Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 310302

Area Forecast Discussion
National Weather Service Bismarck ND
1002 PM CDT MON MAY 30 2016

Issued at 1001 PM CDT Mon May 30 2016

This update will expire the severe thunderstorm watch.

UPDATE Issued at 758 PM CDT Mon May 30 2016

Trimmed some more from the watch. Watch now in effect mainly
James River valley.

UPDATE Issued at 647 PM CDT Mon May 30 2016

Update to cancel a portion of the severe thunderstorm watch for
south central North Dakota.

UPDATE Issued at 525 PM CDT Mon May 30 2016

Two areas of thunderstorms concern the short term. A north to
south line of storms developing from Oliver county south to Sioux
county moving east at 30 mph along a cold front. This line will
move through the Bismarck and Mandan areas between 6 PM and 7 PM
CDT. Current trends suggest the threat for severe weather will
diminish across the Missouri river area after 8 pm CDT.

A second area of thunderstorms formed along and north of a warm
front in northern South Dakota with storms forming east of the
Missouri River through the James River Valley. This area will be
in focus for severe storms through 10 pm CDT.

Northern North Dakota still see widespread showers and scattered
thunderstorms tonight but severe weather is not expected.


.SHORT TERM...(This afternoon through Tuesday)
Issued at 243 PM CDT Mon May 30 2016

Our focus is on the potential for severe thunderstorms through
this evening, especially in south central ND.

The 18 UTC Bismarck sounding sampled relatively steep mid-level
lapse rates near 7.5 C/km, contributing to MLCAPE around 1000 J/kg
despite increasing cloud cover. The sounding also revealed 0-6-km
bulk wind shear just over 30 kt, sufficient for organized storms,
but likely favoring multi-cellular modes, especially given a small
weakness in the wind fields just above 700 MB. The 19 UTC surface
analysis places a surface low just north of Bismarck, with a warm
front extending east of the low from near Washburn to Carrington,
and a cold front south across central Morton and Grant Counties.
That demarcates the severe risk going forward, as supported by
recent convection-allowing model guidance. The 18 UTC sounding
revealed an uncapped air mass, and as a result convection and the
related cloud cover is still posing some issues to the potential
for severe convection. However, very recent visible satellite
imagery shows clearing over Grant County near the cold frontal
zone, which may enable more intense updrafts to form in the next
hour or two. That`s in line with convection-allowing model output
that still suggests a line of storms with hail and wind potential
will move eastward near and south of I-94 from around Bismarck to
Jamestown between 20 and 03 UTC.

On Tuesday, the low pressure system will have occluded and the
surface to 500 MB circulation is forecast to become stacked in
north central ND. Showers and embedded, non-severe storms are
simulated by guidance to be wrapping around the north and west
sides of the stacked low, impacting much of western and north
central ND. There is some uncertainty in the southward extent
of the shower activity, with the ECMWF and 12 UTC NAM slightly
more robust with QPF to the south of Highway 200 than the GFS.
Nonetheless, those models are in relatively good agreement and
a blend of them supports widespread PoPs over 60 percent over
much of western and central ND, save for across the southern
James River valley where a mid-level dry slot will be in play.
Note that there is still a non-zero risk of weak funnels near
the stacked low over north central ND, but diagnostic output
from the 12 UTC guidance suggests that the low-level CAPE-VGP
setting will not favor cold core tornadoes. Conceptually, the
stacked low scenario doesn`t favor cold core tornadoes, either,
as it reduces low-level baroclinicity and vorticity somewhat.

.LONG TERM...(Tuesday night through Sunday)
Issued at 243 PM CDT Mon May 30 2016

Lingering shower activity will gradually end Tuesday night and
early Wednesday as the stacked low pressure system slowly moves
east-northeast into southwest Ontario. The 12 UTC models are in
relatively good agreement suggesting that mid-level flow should
lose its cyclonic nature during the day Wednesday as that low
departs and 500-MB heights rise a bit in its wake. There may be
a low-end shower potential in central ND until those heights do
begin rising by afternoon, but confidence in any showers is low.

The key message we want to convey in the long term is a warming
trend that will commence by late week. The multi-model consensus
calls for highs to warm from the 60s F on Wednesday to the 70s F
Thursday, and upper 70s and lower 80s F Friday through Monday as
a stout 500-MB ridge takes shape over the intermountain west and
exerts its influence downstream across the northern Plains. The
deterministic and ensemble guidance displays low spread with the
ridge axis, but the amplitude of downstream flow differs, as the
00 and 06 UTC GFS simulations are generally deeper with a low in
the Great Lakes region by late weekend. A deeper low would favor
greater potential for somewhat cooler air to be advected into ND
in the general northwest flow aloft. CIPS analogs applied to the
00 UTC GFS ensemble reflect that possibility, offering no strong
signal as to whether temperatures will be above or below normal.
However, the non-GFS guidance supports less amplitude to the low
over the Great Lakes, favoring the warmer regime that`s also the
main influence on our blended-model-driven forecast. CIPS analog
output strongly favors below-normal precipitation in the period
centered on this weekend, especially in western ND, so we have a
mainly dry forecast in play. However, the 00 and 12 UTC GFS and
NAM, and to a somewhat lesser extent the ECMWF, suggest that a
mid-level shortwave trough will cross the region Thursday night
and Friday, offering some shower and thunderstorm potential in
that time frame.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 525 PM CDT Mon May 30 2016

The hazards to aviation include widespread thunderstorms Monday
evening. IFR conditions will develop in moderate rain and
isolated thunderstorms after 06z KISN-KMOT. MVFR conditions
developing KDIK-KBIS-KJMS after 12z.


.BIS Watches/Warnings/Advisories...


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