Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
334 am CDT Thursday Oct 23 2014
Short term...(today and tonight)
issued at 333 am CDT Thursday Oct 23 2014
Main issue today is early morning fog which has developed behind
exiting rain system. Lack of significant flow behind the surface
boundary resulted in near surface moisture remaining in place as
temperatures fell with clearing of middle clouds. This has allowed
fairly extensive area of dense fog to develop east of the James
River Valley to near/just east of the I-29 corridor as of 08z.
Issued a dense fog advisory earlier this morning to cover this
through 15z/10 am CDT. Some high-res models hold on to lowest
visibility until closer to midday...and cannot completely rule out
some patchy lingering fog beyond 10 am given lower sun angles and
continued light boundary layer flow within weak ridge axis. However
greatest consensus among guidance is for visibility improvement by
15z. Clouds/fog will certainly limit temperature rise through much
of the morning...but anticipate a quick recovery after the fog
dissipates and made little change to previous highs in the upper 60s
to lower 70s.
Fair amount of low level moisture remains in place through tonight
and NAM does indicate potential for redevelopment of fog as temperatures
fall into the 40s ahead of approaching surface trough overnight.
Opted to leave out for now as wind speeds are expected to be a bit
higher than we have seen this morning. However will be something for
day shift to investigate with new guidance.
Long term...(friday through wednesday)
issued at 333 am CDT Thursday Oct 23 2014
Friday into the weekend still looks pleasant...with upper ridging
bringing well above normal temperatures and partly to mostly sunny
skies. Friday should be the warmest with highs in the 70s. Some
cirrus could hold down highs a tad...but still think staying on the
warm side of guidance is the way to go given the low humidity and
good mixing behind a weak cold front. Saturday and Sunday will see
slightly cooler temperatures aloft move in...but should still see
highs in the middle 60s to around 70.
Some uncertainty by later Sunday into early next week as troughing
moves across the plains. One area of forcing moves across later
Sunday and Sunday night...although at this time looks like best
precipitation chances with this feature stay northeast of our
area...with dry air preventing any precipitation over US. Looks like
a better chance of showers Monday into Monday night as the main
trough axis swings through the area. Will just keep low chance probability of precipitation
for now as model consistency on quantitative precipitation forecast placement and amounts remains
low...but this period likely has the best chance of rain over the
next 7 days.
What does seem more certain is that cooler temperatures will push
into the area early to middle week. Could still see some 60s on
Monday...but 50s are likely by Tuesday into Wednesday. Lows should
also drop back into the 30s by Tuesday or Wednesday morning. While
these high and low temperatures are much cooler than what we are
currently experiencing...these values are right around average for
this time of year.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1051 PM CDT Wednesday Oct 22 2014
Fog and low stratus continues to build along edge of departing
MVFR stratus deck as cooler air settles into the region. Surface
winds have turned variable...with surface to 925 mb winds very
light from the west. Feel that we will now have a narrow corridor
of IFR to LIFR stratus and fog develop into the morning hours. The
concerns will be with the duration of the fog towards daybreak.
Soundings suggest with little to scour the moisture
out...stratus/fog could linger through daybreak. For now...will
be optimistic and suggest that stratus could move east of the area
before daybreak...or at least stabilize into a low stratus deck
with improved visibility.
Otherwise...VFR conditions will be expected after middle-morning
Thursday as winds increase.
South Dakota...dense fog advisory until 10 am CDT this morning for sdz039-054-
Minnesota...dense fog advisory until 10 am CDT this morning for mnz098.
Iowa...dense fog advisory until 10 am CDT this morning for iaz001.