Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 201744
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1244 PM CDT Thu Apr 20 2017

.UPDATE...
Issued at 1226 PM CDT Thu Apr 20 2017

Updated the 18z Aviation Discussion below.

&&

.SHORT TERM...(Today through Friday)
Issued at 337 AM CDT Thu Apr 20 2017

As expected, this morning`s precipitation type has been a challenge
as surface temperatures so far have been just warm enough for rain,
but a change over to snow in some locations is still expected
towards dawn. A mostly cloudy day as winds decrease and turn more
northerly, with occasional drizzle lingering through the day.
Decreasing clouds from west to east overnight as high pressure
builds in from the west leading to a sunny and warmer Friday.

Primary concern for this forecast is precipitation type over the
next 6-12 hours and snowfall accumulation potential. Model guidance
seems to have finally backed off the cooling trend observed in the
past 36 hours when some SREF members had snowfall amounts in excess
of 6 inches for parts of the Northland - some over a foot! This
seemed extremely unlikely just based on climatology and the large-
scale weather pattern in place, so it was nice to see the 21z and
now 03z SREF come in with much more reasonable (if still a bit high)
snow amounts. As of 3:00 am, surface wet bulb temps all remain
safely above freezing around 34-36 in locations where the risk for
snowfall is greatest. Radar and surface obs depict precipitation
expanding in coverage across northern Minnesota while a dry slot
builds into west-central Wisconsin. This precipitation shield is
expected to continue to expand and increase in intensity through the
early morning hours as a vort max associated with the mid-level
longwave trough over the northern Plains this morning advects into
the upper Midwest. This will cause a period of mid-level large-scale
lift and in some places may be just enough to produce the diabatic
cooling rates needed to change precipitation over from rain to snow,
especially towards dawn in the higher terrain of Duluth and north
along the north shore.

Snowfall amounts have not changed much over the previous 24 hours
with around 1-3 inches possible for higher terrain areas, though
unless snowfall rates are especially vigorous snowfall will probably
melt when it hits road surfaces. Just as fast as the precipitation
changes over to snow, it will likely go back to rain by mid-morning
as the strong solar heating of mid-spring leads to surface
temperatures warming up. Subsidence builds in as the mid-level
longwave trough/upper low moves east towards the upper Great Lakes
this afternoon and eventually high pressure builds in from the west.
Still, occasional drizzle is possible through the day given the
saturated low levels.

Highs today in the upper 30s to mid 40s, except west of
International Falls where highs may approach the low 50s. Northwest
winds at 10 to 15 mph near Lake Superior gradually diminish late
today, though occasional gusts up to 30 mph remain possible through
the morning hours. Lows tonight in the low to mid 30s as winds
become northwesterly and light at around 5 mph or less. Then warmer
and dry Friday with highs in the mid 50s to low 60s with a light
north wind at 5-10 mph.

.LONG TERM...(Friday night through Wednesday)
Issued at 337 AM CDT Thu Apr 20 2017

High pressure will move through the Northland Friday night providing
dry conditions into Saturday morning. A cold front will be moving
out of Canada making it to southern Lake Superior west to the North
and South Dakota Border by 00Z Sunday. The models have come into
better agreement on the timing of the front although the GFS is a
bit faster than the ECMWF. Light rain will be possible mainly behind
the front Saturday afternoon, generally north of Highway 2 in
northern Minnesota. Highs are expected to warm into the mid fifties
north to lower to middle sixties elsewhere. Minimum humidty values
will drop to 25 to 35 percent for most areas but wind speeds will be
less than 15 mph for most areas limiting the fire danger, although
there may be some higher gusts during the afternoon.

The front will continue a bit further south Saturday night before
returning north as a warm front. A chance for precipitation will
occur Saturday night into Sunday over portions of the Northland due
this boundary. Mainly light rain will occur during the day with a
mix or just snow at night.

The chance for precipitation will increase Sunday night into Tuesday
as low pressure moves through the region. The surface low will lift
into South Dakota by 12Z Monday moving into the western Great Lakes
by early Tuesday evening. The models are in decent agreement
considering the system is still several days away. Forcing will be
on the increase Sunday night as stronger southerly flow develops.
Temperatures will be cold enough for a wintry mix or just snow
Sunday night into early Monday morning. The best chance for
widespread precipitation will occur Monday and Monday night as the
main shortwave moves through the region. A mix or just snow will be
possible overnight as boundary layer temperatures cool with mostly
rain during the day. Some snow accumulation will be possible, mainly
over northern portions of Minnesota from Sunday night through Monday
night.

Any period of dry weather after the low pressure system departs will
be brief as another shortwave/low pressure system brings the
potential for more precipitation to the region as early as
Wednesday but more so late next week into the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1226 PM CDT Thu Apr 20 2017

Sfc low pressure continues to move northeast across southern Lake
Michigan and into west central Michigan this afternoon. The
circulation around this low has brought mainly a northeasterly
flow over the Northland, along with some gusty northeast winds and
a mix of light rain and some snow as well. The snow is expected to
remain along Lake Superior this afternoon, with rain and drizzle
away from the lake. Mainly MVFR/IFR ceilings and visibilities are
expected to continue, with some isolated LIFR ceilings possible
over KDLH this afternoon.

There may be some patchy fog developing tonight as well, mainly
for KDLH and KHYR TAF sites, possibly at KBRD and KHIB as well,
although confidence is not as high for KBRD and KHIB. Conditions
expected to improve during the day Friday.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  39  32  54  31 /  90  20   0   0
INL  48  34  61  34 /  40  10   0   0
BRD  46  34  60  35 /  80   0   0   0
HYR  40  33  57  28 /  80  10   0   0
ASX  38  33  53  29 / 100  50   0   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Gale Warning until 4 PM CDT this afternoon for LSZ140>147.

     Small Craft Advisory until 10 PM CDT this evening for LSZ121-148.

&&

$$

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



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