Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 250920

Area Forecast Discussion
National Weather Service Aberdeen SD
420 AM CDT Tue Apr 25 2017

.SHORT TERM...(Today through Thursday Afternoon)
Issued at 420 AM CDT Tue Apr 25 2017

Low pressure is currently over Wyoming, with rain spreading
northeastward out ahead of the system, mainly over southwest SD. Had
already delayed the onset of precipitation across the southwest CWA
as it appears things are slower to move in. Have also recently been
seeing some light fog developing over the eastern CWA where CIGs are
the lowest, especially in the Coteau region. Added a fog mention to
the forecast for the morning hours. Perhaps a bit of drizzle within
this area as well.

Main challenge for today is determining just how far north and east
precipitation will penetrate the CWA in regards to the low over
Wyoming. Models show some eastward progression today, but the
surface low basically dies out while the upper low continues
progressing east. A new low then forms over the central and southern
Plains and moves northeast into IA and MN late tonight. This is when
an area of precipitation is forecast to move from southeast SD
through the I-29 corridor and points east, also affecting the Coteau
region. Thermal profiles throughout the precip event across varying
points in the CWA do show potential for snow during the cold parts
of the day late at night and in the morning hours. Although, with
rather cold temps aloft on Wednesday over eastern areas, would not
be surprised if the higher terrain of the Coteau saw wet snow accums
much of the day within wrap around precip. Now, there is some
question still just how far back to the west precip will occur over
the eastern CWA on Wednesday as it all depends on the track of the
low pressure from IA into MN.

Temperatures throughout the short term will be chilly and well below
normal for this time of year. Highs will only be in the 30s and 40s
the next couple days. By Thursday, we will still be dealing with 40s
and 50s for highs.

.LONG TERM...(Thursday Evening through Monday)
Issued at 420 AM CDT Tue Apr 25 2017

Not much has changed in the out periods forecast compared to 24
hours ago. This cwa remains on the northern fringe of westerlies
aloft (at best) in pronounced split flow pattern heading into the
weekend, which likely means most of the weather systems will be
steered by the expected flow pattern not really anywhere near this
cwa. Tonight, most of the deterministic GSM solutions, with the
support of the 00Z GEFS, are actually in a fair amount of agreement
keeping much of this cwa free and clear of precipitation chances for
much of the period. Slight chance pops don`t make an appearance
across the western third of forecast zones until Monday/Monday
night. Sounding like a broken record now, but for the 5th
consecutive night, the 00Z NAEFS output points to "colder than
normal" temperatures in the out periods. The 00Z deterministic GSM
solutions have not really budged much either. The light at the end
of the tunnel is that the GFS and ECMWF 850hpa thermal progs warm
back up into the +5C to +7C range on Sunday across central South
Dakota and into the +5C to +9C range Monday and Tuesday across at
least the central part of the state, which isn`t far off the "climo-
normal pace" for early May. Unfortunately, the 8 to 14 day outlook
still looks like better chances for temperature to average colder
than normal for the first week of May.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1242 AM CDT Tue Apr 25 2017

IFR/MVFR cigs will be common across the CWA through the TAF period.
One area of precipitation will affect the southwestern CWA late
tonight into the day Tuesday, with a second area affecting the
eastern CWA Tuesday evening. Vsbys may fall into the MVFR category
at times with the precipitation. The temperatures may cool off
enough both late tonight and early Tuesday, and again Tuesday
evening for the rain to mix with or change over to snow at times.
North winds will increase into the 15 to 25 knot range on Tuesday as




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