An increasingly active weather pattern will bring significant fire weather and flash flood concerns to the Treasure Valley and central Idaho mountains Thursday through Saturday as monsoon moisture surges northward and dry lightning gives way to heavy rainfall.
Red Flag Warning: Fire Weather Threat Thursday and Friday
A Red Flag Warning is expected for the Treasure Valley and surrounding areas Thursday afternoon through Friday as a dangerous combination of dry lightning, gusty outflow winds, and low relative humidity creates critical fire weather conditions. A passing upper-level shortwave will accelerate moisture advection Thursday, supporting scattered thunderstorm development from Thursday afternoon through Friday morning across southwest Idaho and eastern Oregon.
The critical concern with these early storms is that the lower boundary layer will remain dry initially, meaning lightning will strike dry fuels without the benefit of wetting rain. This dramatically increases the risk of new fire starts across the region. Gusty outflow winds up to 35 mph will further complicate fire weather conditions, potentially spreading any new ignitions rapidly.
Anyone in the Treasure Valley and surrounding areas should be aware of the elevated fire danger Thursday and Friday. Avoid any activities that could spark a fire, be aware of current fire restrictions, and have an evacuation plan in case of new fire starts near your area.
Flash Flood Threat Develops Friday and Saturday for Central Idaho Mountains
By Friday afternoon, the character of the storm threat will shift dramatically as deep monsoon moisture fully encompasses much of Idaho. Moisture values will climb to near the 80th to 90th percentile of normal, transitioning the primary hazard from dry lightning to heavy rainfall. The central Idaho mountains will bear the brunt of this threat, with a 30 to 40 percent chance of showers and thunderstorms Friday and Saturday.
The National Weather Service is monitoring the potential for a Flash Flood Watch for burn scars in central Idaho, including the Wapiti burn scar, as confidence in heavy rainfall potential increases. Burn scars and steep and rocky terrain are particularly vulnerable to flash flooding and debris flows when heavy rain falls rapidly. Anyone planning to be in the central Idaho mountains Friday through Saturday should monitor conditions closely and be prepared to move to higher ground if heavy rain develops.
Cooler Temperatures Provide Some Relief
Increased cloud coverage and showers will yield cooler temperatures Friday, dropping highs several degrees below seasonal averages to near 86 degrees. Saturday will remain pleasant at 89 degrees before temperatures recover back toward seasonal normals Sunday and Monday.
Weekend Outlook
Saturday will continue the active pattern with a 40 percent chance of afternoon showers and thunderstorms. The flash flood risk for central Idaho burn scars will persist through Saturday afternoon as moisture values remain high. A warming and drying trend will take hold Sunday and Monday as weak upper-level ridging builds into the Intermountain West, with temperatures climbing back to the low 90s. Lingering moisture will maintain a slight 10 to 20 percent chance of afternoon showers and thunderstorms over higher terrain through Monday.
Model guidance suggests another Pacific trough approaching the northwest coast by midweek, which could reintroduce breezy conditions, a slight cooling trend, and increasing precipitation chances.
Tonight
Patchy smoke. Mostly cloudy, with a low around 62. Light wind.
Thursday
Patchy smoke. Mostly sunny and not as hot, with a high near 89. Light wind.
Thursday Night
A 20 percent chance of showers and thunderstorms. Patchy smoke before 10pm, then patchy smoke after 4am. Mostly cloudy, with a low around 64.Light wind.
Friday
A 30 percent chance of showers and thunderstorms, mainly before noon. Cloudy, then gradually becoming mostly sunny and more comfortably warm, with a high near 86. Light wind.
Friday Night
A 30 percent chance of showers and thunderstorms after midnight. Partly cloudy, with a low around 62. Light wind.
Saturday
A 40 percent chance of showers and thunderstorms after noon. Partly sunny, with a high near 89.
Saturday Night
A 30 percent chance of showers and thunderstorms before midnight. Partly cloudy, with a low around 59.
Sunday
Sunny and hot, with a high near 92.
Sunday Night
Partly cloudy, with a low around 62.
Monday
Partly sunny and hot, with a high near 92.
Monday Night
Mostly cloudy, with a low around 63.
Tuesday
Mostly sunny, with a high near 89.
Tuesday Night
A 20 percent chance of showers. Mostly cloudy, with a low around 61.
Wednesday
A 20 percent chance of showers. Partly sunny, with a high near 86.
