Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota
242 PM MDT Wednesday Jul 23 2014

Short term...this evening through Thursday night
issued at 240 PM MDT Wednesday Jul 23 2014

Water vapor imagery shows strong upper ridging across much of the
western to central Continental U.S. With the main axis from Colorado to Montana. An upper low is
sitting just offshore the Pacific northwest with SW flow over the northwest
Continental U.S....then transitioning to northwest flow over the County Warning Area. Surface analysis
shows high pressure across the upper Midwest...and low pressure over
Montana with return flow over the High Plains. Temperatures have struggled
to reach forecast highs with temperatures so far in the 80s to lower 90s.

Strong cap in place across much of the County Warning Area will keep diurnally
triggered convection from developing today. The cap was expected to
be weakest across NE Wyoming where temperatures reaching middle 90s would be enough
to erode it...but temperatures have been short of that so far. Convection
has initiated over Laramie range...and the latest hrrr run shows
this convection moving north/NE into NE Wyoming and SW South Dakota this evening. Have
put in isolated probability of precipitation this evening to account for this...and possible
other convection that moves in from the west. But overall most areas
will stay dry tonight. Any storms that make it into the area may be
severe...but overall severe threat tonight is very low.

Upper ridge axis slides eastward Thursday...crossing the northern plains.
Upper low will cross the northern rockies with the surface low pushing
across the County Warning Area. Temperatures are expected to reach the 90s to 100. A cold
front will slide southeast...crossing the County Warning Area Thursday aftn/night. A strong cap
in place again will help keep convection from developing...but could
see isolated storms develop as the front pushes through...perhaps
elevated storms. Cant rule out a couple storms becoming severe...but
overall threat looks minimal again.


Long term...Friday through Wednesday
issued at 240 PM MDT Wednesday Jul 23 2014

Upper-level ridge over the region breaks down by the end of the week
as an upper low slides southeast across south central Canada. A weak
shortwave in zonal flow to the south could bring another chance for
showers and thunderstorms to at least portions of the County Warning Area Friday
afternoon and night.

As the upper low slides further east of the region...the upper ridge
will rebuild over the western Continental U.S....bringing predominantly
northwest flow to the northern plains. This will result in cooler
temperatures for the rest of the extended period...along with mainly
dry conditions from Saturday through Monday. Weak shortwave
disturbances will begin to rotate around the ridge and into the
northern plains again by the middle of next week. Will keep low
chance probability of precipitation across portions of the area from Monday night through


Aviation...for the 18z tafs through 18z Thursday
issued at 240 PM MDT Wednesday Jul 23 2014

VFR conditions are generally expected through the forecast period.
Isolated thunderstorms are possible late today across northeast Wyoming
and tonight across northeast Wyoming and much of western South Dakota.


Unr watches/warnings/advisories...
South Dakota...none.


Short term...13
long term...26

National Weather Service Glossary of Abbreviations