Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
729 FXUS66 KSTO 162003 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 103 PM PDT Tue Jul 16 2024 .SYNOPSIS... Slightly cooler weather is expected today and Wednesday, with Minor to Moderate HeatRisk over the region. Temperatures begin to trend up again later in the week and over the weekend. && .Key Points... - Slightly cooler today and Wednesday; warming trend expected by the weekend and into early next week. - Potential for isolated mountain thunderstorms returns late in the weekend/early next week. && .Discussion... Satellite imagery early this afternoon shows swaths of clouds over the Sierra, albeit little no radar reflectivity indicating any developed areas of rain or thunderstorm development. This looks to continue this afternoon and evening as dry air moves in from the west, inhibiting convection potential. The better areas of forcing and moisture lie east of the Sierra outside of our area. Granted with onshore flow present and forcing as it moves up the mountain, sprinkles or the stray thunderstorm isn`t a 0% chance. As the weak troughing along the coast and the subsequent onshore flow continues, this will keep things relatively "cool" and near normal temperatures through Wednesday. Highs today and tomorrow will be in the low to high 90s in the Valley, mid 80s to mid 90s in the foothills, and high 70s to low 90s in the mountains. Thursday and Friday warm up again slightly (though right now it looks like it won`t be nearly to the degree we saw with the last heat event) as upper level ridging reamplifies near the Four Corners region late in the week and pushes back west. Widespread Moderate HeatRisk with some isolated areas of Major HeatRisk are expected to return starting Thursday. Right now, the probability of temperatures reaching 100 or higher through the end of the week remain mostly limited to areas where 100 is the normal temperature this time of year, i.e. the northern Sacramento Valley (65-95% probability of reaching or surpassing 100 degrees). Probabilities have increased for hotter weather this week with a 40-85% probability of areas in the southern Sacramento and northern San Joaquin Valleys reaching 100 on Thursday or Friday. && .EXTENDED DISCUSSION (Saturday THROUGH Tuesday)... As the upper level riding over the four corners continues to trend westward, chances for temperatures reaching or surpassing 100 degrees increase across the area over the weekend and early into next week. By Monday and Tuesday, most Valley locations see a 75 to 95% probability of reaching 100 degrees or more, while foothills locations can expect a 30 to 75% probability of this occurring. Monday shows Moderate to Major HeatRisk over the Valley and foothills locations with localized areas of Extreme HeatRisk. Sunday and Monday also may see the return of some monsoonal moisture, with the NBM showing a 10 to 20% probability of isolated thunderstorms along the Sierra crest those days, primarily south of I-80. Confidence is low at this point but we will be continuing to monitor the progression of any monsoonal moisture into the area and the chance for thunderstorms it may bring. && .AVIATION... VFR conditions next 24 hrs. Surface wind gusts generally under 12 kts except local southwest gusts up to 30 kts vicinity west Delta, and areas of southerly/southwesterly gusts 20-30 kts Sacramento Valley and northern Sierra through 07Z Wednesday. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$