Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Aberdeen South Dakota
543 PM CST Sat Dec 20 2014
dropped overnight lows near Pierre a couple of degrees. Otherwise
forecast appears to be on track and no further changes are planned.
See updated aviation discussion below.
short term...tonight through Monday night
Low clouds and fog will once again be the rule overnight as a very
moist low level air mass remains in place. Been closely following
the hrrr low-level cloud cover product which has been doing an
amazing job with handling stratus decks the past several events.
It basically shows the stratus clouds remaining in place all night
with a slight westward push once again on its western edge. Will
go with persistence forecast concerning the fog as it has been
occurring the past few nights underneath the stratus...so no
reason why it wont happen again...and in fact widespread light fog
is already in place...with locally thicker fog. Seems the moist
layer is too shallow for any meaningful freezing drizzle to occur
overnight but something to keep an eye on anyway.
On Sunday...expecting low clouds to hang in tough across the east
once again with no real signals from anything to clear them out.
Will also be watching arrival of the low pressure system which
will enter the Dakotas by Sunday evening...then move into western
Minnesota and Iowa region by Monday night. Models still having a
tough time handling this system in regards to strength mainly.
They really do not know how to handle the eventual closing off and
subsequent movement of the upper low...and its associated moisture
availability. This will be key in figuring out just how much wrap
around precipitation we receive. Basically took a blended approach
for right now which still leaves the area with a couple inches of
snow and some mixed precipitation in the form of freezing rain and sleet
to start things off Sunday evening. Thermal profiles eventually
get cold enough by Monday to change things over to snow. Still
have many doubts and low confidence in exactly just how this
system will evolve and how much moisture will really be associated
with it. Have a feeling models may not latch on to a more
definitive solution until sometime Sunday.
Long term...Tuesday through Saturday
low pressure will be east of the region when the period starts
with the potential for lingering snow showers...mainly across the
eastern part of the County Warning Area through the day Tuesday. A decent pressure
gradient across the area may result in breezy to windy conditions
as well. Weak high pressure then moves in with dry conditions
expected Wednesday. Another low pressure system looks to track
across the Central Plains on Thursday...but the models are not in
very good agreement with strength or timing. The GFS and European model (ecmwf)
agree somewhat on the timing with the Gem being much slower.
However...the GFS brings little in the way of
precipitation...while the European model (ecmwf) plasters most of the state, for
now...will stick fairly close to the superblend keeping schc/chance
probability of precipitation mainly across the southern County Warning Area Thursday into the day Friday.
High pressure will move back in after that with dry conditions
Friday night through the day Saturday.
Slightly above normal temperatures will be the rule for the first
half of the period...with highs mainly in the middle 20s to lower 30s
Tuesday...Wednesday and Thursday. Cooler air then moves in behind
the storm system...with highs in the teens and 20s Friday and
00z tafs for the kabr...Katy...kpir and kmbg terminals
IFR ceilings will remain firmly in place across the eastern half of
the County Warning Area through the taf period. Under the low clouds...visibilities will
generally be MVFR in fog through this evening...but there will
likely be periods of IFR visibilities again overnight and into early
Sunday morning...affecting kabr and Katy. VFR conditions will
prevail across the western half of the County Warning Area with just some high
clouds streaming overhead.