Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 191959
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
259 PM CDT Tue Sep 19 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 259 PM CDT Tue Sep 19 2017

A cold front will move from west to east across the Northland
tonight with a line of showers and storms expected. Thunderstorms
may be strong to severe with a potential for large hail, damaging
winds, and intense rainfall, especially for portions of north-
central into east-central Minnesota. Rain showers are expected to
linger through Wednesday morning, ending towards the afternoon with
skies clearing out and west winds increasing in northern Minnesota.

On the synoptic scale a broad upper low is spinning over the
Canadian Rockies with an accompanying elongated surface low/front
stretching from central Alberta, southeast to southern Manitoba and
south into the northern Plains. Strong southerly flow ahead of this
front is resulting in warm air advection across the Northland today,
and combined with clearing skies temperatures are in the 70s with
dew points in the low 60s. A broad area of showers and few embedded
storms exist across the central Dakotas this afternoon, with
elevated instability advecting north ahead of this front expected to
result in upscale growth of thunderstorms along and ahead of the
front into the evening. Storms will cross into western Minnesota
this evening supported by strong upper level winds aloft and a
strong low level jet, creating an environment with sufficient deep
layer shear to sustain storms.

The primary concern tonight will be how long strong/severe storms
remain organized as they come into north-central Minnesota and
further east tonight will be the state of instability, with maybe
1000 j/kg MUCAPE anticipated to be present when storms cross into
the region. The strong shear and intense low level jet (on the order
of 60 knots) may make up for a the lesser amounts of instability,
producing damaging wind gusts. Intense rainfall is also anticipated
given the unusually moist low levels for early fall, but the line of
storms is expected to be progressive enough (because of the strong
winds at low/mid levels) to preclude a widespread flash flooding
risk. (Still, the intense nature of the rainfall could result in
minor flooding/ponding.) Hail threat seems minimal given the
decreasing amount of instability, though storm mode may favor some
large hail early on.

Based on current convective activity and short-range guidance, there
still remains uncertainly as to just how far east the strongest
storms make it. One scenario may be a few stronger storms along the
line persisting to about the Highway 53 corridor in northern MN
before dissipating, or if storms become more linear in nature, a
line of storms could progress southeast down the instability
gradient stretching from north-central to east-central Minnesota
(from Bemidji southeast to Moose Lake, for example). It also remains
possible that storms dissipate before reaching the north-central MN,
though at this point this does not appear a likely scenario.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 259 PM CDT Tue Sep 19 2017

A warm end to the work week, along with chances of showers and
thunderstorms Friday through Monday, with some storms possibly
strong to severe.

Generally, the Northland will remain under an active weather pattern
through much of the upcoming week as a mid- to upper-level low is
progged to build over the Pacific Northwest/Alberta region Wednesday
night. The Northland should be dry through Thursday afternoon as sfc
high pressure builds in behind the remnants of a cold
front/shortwave trough that will bring showers and storms to the
region overnight tonight through Wednesday morning. A strengthening
120 to 130 kt upper-level jet will dig a longwave trough adjoining
the upper-level low. This trough will linger over the Intermountain
West through the weekend, placing the Northland under strong
southwest flow aloft, and enhanced isentropic upglide. Multiple
impulses of shortwave energy will eject over the Northland, mainly
from Friday evening through the weekend. Moreover, the sfc high
pressure from Thursday will then advance eastward, bringing
southerly return flow on the windward side of the high, increasing
thermal and moisture advection.  In fact, there is the potential for
breaking high temperature records for Friday, and the record high
low temperature Saturday morning for Duluth. Dew point temperatures
Friday afternoon and evening could rise into the upper 60s and even
lower 70s over our southern counties, along with heat index values
in the middle to upper 80s from the Brainerd Lakes eastward over
northwest Wisconsin Friday afternoon.

Severe weather potential will exist for Friday as the 19.12z
guidance is indicating moderate to high MLCAPE values, along with an
enhanced low-level jet impinging on the warm air mass. Deep layer
shear could increase to the 40 to 50 kt range, providing good shear
for storms to tap into as well. Along with the severe weather
potential, heavy rainfall will also be a concern as Pwat values
increase into the 1.5" to 2.0" range, per the 19.12z GFS. These
values would be >99% of climatology per the NAEFS climatological
percentiles for Pwats. Moreover, Corfidi forward propagation vectors
will be parallel to the baroclinic zone, which could lead to
training convection. Flash flooding will be possible if this set-up
comes to fruition.

Chances of showers and storms will continue Monday and Tuesday, but
chances will be smaller compared to those from Friday through
Sunday. Temperatures will also moderate to values closer to seasonal
averages, with highs in the middle 50s north to the lower to middle
60s south.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1236 PM CDT Tue Sep 19 2017

A messy aviation forecast expected for this evening and overnight
as an area of low pressure situated over northwest North Dakota
will lift into Manitoba and bring a cold front boundary through
the region tonight. This front could support strong to severe
storms with it, especially after midnight. Large hail and damaging
winds will be the main threats with these storms. Also, a strong 40
to 50 kt southerly low-level jet will impinge on the front,
leading to high confidence in low-level wind shear at all of the
TAF terminals. Some MVFR to LIFR ceilings are expected as the
front passes through, along with some MVFR to IFR vsby reductions
due to the heavy rain potential with these storms.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  59  67  49  71 / 100  50   0  10
INL  60  65  45  73 / 100  60   0  10
BRD  61  68  49  75 / 100  30   0  10
HYR  63  73  46  77 /  70  50   0  10
ASX  59  75  46  75 /  50  50   0  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement until 8 PM CDT this evening for WIZ001.

MN...Beach Hazards Statement until 8 PM CDT this evening for MNZ037.

LS...Small Craft Advisory until 10 PM CDT this evening for LSZ144>146.

     Small Craft Advisory until 4 PM CDT Wednesday for LSZ140>142.

     Small Craft Advisory until 10 AM CDT Wednesday for LSZ143.

&&

$$

SHORT TERM...JJM
LONG TERM...JTS
AVIATION...JTS



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