Area Forecast Discussion
Issued by NWS Bismarck, ND

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493
FXUS63 KBIS 172333
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
633 PM CDT Tue Jul 17 2018

.UPDATE...
Issued at 624 PM CDT Tue Jul 17 2018

Isolated showers over south central North Dakota are dissipating
as was expected in a region of very weak shear and cape. Several
outflow boundaries remain so cant rule out a brief shower yet this
evening. But after 8 pm CDT the focus will be on the far
southwest for scattered showers and isolated thunderstorms. Severe
weather is not expected.

UPDATE Issued at 413 PM CDT Tue Jul 17 2018

Widely scattered thunderstorms have initiated across far south
central North Dakota in a very weak cape and shear area. Believe
these will be short lived for the next hour or two. Otherwise the
best chance for precipitation will be in the southwest later this
evening and overnight.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 201 PM CDT Tue Jul 17 2018

Quiet weather will continue this evening for all but far southwest
North Dakota where there is a chance of showers and thunderstorms
late tonight.

An upper level low developing over Montana will begin moving into
southwest North Dakota late tonight. This will be the main forcing
mechanism for showers/thunderstorms. The latest CAM model
guidance shows very weak and scattered activity.

Severe weather is not expected with these storms as the 12z
iterations of the NAM/GFS/ECMWF all suggest very weak
environmental wind shear and limited instability.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 201 PM CDT Tue Jul 17 2018

Mild temperatures and several chances for thunderstorms highlight
the long term.

An upper level low will continue to slowly move eastward across
the Dakotas Wednesday through Thursday night, bringing with it
sufficient synoptic scale lift and moisture for scattered showers
and thunderstorms. With the 12z iterations of both the GFS and
the ECMWF showing weak wind shear and low to moderate
instability, widespread severe weather is not likely. The favored
storm mode will be scattered air mass thunderstorms, with locally
heavy rainfall and brief periods of small hail and gusty winds
being the main threat. These storms will be rather slow moving
given weak winds aloft. Forecast NAM/GFS BUFR soundings suggest
moderate to high precipitable water values during this time
period, especially across southern North Dakota where values
approach 2 inches.

A ridge builds in across western and central North Dakota behind
the upper level low for Friday and Saturday, with dry weather
expected.

A cold front will move through Sunday, bringing enough forcing
for another round of scattered showers and storms.

The latest model runs show 40-50 knots of wind shear across the
area Sunday and Sunday night. This looks to be collocated with
moderate instability. Severe weather looks possible on Sunday and
Sunday night as the cold front moves through the area within a
favorable environment.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 624 PM CDT Tue Jul 17 2018

A trough of low pressure across southeast Montana will be the
focus for scattered showers and thunderstorms late tonight and
Wednesday. The showers will move from southwest North Dakota into
central North Dakota by afternoon Wednesday. VFR expected at all
TAF sites. Only added VCTS to KBIS as the south central will have
the better chance.

&&

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

$$

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



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