Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 010443
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1143 PM CDT TUE MAY 31 2016

.UPDATE...
Issued at 1143 PM CDT Tue May 31 2016

Latest water vapor imagery and local/regional radar shows the
persistent closed upper low circulating near Devils lake with
narrow bands of showers continuing to cyclonically rotate around
the low and into northern and central North Dakota. Adjusted pops
per latest radar trends for the remaining overnight period, slowing
down the eastward shift and keeping isolated to scattered rain
showers in the forecast across central ND.

UPDATE Issued at 930 PM CDT Tue May 31 2016

Previous forecast remains on track as thunderstorms in the central
part of the state rapidly diminish. Focus overnight will be on
aviation with low clouds.

UPDATE Issued at 655 PM CDT Tue May 31 2016

Have allowed the wind advisory west to expire as winds are
trending down. A few thunderstorms have formed in the north
central with a report of small hail from one of the more organized
storms over Rolette county. Did extend chances for thunderstorms
through 02 UTC. Small hail and brief heavy rainfall will be the
main threat from these low topped storms along with the chance of
a few cold air funnels.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 342 PM CDT Tue May 31 2016

Showers will gradually end tonight, leaving a cooler, but mostly
dry day on Wednesday, when highs will mainly be in the 60s F.

We will continue the wind advisory over western ND through 00 UTC
as many sites have occasionally been reaching criteria of 45 mph.
Surface pressure rises near 3 MB/3 hours are also moving into
western ND as of 20 UTC, and should continue to enhance winds as
they press southeast the next several hours. Forecast soundings
from the RAP and HRRR continue to show up to 50 kt of wind in the
mixed-layer from Williston to Dickinson and Hettinger through the
early evening, as well, and showers will likely facilitate mixing
of some of that wind to the ground despite marginal subsidence in
the boundary layer.

Otherwise, early afternoon mesoscale analysis output based on the
RAP model shows an axis of non-supercell tornado parameter values
over 2 just west of Minot as of 20 UTC. However, it appears that
is mainly being driven by enhanced surface vorticity tied to the
stacked low pressure system over ND, as 0-3-km SBCAPE values are
less than 100 J/kg per that mesoscale analysis. Thus, while the
risk of funnels or a weak cold-core tornado is non-zero, it is
sufficiently low to negate any mention in outlooks and statements
at this point.

Guidance is in good agreement suggesting that showers will very
slowly wind down tonight as diurnal instability wanes with sunset,
and as dynamics with the stacked low diminish as it slowly moves
east-northeast. We relied on a time-lagged blend of rapid-refresh
and high-resolution model guidance for the PoP forecast tonight
given good agreement with regard to that scenario among various
simulations. A low-end chance of showers was then lingered into
Wednesday morning over parts of central ND in the last vestiges of
cyclonic flow. Even the NCEP WRF-ARW and WRF-NMM suggest a few
showers will linger in that corridor through at least 18 UTC.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 342 PM CDT Tue May 31 2016

The long term forecast period is highlighted by a chance of
showers and thunderstorms late Thursday afternoon through Friday,
and a warmer period late this week through early next week.

The 12 UTC models are in relatively good agreement advertising a
shortwave trough passage in short-lived quasi-zonal 500-MB flow
centered on Thursday night. The 12 UTC ECMWF is slightly slower
with the arrival of the shortwave trough (by about 6 hours), and
would suggest a bit lower late afternoon/early evening chance of
convection in western ND than the 12 UTC NAM and GFS. This small
difference was resolved in the official forecast by relying on a
normally-well-verifying model blend, which justified inclusion of
low-end PoPs across western ND after 21 UTC Thursday. Higher PoPs
are then being carried eastward Thursday night. Southerly flow is
forecast to advect lower 50s F surface dewpoints into the area in
advance of the trough, and relatively steep mid-level lapse rates
are forecast to yield MLCAPE of 500 to 900 J/kg during the late
afternoon and evening, and MUCAPE of a similar magnitude Thursday
night. That`s sufficient for thunderstorms, but calibrated severe
storm probabilities from the 09 UTC SREF are less than 5 percent.

Lingering cyclonic flow in the wake of the shortwave trough could
yield additional showers and thunderstorms Friday, especially in
central ND. Thereafter, confidence is still high in a warmer and
drier regime taking hold this weekend and continuing through early
next week as a well-formed 500-MB ridge takes hold over the Rocky
Mountain region. That scenario is well-supported by deterministic
and ensemble model guidance, including the 12 UTC GFS and ECMWF.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1143 PM CDT Tue May 31 2016

Mvfr cigs/vsbys with occasional -shra continue for all terminals
except KISN. Gusty northwest winds to 28kt will also continue
through 13z Wednesday. Mvfr cigs will slowly lift to low vfr at
KMOT/KBIS around 18z Wednesday, and by 21z at KJMS. KDIK should
transition from mvfr to vfr by 13z.

&&

.BIS Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...KS
SHORT TERM...CJS
LONG TERM...CJS
AVIATION...KS


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