Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 151536
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
936 AM CST Sun Jan 15 2017

.UPDATE...
Issued at 927 AM CST Sun Jan 15 2017

For the mid morning update we interpolated latest surface
observations to 18Z temperatures. 9AM CST temperatures ranging
from 20 at Dickinson to 5 at Glen Ullin and 0 at Hettinger. Nine
below zero at the Bismarck Airport and 5 above at the Mandan
Airport. Short term guidance is not picking up on the wide
variation. An interpolation to early afternoon temperatures keeps
our current forecast highs which still look reasonable most
areas. Otherwise no changes to the going forecast.

UPDATE Issued at 649 AM CST Sun Jan 15 2017

Hourly forecast fields were updated through 18 UTC today with this
update, which mainly meant hourly temperatures were adjusted a bit
to reflect observed trends. Warm air advection aloft is ongoing,
but shallow, modified Arctic air remains entrenched at the surface
and is most pronounced in river and creek valleys. The 12 UTC
Bismarck sounding reflects this scenario well, showing a very sharp
surface-based inversion with a surface temperature near -10 F and
a 925 mb temperature of 32 F. That`s only about 950 ft AGL. This
is yielding a wide variation in temperatures across western and
central ND this morning due to only subtle elevation differences.

&&

.SHORT TERM...(Today and tonight)
Issued at 327 AM CST Sun Jan 15 2017

Temperatures will be the main forecast challenge and highlight in
the short term period.

Currently, the main belt of the westerlies was over central/southern
Canada with weak ridging over the Canadian Rockies and a west-
northwest flow aloft over Canada and the northern tier of the US.
Meanwhile a cutoff low over northern Mexico combined with the weak
ridging over the Canadian Rockies resulted in a weak west-northwest
flow aloft over ND. At the surface, the large Arctic high was
centered over the northern Mississippi Valley/Ohio Valley with low
pressure over northern Canada. This was resulting in a col or weak
flow over ND.

Yesterday (Saturday) this weak flow resulted in weak surface winds
and little to no mixing with the warmer air aloft. Thus the actual
high temperatures for yesterday were several degrees cooler than
what was forecast. We are thinking the same may happen again for
today (Sunday). Weak flow again today should bring southwest winds
at around 5 to 10 mph over most areas of western and central ND.
However, the higher elevations of the area (the Coteau as well as
some areas of southwestern ND south and west of the Missouri River)
usually tap into the winds at/above the surface boundary layer.

Thus today with warmer air than yesterday aloft, those areas of
higher elevation should see higher temperatures than those lower
elevation locales. Instead of using a blend of short term model
guidance, we relied on the CONSRAW output which takes into account
the 2-meter temperatures rather than a mixed lower atmosphere
temperature field. Nudged temps down a tad from this guidance given
the deep snowpack taking energy in melting, etc. Thus going for
daytime highs in the teens over lower elevation areas and lower 20s
over higher elevations. This still may be too high, but confidence
in this temperature forecast is low and did not want to stray too
far from the lower CONSRAW guidance.

Confidence low on minimum temperatures tonight as well. An
approaching upper level shortwave in the flow aloft and an
accompanying cold front should just be enough to keep southwest
winds steady around 5 to 10 mph to keep the temps from bottoming out
too far. So, going with the short term guidance of zero to 10 above
for lows tonight.

.LONG TERM...(Monday through Saturday)
Issued at 327 AM CST Sun Jan 15 2017

Moderating temperatures and dry conditions through the middle of
next week continue to highlight the extended forecast. Active
weather may return towards the end of next week.

On Monday an upper level shortwave in the west-northwest flow aloft
approaches western ND in the morning and moves into central ND by
Monday evening, exiting central ND Monday night. An accompanying
weak surface cold front should keep the lower atmosphere mixed, with
southwesterly winds ahead of the front/trough and northwesterly
winds behind it. The cooler air behind the front is not arctic in
origin. The models are not in good agreement regarding the winds or
temperature field behind this front. However, mixing should occur
and left the max temps in the 20s for our area. This may need to be
adjusted with later model runs, as confidence again is low for
temperatures.

The rest of the week should see a stronger pressure gradient and
wind flow. Another stronger upper level shortwave moves southeast
across the Northern Plains. Good mixing with the warmer air aloft
Tuesday should allow temperatures to rise into the mid/upper 20s
over eastern parts of central ND with highs in the 30s in the west.

Wednesday and Thursday we will see stronger ridging aloft over the
Northern Plains as a longwave trough moves/develops over the west
coast. These should be the warmest days of next week wit highs in
the 30s...perhaps seeing lower 40s in the southwest.

Regarding the developing longwave trough over the west coast, the
GFS and EC are not in good agreement with the evolution/track of
this longwave trough or any of the smaller synoptic features within
it as the trough expands eastward across the Rockies and
encompassing the western and central part of North America. Chances
of precipitation are small/sporadic in the consensus guidance on
Friday, but this set of model runs indicates some chances of
precipitation for next weekend. No big arctic air intrusions in the
offing, so the good news is that we should not expect any extremely
cold conditions through next weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 927 AM CST Sun Jan 15 2017

VFR conditions expected through the forecast period. Weak surface
flow with an arctic high centered over IA/IL and low pressure over
northern Canada. Surface winds from the southwest at around 5-8
knots lower elevation TAF sites like KISN-KBIS. Expect surface winds
of 10-15 knots at TAF sites in relatively higher elevations of the
Coteau and in parts of southwestern ND - these include TAF sites of
KMOT-KDIK-KJMS.

&&

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

$$

UPDATE...TWH
SHORT TERM...JV
LONG TERM...JV
AVIATION...TWH


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