National Weather Service United States Department of Commerce

Ian Forecast to be a Major Hurricane Entering the Gulf of Mexico; Threats to Florida

There is a risk that Ian will bring dangerous storm surge, hurricane-force winds, and heavy rainfall along the west coast of Florida and the Florida Panhandle by the middle of this week. Flash and urban flooding is possible with rainfall across the Florida Keys and the Florida peninsula through the middle of the week. Residents in Florida should ensure they have their hurricane plan in place. Read More >

San Francisco Bay Area, CA

Weather Forecast Office

Probabilistic Snowfall Forecasts

Weather.gov > San Francisco Bay Area, CA > Probabilistic Snowfall Forecasts

Snow Amount Potential
Experimental -
 
Expected Snowfall - Official NWS Forecast
Point Range
Expected Snowfall - Official NWS Forecast
What's this?		 High End Amount
1 in 10 Chance (10%) of Higher Snowfall
Maximum Potential Snow Accumulation
What's this?
Low End Amount
9 in 10 Chance (90%) of Higher Snowfall
Minimum Potential Snow Accumulation
What's this?

Low End Amount – 9 in 10 Chance (90%) of Higher Snowfall

 

This map depicts a reasonable lower-end snowfall amount for the time period shown on the graphic, based on many computer model simulations of possible snowfall totals. This lower amount is an unlikely scenario with a 9 in 10, or 90% chance that more snow will fall, and only a 1 in 10, or 10% chance that less snow will fall. This number can help serve as a lower-end scenario for planning purposes.

Expected Snowfall - Official NWS Forecast

 

This map is the official NWS snowfall forecast in inches during the time period shown on the graphic. This snowfall amount is determined by NWS forecasters to be the most likely outcome based on evaluation of data from computer models, satellite, radar, and other observations.

High End Amount – Only a 1 in 10 Chance (10%) of Higher Snowfall

 

This map depicts a reasonable upper-end snowfall amount for the time period shown on the graphic, based on many computer model simulations of possible snowfall totals. This higher amount is an unlikely scenario, with only a 1 in 10, or 10% chance that more snow will fall, and a 9 in 10, or 90% chance that less snow will fall. This number can help serve as an upper-end scenario for planning purposes.
 
The purpose of these experimental probabilistic snowfall products is to provide customers and partners a range of snowfall possibilities, in complement to existing NWS deterministic snowfall graphics, to better communicate forecast uncertainties during winter weather events. For more information visit this project's Product/Service Description Document, and please provide us your feedback here.
Percent Chance That Snow Amounts Will Be Greater Than...
Experimental -
 
What's this?

Percent Chance That Snow Amounts Will Be Greater Than

 

This series of maps shows the probability (that is, the likelihood) that snowfall will equal or exceed specific amounts during the time period shown on the graphic. These forecasts are based on many computer model simulations of possible snowfall totals.
Hover over thumbnails below to view larger image.
>=0.1"
>=0.1"		 >=1"
>=1"		 >=2"
>=2"		 >=4"
>=4"		 >=6"
>=6"		 >=8"
>=8"		 >=12"
>=12"		 >=18"
>=18"

Snowfall Totals by Location
Experimental -
 
What's this?

Snowfall Totals by Location

 

These tables show the snowfall forecast for individual locations, and provide the same information as the graphics on this web page, just shown in a different way. All of these values are valid for the same time period as depicted on the graphics.
County:
 
Ice Accumulation Potential
 

Expected Ice Accumulation - Official NWS Forecast

This is the elevated flat surface ice accumulation. It is not radial/line ice. Radial/line ice is typically 39% of the elevated flat surface ice. For more information on this, see this module.
Most Likely Ice Accumulation

What's this?

Most Likely Ice Accumulation

Represents our official ice forecast in inches within the next one to three days. The ice accumulation amounts are provided in ranges.
Precipitation Onset/End Timimg
Onset of Wintry Precipitation End Timing of Wintry Precipitation
Winter Precipitation Onset
Winter Precipitation End Time
What's this? What's this?

Precipitation Onset

Most likely time of winter precipitation onset (snow, sleet, freezing rain). Rain is not included here. This information is provided when we issue a Warning or Advisory for expected snow or ice accumulation; typically six to 24 hours in advance. Times are only given for places that are under a Warning or Advisory. They will be blank in areas outside Warnings or Advisories.

Precipitation End Time

Most likely time of winter precipitation ending (snow, sleet, freezing rain). Rain is not included here. This information is provided when we issue a Warning or Advisory for expected snow or ice accumulation; typically six to 24 hours in advance. Times are only given for places that are under a Warning or Advisory. They will be blank in areas outside Warnings or Advisories.
Winter Storm Severity Index (WSSI) Winter Storm Outlook (WSO)
Winter Storm Severity Index
Winter Storm Outlook
National Snow Reports National Snowfall Analysis
National Snow Reports
National Snowfall Analysis
 
Local Snow Reports
Latest snow report
Days 4-7 Winter Weather Outlook
 
Day 4 Winter Weather Outlook Day 5 Winter Weather Outlook
Day 4 Winter Weather Outlook Day 5 Winter Weather Outlook
 
Day 6 Winter Weather Outlook Day 7 Winter Weather Outlook
Day 6 Winter Weather Outlook Day 7 Winter Weather Outlook


Click here for an interactive map
 
CPC Week-2 Experimental Heavy Snow Risk
 
CPC Week-2 Experimental Heavy Snow Risk
 
CPC Temperature & Precipitation Maps
 

Days 6-10
Temperature  Precipitation
6-10 day temperature 6-10 day precipitation
 
 

Days 8-14
TEMPERATURE  PRECIPITATION
8-14 day temperature 8-14 day precipitation
 
 

Week 3-4

TEMPERATURE

PRECIPITATION
Week 3-4 Temperature Week 3-4 precipitation
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