153
FXUS63 KMQT 162258
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
658 PM EDT Thu May 16 2024

.KEY MESSAGES...

- Showers into the evening hours. A few rumbles of thunder possible.

- A slight ~30% chance for thunderstorms exists across the
  western UP Friday afternoon and evening then over the
  Keweenaw Friday night.

- A southerly breeze and very warm temps in the 70s and 80s
  Saturday ahead of a cold front that brings a higher ~50%
  chance for afternoon thunderstorms. The strongest storms may
  contain small hail.

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

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 340 PM EDT Thu May 16 2024

Water vapor imagery and RAP analysis show a well-defined shortwave
trof extending from southern Manitoba to the western Great Lakes. A
vort max is clearly evident over n central WI. After a bit of a
diminishing trend late morning, shra are expanding this aftn ahead
of this feature. There has been some thunder to the s of Upper MI
from the Green Bay area to portions of the Door Peninsula. Current
temps range from the Upper 60s in eastern Upper MI where there has
been some filtered sunshine thru high clouds to the upper 40s/lwr
50s F w where clouds and sct shra have kept temps down.

Vort max will swing ne across Upper MI during the late aftn and
evening, supporting shra in its vcnty and ahead of it. There is up
to 200-300j/kg of CAPE avbl for parcels lifted from above sfc based
stable layer. So, can`t rule out a few rumbles of thunder. The shra
will be more nmrs across the e half of Upper MI where low-level jet,
850mb theta-e advection and weak isentropic ascent will be focused.
Shra will end most areas by midnight. With light winds overnight and
low-level moisture from rainfall, some fog may develop. Expect lows
tonight to range thru the 40s F.

&&

.LONG TERM /FRIDAY THROUGH THURSDAY/...
Issued at 524 PM EDT Thu May 16 2024

Several low to medium-impact forecast challenges persist with the
current forecast package 1) Friday/Saturday afternoon thunderstorm
chances, 2) fire wx concerns interspersed between brief rain
chances, and 3) widespread rain potential next week. Both chances
for thunderstorms include low probabilities for strong storms
capable of gusty winds and small hail, but instability seems
insufficient for severe hazards. Borderline fire wx concerns return
Friday afternoon with elevated conditions possible this weekend,
especially on Saturday when gusty south winds may accompany hot
temperatures >80F. Details of the early next week pattern remain
murky, but potential for frequent rain chances if not widespread
soaking rain seems to be increasing.

Beginning with Friday, the UP will be positioned between systems,
but a weak and low-amplitude shortwave ripples along the northern
periphery of 500 mb ridging during the afternoon hours. This impulse
may be associated with a warm front lifting northeast across the
region. As a result, warm air advection and veering wind profiles
are apparent and would be favorable for thunderstorms -perhaps even
strong storms- if sufficient moisture/instability materializes. HREF
means advertise around 500 J/kg which is insufficient for strong
storms. However, individual CAMs advertise localized pockets of 1000-
1500 J/kg across the interior west, which is sufficient for small
hail and gusty winds. Regardless, the spatial and temporal extents
of this threat appear small and it`s more likely that thunder
doesn`t occur. As the warm front lifts north across the area a
nocturnal thunderstorm threat may emerge on the nose of a ~40 kt
LLJ. Most guidance keeps this activity over the lake, but it could
scrape the Keweenaw so I left schc PoPs. Also with WAA spreading
across the area and EFI guidance highlighting unseasonably warm lows
across the west, decided to nudge the forecast upwards so that
western downslope locations only cool into the upper 50s Friday
night with mid 40s to around 50 elsewhere.

By Saturday morning, 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 supports high temps
surging into the 80s and a stout south breeze should prevent a lake
breeze off Superior, in fact a few downslope locations (e.g. Big
Bay, L`Anse, Ontonagon) may reach the mid-80s. However, south flow
off Lake MI keeps the eastern UP mainly in the 70s to perhaps even
60s along the shorelines. EFI highlights the unseasonably warm temps
well and also hints at the possibility of unseasonably strong wind
gusts across the far west where model soundings indicate potential
for gusts into the 30-35 mph range. 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 also result in afternoon/evening thunder
chances as the systems cold front presses across the area as CAPE
values increase to around 750-1250 J/kg. Bulk shear values are in
the 25-35kt range on most guidance indicating a convective
environment that is barely favorable for marginally severe hail or
winds, but the SPC decided not to outlook our area. Ultimately,
timing of the frontal boundary will be critical for thunderstorm
potential in our area.

A much drier air mass and associated surface ridging follows the
frontal passage for Saturday night into Sunday. Abundant sunshine
and light winds results in deep mixing into an extremely dry mid-
level layer on Sunday. For example, the 12z NAM advertised a -48C
dew point at 734 mb at 1 PM Sunday. Fortunately surface dew points
won`t mix that low, but I still made substantial cuts to Td values
resulting in minRHs around 20% across the interior west. Light winds
less than 10 mph are the silver lining for 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.

Quickly glancing at the long-term period, model support appears to
be increasing for a wet stretch of weather including widespread
soaking rainfall early next week. The latest EPS surface low tracks
develop a low near Rapid City, SD that lifts northeast across MN
into far northwestern Ontario Sunday night into Monday. Warm/moist
air advection ahead of this system brings rain chances back into the
area. As the Ontario low departs on Monday it appears to leave a
trailing frontal boundary across the Upper Great Lakes as a sub-1000
mb surface low develops over the south-central Plains. This
deepening low pressure tracks along the frontal boundary into the
Great Lakes region on Tuesday/Wednesday bringing the potential for
heavy precipitation.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 658 PM EDT Thu May 16 2024

Showers will move continue to move out. As low-level moisture
increases, cigs will stay low. MVFR conditions at IWD will become
VFR overnight and stay that way through Friday. VLIFR conditions at
CMX will continue until later tonight when MVFR moves in and then
VFR by Fri morning. SAW will have LIFR conditions this evening and
then VFR conditions later on tonight.

&&

.MARINE...
Issued at 524 PM EDT Thu May 16 2024

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 a cold front. Patchy dense
fog is possible in areas of rainfall this evening through tonight. A
few rumbles of thunder are possible this evening across the eastern
lake. Additional thunderstorm chances occur as a warm front lifts
across the lake Friday evening followed by a cold front Saturday
evening. The strongest storms along Saturday`s cold front may
contain small hail, gusty and erratic winds, and frequent lightning.
Thunder chances return Monday 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.

&&

$$

SHORT TERM...Rolfson
LONG TERM...EK
AVIATION...07
MARINE...EK