Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 200534

Area Forecast Discussion
National Weather Service Duluth MN
1234 AM CDT Thu Jul 20 2017

Issued at 627 PM CDT Wed Jul 19 2017

Made adjustments to POPs/Weather this evening as confidence in an
evening line of storms developing in east-central Minnesota into
northwest Wisconsin is lower than earlier based on current
conditions and short-range model guidance. Did not eliminate
chances since some storms may still develop, but based on the SPC
Mesoanalysis instability fields it appears the most widespread
storms would be just on the southern CWA border.


.SHORT TERM...(This evening through Thursday)
Issued at 353 PM CDT Wed Jul 19 2017

Chances of showers and thunderstorms could increase this evening,
especially over our southern portions of the forecast area, as
skies look to clear from west to east this afternoon. A
baroclinic zone and CAPE gradient will be draped from northwest to
southeast just south of our southern forecast area boundary. In
general, confidence is rather low for much in the way of showers
and thunderstorms over the area. The latest convective-allowing
models are generally progging a band of strong to severe
thunderstorms along our southern counties, but there is some
disagreement among the models regarding the placement of this
band, as well as the location of convective initiation. The
19.12z GFS and NAM models are indicating a lack of robust
instability across our south, as MLCAPE values range between 300
to 700 J/kg, and the axis of the highest instability looks to
remain to the south. We are also on the northern cusp of the
stronger moisture transport, with the GFS and NAM models
disagreeing on the magnitude of Pwat values. In any case, the axis
of the heaviest rainfall will remain to the south. My suspicion
is that the majority of the strongest thunderstorms will remain to
our south where the higher instability will remain. However, one
or two strong to severe thunderstorms cannot be ruled out for our
southern counties due to the northern gradient of MLCAPE nosing
into the Northland, especially over portions of east-central
Minnesota and southern portions of northwest Wisconsin. If any
strong/severe convection develops over our area, it will likely be
later this evening after 8 to 9 PM CDT, according to the CAMs. The
biggest threats with any strong to severe convection would be
large hail and damaging winds, but confidence is low we could see
anything to this regard.

Overnight: some areas of fog could develop in the wake of the
baroclinic zone that should depart the region later tonight,
especially where it rains this evening. Some chances of showers
and storms will linger over northwest Wisconsin during the early
morning hours Thursday before an area of high pressure moves in
and takes control, bringing mostly sunny skies across the
Northland. High temperatures Thursday will reach to near or above
average, with highs in the upper 70s over the Minnesota Arrowhead
and the lower to mid 80s elsewhere.

.LONG TERM...(Thursday night through Wednesday)
Issued at 340 PM CDT Wed Jul 19 2017

For the longer term period the northland will remain under the
northern branch of the westerlies. This will bring a series of waves
across the region every other day or so, meaning a stormy period.

To begin the period Thursday night surface high pressure will be
over the region. On Friday the high will slide to the east and
another round of showers and thunderstorms will develop as return
flow results in surface and low level warm air advection. So on
Friday afternoon and overnight especially we may see a round of
thunderstorms moving northward from southern MN and WI. It looks
like the better chance for stronger and more widespread
thunderstorms will be Saturday when a significant Canadian upper
level wave and a surface cold front will swing through the
northland. The surface will feature a warm frontal boundary south of
the northland and with plenty of instability (CAPE well over 2500
j/kg) thunderstorms are a good bet. The SPC has outlined much of the
northland in the severe threat area for Saturday. There will likely
be residual showers and storms on Sunday, then high pressure will
bring a calmer day on Monday until yet another upper level Canadian
low approaches to bring another round of storms for Tuesday and


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1234 AM CDT Thu Jul 20 2017

MVFR to LIFR fog possible tonight at all sites, with the highest
risk for IFR or worse visibility at BRD, HIB, and HYR. Clear skies
and VFR conditions will then prevail when fog clears out Thursday
morning. Light northwest wind developing Thursday.


DLH  58  83  60  78 /  10   0   0  10
INL  54  79  56  81 /  10   0  10  10
BRD  59  85  62  81 /  10   0   0  20
HYR  60  84  59  80 /  30  10   0  30
ASX  58  85  57  80 /  30   0   0  20




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