LOCATION & EXPIRATION TIME

This first line for the forecast (or any product we issue) is what computers read for routing to the proper locations. As follows:

CAZ089>092- : CAZ (California zone(s), 089>092- : Zone(s) involved
212300 (day/date expiration time) : 21 - date of month : 2300 - expiration time (in UTC) for product (an updated forecast will be issued by this time). Forecast are updated least twice a day (4 am/pm) but more often when needed.

ZONE(S) AFFECTED BY FORECAST

The zones involved. In the example above, Zones 89 and 90 are the Central San Joaquin Valley and Zones 91 and 92 are the Southern San Joaquin Valley

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TIME/DAY of WEEK/DATE forecast is issued. Be sure to check this line before using this forecast (actually check this line for any of our products).

...HEADLINE... Used to draw attention to any warning, watch, or advisory in effect, or for any significant weather event such as "near record temperatures".

FORECAST PERIODS

Routine forecasts issued before noon contain three forecast periods:
Today (or This Afternoon). . .Tonight. . .the Next Day
Routine forecasts issued after noon contain four forecast periods:
Tonight. . .the Next Day. . .that Night. . .the Following Day.

(Note: Today is the period from the time the product is issued until 6:00 p.m. Tonight is the period from when the product is issued until 6:00 a.m. If the weather is expected to change during the latter half of the forecast period, then the additional qualifier "LATE" can be added.)

SKY CONDITION

The sky is divided into 10 equal sections. The following table lists the terms used to describe the forecasted sky condition depending upon how many tenths of the sky is covered by opaque clouds (clouds that cannot be seen through).

Other terms used to describe the cloud condition include:

Variable cloudiness - Used when the amount of opaque cloudiness will vary from a low of 2/10 to as much as 9/10 during the forecast period.

Variable high clouds - Similar to variable cloudiness except this applies to clouds generally at or above 18,000 feet; they may or may not be opaque.

Fair - Used for conditions that are (1) Less than 4/10 of opaque cloud cover, (2) No precipitation and (3) No extreme visibility, wind, or temperature conditions.

Note: Until the zones are further subdivided into new zones, phrases like "NORTH HALF", "WEST SIDE", "SOUTH END" etc., will be used to represent weather conditions that occur in ½ of the forecast area but not in the other ½. For example, when the Tule fog tends to be in the eastern half of the San Joaquin Valley a phrase similar to "ALONG THE EAST SIDE" will be included.

TEMPERATURE

Numerical temperature values are represented in four ways for the expected temperature range within the zone(s):

1. "Near," "around," or "about" a specific value rounded to the nearest five or zero. Above 100^oF or below 10^oF, any number will be used. For example:

NEAR 40, AROUND 15, ABOUT 85, or NEAR 106.
2. A general range where the terms are defined by the following:

LOWER 50's (50 - 54)
MID 50's (53 - 57)
UPPER 50's (56 - 59)
50's (50 - 59)

3. A specific range rounded to the nearest five or zero (except ranges below 10^oF or above 100^oF, any number may be used). For example:

70 to 75 or 102 to 108
4. Specific numbers for site-specific locations: FRESNO 90/60/92

Note: Since mountain temperatures vary with elevation, temperature forecasts are for the 4000 foot elevation.

WIND DIRECTION & SPEED

A forecast wind (direction and speed) is included in the first two periods of the forecast. The wind is included in the third and/or fourth period if considered significant.

1. Wind direction is the direction where the wind is coming FROM and is based on an 8-point compass (NE, E, SE, etc.). Light wind (usually 5 mph or less) will be handled in the following ways:

LIGHT SOUTH WIND (if direction is known)
LIGHT AND VARIABLE WIND
LIGHT WIND (where "light" implies a variable wind direction)

2. Wind speed will be given in miles per hour. Following is a list of terms sometimes used to describe the wind speed.

Note: A forecast can contain a peak wind speed in gusty situations. For example, "NORTHWEST WIND 20 TO 30 MPH WITH OCCASIONAL GUSTS TO 40 MPH."

TEMPERATURE / PRECIPITATION

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CITY xx xx xx (xx) / xx xx xx (xx)

This last section provides maximum/minimum temperatures and probability-of-precipitation (pop) forecasts at specific points within the overall local forecast. The forecast points in each zone are as follows:

Zone 89 - Los Banos, Coalinga
Zone 90 - Merced, Madera, Fresno
Zone 91 - Hanford, Taft
Zone 92 - Visalia, Delano, Bakersfield
Zone 93 - Mariposa, Oakhurst
Zone 94 - Three Rivers
Zone 95 - Lake Isabella, Tehachapi, Frazier Park
Zone 96 - Yosemite Valley in Yosemite NP, Shaver Lake
Zone 97 - Lodgepole in Sequoia NP
Zone 98 - Inyokern
Zone 99 - Mojave

If the zones are combined within the forecast, the forecast points are combined as well. The temperatures are the highest or lowest reading expected during each forecast period at that point. In the example above, the first number is the forecast maximum during the "Today" forecast period, the second number is tonight's minimum, and so forth. These forecasts may or may not be close to the temperatures you observed at your location due to the variances in the weather.

PROBABILITY of PRECIPITATION (POP)

Usually the most confusing aspect about the weather forecast. It is defined as "the likelihood of occurrence (expressed as a percent) of a precipitation event at any given point in the forecast area". The "given" points are the forecast points mention above. It is usually at airports. For example, in Fresno, it is Fresno-Yosemite Airport and in Bakersfield, at Meadows Field. Now, we know you do not live at the airport but that is where the rain gauges are located and as such are the "official" sites. In the smaller communities, it is usually a fire stations or other cooperative sites.

When there is a probability of precipitation in the local forecast then a number will be included for that probability during each forecast period much like the temperatures above. For example, if the numbers were "00 30 50 20" then the POP forecast is read as 0% chance tonight, 30% chance tomorrow, 50% chance tomorrow night and 20% for the following day. The entire POP section of the local forecast is omitted when the chance of precipitation at each point in the local forecast is zero for the full 36 or 48 hour period.

The NWS uses two different methods to indicate the chance of precipitation for a specific area: numerical or in non-numerical terms. The body of the local forecast will give the probability of precipitation in non-numerical terms with the numerical POP included at the end of the forecast

There are other qualifying terms which are used with the above non-numerical expressions. For example:

For duration - brief, occasional, intermittent, frequent.
For intensity - very light, light, heavy, very heavy.
For precipitation forecast amounts of a trace (<0.01"), the terms "very light" or "sprinkles" will be used.

Cumuliform vs. Stratiform Precipitation

The basic process of producing precipitation is rising air that cools to the point that the atmosphere can no longer hold its moisture. The moisture condenses into the small particles which form the visible cloud. If the moisture is sufficient, the particles continue to combine to form into rain droplets (or if below freezing, snowflakes). When the rain droplets or snowflakes grow to the point where updrafts can no longer support their weight, they fall to the earth.

Cumuliform-type clouds produce showers; precipitation of brief duration created by localized areas of rising moist air. While the areal coverage of showers is relatively small, precipitation rates are usually much greater than those from stratiform clouds. The most intense type of showers are called thunderstorms, which produce thunder and lightning and can produce hail, gusty winds, flash floods, and tornados.

Stratiform precipitation is formed by large areas of rising moist air and last longer than showers. This type of precipitation will affect relatively large areas with the intensity changing slowly during the event.

While you will generally not notice the difference, precipitation will either come from cumuliform and stratiform clouds. NWS products indicate whether precipitation will be stratiform (rain) or cumuliform (showers).