By: Robert Sandberg/Carson City Weather
Synopsis: It’s been quite a while since there was anything real interesting to discuss weather wise for the area. Today was the last day of mild spring like temperatures we will see for the next week to 10 days. Winds have become rather gusty this afternoon with southwest winds of 15-30 mph with some gust to 40 in many areas. A drastic change in the weather will occur tonight and into Saturday ahead of a strong cold front expected to move into the area by Saturday afternoon. This storm system has the potential to be the strongest storm of the season as the front is expected to stall out over the Lake Tahoe area Saturday night into Sunday. Heavy mountain snow and valley rain/snow mix are likely Saturday afternoon through at least Monday, with additional snow expected Monday night into at least early Wednesday.
The big picture: The latest GOES West satellite image this afternoon showing a rather compact storm system dropping down along the Pacific Northwest coast. The latest GFS current 18Z 250mb analysis also shows this system developing in the upper levels as a positive tilt trough is beginning to dig down from Canada into the western US as omega blocking ridge in the Gulf of Alaska has become more amplified and retrogrades slightly to the west. A rather strong jet of 130-150 knot winds over the Arctic Circle into western Canada are driving the low south. As the front approaches the area winds will continue to increase due to increasing thermal and pressure gradients. We will likely see winds top out in the 20-30 mph range with some gusts to 50-60 mph in the wind prone areas of western NV. For the Sierra, ridgetops will likely see some gusts in the 90-100 mph range through Saturday night.
Precipitation forecast: Without further delay, let’s get to the part of the forecast that most are interested in, which is precipitation. The latest runs of the operational dynamic models shown below (ECWMF, GFS, GEFS, ICON, CMC) continue to be in decent agreement on a general bullseye of precipitation over the central Sierra, with the Lake Tahoe area in the general brunt for this storm. In general, the Sierra crest will see what is likely the biggest storm of the season, which isn’t saying much after our dismal water year so far. At this time, total QPF amounts look to average in the range of 4-6 inches, which will bring several feet of snow to the highest elevations of the Sierra. In fact, it would not be out of the realm to see some snow totals in the range of 6 feet over the next 5-day period. Areas in the Lake Tahoe basin will likely see amounts of 1-2 feet over the period.
For those interested in precipitation amounts for western NV valleys, the latest NBM and MOS continue to show significant amounts of precipitation for the Reno/Carson City areas. In fact, the latest 20Z NBM guidance continues to put out QPF totals of around 2 inches for KRNO and KCXP respectively through 12Z Wednesday. The SREF, which only goes through 06Z Wednesday for KRNO only has a total of around .75 inches by that time, so there’s significant disagreements on total precipitation for the Reno area most likely due to shadowing. As for snowfall amounts, the SREF shows up to 5 inches in the Reno area during the 5-day period. Much of this is due to the lower QPF and snow levels will remain at times above the valley floor, so rain will likely fall during the daytime hours. For the Carson City area, snow levels will be even more problematic as the slightly higher elevation may yield higher snow totals during this event. If there is enough cold air entrained in the system, snowfall amounts could be significantly higher as they will just above the valley floors of western NV. Amounts will likely be fine-tuned over the next day or so for the valley areas.
A look ahead: The overall upper level pattern and teleconnections continue to show that that active pattern will continue through the next two weeks, details in any forecasts remain very uncertain. What does look like the main outcome will be an additional low dropping south along the west coast later next week or into the weekend. Unsettled weather will likely continue though the period, but there doesn’t appear to be any major storms on the horizon after the main system passes through over the next several days. At least at this point there will be some mitigation in the very dry conditions we have experienced over that last two months.