Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Aberdeen South Dakota
1156 PM CST Sat Nov 22 2014
see below for an updated aviation forecast discussion.
Made a couple changes to p-type forecast tonight based off
observations and 18z GFS/NAM soundings in BUFKIT. Switched p-type
to rain-only for the overnight. Low level warm air advection and surface moisture
advection ongoing beneath broken-overcast middle and high clouds should keep
temperatures at or above 32f overnight. Snow/freezing rain seems
like a rather low probability occurrence tonight. Also adjusted
coverage/timing of fog mention over the eastern County Warning Area ahead of an
approaching surface trough...where temperature/dewpoint spreads have
fallen to 3 degrees or less.
short term...tonight through Sunday night
A warm front will continue tracking east across the region this
evening...which will keep overnight lows fairly mild. Forecasting
lows tricky this evening as amount of cloud cover and mixing will
greatly affect readings. Models continue to indicate potential for
areas of light precipitation overnight...and depending on temperatures it will
be either rain or snow. Generally went with 20/30 probability of precipitation tonight.
Attention then turns to Sunday and the rather gusty winds that
will developing by late morning over western and central South
Dakota. Decided to issue a Wind Advisory for the Missouri Valley
region based on forecast wind speeds...numerical guidance and
BUFKIT soundings. Will also leave in the mention of rain or snow
showers as the shortwave axis moves through during the afternoon.
Long term...Sunday night through Saturday
main challenge for medium/long term forecast revolves around precipitation
timing...location and model differences.
Models are in decent agreement with 500hpa trough located along the
eastern Dakotas at 00z Monday. Surface low located well southeast of
County Warning Area...but wraparound on backside...coupled with tightening surface
pressure gradient...could make for some tough conditions Sunday
night in light snow and blowing snow...especially for the far NE
part of the County Warning Area. Will have to monitor for potential headlines.
System pulls away during the day Monday...with dimishing winds and
snowfall moving west to east through the day.
Biggest question is going to be weather Tuesday afternoon through
Wednesday morning. GFS is not nearly as strong with surface low
pressure that develops on sagging cold front...while the ec spins
up a fairly potent surface low diving southeast. The NAM at 84 hours offers
up a solution that is closer to the GFS...with a more northward track
of the surface low. This keeps most of the precipitation in North Dakota than
in South Dakota. This will also need to be watched as ec solution
would create some issues...again in that far northestern County Warning Area
region...with light snow and strong northwest winds.
Lastly...for Thanksgiving...the GFS keeps Canadian high bottled up
in southern Canada...which allows surface low to develop along stalled cold
front draped west-east across the County Warning Area. The ec pushes this high
much further south. Difference is GFS solution shows potential for
measureable snow Thursday...while ec not so much. For now will
continue with superblend solution.
Temperature wise...look for subseasonal temperatures to again push into the
region for the beginning of the week...with little if any recovery
06z tafs for the kabr...Katy...kpir and kmbg terminals
Middle and high level clouds continue to drift across the region
bringing some light rain to the kmbg/kpir terminals mainly between
now and 12z Sunday...with some rain chances moving in to the
kabr/Katy terminals mainly between 09z and 15z. Will update the
kabr/Katy tafs to add rain mention as needed. By late Sunday
morning...strong northwest winds are expected to pick up across
central South Dakota behind a cold frontal passage. These strong
winds will mainly impact the kmbg/kpir terminals.
South Dakota...Wind Advisory from 9 am CST /8 am MST/ to 9 PM CST /8 PM MST/
Sunday for Campbell-Corson-Dewey-Hughes-Jones-Lyman-Potter-