A relatively unusual storm system is developing over the Southwest U.S. the next few days. This storm is moving in from the northeast - We typically only see systems from this direction a few times each year. This system may bring:
Slight chance of scattered showers and thunderstorms
Slight potential for flash flooding, especially higher desert areas and mountains
Thunderstorms could contain high winds, blowing dust and even hail
Computer models have been trending toward the development of a low pressure system over our area all week. As of Thursday afternoon, these trends have proven reliable, as recent satellite imagery shows upper winds blowing from the north/northeast over Northern California today, as a low pressure system is developing and strengthening over Nevada today, moving southwest toward Southern California.
In the graphic above, the green solid lines represent the upper level jet stream winds. The wild pattern indicates winds being forced north, then back east and south, around a strong high pressure system anchored off the coast of Oregon and Washington. This high pressure is causing the winds to dive south and southwest over the back side of the high pressure system, and leaves the entire Western U.S. susceptible to storm development, as several low pressure systems have continued to form over the Idaho/Utah area and have moved southwest toward our area.
The latest system is forming this afternoon over Western Nevada, and is expected to continue moving southwest to a position to the west of Santa Barbara by Friday. It will continue to move south off the coast later Friday, and is expected to slowly start moving east over the San Diego area Saturday and into Arizona on Sunday.
Since we are now approaching mid-May, we are experiencing a much higher sun angle, resulting in more daytime heating than what we see earlier in the year. This heating will allow the atmosphere to become increasingly unstable over the next 4-5 days. Combined with the dynamics of the low pressure system moving over our area, it is likely to produce periods of scattered showers and possible thunderstorms.
This is NOT a monsoon pattern of wind and moisture from the southeast that hits during the summer, but is instead due to atmospheric forcing, and instability (colder air aloft, near the low pressure system, but warmer surface temps), allowing showers and storms to develop.
It will be impossible to accurately predict exact rainfall amounts between today and Sunday, but the latest computer models are indicating the possibility of as much as 2 inches of rain over the nearby mountains, with lesser amounts over the deserts.
Most of the Coachella Valley is expected to see 0.15” - 0.5” between today and Sunday, with amounts closer to 1” likely in the higher terrain south of the Yucca Valley/Joshua Tree area, as well as closer to the mountains on the west side of Palm Springs and up in the Banning/Cabezon area.
HOWEVER, it is likely that some areas may see locally higher amounts, close to any heavier thunderstorms that have the possibility of forming. Currently, the weather models predict the highest chance of heavier rains and thunderstorms is Saturday afternoon. Regardless of that, scattered storms are still possible anytime from later today through Tuesday afternoon, especially in the afternoon and evening hours. It will be important to keep an eye on the sky, and be alert for any threatening storms.
Rainfall of these amounts in a quick period of time can cause washes to suddenly fill with mud and water. Anyone near hiking trails or creeks the next 4-5 days should pay attention for any flash flood watches or warnings, should the National Weather Service issue any. Roadways in the Joshua Tree area are particularly susceptible to sudden flooding.
If more than 2 inches of rainfall occurs in the nearby mountains, it is possible that the Whitewater River could flow for a brief time over Indian Canyon Dr. south of I-10. It’s too early to predict if this will occur, but it is certainly worth mentioning, since springtime systems are unpredictable.
UPCOMING WEEK STARTS AND ENDS UNSETTLED
The weather pattern is expected to remain slightly unsettled Monday and Tuesday of next week, with isolated afternoon and evening showers and thunderstorms possible. Mountainous areas have the highest probability of receiving rainfall, which is likely to be widely scattered.
Wednesday and Thursday should return to fair and dry weather, with a warming trend. Windy weather is possible along the I-10 corridor and also into the high deserts, with local blowing sand and dust possible..
Friday through Sunday is likely to cool down once again, with gusty winds, blowing dust and even the slight possibility of showers returning to the mountains at some point. Future weather model runs will need to be watched to see if another system enters our area the following weekend or not. Current trends are indicating this is a possibility. Either way, May is typically one of the driest months here in the desert. If this rainfall does materialize as expected, it will be very anomalous.
Taking a look at the National Weather Service Data at Palm Springs Airport….
May 8 - Hi/Low: 85/63 (Normal is 91/63)
**Last year, May 8 - Hi/Low: 108/69 (we’ve been fortunate not to experience this high heat this year thus far!)
Rainfall since October 2018: 7.76 inches (Normal is 4.68 inches)
High temps the next 5-7 days should remain at or below normal most days, in the 80s and 90s, with lows in the high 50s and 60s most nights. Temps should be very comfortable!
Use caution and watch for weather warnings the next several days, if heavy rains do in fact develop. Otherwise, we will be treated to some fantastic cloud formations and skies during the next several days!