Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 232037
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
337 PM CDT MON MAY 23 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 337 PM CDT Mon May 23 2016

Main concerns for the short term is thunderstorm potential this
evening, associated rainfall, and relative humidity for Tuesday.

Fairly warm conditions were found across the area this afternoon
with low 70s in Brainerd Lakes vicinity to the low 80s over
northwest Wisconsin and in a few locales in northeast Minnesota.
This morning`s quasi-stationary front has advanced to just west of
a line from International Falls to Cass Lake to Staples. A few
thunderstorms had developed just ahead of the front in Koochiching
County during the past few hours.

Overall the guidance is struggling with temps and dewpoints
across the area and seems to be attributing too much influence to
the thin cloud layer. High resolution models are not capturing
incipient storm development over Koochiching County, but rather
expecting storms to fire along and east of I-35 south of Duluth.
Those storms seem to have begun to fire over central Minnesota
into west-central Wisconsin in the past hour. Started with blend
of the high resolutions models for clouds and POPs with some heavy
hand editing to attempt to capture trends. SPC is continuing to
carry a Marginal Risk of severe thunderstorms this evening and
agree with that thinking at this point. Moisture is surging north-
northeastward from southern Minnesota toward my southeast Minn-
esota zones and northwest Wisconsin and MLCAPE and MUCAPE values
along with that moisture surge have been increasing during the
late morning and afternoon. Still think storms will fire along and
east of I-35 by early evening, but slowed timing from previous
forecast. Precipitable water values of 1.2 to 1.5 inches are
already found across much of the area and are expected to increase
a few more tenths by early evening. Expect showers and storms to
be scattered in coverage, with many locales seeing only enough
rain to wet the pavement, and areas under the heavier thunder-
storms seeing up to an inch of rain. A few of the more vigorous
storms may produce some large hail this afternoon and early this
evening. A stray wind gust or two to 40-50 knots is not out of
the question, either.

Thunderstorms should coalesce into two lines, with the first near
the frontal boundary over my western and northern zones, and the
second farther east along the developing instability gradient east
of I-35 into northwest Wisconsin. Once the storms become more
numerous, think the hail threat will diminish, but could still see
a few downdrafts with wind gusts in the 30-40 kt range possible.
Activity will shift eastward with time with only isolated showers
lingering in my far eastern zones by 24.12Z. Areas of fog are
expected tonight as showers and storms clear out and winds
diminish.

Clouds should clear on Tuesday with temperatures recovering
nicely into the 70s to low 80s. Dewpoints and RHs will depend
largely on the coverage and amounts of precipitation tonight, so
confidence in those parameters is low with this package. At this
point expect minimum RH values Tuesday afternoon in the upper 20s
to low 50s. With a little more mixing, and less rainfall, critical
RH values are possible on Tuesday.

.LONG TERM...(Tuesday night through Monday)
Issued at 337 PM CDT Mon May 23 2016

The mid-week through coming weekend period will be characterized
by southwest to south flow aloft across the Upper Midwest and
western Great lakes region as mean troffing remains in place
across the northern Rockies and northern Plains. As was mentioned
this morning, there will eventually likely be several periods
where there is minimal to no precip across the Duluth CWA, but due
to model differences in both placement and timing, it is nearly
impossible to remove POPs from any specific time period due to the
inherent uncertainty several days out. The uncertainty in the
various forecast model mass/moisture fields is complicated further
by the cumulative integrated effects of daily convective evolution
as well.

With all of the above in mind, there do appear to be a couple of
periods where we might be able to add a bit more confidence to a
broad-brush forecast.  First, a more discernible and significant wave
is forecasted to eject northeastward across the Dakotas/western
Minnesota sometime late Tue night into Wed night, with an
associated surface low closing off somewhere over the Red River
Valley. Perhaps just as important, most of the same models have
low level ridging developing to the north of Lake Superior late
Tue/Tue night. With pressure falls developing to our W/SW on Wed,
this type of a set up in May typically results in a rather
strong/reinforced marine layer becoming entrenched across much of
northern MN that is typically very hard to dislodge, and even
more difficult to dislodge if rain spreads atop it, as is forecast
for Wed/Wed night. As such, we have lowered temps across the board
on Wed, and nudged wind speeds/gusts upward from guidance,
especially over the southwest arm of Lake Superior and adjacent
land areas. Overall, the late Tue night into Wed night time frame
could end up being a very cold/windy/wet period for just about all
locales to the northwest of the I-35 corridor, and in particular
in the Duluth-Superior area.

While much of the Thur-Fri time period appears to have lesser
chances for widespread showers/Tstorms, there will still likely be
at least some risk.  The best chances appear to be across northwest
Wisconsin both Thursday and Friday afternoons based on currently
available data.  The second period which appears to have higher
confidence at this time is Sat/Sat night as another rather
significant shortwave trof ejects northeastward into the western
Great Lakes region. This is much more uncertain, however, being
five days out at the current time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1254 PM CDT Mon May 23 2016

A weak front/trof axis lies along the western CWA border as of
midday, and the low level convergence axis associated with this
front will be the focus for the development of showers/T-storms
as it moves slowly eastward through this evening. we have carried
MVFR conditions at most taf sites along with tempo groups for
TSRA between roughly 20-21z and 00-02z, although KINL will begin
a bit earlier. Winds are expected to become more southwest for a
few hours after TSRA end, but should then go light/variable
overnight with a very weak gradient, and this is expected to
result in favorable conditions for fog 08-13z Tue morning. The
highest probabilities for ifr conditions will likely be at the
favored fog locations of KHIB/KHYR.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  55  76  49  63 /  80  30  10  50
INL  51  81  52  73 /  30  30  20  50
BRD  56  82  55  73 /  60  10  10  60
HYR  60  79  53  74 /  80  10  10  50
ASX  57  73  47  65 /  80  20  10  50

&&

.DLH Watches/Warnings/Advisories...
WI...Red Flag Warning until 8 PM CDT this evening for WIZ003-004-009.

MN...None.
LS...None.

&&

$$

Short term...Huyck
Long term...Miller
Aviation...Miller


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