360 
FXUS63 KBIS 131450
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
950 AM CDT Mon Sep 13 2021

.UPDATE...
Issued at 950 AM CDT Mon Sep 13 2021

Showers and thunderstorms continue to progress eastward across
North Dakota this morning, with the strongest storms producing
some brief, heavy rain and possibly some small hail. What little
threat there was for severe weather appears to be over, so not
expecting storms to get much stronger than they currently are. 
There is still narrow corridor of 1000+ J/kg of MUCAPE stretching 
into south central ND from SD, which will continue to fuel storms 
throughout the day, but the best shear remains along and south of 
the state line. Main updates were minor tweaks to near term PoPs 
and sky cover, otherwise the forecast remains on track.

UPDATE Issued at 610 AM CDT Mon Sep 13 2021

Main update was for shower/thunderstorm activity. 

Convection has developed over southwest ND. One stronger storm was
noted near Hettinger. Previous discussion covered the 
precipitation chances. We'll cover the potential for severe storms
briefly here. Over far southwest and south central ND there is 
about 35 knots of shear with over 1000 J/KG of MU Cape. Hail Cape 
is around 600-700 J/kg. Thus think there is a small risk of severe
storms this morning mainly from around Hettinger east to around 
the Missouri River, and north to around Interstate 94. SPC SREF 
page indicates this area, and also NSSL WRF indicates some 
potential for severe hail over this area. As you get north of the 
Interstate the potential drops pretty quick. Stronger winds can't 
be ruled out with Dcape around 1000 J/KG along the SD border, but
think the hail threat is greater. At this time don't expect this 
threat to extend much longer than 15 UTC. 

&&

.SHORT TERM...(Today and tonight)
Issued at 228 AM CDT Mon Sep 13 2021

Chances for showers and thunderstorms today highlight the short
term forecast period.

Latest satellite imagery shows and upper level circulation over
Canada with an upper jet from north central MT into southeast
Saskatchewan. Another strong jet extended from the west coast into
the central Rockies, with an extension of this jet from the 
central Rockies into the Mondak region. between these two upper 
level features is a west to southwest upper flow with impulses 
tracking from Montana into the western Dakotas. At the surface, 
cyclogenesis is occurring over the central and northern High 
Plains. Latest radar shows shower activity over east central MT, 
about as far east as Glendive, and developing thundershowers just
west of the Black Hills. 

Overall, the forecast has changed little, with strong fg forcing 
expected to ramp up over western and central ND shortly and 
precipitation developing over central and southwest ND around 12 
UTC or shortly thereafter. There was little change to the 
placement of qpf with the higher amounts situated over the south 
central into the James River Valley, and tapering quickly to the 
north with little or no accumulations over the northwest and far 
north central. What has changed slightly is the qpf amounts over 
the south central into the JRV, and for the better. Not a lot, 
with most of the area seeing a quart to a half inch from around 
Bismarck south to the State line, and east into the JRV. but 
there is definitely a bit of an uptick in qpf amounts with a 
pretty good area of a half to three quarters of an inch. These
higher amounts still remain mainly south and east of a line from 
Carson to Bismarck to Harvey. Whether this comes to fruition 
remains to be seen, but at least it's trending up a bit as we get 
closer, instead of down, as has been the case lately.

Why the increasing qpf. Not sure. However, we mentioned an
indirect circulation a couple days ago and although it not a slam
dunk case, there are hints of it, with decent upward ageostrophic
flow over the south central 12-18 UTC. Looking at some of the
winter type products, there is strong 2D FG forcing situated 
right over south central ND. The latest RAP13 is particularly 
impressive. In addition, there is strong surface convergence that
develops along a inverted trough with high dewpoint air advecting
northward into south central ND. You can see the upper 50 and
lower 60 dewpoints currently over the Nebraska Panhandle with an
increasing southerly flow ahead of the High Plains surface low.
There is also moderate instability aloft, again most notable on
the RAP but with all forecast models. the RAP develops a nose of 
instability from western SD right into south central ND this 
morning. It weakens and shifts southeast, with another band of 
instability setting up just to the west of this through the 
afternoon, with very unstable showalter indices remaining over the
area through the afternoon. A look at the 700 mb heights shows a 
weak circulation right over south central ND around 18Z on the 
RAP, NAM and GFS. Sometimes in the winter when you have a 
situation with the southern and northern stream jet interaction 
you get an area of enhanced precipitation. This is a little 
different, but some of the same processes are still in play. On
the negative side, it is a quick moving wave and it's the warm 
season with initially a lot of dry air above us. Perhaps the 
mesoscale models are overdoing the convection given the strong 
forcing, thus the higher qpf. The latest 06Z NAM is much wetter 
over the south central with a qpf bomb over Bismarck 15-18 UTC. 
For now we'll stick with our given guidance which overall seems 
quite reasonable. And if we do happen to see some enhanced 
rainfall rates over the south central, given our dry conditions 
through the summer most impacts would be on the positive side, 
with excessive rainfall impacts minimal. The possible exception 
could be locally heavy rains over urban areas. 

Highs will range from the 60s (and maybe even some 50s) south
central, to the lower and middle 70s west an north central. Skies
clear from northwest to southeast tonight with overnight lows in
the lower 40s northwest to lower 50s southeast. We may have to 
deal with some fog late tonight into Tuesday morning, especially 
over areas that receive rainfall.

.LONG TERM...(Tuesday through Sunday)
Issued at 228 AM CDT Mon Sep 13 2021

A relatively quiet weather period is expected through the long
term. Temperatures will be in the 60s and 70s on Tuesday as 
troughing remains aloft. A brief warm up is expected on Wednesday
with ridging building in behind the departing system. A deep
upper trough moving through Canada later in the work week will
cool things off Thursday and Friday with highs in the 60s and 70s
and lows Friday morning possibly into the upper 30s north. We then
warm back up over the weekend. 

The aforementioned deep upper trough will result in southwest 
flow setting up across the northern Plains. No major systems are 
forecast to move through, but the southwest flow with the strong 
upper level jet lingering over the area will result in some hit 
and miss precipitation chances late in the work week and through 
the weekend. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 950 AM CDT Mon Sep 13 2021

For the most part, VFR conditions are expected through the period. Showers
and thunderstorms will continue to move eastward across southern 
ND through the afternoon, mainly impacting KBIS and KJMS. A few
light showers will also be possible across the north (KMOT) with
no real aviation impacts expected. Expecting precipitation to 
move east of KJMS by 21-24 UTC. Best chances of MVFR cigs/vsbys in
shower and thunderstorm activity will be at KBIS 15-17 UTC and 
KJMS 16-21 UTC. Winds will gradually shift from southerly to 
northwesterly through the period and remain relatively light.

Fog/stratus may be a possibility late in the period, but will
revisit this with the 18Z TAF issuance.


&&

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

$$

UPDATE...Gale
SHORT TERM...TWH
LONG TERM...TWH
AVIATION...TWH/Gale