Area Forecast Discussion
Issued by NWS Marquette, MI

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000
FXUS63 KMQT 261931
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
331 PM EDT Tue Mar 26 2024

.KEY MESSAGES...

- A cold front passing today through this evening will bring
  rain turning to snow with a brief period of mixed
  precipitation possible. Rapid cooling behind the cold front
  may result in a flash freeze with untreated surfaces possibly
  becoming icy late today and this evening.

- West flow lake effect snow develops late tonight and continues
  into Thursday. Several inches of snow along with blowing snow
  expected, mainly across the Copper Country. Heaviest snow
  Wednesday night.

- Next chance of widespread precipitation occurs Friday night
  and Saturday, followed by a system worth monitoring for
  Monday/Tuesday next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 331 PM EDT Tue Mar 26 2024

Water vapor imagery and RAP analysis show a tight closed low moving
over western Lake Superior, amid broader midlevel troughing
extending across the Plains and into the Great Lakes. A pronounced
dry slot is evident across the UP and the eastern 2/3rds of Lake
Superior. At the surface, a 990mb surface low is analyzed over
western Upper Michigan, with a sharp cold front directed from
western Lake Superior to far western WI. Most of the area has been
able to enjoy a brief period of dry weather this afternoon, with Day
Cloud Phase showing lower cloud cover even mixing out across much of
the eastern half of the UP. Another embedded shortwave zipping
around the closed low is touching off another round of scattered
rain showers across north-central WI, which are moving into the
central UP already. Temperatures so far have stayed plenty warm
enough for precipitation to remain as all snow, with most of the
area hovering in the upper 40s.

This evening, the closed low will continue to move NNE over Lake
Superior, reaching Ontario closer to midnight. The frontal boundary
will soon begin tracking into the western UP, and should be through
most of the area by midnight. This should kick up another round of
light precipitation, with a quick transition over to snow. Given a
warm nose aloft in model soundings across the western UP, will not
rule out some pockets of freezing rain or ice pellets. A quick
transition over to a lake effect snow regime is expected the second
half of the night as 850mb temperatures quickly fall back to near -
12 to -15C. With winds generally out of the WSW, LES should be
confined to the far western UP, particularly the Keweenaw. Light
snow totals well below an inch are possible across much of the UP
with the passing cold front, with higher totals around an inch in
the WSW snow belts of the western UP.

Otherwise, with a rather tight pressure rise/fall couplet, and
robust CAA resulting in increasing lower level lapse rates (thus
allowing us to tap into stronger winds aloft), expect blustery
conditions to develop along and behind the cold front. Will note
that winds are already gusting up to 20-30mph in eastern MN, where
surface temperatures are already in the upper teens and lower 20s.
Temperatures likewise plummet with the passing front through the
first half of the night here in the UP. This is posing a concern for
a flash freeze tonight given wet roadways following the past day`s
precipitation. However, with most of the area having enjoyed a brief
dry period today, only a brief burst of light rain/snow this evening
with the passing front, and blustery conditions tonight potentially
helping to dry things out, this may not end up being particularly
widespread.

&&

.LONG TERM /TONIGHT THROUGH MONDAY/...
Issued at 459 AM EDT Tue Mar 26 2024

Blocky high latitude flow will prevail this week into next week with
the AO and NAO both in the negative phases, though the AO only
weakly. Positive height anomalies of varying amplitude across
northern and eastern Canada will consolidate into a strong anomaly
over Greenland early next week. Meanwhile, a building ridge over the
N Pacific will shift e and tilt ne into western Canada early next
week. For Upper MI, these changes in the flow with the
shifting/evolving anomalies will result in normal to blo normal
temps thru the middle of next week, though the blo normal temp
departures won`t be significant. Current trof dominating much of
central N America into the western U.S. will be slow to lift out,
but it will reach se Canada and the E Coast by Fri. Into Thu, Upper
MI will remain under its influence and associated pcpn which will
transition from rain to westerly flow lake effect snow. A new trof
will be amplifying down the W Coast late this week in response to
the building upstream ridge over the N Pacific. A disorganized set
of waves ejecting from that amplifying trof will track to the Great
Lakes region by Sat. There is plenty of model spread on these waves
and the resulting sfc reflection, but it offers the next potential
of some pcpn. Early next week, the combination of ridging into
western Canada and consolidating/strengthening positive height
anomaly over Greenland will force troffing into s central and se
Canada. Meanwhile, troffing over the w will begin to shift
downstream. This brings some potential for interaction of that trof
progressing out of the western U.S. with shortwaves forced s and se
due to the western Canada ridge and Greenland anomaly. For many
days, there have been some EPS/GEFS/GEPS ensemble members showing
sufficient interaction for a significant pcpn event for Upper MI,
including accumulating snow, in the first days of Apr. Given the
small overall number of ensembles indicating such an event for Upper
MI, it is, for now, still a low probability, but something to
monitor.

Beginning tonight, mid-level low currently over KS will open up and
lift into the Upper Great Lakes, taking on a negative tilt as it
does so and potentially developing a second sfc low pres wave on
cold front trailing from the parent sfc low lifting n of the
Keweenaw into Ontario. Expect a resurgence of showers into the
evening due to this feature. A number of the models show strong low-
level fgen shifting thru central Upper MI, aiding the pcpn. Whether
or not a sfc low pres wave develops on the cold front, sharp cooling
will occur with fropa. If the fgen ends up supporting a more
organized area of pcpn on the cold side of the boundary, a brief
burst of snow, inch or two of accumulation, could occur thru
portions of central Upper MI where models max out the fgen.
Potential for that to occur remains very low, but will need to be
monitored heading into the evening. Otherwise, sharp cooling will
quickly drop temps blo freezing, raising concerns for wet
roads/sidewalks to become icy, especially where pcpn continues
during the crossover to blo freezing. Details of how this plays out
won`t be known until later today when pcpn trends become much more
certain. By sunrise Wed, 850mb temps will be down to btwn -13 and
-18C over western Lake Superior, supporting developing LES under
brisk westerly flow. Sharp inversion present at 4-5kft will limit
the lake convection, but with the dgz falling into the convective
layer, -shsn should become fairly widespread off of western Lake
Superior. Winds will become blustery across the Keweenaw. Mixed
layer winds to 35-40kt will support sfc gusts to 40-45mph.

On Wed, center of a mid-level low over MN will swing ne across
western Lake Superior. This will work to weaken/lift inversion and
cause a slight backing of low-level winds from w to wsw. Thus,
expect LES to increase into nw Upper MI, Keweenaw in particular.
Snow accumulations should be in the 1-2 to locally 3 inch range.
Winds will continue to gust to around 40 mph across the Keweenaw.
With the deepening/sharpening cyclonic flow and deepening moisture,
-shsn should also increase in coverage across the rest of western
Upper MI Wed aftn, given closer proximity to mid-level low center.
Expect to see some diurnal aspect to the -shsn with late Mar solar
insolation, even with clouds dominating. To the e, drying boundary
layer should mostly preclude any -shsn or flurries from developing.

With a deep moisture profile and 850mb temps around -14C Wed night,
LES will continue. The Wed evening period will offer the best
potential of mdt to hvy snowfall under convergent wsw flow across
the Keweenaw. Low-level winds veer more westerly during the night,
and that will shift heavier snowfall southward toward northern
Ontonagon County/central Houghton County. The LES environment as it
looks now should support snow accumulations of at least 3-6in Wed
night across that area. Combined with winds still gusting 35-40mph,
creating blsn, travel will be hazardous in nw Upper MI Wed night.

Mid-level low lifts to James Bay on Thu, leading to drying and the
start of waa. As a result, westerly flow LES will diminish during
the morning, and shouldn`t be much more than flurries by late aftn.

Disorganized shortwaves moving across the Plains and vcnty of the
International Border will reach the Great Lakes region late Fri/Sat.
Models have shown a slight trending toward one of the waves passing
near Upper MI to be a little more defined. Fcst will reflect a
30-50pct chc of -sn, possibly mixed with rain, Fri night/Sat.

As previously mentioned, fcst early next week will hinge on
potential interaction of a progressing western trof with any
shortwaves dropping around a western Canada ridge. Given the sw-ne
tilt of that ridge, it seems unlikely that a complete phasing of
waves would occur to produce a strong storm system. The 00z
ensembles still have some members that produce a mdt/hvy pcpn event
for Upper MI, including accumulating snow, and the number of members
has increased a little. While still an unlikely outcome, it warrants
monitoring in the coming days. For now, fcst will reflect upwards of
40-60pct chc of -sn/-ra in the Mon/Tue timeframe.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 123 PM EDT Tue Mar 26 2024

Poor flying conditions to persist for duration of TAF period with a
low pressure system moving northward across the UP this afternoon.
This is keeping in rain showers at IWD and CMX so far this
afternoon, though showers are becoming a little more spotty at SAW.
Otherwise, fog and low stratus are keeping in IFR or LIFR ceilings
at all terminals, as well as MVFR or worse visibility at times. A
cold front moving through tonight will help to lift ceilings to
MVFR/IFR, and bring in another quick round of precipitation
(changing to snow) the first half of the night. Lake effect snow
lingers after midnight, mainly at IWD and CMX, with a slight
improvement generally to MVFR at all terminals by the morning.
Meanwhile, surface winds shifting over to the WSW by tonight will
increase above the 12 kt threshold at all TAF sites with gusts up to
24 kts.

&&

.MARINE...
Issued at 459 AM EDT Tue Mar 26 2024

Lake Superior will remain under the influence of low pres that will
track from ne IA early today across western Lake Superior this
aftn/early evening. Result will be changing wind directions and wind
speeds across the lake. Ongoing ne gales of 35-40kt across western
Lake Superior will temporarily subside in the vcnty of the passing
low this aftn. Over eastern Lake Superior, se winds will
occasionally gust to 35kt gales this morning closer to the
International Border. As the low lifts n of the area this evening, w
to wsw winds will ramp up to 35-40kt gales over much of w and
central Lake Superior. These gale force winds will continue thru Wed
before diminishing by late Wed evening. Internal probabilistic
guidance indicates a 25-35pct chc of gusts into the 40-45kt range in
a large area surrounding the Keweenaw Peninsula. Freezing spray will
also occur during these gales, and some hvy freezing spray will
occur at times over portions of western Lake Superior late
tonight/Wed morning. Westerly winds of 25-30kt will then prevail
across Lake Superior late Wed night thru Thu. A high pres ridge will
then arrive on Fri, leading to winds diminishing to mostly under
20kt. Wind should remain mostly under 20kt into and thru the
upcoming weekend.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory from 2 PM Wednesday to 8 AM EDT
     Thursday for MIZ001>003.

Lake Superior...
  Small Craft Advisory until 8 AM EDT /7 AM CDT/ Wednesday for
     LSZ240-249>251.

  Gale Warning until 11 PM EDT /10 PM CDT/ Wednesday for LSZ162-
     244-263-264.

  Small Craft Advisory until 8 PM EDT /7 PM CDT/ this evening
     for LSZ241>243.

  Gale Warning from 8 PM EDT /7 PM CDT/ this evening to 11 PM
     EDT /10 PM CDT/ Wednesday for LSZ241>243.

  Small Craft Advisory until midnight EDT tonight for LSZ245>248.

  Gale Warning from midnight tonight to 5 PM EDT Wednesday for
     LSZ245>248-265.

  Gale Warning from midnight tonight to 11 PM EDT Wednesday for
     LSZ266.

Lake Michigan...
  Small Craft Advisory until 8 AM EDT Wednesday for LMZ221-248-
     250.

&&

$$

SHORT TERM...LC
LONG TERM...Rolfson
AVIATION...LC
MARINE...Rolfson


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