Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 211934
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
234 PM CDT Sun May 21 2017

.SHORT TERM...(This evening through Monday)
Issued at 234 PM CDT Sun May 21 2017

Per latest regional/local radar, isolated to scattered showers
and thunderstorms mainly across the west this afternoon and
evening highlight the near term period.

An increase in areal coverage of showers and some thunderstorms
later tonight and Monday across the west highlight the rest of
the short term period.

First in the west - weak shortwaves in eastern Montana, steep low
to mid level lapse rates of 7C to 8.5C/km, and most unstable cape
values of between 200 and 500 J/Kg - are all contributing to
convection mentioned above. Effective 0-6km Bulk Shear relatively
benign 20kt to 25kt. Thus some thunderstorms could produce gusty
winds and small hail, but nothing reaching severe criteria at this
time.

Latest water vapor imagery shows another shortwave over south
central Saskatchewan which is forecast to dive south tonight
through eastern Montana. This shortwave in combination with the
left exit region of a 100kt 300mb jet streak will provide for
large scale ascent 06z-12z across western ND, per NAM/GFS Q-vector
divergence field. A cold front will also be reflected at the
surface with the above mentioned shortwave, and will enhance low
level convergence. Hence expect an increase in areal coverage for
rain showers overnight through Monday morning in the west, and
this is depicted in the gridded forecast. Closest to the strongest
low level convergence and large scale ascent, expect likely to
categorical pops tonight through Monday morning in southwest North
Dakota. For Monday afternoon, scattered showers and isolated
thunderstorms remain generally confined to southwest ND.

In the east - an upper closed low continues to circulate/spin
along the Ontario/Minnesota border. Another vorticity lobe/shortwave
trough will swing around the upper low and through the Turtle
Mountains/James River Valley Monday. Thus expect another round of
isolated rain showers to emerge Monday afternoon. Not much if any
precipitation expected across central ND as it will remain mostly
cloudy, breezy, and cool.

Highs Monday will reach the upper 50s to lower 60s along with
breezy northwest winds of 15 to 25 mph.

.LONG TERM...(Monday night through Sunday)
Issued at 234 PM CDT Sun May 21 2017

The closed upper low in southwest Ontario Monday will begin to
sag south Monday night and Tuesday. This places the James River
Valley in the western fringes of this system resulting in a mostly
cloudy, cool air regime, along with slight chances for showers.
The rest of western and central ND will be dry, with increasing
sunshine, especially farther west. Warmer afternoon highs can be
expected with more sunshine west and north with mid/upper 60s.
The southern James River Valley will remain in the upper 50s.

Brief transitory ridge slides through Tuesday night through
Wednesday afternoon, before another shortwave trough and surface
cold front sweep through Wednesday night and Thursday. A chance of
showers and thunderstorms Wednesday evening transitions to showers
the rest of Wednesday night and Thursday morning, before exiting
the James River Valley and Turtle Mountains Thursday morning.

Thereafter, Thursday through Sunday, cyclonic flow/an unsettled
weather pattern dominates as a closed upper low hovers over
southern Saskatchewan/Manitoba. The Operational GFS and to an
extent the GFS Ensembles, are slower moving this system east
versus the ECMWF. Despite this, both show a general trend/uptick
in showers/thunderstorms during peak heating in the afternoon/evening
hours then diminishing overnight. This makes sense given the synoptic
pattern and time of year. Highs mainly in the 60s to lower 70s through
this period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 234 PM CDT Sun May 21 2017

Large slow moving surface low pressure across Minnesota will move
northeast. Trough of low pressure will rotate around the low and
pull lower clouds back through the James river valley Monday
morning. MVFR at KJMS will improve to VFR Sunday afternoon then
low VFR/MVFR possible again Monday morning. Clouds at or above 7
thousand agl KISN-KMOT-KDIK-KBIS becoming 3 to 5 thousand AGL aft
08z Monday. Isolated SHRA/TSRA Western North Dakota Sunday
afternoon and evening with too much uncertainty to include in TAF
at this time.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...KS
LONG TERM...KS
AVIATION...WAA



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