Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 220935
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
435 AM CDT Sat Jul 22 2017

.SHORT TERM...(Today through Sunday)
Issued at 435 AM CDT Sat Jul 22 2017

At 430 AM, it was fairly quiet across the Northland. No showers
or thunderstorms were within our CWA borders at 430, although a
line of strong thunderstorms was moving toward our far southwest
CWA. There was quite a bit of fog across the Northland, with
localized visibilities down to a quarter mile. Temperatures ranged
from the lower 50s in the north to the mid 60s further south and
in several locations near Lake Superior.

The main focus for today will be the threat of severe weather. SPC
has our area in a Slight Risk, given a pre-frontal trough expected
to deepen over Minnesota during the day. A major upper level
shortwave will provide ample cooling aloft and substantial height
falls to produce a risk of severe thunderstorms across the entire
CWA this afternoon and tonight. The main risk will be very large
hail due to cold air aloft and strong westerly winds aloft, but
also a risk of damaging winds. CAM`s are all over the place, so
will tie the best chance of thunderstorms in with time of peak
heating and location of surface and upper level features. Will
generally keep POP`s in the scattered range, rather than likely,
as a good deal of the guidance indicates more scattered coverage.
Highs today are generally expected to reach the lower 80s.

Showers and thunderstorms should diminish tonight, as the upper
level trough/low move east, and the best forcing moves with it. A
few storms could even linger into Sunday morning, with the upper
low/shortwave lingering in the Lake Superior region for a time.
High pressure and building heights will then result in a drying
trend for the afternoon. Highs will be a bit cooler on Sunday,
with mainly 70s across the region.

.LONG TERM...(Sunday night through Friday)
Issued at 435 AM CDT Sat Jul 22 2017

Seasonal temperatures ahead for the long-term with a few
thunderstorm chances Monday night through Wednesday morning, then
again Thursday night.

Not much change in the forecast Sunday night through Wednesday
morning. Mid-level ridging will build into the Upper Midwest
Sunday night and continue on Monday with surface high pressure
drifting southeastward across the Northland. Mainly clear to
partly cloudy skies are expected with temperatures rebounding
into the low to upper 70s for Monday afternoon.

A shortwave trough is forecast to move across the northern
Canadian Prairies Monday night and Tuesday, with a surface low
moving from central Alberta to far northwest Ontario by Tuesday
night. A cool front will stretch to the southwest of the surface
low and should provide a focus for showers and thunderstorms late
Monday night through Tuesday evening. Winds aloft will turn south
to southwesterly Monday as the ridge passes east of the
Northland. A robust surge of higher theta-e air will advect
northward ahead of the approaching front, nosing into western
Minnesota Monday night and into the Northland on Tuesday.
Precipitable water will increase in the southerly warm air
advection as well with forecast values in the 1.5 to 2.0 inch
range, well into the 90th percentile for late July. Strong to
severe thunderstorms are possible Tuesday afternoon and evening.

A mid-level ridge will amplify over the western United States
Tuesday night and Wednesday with northwest flow developing over
the Northern Plains and Upper Midwest. A few showers are possible
Wednesday afternoon, but generally drier conditions are expected.
Weak surface high pressure is forecast to move through the
Dakotas and into Minnesota leading to partly cloudy skies.
Temperatures won`t cool much for Wednesday, only a few degrees
from Tuesday`s highs. Thursday should be relatively quiet as well
before a weak shortwave trough rides the northwesterly flow into
the Northland Thursday night and Friday morning. A few showers or
thunderstorms are possible as the disturbance moves through. High
temperatures Thursday and Friday will be in the low 70s to low
80s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1256 AM CDT Sat Jul 22 2017

Shower/storm coverage has been on the decline over the past
couple of hours and that will continue over eastern areas with an
increase again from west to east later tonight into Saturday. An
upper level shortwave will continue to move east-southeast toward
the Manitoba/northwest Ontario/Minnesota border by 18Z Saturday.
The shortwave will continue to western Lake Superior Saturday
night. A frontal boundary will also be moving through the
Northland and strong to severe thunderstorms will be possible
Saturday afternoon into the evening over portions of the
Northland. We highlighted time periods where we have the most
confidence some storms will occur but timing will continue to be
refined through the period.

Fog was already forming as of late evening and we expect that to
continue. IFR/MVFR conditions will expand tonight then improve
through the day Saturday.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  73  57  70  52 /  50  40  20   0
INL  80  56  76  53 /  60  40  10   0
BRD  85  60  75  55 /  20  10  10   0
HYR  81  58  71  51 /  40  30  20   0
ASX  73  56  67  51 /  50  40  20   0

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

SHORT TERM...DAP
LONG TERM...Huyck
AVIATION...Melde


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