Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 260728
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
328 AM EDT Tue Mar 26 2024

.KEY MESSAGES...

- A cold front passing today will bring rain turning to snow
  with a 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,
  especially west.
- Westerly lake effect snow develops early Wednesday morning and
  continues through Thursday evening, mainly across the Copper
  Country.
- Next chance for widespread precipitation comes into the
  weekend, but confidence is low.

&&

.SHORT TERM /THROUGH TONIGHT/...
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 /TUESDAY THROUGH MONDAY/...
Issued at 334 PM EDT Mon Mar 25 2024

The feature of note beginning Tuesday morning is a mature 988mb low
(per 12Z GEFS mean) transiting from northern Wisconsin across the
western UP to north-central Lake Superior and eventually northern
Ontario by Tuesday night. This low will bring a myriad of precip-
types as it passes and gusty winds in its immediate wake. Cool air
behind the low will support Werly to WSWerly LES into Thursday.
While the remainder of the UP will be dry in the end of the week,
the heavy precipitation to begin the week will keep most fire
weather concerns at bay. While precip rates at times may exceed
0.75"/day, persisting drought conditions should limit hydro concerns
significantly. The next chance for widespread precipitation
will come late Friday into the weekend, but model spread is
still high and confidence is low.

Two prominent 500mb troughing features are over central North
America at 12Z Tuesday. The first is a potent shortwave primarily
responsible for the sub-990mb low that will pass over the UP Tuesday
following roughly the same track. The other is a longer wave which
will phase with the shortwave Wednesday and the trough will pivot
around northern Ontario through Thursday. For Tuesday, potent warm
southerly flow will bring morning temperatures into at least the mid-
40s. The NBM 25th-75th percentile range is disappointingly large for
such a short time period, with 25th percentile highs in the upper
40s to low 50s and the 75th percentile is pushing 60, displaying the
large spread in the ensembles regarding the timing of the passage of
the cold front. Regardless of exact values, cooling behind the front
is going to be strong, with 12Z GFS 850mb cold advection rates of up
to -50C/12 hr. This translates into surface temperatures broadly
falling 2-3C/hr, which the WSSI is highlighting as a minor to
locally moderate flash freeze threat. This cooling will also
complicate the precip types in the evening and overnight hours, with
a messy transition from rain to a wintry mix to snow expected. The
12Z HREF does highlight the Ironwood to Ontonagon area as having up
to 50% chance of a glaze of freezing rain accumulation, but the
potential for flash freeze conditions is still expected to be the
primary driver of slick road conditions. Once the transition to snow
occurs, a slushy inch of snow widespread is most likely, but this
also depends on the timing of the arrival of the cold air behind the
front. Whether it falls as solid or liquid, QPF totals will be
highest along the Keweenaw and in the east half, with the central UP
most likely to be under the influence of a dry slot which will limit
precipitation. 12Z HREF probability of exceeding 0.5 inches is 20-
50% along the Keweenaw and 50-90% in the east, with about a 50%
chance of seeing 0.75 inches of QPF around Newberry. No hydro
impacts are expected due to the current drought conditions.

Once synoptic precip departs early Wednesday, the strong surge of
cool air will allow for lake effect snow to develop as 850mb
temperatures fall into the -10 to -15 C range. As the 500mb trough
will be pivoting near the northern shores of Lake Superior Wednesday
into Thursday, the boundary layer winds will be primarily Werly to
WSWerly. EPS mean wind gusts over the Keweenaw are in excess of 40
mph Wednesday, which has a 10-20% chance of a blowing snow threat to
reduce visibility and cause drifting. LES falls off significantly
Thursday as surface ridging builds in with a more dry airmass. The
NAEFS shows PWAT values falling to below 0.25 across the UP and NBM
RHs fall to the 30s Thursday in the interior west, though with the
heavier precipitation from earlier in the week, fire weather
concerns are minimal.

The next chance for precipitation comes late in the week. The
Canadian and GFS bring a shortwave across the Upper Great Lakes over
the weekend, though the Euro has ridging prevailing. GEFS MSLP
clusters show surface low pressures mainly staying south of the UP
but a small cluster does transit near the region. The EPS keeps all
potential low pressures south of the UP, so confidence in this
potential precipitation is low. The GEFS has good confidence that
high pressure will be over northern Ontario to begin next week with
a cluster of members showing a Colorado Low developing and ejecting
northeast sometime for the middle of next week, but confidence in
any solution rapidly drops off in that time period.

&&

.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 334 PM EDT Mon Mar 25 2024

A large and deep area of low pressure tracks northeast toward Lake
Superior tonight then across the lake on Tuesday. This results in a
complex marine forecast with multiple periods of gales from a
variety of directions within both stable and unstable flow regimes.
Easterly gales will overspread the lake by tonight to 35-40 kt.
Winds become more cyclonic and low level stability increases as the
low approaches the lake tonight. Increasing stability lowers
forecast confidence in gale potential, especially across the eastern
lake where the warmest temperatures are forecast. However, low-end
35 kt southeast gales over the eastern lake and northeast gales to
around 40 kts over the western lake appear most likely. As the low
tracks northeast across the lake on Tuesday it drives a cold front
eastward with strong cold air advection resulting in deep mixing. A
period of westerly gales is likely (60-80%) for Tuesday night and
Wednesday. Westerly gales should diminish Wednesday night with winds
subsiding below 20 kts Thursday night. In addition to the wind, wave
heights through Tuesday will mainly be 8-12 ft with some 12-14 ft
waves east of Isle Royale and north of the Keweenaw Peninsula. Waves
fall below 8 feet by Thursday afternoon. A period of moderate heavy
freezing spray is also expected across the lake after the cold front
passes late Tuesday through Wednesday.

&&

.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
     LSZ240-245>250.

  Small Craft Advisory until 2 PM EDT /1 PM CDT/ this afternoon
     for LSZ241>243.

  Gale Warning from 2 PM EDT /1 PM CDT/ this afternoon to 8 PM
     EDT /7 PM CDT/ Wednesday for LSZ241>243.

  Gale Warning until 8 PM EDT Wednesday for LSZ244-263-264.

  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.

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...GS
AVIATION...Voss
MARINE...EK/GS


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