San Francisco, CA 14 Day Weather

Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Wed Oct 20 2021 Valid Thu Oct 21 2021 - Sat Oct 23 2021 ...Back to back Pacific storms to bring heavy rain and mountain snow to Northern California and the Pacific Northwest... ...Severe thunderstorms possible in association with a mature low pressure system bringing rain to the Midwest, Eastern Seaboard, and parts of the Southern Plains through Friday... ...Moderately warm temperatures expected in the East, cooler over the Norther Plains and along the West Coast... A series of Pacific storms will move onshore over northern California and the Pacific Northwest during the latter half of the work week, bringing some much needed rain to the regions. The first, which had already pushed itself ashore earlier today, will predominantly generate modest rainfall throughout northern California and to the west of the Oregon and Washington Cascades. Any snowfall will be isolated to higher elevations, particularly above 5000 ft in the Cascades and above 8000 ft in the northern Sierra Nevada. Precipitation will quickly diminish overnight as the system rapidly decays, providing a brief reprieve before the approach of the second storm on Thursday morning. Carrying within it an abundance of moisture in the form of a moderately strong Atmospheric River, this second system will deliver a considerably greater amount of rain to the area, particularly in northern California. While a welcome sight in light of the ongoing drought, periods of heavy rainfall could be cause for concern, especially in the mountainous areas of northern California riddled with burn scars. Given the potential for rapid runoff and debris flows in these sensitive areas, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for portions of northern California effective Thursday morning through Friday morning. In addition to the rain some isolated heavy snowfall will be possible over portions of the Cascades, Olympics, and northern Sierra Nevada, with Mt. Shasta possibly receiving nearly 2 ft of snow. Further east, a deepening low pressure system is moving through the Upper Midwest, with its trailing cold front passing through the Middle Mississippi Valley and the Southern Plains. Showers and thunderstorms will remain primarily focused around the low pressure center and its associated cold front as they progress east, lift north into Canada Thursday evening, and move offshore late Friday. Rainfall rates and totals are expected to be relatively moderate with this system, however, the risk for the development of severe thunderstorms will persist through Friday morning. The areas at greatest risk for severe weather overnight include southern Minnesota and northern Iowa, where a Marginal Risk has been issued due to the possible formation of large hail. On Thursday the severe weather potential will move east with the progression of the storm system into the Ohio/Tennessee Valleys and Central/Southern Appalachians, where a Marginal Risk has been issued to account for the possible development of isolated strong to damaging wind gusts. Another Marginal Risk area has also been put in place over west Texas, where any storms that form may pose a hail and strong/gusty wind threat. Temperatures will generally remain near or moderately above normal throughout the country during the short range period. Exceptions to this trend include regions that fall immediately behind the progressing low pressure system and the West Coast. The former will experience marginal to modest temperature drops as cool Canadian air is ushered in behind the deepening low. The most extreme anomalies are expected in the Northern Plains, where daily highs are forecast to drop into the 40s, falling 20 degrees below normal. As for the West Coast, persistent cloud cover from the series of systems moving onshore will generally keep the region 10 to 15 degrees cooler than average for this time of year. Zavadoff Graphics are available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php
Storm Prediction Center
United States 2 Day Forecast
WPC Short Range Forecasts (Days ½-2½)