textproduct: Reno

KEY MESSAGES

* Strong high pressure will result in historic March warmth this week.

* The warm temperatures will accelerate snowmelt, leading to rivers running fast and cold.

* Dry and mild weather is favored through the weekend, but a pattern change with some cooling and chances for precipitation returns near the middle of next week.

DISCUSSION

The first day of record highs has occurred (see the Climate section below), although the maximum heating potential was likely held back by a couple of degrees as the sun was filtered by a swath of cirrus Tuesday afternoon. The current March record highs for Reno and South Lake Tahoe held for one more day, but these have a 90+% chance of being broken this afternoon as the high pressure ridge center moves inland over the southwest US. This sets up a more favorable scenario for additional heating to the mid 80s for western NV valleys and lower-mid 70s for Sierra communities. The latest blended guidance is targeting Friday as the warmest overall day of this March heat event, with upper 80s and even up to a 30% chance of touching 90 degrees for warmer valleys of western NV, while E Sierra/Tahoe sites are projected to reach the mid-upper 70s. Small fluctuations in the eventual position and extent of the ridge, and timing of passing cirrus cloud cover could still affect this week's peak temperature by a couple of degrees.

With these very warm temperatures, expect an increase in snowmelt, leading to faster flows on local rivers and creeks. It may be appetizing to cool off in those waterways but the cold water brings the danger of shock or hypothermia. Seek shade or head indoors for a safer way to cool off.

For this weekend, a cooling trend will take place as the ridge retreats southward in response to increasing westerly flow across the Sierra and western NV. Record highs remain within reach for Saturday but not for Sunday, while winds trend upward to more typical zephyr-type levels (gusts near 25 mph).

Next week presents a potential change to a cooler pattern with periods of gusty winds and valley rain/mountain snow shower chances around the Tuesday-Wednesday time frame. However, confidence remains on the low side with a nearly 20 degree spread among ensemble guidance for next week's highs, including some scenarios bringing a short reprise of 80+ degree temperatures. Our overall forecast leans toward a continued cooling trend, especially farther north toward the Oregon border through the middle of next week. Meanwhile, the I-80 corridor southward hangs onto highs about 10 degrees above late March averages (lower 70s for western NV valleys/upper 50s-lower 60s for E Sierra/Tahoe sites. MJD

AVIATION

VFR conditions with light winds prevail for all terminals through much of this week. The only exception may be KTRK between 10-15Z for the next few mornings, where there is a 20% chance of patchy FG. Density altitude concerns may arise due to warming for W NV terminals. Additionally, slantwise visibility reductions may arise due to haze trapped under sharp morning inversions through Friday. MJD

CLIMATE

New record highs were set on 3/17 for both Reno and South Lake Tahoe, surpassing the previous records by 4 degrees. However, the morning was cooler with no new records for warmest lows.

Both area climate sites (Reno at KRNO and South Lake Tahoe at KTVL) are on track to set new record high temperatures each day through Saturday. Although with less certainty, some record warm lows may also be set.

Current record high temperatures for Reno and South Lake Tahoe:

Date Reno NV South Lake Tahoe CA ---- ------------ ------------------- 3/17 82F (prev 78F in 2007) 69F (prev 65F in 2007) 3/18 77F in 1947 63F in 2004 3/19 77F in 1997 65F in 2015 3/20 81F in 2004 68F in 1997 3/21 80F in 2004 68F in 1997

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Current record warmest low temperatures for Reno and South Lake Tahoe:

Date Reno NV South Lake Tahoe CA ---- ------------ ------------------- 3/17 48F in 2015 38F in 2007 3/18 47F in 1945 37F in 2021 3/19 46F in 2013 38F in 2013 3/20 47F in 2013 35F in 2013 3/21 46F in 2015 38F in 1972

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Warmest daily March temperatures on record:

Reno, NV: 83F on 3/31/1966

South Lake Tahoe, CA: 71F on 3/30/2015

REV Watches/Warnings/Advisories

NV...None. CA...None.