Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 121753 AAB

Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
1253 PM CDT Sat Aug 12 2017

Issued at 1253 PM CDT Sat Aug 12 2017

Update for 18Z 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
Minnesota 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

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


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1253 PM CDT Sat Aug 12 2017

VFR conditions are expected through this forecast period. High
pressure over the region will result in relatively light winds
today and tonight. An area of low pressure aloft will move across
central and southern Minnesota tonight and Sunday, which should
result in increasing cloud cover and a chance of rain showers
Sunday morning. Have included a mention of VCSH at BRD, where
the best chance of showers is forecast as of this update. With
cloud cover increasing overnight, think the potential for fog is
low and have kept a slight visibility reduction at HIB from
previous 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  79  54  79  55 /   0   0  10  20




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