Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 150841
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
341 AM CDT Sat Jul 15 2017

.SHORT TERM...(Today through Sunday)
Issued at 341 AM CDT Sat Jul 15 2017

Hot and humid today with a chance for thunderstorms today across
parts of the MN Arrowhead and northwest Wisconsin, then clearing
skies as high pressure builds in from the northwest. This area of
high pressure will be centered over western Lake Superior by Sunday
morning, with cooler easterly flow resulting in highs limited to the
mid 60s along the shoreline, low to mid 70s inland.

On the synoptic scale the driving force behind sensible weather over
the Great Plains and Midwest this weekend is a longwave ridge
building east across the Rockies into the Plains, with the ridge
axis over the Upper Midwest by Sunday evening. A cool Canadian High
Pressure develops in response to this ridge, building from southern
Saskatchewan and Manitoba southeast towards the Upper Midwest late
today into tonight, centered over western Lake Superior on Sunday.
Ahead of this high pressure a fairly warm and moist airmass will
exist, with dew points rising to the mid to upper 60s today before
the cold front separating this warm and moist airmass with the
cooler and drier Canadian high pushing south across the region
during the afternoon today. As the front drifts south there is a
possibility for isolated showers and thunderstorms, limited mainly
to northwest Wisconsin as well as portions of the tip of the MN
Arrowhead. A strong cap may prevent convective initiation, but any
storms that can develop may become strong given 1500-2500 j/kg
MUCAPE and deep-layer shear around 35-40 knots. The better chance
for severe storms is further south into central and southern
Wisconsin later in the day into Saturday night. Otherwise hot and
humid today with highs in the low to mid 80s, though would not be
surprised if some spots near the Saint Croix River Valley hit 90.
Dew points in the mid to upper 60s will feel very sticky.

As high pressure builds in Saturday night winds will turn from
northwest to northeasterly, which may result in low level moisture
convergence along the south shore into the Twin Ports and thus some
low level clouds/showers Saturday night. Our colleagues at the NOAA
Space Weather Prediction Center indicate "G2" (Minor to Moderate)
geomagnetic storms are likely tonight, which if the polarity is
favorable would result in the aurora being visible across the
region. (See www.swpc.noaa.gov for more details.) With the
possibility for low level clouds along the south shore and Twin
Ports, the best chance for clear skies tonight will be inland areas
of east-central to northeast Minnesota. Lows falling to the 50s,
with a few spots in the 40s north of the Iron Range.

Sunny and comfortable Sunday with a light east wind and highs in the
mid 60s along the Lake Superior shoreline to low to mid 70s inland.

.LONG TERM...(Sunday night through Friday)
Issued at 341 AM CDT Sat Jul 15 2017

The Northland can expect a week of seasonably warm weather with
periodic opportunities for showers and thunderstorms. The main focus
is for late Monday afternoon and Monday night, which may bring a
period of strong to severe thunderstorms. There may be another
stormy period late in the week, some time late Friday or Friday
night.

There will be a surface high stretching from the northern Great
Lakes to Quebec as of Sunday evening. A forward-tilted mid-level
ridge will stretch from northern Minnesota to extreme northwest
Minnesota. There will be warm southerly flow across the Northern
Plains. A subtle shortwave trough and surface cold front will extend
from south-central Canada to Montana.

The surface high over the Great Lakes will continue to shift east
Sunday night and Monday, while the mid-level ridge will continue to
shift east and flatten as the shortwave trough to the west
approaches the Northland. It will be a warm day across the Northland
Monday with highs around 80, and even the middle 80s in the parts of
central Minnesota. The approaching shortwave trough will provide
modest large-scale forcing for ascent, which may be enough to help
trigger showers and thunderstorms along the cold front during the
late afternoon and evening. There is model disagreement on the
timing of the cold front, but it will most likely be somewhere over
or near northeast and central Minnesota late in the day. The
environment could be supportive of strong to severe thunderstorms.
The GFS, NAM12, and SREF indicate the potential for up to 3500 J/kg
of MUCAPE, 30 to 40 knots of 0-6 km deep layer wind shear, and 1.5
to 2 inches of precipitable water values. This environment would be
conducive for organized storm development, perhaps some discreet
supercells during the onset of storm development. The storms may be
somewhat isolated though considering the shortwave trough looks
fairly subtle and disorganized. Considering the high precipitable
water values, the storms could be capable of heavy downpours of
rain.

The cold front will slowly work its way through the Northland the
rest of Monday night and Tuesday. Another potential passing wave
could bring another period of stormy weather Tuesday and Tuesday
night, mainly to the southern forecast area from central Minnesota
into northwest Wisconsin.

Surface high pressure will likely bring a period of clearer weather
for the middle of the week. A subtle ridge and following up
shortwave trough could bring storms later in the week, most likely
late Friday or Friday night. The GFS, European, and Canadian models
suggest this wave may be the most potent of the forecast. Its too
far out, though, to speculate on the potential for severe weather.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1220 AM CDT Sat Jul 15 2017

Mainly VFR conditions expected through this period as a weak
disturbance and cold front will move across the region. A
southwesterly low level jet in place late this evening will bring
LLWS conditions to all TAF sites except KHYR through around 13z.
The low level jet and associated warm/moist advection pattern
could also result in isolate to scattered showers developing
overnight, along with at least some small risk for a thunderstorm.
However, limited areal coverage precludes a formal mention in the
TAFs. Some fog could also form at KHYR through around 12z with
some threat of MVFR visibility for a short time.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  84  54  68  50 /  10  20  10   0
INL  77  50  76  55 /  10   0   0  10
BRD  84  58  75  57 /   0   0   0   0
HYR  84  56  73  51 /  30  10   0   0
ASX  85  54  67  48 /  20  30   0   0

&&

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

$$

SHORT TERM...JJM
LONG TERM...Grochocinski
AVIATION...Grochocinski



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