Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1043 PM CDT Friday Mar 27 2015
Short term...(this evening through saturday)
issued at 307 PM CDT Friday Mar 27 2015
Snow area with current short wave acting on strong thermal gradient
will continue to progress east/southeast...then exit the area to the
southeast tonight as the wave moves out. This means the northeast
corner of our southwest Minnesota area will get little. Not that anyone
will get a lot...but there should be some half inch plus
accumulations on grass.
Clouds will clear out of the southwest corner tonight but will be
slow to exit the north and east. Low level moisture has been
collecting in the thermal gradient to greatly modify the initially
very dry air. With the cooled air and moisture added from the
precipitation event as well...low clouds seem likely to be stubborn
east...especially southeast...dissipating gradually late Saturday
morning and afternoon with warming and daytime heating.
Temperatures will cool to several degrees below freezing
tonight...not too far from where they are now in the cool east.
Highs Saturday should be in the 40s east to the 50s west...to the
60s extreme southwest. Winds should pick up to breezy levels from
the southeast to south Saturday.
Long term...(saturday night through friday)
issued at 307 PM CDT Friday Mar 27 2015
Saturday night into Sunday morning showing a faster European model (ecmwf) which
comes in line more with the faster models from yesterday and today.
Increased probability of precipitation a bit from mainly 6z through 12z Saturday in the
northern County Warning Area into southwest Minnesota but mainly looking at amounts
from a trace to a tenth of an inch. The wind will remain pretty
strong through the night going from the south to southwest and west.
So lows likely from about 35 to 45 degrees.
The wave exits by middle Sunday morning with strong subsidence and deep
mixing expected late Sunday morning into early Sunday evening. Went
ahead and issued a Fire Weather Watch for Sunday afternoon with very
strong winds and fairly low afternoon relative humidity values.
Highs will be a bit on the moderate side ranging from the middle 50s
north to 60 to 65 south.
With the wave exiting rapidly a west to southwest wind will be left
behind for Monday which will lead to a very nice day. Winds should
mainly be on the order of 10 to 15 miles per hour...a few higher gusts...with
highs from the middle 60s in southwest Minnesota to the middle 70s down
the Missouri River valley.
In the outer periods(tuesday through friday)...a fairly strong short
wave ridge pushes through which should set up a very warm day across
the area. The only real differences to the amount of warming will be
the wave the scoots through to the northeast of the area on Monday
and how much cool air filters south. The difference right now
between the warmer GFS and cooler European model (ecmwf) is about 5 to 6 degrees at
925mb which equates to about 10 to 15 degrees f at the surface. The
differences then extend into Wednesday as another wave is expected
to swing through. The new 12z European model (ecmwf) has come around to the slower
12z GFS solution for Wednesday which suggests warmer lows everywhere
and warmer highs...especially south and east. Will also introduce
the threat for isolated thunderstorms in mainly northwest Iowa.
Should see a minor surge of moisture Tuesday night into Wednesday
and with a fairly dynamic wave moving through the ingredients will
be there for a few thunderstorms. Main thing will be timing.
Thursday into Friday looking cooler with small chances for
rainfall...especially with cooler air aloft surging south. Highs
about 55 to 65 on Thursday and 45 to 55 Friday.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1037 PM CDT Friday Mar 27 2015
Light snow over southwestern Minnesota and northwest Iowa will
continue to diminish through the night time hours...with lingering
MVFR ceilings generally from the Interstate 29 corridor eastward.
Southerly winds will pick up after 15z on Saturday...with gusts
around 25 kts into Saturday evening.
issued at 440 am CDT Friday Mar 27 2015
Very strong northwest winds are root of cause to expected very
high to extreme fire danger on Sunday. Should have plenty of time
to recover from any light light precipitation later today...and
additional light rainfall threat Saturday night...but it would be
this latter light rainfall which could keep parts of SW Minnesota from
attaining the potential critical behavior. Seems unlikely at this
point but the Saturday night rainfall threat will need to be
watched. At this time... humidities remain locked in at around 20
percent in Lower Brule areas..but in the lower to middle 30s from
Interstate 29 eastward. With winds gusting to 45 miles per hour at times
east of Interstate 29 went ahead with a watch in southwest
Minnesota even though afternoon relative humidity is around 35
percent. West of Interstate 29 the humidity is lower but winds may
decrease during the afternoon. No watch in northwest Iowa or
southeast South Dakota but these areas will need to be watched.
Will also have to watch the Post frontal environment on Wednesday
for at least a very high fire danger...with strong westerly winds
along with lower humidity. The better chances will be west of
Minnesota...Fire Weather Watch from Sunday afternoon through Sunday evening