Marine Weather and Tide Forecast for Sunnyside-Tahoe City, CA

DISCUSSION

* Temperatures peaking today will gradually cool Wednesday and Thursday accompanied by typical zephyr breezes. HeatRisk remains moderate for many areas into Thursday. A few buildups or very isolated t-storms are possible based on HRRR - mainly over high Sierra or far NE California.

* Massive pattern change Friday into the weekend with anomalous cold trough digging into the west, with sub-zero 700mb temperatures expected. Highly unusual for late June.

* Anytime we see max temps drop from the upper 90s to low/mid 70s in summer, we're going to get some wind and sure enough Friday & Saturday will be breezy. ECMWF EFI hitting 0.75 to 0.85 on the wind which is notable. NBM showing 70% chance for gusts 35+ mph for much of W Nevada and the Eastern Sierra, and 20% for 45+ mph (which is our wind advisory threshold). Saturday looks to be more of a sustained wind issue, whereas Friday it's the gusts that'll be impactful. So clearly this is a fire weather concern with dry fuels in lower/mid elevations, even with increasing humidity (RH mins 12-20%) and a few showers possible. Winds could also be impactful for air/road travel and backcountry recreation.

* Showers are looking more likely with deterministic models showing bands of precip developing both Friday & Saturday, mainly I-80 northward. Generally about a 20-40% chance of measurable rain each day along/north of I-80, with 10-20% odds of a wetting rain in places like Susanville, Portola, and Cedarville. With that cold air, snow lines drop pretty low for late June - NBM showing 7200-8500' on Saturday for example.
Within heavier showers a coating of snow is possible. NBM indicating 10-20% chance of measurable snow for Sierra crest.
Could definitely catch backcountry folks off-guard.

* Temperatures will be well below normal for late June, with 80-90% probability of highs below 80F for W Nevada cities including Reno. Similar percentages for mountain communities if you adjust the threshold to 70F. Sunday & Monday mornings will be crisp with 80-100% chance of mountain towns seeing frosts (less than 36F). 30% chance of that at Minden and other typical cold valleys. Could be an issue for sensitive vegetation.

* For next week and as we head into the Independence Day weekend, no significant weather hazards anticipated with temperatures warming to near normal with no big precip or wind signals in the AI ensemble data.

-Chris

AVIATION

* VFR conditions with typical west/northwest breezes each afternoon today and tomorrow. Gusts on the order of 20-25 knots.

* Winds aloft increase tonight with models showing 30 knots at 700mb at 6z/Wed so have included wind shear in TVL/TRK TAFs.

* Slight uptick in the winds Thursday with gusts 25-30 knots as low pressure trough approaches the west coast.

* Small potential for fog at TRK Wednesday 9-15z per LAMP guidance but likely to be patchy and shallow with drier RH versus this morning. 20% chance of brief LIFR at TRK so not included in TAF.

-Chris

FIRE WEATHER

* Unusually strong cold front for late June projected to bring areas of critical fire weather conditions Friday and Saturday.
Fire Weather Watches have been issued for the Sierra Front eastward into the Hwy 95 corridor.

* High confidence in seeing sustained winds 20-30 MPH with gusts above 40 MPH both days, W/SW direction on Friday and W/NW on Saturday. Saturday's winds may end up being more of a sustained wind concern versus just the gusts. Almost an April-like pattern in late June.

* For areas in the watch along and north of a Carson City to Lovelock line, including Reno, the humidity may be just above RFW criteria, around 15-25% for afternoon minimums. But with plenty of dry fuels/grasses and recent significant lightning event last Friday with holdover potential, we felt it best to err on the side of being proactive by issuing the watch.

* One other area to be mindful of is the lower elevations of the Eastern Sierra along Hwy 6 and 395 below 7000' (e.g Chalfant Valley). Once confidence increases further, I could see us expanding the watch to this zone for Saturday as it usually responds well to NW gradient winds.

* Humidity recoveries Friday night into Saturday morning look good (45-75%), but winds will remain breezy for mid-slopes and ridges.

-Chris

REV Watches/Warnings/Advisories
NV...Fire Weather Watch from Friday morning through Saturday evening NVZ420.

Fire Weather Watch from Friday morning through Saturday evening NVZ423-429.

CA...