Pollen calendar by US region
This is the season calendar Breathing Index falls back on when there's no measurement to show: days before today, relay outages, spent quotas. Three species, nine US regions, month granularity. A calendar can't honestly claim more than that, so this one doesn't try.
The calendar
L low, shown as index 1 (Very Low) · M moderate, shown as index 3 (Moderate) · H high, shown as index 4 (High) · blank = out of season
| Region | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Northeast | L | H | M | |||||||||
| Ohio Valley | M | H | L | |||||||||
| Upper Midwest | M | H | ||||||||||
| Northern Plains | L | M | ||||||||||
| Southeast | ||||||||||||
| South | ||||||||||||
| Southwest | ||||||||||||
| West (CA/NV) | ||||||||||||
| Northwest | M | H | M |
| Region | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Northeast | M | H | M | |||||||||
| Ohio Valley | H | H | M | |||||||||
| Upper Midwest | M | H | M | |||||||||
| Northern Plains | M | H | M | |||||||||
| Southeast | L | M | H | H | M | M | M | |||||
| South | M | H | H | H | M | M | M | |||||
| Southwest | M | M | L | L | L | L | ||||||
| West (CA/NV) | M | H | H | M | ||||||||
| Northwest | H | H | M |
| Region | J | F | M | A | M | J | J | A | S | O | N | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Northeast | M | H | L | |||||||||
| Ohio Valley | M | H | M | |||||||||
| Upper Midwest | H | H | L | |||||||||
| Northern Plains | M | M | L | |||||||||
| Southeast | M | H | M | L | ||||||||
| South | M | H | M | |||||||||
| Southwest | L | M | L | |||||||||
| West (CA/NV) | L | L | ||||||||||
| Northwest | L |
How to read it
Each letter is the strength of a typical season that month, mapped to the low edge of its category on the 0–5 pollen index the app uses everywhere else. That's deliberate: a calendar month is a climatology, not a forecast, so it claims the least its category allows. There's no letter for Very High either; a peak is a measurement's claim to make, and this table is an estimate.
About the blanks
Birch pollen barely registers in the South, the Southeast, the Southwest, or California, so those rows carry no tree season at all. There are birches down there — river birch lines half the creeks in the Southeast — but they don't put enough in the air to count as a season. Those places obviously still have tree pollen — mountain cedar in central Texas all winter, oak and pine across the Southeast in spring — but the app learns their timing from the measured feed, which knows what's actually in the air today. This table only says what a calendar can honestly say, and a made-up season would be worse than an admitted blank.
Where the seasons come from
The season shapes follow the AAAAI / National Allergy Bureau picture of North American pollen seasons: tree pollen in early spring, grass from late spring through summer (longer and earlier in the South and West), and ragweed from mid-August to first frost. The NAB's counting stations are the closest thing the US has to ground truth here.
If you want today's reading for where you actually are — per plant, not per category — open the app. Log how your breathing went and it starts working out which of these seasons is yours.
Breathing Index is a breathing lens on public air data — not medical advice. Trust your symptoms and your asthma action plan over anything on this screen.