000
FXUS63 KBIS 280241
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
941 PM CDT Tue Sep 27 2016

.UPDATE...
Issued at 929 PM CDT Tue Sep 27 2016

Decided to hold off on the frost advisory for eastern portions of
central ND. Low dewpoint air (mid 30s) over the far eastern CWA
counties gets pushed westward toward the Highway 83 corridor and
settles around 37 to 39 degrees over eastern portions of the CWA.
In addition, there are still indications from meso-scale models
that there could be some fog developing over this area as higher
dewpoint air to the east settles in with clear skies and light
winds. Whether we get some fog or not...it looks like temperaturesshould
remain mainly in the mid 30s, and then only for an hour or two
before temperatures begin to rise with daybreak. Because it`s such
a shallow layer of moisture that moves into the area, not
convinced about the fog either. Will hold off right now on mention
of fog and will still mention patchy frost over eastern portions
of the CWA.

Otherwise no significant changes to the going forecast. Updated
latest sensible weather elements and blended to late evening
temperatures. Updated text products out shortly.

UPDATE Issued at 626 PM CDT Tue Sep 27 2016

Only a few tweaks to the forecast at this time. Main concern this
evening will be possible frost potential over our eastern
counties. Latest satellite loops show clouds associated with the
upper low over the northern Great Lakes along the eastern ND
border. but from wv loop mid level moisture extends to our easter
CWA border, with a well defined dry slot over the James River
Valley into the Devils Lake Basin. You can see this also with
lowest dewpoints in the upper 20s within this region and higher
dewpoints in the 40s just to the east and west.

Latest runs of the mesoscale models including the HRRR indicate
moisture pushing west into our eastern CWA counties overnight in
response to a wave dropping down the back side of the upper low.
This is resulting in the development of low level moisture in the
form of stratus/fog over eastern portions of central ND after 06
UTC. This is also noted to some extent in the global GFS and NAM.
However, at this time the western extent of cloud cover is not as
far west as models depict.

If the low level moisture does not develop as depicted by models
we may still need to issue a frost advisory over eastern portions
of central ND, although the length of time in frost advisory
criteria may be limited. If we do see the low stratus/fog
develop, it would likely keep temperatures from reaching advisory
criteria. Will continue to monitor this evening and if needed will
get an advisory out before the 10 PM News.

Otherwise a quiet evening with clear skies across the forecast
area.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 337 PM CDT Tue Sep 27 2016

Latest water vapor imagery loop shows an upper level high
circulation over northern Utah with ridging extending northeast
through Montana and into southern Saskatchewan and western
Manitoba. Models continue to show heights building with the ridge
amplifying across western and central ND tonight through
Wednesday. This is in response to a closed low sagging south from
the Great Lakes into the Ohio Valley. The end result will be sunny
and warmer weather conditions Wednesday with highs ranging from 63
in the Turtle Mountains to 74 in the southwest.

Will not mention any frost tonight as the coolest air will be focused
into eastern ND, and just graze our eastern counties, from the
Turtle Mountains south into the James River Valley. Only expect an
hour or possibly two hours where temperatures will drop to around
37 degrees, which is on the upper bound of the frost advisory
criteria. Based on this, will not issue and highlights at this time.
The evening shift can re-evaluate this again for possible changes.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 337 PM CDT Tue Sep 27 2016

Water vapor today also shows an upper low circulating across
southern Arizona. This low is currently cutoff from the main
westerlies to the north, but as a deepening upper trough sinks
south from the Gulf Of Alaska, the cutoff low get picked up is
pushed northeast on the western side of the upper ridge mentioned
in the short term period. Dry weather will prevail Wednesday night
through Thursday evening, with chances of showers and possible
thunderstorms creeping into the west Thursday night, as a 40kt 850mb
flow southerly jet becomes established. Most unstable cape and
0-6km shear values on both the GFS and ECMWF will yield at least a
slight chance of thunderstorm mention Thursday night across the
west. The upper wave shifts across central ND Friday but weakens
at the same time. Ridging briefly returns again Saturday for a dry
day before the aforementioned west coast trough sends successive
shortwave troughs through western and central ND Sunday into
Monday, with another shortwave possibly by midweek; however by the
Tuesday/Wednesday timeframe the GFS and ECMWF depart on overall
timing and placement of the shortwaves.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 929 PM CDT Tue Sep 27 2016

High pressure with light surface winds will remain over the
forecast area through the 00Z TAF period. There are some
indications of possible fog/stratus over eastern portions of
central ND, possibly as far west as KMOT and KBIS. Not confident
enough to jump on this completely given the amount of dry air
currently over the area, with only a very shallow layer of
moisture developing. Did bring a mention of scattered IFR clouds
at KJMS aft 06 UTC. KBIS and KMOT are currently depicted to be
just west of the far western edge of fog/stratus so did not
include them at this time. No issues at KDIK and KISN through the
period.

&&

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

$$

UPDATE...TWH
SHORT TERM...KS
LONG TERM...KS
AVIATION...TWH