Mariposa could receive up to 6.00" of rain
Oakhurst could receive up to 6.00" of rain
Yosemite Valley could receive up to 6.00"of rain
February 12, 2019 - The National Weather Service Hanford Office reports with the incoming weather system the vast majority of this precipitation will fall Wednesday afternoon through Thursday morning.
A Winter Storm Watch is in effect for the higher terrain of the Southern Sierra Nevada.
A Flood Watch is in effect for elevations below 5,000 feet.
The Southern Sierra Nevada foothills are most susceptible to flooding.
Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 246 AM PST Tue Feb 12 2019 .SYNOPSIS...The next in a series of winter storms will move into the area tonight through Friday with heavy precipitation and gusty winds. && .DISCUSSION...Just a few high clouds noted streaming into the forecast area early this morning however out over the Pacific a major rain and snow producing weather system is taking shape. Meanwhile in the mainly clear skies, freezing temperatures are already occuring in colder locations and the freeze warning will continue through the early morning. There are three main players in the very wet and stormy forecast...first the deep moisture plume stretching from just off the California coast out to south of Hawaii. Second the very persistent low pressure area well northeast of the Big Island and third...the very cold Arctic air enhanced deep low moving south along 40N/138W or about 700 miles west of the Bay Area. How these 3 features interact will play a major role in the expected AR (atmospheric river) event in the tonight through Friday time frame. What is known (the potential) is described just above and how the models handle the movement of the two lows and the target of the moisture plume will be paramount in just how much rain and snow falls over the Central California Interior. Both the GFS and ECMWF models have finally come into rather good agreement that the moisture plume will be directed at Central and Southern California as a result of the coming into "phase" of the southern low and the cold northern low over the next 48 hours. With the arctic low being dominant and setting up out along 36N/137W by Wednesday afternoon, the resulting mid and upper level winds will be very favorable to push the bulk of the deep moisture directly at the Sierra and the forecast area. Confidence is high that heavy to very heavy precipitation will occur with model generated output showing as much as 9.00" of liquid in the Sierra by Thursday evening. The biggest (of several) concerns is where the rain/snow line ends up in the Sierra. With the copius projected precipitation amounts, up to 10 feet of new snow is not out of the question where it stays all snow and doesn`t change over the rain. As of now, this elevation looks to be above 8000 feet as the airmass will warm with time in the subtropical moisture feed. By later on Thursday, colder air is progged to infiltrate the area from the northern low and this will bring down snow levels to around 5000 feet. This scenario certainly adds lots of concern at elevations below 8000 feet that very heavy rain will fall on the deep snow pack and the potential for significant flooding is real. Wind will also be a concern for the Grapevine and Tehachapi Mountain areas on Wednesday as higher resolution models produce gusts to well over 50 mph in wind favored areas. Advisories or warnings may be needed over this area. On Thursday evening and overnight the AR will move away from the area of precipitation will quickly diminish or end over the area. Additional rain and mountain snow will arrive however on Friday as a fast moving trough of low pressure swings through the area in the northwest flow that arrives in the wake of the exiting AR and deep assoicated trough. Both GFS and ECMWF models then drive a very cold trough or closed low per the ECM into the forecast area from the north with additional rain and snow. This could bring another round of very low snow levels especially if the ECMWF solution pans out. All in all very stormy with something for everyone over the next few days, to a week. ...Lots of Weather Watches will converted to warnings later today. There is a high potential for flooding and extremely heavy snow over the higher Sierra through Thursday night. Please keep a close watch on the weather over the next few days before traveling...
Source: NWS
