Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 182338
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
638 PM CDT Tue Jul 18 2017

.UPDATE...
Issued at 638 PM CDT Tue Jul 18 2017

Made some adjustments to lower overnight temperatures across the
Iron Range and points north, and expand fog mention in the
forecast tonight. Also nearly removed precipitation chances as the
last of the showers are just exiting Price County now.


&&

.SHORT TERM...(This evening through Wednesday)
Issued at 317 PM CDT Tue Jul 18 2017

At 20z, showers and isolated thunderstorms that have formed along a
cold front boundary will continue to advance eastward over northwest
Wisconsin. Currently, these storms are not severe, although some
stronger storms may develop over our far eastern counties of
northwest Wisconsin, with the main threats being large hail and
damaging winds. MLCAPE values will range from 500 to 1500 J/kg and
effective bulk shear in the 30 to 40 kt range along the front.
Additional support will be given by a mid-level shortwave trough
that will provide enhanced isentropic lift attendant with the front.
Some heavy rainfall will also be possible due to abundant moisture
ahead of the front. Pwat values look to range between 1.5 to 2.0",
which is >90% of climatology from the NAEFS analysis. So, some
ponding of water, and perhaps some localized flooding is possible,
especially over areas that were impacted from showers and storms
from yesterday. However, any strong to severe storms that do develop
will move off to the east quickly.

Overnight should be much quieter around the Northland as an area of
high pressure moves into the region. Mid-level zonal flow will
build, along with the high pressure. Skies will become mostly clear
overnight, except for some lingering clouds over north-central
Wisconsin. Due to the clear skies and light winds over Minnesota as
the high pressure ridge moves through the region, low temperatures
will drop rapidly tonight. Lows tonight could drop into the lower
50s and even lower 40s in some isolated spots over north-central
Minnesota. Most of the day Wednesday will be dry, but clouds will be
on the increase from west to east as another mid-level shortwave
quickly moves in behind the sfc high. I slowly increased POPs
Wednesday afternoon as this wave approaches. There is some
uncertainty how quickly to increase chances of precipitation as
there is disagreement between the convective-allowing models and the
synoptic models, so limited POPs before 00z Wednesday mainly over
the western one-half of the CWA. High temperatures Wednesday will
return to more seasonal values, into the lower 80s for most
locales.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 317 PM CDT Tue Jul 18 2017

A typical mid summer pattern will continue throughout the long term
period, with warm air and periodic opportunities for showers and
thunderstorms. Wednesday night is the first such opportunity for
showers and storms, although there is some fairly strong
disagreement amongst the deterministic models. The 12Z NAM appears
to be the biggest outlier, bringing a large swath of precipitation
across much of the CWA Wednesday night. The GFS is furthest south,
generally south of our CWA entirely, while the ECMWF is a compromise
solution in between the NAM and GFS. SPC has issued a Slight Risk
for Severe Thunderstorms just south of our CWA, more in line with
the ECMWF and to some extent the GFS. Given those inconsistencies,
but favoring the ECMWF, will carry the highest POP`s across the
southern third of the Northland, with lesser POP`s northward. In any
regard, the best chance of severe thunderstorms, either from the
NAM, GFS or ECMWF would be south of our CWA. The main question is
whether MCS activity will develop further north as well. High
pressure will move in behind the system, bringing dry weather for
Thursday and most of Thursday night. Another shortwave and elongated
area of low pressure will move into the Northern Plains on Friday,
bringing the next chance of showers and thunderstorms to the region
on Friday and early Friday evening. Saturday and Sunday represent
the best chance of showers and storms for this weekend, although
there are some pretty important differences between the GFS and
ECMWF. The ECMWF amplifies an upper level trough and surface low
over the Lake Superior region over the weekend, while the GFS
generally keeps it in Ontario. The differences are amplified over
the weekend and into early next week, so confidence in any
particular solution is fairly low. Highs throughout the period will
range from the 70s to lower 80s, while lows range from the 50s to
lower 60s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 638 PM CDT Tue Jul 18 2017

High pressure building in will lead to clear skies overnight into
much of Wednesday. There is a possibility for fog tonight at most
sites, with IFR to LIFR visibility expected at times at HIB and
HYR based on current trends, short-range models, and climatology
for these sites. Wednesday morning any fog that developed
overnight will quickly dissipate with clear skies for much of the
day. Some increasing VFR clouds from west to east in the
afternoon, with a shower or thunderstorm possible at BRD towards
00z. Winds nearly calm overnight, becoming southerly at 5-10 knots
Wednesday afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  54  82  59  83 /   0  10  30  10
INL  49  80  56  82 /   0  10  10   0
BRD  55  82  62  85 /   0  30  40  10
HYR  53  83  62  84 /  10  10  40  10
ASX  55  85  59  84 /  10  10  30  10

&&

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

$$

UPDATE...JJM
SHORT TERM...JTS
LONG TERM...DAP
AVIATION...JJM



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