Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 212011
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
311 PM CDT SUN AUG 21 2016

.SHORT TERM...(This evening through Monday)
Issued at 310 PM CDT Sun Aug 21 2016

An upper level trough continued to slowly move east this afternoon
as low level ridging moved into the Northland. There has been
plenty of cumulus this afternoon but showers have not
materialized. Warm air advection will strengthen tonight as the
ridge moves east. Mid to upper level clouds were already moving
into northwest Minnesota in response and that will continue
overnight. In addition to the clouds, some showers may develop in
far northern Minnesota exiting Monday morning. Another cool night
is expected, especially over eastern areas that will see the
clouds come in later. Light winds should allow for temperatures to
drop to the mid forties over the Arrowhead and over portions of
northwest Wisconsin inland from Lake Superior. There could also
be some patchy fog over parts of northwest Wisconsin.

A southerly flow will occur Monday and winds will become gusty as
mixing deepens through the afternoon. It will be a much warmer day
with highs for most areas from the upper seventies to lower
eighties. Areas along the North Shore will be cooler due to
the southerly flow.

.LONG TERM...(Monday night through Sunday)
Issued at 310 PM CDT Sun Aug 21 2016

Summary: An early week warming trend will culminate Tuesday, with
high temperatures building to between 10 and 15 degrees above
seasonal normals. A cold front, though, will move through the
Northland Tuesday night and Wednesday, bringing showers and storms,
followed by cooler air for the middle of the week. Temperatures will
bottom out Thursday, but then rebound to near seasonal normals by
the weekend.

A strong southwesterly low-level jet (about 40 to 45 knots) will
develop Monday night as the warm air builds into the region with an
approaching upper level ridge and as low pressure develops in the
northern High Plains. While there will be a lack of synoptic
support for overnight convection, the GFS and Canadian models are
indicating some precipitation across the Northland. Considering
the strong low-level jet, the potential for shortwaves in the
upper flow, and an elevated warm front likely near the southern
forecast area, there could be enough forcing to produce those
showers and storms, even though the majority of models are dry.
Therefore, maintained and refined a slight chance of showers and
storms across much of the Northland.

Tuesday is expected to be the culmination of the warming trend as
gusty southerly flow develops across the Northland in advance of an
approaching cold front in the Dakotas. The south-southwest flow
aloft will advect 850 hpa temperatures of 18 to 22 degrees celsius,
quite warm for the late summer, over the Northland. A cap from the
warm air aloft will likely suppress convection and low-level cloud
cover, and since temperatures will already start relatively warm
Tuesday morning, suspect the warmer model guidance is on the right
track. It should be a gusty day (20 to 25 mph, at least, but maybe
higher) as a low and its cold front move east across the Dakotas.
The highs will build well into the 80s, especially across the
western forecast area. Used a blend with a weighting towards the
GFS, which remains the warmest of the available guidance. Forecast
is for low 80s across the eastern forecast area, ranging to the
upper 80s across central to north central Minnesota, where the
humidity will result in heat indices in the 90s.

A potent upper level low over south central Canada, which will be
associated with a surface low in southern Manitoba, will begin to
catch up with the surface low Tuesday night. The Northland will
experience increasing upper-level support for convection Tuesday
night due to the falling heights from the approaching upper low,
as well as low-level convergence support from the cold front
moving into the Northland from the west. There is a good chance of
elevated overnight convection, tapping into the warm and humid
southerly low-level jet. The GFS indicates there could be up to a
few thousand J/kg of most unstable CAPE overnight, but deep-layer
wind shear looks fairly weak until behind the cold front.
Therefore, thunderstorms are probable overnight, but the threat of
severe weather is limited by the trailing wind shear. The
precipitable water values around 1.5 to 1.75 inches will promote
brief heavy rain with the showers and storms.

The Canadian model is about 6 to 12 hours slower than the GFS and
ECMWF at bringing the cold front and associated showers and storms
through the Northland. Leaned on the faster GFS/ECMWF/NAM12/SREF
models, but did trail low precipitation chances well into Wednesday
to account for the Canadian.

Much cooler weather will build into the Northland Wednesday into
Thursday in the wake of the passing front. Unless the slower Canadian
pans out, most of Wednesday should be dry, but expect partly cloudy
skies and breezy westerly flow. There could be showers across
northern Minnesota late Wednesday into Thursday when the much cooler
air builds into the region and the upper level trough/low passes the
International Border area. Highs will bottom out in the upper 60s
on Thursday.

Southerly flow will redevelop Friday, bringing a warming trend into
the weekend, with highs returning to the lower 70s. Showers and
storms are possible Friday night and Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1245 PM CDT Sun Aug 21 2016

The VFR conditions will continue through Monday afternoon.
The scattered/broken cumulus around 5 to 7 kft, as of early this
afternoon, will gradually clear later this afternoon into this
evening as high pressure moves into the region.

Southerly flow will develop tonight in the wake of the passing
high pressure to the east. A warm front will be near far northern
Minnesota and the Ontario/Manitoba border. A band of light rain
will likely cut east across the international border area during
the middle of the night, possibly bringing very light rain to KINL
around midnight. Left it out at this time since the rain will
likely have little impact.

A strong southwesterly low-level jet, of about 30 to 50 knots in
the 1 kft to 2 kft layer, will develop later tonight from west to
east. The northeast Minnesota terminals can expect a period of
significant low-level wind shear late tonight until a couple
hours after sunrise. Considered adding LLWS to KHYR, too, but not
confident the LLWS will be strong or lengthy enough to add at this
time.

Gusty south-southwest flow will begin to develop late Sunday
morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  52  81  64  85 /  10   0  20  10
INL  52  83  62  87 /  20   0  10  10
BRD  55  83  66  88 /   0   0  20  10
HYR  46  79  64  85 /   0  10  20   0
ASX  51  81  65  85 /  10  10  20  10

&&

.DLH Watches/Warnings/Advisories...
WI...None.
MN...None.
LS...Small Craft Advisory until 4 PM CDT this afternoon for LSZ148.

&&

$$

SHORT TERM...Melde
LONG TERM...Grochocinski
AVIATION...Grochocinski



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