textproduct: Reno

KEY MESSAGES

* Warmer than average temperatures persist through Memorial Day with area waterways continuing to run dangerously cold and swift due to continued snowmelt.

* Afternoon showers and isolated thunderstorm chances are expected within the region today and tomorrow, posing impacts to outdoor activities. * Gusty winds will bring aviation, recreation, and fire impacts Monday and Tuesday with cooler, showery weather from mid to late week.

DISCUSSION

Forecast guidance shows a weak upper trough pushing through southern CA today. With this upper air pattern, shower chances (at least 15%) for this afternoon and evening expect to be confined generally to areas south of US-50. The best chances (25-45%) will be in Mono County and adjacent portions of Douglas/Lyon/Mineral Counties where there is also a 15-25% chance for isolated thunderstorms to develop. While thunderstorms expect to be sub- severe today, potential hazards for these storms include lightning strikes, gusty outflow winds (which could blow dust or cause choppy lake waters), brief heavy rainfall, and small hail/ice pellets. Those with outdoor activities planned should have a way to receive the latest weather updates today as they could be impacted by these storms. While daytime high temperatures look to be around 5-10 degrees above seasonal normals, please refrain from entering area lakes, rivers, and creeks to cool off as they continue to run cold and swift. Winds are forecast to gust up to around 15-25 mph from the west this afternoon before subsiding overnight.

On Memorial Day, models depict a PacNW upper low moving down into the NW CONUS late in the day. This pattern will allow for one last day of W NV and NE CA valley high temperatures in the 80s and Sierra high temperatures in the upper 60s to middle 70s range. However, the primary concern within the region will be increased winds ahead of a cold front approaching from the northwest. Afternoon winds expect to be out of the west to southwest and gust up to around 35-40 mph. As such, Lake Wind Advisories have been issued for some area lakes (including Lake Tahoe and Pyramid Lake) beginning in the afternoon hours of the holiday. Please refer the advisory product for more details. Also, the forecast shows quicker winds closer to the OR border (gusts up to around 45 mph possible), which has merited a Red Flag Warning issuance for Pershing, Eastern Lassen, and North Washoe Counties as well as Surprise Valley in Modoc County (See the product and the Fire Weather section for additional information). Blowing dust will be possible near desert sinks and playas in W NV with these winds, which could potentially reduce visibility. It is also worth mentioning that these winds look to continue into at least the late evening while Sierra ridge winds may gust up to around 60-70 mph overnight. Please keep these increased winds and critical fire weather concerns in mind for the holiday especially if you have travel and outdoor plans. While the region looks to stay mostly dry on Memorial Day, there is a 15-20% chance for afternoon showers and isolated thunderstorms in Mono, Western Mineral, and Southern Lyon Counties.

For Tuesday, model guidance has the cold front moving through the CWA as the upper low pushes across OR and over the CWA by Tuesday evening. Cooler daytime high temperatures are on tap as the forecast calls for highs around 5 to 15 degrees below late May normals. Increased winds (gusts up to around 30-40 mph) will continue on Tuesday though direction will shift to northwesterly behind the front. While another day of hazardous lake winds may occur within the region, critical fire weather is not anticipated with these winds as minimum relative humidity values expect to be around 30% or more. Currently, precipitation chances (40-70%) are seen for NE CA and Northern Washoe County portions of the CWA during the morning and afternoon hours of Tuesday as the cold front moves through. The Greater Lake Tahoe area also has around a 15-25% chance in the late afternoon. Snow levels in these areas look to be around 6.5-7.5 kft so snow could be possibly mixed in with rain at higher elevations that see showers.

For Wednesday and Thursday, the upper low continues to reside over the CWA. This will push in more cooler air from the north, dropping area high temperatures even more. While Thursday looks to be slightly warmer than Wednesday, W NV and NE CA valley will see highs in the 60s on both days with Sierra communities being between the upper 40s and middle 50s range. Widespread precipitation chances are to be expected on these two days as well. Snow levels are forecast to drop to around 6-6.5 kft on Wednesday morning, but gradually rise to around 7-7.5 kft during the day and remain there through the night. When looking at the latest NBM snowfall probabilities, the highest Sierra peaks around the Tahoe region see a 30-50% chance for 4+ inches of snow by Thursday afternoon with the Eastern Sierra peaks in Mono County seeing around a 80-90% chance of the same. Virginia City even sees around a 10-40% chance for 0.1+ inches of snow. Will be keeping an eye on this midweek showery precipitation, but please prepare now if you can for the upcoming cooler temperatures especially if you have already started your gardening outdoors. Temperatures do look to warm to closer to seasonal normals by the weekend. -078

AVIATION

VFR conditions are anticipated for all area terminals today and tonight. Westerly winds gusting up to around 20-25 kts are expected at most TAF sites (the exception being KTRK) through around 25/03-05Z. While areas south of US-50 see at least a 15% chance for showers this afternoon, the best chances (25-45%) are seen in Mono County and adjacent portions of Douglas, Lyon, and Mineral Counties. KMMH also sees up to around a 30% chance for an isolated thunderstorm through 25/03Z, which could yield MVFR conditions from brief heavy rain along with lightning, gusty outflow winds, and small hail.

Increased winds are anticipated on Monday ahead of an approaching cold front that passes through on the region on Tuesday, bringing a second day of gusty to strong winds. These winds could cause turbulence and LLWS in the region along with reduced visibilities due to blowing dust particularly at terminals near desert sinks (KHTH/KLOL/KNFL). -078

FIRE WEATHER

* Critical fire weather conditions due to gusty winds and low humidity are expected Monday afternoon and evening as a strong cold front approaches NE California and NW Nevada.

* A RED FLAG WARNING has been issued for Eastern Lassen County, the Surprise Valley, Northern Washoe County, and the Western Humboldt Basin, including the Quartz Fire (NE Pershing County) in anticipation of gusty winds and low RH Monday afternoon and evening.

* Southwest to west winds will increase early Monday afternoon with sustained winds of 20-30 mph with gusts up to 45 mph across NE California and Northern Washoe County. Areas across Pershing County (Western Humboldt Basin) may see gusts slightly lower up to around 30-40 mph. Minimum relative humidity is expected to be around 10-20%.

* The duration of critical wind/RH is trending towards 3-7 hours in Lassen and far Northern Washoe County with 2-6 hours in Pershing County.

* Uncertainty remains on the continuity of receptive fuel beds, but local intel from local fire partners and the recent Quartz Fire ignition suggests the cured grasses and sagebrush will be capable of carrying fire in valleys/midslopes of far NW Nevada. Farther south, elevated fire weather conditions will be possible, but fuel conditions aren't as dry per local units.

* Winds remain elevated on Tuesday and will shift from southwesterly to north/northwesterly as a cold front sweeps through the region. Temperatures cool and humidity rises behind the front, with increasing chances of showers Wednesday and Thursday. Fuentes/078

REV Watches/Warnings/Advisories

NV...Red Flag Warning from noon to 11 PM PDT Monday NVZ458.

Lake Wind Advisory from 5 PM Monday to 2 PM PDT Tuesday NVZ002.

Lake Wind Advisory from 2 PM Monday to 5 AM PDT Tuesday NVZ003.

Lake Wind Advisory from 2 PM to 11 PM PDT Monday NVZ004.

Red Flag Warning from 2 PM to 11 PM PDT Monday NVZ423.

CA...Red Flag Warning from noon to 11 PM PDT Monday CAZ270-278.

Lake Wind Advisory from 5 PM Monday to 2 PM PDT Tuesday CAZ072.