509 
FXUS63 KBIS 301759
AFDBIS

AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
1159 AM CST Fri Dec 30 2022

.UPDATE...
Issued at 1146 AM CST Fri Dec 30 2022

Stratus has been eaten away across the west and central and
continues a northward erosion in the north. High-res models want 
to rebuild stratus from the south central late this afternoon, and
there are fingers of stratus seen on GOES-East imagery over
Sioux/Emmons/Grant counties. Still somewhat uncertain about
stratus redevelopment so quickly in the afternoon, but there is a
bit of an observed trend and good agreement in forecast soundings.
Additionally, reduced visibilities from fog or very low ceilings
are expected to develop tonight, especially central and east.
Increased fog coverage in the forecast tonight based on high-res
model output. 

UPDATE Issued at 927 AM CST Fri Dec 30 2022

Stratus and fog will continue to be the forecast challenge through
tomorrow. Stratus has eroded in the south central this morning,
but short term guidance wants to rebuild this stratus this
afternoon. Confidence is pretty low in the redevelopment of this
stratus during the daylight hours, but widespread stratus tonight
looks reasonable for most areas outside of the far west. Overall
visibilities this morning have gradually improved, though there
remains a couple sites in the northwest that are at one quarter
mile visibility. With this trend, will refrain from issuing
another SPS for now. 

UPDATE Issued at 547 AM CST Fri Dec 30 2022

Areas of fog have developed across portions of western and central
North Dakota over the past couple of hours as evidenced by surface
observations and traffic cams. Observations have shown various 
sites at a half-mile visibility or less at times, in particular 
Hettinger, Mandan, Hazen, Tioga, and Stanley. This fog should 
slowly expand east through the morning. There is some uncertainty 
about how long fog will last as some of the CAMs keep it in place 
through the entire day across many areas, but this looks to be a 
bit overdone and may end up being mainly stratus. For now, we 
decided to go ahead and issue an SPS for areas of fog across 
portions of the west and central through 15z. There's a chance we 
could end up needing a Dense Fog Advisory eventually, but for now 
the lower visibility observations continue to be fairly transient.
Otherwise, the forecast looks to be on track. 

&&

.SHORT TERM...(Today and Tonight)
Issued at 302 AM CST Fri Dec 30 2022

Widespread low stratus and patchy fog will continue this morning
over much of western and central North Dakota. Weak surface high
pressure is currently centered over eastern North Dakota and will
continue to slide east southeast through the day. This will mean
some clearing across the west and rising ceilings for most across
the central in the afternoon. However, lower stratus may hang on 
over the James River Valley through the day. Some of the CAMs are
also hanging onto fog through the day across portions of the 
central and east, but CAMs were also suggesting fog would be 
widespread by now. Thus far we are only seeing a few dips in 
visibility here and there across the southwest this morning. Did 
go ahead and paint in widespread patchy fog again tonight given 
the weak southerly flow and abundant snowpack. CAMs are also once 
again on board with this potential, but could be a bit too 
aggressive. 

At the upper levels, weak zonal flow will keep the area dry with 
highs generally a touch warmer than yesterday: from the mid teens 
northeast to the lower 30s southwest. Tonight's lows will
mainly range from mid single digits above zero to the mid teens.

.LONG TERM...(Saturday through Thursday)
Issued at 302 AM CST Fri Dec 30 2022

Fog may linger Saturday morning, but a weak short wave will move
through in the afternoon which should clear things out. This wave
should generally be dry but a few flurries may be possible in the
afternoon or evening. Expect some subsidence in the afternoon
across the west and into portions of the central which should
promote some clearing and slightly warmer temperatures. Highs 
will range from around 20 northeast to the low to mid 30s 
southwest.

Sunday may see a period of transient ridging in advance of the
next strong trough which will dig into the desert southwest.
Precipitation chances will then increase Sunday night across the
far south in advance of the next Colorado Low set to impact
portions of the Central/Northern Plains and into the Upper
Mississippi Valley/Great Lakes region. The chance for significant
precipitation continues to shift even more south with seemingly 
each successive suite of guidance. While it is not out of the
question that we could see some light snowfall accumulations
across the south Sunday night through Tuesday morning, it is
looking more and more likely that the brunt of the storm will
track over South Dakota and into the southern half of Minnesota.
The latest NBM 4.1 probabilities for 6 inches or greater max out
(at least in our forecast area) in the 20 to 30 percent range 
across the far south central and southeast near the South Dakota 
border. GEFS plumes for Bismarck and Jamestown continue to show
substantial spread with mean liquid QPF values of around 0.2 and
0.3 inches respectively. However, it is worth noting that a few
outliers continue to show some higher QPF amounts, moreso over 
Jamestown. ECMWF ensemble members continues to be much lower 
across the board with the CMC somewhere in between. Those with 
travel plans across the region should continue to monitor the 
forecast closely.

The passage of this system will bring cooler temperatures to the
area with highs on Monday and Tuesday in the mid teens to mid 20s,
and then down into single digits and teens for most by Wednesday
and Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
Issued at 1146 AM CST Fri Dec 30 2022

MVFR to IFR, LIFR in some places, stratus continues but is eroding
over the north and east, impacting KXWA-KMOT-KJMS to start the
forecast period. Guidance indicates a quick redevelopment of
stratus again from the south central late afternoon, though
confidence on timing is somewhat low regarding if stratus develops
rapidly during the daytime hours. That said, there are indications
of this stratus developing south of KBIS, so IFR cigs were added
to the TAF at 22Z. IFR to LIFR ceilings and visibilities expected
across the central and the east tonight, with LIFR conditions
possible at times. KXWA-KDIK should remain VFR. 

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...AE
SHORT TERM...ZH
LONG TERM...ZH
AVIATION...AE