667
FXUS63 KMQT 301752
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
152 PM EDT Tue Apr 30 2024

.KEY MESSAGES...

- Patchy but locally dense fog diminishes this morning.
- Active pattern continues through next week as a series of low
  pressure systems track across the U.S. and affect Upper MI.
  Above precipitation expected, including chance of
  thunderstorms at times.
- Temperatures won`t stray too far from normal, but they will
  probably be above normal more often than below normal.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 436 AM EDT Tue Apr 30 2024

The latest 07Z surface analysis shows a 1006 mb surface low over
Lake Michigamme that is expected to weaken while tracking east-
northeast across Lake Superior today. Nighttime RGB composite
satellite imagery shows an expansive area of low clouds that appears
more scattered across Wisconsin. Surface observations indicate
locally dense fog near Lake Michigan in the vicinity of a subtle
wind shift from SSE to SSW that corresponds to the low
pressure`s cool front. Radar imagery shows an area of rain
showers along and ahead of this front with most of the activity
over Lake Superior. Visibility is improving behind the front
except for the higher elevations of the Copper Country where
webcams show fog/mist supplemented by westerly upslope flow off
Lake Superior.

Overall, expect improving weather conditions today as the low
departs allowing for low clouds to lift and perhaps scatter out this
afternoon. HREF guidance shows decreasing probabilities for low
cloud cover this afternoon and evening across the west half. BUFKIT
analysis suggests low clouds will scatter out at the same time as
mid/high level clouds increase associated with the next system.
Breaks in cloud already apparent on satellite imagery combined with
the time of year (beginning of the stable season) implies skies
clearing more quickly, but it could go either way. Cloudiness is
mostly only relevant to today`s high temps that should be maximized
across the south-central where westerly downslope should give an
extra boost to temps. As is usually the case with light west flow,
convergent lake breezes seem likely across the east this afternoon.
This may result in a few afternoon sprinkles, but measurable
rainfall seems unlikely at this time.

&&

.LONG TERM /TONIGHT THROUGH MONDAY/...
Issued at 517 AM EDT Tue Apr 30 2024

The recent active pattern that has developed across the Lwr 48 will
continue thru next week as a series of vigorous waves track off of
the N Pacific and then across the U.S. This pattern will be
beneficial in easing ongoing drought over western and eastern Upper
MI as frequent rainfall events are expected, some potentially mdt to
hvy. The latest drought monitor from 4/25 indicated drought
conditions in western Upper MI were into the severe category in
portions of Gogebic/Ontonagon counties. To the e, moderate drought
was indicated from eastern Delta to western Mackinac counties. Given
the dry conditions heading into spring, there were also concerns
that the spring wildfire season could be active. For now, this
pattern of frequent pcpn events will ease those concerns as well.
So, expectation is for above normal pcpn through next week. As for
temps, with the progressive nature of the flow and frequent
shortwave passages, expect temps fluctuating around normal, likely
not straying too far from normal on most days, rather than any
prolonged periods of well above or well blo normal temps. Daily
temps will probably end up on the warm side of normal more often
than the cool side.

Beginning tonight/Wed, the next vigorous shortwave heading out over
the Northern Plains today will briefly swing negative tilt as it
reaches Upper MI late tonight, leading to a band of vigorous forcing
crossing the area. Models are in overall agreement in showing
convection organizing over MN this aftn, then moving into WI this
evening. Much of the model guidance shows the negatively tilting
shortwave supporting sfc low development within the convection.
Track and strength of this feature will have implications for where
the heaviest rainfall occurs in Upper MI tonight. Consensus points
toward a track to western Lake Superior, suggesting western into n
central Upper MI probably has the best chc of seeing the heavier
rainfall amounts. Instability for parcels lifted from the top of sfc
based inversion wanes as the system moves toward Upper MI, so not
anticipating any thunder tonight. Expect shra to reach western Upper
MI toward midnight and the eastern fcst area late tonight. Shra
shouldn`t last more than about 3-5hrs at any location. Given the
late night arrival over the e, shra will linger there until about
mid morning on Wed. Sfc trof associated with the low moving across
the lake won`t exit the eastern fcst area until early aftn, so a few
more -shra may develop e into early aftn until trof exits. Rainfall
amounts should range from about 0.2 to 0.5 inches, but potential is
there for some higher amounts up to 0.75 inches across the w. Fcst
soundings indicate abundant, mostly shallow moisture following the
wave, so westerly flow upslope -dz is possible over the w Tue
morning, and low clouds may linger over the e for much of the day
under developing flow off of Lake Superior. Would expect the shallow
low-level moisture to mix out over western into central Upper MI
during the day, but majority of model guidance suggests this won`t
happen. In fact, a few of the models have rather deep moisture.
There is abundant dry air to bring down as mixed layer builds, but
the potential of clouds to linger for quite a while will at least
shorten the window for dwpts/RH to tumble. WRF-ARW is the only model
aggressively mixing out moisture, but it does often correctly
capture this potential. Given that we`re less than 2 months from
highest sun angle of the year, inclined to partially lean fcst in
that direction. Best drying will occur across interior w into s
central Upper MI. With the clearing, building mixed layer will tap
stronger winds. Westerly winds could gust up to 35-40mph Wed aftn,
depending on how high mixing builds. Even if deeper mixing occurs
and RH falls under 30pct, wetter fuels from recent rainfall,
including the rain tonight, will work to limit fire wx concerns.
Expect high temps to reach well into the 60s s central, ranging down
to around 45-50F near Lake Superior where westerly winds are an
onshore wind. If clouds linger thru the day, temps will be a good
5-10 degrees lwr.

Sfc high pressure ridge builds over the area Wed night, resulting in
a dry, quiet night. Attention then shifts to the next shortwave
swinging across the Rockies Wed night and out over the Northern
Plains on Thu. In response, sfc warm front will lift n toward Upper
MI with a waa/isentropic ascent regime advancing across the Upper
Mississippi Valley into Upper MI. Expect shra to spread into w and
central Upper MI during the aftn, then continue Thu night. With
precipitable water increasing to 200-250pct of normal, decent
rainfall should occur. Ensemble probability guidance suggests a 30-
60pct chc of rainfall of at least 0.5 inches and a 10-20pct chc of
exceeding 1 inch. Probabilities are highest over s central Upper MI.
Some thunder is possible with potentially several hundred j/kg of
cape avbl for parcels lifted from top of sfc based inversion.

With a cold or occluded front passing and exiting sometime btwn late
Thu night and early Fri aftn as low pres lifts over northern
Ontario, would expect a trend toward dry weather on Fri, continuing
thru at least Sat morning. Then, next shortwave will already be
approaching by Sat aftn, resulting in the next round of shra
spreading w to e Sat aftn/night. This round of shra will be lighter
than the previous.

High pres ridge arriving on Sun will support a dry day. Uncertainty
in timing shortwaves grows significantly early next week, but that`s
not a surprise given the time range. Next wave should arrive at some
point Mon/Tue, bringing the next chc of shra in the ongoing active
pattern.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 152 PM EDT Tue Apr 30 2024

As low pressure continues to move into Ontario the rest of today,
expect the cigs to progressively improve to VFR by this evening
across the TAF sites. However, don`t expect the better conditions to
last all that long as a second low pressure system lifts from the
Upper Mississippi Valley into Lake Superior late tonight. This
brings showers and a low chance (10 to 20%) of thunder across the
area after midnight tonight into Wednesday morning. This will tank
cigs LIFR conditions across the TAF sites late tonight/early
Wednesday morning, although some low-level cloud cover is looking to
set up in the north central U.P. near KSAW before the rainfall
arrives. Thus, there may be some patchy fog or low-level stratus
near KSAW late tonight before the rainfall. As the warm front of the
low moves through late tonight, we could see some marginal LLWS
across the terminals (around 50% chance). While KIWD was the only
one with the LLWS mentioned, each of the TAF sites could see the
marginal LLWS; the LLWS will largely be dependent on how much of the
higher winds aloft mix down to the surface and the direction of the
winds between the sfc and 2 kft aloft. The LLWS threat ends
Wednesday morning as the cold front pushes through the U.P. from
west to east and brings breezy westerly winds (and gusts) to the
sfc. Ahead of the cold front, we could see some patches of
drizzle/light rain and fog; once we get behind the front, expect the
conditions to slowly improve.

&&

.MARINE...
Issued at 517 AM EDT Tue Apr 30 2024

Weakening low pres currently just nw of the Keweenaw will exit to
the ene today, followed by a weak sfc high pres ridge building over
the area by evening. As the low tracks ene and off of the lake,
westerly winds on the s side of the low may gust up to 25kt e of the
Keweenaw later this morning into early aftn. Otherwise, expect winds
mostly under 20kt today, diminishing this aftn to under 15kt by
evening. E to SE winds then increase up to around 25kt tonight as
the next low pres trof approaches from the w. A low pres will spin
up on this trof, and the low is likely to pass over western Lake
Superior Wed morning and then exit eastern Lake Superior near
Michipicoten Island mid to late aftn on Wed. Marine interests will
need to monitor upcoming forecasts closely as there is the potential
for this low to intensify sufficiently for gales to occur with
shorter notification than desired. This would include the potential
of a short period of NE gales to 35kt over western Lake Superior
late tonight/early Wed. Of more concern is the westerly winds that
strengthen on the s side of the low as it moves toward Michipicoten
Island on Wed. Trends from a few models are suggesting potential of
a 3-6hr period of 35-40kt gales from just e of the Keweenaw due e
across the lake during Wed aftn. Internal probabilistic guidance
even indicates about a 20pct chc that high end gales will be
achieved. After this period of stronger winds, high pres ridge
arrives Wed night, resulting in a quick drop of winds to under 20kt
across the lake. These lighter winds will linger across eastern Lake
Superior on Thu. Over western Lake Superior, ne winds will be on the
increase again on Thu as the next low pres moves out over the
central Plains. Expect NE winds to 30kt by late Thu aftn over
western Lake Superior. E to SE winds will increase to 30kt over
eastern Lake Superior Thu night. There is a 25-40pct chc that low
end gale gusts could occur. As low pres lifts into northern Ontario
and Fri, winds will shift s to sw. While gusts up to 30kt will
continue over western Lake Superior, winds will fall off to under
20kt over the eastern lake. Over the weekend, expect winds mostly
under 20kt across the lake.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Small Craft Advisory from 7 AM EDT /6 AM CDT/ to 3 PM EDT /2
    PM CDT/ Wednesday for LSZ240.

  Small Craft Advisory from 7 AM EDT /6 AM CDT/ to 8 PM EDT /7
    PM CDT/ Wednesday for LSZ241-242.

  Small Craft Advisory from 2 AM to 11 PM EDT Wednesday for
     LSZ243-244.

  Small Craft Advisory from 5 AM to 8 PM EDT Wednesday for
     LSZ245-246.

  Small Craft Advisory from noon to 8 PM EDT Wednesday for
     LSZ247-248.

  Small Craft Advisory from 5 PM to 11 PM EDT Wednesday for
     LSZ249.

  Small Craft Advisory from 3 PM Wednesday to 5 AM EDT Thursday
     for LSZ250-251.

Lake Michigan...
None.

&&

$$

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