Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 160548 AAA
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1248 AM CDT Mon Apr 16 2018

.UPDATE...
Issued at 1230 AM CDT Mon Apr 16 2018

Updated for the 06z Aviation Discussion below.

UPDATE Issued at 1157 PM CDT Sun Apr 15 2018

Snow was slowly diminishing across the Northland late this
evening. Moderate to heavy snow was still occurring over portions
of central to northern Saint Louis County into the Arrowhead with
more moving into Douglas/Bayfield Counties. The wind has gradually
decreased as well and blizzard conditions look unlikely for the
rest of the night across Douglas County. The wind at
KDYT/KSUW/KDLH have been less than 35 knots for a few hours. We
changed the Blizzard Warning to a Winter Storm Warning for Douglas
County and dropped the headline across the southern CWA. The
Blizzard Warning for Ashland and Bayfield Counties continue.

UPDATE Issued at 919 PM CDT Sun Apr 15 2018

Snow, heavy at times, continued over much of the Northland. The
heaviest snow was located in a north to south band across
central/western Saint Louis County south into Pine County with
more heavy snow over Lake Superior into the Twin Ports region. We
extended the Advisories and Warnings for most of our southern
areas through midnight and upgraded the Winter Weather Advisory in
the Arrowhead to a Winter Storm Warning. We still expect the snow
to diminish in intensity for most areas overnight, it just may
take longer. The snow should diminish first in southern areas,
slowly working its way north late tonight into Monday morning.
Additional snowfall accumulation is possible on Monday in the
Arrowhead and along the South Shore.

The wind was slowly subsiding and that trend will continue but it
will remain windy along the South Shore.

&&

.SHORT TERM...(This evening through Monday)
Issued at 309 PM CDT Sun Apr 15 2018

Snow and blizzard conditions continue today with dangerous to near
impossible travel conditions across northwest Wisconsin and parts of
northeast Minnesota, including the Twin Ports. While no time is
great for a blizzard, the timing of this storm on a Sunday and
mainly wrapping up tonight should mean few people will venture out
on to the roads and road crews should be able to get the upper hand
against the weather in time for the Monday morning commute. Some
snowfall will linger into the day Monday but overall new snow
accumulation will be limited - the main focus is today/tonight.

On the synoptic scale the upper low associated with this spring
storm is centered over southern Iowa per RAP and 12z upper air
sounding analysis. Over the next 24 hours the upper level longwave
trough axis becomes negatively tilted with a 120-150 knot southerly
jet ahead of it, resulting in height falls over the lower Great
Lakes region. The surface low currently over the Ohio RIver Valley
will track north, with the deep moisture that has advected across
the Tennessee and Ohio valleys today being transported around the low
to the Upper Great Lakes region, supporting a continued supply of
deep moisture. This afternoon water vapor channel imagery from GOES-
16 vividly depicts this moisture transport process - while there has
been a brief break in the precipitation over parts of northern
Wisconsin today, the moisture transport continues to help saturate
low and mid levels of the atmosphere. This will come together as the
broad-scale lift intensifies today and tonight due to both the mid-
level PVA as the mid-level closed low tracks eastward and weak warm
air advection at low levels.

In addition to the broad-scale pattern, lake-enhanced bands of snow
are anticipated due to very favorable low level winds producing a
long fetch over Lake Superior. While temps aloft are somewhat
marginal (barely meeting the -12C to -19C ideal difference between
air and water temp) and there is some concern about the speed of the
low level winds producing too much turbulence to support long-last
bands, the plentiful low level moisture, broad scale lift already in
place, and very little directional shear is good enough to produce
locally higher snowfall amounts. At this point wind directions look
to favor more of a western Douglas county to eastern Carlton county
band, but this should shift west or east, or we could even see a few
different bands develop late today/tonight as winds shift to become
more north-northeasterly. Along the north shore today there may also
be a bit of terrain-driven enhancement along the ridge of higher
elevations.

.LONG TERM...(Monday night through Sunday)
Issued at 309 PM CDT Sun Apr 15 2018

The strong storm system will continue to move slowly east of the
region on Monday night and Tuesday. Some lingering snow showers will
be found across eastern portions of the region Monday night, and
along the south shore on Tuesday. A couple inches of snow will be
possible across the Gogebic Range of mainly Iron county. Otherwise,
Tuesday is shaping up to be a fairly quiet day with some sunshine
across most of the area. The long range models continue to show a
low pressure system moving across the Central Plains on Wednesday
and Wednesday night, but only indicate a small chance of
precipitation across our area. After Wednesday night, strong upper
level ridging will move into the mid section of the country. This
ridge will bring dry weather for the period from Thursday into
Sunday. Temperatures will warm from the upper 30s to lower 40s on
Tuesday, to the 50s on Friday, Saturday and Sunday. Overnight lows
will generally be in the 20s throughout the period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1248 AM CDT Mon Apr 16 2018

A broad area of light to moderate snow continues to move through
the Northland from east to west on the backside of a surface low
pressure currently situated near the Ohio River Valley. Flight
categories ranged greatly at the time of TAF issuances, so overall
confidence in these values are lower than average, but light to
moderate snow should continue for the next few hours, resulting in
MVFR/IFR visibilities. There is still quite a bit of dry air in
the low levels over KINL, as evident in the recent 00z sounding,
so kept visibilities and ceilings higher there. Conditions should
improve through the early morning hours or so in terms of snow
intensity, and mainly VCSH possible through the day Monday,
particularly along Lake Superior.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  21  35  20  39 / 100  20  10   0
INL  19  38  20  43 /  80  30   0   0
BRD  20  40  20  43 /  90  10   0   0
HYR  23  33  20  40 / 100  40  20   0
ASX  22  33  23  38 / 100  70  40  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Warning until 7 AM CDT this morning for WIZ001-004.

     Blizzard Warning until 7 AM CDT this morning for WIZ002-003.

MN...Winter Weather Advisory until 7 AM CDT this morning for MNZ011-
     019.

     Winter Storm Warning until 7 AM CDT this morning for MNZ012-020-
     021-037.

LS...Gale Warning until 4 AM CDT early this morning for LSZ121-
     140>148.

&&

$$

UPDATE...JTS
SHORT TERM...JJM
LONG TERM...DAP
AVIATION...JTS



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