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Monday, 13 March 2023, 22:30 UTC





500 hPa geopotential and surface pressure
over North America, 14.03 12 UTC
Source: Wetterzentrale 		850 hPa pseudopotential temperature
over North America, 14.03 12 UTC
Source: Wetter3 		48 h precipitation over the southwestern part of the US,
15.03 12 UTC
Source: SPC 		Flash flood potential over the US for
14.03
Source: WPC


Heavy rain and snow
California, USA

Issued: Monday, 13 March 2023, 22:30 UTC

Another storm system will be affecting the state of California starting tomorrow, March 14, 2023, until Wednesday, March 15, 2023, bringing heavy rain to the state with intense snowfall at higher elevations, massively increasing the potential for flash and river flooding along the foothills of the Sierra Nevada.

13.03.2023

Another potent low-pressure system moving from the Eastern Pacific into California will bring moist air masses into the state of California. Combined with the strong orographic lift of both the coastal mountain ranges and the Sierra Nevada, this will lead to intense precipitation especially along the western facing flanks of said mountain ranges. At lower elevations precipitation totals are expected to reach 50 mm, while along the western facing flanks of the mountains ranges precipitation totals of up to 150 mm in 48 h must be expected.

Due to the already exceptionally wet winter season 2022/23, the once drought-plagued state is at risk for widespread for flash flooding during the most intense precipitation periods with the potential for subsequent river flooding especially in the Central Valley. The intense precipitation at higher elevations will once again lead to substantial fresh snow accumulations of more than 1 m, increasing the already massive snowpack of the Sierra Nevada, running at 206 % of the seasonal average with a snow-water-equivalent of nearly 1400 mm.

Thursday, 09 March 2023, 11:30 UTC





Polarstenographic view of the 500 hPa geopotential
and surface pressure, 09.03, 12 UTC
Source: Wetterzentrale 		850 hPa pseudopotential temperature
over North America, 10.03 12 UTC
Source: Wetter3 		48 h precipitation over the southwestern part of the US,
11.03 00 UTC
Source: SPC 		Expected river stages of the
San Joaquin River River at Newman, CA,
09.03 08 UTC
Source: CNRFC


Heavy rain and snow
California, USA

Issued: Thursday, 09 March 2023, 11:30 UTC

An exceptional wet winter season continues in California, with two atmospheric rivers effecting the state in the coming days. Heavy precipitation is expected with precipitation totals of up to 500 mm/7 days and heavy snowfall at elevations above 2000 to 2500 m.

09.03.2023

A strong zonal flow across the Pacific is persistent, with a strong trough over the Eastern Pacific, leading to the advection of very humid air masses into the state of California in front of said trough. Due to the orography of California, this westerly flow is lifted by the high mountain ranges running from north to south in California. Especially, along the Sierra Nevada the orographic lift is massively enhanced, leading to intense orographic precipitation along the western facing flanks of the mountain ranges.

The winter season 22/23 has been exceptionally wet in many parts California, improving the persistent drought in California and filling the water reservoir across the state, with the snow-water-equivalent of the snowpack in the Sierra Nevada, reaching locally more than 200 % of the seasonal average. Today, March 09, 2023, and tomorrow, March 10, 2023, another strong storm system is expected to move through California bringing widespread heavy precipitation with precipitation totals of up to 50 mm/48 h, along western facing flanks precipitation totals of up to 200 mm/48 h must be expected.

Due to higher temperatures, saturated soils, and a substantial snowpack at elevations below 2000 m to 2500 m the heavy precipitation will be accompanied with strong thawing, raising flood concerns in lower elevations. In the High Sierra heavy snowfall is expected, with snowfall rates of more than 10 cm/h and fresh snow accumulations of up to 2 m/48 h. Further storm systems are expected to reach the state early next week, leading to 7-day precipitation totals of more than 200 mm, along western facing flanks precipitation totals of more than 500 mm/7 days must be expected.

Issued: March 09, 2023, 11:30 UTC
KG
Issued: March 13, 2023, 22:30 UTC
KG

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