007
FXUS63 KMQT 181121
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
721 AM EDT Fri Oct 18 2024

.KEY MESSAGES...

- Elevated fire weather concerns today across western and
  central Upper Michigan thanks to gusty southerly winds of
  20-30 mph and relative humidities falling to near 25%.

- Unseasonable warmth Sunday and Monday with highs in the 70s,
  turning much cooler Wednesday, but only back to around normal
  for late October.

- Most days over at least the next 7 days will be dry. Best
  chance of showers Tuesday night into Wednesday (50-80 percent
  chance), but significant rainfall not expected.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 223 AM EDT Fri Oct 18 2024

Mid to upper level ridge axis extending from Lake Huron north into
James Bay is apparent on RAP analysis. This positions Upper Michigan
along its western flank within a dry airmass, tight pressure
gradient, and southwesterly flow. Overnight winds across the
interior have been mostly 10-20 mph, but downsloping locations along
Superior have been windy. Highest gust observed so far has been 39
kts at Granite Island. Big Bay has also gusted to 32kts and the
observation platform near the USCG in Marquette has gusted to 29kts.
The southwesterly flow has also continued to advect in a warm
airmass, and with the elevated wind profiles overnight lows have
remained mild. As of this writing, most locations were in the mid
40s to mid 50s. This with the dry air over the area, dewpoint
depressions have been large, with many locations observing 15
degrees of spread between dewpoints and temperatures, which is
yielding relative humidities across the west half in the 30 to 50
percentage. All this to say that yesterday`s elevated fire weather
conditions remain overnight across parts of western Upper Michigan.

Today, low level jet aloft will continue to produce gusty winds.
However, expecting lighter winds with most locations capping out
near 25 to 30 mph. PWATS will increase a little today, but daytime
mixing and the continued presence of a dry airmass will enable
elevated fire weather conditions. Main area of concern today is the
central portions of Upper Michigan, which has the best chance of
seeing relative humidities fall to near 25%. With that said though,
much of the interior west could fall to near 30% and most of the
forecast area should see relative humidities fall to at least 40%.
Daytime temps will be almost 15 degrees above normal and most
locations will climb into the 60s. Some low 70s can`t be ruled out
in the western half where downsloping could aid warming.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 425 AM EDT Fri Oct 18 2024

Thru next week, most days will be dry, and the majority of days will
have above normal temps with some well above normal. Medium range
model guidance is in good agreement on the large scale evolution of
the pattern across N America. Eastern N America ridging, which will
feature a strong positive height anomaly of ~330m at 500mb to s of
James Bay today, will flatten out to zonal flow along the
U.S./Canada border over the weekend as a couple of shortwaves track
e across southern Canada. However, positive height anomalies will
dominate all along the vcnty of the International Border in this
zonal flow. A shortwave over sw Canada on Mon will then weakly
amplify as it progresses downstream, reaching the Great Lakes on
Wed. Positive height anomalies will then rebuild into the Great
Lakes region by the end of the week in response to modest trof
development along the W Coast. For Upper MI, this pattern evolution
will favor above normal temps until the midweek trof arrives. In
fact, unseasonable warmth is likely on the way for Sun and Mon and
probably Tue. ECWMF EFI as high as 0.7-0.8 across portions of Upper
MI on those days indicate the potential for unusual warmth for this
time of year. Cold front associated with the midweek trof will drop
temps back to around late Oct normals for Wed/Thu. Warming will then
follow late week with temps potentially well above normal by Sat. As
for pcpn, there are only 2 opportunities for any rainfall thru next
week. The first occurs on Sat as tail end of shortwave tracking e
thru Canada pushes a dissipating front over Lake Superior/Upper MI.
Shra will likely be confined mainly to nw Upper MI given that the
front will be dissipating. The second opportunity of rainfall occurs
Tue night with aforementioned shortwave reaching the Great Lakes.
This wave will provide a better chc of showers, though rainfall will
be light. Some lake effect showers will probably follow Wed into
Wed night. Dry weather should then round out the week.

Beginning tonight/Sat, positively tilted shortwave extending from
Manitoba to MT this evening will progress to northern Ontario and
northern MN by sunrise on Sat with associated cold front pushing e,
extending from James Bay thru ne MN. Right entrance of 100kt upper
jet extending from the eastern Dakotas/nw MN to Hudson Bay and
resulting low-mid level fgen will support pcpn vcnty of the front.
This pcpn will spread out over western Lake Superior tonight, but
with vast majority of model guidance keeping pcpn w of Upper MI,
will maintain a dry fcst thru 12z Sat. With jet streak and shortwave
lifting ene on Sat, southern extent of forcing will weaken. Cold
front will also weaken and eventually dissipate as it continues
eastward. As a result, potential of pcpn will diminish with time and
eastward extent. Fcst will only include pops of 20-50pct over nw
Upper MI on Sat. Expect high temps ranging thru the 60s F, coolest
nw under thicker cloud cover and some shra.

On Sun, next shortwave tracking from s central Canada to northern
Ontario will push associated cold front eastward, extending from
James Bay to nw MN by evening. Pres gradient btwn a 1030mb high over
the Ohio Valley and the front to the nw will result in a breezy day.
Mixing potential on model fcst soundings indicates that wind gusts
to 20-30mph will be common. Lower level moisture depicted on fcst
soundings suggests that sfc dwpts won`t mix out to result in low RH
on Sun. For now, don`t anticipate RH to fall blo 40-45pct at lowest.
With 850mb temps around 11C, highs on Sun will be mostly in the
low/mid 70s F, roughly 20-25 degrees above normal. Will be cooler
near Lake MI under sw winds.

Cold front will sag s over Lake Superior Sun night then lift n on
Mon as sfc trof moving out over the Northern Plains/Canadian
Prairies forces sw low-level flow downstream into the Great Lakes.
This trof is associated with a shortwave moving onshore over the
Pacific NW/BC. That wave will reach the Great Lakes on Wed. The sw
flow will bring 850mb temps up to 12-13C on Mon, and that will
translate to highs ranging thru the 70s F, except near Lake MI under
ssw sfc winds.

As the aforementioned shortwave progresses downstream, associated
sfc cold front will approach. 00z medium range models show good
agreement in timing front into and across Upper MI during Tue night.
So, Tue will be another warm day, but probably not quite as warm as
Mon as peak 850mb temps shift off to the ne. Upper 60s to mid 70s F
should be the rule. Passing cold front Tue night should bring a
period of shra to most locations. With ensembles then showing median
850mb temps falling to btwn -3 and -5C, conditions will become
marginally cold enough for lake effect shra Wed into Wed night. Will
be much cooler on Wed with high temps in the mid 40s to mid 50s F.
Warming and likely dry weather will follow Thu thru Sat.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 721 AM EDT Fri Oct 18 2024

VFR conditions are expected to prevail in this TAF period for all
sites. Gusty southerly to southwesterly winds will develop today
with daytime mixing, enabling 20-30kts at all terminals. In the
absence of mixing this morning and tonight, low level wind shear is
expected.

&&

.MARINE...
Issued at 425 AM EDT Fri Oct 18 2024

With a tight pressure gradient over Lake Superior, s to sw winds
gusting to 20-30kt will continue thru this morning. Early this
morning, low-level jet translating across the area will support 35-
40kt gales from roughly the Huron Islands to a little east of
Marquette as downsloping ssw flow leads to increased mixing of
higher winds downward. The pressure gradient slackens this aftn and
tonight as a weakening cold front approaches. This will result in
winds decreasing from west to east across Lake Superior. Expect
winds to fall to mostly under 20kt during the mid and late aftn
across the w half of Lake Superior. Winds will diminish across the e
half tonight. With the cold front dissipating as it continues
eastward on Sat, expect winds under 20kt. The next approaching cold
front will then result in increasing winds Sat night. Wind gusts
over western Lake Superior will reach up to 25kt late in the night.
The sw winds will increase further on Sun, gusting up to 25-30kt,
strongest btwn Isle Royale and the Keweenaw. Winds across eastern
Lake Superior should remain mostly under 20kt. The cold front will
sag s over Lake Superior during Sun night, resulting in winds
falling to under 20kt. Winds will remain under 20kt on Mon. Another
approaching cold front will bring some increase in winds on Tue,
gusts up to 25kt, but strongest winds will follow passage of the
cold front Tue night. Early indications from ensemble model guidance
point toward a 30-60pct chance of nw gales late Tue night/Wed.

&&

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

&&

$$

SHORT TERM...JTP
LONG TERM...Rolfson
AVIATION...JTP
MARINE...Rolfson