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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
637 am CDT Friday Mar 27 2015

Short term...(today and tonight)
issued at 440 am CDT Friday Mar 27 2015

Clear and cool start to the day as surface ridge moves across the
forecast area. Main focus through tonight is on quick moving middle
level wave currently dropping through northern Saskatchewan. This
wave forecast to drop southeast across the northern plains over the
next 24 hours...bringing a relatively quick shot for light precipitation
late this afternoon and evening.

Main problem is the wave will be encountering air mass which is
starting out quite dry below initial lift will be lost to
saturation which should not only delay the start of precipitation...but
also reduce potential snow amounts. Have removed mention of precipitation
altogether through 18z in our County Warning Area...with only 20-30 probability of precipitation through the
central portions of the area prior to 00z. Some high-res models
already pointing to even slower progression of measurable precipitation...
so this is something the next shift will want to monitor through the
day. Precipitation type...if anything reaches the surface...also a little
tricky given the dry air mass. Forecast surface temperatures alone
suggest a better rain potential...but depth of temperatures above
freezing is relatively shallow...and saturation should cool the dry
layer to near/below freezing as precipitation falls through it. Given low
confidence of precipitation reaching the ground this afternoon...will stick
with temperatures largely in the upper 30s and 40s this afternoon.
However...will carry a potential for light snow at temperatures as
warm as 40 or that is the more likely scenario if precipitation
does occur.

Precipitation chances should increase this evening across the eastern half
of the area...though again with the speed of the wave and questions
on extent of saturation...felt most comfortable leaving probability of precipitation in the
middle-high chance range for now. Any snow accumulations should be on
the lighter most in the 1/2 to 1 inch range...though most
areas will likely see less than that. Snow should slide southeast of
the area after 06z...but clouds linger through the night...holding
temperatures in the 20s.

Long term...(saturday through thursday)
issued at 440 am CDT Friday Mar 27 2015

Lower clouds should have backed well through the County Warning Area to start the
day Saturday...perhaps enough to temporarily leave the far
east/northeast. The stabilized lower levels will make for a slow
and arduous departure of lower clouds...but by early afternoon the
strengthening low level jet and erosion along the edges should
have it well to the decreasing side across southeast South Dakota.
Continued decreasing clouds for the eastern areas through the
afternoon...but enough damage will be done to warming potential to
hold highs mainly middle 40s to lower 50s east of the James
River...with some lower to middle 60s across the far west. South
winds will get quite strong during the day...and strongest
gradient likely across the area during the evening hours...
which favor a Buffalo Ridge enhancement..perhaps gusting to 35 to
40 miles per hour.

Largest challenge on Saturday night and early Sunday is
the variation in timing of wave pushing across the northern
plains. European model (ecmwf) continues to indicate a much more split trough
energy and slower progression to system...while GFS/NAM/Canadian
remain much quicker on progression. Ec at least a full 6 hours
later on bringing in the better lift forcing. GFS ensemble
solutions do indicate a small subset in hard to fully
ignore. Therefore...have stretched out the lower probability of precipitation a bit slower
and westward in the later Saturday night and early Sunday periods.
Steep middle level lapse rates in place ahead of approaching
dynamical lift still would not be shocked to see a
couple rogue rumbles of thunder. Overall...should not be a
widespread event with a fair degree of lower level dry air... more
toward scattered showers than a widespread event.

The other story will be the very strong winds developing behind
the strong frontal boundary as it moves across the area later
Saturday night and Sunday. Pressure rises of 8-10 hpa/3h will
push in behind boundary...directionally supporting 40 to 45 knots
of northwest wind in the upper mixed layer...especially through
SW Minnesota and into the Iowa Great Lakes region. Subsidence and
trend to greater sunshine potential through the day will support
the strong winds surfacing. Certain impact on fire danger
discussed below.

Milder period for Monday to models indicate a
progressive zonal pattern across the northern plains. Monday
should be a fairly mixy day...but the gradient not as strong as
other days. Main impact of mixing will be to warm temperatures
and drive afternoon dewpoint lower...and have placed a bit higher
confidence to the warmer side of guidance closer to consensus
mixing from around 850 hpa.

Weak back door front should sag into the area with little fanfare
on Tuesday...other than to shift winds around a bit. Temperatures remain
largely near those from Monday aloft...perhaps a shade cooler
northeast...and expect mainly pleasant middle 60s to lower 70s.

Next more significant wave appears around Wednesday time frame...
which will be accompanied by another strong cold front and
enhancement of mixing. Have continued mention of showers at this
time...but some indication that there could be enough potential
instability to get some thunder into the eastern County Warning Area later Tuesday
night and early Wednesday. Depending on any rainfall...Wednesday
could very well be the next significant fire danger day...but
westerly winds likely not as strong as Sunday.

Temperatures slip back somewhat toward normal Thursday with more
clouds...and more impact of northern stream into the region.
Not enough evidence to warrant deviations from initialization
grids at this time.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 637 am CDT Friday Mar 27 2015

VFR conditions expected through midday across the area. Lowering
ceilings will accompany a weak wave dropping southeast through the
region this afternoon and tonight. MVFR ceilings/periods of MVFR
visibility in -sn will be possible...more likely east of our taf
locations. Lower confidence of MVFR conditions at the taf sites...
so will stick with predominant VFR ceilings in the tafs at this


Fire weather...
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 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. 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.

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.


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


Short term...jh
long term...Chapman
fire weather...Chapman

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