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203
FXUS63 KBIS 220520
AFDBIS

Area Forecast Discussion
National Weather Service Bismarck ND
1220 AM CDT Fri Sep 22 2017

.UPDATE...
Issued at 1220 AM CDT Fri Sep 22 2017

Latest RAP soundings for BIS-JMS have strong low level helicity
300-500 and shear values greater than 50 kts. Thunderstorms that
develop will be elevated with the LCLs above 7k between 10-14Z. So
expect the chance for thunderstorms per previous discussion and
forecast.

UPDATE
Issued at 1012 PM CDT Thu Sep 21 2017

CAMs pushed up the timing of possible convection closer to 12Z so
POPs were adjusted for this. SREF t-storm probs continue to depict
thunderstorm potential increasing after 09Z across southern ND
then expanding northward with time. Shear profiles within the
elevated instability ranges from 50-65Kts. Would not be surprised
to see a few stronger storms near warning-worthy given all the
ingredients in place. Time will tell. Products were updated to
increase the t-storm potential wording.

UPDATE
Issued at 705 PM CDT Thu Sep 21 2017

Forecast through this evening remains on track.

For the overnight period (after midnight), models are showing a
band of precipitation forming across southwest and south central
ND 9-12Z as a ribbon of instability lifts north along the
frontogensis zone north of the surface low across SD. Modified
POPs to better reflect this. SREF thunderstorm probs start to ramp
up as well after 09Z and remains rather high through the day
Friday. Coupled with SPC having the entire state in at least the
general t-storm outlook, I spread isold thunder across the board
Fri aft. Will take a closer look at the nocturnal showers as I
may need a mention of thunder as early as 9-12Z if model MUCAPE
projections are accurate. ESRL HRRR and NAMNest also trigger
convection early Friday morning. The ESRL HRRR as early as 1145Z
and the NAMNest 14Z. Right now I have isold thunder in the
forecast starting at 15Z for the southwest and south central.

&&

.SHORT TERM...(This evening through Friday)
Issued at 307 PM CDT Thu Sep 21 2017

An upper level trough over the western U.S. into southern Canada
will influence the weather over the northern plains over the next
several days. Tonight, jet energy propagating through broad
southwest upper flow will continue to produce an area of light
showers/virga extending from south central MT into northwest and
far north central ND. Associated surface low pressure from central
North Dakota into southwest South Dakota will push slowly east.
Strong southerly winds over the James River Valley, ahead of the
surface trough, will diminish late this afternoon and evening.
Capping over this same region is expected to inhibit any
afternoon/evening convection despite a moderately unstable
atmosphere.

Moderate to strong 700-500mb frontogenesis develops tonight over
a good portion of central and northwest ND north of the surface
trough. Although synoptic scale forcing is not strong, it does
persist over this same area. Global models have been persistent
the last couple of runs in developing a band of light
precipitation over western and central ND late tonight into friday
morning, which is handled well with the current forecast.

Continued surface and mid level forcing along the surface front,
combined with upper level divergence over the region, will
support an area of thunderstorms Friday, but most likely just to
the south and east of the forecast area. Although we will need to
monitor the southern James river valley for possible thunderstorm
activity in case there is some north and/or westward shift to the
surface boundary. Most of the CWA will be cooler on Friday (50s
and 60s) but the southern James River Valley could see some
readings near 80.

.LONG TERM...(Friday night through Thursday)
Issued at 307 PM CDT Thu Sep 21 2017

Cool and showery weather remains through the upcoming weekend and
into early next week. Highs mainly in the 50s and lows generally
in the upper 30s to mid 40s. Substantial cloud cover should
inhibit any widespread frost, but will certainly have to monitor
the western half of ND in case we would happen to clear out more
than expected.

Precipitation chance wane as we head into the middle of next week
but we remain at or below seasonable normals.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1220 AM CDT Fri Sep 22 2017

MVFR ceilings will lift northward into North Dakota after 12Z
Friday bringing MVFR ceilings to KJMS and KBIS by 15-18Z. MFVR
ceilings will also be possible for KDIK and KMOT after 18Z.

Isolated showers and thunderstorms are possible over the TAF sites
through 12z...then more coverage with convection is expected as
scattered showers and thunderstorms are forecast to develop
around/after 12z, with chances of showers and thunderstorms
continuing through the day Friday.

&&

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

$$

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