Atmospheric River Brings Dangerous Flash Flooding and Heavy Mountain Snow to Central and Southern California

Source: National Weather Service

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Mon Feb 05 2024

Valid 12Z Mon Feb 05 2024 - 12Z Wed Feb 07 2024

...Life threatening Flash Flooding continues for Southern California Monday...

...Heavy Snow for parts of the Sierra Nevada, Great Basin, Northern Rockies, and Four Corners Region...

...Much above average high temperatures continue for the Northern/Central Plains and Upper Midwest...

The threat for flash flooding centers on Southern California Monday as a deep upper-level trough/Pacific storm system and associated Atmospheric River slowly pivots along the West Coast and pushes further inland. Ongoing showers and thunderstorms will continue to produce very heavy rainfall fueled by the influx of anomalously high moisture, favorable upslope flow, and increasing instability. A High Risk of Excessive Rainfall (level 4/4) is once again in effect Monday for portions of the LA Basin and the eastern Transverse Ranges, with an encompassing Moderate
Risk (level 3/4) extending westward along the Transverse Ranges and southward along the Peninsular Ranges. Additional rainfall totals generally between 5-8" will be possible, which will bring 48-totals as high as 8-14" for some locations. Increasingly saturated conditions and ongoing flooding will be further exacerbated by this additional rainfall, continuing the threat for life-threatening, locally catastrophic flash, urban, and small stream flooding, as well as a threat for debris flows and mudslides. A Slight Risk remains in effect for lingering locally heavy rainfall northwestward towards the central California coast, and also into portions of the Mojave Desert. In addition, some strong gusty winds will remain possible, though wind speeds/gusts should be trending downward overall. Coastal flooding and high surf will also remain a concern through Monday evening.

Very heavy mountain snows will continue for higher elevations of the Sierra Nevada, generally above 5000 feet, with storm total snowfall of several feet expected. Snowfall rates of 2-3"/hr and gusty winds upwards of 60 mph will keep travel dangerous to impossible due to whiteout conditions. Moisture from the system will also continue to spread further inland, bringing heavy higher elevation snows to the regional mountain ranges of the Central Great Basin of Nevada northeastward into portions of the Northern Rockies of Idaho and Wyoming Monday, and into the Four
Corners region Tuesday. Storm total snowfall of around foot will be common, with some locally higher totals of 2+ feet possible. Lower elevations of the Great Basin will see a mix of rain and some snow, but any snow accumulations should be limited. Further south into the Desert Southwest, the ongoing influx of moisture will lead to heavier rainfall Tuesday, with a Slight Risk of Excessive Rainfall in effect for portions of western Arizona and Southern Nevada. Rainfall totals generally between 1-3" may lead to some scattered instances of flash flooding.

Elsewhere, some moderate to locally heavy showers are expected further north from Northern California into the Pacific Northwest as the Pacific system pushes inland. Some showers and thunderstorms will remain possible for portions of Florida and northeastward along coastal Georgia and South Carolina as a low pressure system pushes away from the coast. The rest of
the central and eastern U.S. should remain dry. High temperatures will remain anomalously warm for the Northern/Central Plains and Upper Midwest as upper-level ridging remains in place. High temperatures in the 40s and low 50s are upwards of 20-30 degrees above average. Some daily record-tying/breaking high temperatures will be possible for the Upper Midwest on Tuesday. Highs temperatures generally from the Rockies to the Northeast will be above average and mild.  

Putnam

Here is a link to the full Forecast Discussion on NWS wbesite; http://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdspd