Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 221549

Area Forecast Discussion
National Weather Service Bismarck ND
1049 AM CDT Tue May 22 2018

Issued at 1036 AM CDT Tue May 22 2018

Lowered high temperatures for today across the northwest into the
mid 70s given expected cloud cover. Otherwise, isolated to
scattered rain shower and thunderstorm development is still
expected late this afternoon, continuing into the evening per the
CAMs through the 14 UTC HRRR, and the 12 UTC GFS/NAM. Overall
forcing is greatest across the northwest where mid level impulses
will propagate across, otherwise, forcing is weak elsewhere
through most of the evening. While a strong storm or two are
possible, the severe weather risk is marginal and confined to the
southwest where weak instability and marginal deep layer shear
will be locally the highest. A developing low level jet and warm
air advection may continue the thunderstorm threat through the
night southwest.

UPDATE Issued at 614 AM CDT Tue May 22 2018

Expanded patchy fog westward a bit based on current surface
weather and satellite observations. Also blended in the current
11z observations. No other notable changes were needed for this

UPDATE Issued at 456 AM CDT Tue May 22 2018

Current satellite and surface weather observations show patchy fog
across far southeast North Dakota. Added in patchy fog to the
forecast for these areas through 14z.


.SHORT TERM...(Today and tonight)
Issued at 327 AM CDT Tue May 22 2018

Showers and thunderstorms highlight the short term forecast, with
a few strong to severe storms possible across southwest North
Dakota later this afternoon and evening.

Current radar, satellite, and surface weather observations show a
cluster of slow-moving showers with a few embedded thunderstorms
across eastern Montana along a convergence zone. This area of
precipitation has not been well-handled by the latest model
guidance, albeit the HRRR and the RAP have finally begun to pick
up on it.

These showers and storms will slowly try to work into western
North Dakota this morning. CAM model guidance suggests showers and
storms will increase in coverage and intensity this afternoon and
evening across western and central North Dakota. A few strong to
severe storms cannot be ruled out later this afternoon and early
evening across southwest North Dakota, where sufficient
instability from daytime heating looks to be collocated with
marginal effective shear around 30 kts and steep low and mid-level
lapse rates. NAM BUFR soundings suggests these storms will be
slow-moving, around 10 to 15 kts from southwest to northeast.
Given the rather high forecast precipitable water values up to
1.25 inches in this area, heavy rainfall will be a concern. Gusty
winds to 60 mph and large hail up to 1 inch will also be possible
in some stronger cells.

.LONG TERM...(Wednesday through Monday)
Issued at 327 AM CDT Tue May 22 2018

Showers and storms continue through the end of the work week, with
above average temperatures expected through Monday.

Broad synoptic-scale lift ahead of a closed upper-level low
centered over Montana with weak to modest mid-level frontogenesis
will support the development of widespread showers and
thunderstorms across western and central North Dakota on Wednesday
and Wednesday night. Forecast NAM/GFS BUFR soundings suggest very
high precipitable water values up to 1.5 inches across much of
western and central North Dakota due to moisture advection from
the south. With the possibility of training storms, heavy rainfall
may be an issue on Wednesday through Wednesday night.

Severe storms cannot be ruled out on Wednesday across western and
central North Dakota, with moderate to high instability suggested
by both the GFS and the ECMWF 00z iterations. Although MUCAPE
values look to be in the 2000 to 3000 J/kg range for much of
western and central North Dakota, the shear looks more
questionable... with generally less than 30 kts of effective shear
in most areas Wednesday afternoon and evening. The main threats on
Wednesday look to be heavy rainfall and large hail at this time.

Widespread showers and storms look likely across northern and
eastern North Dakota on Thursday as the upper level low over
Montana slides northeast into Canada. The severe threat appears
limited to eastern North Dakota on Thursday, where instability,
shear, and lift are the highest within the warm sector of a
developing surface low.

The ECMWF/GFS show the upper-level low stalling out a bit over
southern Manitoba on Friday, with a shortwave rotating around the
main low. This shortwave will likely bring one last round of
showers and thunderstorms across western and central North Dakota
on Friday, before a ridge builds in from the west on Saturday and
Sunday. This will lead to a well above average temperatures this
weekend, with the latest suite of model guidance suggesting highs
in the mid to upper 80s through Sunday.

Showers and thunderstorms return to the forecast on Monday as the
ridge tries to break down.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1036 AM CDT Tue May 22 2018

Isolated rain showers across southwest North Dakota this morning.
Isolated to scattered rain showers and thunderstorms developing
across the west this afternoon, and continuing through the
evening. Scattered thunderstorms entering central North Dakota by
early this evening. Thunderstorms may continue across the
southwest through the night. More widespread thunderstorms are
expected Wednesday, especially during the afternoon and evening,
across most of western and central North Dakota. A few storms
could be severe Wednesday. VFR conditions outside of rain showers
and thunderstorms.




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