Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
737 FXUS66 KSTO 232032 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 132 PM PDT Thu May 23 2024 .SYNOPSIS... Seasonably warm, dry, and breezy weather continues today. A brief cool down is then expected on Friday and Saturday before temperatures warm back up from Sunday into next week. A few isolated showers or thunderstorms will also be possible Friday across the northern Sacramento Valley and northern Sierra. && .DISCUSSION... As the trough responsible for the northerly winds last night-this morning continues to progress eastward across the northern Rockies, the northerly pressure gradient will continue to relax through this evening, resulting in lighter winds. Another shortwave trough will dig southward from the Pacific Northwest tonight through Friday, then rapidly transition toward the intermountain West throughout the day on Saturday. There remains some ensemble uncertainty on exactly how the shortwave will evolve, but overall impacts for interior NorCal look to remain minor at most. Regardless, as this shortwave moves within the vicinity of interior NorCal late day Friday into early Saturday, a few isolated showers and thunderstorms may pop up (10% to 25% chance) across the northern Sacramento Valley and northern Sierra. Otherwise, the region looks to trade northerly winds for south to west winds in onshore flow from Friday into the weekend. Additionally, a somewhat pronounced cool down is anticipated, with Valley high temperatures in the 70s to low 80s and 50s to 60s at higher elevations. This cool down looks to remain short lived, however, as heights aloft begin to rise on Sunday and temperatures return to near normal by Sunday afternoon. && .EXTENDED DISCUSSION (Monday THROUGH Thursday)... Cluster Analysis and ensembles have upper-level ridging develop over the Great Basin region through at least mid week next week. This will allow high temperatures to be in the upper 80s to mid 90s for the Valley. With increased heights aloft, daytime heating will be enough for some limited instability to develop along portions of the central/southern Sierra crest early next week, potentially allowing for some limited isolated showers and thunderstorms to develop mainly in southern Tuolumne County. By mid week next week, some notable variance in the clusters develops with the ridge heights (intensity) and how quickly it is shifted eastward with weak shortwaves progged to move through British Columbia/WA late week. Given the location of the ridge axis, some variation of weak west to southwest flow will be overhead late week next week, keeping onshore flow, and thus somewhat limiting the upper-end potential of the NBM forecast highs late week. Even so, the shortwave trough may not influence our apparent weather much late next week, allowing for temperatures to be warmer than currently advertised, especially for areas less likely to be influenced by onshore flow (central/northern Sacramento Valley). The NBM forecast high temperature spread between the 25th and 75th percentiles for Thursday and Friday next week differ by 12-15 degrees. Given these uncertainties, confidence in the temperatures forecast late week isn`t super high, so stay tuned as the forecast gets closer and details become more clear. //Peters && .AVIATION... VFR conditions next 24 hours. Winds in the northern Sacramento Valley continue to taper off through this afternoon becoming light by overnight hours. In the afternoon, areas near the Delta will see gusts 15-20 kts continuing into Friday morning. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$