Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
536 PM CST sun Jan 25 2015
Short term...(this evening through monday)
issued at 333 PM CST sun Jan 25 2015
An area of low pressure moving to our north will drag a front
across the area overnight into early Monday. The entire County Warning Area is
currently stuck in low stratus...but expect this to erode from west
to east tonight...with developing southwesterly flow ahead of the
wave aiding in the process. Given the cloud cover...temperatures
probably will only fall a few degrees this evening...then as
southwesterly flow increases...expect a warming trend later tonight.
Could be a few sprinkles of flurries with the wave later tonight
across southwest Minnesota...but weak lift and dry middle levels may
even prevent that.
Northwesterly winds will be blustery tomorrow behind the
front...sustained 15 to 20 miles per hour and gusting to around 30 miles per hour. No cold
air behind the front...and with enhanced mixing will be quite a warm
one. Stayed on the warmer side of guidance...with 40s and 50s
likely. Not out of the question we even end up a degree or two
warmer than the current forecast. Should also be a mostly sunny day
with any middle and high clouds exiting.
Long term...(monday night through sunday)
issued at 333 PM CST sun Jan 25 2015
The intermediate periods are marked by a fairly benign...but mild
synoptic pattern. Surface high pressure moves across the forecast
area Monday night. This will produce light winds...and in the middle
levels a band of clouds may move through the area but should not
impact temperatures. Therefore lows will generally be in the 20s.
Did however lower the favored cooler locations about a category
and below guidance readings due to the light flow. Tuesday still
looks very warm with 50 to 55 throughout the MO River Valley zones
and 40s elsewhere.
On Tuesday night...the southerly surface flow of air will be a bit
brisk...so trended lows toward the warmer guidance readings which
were once again about anything that has been bias corrected. And on
Wednesday...a cold front still clears our forecast area by late in
the day. Cool air advection is still on track for the afternoon
hours which will be somewhat offset by a mixing northwest wind.
Therefore highs on Wednesday look similar to tuesdays highs...with
readings around 50 to 55 in our MO River Valley counties...with 40s
elsewhere. Wednesday night will follow with windy northwest winds
generally in the 20 to 30 miles per hour range...with some gustiness of 30 to
35 miles per hour. This will be coupled with a chance for light snow across the
northeast half of our forecast area...generally along and east of a
Huron...to Sioux Falls to Storm Lake Iowa line. The low probability of precipitation are
deceiving in that it is pretty likely that light snow will
fall...but will it be heavy enough to actually measure more than a
trace. Concerning lows Wednesday night...they will be moderated by a
lack of strong cold air advection...wind and clouds. Therefore
despite the cold frontal passage on Wednesday...lows should remain
in the 20s to lower 30s which are more in line with normal highs for
this time of year.
Further out Thursday through Sunday...Thursday and Friday will have
high temperatures which are still mild...but cooler than what we
will have early this upcoming week. Large discrepancy then exists
for the weekend. Most certain is an Arctic cold front which the
models have locked onto for Friday night. Therefore more seasonal
temperatures will be in store Friday night and Saturday along with
breezy conditions. The question is what happens to the cold air
after Saturday. The 00z European model (ecmwf)...and current GFS quickly shunt the
Arctic air eastward and are actually quite mild by what would be day
8 Monday Feb 2nd. However the latest 12z European model (ecmwf) is back to a pretty
cold solution next Sunday and following afterward. Therefore at this
time using a superblend solution for day 7 Sunday is prudent until
the solutions settle down. More often than not the past few days...
the European model (ecmwf) has not shown a rapid warmup after Saturday so am inclined
to believe that the cold 12z European model (ecmwf) solution may be more correct at
this time...but this is conjecture. The ensembles of course have
clustered around each model so they are not a lot of help at this
Aviation...(for the 00z tafs through 00z Monday evening)
issued at 536 PM CST sun Jan 25 2015
Ceilings 1-3k feet are expected to improve to VFR from 26/00z-08z.
VFR is then expected to continue through 27/00z.