Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kabr 180525 aab 

Area forecast discussion...updated
National Weather Service Aberdeen South Dakota
1125 PM CST sun Nov 17 2019

issued at 528 PM CST sun Nov 17 2019

Increased sky cover through the night, especially along and east
of I-29. Also continued to back off on precip chances tonight,
especially west of the James River.


Short term...(this evening through Monday afternoon)
issued at 156 PM CST sun Nov 17 2019

The area will be under northwesterly flow through the short term
forecast period, with couple of weak shortwaves moving through or
brushing the area.

The low clouds that covered much of western South Dakota this morning have
been eroding on the western side as a low level ridge has shifted
winds to the west-southwest and is advecting drier air into the
area. Expect this eastward trend to continue through the afternoon
and will give some peeks of sun to eastern South Dakota. But with increasing
high clouds ahead of tonights weak system, the sun make be filtered
for many areas before sunset.

As for the system tonight, confidence is low on the exact location
and amounts of precipitation that may occur. Forcing is very
limited, with only subtle/weak vorts indicated in the deterministic
models. Mid level warm air advection is largely disconnected from
the best moisture and only limited q-vector convergence. As expected
with limited/weak forcing, seeing blotchy nature to the
precipitation and variable locations. Using a general consensus, it
seems like the first wave of light precip will track over the far
western part of the County Warning Area and then try to expand more into the eastern
County Warning Area. Due to the limited confidence, have keep pops in the chance or
slight chance category. As for p-type, wetbulb0 heights are
generally fairly high over much of the area, leading to a deep
melting layer (3kft or more) with low level temps in the 3 to 7c
range. Thus, thinking that much of the precip will fall as rain and
type will depend on the surface temps. In addition, NAM/GFS BUFKIT
soundings for the northeastern County Warning Area point to a 4-5kft dry layer
within the dgz, likely reducing the ice crystals within the cloud
and keeping initial precip in liquid form. At this point, the best
opportunity for freezing rain would be along or east of I-29, where
temps will cool off the most this evening and the early overnight

Behind the weak wave, tomorrow remains uncertain too, with cloud
cover, precipitation chances, and temperatures. Mid level moisture
tries to pull out of the area and at this point, models don't point
to too much low level moisture to keep low clouds in. But there are
indications of a stronger shortwave dropping southeast through ND
and could keep clouds around a little longer and even produce a few
rain showers. Models very on timing/track of this shortwave, but the
general idea is isolated showers in the afternoon over the
northeastern part of the County Warning Area. As for temps, they'll largely depend
on amount of sunshine we can get, but should see above normal highs
with values in the upper 40s and 50s.

Long term...(monday evening through sunday)
issued at 156 PM CST sun Nov 17 2019

Upper-level ridging builds Monday night into Tuesday, leading to dry
conditions and the presence of warmer air aloft during this time.
Scattered cloud cover, especially later in the day, may limit
daytime heating some, but highs will be above average/in the 40s and
50s regardless.

At the same time, a western Continental U.S. Trough will begin to dig and shift
east. This offers the area an extended period of precipitation
chances, from Tuesday night through Wednesday evening as an upper-
level disturbance/trough tracks across the northern plains and
Wednesday evening through Thursday morning (southeast/eastern cwa)
as the trough continues on and a surface low pressure system tracks
from Kansas to Wisconsin. While it looks like at this time the bulk
of the precipitation will glance by the area through this period,
there is still a bit of concern regarding p-type. Limited ice aloft
combined with below-freezing surface temperatures could lead to
light snow and/or freezing drizzle Wednesday morning. Otherwise,
light rain/drizzle Wednesday afternoon is most likely as
temperatures warm, changing back over to light snow in the evening.

High pressure and colder air slides in across the region Thursday,
with dry conditions and highs in the 30s most likely. Thereafter,
northwest flow aloft develops, temperatures moderate, and a couple
disturbances may impact the area before the weekend is through.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1124 PM CST sun Nov 17 2019

VFR conditions are forecast at all sites through the period. Light
rain showers are possible with a couple of weak waves tonight and


Abr watches/warnings/advisories...
South Dakota...none.


National Weather Service Glossary of Abbreviations