Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kdlh 211535 
afddlh

Area forecast discussion
National Weather Service Duluth Minnesota
1035 am CDT Mon Oct 21 2019

Update...
issued at 1028 am CDT Mon Oct 21 2019

Winds have been increasing here in the twin ports this morning,
with gusts around 50 mph on the blatnik bridge. These winds are
only going to accellerate through the rest of the morning and this
afternoon before diminishing again this evening. The duration of
these strong winds is only going to be about 12 hours, which would
not normally cause coastal flooding. However, the latest water
level report from near the bridge shows that it is over 604 feet,
similar to what we have seen with other coastal flooding events,
and we still have another 6-8 hours of these strong winds. Webcam
feeds from around the Canal Park area show waves splashing up onto
the lake walk, and also onto the canal piers. Thus, I have
decided to issue a coastal flood advisory through this evening. By
early evening the winds will have turned to the northwest and the
water should stop piling up onto the Lake Shore, and have added on
a few hours to allow the water to drain out of these low lying
areas.

Update issued at 656 am CDT Mon Oct 21 2019

Updated below for 12z aviation discussion.

&&

Short term...(today through tuesday)
issued at 350 am CDT Mon Oct 21 2019

A powerful low pressure system will approach the Northland today
bringing widespread rain, heavy at times, along with strong winds.
Rain begins from south to north this morning with strong east-
northeast winds around 15-20 mph with gusts to 30 mph, as high as 40-
45 mph along the Lake Superior shoreline. Tonight the low lifts
north across Western Lake Superior leading to a break in the heavy
rain and a shift in the winds, with north to northwest winds
increasing late tonight and through Tuesday. Rain showers linger
through the day Tuesday as the low slowly lifts northward with
northwest winds 10-20 mph gusting to around 35 mph at times. Total
rainfall amounts today through this evening will be around an inch
to inch and a half, with an additional quarter to half inch falling
late tonight through Tuesday. Temperatures turn cooler, with highs
in the 50s today, lows in the upper 30s to near 40 tonight, then
remaining in the upper 30s to mid 40s through the day Tuesday as
cooler air moves in from the northwest.

On the synoptic scale a fairly typical late fall mid-latitude
cyclone is deepening across the central/northern Great Plains and
will lift northeastward towards Lake Superior today into tonight. At
mid/upper levels the closed low is located over South Dakota and
Nebraska with strong height falls as the closed low moves east-
southeast towards northwest Iowa this morning. At upper levels there
is a very strong south-southwest 120+ knot jet streak at 250mb
leading to divergence and thus strong broad-scale lift across the
upper Mississippi River valley today, with the jet increasing to
over 140 knots over the upper Great Lakes this afternoon as the
mid/upper level low lifts northward towards Western Lake Superior.
Strong southerly/southeasterly flow at low levels ahead of the front
is advecting warmer air and increasing low level moisture ahead of
the low, aiding in the strong-large scale lift across the upper
Midwest today and causing precipitable water values in excess of
0.75" across the Northland, which is above the 90th percentile of
area sounding climatology. Guidance is very consistent in the
strength and track of the low, and while there are small-scale
differences in the precise track of the surface low which will cause
some impacts to where and when a dry slot moves into region tonight,
overall confidence in the forecast is extremely high. (Recent trends
for most guidance has been a small westward shift in the low and
accompanying precip amounts, but even if this trend continues there
would be little change in the sensible weather forecast.)

Rainfall amounts have increased a bit due to an increase in the
broad-scale lift strength across all available guidance with
accompanying increases in quantitative precipitation forecast output over the past 24 hours. For
example, the gefs mean quantitative precipitation forecast at Duluth was around an inch yesterday,
while the past 2-3 runs have means near 1.90". In general, current
precipitation forecast is for at least one inch of rain, with a
broad area over 2 inches likely across part of central Minnesota
include the Brainerd lakes region. There is also expected be locally
higher precip amounts along the North Shore due to the strong east
winds today leading to some orographic enhancement. There is a
chance for a few embedded thunderstorms late this afternoon into
this evening across northwest Wisconsin due to some elevated
instability, but in general the risk for thunderstorms is low. Since
the most intense rainfall amounts will be over a 6-10 hour period,
flash flooding is not anticipated to be a concern, but this
widespread heavy rainfall will cause rises on all rivers and streams
and some minor ponding can be expected in urban areas and low spots
in rural areas. With the strong winds and current High Lake levels,
there is a possibility for Lakeshore flooding, but looking at
previous Lakeshore flood events over the past few years, the
duration of the strongest winds does not appear to be as long as
previous events since the low is moving basically directly over Lake
Superior in contrast to previous events where the surface low took a
track further away from the lake and thus resulted in a longer run-
up period for water levels to build up and cause Lakeshore flooding
issues. A Lakeshore flood advisory may need to be issued later today
if water levels rise faster than currently anticipated, but the
potential for destructive Lakeshore flooding like seen last October
seems low. Winds will certainly be intense, though, with a period
this afternoon of gusts to 45 mph, strongest in the twin ports and
long the North Shore. A Wind Advisory may be needed, but confidence
just is not high enough that there will be a long enough period of
45+ mph gusts to warrant an advisory before the low approaches from
the south and winds weaken/change direction.

Tonight as the surface low lifts north across the region there will
be a break in the rainfall for parts of eastern Minnesota and northwest
Wisconsin. There may be a period of fog along the North Shore with
the dry slot due to the richest low level moisture being advected
across the lake and onto the North Shore as the low moves across,
possibly some visibilities less than a half mile on the North Shore
towards Tuesday morning. Winds will be weaker for a few hours until
the low lifts north of Lake Superior towards Tuesday morning at
which time northwest winds will increase from west to east. Winds on
Tuesday will likely be around slightly weaker than the winds on
Monday. There will be a continued chance for scattered light rain
showers in the cooler wrap-around flow, with temps warm enough for
mainly rain tonight through Tuesday afternoon. Another tenth to
quarter inch of rain will fall on Tuesday in the northwest flow.
Temperatures will be nearly steady Tuesday in the cool northwest
flow, highs in the upper 30s to mid 40s.

Long term...(tuesday night through sunday)
issued at 350 am CDT Mon Oct 21 2019

After a strong low pressure system departs at the beginning of the
period, the pattern turns quieter heading into the weekend with
temperatures trending warmer as the week progresses.

A strong area of low pressure located over northern Ontario Tuesday
night will continue to slowly drift northeast over Hudson Bay into
Thursday. This will lead to a weakening gradient overhead on
Wednesday allowing winds to diminish. Cold air advection on the backside of the low
will continue for Wednesday into Thursday morning and keep the
threat of showers in place through much of this period. Overnight
temperatures and a continued stream of cold air filtering in aloft
with allow this activity to be a rain/snow mix or all snow at times,
but little to no accumulations are expected.

An upper-level ridge then starts to build in heading into Friday,
but a weak shortwave will be on the leading edge of this for Friday.
The European model (ecmwf) is the strongest with this feature and does bring some
shower activity to the Northland for Friday while the GFS/Gem remain
dry. Heading into the weekend, the upper-level ridge moves through,
albeit with timing differences among the models. Guidance shows the
presence of an area of low pressure and cold front for the latter
half of the weekend, but the front looks moisture starved as it
moves across the region. The best chances for any precip at this
time look to be along the international border for the back half of
the weekend.

High temperatures will be in the 30s and 40s for Wednesday and
Thursday before the upper ridging brings in warmer air. This will
lead to highs in the 40s and 50s for the beginning of the weekend,
but they may start to trend cooler again by the end of the weekend
depending on a cold front moving through.

&&

Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 656 am CDT Mon Oct 21 2019

VFR conditions are in place currently but are expected to worsen
as a strong area of low pressure moves into the region. Rain will
spread from south to north through the day leading to ceilings
lowering to MVFR and IFR and visibilities lowering to MVFR. Some
periods of IFR visibilities will also be possible during heavier
rainfall. A few embedded thunderstorms will also be possible at
khyr this afternoon. Periods of LIFR ceilings are expected later
this evening and tonight as the low moves overhead. Khyr may see
improvement in both ceilings and visibilities for a time this
evening as a dry slot moves through. Winds will also be very
breezy with gusts to 30+ knots and periods of low level wind shear at kdlh, kbrd
and khyr.



&&

Marine...
issued at 350 am CDT Mon Oct 21 2019

Low pressure will move northeast today and will lead to increasing
northeast winds through the day across Western Lake Superior. Winds
will be sustained this morning from the northeast at 10 to 20 knots
with gusts to 30 knots. Small craft advisories are already in effect
and with wind gusts expected to reach to 40 to 45 knot range with
higher gusts to 50 knots later this morning, gale warnings are in
effect along the North Shore and much of the South Shore, including
the twin ports. These strong winds will lead to waves building to 8
to 16 feet this afternoon. Periods of rain will be seen today into
Tuesday with a few thunderstorms being possible from Taconite Harbor
to the twin ports and the South Shore this afternoon and evening.
The low will move over Western Lake Superior tonight allowing winds
to diminish significantly and then turn northwesterly late tonight
and into Tuesday. As the low moves away, winds will again pick up
and become strong during the day on Tuesday and persist into
Wednesday morning. Small craft advisories will likely be needed once
again and there may be another period of gales as well. Winds and
waves will then diminish on Wednesday as the low moves further into
Ontario.

&&

Preliminary point temps/pops...
dlh 47 40 43 33 / 100 70 70 20
inl 50 40 42 33 / 90 100 90 60
brd 50 37 40 31 / 100 90 70 0
hyr 52 40 44 34 / 100 70 80 40
asx 53 41 48 34 / 100 50 70 60

&&

Dlh watches/warnings/advisories...
WI...coastal flood advisory until 10 PM CDT this evening for wiz001.

Minnesota...coastal flood advisory until 10 PM CDT this evening for mnz037.

Ls...Gale Warning until 9 PM CDT this evening for lsz140>147.

Small Craft Advisory until 7 am CDT Tuesday for lsz148.

Small Craft Advisory until 9 PM CDT this evening for lsz121.

&&

$$

National Weather Service Glossary of Abbreviations