NWS Duluth, MN wrote its last area forecast discussion before the first event at Apr 12, 8:25 PM CST, 35 minutes earlier.
Area forecast discussion, Apr 12, 8:25 PM CST, 35 minutes before
Area Forecast Discussion
National Weather Service Duluth MN
925 PM CDT Tue Apr 12 2022
.DISCUSSION...(This evening through Monday)
Issued at 349 PM CDT Tue Apr 12 2022
Summary: the strong spring storm system we have been talking about
for days has finally arrived. Rainy, windy conditions are expected
to get things started, with a transition to snow still on track to
occur late Wednesday into Thursday. Some strong to severe storms are
possible over our southern reaches late this afternoon and evening.
Potential for snow squalls remains for Thursday. Precipitation
finally comes to an end late Friday before a clipper system moves in
and drops some additional snowfall, although timing is more
uncertain.
Well, we've had three mid-week spring storm systems in as many
weeks. Why not make it four? Chances of rain showers and gusty
easterly winds will continue to increase this afternoon as a
Colorado Low approaches the region. We are already seeing some
strong to severe storms south of our region within the warm air
advection wing ahead of the surface low. Okay, let's breakdown this
system.
* Severe Weather This Evening
The Storm Prediction Center continues to have our far southern tier
of counties in a Marginal Risk of severe weather. We will have a
strong push of equivalent potential temperature into our region
along the warm air advection wing, with dew point temperatures
increasing to the middle to upper 40s. There will be a pretty stout
low-level thermal inversion that will make it very difficult for any
convection to become surface-based, so despite a strong shear
profile, including a clockwise-curved hodograph in the low-levels
and large amounts of storm-relative helicity, the threat for
tornadoes and damaging winds are slim to nil. Elevated instability
appears to be modest, with most-unstable CAPE values on the order of
500 to 1000 J/kg, so some hail is possible, with perhaps some hail
stones up to one inch in diameter. This activity looks most likely
late this afternoon through the evening hours, mainly over northwest
Wisconsin.
* Strong Winds Along North Shore
As the surface low approaches, easterly winds will strengthen this
evening into the overnight hours. Winds will be more northeasterly
over western Lake Superior tonight, with gale-force gusts across
most of the nearshore waters. This on-shore flow will lead to strong
wind gusts along the North Shore areas, including Duluth, Two
Harbors, Silver Bay, and Grand Marais. Gusts in excess of 40 mph are
expected, so we have issued a Wind Advisory for the North Shore,
including the southern St. Louis county zone.
* Nuisance Flooding and River Flooding Risk
Due to the threat for heavy rainfall from the aforementioned
convection over northwest Wisconsin, and QPF amounts between 0.50 to
1.00 inches on top of a ripe, melting snowpack, there is the threat
for flooding - including basement flooding in and around the home,
as well as river flooding, especially along the Tyler Forks River in
northern Ashland county. The bulk of the rainfall with this system
over northwest Wisconsin will occur this evening and overnight, so
it will dump pretty quickly. Due to the concern for this flooding,
we have issued a Flood Watch for Bayfield, Ashland and Iron counties
due to the heavy rain on top of the existing snowpack, as there is
roughly 4.5 inches of average snow-water equivalent in the area of
highest concern.
* Transition to Snow Late Wednesday
As the surface low gets wrapped up and begins shifting off the
northeast, cold air advection will wrap into the system late
Wednesday into Thursday, leading to a transition to snow. There may
be a wintry Accumulations aren't expected to be too heavy, nor does
it appear to impact a large portion of our region, mainly the
Borderland at this time. Some shovelable snow amounts are possible
for Thursday, which may make road conditions slick.
* Snow Squall Potential Thursday
As the surface low lifts off to the northeast, there is some concern
for snow squall potential on Thursday, with steepening low-level
lapse rates, increased instability, some low-level FGEN forcing, and
a strengthen pressure couplet/isallobaric component. Confidence in
snow squalls has increased with this forecast package, so it
definitely looks to be a possibility. The low-level lapse rates look
pretty impressive, with strong momentum transfer to the surface. We
did increase the wind forecast for Thursday, due to these steepening
low-level lapse rates and pretty strong flow aloft to be able to mix
down.
Some lingering light snow will continue across the Northland Friday,
but will gradually taper off, with little additional snow
accumulations. Forecast confidence diverges a bit for Sunday through
Tuesday, as there appears to be a clipper system that will sweep
through the region early next week, but timing is quite uncertain.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 617 PM CDT Tue Apr 12 2022
Long-duration flight restrictions expected to impact area
terminals this forecast period as low pressure slowly lifts north
from the Mid- Mississippi Vly. Fcst guidance very instant that
IFR/LIFR conditions will persist through much of the fcst period
beginning around 03z. Main concern aside from low cigs and poor
visibilities will be chance for scattered storms as main band of
precipitation lifts north with time. As of right now, high-res
model guidance suggests this activity will lift north into
southern terminals around the 03z time frame, impacts mainly
expected at BRD/HYR and possibly DLH. For now, have decided to
make minimal changes from previous fcst and trends will have to be
monitored in the coming hours. Otherwise, LLWS will also be a
concern during the overnight hrs as strong easterly winds prevail
in the sub-2kft layer at all terminals except BRD and HYR. IFR
ceilings and MVFR vsbys are then expected to persist through much
of the daylight hours on Wednesday.
&&
.MARINE...
Issued at 925 PM CDT Tue Apr 12 2022
A strengthening pressure gradient will lead to strong winds over
western Lake Superior overnight. Gale-force winds are expected
along the entire North Shore, as well as from the Twin Ports out
to the outer Apostle Islands. Further east, small craft conditions
are expected from Chequamegon Bay east through Saxon Harbor.
Gale Warnings will continue into Wednesday morning before the
winds gradually weaken later in the day. Small Craft Advisories
will be needed once the Gale Warnings expire by mid-morning
Wednesday.
There will be a brief respite from the winds Wednesday afternoon and
evening before they strengthen once again Wednesday night/Thursday
morning. Once again, hazardous conditions to small craft are
expected, with perhaps more gale-force wind gusts Thursday into
the Friday time frame.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 35 40 27 36 / 90 40 20 70
INL 32 39 23 34 / 100 80 50 80
BRD 37 45 27 36 / 80 30 20 60
HYR 41 51 26 37 / 90 30 20 60
ASX 37 45 28 40 / 90 40 40 50
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch through Thursday morning for WIZ002>004.
MN...Wind Advisory until 7 AM CDT Wednesday for MNZ020-021-037.
LS...Gale Warning until 10 AM CDT Wednesday for LSZ140>147-150.
Small Craft Advisory until 10 AM CDT Wednesday for LSZ121-148.
&&
DISCUSSION...JTS
AVIATION...32
MARINE...32