Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 160525

Area Forecast Discussion
National Weather Service Duluth MN
1225 AM CDT Sun Jul 16 2017

Issued at 1225 AM CDT Sun Jul 16 2017

Updated for the new 06Z Aviation Discussion below.

UPDATE Issued at 850 PM CDT Sat Jul 15 2017

Cold front has moved well south into central Wisconsin as of mid
evening, with cooler and drier air filtering into the Duluth CWA
as high pressure builds in from the north. Overall, we expect a
fairly quiet weather night.

However, GOES-16 imagery and surface obs indicate a fairly well-
organized secondary northeasterly surge moving southwest-ward
near Isle Royale and the Minnesota Arrowhead, with a well-defined
wind shift/cloud line, and Rock of Ages is now gusting to 25 knots
from the northeast. The previous forecast and hi-res guidance
hinted at this feature earlier, and it appears that guidance was
on to something. Confidence in any meaningful precip with this as
it reaches the south shore later tonight is very low, but it
should be sufficient for a period of locally stronger winds,
cooler temps, stratus clouds and perhaps some drizzle in the
primary upslope areas prone to northeast flow. We have updated the
forecast to reflect these trends, and also increase the coverage
of patchy fog in many areas during the overnight hours.


.SHORT TERM...(This evening through Sunday)
Issued at 330 PM CDT Sat Jul 15 2017

At 330 PM, skies were partly to mostly sunny across the Northland.
Temperatures ranged from 86 at McGregor, to 73 in Crane Lake,
where there was a bit more extensive cloud cover. Winds had
generally shifted to the north/northwest across the entire CWA.

The focus for tonight will be the potential for a few showers and
thunderstorms, along with the potential for some late night
stratus/rain showers off Lake Superior.

Quite unstable air across northwest Wisconsin this afternoon. CIN
has been decreasing across that area, although there was still a
bit of a cap on forecast soundings across that area. These
forecast soundings indicate there will exist a small window where
storms could develop late this afternoon or early evening,
although the threat will quickly shift south of the CWA with time.
The CU field elsewhere across the CWA has not shown much growth at
all, but would not be surprised to see a few showers or a storm
across the Minnesota Arrowhead this afternoon. Still, the best
chance for some development would be south of a line from Hayward
to Ironwood. Dewpoints in this area are in the lower 70s as of 3
PM. The rest of the Northland should see skies generally clear
overnight. The HRRR is consistent in trying to bring some stratus
and perhaps some spotty rain showers or drizzle to the areas
surrounding Lake Superior overnight, first along the south shore,
and then across the Twin Ports and portions of the North Shore.

Any clouds/showers that do develop overnight should gradually
break up on Sunday, as high pressure brings sunshine to the CWA.
Lows tonight will range from the 40s in the north to the 50s to
around 60 south. Highs on Sunday will range from the 60s to lower
70s near Lake Superior, to the 70s inland.

.LONG TERM...(Sunday night through Saturday)
Issued at 330 PM CDT Sat Jul 15 2017

A ridge of high pressure will build southeastward into the central
Great Lakes Sunday night, while a trough lifts into the central
Canada. At the surface, high pressure will slide from the Upper
Midwest into the central Great Lakes. Behind the surface high, a
cold front will move into the northern Plains and northwest
Minnesota. On Monday the front will slide southeastward through much
of northern Minnesota. This will bring increasing chances of showers
and thunderstorms late Sunday night through Monday. It will be humid
with mid 60s to near 70 degree dewpoints advecting into the region
ahead of the front due to southerly flow. In addition, there will be
1500-3000 J/kg of MLCAPE, 0-6 km bulk shear increasing to 25 to 40
kts, and PWATS of 1.5 to 2.0 inches per the GFS/NAM/ECWMF. Based on
these parameters combined with forcing from the front, strong to
severe storms will be possible as highlighted in the current SPC Day
3 Outlook. With PWAT values near the 90th percentile for this time
of year, heavy rainfall will also be a concern. Highs on Monday will
range from the mid 70s along the Lake Superior shoreline, to the
upper 80s in the Brainerd Lakes region.

The cold front will slowly continue sliding southeastward through
the Northland Monday night and Tuesday. Aloft, another shortwave
will be moving through bringing continued shower and thunderstorm
chances. Cannot completely rule out strong to severe storms on
Tuesday especially if the latest GFS pans out with MLCAPE of 1500-
2500 J/kg with 0-6 km bulk shear of 40-50 kts. Think these
instability values may be a bit overdone as cloud cover from the
ongoing/previous days convection should inhibit the amount of
daytime heating. By Wednesday, the GFS stalls the cold front across
southern portions of the CWA, while the ECMWF/CMC are more
progressive and have already moved the front through. Uncertain at
this point how things will evolve, but opted in continuing
shower/storm chances as another shortwave will be moving through.

High pressure will build into the region Thursday/Friday as an 850
hPa ridge axis moves northeastward from the northern Plains into the
Upper Midwest. Late in the week and heading into the weekend, a
trough will move into the Upper Midwest from central Canada bringing
more chances of showers and storms. Expect seasonable highs for
Tuesday through Saturday with readings in the 70s and low 80s. Lows
range from the 50s to low 60s Tuesday night through Friday night.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1225 AM CDT Sun Jul 16 2017

High pressure will continue to build into the area overnight with
generally VFR conditions expected through the 24 hour TAF period.
The one exception is that a weak surge moving southwestward
across Lake Superior could bring a short period of MVFR ceilings
to KDLH/KHYR overnight as it comes ashore the first 6 hours of the
period. Otherwise, expected winds to gradually veer from
northeast to east, and eventually southeast on Sunday, with
scattered VFR cumulus during the day.


DLH  57  69  48  78 /  10  10   0  20
INL  48  77  54  79 /   0   0  10  50
BRD  57  77  58  87 /   0   0   0  20
HYR  53  74  50  82 /  10   0   0  10
ASX  55  69  48  82 /  10   0   0  10




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