Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 202349 AAA

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
649 PM CDT Sat May 20 2017

Issued at 649 PM CDT Sat May 20 2017

An updated aviation discussion is below for the 00z TAF issuance.


.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 00Z TAFS through 00Z Sunday evening)
Issued at 649 PM CDT Sat May 20 2017

Widespread light/moderate rain has spread across all terminals
except KINL as of 2330z, and is expected to begin within the next
few hours at KINL as low pressure over Iowa slowly moves
northeastward through the 24 hour period. Confidence is rather
high in conditions continuing to deteriorate to MVFR and
eventually IFR in most location overnight and persist for much of
Sunday. While widespread light/moderate rain is expected to
diminish in coverage/intensity after the first 4-6 hours, the
development of widespread low ceilings and fog is expected area-
wide. Winds should slowly back to north and eventually northwest
by the end of the period as the center of the low pressure area
moves to Lake Superior.


DLH  38  48  40  56 / 100  70  50  30
INL  40  49  41  53 /  80  80  50  50
BRD  40  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 Sunday for LSZ121-140>143-

     Small Craft Advisory from midnight tonight to 10 AM CDT Sunday
     for LSZ144-145.

     Gale Warning until midnight CDT tonight for LSZ144-145.



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