069
FXUS63 KMQT 191826
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
226 PM EDT Sun May 19 2024

.KEY MESSAGES...

- Borderline elevated fire weather conditions today with warm
  and very dry conditions, but winds on the lighter side.

- Leading edge of next round of showers could reach into the far
  western U.P. toward sunrise Monday. Then, periods of showers
  Monday through late week, but mainly focused on Monday and
  also late Tuesday afternoon and Tuesday night.

- A windy day possible on Wednesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 336 AM EDT Sun May 19 2024

Today, sfc high pres ridging and an associated very dry air mass
will build into the Upper Great Lakes in the wake of last night`s
frontal passage. Full sun thru the morning will give way to
thickening mid/high clouds arriving from the w in the mid-late
afternoon ahead of a weak shortwave rippling thru the mid-level
ridge. Strong insolation will result in deep mixing into extremely
dry mid-levels. NAM soundings show late morning dewpoints at
800mb/~5kft AGL ranging from -20 to -40C, though this is the low end
of the model guidance. Even though moisture aloft does increase
during the afternoon, mixing potential still supports sfc dewpoints
falling thru the 30s F. Some locations will see upper 20s F. The low
dewpoint potential is also evident thru the local mixed dewpoint
tool and simply in some of the raw model guidance, which the HRRR
appears to capture quite well. With high temps fcst in the mid/upper
70s F across the interior, the low dewpoints will drive RH down to
around 20pct across much of the interior of Upper MI this afternoon.
The good news is winds will be on the lighter side, though a little
higher than previously expected. Sustained winds will be around 10
mph with gusts to around 15 mph. Winds will be strongest across the
Keweenaw where gusts to around 25mph are possible. Lake breeze
development should help limit fire wx concerns close to the Great
Lakes shorelines due to cooling conditions (temps falling into the
60s F), and higher dwpts, resulting in higher RH.

Tonight, the next significant shortwave and rainmaker, now over the
SW U.S., will be approaching through the Central Plains and Upper
Midwest late tonight. Increasing q-vector convergence and isentropic
ascent ahead of the shortwave could lead to some showers forming
over the far western U.P. around sunrise Monday morning. Model
soundings indicate that dry low-levels should keep much of the rest
of the U.P. dry through tonight. Expect min temps in the upper 40s
to around 50F. under mostly cloudy skies.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 536 AM EDT Sun May 19 2024

An active pattern will continue across the U.S. during this week.
Troffing currently over western Canada into the northern U.S.
Rockies will amplify over the next couple of days, leading to
western Canada/western U.S. troffing this week. A series of
shortwaves dropping into this trof from the N Pacific will then
eject e and ne across the U.S., supporting the active pattern. For
Upper MI, the result will be several opportunities of rainfall this
week. The next period of rainfall occurs late tonight thru Mon
evening, the second Tue aftn into Wed, possibly lingering into Thu,
associated with the strongest low pres of the week, and finally the
third at some point Fri-Sun. Models are in overall good agreement
thru midweek. Timing of the last system is most uncertain, but
that`s expected given the farther time range out in the model runs.
That said, the spread has narrowed a little over the last 12hrs of
model runs. So, expectation is for overall above normal pcpn across
Upper MI over the next 7 days. This will work to ease still
lingering drought over portions of western Upper MI where, per the
5/16 U.S. Drought Monitor, severe drought was still indicated,
centered around the Porcupine Mtns, and also in eastern Upper MI
where moderate drought was still indicated from eastern Delta to
western Mackinac counties. As for temps, readings will be around
normal to above normal early this week, warmest today. Temps will
then trend downward to blo normal Thu/Fri, due to the flow around
the deep low that passes across the area midweek. A return toward
normal expected over the weekend. Looking farther ahead, ensemble
guidance suggests that the pattern of this week will break down next
week as western N America troffing transitions to ridging, bringing
an end to the train of shortwaves tracking e and ne to the Great
Lakes. The western ridging will also force eastern troffing, so
temps for Upper MI will likely be around normal to a little blo
normal next week with the cooler weather more likely during the last
half of the week.

Beginning Mon/Mon night, out of the amplifying mid-level trof over
the western CONUS, next shortwave will lift to the Upper Great Lakes
on Mon, accompanied by a surge of precipitable water to ~200pct of
normal. This increase in moisture along with increasing isentropic
ascent will lead to shra/isold tsra, a widespread wetting rain,
across much of the fcst area. One recent model trend is for much
more pronounced upper diffluence over western Upper MI due to the
right entrance of 110kt upper jet across northern Ontario into
Quebec. This results in an increase in qpf over the w compared to
previous fcst. 00z EPS now has the probability of at least 0.5
inches of rainfall highest over the w at 50-80pct. Probability
ranges down to 20-40pct e. Pcpn will diminish/end from nw to se in
the aftn/evening. There is disagreement on how quickly the shra exit
the area Mon night, but trends seem to support shifting the shra out
of the area overnight. Abundant low-level moisture/stratus may
linger into Tue morning. Some fog and maybe patchy -dz are a
possibility as well. With the clouds and shra on Mon, high temps
were knocked down at least a few degrees over the area compared to
previous fcst. Expect highs mostly low/mid 60s w and central to
around 70F e where rain begins latest.

After a period of dry weather late Mon night thru at least Tue
morning, a notably stronger shortwave ejecting from the western trof
will strengthen as it reaches the Upper Mississippi Valley Tue
night, resulting in healthy 12hr 500mb height falls of 150m. At the
sfc, associated low pres will deepen to around 990mb as it
approaches and then lifts across or just w of Lake Superior on Wed.
While the low track passing to the w of Upper MI will support the
widest coverage of heaviest rainfall to the w of Upper MI, mdt to
locally hvy rainfall will still be possible across the fcst area
during the period of strong isentropic ascent/strong 850mb theta-e
advection to the e of the low Tue night. Precipitable water
increases to ~200pct of normal as well. Expect widespread shra and
some tsra across the area. EPS probabilities show a 20-60pct chc of
at least a half inch of rainfall from this system with the highest
probabilities se and w. Shra coverage will diminish significantly
for Wed. Some areas may slip in dry weather for much of or all of
the day, especially e half. Winds may become an issue. ECMWF
EFI/shift of tales has been increasing for Wed with Upper MI mostly
in the 0.8 to 0.9 range now, suggesting a potentially very unusual
wind event for this time of year based on last 20 years of model
climate. Median wind gusts from the EPS for Wed are mostly 40-45mph
across the fcst area. While winds for this fcst were increased from
what NBM indicates, they are not as high as the median from the EPS.
Will be a time period to reevaluate for higher winds in later fcsts.

As the low lifts across northern Ontario on Thu, isold/sct shra will
remain possible under lingering cool, cyclonic flow. Thu should be
the coolest day of the week with highs in the lwr 50s to the lwr 60s
F warmest s central. Timing shra potential Fri-Sun is uncertain. For
now, of the 3 days, Fri and Sun have the better shot at being dry
days.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 225 PM EDT Sun May 19 2024

VFR cigs/vsby prevail through this evening at all terminals. Gusty
west winds continue at CMX until closer to sunset when light and
variable winds spread across all terminals. Conditions deteriorate
late tonight into Monday morning as a wave of rain and perhaps a few
embedded thunderstorms lifts north across Upper Michigan. Model
guidance drops cigs down to IFR/LIFR on Monday as this area of rain
moves through and am most confident in this occurring at CMX/SAW due
to east/southeasterly upslope flow.

&&

.MARINE...
Issued at 536 AM EDT Sun May 19 2024

With low pres over northern Ontario and high pres setting up over
the western Great Lakes today, sw winds across the w half of Lake
Superior will gust up to 20-25kt, strongest btwn Isle Royale and the
Keweenaw. Winds will diminish to under 15kt across the eastern lake
today. Winds will settle back to under 15kt lakewide tonight, and
will be under 20kt Mon/Mon night. Deepening low pres will then lift
toward western Lake Superior, reaching the lake Wed morning. Expect
e to ne winds to ramp up as the low approaches. NE winds will
increase to 25-30kt over western Lake Superior by Tue evening. Winds
increase further Tue night. Probabilistic guidance indicates a 50-80
percent chance of reaching gale gusts Tue night into Wed morning
across w and central Lake Superior. As the low lifts n of the lake
Wed/Wed night, 20-30kt winds will become southerly then westerly.
Probabilistic guidance indicates at 30-60pct chance of gale gusts
continuing into Wed evening. It is noted that some of the models
that track a deep low just w of Lake Superior into northern Ontario
show higher end westerly gales across the lake Wed into Wed night,
especially across the w half. Will be something to monitor. Winds
will gradually diminish on Thu.

&&

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

&&

$$

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