Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 251336

Area Forecast Discussion
National Weather Service Duluth MN
836 AM CDT Thu May 25 2017

Issued at 835 AM CDT Thu May 25 2017

Latest short term guidance indicates a slower onset time to the
rain to late this afternoon. Have adjusted accordingly. Made some
other minor adjustments.


.SHORT TERM...(Today through Friday)
Issued at 339 AM CDT Thu May 25 2017

A mid- to upper-level ridge axis will continue to translate over the
Northland through the morning hours today. This will keep conditions
dry for a time before a new upper-level low brings our next chances
of precipitation throughout the short-term fcst period. The upper-
level low will churn over southern Saskatchewan today through much
of Friday, which will bring a few mid-level shortwave impulses
and a push of 850-700 mb layer warm air and moisture advection,
which will support chances of rain showers, with some
thunderstorms possible Friday afternoon. More widespread chances
of rain showers don`t ramp up today until the evening hours when a
fairly robust, yet diffuse, wave of positive vorticity advection
maxima ejected from the primary shortwave sweeps eastward through
the Northland. QPF amounts will remain light for most locations
through Friday morning, with up to a few tenths of an inch

There could be some strong storms from this system, which are
progged by the NAMNest/ARW/NMM high-res models Friday afternoon,
which are showing some decent agreement on the timing and placement
of this line of thunderstorms (ramping up by 21Z Friday, mainly
from INL southward towards Lake Mille Lacs). The synoptic models
are progging some higher instability values as low- to mid-level
lapse rates steepen a bit, with MUCAPE values Friday afternoon and
evening ranging from a few hundred J/kg up to roughly 1000 J/kg
between the 25.00z NAM/GFS models. The NAM is more bullish with
the instability compared to the GFS. Also, the GFS model focuses
the axis of the strongest instability to the east. Considering the
progged instability values from the ECMWF/CMC/SREF models appear
to be more in-line with the placement of the instability from the
NAM compared to the GFS, so leaned toward the NAM solution in
regards to the placement of thunder in the forecast. This
placement is a bit further west compared to the previous forecast.
Sfc moisture looks to become enhanced ahead of this system, as
sfc dew point temperatures reach into the lower to mid 50s across
the Northland. Severe weather is not expected with these
thunderstorms, but the NAM model does indicate 0-6 km bulk shear
values between 30 to 40 kts, with the GFS model going quite a bit
lower than that. The limiting factor appears to be a lack of
robust lift with this system. However, given the progged
instability, and the enhanced moisture profile, there may be some
strong thunderstorms possible as things ramp up Friday afternoon.

.LONG TERM...(Friday night through Wednesday)
Issued at 329 AM CDT Thu May 25 2017

The next weather system to affect the Northland for quite a few days
is seen on water vapor imagery over the southern areas of the
western Canadian provinces. This upper low and trough will move into
the northland`s area, then rotate across the northland into early
next week. This vertically stacked low will mean another extended
period of showers and occasional storms. Saturday looks to be the
nicest day of the holiday weekend, but even that will be subject
to the whims of the upper low. Both the GFS and NAM are already
pointing to the first of many positive vorticity maxima to move
through the upper low and over northern Minnesota Saturday
afternoon. And this is reflected in the small POPS in western
section of the forecast area Saturday afternoon and then across
the whole region Saturday night. Confidence is fairly high that
there will be showers Saturday afternoon, but the scattered nature
of them results in lower probabilities. By Saturday night, the
500 mb closed low will be near Lake Winnipeg with the trough
stretching south across western MN. The associated surface low
will also be in Canada, north of MN, with a cold front trailing
south of the low. Sunday afternoon and evening will be the best
chance of thunderstorms with increasing instability ahead of the
cold front. The GFS MUCAPE values are forecasted in the 800 to
1600 j/kg range. SPC does have the region in the general thunder
region for Saturday afternoon and evening. Once the front passes
cloudy and cooler weather will follow. By midweek, the upper low
will be off to the east and the northland will finally be out of
the cyclonic flow, which will mean more sunshine and warming


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 748 AM CDT Thu May 25 2017

VFR through the afternoon as a low amplitude ridge builds
eastward from eastern Minnesota into Wisconsin. Expect ceilings
in the 4 to 5 kft range through the afternoon per the latest
RAP/DLHWRF/NAM guidance. This evening a cold front will slide into
western Minnesota, which will spread rain showers into Minnesota
terminals late tonight. As the lower levels moisten, expect
ceilings to lower to 2 to 4 kft. In the heavier showers visibility
will reduce to the MVFR range as hinted at by the GFSLAMP/GFS


DLH  58  46  64  47 /  10  40  40  30
INL  67  50  71  47 /  10  50  40  10
BRD  68  52  73  49 /  10  50  20  10
HYR  70  52  70  49 /   0  50  40  20
ASX  58  43  67  48 /   0  50  40  20




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