Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 151740

Area Forecast Discussion
National Weather Service Duluth MN
1240 PM CDT Tue Aug 15 2017

Issued at 1240 PM CDT Tue Aug 15 2017

Updated aviation section below for 18Z TAF TAF issuance.


.SHORT TERM...(Today through Wednesday)
Issued at 354 AM CDT Tue Aug 15 2017

An increasingly active weather pattern through the middle of the
week. Today will be dry during the day as a broad area of high
pressure across the Upper Great Lakes region shifts eastward and a
warmer airmass advects into the region. A broad area of light to
moderate rain will spread across the Northland tonight into
Wednesday, with a few embedded thunderstorms possible mainly south
of Highway 2. As with the rain that fell Sunday into Monday, the
greatest rainfall amounts will be south of Highway 2, though unlike
the previous rainfall areas as far north as the international border
should see at least a quarter to half inch of rainfall. Highs today
in the 60s to 70s, coolest along the north shore to an east-
southeast wind off Lake Superior. Cooler Wednesday as east-southeast
winds increase, highs in the 60s to low 70s.

On the synoptic scale southwesterly flow develops over the Upper
Midwest through mid-week as a deep longwave trough axis swings east
across the Rockies into the Great Plains. There will be numerous
shortwave troughs embedded in the overall southwesterly flow at mid-
levels, with southerly flow at low levels supporting increasing low
level moisture. A broad area of precipitation develops in response
to the approaching waves tonight into Wednesday with moderate to
strong large-scale lift from the mid-level PVA and some weak-
moderate low level warm air advection. Surface low deepens over the
eastern Great Plains into southern Minnesota through the day
Wednesday resulting in increasing east-southeasterly winds. A few
embedded thunderstorms possible due to a bit of elevated instability
in place, but overall the threat for storms appears low.

.LONG TERM...(Wednesday night through Monday)
Issued at 354 AM CDT Tue Aug 15 2017

Wednesday night and early Thursday the main upper level trough and
surface low move from central Minnesota northeast to upper Michigan.
This is going to bring a period of moderate to heavy rainfall to
mainly northwest Wisconsin.  The models have finally come into
fairly good agreement on this storm, with a rapidly deepening
surface low as it moves across northwest Wisconsin, plenty of
available moisture and instability.  It looks like we are going to
get a decent amount of rainfall from this event, with PW values in
the 1.5"-1.75" range, which is the top 10 percent of climatology for
this time of year.  The storm system and associated convection
should move in a fairly progressive nature across the forecast area
though, which should reduce the threat of flooding across the area.
That said, the threat remains possible as depicted in the WPC day 2
excessive rainfall outlook.  Precipitation comes to a fairly rapid
end on Thursday, with drier conditions and clearing skies for
Thursday night.

Friday and Saturday should have some afternoon and evening diurnally
driven convection, aided by a weak shortwave aloft.  Temperatures
should warm through the weekend with highs near to slightly above
normal by Saturday.  A cold front will move through the area on
Sunday, but with no shortwave aloft and little convergence along the
boundary, do not expect much and have kept to slight to low end
chance pops. Temperatures to continue to warm and should be above
normal Sunday.

Another fairly strong upper level trough to move through the area
early next week, bringing another round of showers and
thunderstorms.  In fact, we may have more cloud cover than local sky
watchers would prefer for the eclipse on Monday.  Being this far
out, expect timing to shift in the next few days, hopefully towards
a slower solution that leaves skies clearer for more areas.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1240 PM CDT Tue Aug 15 2017

High pressure was aiding in keeping the Northland dry under
mainly VFR conditions. A cumulus field has formed and there will
be a period of broken ceilings in spots, again mainly VFR. An area
of low pressure will approach the region tonight then slowly move
through the region through Thursday. Rain will develop from west
to east tonight into Wednesday and the rain will be heavy at
times. VFR ceilings will become widespread tonight then lower to
MVFR or IFR later tonight into Wednesday. Visibility reductions in
rain and fog will occur as well.


DLH  70  57  62  58 /   0  50  90  80
INL  77  57  65  56 /  10  50  90  60
BRD  75  61  70  59 /  10  80  80  50
HYR  76  56  71  61 /   0  30  90  90
ASX  71  54  69  61 /   0  20  80  90




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