Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Sioux Falls South Dakota
413 am CDT Wednesday Jul 30 2014

Short term...(today and tonight)
issued at 413 am CDT Wednesday Jul 30 2014

Another unseasonably cool but pleasant day on tap for the region
with weak northwest upper flow locked into northern and Central
Plains. Some minor Theta-E advection sets up across central South
Dakota and noses towards our western boundary this afternoon. Expect
the main impact of this feature to be an increase in middle and high
clouds mainly along and east of the James River. To the east...skies
will be mostly sunny some widely scattered diurnal cumulus popping
up by afternoon. With a slight boost in middle level temperatures and
decent mixing under mostly sunny skies...temperatures should be a
few degrees warmer than yesterday with highs in the upper 70s and
lower 80s.

Light and variable winds tonight...clearing skies and the persistent
cool airmass will allow for another chilly night. Following recent
forecast trends...did nudge towards the cooler end of guidance for
lows. The exception will be across south central South Dakota where the
thermal boundary and middle level clouds persist overnight. A very
subtle middle level wave drops southward and clips this area late
tonight...so will leave very low end probability of precipitation in place - isolated shower
mention. Quantitative precipitation forecast will be very light without much moisture to work with
and dry low levels...and may be more Akin to sprinkles than showers.
Lows tonight fall into the low 50s to near 60.

Long term...(thursday through tuesday)
issued at 413 am CDT Wednesday Jul 30 2014

Noisy northerly flow into the start of the weekend does pose the
possibility of getting a few hard to resolve periods of
convection. Wave sliding down on Thursday through the eastern
plains has gained quite a bit of consistency over the last several
runs. Water vapor loop verifies location and strength of
wave...and several other subtle upstream impulses set to cross
ridge and dive into the northern plains.

Best thermodynamics in terms of Theta-E advection seem to focus
through the western County Warning Area early in the day Thursday...but eventually
as some cooler middle level air works southward...and weak and ill
defined low level convergence boundary sinks southward...possible
to find at least a few showers or thunderstorms during the peak
diurnal heating cycle across most of the area. Far from a
washout...and most likely to remain dry.

On Friday...another wave indicated...more formidable in the NAM
and sref than other solutions. Could easily argue that with the
weak low level flow...boundaries from any earlier convection
during this diurnal cycle may focus a little development across
the County Warning Area with distinct middle level thermal boundary in place...but
start to see warming aloft with building heights...and expect
a solution toward more of a cap developing...and will not add
in any additional precipitation chance for this period at this time
with temperatures probably nudging just a touch warmer than Thursday.

Weekend should be dry with weakening ridge shifting toward the
northern plains...allowing a south to southwest flow to develop
with falling pressure north and west. Warmest of the airmass will
position west of the County Warning Area on Sunday...but this will be the most
likely day of having temperatures at or above normal...but Saturday not
too far behind.

The Prospect for precipitation looks to finally improve at the
start of next week...as ridge breaks down with wave pushing into
the plains around Tuesday. Should be led into by a period of
increasing low level moisture/dew point...and potential for
slightly above normal temperatures south of increasingly frontogenetic
boundary. Could even start to consider at least a small heavy rain
and severe weather threat with increasing directional shear and
instability.

&&

Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1035 PM CDT Tuesday Jul 29 2014

VFR is expected to continue over the area through 31/06z. The low
level air appears too dry for patchy late night and early morning
fog despite light winds and mostly clear skies.

&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...
long term...Chapman
aviation...

National Weather Service Glossary of Abbreviations