Scientific Forecaster Discussion
000 FXUS66 KSTO 132320 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 320 PM PST Wed Nov 13 2019 .SYNOPSIS... Dry weather pattern continues this week with a cooling trend. Warmer this weekend with well above normal high temperatures. && .DISCUSSION... Temps mostly trending a little cooler and likely reached their maximum earlier in the afternoon due to increasing high cloud cover ahead of the Pacific trof with the low center near 35N/135W. This trof is forecast to move inland Thu/Fri with synoptic cooling and continued thickening clouds into Fri morning. The 700-500 RH prog suggests the cloud cover will be thicker (more prevalent and opaque) tonight into Fri morning than the past couple of days for "cloudy" or "mostly cloudy" sky conditions. The trof will weaken drastically as it moves inland and into the strong ridge. The high resolution REFs from the NAM 3km keep radar echoes (precip) to the WNW of our CWA, and will opt for the lower (dry) PoPS on Fri. Behind the trof, a brief period of locally breezy conditions is possible over the NE Sac Vly Fthls, and Valley late Fri nite and into Sat morning. The average gusts are forecast in the 20-25 mph range at RDD and RBL on the ECMWF ensembles. Although temps will cool through Fri, they will continue to run above normal for the middle of Nov. As this trof passes over the ridge and digs into the Great Basin and 4-Corners area an Omega-Rex Blocking pattern will develop along the W Coast of NOAM this weekend. Anticyclonic flow from the repositioning of the strong ridge will return warmer temps to the CWA. Valley and Foothill max temps will warm into the 70s on Sat (low 80s far N on Sun). These temps are some 6 to 17 deg above normal on Sat, and some 9 to 21 deg above normal on Sun, with the greatest departures from normal over the Nrn Sac Vly. Probabilities are quite high that max temp records for the dates (Nov 16 & 17) will be equaled, if not exceeded, in the North Valley including RDD and RBL. The Day 7 500 mb heights Cluster suggests a positively tilted trof will develop over the Great Basin region which could bring some windy conditions to our CWA, and much cooler wx and possibly a few light showers mainly over the mtns. This 5H Cluster would support the retrograding solution of the ECMWF and closed low developing over Socal later next week. JHM && .EXTENDED DISCUSSION (Sunday THROUGH Wednesday)... High pressure will be the dominate feature this weekend as it brings warmer and drier air back to the region. Temperatures are forecast to peak in the mid 70s to low 80s for the Valley on Sunday, while those in the mountainous terrain can expect highs ranging from the mid 50s to the low 70s. Relative to climatology, this is roughly 10 to 20 degrees above average. With a daily record high in Redding of 83 degrees (dating back to 1893), would not be surprised to see this either tied or broken. Well above average readings will continue into Monday given the ridge lingers yet another day. From Tuesday into later in the week, the upper ridge will finally have advanced into the Rockies. A seasonably strong trough enters the picture while accelerating through the Pacific Northwest early Tuesday. While a few ensemble members support the trough taking a farther west track bringing some scattered showers to the region, a vast majority carry the system through the Central Great Basin instead. The latter scenario would favor an uptick in northerly gradients which lowers humidities and enhances wind fields. Given this trough remains nearly a week out, it will need to be closely monitored for any notable impacts. In the meanwhile, high temperatures from Tuesday onward should be noticeably cooler, but still roughly 3 to 6 degrees above average. ~BRO/KR && .AVIATION... VFR conditions the next 24 hours except local MVFR visibilities from KSAC southward 12Z-17Z. Winds generally below 10 knots. && .STO WATCHES/WARNINGS/ADVISORIES... None.