Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 251736
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1236 PM CDT Thu May 25 2017

.UPDATE...
Issued at 1236 PM CDT Thu May 25 2017

Please see the 18Z Aviation Discussion below.

UPDATE 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
possible.

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
temperatures.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1236 PM CDT Thu May 25 2017

A 500 hPa ridge will slide from eastern Minnesota this afternoon
into eastern Wisconsin late tonight. Despite the ridge, fair
weather cumulus has developed across the Upper Midwest due
heating with ceilings ranging from 2.9 to 4 kft. Expect the CU
field to remain in place until this evening with gusty winds at
BRD/INL/HIB due to the tightening pressure gradient from the
departing high and cold front. The gusty winds will subside this
evening once the mixed layer decouples per the RAP/NAM.

The front will slide eastward across Minnesota tonight and early
on Friday. This will provide enough lift for rain showers to
develop and in addition, lowering ceilings as the lower levels
moisten. Expect MVFR ceilings to gradually develop and per the
the NAM/RAP/DLHWRF soundings think that IFR ceilings are a
possibility with visibility reduction as fog develops.
Thunderstorms are a possibility at INL/BRD/HIB towards the end of
the TAF period as there is sufficient instability developing
ahead of the front. However, think the possibility is too low at
this point to include in the latest TAF set.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  58  46  64  47 /  10  40  40  30
INL  68  50  71  47 /   0  50  40  10
BRD  67  52  73  49 /  10  50  20  10
HYR  70  52  70  49 /  10  50  40  20
ASX  59  43  67  48 /   0  50  40  20

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

UPDATE...WL
SHORT TERM...JTS
LONG TERM...CLC
AVIATION...WL


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