Area forecast discussion for western South Dakota and northeastern Wyoming
National Weather Service Rapid City South Dakota
704 PM MDT Sat may 18 2013
Update...
issued at 658 PM MDT Sat may 18 2013
Showers and thunderstorms will continue across much of the area
this evening. Best chances for severe storms will be along a weak
surface boundary from Ziebach County through Jackson and Bennett
counties. Some of these storms along the boundary have been slow
moving and producing heavy rainfall...so localized flooding will
be an issue through the evening. As the evening
progresses...storms will slowly shift east into south central
South Dakota.
&&
Short term...this evening through Sunday night
issued at 203 PM MDT Sat may 18 2013
Current surface map places weak trough/warm front across southwest
into south central South Dakota. Low clouds gradually dissipating
across the area. Isolated thunderstorms and rain over the Black Hills and southwest
South Dakota. Convection coverage/intensity will increase rapidly
this afternoon with 1000-2000j/kb SBCAPE. Severe thunderstorms
possible from the Black Hills into south central South Dakota this
afternoon and evening.
Upper low closes off over South Dakota on Sunday...with some
differences among models. GFS/Gem more intense and a little further
west with 700mb low than NAM. Widespread showers expected across
northeast Wyoming/western South Dakota as strong Theta-E advection
wraps around the north-northwest side of upper low. Increasing low
level flow out of the north and steep low/middle level lapse rates will
result in upslope enhanced rainfall over the northern Black Hills
and bear Lodge mountain...especially Sunday night. Will become windy
across plains of western South Dakota.
&&
Long term...Monday through Saturday
issued at 203 PM MDT Sat may 18 2013
Medium range models remain in good general agreement with
progression and track of upper low early next week. With the low
still projected to stall out across the northern and Central Plains
Monday into Tuesday...plenty of wrap around rainfall can be expected
across much of the forecast area. There is still some uncertainty at
this point...but 1 to 2 inches of rain should be common across the
area from later Sunday into Tuesday...with some higher amounts
likely across the northern Black Hills area...where upslope enhanced
precipitation will occur. Cool and windy conditions can be expected
Monday and Tuesday...with highs in the upper 40s to upper 50s.
System will slowly drift east out of the region Tuesday night or
early Wednesday...with gradually improving conditions from west to
east. Beyond Wednesday...there should be a gradual warmup through
the latter part of the week...especially across western areas...as a
weak ridge moves into the plains. Will go with a mainly dry forecast
for late Wednesday into Thursday. Southwest flow aloft will develop
again by the end of the week...so will see chances for showers and
thunderstorms increase Thursday night into next weekend.
&&
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 520 PM MDT Sat may 18 2013
Areas of MVFR ceilings and visibilities with scattered showers and
thunderstorms will continue into tonight...with severe thunderstorms
expected through this evening from the Black Hills eastward. Local
IFR/LIFR conditions expected near stronger storms. Widespread IFR
ceilings and some -shra will develop across the area after midnight.
&&
Unr watches/warnings/advisories...
South Dakota...none.
Wyoming...none.
&&
$$
Update...15
short term...7
long term...15
aviation...10
