Area Forecast Discussion
Issued by NWS Reno, NV
Issued by NWS Reno, NV
648 FXUS65 KREV 032238 AAA AFDREV Area Forecast Discussion...UPDATED National Weather Service Reno NV 338 PM PDT Fri May 3 2024 .SYNOPSIS... Warmer temperatures continue today, with light winds. Active weather returns tomorrow with a storm system bringing gusty to strong winds along with valley rain and mountain snow, with conditions slowly improving Sunday. For next week, a slow warming trend with low chances for precipitation remains in the forecast. && .DISCUSSION... REST OF TODAY: The latest RAP analysis shows the CWA underneath a weak upper air ridge this afternoon with a pretty robust upper air low residing over the Pacific Ocean west of the U.S./Canada border. Current surface observations report back mostly light and variable winds with a few breezy gusts out of the east in some locations. Model guidance then forecasts the low to move southeast towards the U.S. coast going into the night and pushing the ridge to the east. At the surface, daytime high temperatures expect to range between the 60s to the lower 70s with cooler highs in the Sierra Crest. While most of the region expects to stay dry, the HREF shows a 10-20% probability for an isolated shower or two later this afternoon/evening in Mono County and the bordering areas though not much moisture is expected with these showers. THE WEEKEND STORM: Forecast guidance projects the upper air low continuing a progression towards the CWA throughout Saturday and then passing over the northern portion of the CWA on Saturday Night and going into Sunday morning. By late Sunday evening, the low is forecast to have moved east of the CWA allowing for a north- northwesterly flow over the CWA going through the night. With this upper air pattern, a low pressure system looks to move east- southeastward across OR on Saturday and make its way over northern UT by Sunday morning. This will cause a quick moving cold front to begin to sweep across the CWA on early Saturday morning. This front will cause the region to see two impactful weather concerns for Saturday: gusty to strong southwesterly winds along with winter-like precipitation including accumulating mountain snow and valley rain. * Winds: Upon looking at the latest ECMWF EFI (Extreme Forecast Index) for wind gusts on Saturday, there is a "bulls-eye" of 0.90- 0.99 values in southern portions of the region (southern Lyon, Mineral, and Mono counties) that slowly lowers going northward into the CWA. There is a second maximum seen in northern Washoe county as well of 0.8-0.9. What this means is that there is a really good signal for strong (~60+ mph) wind gusts within the region on Saturday. Please refer to the High Wind Warning as well as the Wind Advisories for more detailed information on expected maximum wind gust values as well as locations. There is also information on strong winds contained within the Winter Weather Advisory and Winter Storm Warning that should be referenced as well. These winds will cause hazardous traveling conditions including potential blowing dust beginning on Saturday morning and going into the evening. Travelers are encouraged to check conditions within the region be embarking on their journeys. The winds look to decrease a bit by late Saturday night/early Sunday morning as the system moves more eastward away from the CWA. * Snow and Rain: With the latest QPF updates, snow totals particularly for the Sierra Crest and Tahoe Basin have come up a bit on Saturday and going into Sunday. As a result, the Winter Weather Advisory on Saturday and Sunday for the Lake Tahoe Area and Mono County has been upgraded to the first ever NWS Reno Winter Storm Warning issued for the month of May in recent history. Lassen, Eastern Sierra and Eastern Plumas counties remain in the Winter Weather Advisory Please refer to the Winter Weather Advisory and the Winter Storm Warning for more details such as timing, locations, and forecast snowfall amounts for the these areas above 5000 feet. Weather.gov/rev/winter also is a source for this information along with the latest Winter Storm Severity Index (WSSI) which shows moderate to major impacts along the Sierra Crest and some of the mountain passes. The latest HREF is showing the potential for 1-2 inch per hour snowfall rates in the afternoon and evening which is not very common to see this time of year. Once again, travelers should be prepared due to the expected hazardous traveling conditions in these areas that will include blowing snow (with the strong winds) and accumulating snow that may cause slick roadways. While the higher elevations see good snowfall chances, lower elevations particularly in the valleys will see rain more as their P-type though some areas may see some snow mixed in on Saturday night with temperatures cooling and snow levels dropping. Snow flurries may be possible going into Sunday morning within western NV. The latest QPF values range from around a trace in Mineral county to around almost 2 inches in the Sierra Crest on Saturday and Sunday. Precipitation chances look to begin Saturday morning in the west with the front approaching and spread through the rest of the CWA by the afternoon hours. These chances then look to depart out the east with the system by late Sunday afternoon allowing for a drier evening and night. * Temperatures: Temperatures do come crashing down and are pretty cold for May standards on Saturday and especially Sunday due to the cold front passage. High temperatures will be upwards of 15-20 degrees below average, as the region barely reaches 40 degrees for Sierra communities with western NV seeing lows as high as the low to middle 50s. There is additionally the chance for sub-freezing temperatures in western NV and northeast CA on Sunday morning as well as Sunday night into Monday morning. BEYOND THE WEEKEND: Model guidance shows the upper air low opening up into more of a negatively tilted trough on Monday over the Rocky Mountains allowing for a mostly northwesterly flow over the CWA that continues through Tuesday. It also continues into Wednesday with the trough becoming more neutral over the central CONUS as a ridge moves over the Pacific Coast. As a result, temperatures look to rebound a bit though still being cooler on Monday before slightly cooling on Tuesday with a warming trend beginning on Wednesday. While the upper air pattern is unsettled at this time, signals do point to the warming trend continuing through Thursday and Friday. Precipitation chances look to be minimal at best currently during the next work week. There may be some fog concerns during the morning hours around the Truckee area during mornings to begin the work week, so will continue to monitor this potential. -078 && .AVIATION... * Friday will feature pleasant flying conditions with light winds and mostly clear skies into the evening. There are a few showers around KMMH into the eastern Sierra that will quickly dissipate after sundown this evening. Weekend Storm Update: A strong, unseasonably colder spring storm system is moving into the region overnight tonight through Saturday. * Snow/Rain: Widespread mountain snow showers and valley rains are likely (>70-90%) overnight into Saturday evening throughout the northeast CA, the Sierra, and western NV. This colder airmass will allow for snow levels to drop to 5000-5500 feet by Saturday night. Sierra terminals KTRK, KTVL, and KMMH could see between 3-5" of snowfall with a 80-90% chance for at least 2". However, high sun angle in May may limit accumulations on runways at those terminal during the day. There is also a slight chance for snow flurries Saturday night into Sunday morning for far western NV terminals (KRTS-KRNO-KCXP-KMEV). * Winds: Strong west to southwest winds will increase across the Sierra overnight and continue through Saturday night. Look for sustained ridgetop winds across the Sierra of 40-50kts with gusts upwards of 70-90kts during this time period. Expect periods of mountain wave turbulence, as well as LLWS for all area terminals. Strong west to southwest winds are possible as well for all western NV and Sierra terminals through Saturday. -Amanda && .REV Watches/Warnings/Advisories... NV...Wind Advisory from 8 AM to 5 PM PDT Saturday NVZ005. Winter Storm Warning from 11 AM Saturday to 8 AM PDT Sunday NVZ002. High Wind Warning from 8 AM to 8 PM PDT Saturday NVZ001-003. Lake Wind Advisory from 8 AM to 8 PM PDT Saturday NVZ004. CA...Wind Advisory from 8 AM to 5 PM PDT Saturday CAZ070. Winter Weather Advisory from 11 AM Saturday to 8 AM PDT Sunday CAZ071. Winter Storm Warning from 11 AM Saturday to 8 AM PDT Sunday CAZ072-073. && $$