Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EST Tue Dec 14 2021 Valid 00Z Wed Dec 15 2021 - 00Z Fri Dec 17 2021 ...Flash flooding risk continues over southern California as a moderately strong atmospheric river delivers more heavy rain today... ...Widespread heavy snowfall to persist over the western U.S. through Thursday... ...A deep low pressure system developing on Wednesday is forecast to generate high winds from the Southwest to the Upper Midwest where severe weather will also be possible... ...Record breaking heat to impact the central/eastern U.S. through Thursday... ...Critical to Extreme Fire Weather risk for parts of the Central/Southern Plains through Thursday... During the short range period a flurry of activity is expected over the CONUS starting with a moderately strong atmospheric river presently guiding a significant amount of moisture into southern California. At lower elevations 2-6" of additional rainfall are expected through Wednesday morning generating flooding concerns for the area, particularly over the Bobcat burn scar. Given the potential for flash flooding in the highly urbanized Los Angeles and San Diego metro areas and debris flows over burn scarred areas, the Weather Prediction Center has issued a Slight Risk of Excessive Rainfall for portions of southern California through Wednesday morning. At higher elevations the intense influx of moisture will result in heavy snowfall accumulations from the Sierra Nevada to the Rockies. Snowfall rates of 2-3"/hr will be possible over the Sierra, where an additional 1-3 ft of snow are expected to accumulate in the 24 hour period from Tuesday morning to Wednesday morning. Through Wednesday night an additional 12+" will likely accumulate in the mountain ranges of the Central Great Basin and Northern/Central Rockies as the moisture interacts with a draping cold front progressing through the regions. To account for the minor to moderate impacts associated with this event a menagerie of Winter Storm Watches and Warnings as well as Winter Weather Advisories are currently in effect from the West Coast through the Rockies. Without skipping a beat another round of heavy snow will affect the Sierra Nevada and neighboring Cascades as a Pacific system makes its way onshore Wednesday afternoon. Snowfall accumulations of 8-12" with isolated higher amounts are expected with lesser totals likely further inland. Further east, a deep low pressure system is expected to develop over the Northern High Plains Wednesday morning in association with a cut off low aloft and the aforementioned draping cold front at the surface. At the same time the system is deepening high pressure is forecast to build immediately to the west, resulting in the development of a very tight pressure gradient over the Rockies. This tightening of the pressure gradient will generate strong winds with gusts up to and in excess of 75 mph in some areas. As the system progresses eastward it is forecast to deepen further, allowing the blustery winds to continue to blow all the way to the Upper Midwest. Because these strong winds could blow down trees and power lines as well as make travel difficult, High Wind Watches and Warnings as well as Wind Advisories have been put into effect from the Desert Southwest to the Upper Midwest. In addition to the high winds this system is expected pull moisture north from the Gulf of Mexico, bringing a mix of rain and snow to the Northern Plains and Upper Midwest as well as showers and thunderstorms from the Southern Plains to the Great Lakes. Favorable environmental conditions ahead of the low pressure system will support the development of severe thunderstorms over portions of the Upper Midwest. Given the potential for these storms to generate damaging wind gusts as well as a few tornadoes, the Storm Prediction Center has issued a Slight Risk of Severe Thunderstorms over portions of southern Minnesota and northern Iowa effective Wednesday morning through Thursday morning. By Wednesday night, surface instability ahead of the system will allow for some snow to fall over interior New England before switching over to freezing rain Thursday morning then finally rain Thursday night with the passage of a warm front. High pressure settled both aloft and at the surface over the eastern U.S. will serve to push warm, tropical air northward into the central and eastern U.S. throughout much of the period. This warm air advection will allow daily high temperatures to skyrocket to over 30 degrees above average on Wednesday throughout the Plains and Mississippi Valley. With spring-like highs anywhere from the 50s and 70s in the forecast, over 50 daily high records stand to be broken on Wednesday. As this warm air is pushed eastward ahead of the deep low pressure system on Thursday, more modest temperature departures of 20 to 30 degrees above normal are expected to extend from the Southern Plains to the Northeast where an additional 45 daily high temperature records will be put to the test. Elsewhere in the Central/Southern Plains, abnormally high temperatures, very strong winds, extremely dry fuels, and low relative humidity levels are all forecast to coincide over the next few days, producing highly favorable conditions for the spread of wildfires. To highlight these dangerous conditions the Storm Prediction Center has issued a Critical Risk of Fire Weather for much of the Texas and Oklahoma Panhandles through Wednesday morning. Additionally, an Extremely Critical Risk of Fire Weather has been issued for Wednesday morning through Thursday morning from the northern Texas Panhandle through central Kansas, which is surrounded by a Critical Risk area from northeastern New Mexico to southern Nebraska. Zavadoff Graphics are available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php