Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260903
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
503 AM 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 TODAY/...
Issued at 326 AM EDT Tue Mar 26 2024

Latest water vapor imagery shows a vort max/closed low over
northwest MO embedded in the base of a negative-tilt mid-level
trough across the Central Plains. Strong transport of Gulf Moisture,
PWATs of .8 to .9 inches and upper diffluence ahead of the trough
has supported areas of rain across Upper Michigan early this
morning. Onshore easterly flow off Lake Superior has also supported
areas of fog off across the Keweenaw Peninsula with low stratus
observed elsewhere across Upper Mi.

Models in good agreement lifting the negative-tilt mid-level trough
north-northeast across Upper Great Lakes later today as the mid-
level low tracks across far western Lake Superior and the
approximate 990 mb sfc low tracks over the western U.P. and central
Lake Superior. Models hint at a dry slot ahead of the mid-level low
moving across the central and eastern U.P. later this morning into
the afternoon which should help taper the steady rain off to
scattered light rain showers. Meanwhile, the advance of the system`s
cold front into the western U.P. this afternoon will allow light rain
to mix with or transition over to light snow over the western
third of the U.P. Although given only light pcpn expected and
temps barely dipping blo freezing, snow accumulation should be
less than an inch.

High temps today under cloud cover will range from the mid 30s to
lower 40s west, where the cold frontal passage will be felt first,
to the upper 40s to near 50F east half ahead of the front. Temps
over the west will continue to fall through the afternoon hours
in the wake of the frontal passage.

&&

.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 /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 131 AM EDT Tue Mar 26 2024

Poor flying conditions to persist for duration of TAF period as a
low pressure system tracks across northern Wisconsin and into the
western UP.  Ptype will generally be rain at all TAF sites for the
majority of the TAF period until colder air filters in later
today. At that point, could see a transition to snow. At CMX
and SAW, LIFR will be the primary flight category with IFR
prevailing at IWD. And, with rising dewpoints at CMX, fog will
especially be a threat early this morning. Little improvement is
expected until late in the TAF period and even then it will be
MVFR at best. CMX and SAW should have some improvement though
from LIFR to IFR by this afternoon. In addition, will continue
to carry LLWS threat at CMX and SAW this morning to account for
strong southerly low level jet. Meanwhile, surface winds 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...
None.
Lake Superior...
  Gale Warning until 5 PM EDT /4 PM CDT/ this afternoon for
     LSZ162.

  Small Craft Advisory until 8 AM EDT /7 AM CDT/ Wednesday for
     LSZ240-249-250.

  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.

  Gale Warning until 11 PM EDT Wednesday for LSZ244-263-264.

  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 until 2 PM EDT this afternoon for LSZ251-266-267.

  Small Craft Advisory from 2 PM this afternoon to 8 AM EDT
     Wednesday for LSZ251.

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

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

  Gale Warning from 8 AM this morning to 2 PM EDT this afternoon
     for LMZ221-248-250.

&&

$$

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


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