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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Thursday
• 
• High: 55 °
• Low: 34 °
• T-Storms

• Friday
• 
• High: 54 °
• Low: 41 °
• T-Storms

• Saturday
• 
• High: 72 °
• Low: 43 °
• Chance of T-Storms

• Sunday
• 
• High: 61 °
• Low: 41 °
• Chance of Rain

• Monday
• 
• High: 68 °
• Low: 39 °
• Partly Cloudy

Area forecast discussion for western South Dakota and northeastern Wyoming 
National Weather Service Rapid City South Dakota 
829 PM MDT Wednesday may 23 2012 


Discussion...current surface map shows weak high pressure ridge 
across northern Wyoming into western South Dakota. A few showers 
located across northeast Wyoming into southwest South Dakota. 


For the rest of the night...left exit region of strong jet steak will 
focus shower development across portions of northeast Wyoming and 
southwest South Dakota. Probability of precipitation adjusted for the remainder of the 
night. 00z kunr sounding has freezing level above 9k feet and wet 
bulb zero near 8k feet. 00z NAM/RUC show some slight cooling 
overnight around 700mb...but 850mb temperatures remain above +8c. 
Will remove mention of snow for the higher elevations of the Black 
Hills. 


&& 


Aviation...00z/06z tafs 
isolated/scattered showers will persist through the night across 
portions of northeast Wyoming and southwest South Dakota. Local 
MVFR visibility/ceilings with the showers. More widespread shower activity 
expected during the day Thursday across most of the forecast area. 


&& 


Previous discussion... /issued 320 PM MDT Wednesday may 23 2012/ 


Tonight through Friday night 


Mean western Continental U.S. Troughing to persist in the period...with several 
impulses passing through the flow. Once such impulse is in the 
process of advecting through western South Dakota...supporting rain showers activity. 
Wake impulse subsidnet clearing over Wyoming will follow on this 
impulse/S heels with another round of concentrated large scale 
ascent supporting increasing chances for rain once again tonight 
over western portions of the forecast area. Closed low over the Pacific northwest is still 
on track to the be the strongest middle level wave in the 
period...supporting a staunch surface cyclone over the central rockies 
later Friday. Robust mass field adjustment is expected with a 
decent chance for rain associated with this system. Only subtle 
changes made to the previous forecast...mainly in pop and temperature 
trends. 


Tonight...secondary impulse now traversing northern Wyoming will advect 
east overnight...supporting a renewed rounded of high centered 
upglide with chances for rain showers...especially over the far SW forecast area. 
Nearly all forecast models support some degree of reflected backing 
flow at 700 mb with Theta-E riding at this level. Given a lingering 
elevated frontal boundary being in place...sufficient moisture is 
expected to be in place to interact with this wave as it slowly 
pushes east overnight. Highest elevations of the Black Hills could 
see a mix of snow with any overnight/morning activity given 
supportive thermal profiles. Did add a slight chance SW mention 
there. Expect mean mostly cloudy conditions with breaks/clearing 
expected on the back side of each aforementioned impulse...likely 
supporting strong radiational cooling in areas which do see clearing 
toward dawn. 


Thursday-Thursday night...secondary impulse will slowly advect across the 
southern forecast area....with disturbed westerly flow aloft offering the 
potential for additional small scale disturbances...retained highest 
probability of precipitation south closest to best large scale ascent/Theta-E advection/and ll 
convergence. Lingering rain showers activity is possible through evening with 
clearing/drying likely after midnight in areas given shortwave 
ridging. 


Friday-Friday night...digging central rockies impulse will eject east-northeast into 
the Central Plains and support appreciable mass field adjustment. 
Theta-E advection regime in a broad large scale ascent pattern will 
support increasing chances for rain Friday into Friday night...with 
sig isentropic ascent indicated in all model solutions given 30-40 
knots of cross-isobaric flow in the 295-305k layer. Expect 
increasing clouds through the period...with ll upslope flow 
supporting cool temperatures with the increasing potential for low 
clouds/fog. 


Extended...a significant upper trough will remain west and 
north of the area during the weekend. Southwesterly flow aloft will 
bring a series of upper level disturbances through the area...with 
chances for showers and a few thunderstorms for the weekend. Mainly 
dry conditions are expected Monday. Showers and thunderstorms will 
return Tuesday and Wednesday as a strong shortwave crosses the 
region. Temperatures will generally be near or slightly below 
average over the weekend...with a warmup to near or slightly above 
average temperatures early next week. 


&& 


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


$$ 


Short term...07 
long term....WFO unr 
aviation...07