Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 170527

Area Forecast Discussion
National Weather Service Aberdeen SD
1227 AM CDT Thu May 17 2018

Issued at 912 PM CDT Wed May 16 2018

For the most part, the current forecast is on track. Did remove
the small POPs for the remainder of the evening hours, with most
CAM solutions in agreement that should any isolated activity
develop tonight, it will be after midnight or later. No changes
made to winds or temperatures.


.SHORT TERM...(This Evening through Thursday Afternoon)
Issued at 358 PM CDT Wed May 16 2018

Tonight into Thursday morning, only a mediocre environment involving
1000 J/kg MUCAPE and a 30 knot LLJ may support isolated elevated
storms which could develop in response to an incoming weak 500mb
shortwave. Low confidence yields only low POPs for portions of
central SD during this time. On Thursday, the area should see a mix
of sun and clouds with increasing southeast winds in response to a
tightening pressure gradient as the main shortwave, currently across
California/Nevada, approaches the area. Temperatures warm back
comfortably into the 80s across the CWA as we should be within the
warm sector. CAPE is expected to build throughout the day, reaching
2000-3000 J/kg by the early evening along and west of the Missouri
River. Thunderstorms should stay mostly across western South Dakota
by the end of the short term.

.LONG TERM...(Thursday Evening through Wednesday)
Issued at 358 PM CDT Wed May 16 2018

An interesting weather pattern is expected to continue across the
CONUS during the period. Through much of the period mid level
ridging is in place across western Canada. However, energy continues
to slide underneath that ridge and into the southwest CONUS, and
then out across the region. The first decent wave ejects into and
across the area Thursday night into Friday. This wave will interact
with a nearly stationary front located over western South Dakota.
Increasing LLM/instability should lead to a broken line of storms
out west in the late afternoon and evening, but how far east will
those storms migrate?  Deep layer shear doesn`t look particularly
impressive, and MLCAPEs drop quite a bit once you move toward the
James River valley. So, Thursday night`s activity may struggle to
get into the northeast parts of the state. Friday looks better for
rain in the east as the frontal boundary begins moving east due to a
surface high dropping south out of Canada, thus giving the front
better forward momentum, especially by afternoon and evening. Severe
parameters don`t look especially great, but an isolated svr storm is
possible over the northeast CWA Friday afternoon and evening. As the
front slides south on Saturday and Sunday, the higher rain chances
will also shift to the south. After the weekend, the forecast
becomes a low confidence endeavor with the latest models in only
slight agreement on the pertinent features. Temperatures over the
weekend will favor near to below normal, especially Saturday.
However, they will rebound for the remainder of next week.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1224 AM CDT Thu May 17 2018

VFR conditions will prevail across the area overnight and through
the day Thursday. An isolated shower or weak thunderstorm is
possible during the day, then look for a more solid line of
showers and thunderstorms to reach the western CWA after 00Z
Friday. Some of the storms may be strong, and may affect KPIR and




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