Area Forecast Discussion
Issued by NWS Duluth, MN

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000
FXUS63 KDLH 161149
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
649 AM CDT Wed Aug 16 2017

.UPDATE...
Issued at 640 AM CDT Wed Aug 16 2017

Updated aviation section below for 12Z TAF TAF issuance.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM CDT Wed Aug 16 2017

A significant slow-down in the precipitation today into tomorrow,
but still expecting widespread light to moderate rainfall rates with
a broad area of 1"+ rainfall expected. Precipitation placement
remains a challenge, but guidance has generally shifted westward
with axis of heaviest precipitation, now focused primarily over the
Mississippi River basin in central/north-central Minnesota, though
areas in far north-central Minnesota where drought is ongoing may
miss out on the greatest precipitation amounts. Increasing easterly
winds today as the low pressure system approaches the area, becoming
northerly as the low pressure system tracks northeast across
southern Minnesota into northern Wisconsin. Highs today and tomorrow
in the mid 60s to mid 70s, lows tonight in the mid 50s low 60s.

On the synoptic scale a mid-level shortwave trough ejects out of the
central Rockies into the Great Plains today, deepening as it tracks
northeast towards the Upper Mississippi River Valley tonight. A
resulting surface low will deepen over southern Minnesota and track
northeast towards the U.P. through Thursday evening. At low levels
southerly flow is apparent on area VWPs, with a boundary of more
moist air at 850mb stretching from the eastern Dakotas southeast
through southern Minnesota per SPC mesoanalysis. This richer low
level moisture will lift north into northern Minnesota and northwest
Wisconsin today, with a few rounds of showers and perhaps a few
thunderstorms. Moderate broad-scale lift due the mid-level shortwave
lifting across the region and some warm air advection over the Upper
Midwest ahead of the low today should help produce widespread light
to moderate rainfall by tonight. With a slower approach than
originally anticipated, some better instability will advect further
north into parts of the Northland today resulting in isolated
thunderstorms, though risk for severe storms remains low.

A swath of 1-3" of rainfall is expected across a portion of the
Northland associated with this low pressure system. While
precipitation rates overall should remain light to moderate, there
remains a risk for thunderstorms to produce heavy rainfall rates
this evening given precipitable water values around 1.75", which is
near the 96-98th percentile per observed sounding and CFSR
climatology data, and given a 3-6 hour period of training possible
as the low deepens and favorable moisture transport, flash flooding
is possible. The area best favored for flash flooding will be along
a narrow swath depending on the low track and how convection
evolves, but at this point areas of central to northeast Minnesota
are best favored, possibly into adjacent areas of northwest
Wisconsin. The WPC Day 1 Excessive Rainfall Outlook depicts a slight
risk for this area.

.LONG TERM...(Thursday night through Tuesday)
Issued at 330 AM CDT Wed Aug 16 2017

Thursday night is the tail end of the strong low pressure system
that will affect the short term forecast.  Showers should still be
lingering over the eastern portions of the forecast area, mainly NW
WI and the MN Arrowhead, tailing off overnight.  With at least some
clearing on the west side of this system, expect cooler conditions
across the western forecast area. Have lowered mins there into the
lower 50s, with some upper 40s possible.

Friday and Saturday there should be some mainly diurnally driven
afternoon and evening showers and thunderstorms with weak ridging
over the area.  Am carrying mainly slight chance pops both days.
Also expect a gradual warming trend, with highs in the mid 70s to
low 80s by Saturday.

Saturday night and Sunday a weak cold front drops through the area,
but with only a weak shortwave aloft, and the associated low is in
northern Ontario. With the features weak, have kept pops to slight
or low end chance, with above normal temperatures.

The upper level flow for early next week has a broad upper level
trough over the region, which is likely to produce fast moving
shortwaves that move across the area.  Confidence is very low at
this time range that the models will be able to correctly depict
this scale of feature, so while I have some small chance pops in the
forecast, expect these to be adjusted as we get closer in time.  For
now, sky cover Monday is not very favorable for eclipse watching,
but given the confidence factor am not too concerned just yet.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 640 AM CDT Wed Aug 16 2017

A low pressure system advancing towards the area today and tonight
will bring increasing chances for showers and thunderstorms
through 00z, then remaining high through the end of the period.
Conditions are initially VFR, but expect conditions to deteriorate
as MVFR ceilings along with rain showers with VFR visibilities to
spread in from southwest to northeast through 22z. After 02z
expect ceilings and visibilities to deteriorate farther, with most
sites into IFR ceilings by 06z tonight, and then also to LIFR
after 09z. Thunder will be possible for all terminals after 16z.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  66  58  64  55 /  80 100  90  20
INL  71  58  68  50 /  70  80  50  10
BRD  70  59  71  55 /  90  90  70  10
HYR  75  62  70  56 /  30  90  70  20
ASX  75  61  67  57 /  30 100  90  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Beach Hazards Statement through this evening for WIZ001.

MN...Beach Hazards Statement through this evening for MNZ037.

LS...Small Craft Advisory from 4 PM this afternoon to 10 AM CDT
     Thursday for LSZ144-145.

     Small Craft Advisory from 4 PM this afternoon to 4 PM CDT
     Thursday for LSZ141>143.

&&

$$

UPDATE...LE
SHORT TERM...JJM
LONG TERM...LE
AVIATION...LE



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