Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 151622

Area Forecast Discussion
National Weather Service Aberdeen SD
1122 AM CDT Tue Aug 15 2017

Issued at 1122 AM CDT Tue Aug 15 2017

Will continue to monitor the latest radar trends, and incorporate
them into the forecast. Light showers are diminishing as they exit
northeastern SD this morning, as an additional round of showers
nears from around PIR. Limited the mention of thunderstorms, and
highlighting mainly areas to our south for the heaviest rain
potential (where the WPC excessive rainfall outlook is
highlighting). May need to cut back thunderstorms again shortly.
Otherwise, the forecasts looks to be on track.


.SHORT TERM...(Today through Thursday Afternoon)
Issued at 342 AM CDT Tue Aug 15 2017

Expansive area of showers and embedded thunderstorms earlier across
western and central SD continues to push eastward while diminishing
in areal coverage. Hi-res CAM solutions continue to suggest this
activity pushes eastward into the James River valley over the next
few hours, while diminishing in coverage somewhat. Have made
appropriate changes to POP grids based on latest thinking. Will also
be watching potential for fog up through sunrise. Hi-res models
continue to suggest areas along and east of I-29 will see reduced
VSBY over the next few hours so will continue to monitor. ETH and
VVV have recently come down to 4SM, with lower VSBY being reported
just across the border into ND and MN. Fog could become dense and
will monitor for possible headline.

For later today, next piece of upper level energy will move across
the Dakotas while a surface frontal boundary slowly drifts southeast
through the area. This will provide focus for additional shower and
thunderstorm development later this afternoon and into the overnight
hours. Threat for strong to severe storms looks to be confined to
the southern half of SD based on instability parameters. Heavy rain
is a possibility as well with any of the stronger storms that
develop today.

During the day Wednesday, surface high pressure will be building
into the region with conditions beginning to dry out by the
afternoon hours. Will continue with precip chances for eastern areas
during the day Wednesday as shortwave energy continues to affect
that area. It doesn`t appear completely dry conditions will
overspread the CWA until Wednesday night when the surface ridge axis
sets up over the area. For Thursday, looks like conditions will
remain dry as the ridge largely remains in place while only slowly
moving eastward. Warmer temperatures will arrive by Thursday as well.

.LONG TERM...(Thursday Evening through Monday)
Issued at 342 AM CDT Tue Aug 15 2017

An upper trough will move through the region Thursday night and
Friday. Coupled with weak low pressure at the sfc and fairly potent
shortwaves moving through the upper flow, expect showers and
thunderstorms to develop and move from west to east, finally
departing Friday night.

Upper ridging builds in for the weekend. This feature will kick the
temperatures back up around average and even a little above near the
Missouri River. Enhanced mixing ahead of and with a sfc cold front
will help temperatures climb quickly. By Sunday afternoon, the ridge
will flatten and shortwaves aloft with a weak but strengthening low
over southern SD will produce enough instability to trigger showers
and thunderstorms through early Monday morning. Lingering clouds and
instability may hamper eclipse viewing across eastern SD and west
central MN on Monday afternoon.

Sfc high pressure takes hold on Tuesday bringing drier conditions
into Wednesday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1122 AM CDT Tue Aug 15 2017

While VFR ceilings and vis have dominated the picture, IFR
ceilings have developed at PIR around 14Z. These lower ceilings
should give way to VFR ceilings around 18Z or shortly after, as
has been the trend at WBC to the southwest. Expect moderate to
possibly heavy rain to impact the TAF sites late this
afternoon/early this evening, and mainly PIR 00-03Z and ATY
closer to 03-06Z.




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