Area Forecast Discussion
Issued by NWS Bismarck, ND

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899
FXUS63 KBIS 230535
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1235 AM CDT Sat Sep 23 2017

.UPDATE...
Issued at 1235 AM CDT Sat Sep 23 2017

Global and CAM models show limited instability across western
North Dakota tonight although showers will continue moving into
the southwest. The lightning network showers the preponderance of
flashes well east of the Missouri River in South Dakota. So with
this updated see little to change from previous forecast.

UPDATE Issued at 934 PM CDT Fri Sep 22 2017

Shower activity centered on western SD as of 02 UTC is associated
with the next impulse expected to move northeast into ND tonight.
The forecast is generally on track, but once again we focused on
refining PoPs with this update, particularly relying on iterations
of the HRRR through its 01 UTC cycle since it appears to be doing
the best job assimilating current radar returns in southwest ND.
Lingering steep lapse rates aloft may still support thunderstorms
in the southern James River valley as the impulse reaches there,
but forecast soundings taken across Dickey County from the 00 UTC
NAM and recent RAP cycles suggest MUCAPE will be limited to 200 to
700 J/kg, and that will be driven by parcels originating above 700
mb, with resultant small normalized CAPE supportive of only a low
(though certainly non-zero) probability of a strong storm in that
area.

UPDATE Issued at 645 PM CDT Fri Sep 22 2017

Elevated convection increased in coverage from Stutsman into
Foster Counties late this afternoon, on the nose of the strongest
mid-level warm air advection centered near 850 mb per RAP-based
guidance. That forcing is expected to be the primary driver of
precipitation through the evening and so we refined PoPs slightly
accordingly with this update, focusing on that area northward
toward Rolla. Earlier brief subsidence in the wake of what
appeared to be an eastward-propagating gravity wave per
preliminary, non-operational GOES-16 visible satellite imagery
has shifted eastward. The exit of that mesoscale subsidence also
likely contributed to the convection, but the warm air advection
is also forecast to refocus eastward by mid evening and so that
will cause precipitation chances to dwindle until after 06 UTC,
when another vorticity maximum embedded in southwest flow aloft
will reach southern ND. Some recent HRRR simulations suggest a
strong storm could affect Dickey and LaMoure Counties with that
wave late tonight, where MUCAPE will likely still be sufficient
for isolated stronger, elevated updrafts.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 139 PM CDT Fri Sep 22 2017

Scattered showers and thunderstorms will continue through the
evening hours for most of western and central North Dakota. Later
tonight precipitation shifts south and east as the surface trough
swings into Minnesota. With ample elevated instability, shear and
a low freezing level, several storms could produce marginally
severe hail this afternoon and evening. A very cool night is in
store with northerly winds and temperatures in the 30s and low
40s for most.

.LONG TERM...(Saturday night through Friday)
Issued at 139 PM CDT Fri Sep 22 2017

The main focus for the Long term will be cooler temperatures with
a good chance for showers Saturday and Sunday. The cool weather
will last at least through next Tuesday. Highs during this period
will be in the 50s and lows in the mid 30s to mid 40s. There could
be some patchy frost during this period. Chances for showers will
continue through Tuesday until the upper trough finally moves
through. Then moderating temperatures at least into the 60s are
expected with mainly dry weather for Wednesday and Thursday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1235 AM CDT Sat Sep 23 2017

MVFR and IFR ceilings are expected to remain widespread across
western and central ND this morning. Showers were developing in
southwestern ND, and are expected to continue developing southwest
and expanding into south central ND. A few thunderstorms are also
possible south of KJMS.

Conditions to improve a bit this afternoon with varied VFR and MVFR
ceilings. However a more widespread area of rain is expected to
develop in southwest ND Saturday afternoon as a stronger disturbance
approaches. This widespread area of rain will expand into northern
North Dakota Saturday night and continue into Sunday, with MVFR and
IFR conditions at all TAF sites.

&&

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

$$

UPDATE...WAA
SHORT TERM...AJ
LONG TERM...AJ
AVIATION...JV



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