Napa Valley

Napa Valley is an American Viticultural Area in California, established by the TTB in 1981. Its official boundary encloses 1,624 km².

Delimited area

1,624 km²

Average season GDD

2223

The delimited zone

The official boundary, as digitised by the UC Davis AVA project from the TTB legal description, shown over its surroundings. Backdrop cartography: Natural Earth (public domain).

How it sits with its neighbours

The TTB records Napa Valley as sitting inside a wider appellation. Smallest first:

North Coast 13,353 km²

The rules of the appellation

Established	1981-02-27
State	California
CFR reference	9.23
Within	North Coast

The legal boundary

From the TTB's official boundary description (9.23):

From the beginning point at the conjuction of the Napa County-Sonoma County line and the Napa County-Lake County line, the boundary runs along- (1) The Napa County-Lake County line; (2) Putah Creek and the western and southern shores of Lake Berryessa; (3) The Napa County-Solano County line; and (4) The Napa County-Sonoma County line to the beginning point.

Every vintage since 2000, measured

We calculate each growing season (April–October) from the Open-Meteo historical archive, taken at the centre of the appellation. Degree days use the Winkler scale, base 10 °C. It is the same data the textbooks use, simply done for every region and every year.

Growing degree days by vintage. Dashed line: 26-year average (2223).

Growing-season rainfall by vintage, mm. Dashed line: average (102 mm).

Vintage	GDD	Rain mm	Harvest rain*	35 °C+ days
2000	2137	159	66	14
2001	2316	59	28	18
2002	2220	24	1	18
2003	2220	126	1	24
2004	2236	87	78	11
2005	2091	131	6	17
2006	2238	185	8	26
2007	2162	93	46	16
2008	2353	27	17	26
2009	2228	138	90	34
2010	1992	175	64	19
2011	2023	130	35	9
2012	2212	73	20	19
2013	2334	36	9	18
2014	2408	62	29	17
2015	2346	50	12	21
2016	2227	185	120	22
2017	2325	91	6	36
2018	2168	61	5	38
2019	2149	105	4	25
2020	2436	58	0	37
2021	2208	249	241	42
2022	2248	103	30	37
2023	2021	86	38	26
2024	2437	69	6	58
2025	2069	80	56	19

*rain in the final 45 days of the season.

Sources. Boundary + legal description: TTB via the UC Davis AVA Digitizing Project (open licence). Weather: Open-Meteo historical archive (CC BY 4.0). Every number on this page is calculated from the records cited above, and every rule is taken straight from them. Nothing here is machine-written filler.