ahead of the front. Gut feeling is that the
drier and more stable NAM soundings may have a better handle on
the fcst instability, leading to perhaps decreased coverage for
t-storms and thus a lower threat of SVR storms.

A much drier air mass and associated surface ridging follows the
frontal passage for Saturday night into Sunday. Abundant sunshine
and light winds will result in deep mixing into extremely dry mid-
levels on Sunday. For example, the 00z NAM fcst sounding advertised
a -33C dew point at 760 mb at 1 PM Sunday. Fortunately, surface dew
points won`t mix that low, but will still incorporate the local
mixed dew point tool to cut back on Td values resulting in min RHs
closer to 20% across the interior portions of the cwa. The good news
is light winds less than 10 mph should ease fire wx concerns,
because critically low RHs appear nearly certain across interior
portions of the UP. Lake breeze activity should limit fire wx
concerns along the shorelines due to cooler temps and higher RHs.
Expect max temps reaching near 80F over much of the interior west
half and mid to upper 70s over the interior east half. Developing
lake breezes will keep readings near the Great Lakes shores in the
mid to upper 60s.

Models advertise a mid-level trough amplifying over the western
CONUS early next week. Periodic shortwaves in a warm/moist sw flow
developing ahead of the western CONUS trough will bring more rounds
of showers into the area early to mid next week. The first shortwave
moves through late Sun night into Monday bringing the initial batch
of showers for early next week. It looks like the best chance for
widespread and possibly heavy rainfall will be in the late Tue into
Wed time frame when models indicate more substantial shortwave
energy lifting across a nearly stationary frontal boundary draped
across the area. Model uncertainty increases later into the week but
it certainly looks possible that some scattered showers could linger
at least into Thursday as temps trend cooler in the wake of the
midweek low pressure system/frontal boundary pushing off to the
east.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 152 PM EDT Fri May 17 2024

VFR will prevail thru this fcst period at IWD/CMX/SAW. Light shra
associated with a weak disturbance have been moving across western
Lake Superior today, but they mostly dissipate before reaching Upper
MI. Not out of the question that a few sprinkles could occur at CMX
over the next couple of hrs. With continued daytime heating, it`s
also possible that new shra could develop over western Upper MI late
this aftn, but potential is too low to include mention in fcst.
Finally, low-level jet developing toward the area tonight could also
generate a few shra/tsra into western Upper MI during the night, but
potential here is also too low to include mention in fcst. The low-
level jet will result in LLWS developing at IWD/CMX tonight. Gusty
winds to 20+kt will then set in at all terminals mid to late morning
on Sat. Winds will increase further during the aftn.

&&

.MARINE...
Issued at 320 AM EDT Fri May 17 2024

Stable conditions will lead to light winds of generally 20 knots or
less continue today into early next week, except for Saturday
afternoon and evening when southerly gusts of 20-25 kts are forecast
ahead of an approaching cold front. Patchy dense fog is possible
into early morning from last night`s rainfall. Thunderstorms are
possible this evening over west and north central Lake Superior as a
warm front lifts across the lake. More thunderstorms are possible on
Saturday into Saturday night as the same system`s cold front moves
across the area. These storms may contain small hail, gusty and
erratic winds, and frequent lightning. More thunder chances return
late Sun night into Monday and then again late Tuesday into Tuesday
night as a series of disturbances track northeast across the Upper
Great Lakes region.

&&

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

&&

$$

UPDATE...
SHORT TERM...Rolfson
LONG TERM...Voss
AVIATION...Rolfson
MARINE...Voss