Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 161209

Area Forecast Discussion
National Weather Service Duluth MN
709 AM CDT Tue May 16 2017

Issued at 701 AM CDT Tue May 16 2017

updated aviation section below.


.SHORT TERM...(Today through Wednesday)
Issued at 502 AM CDT Tue May 16 2017

The short-term forecast begins with some areas of fog this morning,
especially along and downstream of Lake Superior, due to cooler
temperatures and lower dew point depressions. Some locally dense fog
will be possible, especially from near the Twin Ports and points
north and west towards Hibbing. This fog should lift by mid morning.
Then, a more volatile weather pattern will develop today and
continue through Wednesday.

For today, a 120+ kt 250 mb level jet streak will build over Ontario
Canada and lift towards the north and east. This will place the
region under the right-entrance quadrant of the upper-level jet
streak, and within the upper-level divergence region of the jet. A
mid-level ridge will continue to translate eastward over the eastern
United States, allowing some enhanced moisture return flow into the
region today. This will allow a mid-level shortwave trough to bring
stronger isentropic lift into the region as well, setting the stage
for the potential for severe weather and heavy rainfall. 850-700 mb
layer warm air advection will support precipitation chances across
much of the Northland. A decent southerly 850 mb low-level jet with
magnitude of 25 to 35 kts will nose into the region as well,
providing good moisture transport. Precipitable water (Pwat) values
will increase due to this low-level moisture advection, with values
between 1.1 to 1.5" this afternoon, as progged by the 16.00z GFS and
NAM models. The NAEFS standardized anomalies indicates that these
values are between 2 to 3 standard deviations, or 97 to 99 percent,
above the climatological average for this time of the year.
Instability will also be present with this system as MLCAPE values
are progged to range between 500 and 1500 J/kg between the
GFS/NAM/CMC models. Thus, a severe threat is possible for today,
with the Storm Prediction Center bringing a Slight Risk of severe
weather south of a line from Hinckley to Moose Junction to Lac Du
Flambeau. A Marginal Risk of severe weather is also in place for a
good chunk of the Northland, reaching as far north as Isabella and
Embarrass. The primary threats for storms will be large hail and
gusty winds. Some hefty rainfall amounts are also possible for
today, with an expected range between a few tenths up to three-
quarters of an inch. There may also be higher amounts if
thunderstorms can train and bring repeated rounds of rainfall. Some
areas of fog will again be possible along and downstream of Lake
Superior tonight due to lingering moisture in the boundary layer.

The shortwave that will cause today`s showers and thunderstorms will
move off to the east by this evening and overnight, only to be
replaced by another mid- to upper-level trough that will mature over
the Four Corners region of the Intermountain West and ascend into
the region, bringing another shot of showers and thunderstorms for
Wednesday. Once again, good Pwat values indicate some heavy rainfall
is possible, especially over northwest Wisconsin, due to better
moisture. WPC`s excessive rainfall forecast outlook has a slight
risk of rainfall exceeding flash flood guidance over northwest
Wisconsin both today and Wednesday. The axis of instability will
shift to the south and east Wednesday, so only northwest Wisconsin
will be most likely to see thunderstorms, and the heaviest rainfall
amounts. Confidence is better for higher QPF values for Wednesday,
with QPF amounts ranging from one to two inches possible over
northwest Wisconsin, and three-quarters of an inch to one inch for
adjacent locations in northeast Minnesota. Temperatures should be
slightly cooler Wednesday compared to today as a cold front boundary
will sweep through the region tonight to help moderate the air mass.
Precipitation should continue into the evening hours Wednesday and
into Thursday morning. Some heavy rain is expected to continue
during this time, so the threat of flooding will persist.

.LONG TERM...(Wednesday night through Monday)
Issued at 502 AM CDT Tue May 16 2017

Wednesday night the main upper low moves across the region, and from
a QG perspective produces the strongest synoptic scale lift of this
string of shortwaves we are in the midst of.  A broad band of
frontogenesis will be already in place across the region in the
early evening, and together with the instability will produce a
large area of showers and thunderstorms that will roll across the
forecast area Wednesday night and Thursday morning.  As has been
consistent in the models for a few days now is the signal for heavy
rainfall, with precipitable water values of around 1.25 inches,
which is approaching 2 standard deviations above normals for this
time of year.  This is the same airmass moving into the area now,
and on top of tonights precipitation, precipitation I expect
Wednesday night, we could have some real flooding issues by this
upcoming weekend.  From Wednesday morning to the time the rainfall
ends Thursday, we could have widespread rainfall amounts in the 1.5
to 2 inch range over northwest Wisconsin, producing some impressive
3 day rainfall totals of more than 4 inches, and that does not
include some locally higher amounts that tip local conditions into

We are looking at getting a quiet lull Thursday night into early
Friday, with a fairly strong surface ridge pushing into the area
from the north.  In fact, we are looking at some freezing
temperatures along the Canadian border and some of the Iron Range by
Friday morning.

Another strong upper low moves out of the Rockies on Friday and
sweeps northeast in our direction, on a similar track to the one we
expect Wednesday.  There are still some differences in the models in
how they eject this energy, with the GFS a little more fragmented
than the ECMWF.  Either way, we are looking at another strong storm
system moving in late Friday and continuing through Friday night and
into Saturday. With the colder air already in place, it will be
colder and with less convection than the Wednesday storm, but expect
we will still be looking at some decent precipitation amounts.  It
will be a chilly, wet and stormy weekend, so hopefully everyone got
outside for some sunshine last weekend.  This storm moves off to the
northeast by Monday, leaving us in northwest flow for drier but
cooler conditions which continues into much of the upcoming work
week.  The models differ on bringing some chances for precipitation
across the area with some weak shortwaves, but there is little
agreement and confidence is low.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 701 AM CDT Tue May 16 2017

Active weather this TAF period with waves of showers and
thunderstorms moving across the terminals. Initially we have LIFR
stratus affecting KDLH, KHIB and KBRD, but there is an initial
wave of showers and thunderstorms moving north across the
terminals, which will continue through 15z. This wave should bring
ceilings and visibilities to MVFR. Behind it most locations should
return to MVFR/VFR depending on location with additional waves of
showers and thunderstorms expected after 18z, which may bring IFR
conditions. Expect a gradual lowering of ceilings and
visibilities after 03z this evening with potential for IFR


DLH  59  49  58  40 /  70  60  60  90
INL  65  47  58  38 /  70  50  10  10
BRD  74  52  63  44 /  70  50  60  90
HYR  78  56  66  43 /  70  90  80  90
ASX  67  50  59  40 /  60  70  70 100




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