Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 211749
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1249 PM CDT Thu Sep 21 2017

.UPDATE...
Issued at 1245 PM CDT Thu Sep 21 2017

Only changes to the forecast were to tighten the temperature
gradient from northwest to southeast a bit today. Also bumped up
winds bit early this afternoon southeast.

UPDATE Issued at 939 AM CDT Thu Sep 21 2017

Jet induced showers/virga continue to lift northeast across
northern portions of the forecast area while skies clear across
the south. Made some minor changes to sky cover, clearing clouds
out a little more across the south. With mostly sunny skies and
strong warm advection in the far south central, bumped up
temperatures here a bit this afternoon. Will also keep an eye on
late morning through mid afternoon winds far south central into
the James River Valley, but current forecast looks reasonable.
There is some elevated instability in the southern James river
valley this afternoon, but think we will see enough capping here
to inhibit convection.

UPDATE Issued at 618 AM CDT Thu Sep 21 2017

Current observations suggest quite a bit of VIRGA moving into
western North Dakota this morning associated with the strong mid
level jet lying across Montana. Eventually some precipitation
should reach the ground so have left the POPs in place. As with
jet induced precipitation in general, its movement and
orientation will follow the jet and move quickly north.

The next challenge will be the development of gusty southerly
winds in south central North Dakota today with the James River
Valley the best place for the gusty winds. Quick look at the 12Z
Bismarck sounding so far shows 25KT low level winds. Will hold off
on any wind advisory for today. Current forecast looks ok.

&&

.SHORT TERM...(Today and tonight)
Issued at 324 AM CDT Thu Sep 21 2017

For the near term, a possible wind advisory mid morning for south
central and the James River Valley. A cold front stretching from
western Saskatchewan into eastern Montana will gradually move east
today. A pronounced 850mb baroclinic zone will shift through
western ND during the morning, across central ND by mid afternoon,
then stalling out in the southern James River Valley this
evening/tonight. Latest RAP/HRRR indicating a strengthening low
level southerly jet south central and the James River Valley,
between 50kt and 60kt. Trends in the BUFKIT soundings are for the
thermal profiles to transition from an early morning surface
inversion to adiabatic by 15z, with mixing heights increasing
thereafter, and tapping/mixing into the stronger winds aloft. The
RAP and HRRR have trended lower with overall mixing heights during
the morning, allowing the strongest winds aloft to remain there
and not be tapped into. It appears now that we could tap into
winds between 35kt and 40kt. Will continue to monitor the BIS VAD
wind profile for verification and the 12z BIS upper air sounding
for added confidence that winds are materializing as to the models
expectations before issuing any highlights at this time.

The latest suite of satellite imagery shows thickening mid/upper
level clouds across northwestern South Dakota, into southwestern
and portions of north central North Dakota. Regional radar,
including the Bowman radar indicates increasing reflectivity`s
south of the border, steadily moving northeast. Synoptic scale
vertical motion well underway per NAM Q-Vector Convergence Field
across southeastern Montana, southwestern ND, and western SD. This
will propagate northeast through 18z. Vertical motion will be
enhanced somewhat with the proximity of an upper level jet streak
atop the surface/low level front. Will follow the gridded data
which increases pops/scattered to numerous rainshowers developing
from southwestern ND, up through the west and into the north
central through 18z. There should be a quick diminish and ending
to the showers after 18z, as the main area of ascent pushes across
the northern border, being replaced by low to mid level
subsidence.

Looking broader, the latest water vapor imagery loop shows a
large elongated positive tilted upper trough stretching from
central Manitoba, southwest to the tip of the Oregon/California
coastline. Several circulations were embedded within/around this
large trough. A fairly solid 120kt to 130kt 300mb jet core was
established from just off the California coast, through the
Intermountain West, and into the southern Canadian Prairies.
Through Friday, an additional jet streak and cold pocket on the
western side of the trough will help form a closed Low in southern
Idaho. As the upper flow buckles, a strong southwesterly flow
initiates across western/central North Dakota along with weak
height rises through Thursday night. This trough will be with us
through Tuesday of next week, and as it approaches this weekend,
much cooler air along with increased chances for showers will
commence. More on this in the long term discussion.

.LONG TERM...(Friday through Wednesday)
Issued at 324 AM CDT Thu Sep 21 2017

With southwesterly flow aloft paralleling the surface front
across the southern James Valley, very little movement is
expected with it Friday and Saturday. Precipitation amounts
heaviest near/along the front, with lesser amounts farther west
and north. Overall the models are in decent agreement that
Saturday, Saturday night and Sunday represent the highest
probabilities for showers. This is when the strongest ascent and
jet dynamics are overhead and interacting with the stalled
frontal system in the southeast. SPC does highlight a Marginal
Severe Risk from Minot to Jamestown Friday. Despite strong ascent
pushing across the north central Friday, the strongest instability
and shear resides in the James River Valley per NAM/GFS/ECMWF.
Showers will become much less Monday and Tuesday with a dry day
forecast on Wednesday. Temperatures will cool into the mid 50s
Friday through Monday, with a slow rebound into the lower 60s by
Wednesday as the upper trough departs.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1245 PM CDT Thu Sep 21 2017

A cold front will move through central ND this afternoon and
evening. Strong southerly winds ahead of the front will shift
north to northwest behind the front. Mid level VFR conditions
expected behind the front tonight. MVFR ceilings will lift from
south Dakota northward into ND after 12 UTC Friday bringing a
period of MVFR ceilings to KJMS and possibly KBIS 15-18 UTC.

&&

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

$$

UPDATE...TWH
SHORT TERM...KS
LONG TERM...KS
AVIATION...TWH



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