National Weather Service - Discussion
Area Forecast Discussion
National Weather Service - San Joaquin Valley / Hanford, CA
Issued: Thursday, January 21 2021 - 4:49 PM PST
UPDATE...Air quality forecast section
SYNOPSIS...Dry weather will continue across the area through tonight. A series of storm systems will bring episodes of rain and mountain snow to the central California interior Friday through at least the middle of next week along with significantly cooler temperatures.
DISCUSSION...Once again, mostly sunny skies are prevailing across our area this afternoon with light winds and temperatures running well above seasonal normals as surface high pressure and a short wave ridge aloft high pressure prevail over central CA.
A big change will begin on Friday as the first of three storms that will impact our area over the next week as a upper low pressure system which dropped out of the Gulf of AK yesterday and now situated off the PAC NW coast as depicted by WV imagery drops into Norcal Friday morning and into central CA Friday afternoon through Saturday. Progged QPF amounts are expected to be fairly light with this system with generally a tenth of a quarter inch of rainfall across the San Joaquin Valley and the Kern County Mountains a quarter to half an inch of liquid precipitation over the Sierra Nevada with the snow level expected to be between 4000 and 4500 feet at the onset of the precipitation on Friday lowering to 2500 to 3000 feet by Saturday when the precipitation tapers off. Snowfall totals of a dusting to a few inches of snow will fall in the mountains with local amounts of up to 6 inches possible in the high Sierra near the crest. The Kern County desert areas will only pick up trace amounts to a few hundredths of an inch of rainfall.
Shortwave ridging will provide for dry conditions with more seasonable temperatures Saturday night and Sunday morning as the first storm moves into the desert southwest region. The medium range models are in decent agreement with a deep trough dropping into CA by Sunday night which will bring a period of significant precipitation to our area Sunday night and Monday. Although QPF progs are trending downward with this second system, it is expected to have more moisture with it than the Friday system and will bring a quarter to half an inch of rainfall to the San Joaquin Valley and a half to three quarters of an inch of liquid precipitation to the Sierra Nevada and the Kern County Mountain areas. This second system is of Arctic origin and will have low snow levels with it (generally between 1000 and 2000 feet) which means that most of the precipitation across the the Sierra foothills and slopes of the Kern County Mountains will be in the form of snow, and impacts to travel will be possible Sunday night and Monday in the mountains and foothills.
After a short break on Tuesday following the departure of the Monday system, a potentially strong low pressure system will impact central CA on Wednesday and Thursday. Although precipitation looks likely for this timeframe, there is still a lot of uncertainty dealing with how much precipitation our area will receive. It has the potential to tap into some subtropical moisture as it moves into central CA on Wednesday which would produce periods of moderate to heavy precipitation if it pans out. Currently snow levels are progged by the NBM to be around 4000 feet during this time frame, but if subtropical moisture enters the picture they would be much higher and there would be a potential for snowmelt runoff and flooding across our area. We will have a better idea on how this potentially strong storm will pan out by this weekend.
AVIATION...Increasing areas of MVFR and local mountain obscuring IFR over the Sierra Nevada after 12Z Fri in low clouds and precipitation. Becoming mainly mountain obscuring IFR over the Sierra Nevada and Tehachapi Mountains after 18Z Fri. Otherwise, VFR conditions will prevail over the central CA interior during the next 24 hours.
AIR QUALITY ISSUES... On Friday January 22 2021... Fireplace/Wood Stove Burning Status is: No Burning Unless Registered in Fresno and Kern Counties. Further information is available at Valleyair.org
The level of certainty for days 1 and 2 is medium. The level of certainty for days 3 through 7 is low.
Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information an/or to provide feedback.
HNX WATCHES/WARNINGS/ADVISORIES... None.