Area Forecast Discussion
Issued by NWS Bismarck, ND

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196
FXUS63 KBIS 190248
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
948 PM CDT Wed Apr 18 2018

.UPDATE...
Issued at 937 PM CDT Wed Apr 18 2018

No big changes to the going forecast. Did make some minor changes
to fog tonight.

Surface high pressure is situated over southeast Saskatchewan and
will continue to drop southeast overnight. Latest NAM surface
analysis shows the High situated over northwest ND at 12 UTC.
This appear to be the favored area for stratus/fog tonight. Latest
satellite shows this area is already under a patch of stratus. As
you move farther south, skies are clear over southwest ND, and
east of the area, high clouds are scooting east. However, looking
at BUFKit soundings, turbulence appears too great for fog
development in these areas until later tonight, as the surface
high moves closer. Thus we limited the areal extent of fog this
evening and limited mention of widespread fog until late tonight
into Thursday morning. Also a question of whether or not fog
develops under current area of stratus in the northwest. BUFKIT
indicates this may not be until 06Z or after when conditions for
fog, instead of stratus become more favorable.

Updated text products will be sent shortly.

UPDATE Issued at 619 PM CDT Wed Apr 18 2018

High pressure will build over the forecast area tonight with the
center of the high pretty much over the same area as the inverted
trough was located the past two days. Thus abundant surface
moisture remains under the high with clearing skies and light
winds expected overnight. Previous forecast already added fog to
the forecast and mesoscale models continue to hit KMOT and KISN
hardest with at least a mention of fog at KDIK and KBIS tonight
into Thursday morning. Will continue to monitor. Updated latest
sensible weather elements. Updated text products will be sent
shortly.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 150 PM CDT Wed Apr 18 2018

Widespread fog returns tonight and into tomorrow morning.

A surface high pressure system will build into North Dakota
tonight. Light winds combined with a lowering stratus deck will
lead to widespread fog across most of western and central North
Dakota beginning tonight and continuing through tomorrow morning.
The latest CAM model guidance through their 18 UTC iterations
supports fog development during this time, as well as the
forecast NAM and GFS BUFR soundings. It is possible that fog will
linger into the early afternoon hours tomorrow across northwest
North Dakota.

Expect sunshine to break out for most of western and central North
Dakota tomorrow afternoon as much drier air moves into the area,
as suggested by forecast BUFR soundings. This will help warm
southwest and south central North Dakota well into the 50s, while
the far northwest may stay stuck in the upper 40s due to lingering
fog and low stratus. Areas with snowpack still on the ground may
also stay in the 40s, however any leftover snow is continuing to
rapidly melt.

.LONG TERM...(Thursday night through Wednesday)
Issued at 150 PM CDT Wed Apr 18 2018

A pattern change to warmer temperatures and drier weather will
overtake western and central North Dakota this weekend.

A split flow synoptic pattern will prevail Thursday night through
the weekend across the CONUS, with nearly zonal flow aloft over
North Dakota and a large upper-level low over the Central Plains.
This will set the stage for a mainly dry pattern through the
weekend, with very little to no synoptic scale lift expected and
no shortwaves or fronts moving through the region to support
precipitation.

The latest 12 UTC global suite suggests a rather cloudy day on
Friday, leaving temperatures stuck mainly in the 50s across
western and central North Dakota. Clouds decrease significantly
after that with plenty of sunshine expected on Saturday and Sunday
when forecast GFS BUFR soundings suggest low relative humidities
with a well mixed boundary layer up to nearly 700 mb.

As the air aloft mixes down to the surface, compressional warming
will likely lead to high temperatures that are noticeably higher
than what the latest model guidance suggests. The HRRR, RAP, and
the NAM all show model snow depth values that are much too high
compared to observations, which is keeping the forecast
temperatures too low. In addition, bias-corrected model guidance
is too cold as well, likely due to a pattern change. For these
reasons, high temperatures have been manually increased by
several degrees across western and central North Dakota for
Thursday through Sunday over the 12 UTC guidance consensus.

A potent shortwave will swing through North Dakota from the west
on Monday through Tuesday, leading to chances for rain across
southern North Dakota. Conditions look to dry back out for
Wednesday as a ridge tries to build back in.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 937 PM CDT Wed Apr 18 2018

VFR conditions to begin the TAF period but mvfr ceilings lingering
around KISN and KMOT. Mesoscale models indicate low stratus/fog
developing in this area 03-06 UTC and expanding south to KDIK &
KBIS around 08-10 UTC. Low stratus/fog dissipate during the
morning hours Thursday with VFR conditions by 18 UTC. Light and
variable winds through the forecast period.

&&

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

$$

UPDATE...TWH
SHORT TERM...TK
LONG TERM...TK
AVIATION...TWH



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