Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 142024

Area Forecast Discussion
National Weather Service Aberdeen SD
224 PM CST Tue Nov 14 2017

.SHORT TERM...(This Evening through Wednesday Afternoon)
Issued at 222 PM CST Tue Nov 14 2017

Forecast challenges include precipitation chances tonight and extent
of cool down late tonight into Wednesday morning on strong low level
caa (925hpa) winds.

Currently, a cold front has pushed appx half-way through the state
turning winds behind it around to the northwest. Out ahead of the
front, southerly winds continue to pump in/replace low level
moisture into northeast South Dakota, supporting the continuation of
light fog and widespread low stratus cloudiness. Heavy fog from
earlier has continued to dissipate, but this afternoon there remains
areas of light fog and low clouds, which have kept the lid on
temperatures (40s). In fact, some of the warmest temperatures of the
day are (out west) noted over areas where the better northwest
mixing winds are bringing the warmest air (at 925hpa-850hpa) in the
region down to the surface (upper 40s to around 60F).

Tonight: the cold front will finish working out of the eastern
forecast zones this evening. The process of switching winds around
to the northwest and initiating cold air/dry air advection should
help to scour out/eliminate any remaining areas of fog. The low
stratus may also end up moving east and departing the eastern
forecast zones overnight. Short range guidance hints at it being
replaced Wednesday morning by a fresh new batch of low clouds moving
down from the north. Anyway, there are a couple things supporting a
brief period of light precipitation tonight. The first is a
shortwave (over Wyoming) embedded within the fast nearly zonal
flow overhead, and the second is the fast nearly zonal flow
overhead (120kt upper level jet streak in play tonight). Most of
the CAM solutions, and to a lesser extent, the 12Z GSM solutions,
support a small skinny band of light rain (perhaps the beginnings
of it can be seen over sern MT/nwrn SD) developing/moving through
South Dakota overnight. Models all very low on QPF, so, felt the
20 to 30-something pops ECAM produced earlier on shift for tonight
seemed justified.

Wednesday: by 12Z Wednesday, the cwa is in the throws of some rather
strong low level caa, where 925hpa temps are progged in a number of
solutions to drop from appx +5C at 06Z (KABR) to -5C at 18Z (KABR).
So, prolly looking at a rather diverse range of high temperatures on
Wednesday, where the southwestern zones could be warming into the
40s, but the northeastern zones may be having trouble holding onto a
high of 30 degrees. Wednesday could also have some stratus/strato-cu
around on continued breezy to windy northwest winds.

.LONG TERM...(Wednesday Evening through Tuesday)
Issued at 222 PM CST Tue Nov 14 2017

The period begins with an area of high pressure sliding SSE across
eastern SD and western MN. By 12Z Thursday, the center of the high
pressure should be located over central Iowa with WAA developing
over much of this CWA. Would not be surprised if temperatures become
steady, or slowly rise Wednesday night into Thursday morning. The
WAA will spread across the region with highs on Thursday reaching
the lower 40s in western MN, to the 60s, west of the Missouri
Valley. A tight pressure gradient of 20 mb across the state will
result in windy conditions on Thursday. Based on the NAEFS return
interval and ERSL`s extreme percentile plots, the strongest winds
should occur along and east of the James Valley where gusts of 45
mph will be possible. A wind advisory may be needed in the near
future for Thursday.

An area of low pressure and associated cold front will slide across
the region Thursday night through Friday. Models are significantly
drier with this system with little, if any pcpn. Light pcpn is
possible Friday afternoon as a broad upper level trough passes
through the region.

A strong shift in the flow pattern to a negative NAO should leave
this area dry through the remainder of the long term.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday Afternoon)
Issued at 1129 AM CST Tue Nov 14 2017

VFR conditions in place at KPIR and KMBG with cold front just
about to sweep through that (central South Dakota) region of the
state. Further east, KABR/KATY are in the soup (LIFR), and it`s
expected that they will remain so for at least the next 6 hours
(KABR), and possibly longer (KATY) before any improvement will be
had. There is a cold front moving through the region, and if
daytime heating/mixing doesn`t get things back to "better-than-
IFR", the cold frontal passage is expected to later this
evening/overnight. There could also be a quick shot of light rain
or some sprinkles later this evening/overnight as the main area of
low pressure aloft moves through. If confidence/areal coverage
increases over the next 3 to 6 hours, there may be some light
precip mention added to the TAFs.




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