Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 270811

Area Forecast Discussion
National Weather Service Duluth MN
311 AM CDT Thu Jul 27 2017

.SHORT TERM...(Today through Friday)
Issued at 306 AM CDT Thu Jul 27 2017

Today will start off quiet across the Northland, except for areas of
fog that have developed in some spots. Visibility may drop down to
roughly 1/2 SM or so before dissipating around 8 AM CDT as
temperatures increase.

The main focus of the short-term forecast period continues to be
increasing chances of showers and thunderstorms as a compact
shortwave descends southeastward into the Northland from southern
Manitoba Canada. There should be some decent lift associated with
this wave, given a robust positive vorticity maxima associated with
it, as well as enhanced values of isentropic omega in the 850-300 mb
layer per the Thaler QG analysis. The convective-allowing models are
progging showers to ramp-up after noon today, with some
thunderstorms possible later in the afternoon. The NAM/RAP model
soundings show some drier air in the low-levels as the boundary
layer mixes via diurnal heating. This may hinder precipitation
amounts a bit, but given MLCAPE values ranging from a few hundred up
to 1000 J/kg, there should be ample instability to generate some
stronger updrafts in the strongest convection, which should overcome
this drier low-level air. The best chances of precipitation will be
over north-central Minnesota and into the Arrowhead region as the
better instability and forcing will reside there. This activity
should decrease once the sun sets and instability decreases. Today`s
highs will reach into the upper 70s and lower 80s.

The remainder of the short-term forecast period will be quiet and
dry once the mid-level shortwave departs the region this evening.
Mid-level ridging and sfc high pressure will build behind this
shortwave, leading to mostly clear conditions tonight and Friday.
Looks like there will be another night of some areas of fog tonight
as the sfc high pressure builds overhead. Overnight lows will again
be on the cool side, ranging from the lower 50s over the Minnesota
Arrowhead region to the mid 50s elsewhere. Highs Friday will again
be in the upper 70s and lower 80s.

.LONG TERM...(Friday night through Wednesday)
Issued at 306 AM CDT Thu Jul 27 2017

Friday night and Saturday finds upper level and surface ridging
covering the forecast area. Model differences begin Saturday night.
Weak upper level shortwaves are progged to begin flattening the
upper ridge a bit on all models. However, the GEM/GFS shows signs of
some feedback as they try to push some QPF to the western edge of
the area. The ECMWF maintains the surface ridge and keeps the QPF
out of the area until late Saturday night and just over Koochiching
county. Used a blend which keeps pops over the western edge in the
evening, then spreads them eastward overnight. Northwest Wisconsin
will remain dry. Instability is lacking, but enough in the evening
for a mention of thunder out west, then just showers overnight. On
Sunday, the surface ridge is shoved to the south of the region. The
GFS is stronger with an upper trof diving through the region, but
suffers from more pronounced feedback. The GEM and ECMWF are much
weaker with the trof and subsequent QPF field. Blended toward the
GEM/ECMWF with less of the GFS. Sunday night finds the upper ridging
building back across the area on the ECMWF/GFS and will follow suit.
Another short wave flattens the ridge a bit on Monday. Have some
small pops in the morning over north central Wisconsin where the
best forcing will be located. The parade of short waves continues
Monday night and Tuesday. The GFS/GEM are the most robust with the
trofs and the surface cold front driven through the heart of the
forecast area. The ECMWF is much weaker and has less QPF. Maintained
the use of a blend of models for pops. Held off on thunder mentions
until Tuesday afternoon when thermodynamic profiles get a bit
stronger favoring the thunder mention. Will lean toward the GFS/GEM
for Tuesday night as they continue to push the cold front through
northwest Wisconsin. Meanwhile, high pressure builds into northeast
Minnesota. The GFS/GEM have high pressure over the region on
Wednesday, while the ECMWF brings a fairly strong upper wave and
cold front toward the region. Kept with the blend which favored the
GFS/GEM with a nod towards the ECMWF.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1215 AM CDT Thu Jul 27 2017

High pressure will bring mainly VFR conditions to the Northland
overnight. There may be a bit of fog in spots, although it looks
like it will be fairly spotty. Have included mention of fog in
some of the TAF`s, and will need to watch carefully to see if it
crops up anywhere else. A vigorous shortwave will dive southward
across the western Lake Superior region on Thursday. This system
will generate scattered showers and a few thunderstorms. Will
leave thunder out for now, as it is toward the end of TAF cycle,
but may need to add mention of it in subsequent TAF`s.


DLH  79  56  79  55 /  30  30   0   0
INL  79  54  82  57 /  50   0   0   0
BRD  80  57  81  58 /   0   0   0   0
HYR  80  54  80  54 /  20  10   0   0
ASX  80  54  78  53 /  20  10   0   0




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