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The US National Weather Service is responsible for the weather forecasts that most of us rely on, including the forecasts provided by most radio stations and newspapers. The NWS makes freely available a wide range of weather products on the web. One of the most interesting and useful of those products is the Area Forecast Discussion. Unfortunately, it's rather difficult to read, and doesn't have an RSS feed.
The most familiar forecasts are the NWS Zone Forecasts. In their raw form, they look something like this:
SAN FRANCISCO BAY AREA/CENTRAL CALIFORNIA ZONE FORECAST NATIONAL WEATHER SERVICE SAN FRANCISCO CA CAZ006-505-509-170515-SAN FRANCISCO- COASTAL NORTH BAY...INCLUDING POINT REYES NATIONAL SEASHORE- SAN FRANCISCO PENINSULA COAST- 259 AM PST SAT FEB 16 2008 .TODAY...PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY SUNNY. PATCHY FOG IN THE MORNING. HIGHS IN THE MID 50S TO LOWER 60S. SOUTHWEST WINDS AROUND 5 MPH. .TONIGHT...PARTLY CLOUDY. PATCHY FOG. LOWS IN THE UPPER 30S TO MID 40S. WEST WINDS 5 TO 10 MPH. .SUNDAY...PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY SUNNY. PATCHY FOG IN THE MORNING. HIGHS IN THE MID 50S TO LOWER 60S. WEST WINDS AROUND 5 MPH. .SUNDAY NIGHT...PARTLY CLOUDY. PATCHY FOG THROUGH THE NIGHT. LOWS IN THE MID 40S. WEST WINDS 5 TO 10 MPH. .PRESIDENTS DAY...PARTLY CLOUDY. PATCHY FOG IN THE MORNING. HIGHS IN THE MID 50S TO LOWER 60S. NORTHWEST WINDS 5 TO 10 MPH. .MONDAY NIGHT...PARTLY CLOUDY. LOWS IN THE MID 40S. .TUESDAY THROUGH WEDNESDAY...MOSTLY CLOUDY. CHANCE OF RAIN. HIGHS IN THE MID 50S TO LOWER 60S. LOWS IN THE 40S. .WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...RAIN LIKELY. LOWS IN THE 40S. HIGHS IN THE 50S. .FRIDAY...MOSTLY CLOUDY. CHANCE OF RAIN. HIGHS IN THE MID 50S.
Compare them to the forecasts in your local paper or on your local radio station, and you'll see the connection. Zone Forecasts are typically issued several times a day—more often when the weather is "interesting".
The NWS has Weather Forecasts Offices (WFOs) scattered across the country, each responsible for a County Warning Area, or CWA. Here are maps of the CWAs for the continental US and Alaska (Hawaii is its own CWA). Forecasters in each WFO are at work work around the clock analyzing weather data and computer models to come up with their forecasts.
Weather forecasting involves considerable judgement on the part of meteorologists. Computer models are getting better, but they're still far from perfect, and more often than not disagree with each other. Forecasters use data from multiple sources along with their experience and judgement to come up with their forecasts, and they document the process in Area Forecast Discussions. These AFDs discuss the thinking behind the public forecasts, often illuminating their ambiguity and uncertainty. The AFDs also include aviation and marine forecasts, as well as weather advisories, warnings and watches. An AFD looks like this:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
939 AM PST SAT FEB 16 2008
.DISCUSSION...LOW CLOUDS AND FOG ARE HANGING TOUGH ALONG THE COAST...
IN SF BAY...AND IN THE INTERIOR VALLEYS. WITH LITTLE IN THE WAY OF
PRESSURE GRADIENTS ANY MIXING IS WEAK...AS A RESULT PLENTY OF LOW
LEVEL MOISTURE IS TRAPPED IN THE BOUNDARY LAYER...AS DEPICTED IN
THE SFC OBS WHICH SHOW DEW PTS SIGNIFICANTLY HIGHER THAN YESTERDAY.
THE LOW CLOUDS AND FOG SHOULD BURN OFF LATER THIS MORNING LEADING TO
SUNNY SKIES. HIGH PRESSURE WILL REMAIN IN CONTROL OF THE WEATHER
ACROSS THE DISTRICT THROUGH SUNDAY. THE PATTERN BEGINS TO CHANGE ON
MONDAY AS THE FIRST IN A SERIES OF SHORTWAVES MOVES TO THE COAST.
TEMPS WILL BE COOLER WITH AN ONSHORE FLOW.
THE UPCOMING WEEK COULD BE WET AT TIMES. MORE ON THIS IN THE AFTN
DISCUSSION (AFTER ALL THE 12Z MODELS ARE IN).
.AVIATION...STRATUS DECKS OVER THE BAY AREA ARE STARTING TO SHRINK...
ALTHOUGH IT LOOKS AS THOUGH CONDITIONS AT SFO WILL BE SLOWER TO
IMPROVE. CLEARING BETWEEN 18Z AND 19Z IS ANTICIPATED AT THIS TIME.
LIGHT SOUTHWEST/WEST WINDS ARE EXPECTED TODAY. HIGH PRESSURE RIDGE
AXIS MOVING OVER CALIFORNIA TODAY AND TONIGHT WILL ALLOW LOW
CLOUDS/FOG AGAIN TO FORM OVERNIGHT.
.MTR WATCHES/WARNINGS/ADVISORIES...
.TDA...SCA....ROUGH BAR.
The NWS forecasts above are great, but for most of us they're not particularly readable. The AFD in particular is full of jargon and abbreviations, and being in all caps doesn't help. This is no great problem (and even an advantage) for habitual consumers of these products, such as pilots. But most of us could use a little help. Enter the Lobitos Weather Project.
We collect the current Zone Forecast and Area Forecast Discussion for a specific location (by zip code or city name) and present them, along with selected maps, in a more readable form.
Area Forecast Discussion
FXUS66 KMTR/Monterey 161739
AFDMTRArea Forecast Discussion
National Weather Service San Francisco Bay Area CA
9:39am PST Sat Feb 16 2008Discussion. Low clouds & fog are hanging tough along the coast…in SF Bay & in the interior valleys; with little in the way of pressure gradients any mixing is weak…as a result plenty of low level moisture is trapped in the boundary layer…as depicted in the surface observations which show dew points significantly higher than yesterday.
The low clouds & fog should burn off later this morning leading to sunny skies; high pressure will remain in control of the weather across the district through Sunday; the pattern begins to change on Monday as the first in a series of shortwaves moves to the coast; temps will be cooler with an onshore flow.
The upcoming week could be wet at times; more on this in the afternoon discussion (after all the 12Z models are in).
Aviation. Stratus decks over the Bay Area are starting to shrink…although it looks as though conditions at SFO will be slower to improve; clearing between 18Z & 19Z is anticipated at this time; light southwest/west winds are expected today; high pressure ridge axis moving over California today & tonight will allow low clouds/fog again to form overnight.
MTR watches/warnings/advisories
Today: Small Craft Advisory…rough bar.
Not only do we have readable capitalization, but abbreviations are expanded, and, as you'll see if you hover over colored terms such as the UTC (Z for Zulu) times in the sample, additional information is glossed.
The complete forecast page for zipcode 94019 (the home of the LWP) can be seen here.
LWP is very much a work in progress. Some of the things we're working on:
Forecast discussions needn't be dry as dust, and they often provide insight into uncertain forecasts; herewith some samples.
Expecting a quiet period of weather with Mr. Sunshine making a rare appearance this weekend. It was pointed out by a valued colleague that this will be the first weekend in a long time…maybe early October…that we have had a sunny weekend. OK…this may be a slight exaggeration…but the surface ridge moving over the region will bring a welcome respite from the dreary conditions seen by most of the region for much of this winter. Unfortunately…all things must pass and this will be true for Mr. Sunshine as well. Chicago
"Skies will have a few more clouds in them and will let the philosophers decide if it counts as mostly sunny or partly cloudy." Los Angeles (The philosophers in charge of the zone forecast went with "mostly clear".)
Here, the regular forecast for Tuesday (four days ahead) said simply "chance of snow or rain showers." Reading the forecast discussion, you'd have seen what "chance" sometimes means:
On the other hand…the 12Z ECMWF has the low pressure moving east off the mid-Atlantic coast and affecting southern New England as more of a coastal system. This discrepancy is going to affect where there is precipitation…how much precipitation…precipitation type…etc…etc. Since it is February…there is a high likelihood that there will be some wintry precipitation somewhere in southern New England with this storm. Exactly where will have to be determined as models come to more of a consensus on the low track. Because the low track through New York and northern New England has been fairly consistent through previous runs…am leaning more towards that track at this time. However…things could easily change before Tuesday.
Ambiguous abbreviations. In weather reports, "A" means hail. But of course it also means the indefinite article, and while the meaning is generally clear from context for a human, it's not for a computer program. Likewise, we can expand "lo" to "low", but "hi" might be "high" or "Hawaii". Is "in" Indiana? Is "ca" California or Canada?
We try to detect context for some common ambiguous words. For example, "on Sun" and "by Sun", but "the sun". CAPE is an acronym, but we know about "Cape Cod" and "the Cape".
Place names. In brief: there are too many of them. We're adding them as we go, but we'll never be complete. We can be systematic sometimes: all the state, and most of the state abbreviations (but not IN, for example). A list of big cities. San (or Santa) Anything. Santa Clara Valley, because we capitalize Santa Clara, and we capitalize Valley if it follows a capitalized word. We capitalize everything starting with "Waik" (useful in Hawaii), but we can't capitalize "wait". And so on.
Format variations. Different WFOs use different formatting conventions. That makes it challenging to identify different sections of a forecast discussion, and to find headings within sections.
Help! We're open to suggestions. One thing we're looking at is dictionary lookup, but that's something that can't be done blindly, because of ambiguities; too many words exist in both capitalized and uncapitalized forms.
We've started a weather resources page with pointers to informantion on matters relating to weather forecasts.
Please send feedback, questions and suggestions to .
To try it out, use the form at the top of this page.