Area Forecast Discussion
Issued by NWS Duluth, MN

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492
FXUS63 KDLH 241807 AAC
AFDDLH

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
107 PM CDT TUE MAY 24 2016

.UPDATE...
Issued at 1256 PM CDT Tue May 24 2016

updated aviation discussion below for 18z taf issuance.

&&

UPDATE Issued at 1050 AM CDT Tue May 24 2016

Main update was to reflect convective trends from this morning and
lingering cloud cover. Trended temps slightly cooler through
remainder of morning over northern Minnesota and portions of
northwest Wisconsin where clouds are limiting heating thus far
today. Still think skies will become partly cloudy and temps will
recover by afternoon, so only negligible reductions in max temps
with this package.

Continuing to watch advancing shortwave moving through northwest
Minnesota. Storms over Hubbard and Beltrami seem to be along
leading edge of vort max and along the northern periphery of
1000-1250 J/kg of MUCAPE. International Falls sounding from this
morning supported around 750 J/kg for parcels lifted from above
the stable boundary layer. Have no reason to suspect much less
farther south. Think storms may re-intensify and expand in
coverage along the leading edge of the large scale ascent and on
the CAPE gradient by early afternoon over north-central and
northeast Minnesota.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 345 AM CDT Tue May 24 2016

The main challenge for today is chances for additional showers and
storms through this evening. Forecast confidence is low due to
poor model agreement and lack of definitive features for forcing.
Used a wide blend for pcpn chances and capped at 30%.

The Northland finds itself today in a warm and humid airmass in
the wake of a passing shortwave trough exiting to the east, and
lifting shortwaves through the Northern Plains in the SW flow
aloft. There is very light low level flow, but a 50 to 70 knot
jet stream aloft.

Early this morning...there will be some lingering showers and
storms across the eastern forecast area as a shortwave trough
finishes exiting the Northland. Additional showers and storms are
possible over the west central forecast area due to the PVA caused
by shortwaves lifting through the Northern Plains. Fog is possible
across much of the Northland because of the moist boundary layer
and lack of wind.

Today...there will likely be building instability across the
Northland with daytime heating. Passing shortwaves could help
spark off isolated/scattered showers and thunderstorms by this
afternoon. Complicating the forecast is the wide variety of model
guidance, ranging from developing storm complexes swinging through
the Northland this afternoon (ARW/NMM/NCEPWRF) to very little pcpn
(GFS20). The lack of low level flow makes it difficult to believe
the the former solutions because of the lack of flow to feed those
supposed storms. Whereas the GFS20 seems too dry considering the
warm and relatively humid airmass today and passing shortwaves,
which could easily develop scattered convection. Also, it appears
surface high pressure may settle over Lake Superior this
afternoon. Cooler easterly flow from Lake Superior may work itself
inland and cause low level convergence (and a means for storm
development) as it butts up against westerly and southern flow.
Decided to use a wide blend of the models, leaning a little bit
more towards the drier GFS, but providing low precipitation
chances for at least most of the forecast area. High temperatures
should range from the lower 70s near Lake Superior to the upper
70s and low 80s inland.

If any storms develop today, they may tap into an environment of
500 to 1250 J/kg of mixed layer cape, 30 to 40 knots of deep layer
(0 to 6 km) wind shear, and freezing levels around 10 kft agl.
Despite the lack of low level flow, any storms will be able to tap
into decent westerly steering flow, allowing any storms to move
and graze on instability, instead of remaining stationary and
quickly dissipating. Given the environment, there could be
isolated strong storms capable of producing hail and gusty winds.
The SPC thunderstorm threat outlook would likely be more than
marginal if it were not for the lack of low level wind to feed the
storms, as well as the overall lower confidence in today`s
forecast.

Tonight...any showers and storms should dissipate with the waning
instability after sunset and as an upper level ridge lifts into
the Northland, suppressing convection. Some models are producing
light pcpn near Lake Superior overnight, but this would more
likely be drizzle because of the likelihood of fog and low stratus
developing from the cool and humid easterly flow from the lake.
Lows should range from the upper 40s near Lake Superior to the low
to middle 50s well inland.

Wednesday...the upper level ridge will lift north of the
Northland, while a WNW to ESE orientated shortwave trough will
likely lift into the Northland. The lifting trough will bring a
wave of moisture and increasing chances of showers and storms. The
chances of thunder will be better across the western and southern
forecast area because of the cool easterly flow from Lake Superior
limiting heating near the lake. Any thunder over the lake will
likely be the result of elevated convection caused by the PVA from
the shortwave. Prefer the GFS20 and SREF instability, which
depicts much less instability near Lake Superior, unlike the more
robust NAM12. High temperatures will likely range from the upper
50s near Lake Superior to the upper 60s and lower 70s inland.

.LONG TERM...(Wednesday night through Monday)
Issued at 345 AM CDT Tue May 24 2016

An unstable southwest flow will lift several waves across the
region through the upcoming week...keeping ongoing
rain/thunderstorm chances in the forecast through much of the
extended period.

A closed low will makes its way into the upper plains wednesday
night...tracking across the northern minnesota border thursday.
The low will lift a large swath of showers and thunderstorms over
MInnesota and wisconsin during this time. locations in portions of
central may see an earlier end to the convection thursday
morning...depending on the placement of the dry slot.

Northeast winds will prevail Friday and Saturday as the next wave
lifts into the northern plains...keeping conditions cooler near
Lake Superior. Models are in good agreement that the next low
tracks northward across minnesota during the Holiday
weekend...bringing increasing PWATs...along with widespread
showers and thunderstorms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1256 PM CDT Tue May 24 2016

Main arc of forcing for ascent has now translated into NW Ontario
and the MN Arrowhead as of midday, with large scale subsidence
occurring across most of the DLH TAF sites. VFR conditions with
cumulus clouds are expected this afternoon, with generally light
and variable winds that should trend toward southeast by this
evening. The one exception to the above is the convergence axis
that lies just southeast of KHYR, where additional T-Storms are
expected to redevelop this afternoon. However, we believe that
they will stay east of the 5 nmi TAF area for KHYR. Increasing
east flow in advance of the next system will bring MVFR conditions
beginning tonight at KDLH, and spreading across all TAF sites
except for KINL by 18z Wed morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  74  49  60  50 /  60  20  60  60
INL  79  52  74  53 /  40  20  60  60
BRD  82  56  73  56 /  30  20  60  50
HYR  80  52  73  57 /  50  20  60  60
ASX  74  46  63  51 /  50  20  60  60

&&

.DLH Watches/Warnings/Advisories...
WI...None.
MN...None.
LS...None.
&&

$$



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