National Weather Service United States Department of Commerce

Unsettled Weather Continues for the Northern U.S., Alaska, and Hawaii

Low pressure will bring strong winds and heavy snow to the northern Plains and upper Great Lakes into Monday. Farther south, strong to severe thunderstorms accompanied by locally heavy rainfall are possible over the ArkLaTex and lower Ohio Valley through tonight. Meanwhile, a major winter storm will affect western and central Alaska. Heavy rainfall and flooding are possible for much of Hawaii. Read More >

A Dense Fog Advisory is in effect for the southern portion of the San Joaquin Valley until 11 AM PST this morning. A Dense Fog Advisory means that visibilities will frequently be reduced to less than one quarter of a mile. If driving, slow down, use low beam headlights, and keep plenty of distance between your vehicle and the vehicle in front of you. Highways affected include, but are not limited to Highway 58, Highway 65, Highway 46, Highway 190, Highway 99 south of Selma, and Highway 198 from Visalia to Lemoore.
A Dense Fog Advisory is in effect for the southern portion of the San Joaquin Valley until 11 AM PST this morning, resulting in a high transportation risk. Highways affected include, but are not limited to Highway 58, Highway 65, Highway 46, Highway 190, Highway 99 south of Selma, and Highway 198 from Visalia to Lemoore.
A dissipating cold front will move southward through Central California Monday night. This feeble atmospheric disturbance will be responsible for a chance of precipitation in the Sierra Nevada and a slight chance of precipitation in the San Joaquin Valley north of Kern County. Precipitation amounts in the Sierra Nevada will remain below one quarter of an inch. Precipitation amounts, if any, in the San Joaquin Valley will remain well below one tenth of an inch. Snow levels will be around 8,000 feet.
A significant atmospheric disturbance will impact Central California Wednesday night through Thursday evening, resulting in the distinct possibility of widespread precipitation. In the San Joaquin Valley, rain amounts should remain below one half of an inch. Snow levels will fall from around 8,000 feet Wednesday night to about 6,000 feet by Thursday afternoon. Thereafter, snow levels will plummet to around 3,000 feet Thursday evening.
Rain is likely in the San Joaquin Valley Thursday. Here are probabilities of rainfall amounts of one tenth of an inch or more for select locations in the San Joaquin Valley for the twelve hour period from 4 AM PST Thursday, December 9th, 2021 until 4 PM PST Thursday, December 9th, 2021.

 

Text Product Selector (Selected product opens in current window)

Purpose: Outside of the probability of precipitation (PoP), forecasts supplied by the National Weather Service are entirely deterministic. Research shows that customers desire knowing the level of certainty/uncertainty in the forecast (Morss et al. 2008). The only method in which the NWS habitually provides such information is the Area Forecast Discussion (AFD).
The AFD is an open-format narrative written by the NWS forecaster when issuing a forecast and is "a means to explain the scientific rationale behind a forecast" (NWSI 10-503).
Often this includes some mention of the level of certainty in the forecast, though that information is usually obtained by the reader by getting an overall sense of the forecaster's sentiment, it is not explicitly stated. To provide certainty information in the shortest, easiest, and least obtrusive way, this project will ask NWS forecasters to explicitly state the level of certainty in the seven day forecast as a whole in a special section of the AFD (see example below). Certainty will be expressed for two separate periods (Days 1-2 and Days 3-7) and three levels (low, medium, high).

 

Verification: Two methods of verification will be utilized. The first will be based on solicited customer feedback and focused on the usefulness of the information. The second method will pair the certainty information with internal forecast verification statistics to determine if maximum temperature, minimum temperature, and PoP verified differently with varying levels of certainty. Additional verification aspects may be explored.

 

Click Here to View the Current AFD

 

Send us feedback on this project!

 

Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 1000 AM PST Fri Jan 5 2018 .DISCUSSION... A low pressure system tracking across the northwest US will weaken and displace the high pressure over central California. This will moderate temperatures a bit through the weekend, although readings will remain above normal. Warming conditions return for the first part of next week as high pressure rebuilds over the area.
&& .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.php for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories...None. && public...forecaster avn/fw...forecaster synopsis...forecaster

References:
Morss, R. E., J. L. Demuth, and J. K. Lazo, 2008: Communicating Uncertainty in Weather Forecasts: A Survey of the U.S. Public. Wea. Forecasting, 23, 974-991.

National Weather Service Instruction (NWSI) 10-503, 2012.