Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 131511
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1011 AM CDT Thu Aug 13 2020

.SHORT TERM...(Today through Friday night)
Issued at 458 AM CDT Thu Aug 13 2020

Showers and a few thunderstorms have been percolating across the
southern half of the Northland overnight. These elevated storms
appear to be rooted along a mid level baroclinic zone, draped from
northern North Dakota southeast across the southern portions of
the forecast area and into northwest Wisconsin, which has some
warm air advection going on along it, as well as moisture
transport on the low-mid level flow moving northeast across the
boundary. In the next several hours I expect this boundary to lift
north across the area, continuing to generate spotty convection
along it. As the low level jet/850mb flow weakens for the early
morning hours the convection should gradually weaken and diminish
by mid to late morning. Back at midnight, the convection was
mainly focused over northwest WI, with mostly clear skies over
northern MN. This allowed temperatures to drop off into the 50s
overnight there. With storms forming farther west, cloud cover is
increasing over northeast MN, and expect temperatures to stop
falling off, and even start rising again already. Temperatures
will be slightly cooler than yesterday with the extra cloud cover
around, but only by a few degrees.

A low pressure system out over the MT/ND border will advance east
across ND today, allowing the warm front and mid level baroclinic
zone to shift north, with the surface boundary draped across the
area by this afternoon and evening. We expect thunderstorms to
form ahead of the surface low and accompanying cold front this
afternoon and evening as it crosses the MN/ND border. A decent
amount of low level instability should build ahead of the cold
front, but as has happened over the last few days shear is on the
weaker side. Still, this should come with a risk for severe
storms, mainly out in the Red River valley, but extends east into
the forecast area as depicted on the SPC day 1 outlook for today.
The later that storms move into the forecast area the less severe
weather we are likely to see, but I anticipate a busy night as
even marginal storms will need close watching as they slide across
the forecast area overnight tonight.

After the overnight convection either slides east of the area or
weakens and falls apart, things begin re-loading out over the
Dakotas. A strong shortwave moves toward the area from the west,
forming a new surface low along the low level baroclinic zone over
western SD tonight, which then moves northeast across the western
forecast area Friday afternoon and evening. With the strong
shortwave aloft, a very unstable airmass ahead of it and decent
shear in the area, am more confident in a greater risk of severe
storms, affecting more of the forecast area Friday afternoon and
evening. Right now SPC has placed us in a SLIGHT risk for Friday,
but this may be upgraded as the details become better defined.
Temperatures will be a little warmer on Friday than Thursday, as
we should get at least a short period of time with sunshine to
help build the instability.

Tonight`s event should be fairly fast moving, and while there will
be a lot of heavy rainfall due to the high precipitable water
content in the incoming airmass, flash flooding does not appear to
be more than an isolated risk. Friday night we will have a similar
high moisture atmosphere to work with, and a shortwave with
stronger dynamics moving across it. If we can get some repeat
thunderstorms over the same areas, the threat for flash flooding
increases.

.LONG TERM...(Saturday through Wednesday)
Issued at 458 AM CDT Thu Aug 13 2020

A ridge of high pressure should build into the area on Saturday
behind the Friday night convection, producing some quiet weather
for at least part of the day with warm temperatures and drier
humidity levels. This is short lived, as a fast moving shortwave
should bring a wave of showers and thunderstorms to mainly the
northern half of the area Saturday night.

Another ridge of high pressure builds into the area on Sunday and
Monday with north flow across the area producing cooler
temperatures for both days, with highs in the mid 60s to mid 70s.

The main upper level trough remains to our northeast through at
least the middle of the week, keeping northwest flow going aloft
and cooler temperatures for the area. There will be chances for
showers and thunderstorms through the middle part of the week as
shortwaves move through the upper level flow. Am less concerned
about severe weather for this time range due to the generally
cooler conditions and weaker upper level dynamics over the area.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 712 AM CDT Thu Aug 13 2020

A mixture of IFR, MVFR And VFR ceilings with VFR visibilities in
place this morning with a warm front draped across the region.
Expect these ceilings to slowly rise through 18z, with sites
returning to VFR no later than 20z. Isolated shra/tsra in vicinity
of KHYR, but may also affect KDLH, KHIB and KBRD until 16z.
Thunderstorms to move into the area from the west/northwest after
22z, sliding through the terminals through the remainder of the
TAF period. Timing is somewhat uncertain at this point, and we
will have to refine that in following TAF issuances. The
thunderstorms will be followed by a period of shra with MVFR
ceilings, and perhaps MVFR visibilities as well.

&&

.MARINE...
Issued at 1010 AM CDT Thu Aug 13 2020

Cloud cover will continue to increase this morning and afternoon, as
a warm front approaches the area from the southwest. A slight chance
of showers are possible this morning. Winds today will be out of the
northeast at 10 to 15 knots with gusts from Silver Bay to Sand
Island reaching up to 20 knots. At this time, a Small Craft Advisory
is not anticipated. Chances for showers and thunderstorms increase
this evening into overnight. A few storms late tonight into early
Friday morning may be severe. A shift in wind direction is expected
tomorrow, with winds transitioning to the southeast at 5-10 knots
ahead of an approaching cold front. Another round of showers and
thunderstorms are possible Friday evening. A few storms Friday
evening may be severe, with strong and gusty winds, large hail, and
heavy rainfall being the primary hazards. Waves over the next 48
hours are expected to be 3 feet or less, with locally higher waves
possible near severe thunderstorms.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  76  64  81  58 /  60  70  70  80
INL  81  64  79  52 /  40  80  70  60
BRD  84  67  82  55 /  20  60  70  50
HYR  82  63  83  59 /  60  60  50  70
ASX  83  65  86  61 /  70  60  50  70

&&

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

$$

SHORT TERM...LE
LONG TERM...LE
AVIATION...LE
MARINE...Unruh/Huyck


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