Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 121120

Area Forecast Discussion
National Weather Service Duluth MN
620 AM CDT Sat Aug 12 2017

Issued at 620 AM CDT Sat Aug 12 2017

Please see the 12Z Aviation Discussion below.


.SHORT TERM...(Today through Sunday)
Issued at 338 AM CDT Sat Aug 12 2017

A broad upper trough covers much of the U. S. this morning and
it is this trough that will bring our next chance of rain. In the
mean time, surface high pressure will bring sunshine and very
light winds to the northland today. In the afternoon there will be
some cumulus development as sites reach their convective
temperatures around 72-75 degrees. There may be a few light
showers in the tip of the Arrowhead where a weak Canadian
shortwave rotating through the upper trough may be enough to lift
to generate some spotty showers. On Sunday the surface high will
gradually move southeast with the axis from the Minnesota
Arrowhead and and Wisconsin, while aloft another strong shortwave
will be moving across the southern two thirds of Minnesota. The
increasing low level warm air advection and the shortwave will
spread showers and isolated thunderstorms across southern and may
reach up into southwestern areas of the northland, mainly in the
Brainerd lakes area. Expect mainly showers, but with some weak
instability, cannot rule out an isolated thunderstorm.

.LONG TERM...(Sunday night through Friday)
Issued at 338 AM CDT Sat Aug 12 2017

Cyclonic northwesterly flow will persist across the Upper Midwest
through the weekend. Early this upcoming week flow aloft will become
quasi-zonal and continue until late in the week when cyclonic flow
northwesterly flow returns. This will bring several periods where
showers and thunderstorms will be possible.

Initially, a shortwave will dig southeastward from the eastern
Dakotas late on Sunday into southern Minnesota by Monday evening.
Despite the trough aloft at 500 hPa, portions of the Northland will
remain dry as a 850 hPa ridge axis remains firmly in place. The best
chance for any showers/storms Sunday night through Monday will be
from the Brainerd Lakes east to the I-35 corridor, and through all
of northwest Wisconsin.

Late on Monday through early Tuesday a weak 500 hPa ridge will build
into the region from the northern Plains, this will provide dry and
quiet weather heading into Tuesday morning. As Tuesday progresses
precipitation chances will increase, as a shortwave lifts into the
northern Plains on the western side of the ridge axis. 850 hPa flow
will become southerly, which will advect warm moist air into the
region. Expect precipitable water values to range anywhere from 1.0
to 1.5 inches, which per SPC sounding climatology falls between the
75th percentile and maximum at INL/MPX for this time of year. There
will be a few hundred to 1500 J/kg of MUCAPE with 10 to 20 knots 0-6
km bulk shear. Thunderstorms will be possible which may produce
heavy rainfall at times. Expect the mildest highs of the extended on
Tuesday with readings ranging from the mid 70s to low 80s.

The shortwave will lift northeastward into Ontario on Wednesday,
however at the surface a broad area of low pressure will remain over
the region. Flow at 850 hPa will remain southerly, which will
continue advecting warm, moist air originating from the Gulf o
Mexico. Precipitable water values will increase to 1.5 to 2.0 inches
across the Northland, which is greater than the 90th percentile for
this time of year. The GFS/ECMWF still show a few hundred to 2000
J/kg of MUCAPE with less than 20 kts of 0-6 km bulk shear. Suspect
the instability values may be a bit too high due to cloudiness over
the region. Regardless, thunderstorms will be possible and rainfall
may be heavy at times.

Guidance becomes a bit more murky late in the week and heading into
the weekend, as the GFS/ECMWF are somewhat similar lifting a trough
located in central Canada into northern Canada by Thursday/Friday.
Into the weekend both pieces of guidance build a ridge into the
Upper Midwest from the northern Plains/central Canada. The CMC is
the outlier at this point cutting off the trough in central Canada
and moving it southeastward into the Upper Midwest/central Great
Lakes for the weekend. Leaning on the latest GFS/ECMWF at this point
with showers/storms possible on Friday and a drier Saturday in store
with high pressure building in.

High temperatures will generally be in the 70s through the extended
with lows ranging from the upper 40s to 50s.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 620 AM CDT Sat Aug 12 2017

Main concerns in the TAFs are for the next 2 to 3 hours where
radiation fog will be dissipating as the mixed layer develops.
Visibilities and ceilings will improve to VFR. VFR conditions will
prevail through the TAF period with high pressure firmly in place
over the Northland. A fair weather cumulus field will develop late
this morning and persist into the afternoon with ceilings around
5000 to 8000 feet. Late tonight, patchy fog may develop at
HIB/BRD. Feel more confident in radiation fog chances at HIB as
skies will be clearer. At BRD cloud cover will increasing due to
the shortwave moving in from the northern Plains, so have held off
from including fog at this point. With high pressure in place,
winds will remain below 10 knots through the forecast.


DLH  77  56  76  54 /   0   0  10  20
INL  77  51  78  51 /  10   0  10   0
BRD  77  55  73  54 /   0  10  40  40
HYR  78  51  77  53 /   0   0  10  30
ASX  78  54  79  55 /   0   0  10  20




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