Hockinson, WA (45.7243°N, 122.5184°W) — non-structural carbohydrate estimate
Sets the baseline NSC pool. Defaults match the field-identified stand (Aug 2026): bluegrass-dominant volunteer pasture. Percentages are normalized, so rough estimates are fine.
Total NSC includes fructan, which ferments in the hindgut and produces no insulin response. ESC+starch is the insulinogenic fraction — the basis for the widely used 10% limit for insulin-dysregulated horses. Both values are always shown; this picks which one drives the colors, the safe window, and the alerts.
These four coefficients set how fast sugar accumulates and burns off. Defaults are literature-plausible for PNW cool-season pasture but are not calibrated to your field. Adjust them against your own assay results — raise the accumulation rate if the model reads low at mid-afternoon, raise the burn-off rate if it reads high at dawn.
Applied only when the NWS forecast text mentions smoke or haze — sky cover reports cloud, not particulates. 0.80 is a rough allowance for typical late-summer smoke; set it to 1.00 to ignore smoke entirely, or lower it when the air is genuinely thick.
NSC is treated as a pool that fills and drains, not as a value computed from the current hour's weather. Each hour the model adds photosynthate — scaled by solar elevation for this latitude and date, by cloud cover, and by a temperature-response curve peaking near 18 °C — and subtracts respiration and growth, which double with roughly every 10 °C rise. Growth stops below the shutdown temperature while photosynthesis continues, which is the mechanism behind frost-related sugar spikes.
Because the pool carries across hours, sugar accumulated on a sunny day is still there at dusk and drains overnight. The result peaks in late afternoon and bottoms out shortly before dawn, which matches the published diurnal pattern for cool-season grasses. Cold nights leave more sugar behind for the next day, so consecutive cold-night/sunny-day cycles ratchet the whole curve upward.
Why two numbers. Total NSC is everything the plant stores: fructan, simple sugars (ESC), and starch. Only the second two raise blood insulin — fructan passes to the hindgut and ferments there, producing no insulin response. Since endocrinopathic laminitis is driven by insulin, ESC+starch is the number that matters for a metabolic horse, and it is the basis for the 10% limit commonly cited for insulin-dysregulated horses. Thresholding on total NSC counts fructan that the standard excludes, which is stricter than intended.
The split is estimated from your grass mix. Heavy fructan accumulators like timothy carry a smaller insulinogenic share; legumes like clover carry a much larger one. Cold shifts accumulation toward fructan, so the share falls as temperature drops — which is why a frost spike in total NSC is less dangerous than the number looks. Current mix and coefficients put the mild-weather share near 56%, falling toward 39% at freezing.
Both fractions are estimates layered on an already-estimated pool. An Equi-Analytical 603 panel reports WSC, ESC, and starch separately, which would replace the guesswork with measurement.
The model runs a 72-hour spin-up before the forecast window so the starting pool reflects recent conditions rather than an arbitrary value. It is a management aid, not a substitute for assaying your own grass.