Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 210534

Area Forecast Discussion
National Weather Service Duluth MN
1234 AM CDT Sun May 21 2017

Issued at 904 PM CDT Sat May 20 2017

The back edge of the main area of rain is continuing to make
steady progress northward this evening, as the dry slot evident in
GOES-16 band 10 water vapor imagery continues to rotate northward.
Steady rain should be confined to the northern part of the CWA
for the rest of the night, with a south to north decreasing trend
with time.

With that said, there is still decent forcing for ascent within
the dry slot as evidenced by redevelopment of showers from the MSP
metro area into northwest Wisconsin. This is in an area of
moderate forced ascent per QG diagnostics and decreasing
stability, so we expect continued redevelopment of showers in this
area for much of the night, just not the widespread steady rains
of the past several hours. Finally, the rapid development of fog,
very low stratus clouds, and drizzle has followed within an hour
or so of the end of the steady rain, and this will likely spread
northward with the leading edge of the dry slot aloft through the
rest of the night.


.SHORT TERM...(This evening through Sunday)
Issued at 401 PM CDT Sat May 20 2017

Light to moderate rain showers will continue to expand northward
this afternoon and evening as a mid- to upper-level trough,
characterized by upper-level diffluence and stronger isentropic
lift at the mid-levels, will continue to ascend into the area.
Some 850-700 mb layer warm air advection will also provide
additional support for these rain showers. There have been reports
of some sleet with the leading edge of the precipitation shield,
which should continue through the afternoon, but taper off by the
evening as warmer low-level air moves in. There is the potential
for some thunderstorms, especially over northwest Wisconsin and
adjacent counties of northeast Minnesota. MUCAPE instability
values look to increase after midnight tonight due to steepening
mid-level lapse rates. Winds will remain gusty into the evening
and early Sunday morning hours before gradually weakening through
the night-time hours. Strongest wind gusts will remain over
adjacent locations near Lake Superior as winds remain from the
east and northeast, providing better fetch to intensify these
winds. The NAM model was indicating the potential for some light
snow over Itasca and Koochiching counties mainly after midnight.
However, if it does occur, it should be brief, and not expected to
lead to any accumulation as the sfc temperatures are just too
warm for it.

As the sfc low pressure center drifts closer to the region, there
may be a brief period of drier conditions over northwest Wisconsin,
due to a dry slot, mainly between 03z and 07z Sunday, as evidenced
by the latest HRRR/NAMNest models. Reduced the POPs accordingly over
this area. However, a corridor of positive vorticity advection will
bring another round of showers of northwest Wisconsin after 07z,
again as per the HRRR model.

Rain showers should turn to more drizzle on Sunday, especially over
our southern counties, due to decreasing moisture depth as seen in
the 20.12z NAM/GFS soundings. The NAM soundings indicate the depth
of the saturation layer to be around 6000 ft, which is sufficient
moisture depth for drizzle. Moreover, Pwat values gradually decrease
through the day Sunday. Still expecting chances of rain showers to
linger over most of the Northland through the day Sunday, with the
best chances lingering over the Iron Range and Arrowhead regions.
Overall rainfall amounts up to three-quarters of an inch will be
possible by Sunday evening.

.LONG TERM...(Sunday night through Saturday)
Issued at 355 PM CDT Sat May 20 2017

The large upper low over the region will continue to wobble slowly
north Sunday night through Monday night, keeping a chilly airmass
over the area with chances for rain/drizzle.  Even as the low drifts
farther away from the area on Tuesday, a shortwave dives into the
area on the back side of the low to generate still more clouds and
showers.  With the cloud cover, temperatures will only get into the
50s both Monday and Tuesday, with overnight lows in the mid 30s to
low 40s.

Tuesday night there is potential for clearing and drier air to move
into the area from the north, and with the north flow continuing, we
are likely to have another cold night, with lows around freezing
possible in the Arrowhead.  We will have to watch this, as there may
be need of a frost/freeze headline.  This area got down around
freezing the last two mornings, as well as a week ago so there
probably won`t be much of an impact yet.

Upper level ridging builds into the area for Wednesday and
Thursday, which should bring us a period of warmer and drier weather
for both days.  However, towards Friday the ridge shifts far enough
east to allow chances for rain to return to the area for Friday and
Saturday.  Would not be surprised to see this pushed later as the
ridging pattern is somewhat blocky in nature and may slow down in
later model runs.  The return of southwest flow will also bring
above normal temperatures back to the region for the later part of
the week.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1233 AM CDT Sun May 21 2017

Low pressure will move northeastward from southern Minnesota late
tonight to just north of Lake Superior by late Sunday night. Rain showers
and drizzle will persist with the low over the region. Due to moisture in
the lower levels, expect ceilings to range from LIFR to MVFR through the
forecast per the latest RAP/NAM and HRRR guidance. In addition to the low
ceilings, expect visibility reduction due to fog. Expect visibilities to
gradually improve during the day Sunday due to daytime heating and
increasing surface winds. Wind directions will gradually change from
easterly to westerly/northwesterly as surface low moves into Lake


DLH  37  48  40  56 / 100  70  50  30
INL  40  49  41  53 /  80  80  50  50
BRD  39  50  41  60 / 100  40  40  30
HYR  44  53  42  58 /  90  70  50  30
ASX  39  51  41  57 / 100  70  50  30


LS...Small Craft Advisory until 10 AM CDT this morning for LSZ121-



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