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Area Forecast Discussion (AFD)

Issued by Bismarck, ND (BIS)

FXUS63 KBIS 201943

Area Forecast Discussion
National Weather Service Bismarck ND
243 PM CDT Fri Jul 20 2018

.SHORT TERM...(This evening through Saturday Night)
Issued at 212 PM CDT Fri Jul 20 2018

Possible smoke impacts this evening into Saturday, and severe
thunderstorm potential west Saturday evening highlight the short
term forecast.

The main question for this evening through tomorrow is possible
smoke impacts from a fire approximately 115 miles northeast of 
Winnipeg as smoke may be transported in the low levels around the
surface high. Visibility across the northern Red River Valley and
northwest Minnesota downstream of the fire is reduced as low as 4
to 7 miles. The experimental 12Z HRRR-Smoke forecast would 
suggest an increasing potential for near-surface smoke across 
western and central North Dakota this evening through tonight, and
possibly lingering into Saturday. Will continue to monitor 
upstream satellite and surface observation trends. 

For Saturday, did increase highs across the west into the upper
80s and lower 90s, closer to the warm edge of the 12-15 UTC
guidance envelope with the low level thermal ridge axis. 
Regarding convective potential, SPC has placed a Slight Risk 
across northeast Montana, into far northwest North Dakota, with a 
Marginal Risk extending east to approximately Portal through 
Dickinson and Hettinger. The 12 UTC CAM and global consensus is 
for convection to initiate late Saturday afternoon or early 
evening across eastern Montana along the cold front and inverted 
trough. This convection may approach the North Dakota border 
around 00-03 UTC. While deep layer shear is strong, around 
40-50kts and oriented generally orthogonal to the surface 
boundaries, the zone of 1500-2000 j/kg of MLCAPE is rather narrow,
and quickly drops off across western North Dakota. While 
organized convection, including possibly a supercell or two, may 
enter western North Dakota Saturday evening, the approach of 
sunset and propagation too far east of the best instability should
limit the severe threat to the west and likely ending by 06 UTC. 
Thunderstorms may be sustained into the night across central North
Dakota with the low level jet, however, their intensity should be
weaker and likely less organized. 

.LONG TERM...(Sunday through Friday) 
Issued at 212 PM CDT Fri Jul 20 2018

Severe thunderstorm potential central on Sunday highlights the
extended forecast.

A cold front with a mid level jet streak/shortwave will be the
focus for thunderstorm development across central North Dakota
Sunday afternoon and into the early evening. Cloud cover impacts
from likely ongoing morning convection adds uncertainty to
afternoon heating and destabilization. Deep layer shear around
40kts, and generally orthogonal to the cold front, would support 
the potential for discrete organized convection. Precipitable 
water climbing to around 1.75 inches supports the potential for 
locally heavy rainfall, including across portions of the James 
River Valley that saw very heavy rainfall earlier this week. 

For much of next week, rather fast west-northwest mid level flow
south of the Canadian upper level low supports sporadic chances
for thunderstorms associated with low predictability impulses. 


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 212 PM CDT Fri Jul 20 2018

VFR conditions are forecast across western and central North
Dakota for the 18 UTC TAF cycle. However, smoke from a fire
approximately 115 miles northeast of Winnipeg could be transported
southwest into western and central North Dakota this evening into
Saturday. This could impact surface visibility, however, this
remains somewhat uncertain.