Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 221119

Area Forecast Discussion
National Weather Service Sioux Falls SD
619 AM CDT Sat Apr 22 2017

.SHORT TERM...(Today and Tonight)
Issued at 251 AM CDT Sat Apr 22 2017

A nice weekend day for outdoor activities today, with early morning
cirrus shield over the southeast forecast area shifting further
southeast, and upstream cirrus dissipating as it attempts to spill
over the upper ridge. This should leave us with abundant sunshine
today, along with light winds as surface ridge axis works slides
southeast through the area. Wind directions will be quite variable
within the ridge axis, but should generally settle around to west or
southwest as the surface ridge passes.

Mixing will be somewhat limited given the light wind profile, with
even the normally super-mixy RAP only mixing to 800mb or slightly
higher. This yields high temperatures generally in the mid 60s, with
afternoon dew points in the lower-mid 30s.

Skies remain mostly clear tonight, with lingering ridge axis across
northwest Iowa allowing for a fairly quick temperature drop in the
evening. Readings should steady out a little more overnight, though,
as the low level ridge shifts farther southeast and stronger low
level southwesterly flow begins to develop. Generally looking for
lows in the lower 40s, with some upper 30s in parts of northwest
Iowa/extreme northeast Nebraska.

.LONG TERM...(Sunday through Friday)
Issued at 251 AM CDT Sat Apr 22 2017

The extended period looks to be characterized by below normal
temperatures and frequent rain chances.  The start of the period
will not be that bad however, with Sunday having above normal
temperatures in a strong southwesterly low level flow and highs
running upper 60s to lower 70s. It will be a breezy day in a
tightening gradient as a surface trough approaches from the west.
Sunday night looks to remain mild with southerly winds staying up
overnight, and lows upper 40s to around 50.

On Monday an upper level shortwave tracks across the region while a
surface boundary slides across our CWA during the day. It will be
another windy day, especially in our east with a tight gradient and
decent mixed layer winds out ahead of the boundary. Moisture is not
that impressive with the passage of the front, but cannot rule out a
few showers across the area during the day. Instability is meager,
with model computed CAPE values running 100 to 400 J/KG in parts of
our south during the afternoon, so did include some isolated thunder
during that time period. Monday will be another fairly warm day with
highs mid 60s to lower 70s.

The bottom drops out for the remainder of the week as an upper level
trough settles into the central CONUS with sub zero C 850 mb temps
over the area through at least Thursday. This will play out to highs
averaging in the lower 50s and lows in the 30s to lower 40s. Raw
model guidance and 925/850 mb temps through the period would
actually suggest that temperatures could be cooler than currently
populated Superblend values, and did try to trend this way for
Monday night and Tuesday to start with, going below given guidance
for that time period. Precipitation chances exist for much of the
week with a series of shortwaves sliding through the region. The
better chances are focused on the Tuesday and Thursday night/Friday
time frame, and cannot rule out a little snow mixing in at night in
portions of our northern locales for any precipitation that occurs
during the nighttime period.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 619 AM CDT Sat Apr 22 2017

VFR conditions and light winds will prevail through this evening.
Expect increasing southwesterly flow aloft after 04Z, and while
little effect will be seen on the surface through 12Z Sunday, may
see period of low level wind shear develop in areas west of I-29,
including at KHON, late in this TAF period.




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