Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Aberdeen South Dakota
801 PM CDT Sat Aug 1 2015
issued at 745 PM CDT Sat Aug 1 2015
Severe Thunderstorm Watch 460 continues through midnight.
The 00z kabr sounding did show a very unstable environment
/MLCAPE ~2600 j/kg/ and rather weak cinh /-14 j/kg/. However...it
is appearing less and less likely that new convection will
initiate due to very weak upper forcing and the further onset to
diurnal planetary boundary layer stabilization. One storm over Hand County did produce
several instances of quarter sized hail earlier this
afternoon...but it has long since diminished. Probably the only
hope for new convective initiation is for low level jet induced ascent...but
the latest guidance is suggesting that impacts from low level jet will
likely be well east of this area. Will continue to monitor...
Updated discussion for 00z tafs is below.
Short term...(this evening through Monday night)
issued at 252 PM CDT Sat Aug 1 2015
Overall a dry pattern shaping up in the short term with
cooling temperatures..once we get past this evening. Main forecast
challenge is probability of storms late this afternoon through middle
evening. Cams do not have a good handle on convective initiation
placement though most do go as far west as the James River Valley.
Afternoon analysis..a weak shortwave on WV imagery is moving
southeast just clipping the central South Dakota/ND border. This is helping to
generate some altocumulus castellanus in ND. There is also a boundary just east of
Mobridge..with no shear west of the line but around 40 kts east of
the line. A moisture axis extends from Bismarck southeast to
Ortonville. This would be the most likely Avenue for any discrete
cell formation later today since LCLs are around 1500. This would
also mean most storms would stay north and east of Aberdeen which
gels well with the 4000 j/kg bulls-eye of cape across northern Brown
County this afternoon. Another shortwave across eastern Montana may help
increase forcing as well if it manages to arrive in a timely manner.
Kept isolated to scattered probability of precipitation across the eastern County Warning Area through 3z.
Did not mention t+ but if and when anything does fire chances of it
going severe are good since the environment is favorable. With good
shear and lapse rates of 7 to 8 large hail and gusty winds will be
the main threats.
Long term...(tuesday through saturday)
issued at 252 PM CDT Sat Aug 1 2015
Long term period now shows decent agreement in regards to thermal
forecasts...which highlight a relatively cooler regime compared to what
the northern plains have been experiencing in recent weeks.
Superblend reveals upper 70s to low 80s through most of the period
and this seems OK given models 850 mb temperatures. Unfortunately...the
forecast is still plastered with probability of precipitation through much of the period.
Granted...the pattern does get a bit more active but it still
appears the best chances will be Tuesday night through Wednesday
night...with much more uncertainty after that since models are not
in good agreement with weak shortwave energy crossing the region.
There may be more of a surface high influence from the northeast as well
towards the end of the week which may allow for some removal of probability of precipitation
over the course of the next several model runs.
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1250 PM CDT Sat Aug 1 2015
Still watching for the potential for isolated thunderstorms this
evening. However...confidence on this occurring is waning as
there is little in the way of upper support to initiate new
storms. Winds will continue to shift more west/northwesterly this
evening...but expect that winds may simply become more variable
overnight due to a weak pressure gradient.
VFR conditions are then expected through the day on
Sunday...although it will likely become breezy with northwest
winds of 15 to 25 kts.