Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Sioux Falls South Dakota
309 PM CST Sat Feb 28 2015

Short term...(this evening through sunday)
issued at 309 PM CST Sat Feb 28 2015

Northern edge of the Southern Plains system will scrape by the far
southern County Warning Area with little fanfare through early evening...more clouds
and maybe a few flurries toward sunset. Otherwise...the general
conditions across the are expected to be mainly quiet as northern
stream wave across western North Dakota pushes eastward tonight.
Wind shift will slide across the area. Area of lower clouds trailing
this boundary will likely undergo a gradual dissipation pushing
eastward with increase in subsidence. Later night and early
morning...a little increase in middle level frontal forcing will occur
through the southern County Warning Area as northern stream trough wanders through
the area...but lower levels will end up much drier by this time.
Perhaps could get a couple of flurries through the lower Missouri
Valley...but no more than that. Rest of the day will gradually find
increased mixing potential with westerly flow. With southwest half
of the County Warning Area lacking hesitant to expect temperatures to be all
that much cooler than today...and 925 hpa temperatures would suggest fairly
similar to today.

Long term...(sunday night through saturday)
issued at 309 PM CST Sat Feb 28 2015

Sunday night will see high pressure move through with southeast flow
developing. The last to get into the southeast winds will be
northwest Iowa so will go with the coldest lows there. Mainly single
digits in northwest Iowa and around 10 in south central South Dakota. Some of
the radiational effects will be offset by increasing clouds

Monday should be mainly quiet with continued increasing clouds. Not
much of a threat for precipitation but will keep a low threat in the
far southern County Warning Area in the afternoon as the middle level front gradually
becomes organized and moisture moves into the area. Will aim for
highs in the 20s over the snow pack and high in the 30s over the
snow free locations.

Monday night into Tuesday still bringing a very good chance for
snowfall to the area. Latest models just a touch faster with the
wave thus the low level cold air coming in a little quicker as well.
On Monday night the low and middle level front will become organized as
the wave moves onto the plains. For now will go with a blend of the
European model (ecmwf) and GFS quantitative precipitation forecast amounts as location and forcing is pretty similar
with the NAM slower and farther north...also indicating two bands
instead of a broad area of precipitation. Without very much
instability above the middle level boundary it seems like a broader
solution to the quantitative precipitation forecast makes more sense. So far this winter the European model (ecmwf)
in cases like this has come up short on quantitative precipitation forecast so will go Half Way
between the GFS and European model (ecmwf)...which gives a maximum of about a third
of an inch and snowfall amounts about 4 inches. By late Tuesday
afternoon and Tuesday evening the colder drier air will have worked
south and the snowfall should be out of the area. Will go somewhat
close to 10:1 snow ratios...especially early in the event when a
little sleet could mix in around the Sioux City and Storm Lake
locations...before the really cold air settles in on Tuesday
afternoon. By Tuesday afternoon and Tuesday and Tuesday night north
winds will gust to about 40 miles per hour at times and with fresh snow on the
ground do expect some blowing snow.

As for temperatures Monday night into Tuesday we will see the
warmest temperatures early Tuesday morning with falling temperatures
through the day.

In the outer periods (wednesday through saturday)...pretty good
agreement on Wednesday and Thursday as a large scale trough moves
through the area and a more mild west to northwest flow aloft
develops Thursday into Friday. Still some very strong signals from
the European model (ecmwf) for much above normal 850mb temperatures Saturday through
the next week but at this time the 12z GFS is in disagreement
bringing a shot of cold air into the region for next weekend. At
this time will lean more towards the European model (ecmwf) since 49 of 50 members
are above normal. Will not go hog wild however as a more widespread
snow on Tuesday could eat away at a few of these days using up the
heat for warming. And with snowmelt and warming aloft there would be
a potential for stratus and fog development which would further
delay any warming at the surface. No major threat for precipitation
through this period.


Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1144 am CST Sat Feb 28 2015

A period of MVFR ceilings is likely for ksux this afternoon as
low level moisture advects off the north edge of system in the
Southern Plains. Further northward...should remain scattered or
perhaps a brief period of lower end VFR broken ceilings. Remains
to be seen if MVFR ceilings behind wind shift currently across
eastern Montana and northeastern Wyoming will survive as full
fledged ceilings advecting toward khon and eventually kfsd later
in the night...but for now expect subsidence to keep from a
prevailing condition.


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


Short term...Chapman
long term...08

National Weather Service Glossary of Abbreviations