Area Forecast Discussion
Issued by NWS Rapid City, SD
FXUS63 KUNR 261421
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
821 AM MDT TUE JUL 26 2016
Issued at 820 AM MDT Tue Jul 26 2016
There is some uncertainty about how much the atmosphere will
recover this afternoon from this morning`s round of convection.
Short term guidance does have convection developing in the CWA
this afternoon, however, it is not handling the morning convection
very well in terms of its extent and duration, so do not have a
lot of faith in the model output. Regardless, visible satellite
reveals clearing in Northeast Wyoming behind the storms, and with
differential heating/outflow boundaries setting up across the
CWA, would expect new storms to develop in the afternoon off the
Black Hills and near the aforementioned boundaries. Severity of
the storms will ultimately be determined by how much the
atmosphere recovers this afternoon.
.SHORT TERM...(Today Through Wednesday Night)
Issued at 203 AM MDT Tue Jul 26 2016
Active zonal flow will persist in the period. A slow moving
impulse will force a lee side trough east today across the region.
Moist southerly flow east of this feature will allow appreciable
moisture into the area, with pos theta-e adv ongoing this morning.
Isold shra/ts will be possible this morning, trending east across
the fa associated with waa under steep mid level lapse rates.
Diurnal heating with a sfc trough in place across western SD will
support shra/ts over much of the fa this afternoon, esp invof the
Black Hills. Appreciable cape (2000 j/kg +) with around 40 knots
of deep layer bulk shear will certainly support a severe threat
with any cells, esp across western SD this afternoon and central
SD this evening. Cells should gradually merge into a forward
propagating mcs given a llj and wind profiles this evening as
activity pushes into central SD, thus better coverage expected
there. Retained at least an isold mention most places through
tonight given jet streak lift and residual moisture under steep
mid level lapse rates. Weak cool front will settle across the
western fa and stall wed. Weak impulses in westerly flow coupled
with moist easterly upslope flow and weak inhibition should
support sct-isold ts activity in the afternoon, esp invof the
Black Hills. Isold severe cells will be possible, esp in the Black
Hills. Lingering activity will be possible in the evening with
coverage waning overnight. Kept a slight chance mention overnight
wed given jet streak forcing which will be present once again.
Hot conds expected most places today with highs in the 90s, with
cooler conds wed given easterly flow.
.LONG TERM...(Thursday Through Monday)
Issued at 203 AM MDT Tue Jul 26 2016
As high pressure slowly slides southeastward over the northern
plains, a boundary will set up over the CWA on Thursday. Models
are showing around 2000 J/kg MLCAPE developing over northeastern
WY and western SD by midday, with 0-6 km bulk shear around 30 kts.
As weak energy moves over the region, the boundary will be the
focus of shower and thunderstorm development...mainly across
northeastern WY and far western SD. Highs will be in the low to
Chances for showers and thunderstorms continue on Friday, but a
warming and drying trend will begin as an upper ridge builds over
the region. Weekend highs will be in the upper 80s to mid 90s, with
low chances of precip mainly over the Black Hills.
.AVIATION...(For the 12Z TAFS Through 12Z Wednesday Morning)
Issued At 505 AM MDT Tue Jul 26 2016
Thunderstorms with MVFR ceilings and visibilities will
continue moving across the area this morning, mainly over
northwestern SD. More widespread thunderstorm activity is expected
this afternoon and evening, especially over the Black Hills and
western SD. IFR conditions are possible in stronger storms. Some low
clouds/fog may develop after midnight across parts of the plains,
with MVFR conditions possible.