A quick-hitting weather system drops down today into tomorrow. Breezy to locally gusty west-northwesterly winds will develop today, with gusts up to 20-30 mph. Any precipitation that falls will likely be in far northern Shasta County, the Burney Basin, and the Southern Cascades where there is about a 10-15% probability of isolated thunderstorms as well. As the system exits the region tomorrow, winds will then be from the northerly direction, with gusts up to 30 mph during the day, strongest along the I-5 corridor. Then locally gusty northeast/downslope winds develop Thursday evening through Friday morning, especially for the gaps, canyons, and wind-prone areas, leading to elevated fire weather concerns. Cooler high temperatures prevail through the rest of the week. Next week, another weather system arrives bringing more widespread precip chances for the area and continued cooling.
Discussion
Breezy winds already being observed across interior NorCal this morning, as well as cooler temperatures. Redding is still coming in at 78 at the time of this writing, with upper 50s and low 60s elsewhere in the Valley. Troughing is aiding in enhancing wind speeds and lower temperatures, and that trend will continue as we move throughout the day. An upper level low will dig further south out of the PacNW and move inland in Oregon/Washington today. Based on the forecasted track, most of the moisture will be well north of our area with the Valley getting shadowed from any significant precipitation. North Shasta County and into the Burney Basin stand the best chances of any precip, with around a 5 to 15% chance of a shower and a 5 to 15% chance of a thunderstorm developing. Elsewhere in the Valley, breezy to locally gusty west to northwest winds develop this morning through the evening. The National Blend of Models (NBM) projects around a 30-90% chance of wind gusts greater than 25 mph, with the best probabilities along the I-5 corridor and in the higher elevations of the Coastal Range and Sierra Nevada.
The closed low will then move east and out towards Idaho Wednesday night into Thursday, which will prevent the low from following the classic inside slider pattern but the pressure gradients will still be fairly strong enough to create breezy to gusty northerly winds to develop on Thursday morning through the evening hours. Locations along and west of the I-5 corridor, our wind prone areas, stand the best chances of wind gusts of 25 mph or greater at around 30-70%. With the northerly winds Thursday afternoon and evening, there will be elevated fire weather conditions, mainly in the northern Sacramento Valley.
Thursday evening into the overnight the low continues to move eastward and will setup east/northeast gap flow winds to develop on the western side of the Sierra, with wind gusts around 20-35 mph Friday morning. This will setup a few hours of Red Flag conditions, but will not meet the temporal limits for a product issuance for the area, as the conditions will improve as we move into Friday afternoon and evening. Still, elevated fire weather conditions will exist during the overnight and morning hours. Saturday our area will be under the influence of broad upper level troughing, with continued onshore flow and slightly higher minimum humidity values in the low 20s to low 30s around the region.
A welcome aspect of the upcoming pattern change will be cooler afternoon high temperatures. The NBM has afternoon high temperatures in the mid 80s to low 90s today through Saturday for the entire forecast area. The much welcomed cooling and higher RH values are projected to last into next week as well.
Extended Discussion (Sunday through Wednesday)
Cluster analysis and ensemble guidance indicate a weather system dropping down from the Gulf of Alaska over the extended forecast period. Cooler temperatures are in the forecast over this timeframe as a result of this feature. The National Blend of Models (NBM) suggests a 55 to 95 percent probability of high temperatures less than 80 degrees each day, with Little to No/Minor HeatRisk.
The Extreme Forecast Index (EFI) does have a portions of interior northern California highlighted for below normal temperatures early next week as well.
As far as precipitation, there is still some uncertainty in the rain chances across the area which we will be monitoring closely in the coming days. The NBM currently has a 45 to 75 percent probability of a tenth of an inch of rain or greater, with best chances over the Monday into Tuesday timeframe.
We will also be keeping an eye on the potential for some isolated thunderstorms with this system as well, where the NBM currently offers a 10 to 20 percent probability of thunderstorm development, mainly over higher terrain in the afternoons and evenings.
Be sure to continue to monitor the latest forecast for further updates regarding the next weather system.