Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 150241

Area Forecast Discussion
National Weather Service Bismarck ND
941 PM CDT Mon Aug 14 2017

Issued at 940 PM CDT Mon Aug 14 2017

This update included a mention of patchy fog late tonight/early
Tuesday morning, as well as some minor adjustments for chances of
showers overnight.

Latest iterations of the short term high res models indicate some
areas of reduced visibility in fog...either ahead of showers in
central ND with increasing dewpoints...or behind/with showers with
increased soil moisture/dewpoints in the west half of the state.
Confidence is fair that some fog may form tonight, but confidence is
low on placement of where fog will form and how long it might last.
Added a mention of "patchy fog" late tonight into just after sunrise
for western and central ND.

Otherwise still expecting showers to increase in areal coverage
overnight and spread into central ND late tonight.

UPDATE Issued at 624 PM CDT Mon Aug 14 2017

This update was mainly focused on chances of showers and possible
thunderstorms in western ND for the evening hours. Latest iterations
of the short term high res models indicate current line of
weak/isolated showers that extended from northeast
MT/Williston/Crosby area southeastward to near Dickinson and Fort
Yates to hold together for a couple more hours into the early
evening, then dissipating. Another upper level shortwave over
northeastern MT is forecast to move into western ND this evening,
keeping chances of showers - possible thunder - over the western
third of the state...then expanding into the central third after
midnight. This is handled well with the previous forecast issued
earlier this afternoon.

Otherwise, temperatures were a tad cooler than expected this
afternoon with the increased mid level and somewhat lower clouds at
Bismarck and Jamestown. Thus adjusted late afternoon/early evening
temperatures with latest high res guidance.


.SHORT TERM...(This evening through Tuesday)
Issued at 322 PM CDT Mon Aug 14 2017

Main forecast issue in the short term period will be precipitation
chances and thunderstorm risk tonight and Tuesday.

Deterministic global models have been fairly consistent the last
few runs regarding the precipitation timing and placement. The
overall trend has been slightly slow with the onset coming into
the west this afternoon, with a lower threat of thunder, and thus
severe weather.

The latest satellite imagery indicates an upper level trough
extending from western Canada into California with a series of
impulses tracking through Montana into Idaho and northern Wyoming.
The strongest dynamic forcing this afternoon and this evening will
lift from eastern Montana into southeast Saskatchewan, but
instability and bulk shear are weak in this area, and into
northwest ND. Cape and shear are greater over the northern high
plains around 21-06Z but the greatest instability remains well
south of southwest ND. There is some quite weak CAPE to around 500
J/KG that pushes into southeast MT around 00 UTC with bulk shear
to around 25 to 40 kts, so a few storms could approach the
southwest around this time, with a marginal threat of reaching
severe levels. Certainly not enough to add severe wording in the
gridded forecast. As we go through the night, precipitation
chances increase across the west with the threat of thunder mainly
limited to the southwest quarter.

On Tuesday, synoptic scale forcing and frontogenetical forcing
swing through central and eastern ND bringing scattered to
numerous showers and isolated thunderstorms to the area. The
greatest instability remains south of the forecast area so the
severe threat appears limited. The far southern tier counties of
the southwest and south central, and the far western tier counties
appear to be the only areas where a limited severe threat would
exist. Limited surface heating with cloudy skies and forecast
highs in the upper 60s to mid 70s will limit the severe potential
Tuesday but isolated thunder is possible across the forecast

.LONG TERM...(Tuesday night through Monday)
Issued at 322 PM CDT Mon Aug 14 2017

Warmer and drier weather expected in the long term period

Widespread precipitation exits the eastern forecast area Tuesday
night. Thereafter, upper level ridging tries to become more
established over the region. Generally, Wednesday and Thursday
appear dry. A shortwave trough drops through the area on Thursday
night and Friday bringing a chance of showers and thunderstorms
northwest to southeast across the forecast area. Then another
chance of storms Sunday. After highs in the 70s Wednesday, daytime
highs are expected to be mainly in the low to mid 80s Thursday
through Monday.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 624 PM CDT Mon Aug 14 2017

Scattered to broken clouds around 3000 feet at KBIS and KJMS to
start the TAF valid period. Latest short term high res models
indicate these clouds dissipating early this evening - likely due to
loss of daytime heating.

Farther west, mid clouds over western ND are forecast to expand
eastward across central ND during the evening and overnight.
Meanwhile lower MVFR and some IFR ceilings developing around 09z-12z
mainly over much of western and central ND. Look for increasing
chances of showers over western ND aft 03z...expanding into central
ND aft 06z...continuing into the daylight hours on Tuesday -
especially for central ND. Isolated thunder is also possible across
southern TAFs of KDIK/KBIS tonight...with isolated thunder possible
at all western and central TAF sites daytime Tuesday.




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