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000
FXUS63 KMQT 221038
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
638 AM EDT Mon Apr 22 2024

.KEY MESSAGES...

- Elevated fire weather conditions this afternoon with low RHs
  and gusty winds.
- A Clipper Low system brings two rounds of precipitation. The
  first is a west-to-east moving line of showers with ~15%
  chance of thunderstorms tonight.
- The second round of precipitation comes Tuesday with rain
  changing to snow with a few rumbles of thunder possible (~15%)
  in the south and generally less than an inch of snow in the
  north.
- Dry weather in the midweek under high pressure.
- Active weather pattern continues with above normal
  precipitation and temperatures favored for the weekend and
  beyond (40-50%)

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 231 AM EDT Mon Apr 22 2024

Upper air pattern consists of closed 500 mb low over southern
Saskatchewan which moves to near Lake Winnipeg by 00z Tue. 850-500
mb q-vector convergence moves in this afternoon, but the deeper
moisture is lacking and stays west of the area through 00z Tue.
Looking at dew points upstream Sun afternoon, they got down into the
mid to upper teens in ND and western MN and this airmass will be
over the area today. Ended up using the mixed dew point tool with
the NAM and blending in the adjmav guidance and this gave me dew
points mixing down into the upper teens to lower 20s across most of
the area. Using mixed dew point tool alone using the RAP model gave
me dew points in the single digits, the NAM in the lower teens and
the GFS in the upper teens, so took the NAM as the middle approach
and mixed it down and mixed with adjmav which gave me dew points
this afternoon that looked reasonable based on what happened
upstream Sun afternoon. Mixing looks to be up to about 5000 to 7000
feet across the area as well based on bufkit soundings. Will be
issuing a special weather statement for fire weather concerns for
this afternoon, otherwise did not make too many changes to the going
forecast.

&&

.LONG TERM /TONIGHT THROUGH SUNDAY/...
Issued at 511 AM EDT Mon Apr 22 2024

An active weather pattern will be over Upper Michigan for this
forecast period beginning with the approach of a Clipper trough and
subsequent low pressure tonight and Tuesday. Ridging aloft will
induce high pressure and calm, dry conditions in the midweek period
ahead of the next low pressure ejecting out of the Plains Friday
into the weekend. Broadly speaking, late April and early May show no
signs of stopping this active pattern, though the details become
largely uncertain beyond this weekend.

Beginning with tonight, the initial wave of showers encroaches on
the western UP beginning at around 00Z Tuesday. Model guidance has
continued to slow down the onset of showers with each run. While
these rain showers will not be a hydro threat, the thunderstorm
potential with these showers is intriguing. Among the HREF ensemble
suite, the HRRR is the most aggressive with convection, showing
multiple zones of simulated 40+ dBZ with MUCAPE values near 500
J/kg. HRRR soundings show that this MUCAPE is entirely limited above
750mb, so strong forcing may be the limiting factor. However, should
an energetic storm initiate, there will be shear present, as HREF
mean SRH is up to 400 m2/s2, though there is some spread in the
guidance as to whether the shear and instability line up properly.
Even if parcels are not super buoyant, low-CAPE/high shear storms
tend to overperform expectations, so if a storm can get going, an
isolated severe wind threat is not out of the question along with
some small hail. However, given the failure modes, chances of
thunderstorms are broadly about 15% for the first line of showers in
this forecast package.

Following the passage of the first line of showers by 12Z Tuesday, a
brief break in precipitation is expected before the low drops
through the eastern portions of Upper Michigan during the day
Tuesday. This will bring a surge of cooler air, sufficient
wraparound moisture, and lift from convergence and orographic lift
to cause showers. The north half of the UP will face rain showers
turning to snow while the south half will be dealing with another
round of thunderstorm potential. The HREF indicates that for much of
the UP, chances are below 10% of exceeding an inch of snow, however,
the high terrain of Baraga and Marquette counties as well as the
entire sine of the Keweenaw could see 1-2 inches of snowfall.
However, the springlike conditions lately have warmed the ground
notably, making the likelihood of accumulation less than the same
amount of QPF in a typical winter setup, so even in the heavier
areas of snowfall, impactful accumulations are not expected. Further
south, clearing skies in the dry slot of the low will allow
temperatures to climb into the 60s in the southern reaches of the
UP, which the HREF suggests could allow SBCAPE to build above 250
J/kg. Despite more surface-based storms being possible, a much less
favorable shear environment should keep the strength of any
thunderstorms limited.

Once showers end Tuesday evening across all of the UP (whether snow
showers in the north or thundershowers in the south), ridging aloft
will quickly build in behind the departing shortwave trough. This
will ultimately result in high pressure building over the lake, with
the 00Z GEFS suggesting 1030mb high pressure centered directly
over Lake Superior by Wednesday afternoon. This will keep
Wednesday and Thursday dry, not only in lack of precipitation
and clouds, but also in RH. The LREF shows about 5-15% chances
of RHS falling into the teens in the interior west, which given
how medium range guidance often usually misses low-RH signals in
high pressure scenarios, the actual forecast likelihood of RHs
falling into the teens is more like 50%. While this is not good
news for fire weather, the silver lining is that winds should be
light, with even the 90th percentile of LREF winds showing
around 10 mph.

The tranquil weather will be interrupted by the arrival of the next
trough and resultant low pressure Friday. Ensembles have trended
slower with precipitation and the ensemble spread on timing is still
somewhat high, but the GEFS is surprisingly consistent with the
track of the low passing through Lake Superior, the UP, or northern
Lake Michigan. Showers become likely (70+%) by Saturday, with
thunder at least 15% likely, though impacts are tough to say given
the current spread in intensity and timing. Ridging building back
over northern Ontario will bring an eventual end to showers,
but with each passing feature, the chaos in the system grows and
uncertainty continues to build in the details. Looking forward,
the pattern continues to be quite active with multiple trough
and ridge passages expected to come. Despite the details
disagreeing, there is good agreement in above normal
precipitation and temperatures, with the CPC outlooks reflecting
this with up to 50% chances of above normal conditions in the
8-14 day outlook.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 638 AM EDT Mon Apr 22 2024

Dry air will remain in control into this evening before a narrow
band of rain moves through. When the rain moves through conditions
may drop down to MVFR this evening for an hour or so...otherwise VFR
conditions will prevail for the period at all sites. SW winds will
quickly increase this morning in response to low pressure tracking
ese across s central Canada. Expect gusts to around 25kt at all
terminals by late morning or early aftn. Gusts could reach 30kt
later aftn.

&&

.MARINE...
Issued at 511 AM EDT Mon Apr 22 2024

Southwesterly winds will gust today from just below 20 kt to 25 kt
throughout today. A line of showers with a slight (~15%) chance of
thunderstorms will pass over the lake from west to east tonight,
which may also be accompanied by gusty winds above 20 kt. A brief
respite behind the showers will not last long as winds turn
northerly and northeasterly Tuesday as an Alberta Clipper low passes
from northern Ontario across the eastern reaches of Lake Superior.
This low will force gales to 35-39 kt across much of the lake along
with 8-10 foot waves. The low will depart quickly though and waves
will fall below gales Tuesday night and below 20 kt early Wednesday.
Winds remain light and somewhat variable under high pressure
Wednesday and Thursday before a system approaching Lake Superior
Friday will bring gale potential, though uncertainty is high in
regards to timing.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 8 AM to 2 PM EDT Tuesday for LSZ243>245-
     263>266.

  Gale Warning from 2 PM Tuesday to 2 AM EDT Wednesday for
     LSZ267.

Lake Michigan...
  Small Craft Advisory from 5 PM this afternoon to 8 AM EDT
     Wednesday for LMZ248-250.

&&

$$

SHORT TERM...07
LONG TERM...GS
AVIATION...07
MARINE...GS