463 
FXUS63 KBIS 130902
AFDBIS

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

.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 06Z TAFS through 06Z Monday night)
Issued at 228 AM CDT Mon Sep 13 2021

VFR conditions at all terminals to start the TAF period, with
chances for showers and a few thunderstorms beginning after 09
UTC. Expect chances increasing in central North Dakota after 12Z.
Higher chances exist at southern terminals, with only VCSH at 
KMOT and no mention of showers at KXWA. Precipitation will 
continue moving east through the day, tapering off in the James 
River Valley 21-24 UTC. Best chances of MVFR cigs/vsbys in shower
and possible thunder activity will be at KBIS 13-17 UTC and KJMS 
16-21 UTC.

&&

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

$$

SHORT TERM...TWH
LONG TERM...TWH
AVIATION...TWH