Area Forecast Discussion
Issued by NWS Reno, NV
Issued by NWS Reno, NV
543 FXUS65 KREV 180903 AFDREV Area Forecast Discussion National Weather Service Reno NV 203 AM PDT Wed Sep 18 2024 .SYNOPSIS... * Well-below average temperatures continue through most of the week. * The next storm system brings additional precipitation and thunder chances today and tomorrow. * Afterwards, a warming and drying trend starts on Friday and into the weekend as the storm leaves the area. && .DISCUSSION... Nighttime Microphysics satellite imagery continues to show multiple layers of clouds across the whole region very early this morning. Radar shows a few very light showers in portions of the CWA. Conditions will slowly deteriorate during the morning hours as the upper low seen offshore of the CA coast slowly moves inland this afternoon and evening. Therefore, expect more clouds and better chances for rain, snow above 8500 ft and thunder. This afternoon, the HREF members continue to indicate showers and isolated thunderstorms across the Sierra, the Sierra Front and vicinity as the upper low swings to the southeast towards southern NV. The best dynamics with this system remain to the north of it, where the jet streak is located in the vicinity of the Eastern Sierra. The HRRR has been showing this consistently since yesterday. So, there is moderate confidence on this. However, the uncertainty comes with the intensity of the shower activity. Ensemble members have drastic differences. Therefore, expect light to moderate rain with isolated areas of heavy rain. That would be the best bet. The best timing for the precipitation will be from 2 - 7 PM. Showers should slowly dissipate and moves south from the northern Sierra and the Sierra Front overnight. Then the focus continues/shifts more to the south towards the Eastern Sierra. Down in Mono County and the Eastern Sierra is where we have the best chances of seeing snow in the higher elevations above 8500 ft. Snow amounts have gone down a bit, but we are still expecting 2-4 inches of snow above 9 kft. NBM probabilities for amounts greater than 4 inches went down, but it is still showing a 20-50% chance. Amounts greater than 6 inches went down below 20% above 10 kft. Sierra passes including Ebbetts, Sonora and Tioga have only a 10-20% chance of seeing 4 inches of snow. This came down significantly from yesterday when it was up to 40%. The main reason is snow levels have come up to 9000 to 10000 ft, which means that this system is pulling on some warmer subtropical moisture. We still have a Winter Weather Advisory, but have lowered the snow amounts to reflect this change in the forecast. Anyways, isolated higher amounts are still possible, especially near the highest peaks along the Sierra crest. Once the system leaves on Friday morning, drier conditions return to the area along with a slow warming trend. A north to northwesterly flow is set aloft as an upper ridge develops in the Eastern Pacific. There is good agreement among the ensemble members of the GEFS, ECMWF and CMC for this scenario over the weekend. Afternoon temperatures will reach near seasonal values by the weekend, and slowly climb to above normal next week. -Crespo && .AVIATION... VFR conditions are expected through the morning hours, then VFR to MVFR conditions due to lower CIGS after 18Z. Periods of SHRA and -TSRA are expected between 19Z Wed to 04Z Thurs across the Sierra and Sierra Front with a 25-35% chance of lightning for all TAF sites, except KRNO with a 10-20%. The stronger cells could drop VIS down to 4 SM. Snow is expected generally above 8.5 kft, but KMMH may see a light RA/SN mix tonight. Also expect mountain obscurations through Thursday late morning or early afternoon. Winds will be generally less than 10 kts from the northeast, except KMMH/KTRK been from the south this afternoon. Light and VRB winds expected during the overnight hours. -Crespo && .REV Watches/Warnings/Advisories... NV...None. CA...Winter Weather Advisory from 2 PM Wednesday to 8 PM PDT Thursday CAZ073. && $$