Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 012335

Area Forecast Discussion
National Weather Service Bismarck ND
635 PM CDT FRI JUL 1 2016

Issued at 625 PM CDT Fri Jul 1 2016

Shower and isolated thunder activity is pretty much confined to
our southeast CWA at this time. This area continues to move slowly
east and is slowly dissipating. For the most of us it looks like a
dry evening and lowered or removed pops across a good portion of
the north and west. Global models are still hinting at an area of
shower or thunderstorms activity across the north after midnight,
and possibly some isolated convection in eastern MT tracking
across the border. Mesoscale model do not really offer much help
with this so will take another look after 00 UTC models start
coming in.


.SHORT TERM...(This evening through Saturday)
Issued at 345 PM CDT Fri Jul 1 2016

There will be a chance of showers and thunderstorms across western
and central ND through Saturday night and beyond, but it will not
by any means be a washout.

As of 20 UTC, A band of showers and a few weak, embedded storms is
moving across the Highway 83 corridor in central ND. The lightning
detection network has shown a decreasing trend in both in-cloud
and cloud-to-ground lightning with this activity the further east
that it propagates, which is consistent with a lack of MUCAPE to
the east of Highway 83 per the SPC mesoscale analysis and recent
RAP and HRRR simulations. Even so, water vapor imagery continues
to suggest that the mid-level shortwave trough that`s responsible
for this convection is relatively dynamically-healthy as signaled
by modest darkening in its wake centered on Lake Sakakawea at mid
afternoon. The post-wave subsidence has allowed clearing to boost
temperatures into the 80 F range over eastern MT and far western
ND, and with dewpoints in the lower to middle 50s F, MLCAPE from
500 to 800 J/kg is expected there late this afternoon and this
evening. That may incite isolated thunderstorm development and a
brief/local strong storm is not out of the question in the west,
as has been suggested by some HRRR simulations today. Meanwhile,
the forcing with the wave is likely sufficient to carry showers
eastward through the remainder of central ND through evening.

Water vapor imagery suggests there is another weak shortwave
trough embedded in broad northwest flow aloft upstream in central
MT this afternoon. The 12 UTC GFS, NAM, and ECMWF and most of the
convection-permitting model guidance suggests this wave may assist
shower development/concentration over northern ND tonight in close
proximity to some modest mid-level frontogenesis. We used a multi-
model consensus to build the PoP forecast through tonight given
relatively good model-to-model agreement and support of the wave`s
existence in observational (satellite) data this afternoon. Storm
potential will be limited by modest mid-level lapse rates 6 C/km
or less in the 700-500 MB layer overnight.

On Saturday, temperatures will warm a bit with highs forecast to
reach the lower to middle 80s F along and west of the Highway 83
corridor. That will be thanks to modest low- and mid-level warm
air advection on southerly flow resulting from lee-side pressure
falls centered on MT. There is some uncertainty with the quality
of moisture return, but most 12 UTC guidance calls for surface
dewpoints only in the 50s F over western ND. Moreover, mid-level
lapse rates will be slow to steepen, which in turn is forecast to
keep CAPE relatively modest. The 12 UTC NAM and GFS nonetheless
support MLCAPE of around 1000 J/kg along with 0-6-km bulk wind
differences of 30-35 kt in northwest and west central ND Saturday
evening, supporting a marginal risk of severe storms. The most
likely scenario is that a few storms will develop over MT near the
lee-side pressure trough Saturday afternoon and then move into
western (and especially northwestern) ND Saturday evening.

.LONG TERM...(Saturday night through Friday)
Issued at 345 PM CDT Fri Jul 1 2016

The long term forecast period will be characterized by a nearly
daily chance of thunderstorms in southwest flow aloft. Such a
pattern with low-amplitude shortwaves makes it difficult for us
to confidently pin down periods of higher and lower chances of
precipitation, so we allowed the multi-model consensus to drive
the forecast with 20 to 40 percent PoPs for much of the period.
Highs will be warmest Sunday and Independence Day Monday when
we are calling for temperatures of 80 to 90 F. A cooling trend
back toward the upper 70s and lower 80s is then being shown in
our forecast by late next week.

Trends we do see in the 12 UTC guidance are that 1) The chance
of storms may be focused over western ND Sunday afternoon and
evening in a relatively narrow axis of instability, and 2) The
chance of storms on Independence Day and Monday night could be
greatest (albeit still only near 30 percent) in the James River
valley. Both periods offer up some potential for locally strong
or severe storms, but deep-layer shear is forecast to only be
near 35 kt, suggesting any risk will not be high-end.

It does appear that deep-layer wind fields will strengthen in
the Tuesday through Friday period, which in and of itself may
suggest increasing potential of strong to severe storms during the
middle part of next week. However, there is uncertainty with where
an east-west frontal zone and axis of higher theta-E air may end
up residing. True to that point, the 12 UTC ECMWF suggests that
the deeper moisture and greatest risk of showers and storms may
stay south of western and central ND.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 625 PM CDT Fri Jul 1 2016

Mainly VFR conditions expected through the forecast period with a
southeast surface flow and isolated thunderstorm chances through
00 UTC Sunday. Any thunderstorm could produce a brief period of
mvfr vsbys but at this time confidence and coverage is too low to
mention in any one TAF. It appears the northern sites of KISN and
KMOT would have the best chance of an isolated shower or
thunderstorm after midnight through mid morning Saturday. A
thunderstorm is possible again late Saturday afternoon at KISN
and KDIK but too isolated attim to mention.


.BIS Watches/Warnings/Advisories...


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