190 
FXUS63 KBIS 250620
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1220 AM CST Thu Jan 25 2018

.UPDATE...

Issued at 1202 AM CST Thu Jan 25 2018

Dense fog advisory remains in good shape as visibility remains
around a quarter mile in Rolla. Only change to forecast was to
stretch overcast cloud cover to the southeast a bit based upon
latest satellite trends.

UPDATE Issued at 946 PM CST Wed Jan 24 2018

We issued a Dense Fog Advisory for parts of north central ND into
the Turtle Mountain region in collaboration with NWS Grand Forks.
The Rolla AWOS has reported 1/4SM visibility for several hours,
and while we believed that to be localized earlier, trends in the
web camera images at Dunseith and GOES-East nighttime microphysics
RGB imagery suggest the fog is expanding into a wider area. The
last few cycles of the RAP, HRRR, and especially the ESRL HRRR 
are also supportive of dense fog in that area overnight, though we
do have to admit confidence in the longevity of low visibility 
even in that area is tempered by modest low-level turbulence seen
in model forecast soundings viewed in BUFKIT. Interestingly, the 
rapid-refresh model suite has backed off considerably on the fog 
potential in the James River valley the last few hours, so we are 
less confident in the eventual possibility of an advisory in that 
area than earlier. Mid- and high-level clouds streaming southeast 
across the area may be slowing surface cooling a bit and that may 
be one reason fog and stratus in general has been slower to form 
than earlier thought, especially in the James River valley. Those 
trends did support raising lows a bit in central ND overnight, but
we tempered changes slightly there too since even minor breaks in
the higher-level clouds have allowed for efficient cooling in low-
lying areas less susceptible to the increasing warm air advection
aloft. For example, Tioga quickly fell to 9 F this evening when a
break in the cloud cover passed that area.

UPDATE Issued at 556 PM CST Wed Jan 24 2018

Little change was made with this update cycle. GOES-East-based IFR
probability output from SSEC suggests stratus in north central ND
is beginning its westward propagation, and the latest iterations
of the RAP, HRRR, and NBM continue to support both that expansion
of low clouds and development of fog overnight in central ND. The
consensus of that guidance suggests the lowest visibilities and
thus highest probability of Dense Fog Advisory issuance is across
the James River Valley, but forecast soundings suggest a slightly
more turbulent near-surface layer than last night and thus the
longevity of the lowest visibilities is still too uncertain for us
to issue a headline just yet. Otherwise, the going forecast calls
for lows in the single digits F on the immediate west side of the
expected low cloud deck, from Garrison to Bismarck/Mandan, and we
have retained that given persistence trends from the past couple
nights when radiational cooling was enhanced in that region. That
said, MOS-based guidance and observed late afternoon dewpoints in
that area suggest that may be too cool, so we will be monitoring 
trends the next few hours in case lows need to be increased over 
that part of central ND.

UPDATE Issued at 349 PM CST Wed Jan 24 2018

Quick update to blend recent observational trends into the late
afternoon forecast, and to increase cloud cover across central ND
through the mid evening in respect to recent GOES-East imagery
which shows high-level cloud cover streaming across the area as of
21 UTC. ASOS/AWOS trends also show stratus lingering across parts
of east central ND at this hour, and we still expect expansion of
the stratus westward during the evening.

&&

.SHORT TERM...(This evening through Thursday)
Issued at 148 PM CST Wed Jan 24 2018

Another night of weak southeast surface winds and generally clear 
skies should allow fog to again form and spread westward from east 
central North Dakota into portions of the south central and west 
central this evening and overnight. Used the CONSHORT for guidance 
for the timing and extent of the fog. At this time some uncertainty 
on how dense the fog will be, but suspect there will be areas of 
dense fog that may eventually require an advisory. However the 
timing and extent are uncertain so will leave the advisory decision 
during the evening period. 

Will Thursday finally bring an end to the threat of fog?. Models 
show strengthening h850/h925 warm advection flow and the a much 
shallower inversion Thursday afternoon, that finally mixes out 
Thursday night with the advancing surface trough and cold advection. 
So do believe this will be the last night for fog. 

Followed the Superblend for Thursday's highs but did raise the high 
temperatures a few degrees southwest into the mid 40s. 

.LONG TERM...(Thursday night through Wednesday)
Issued at 148 PM CST Wed Jan 24 2018

A generally progressive flow remains in place for the extended so a 
bit of a roller coaster temperature profile appears in store. The 
building ridge across the region Thursday will maintain mild 
temperatures in the 30s to middle 40s Thursday with the warmest 
temperatures southwest. This will be followed by a Pacific cold 
front Friday with colder air arriving behind a secondary frontal 
passage Friday night. Friday looks breezy but not windy with spotty 
chances of snow. The weekend looks cooler with highs in the teens 
and 20s Saturday and single digits to the teens and 20s Sunday as 
the colder air hours in. Wind chill temperatures could approach 20 
below across the north central Saturday night. 

A return to milder temperatures is forecast Monday and Tuesday as 
the progressive flow brings in another h500 ridge, followed by 
cooler air Wednesday. Teleconnections suggest a longer cold 
period is possible after Wednesday as a broad h500 trough sets up 
over Hudson bay ending the progressive flow regime. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)

Issued at 1215 AM CST Thu Jan 25 2018

Latest model trends have backed off on the south and west push of
the low stratus into KMOT and KJMS. Current westward extent of the
stratus and fog has remained quasi-stationary just east and north
of KMOT and KJMS, with models keeping it here or even retreating.
Latest satellite trends support this so have kept both terminal 
forecasts MVFR-IFR at worse through 12Z versus LIFR-VLIFR 
conditions. Elsewhere for KISN-KDIK-KBIS, VFR conditions should 
prevail with a SCT-BKN upper level cloud deck through the period. 


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 10 AM CST this morning for NDZ003>005-
012-013.

&&

$$

UPDATE...JJS
SHORT TERM...WAA
LONG TERM...WAA
AVIATION...NH