· Analytic
Z4422 Corn Belt SPI (IL + IA 3-month)
The 3-month Standardized Precipitation Index for Illinois and Iowa, inverted so drought conditions in the two highest-production US corn states register as positive signal values. The highest-weighted input in ML Auto Corn Composite V9 ML Auto Corn Composite at 13.5 percent of model weight.
At a glance
Current composite
+0.0765
On the plus-or-minus one scale; IL + IA cumulative moisture mildly below normal
Signal state
Normal
102 consecutive days in state
All-time percentile
66.3th
Upper-half of 36 years
EXTREME_POS corn fwd 60d
+2.33%
542 days (6.0% of sample), HAC t +1.44
MODERATE_NEG corn fwd 60d
-1.19%
2,106 days (23.5% of sample), HAC t -1.72
ML Auto Corn Composite V9 contribution today
-0.097
Highest-weight ML Auto Corn Composite V9 input at 13.5 percent × polarity +1
As of Oct 30, 2026. Updated nightly.
OBJECTIVE
The Standardized Precipitation Index is a drought-monitoring metric developed by the US climate research community in the 1990s and now standard across all 50 US state climatologists and NOAA’s National Climatic Data Center. The 3-month SPI compares cumulative precipitation over the trailing 90 days against the historical distribution for that same 3-month window; the resulting z-score is positive during wet periods and negative during droughts. This signal computes a production-weighted average of the SP03 index for Illinois and Iowa , the two largest-production US corn states (combined approximately 34 percent of US corn production) , and polarity-inverts so drought maps to positive signal. The LightGBM feature-selection in Truthsayer y_proposer picked this signal as the single highest-weight input to ML Auto Corn Composite V9 ML Auto Corn Composite at 13.5 percent of model weight. The economic logic is direct: cumulative moisture deficit across the IL + IA growing-season window directly reduces corn yield via silking-and-grain-fill water-stress mechanisms. The signal reads plus 0.0765 as of October 23, 2026, in NORMAL territory for 102 consecutive trading days at the 66.3 percentile of 36 years of history. The empirical state-conditional pattern across 36 years is directional but weak at state significance. EXTREME_POS state (SPI below 1.5 standard deviations, deep drought) delivers mean corn fwd 60d of plus 2.33 percent (HAC Newey-West t plus 1.44, 542 state-days). MODERATE_NEG state (modestly wet, SPI between plus 0.2 and plus 0.5 as z-score of inverse) delivers minus 1.19 percent (HAC t minus 1.72, near 10 percent significance). Neither tail clears 5 percent significance individually. The signal’s edge in ML Auto Corn Composite V9 comes from combination with the other 14 members rather than standalone state-conditional edge. Read on for the mechanism, the three signature historical cases, and the current reading in context.
LIVE CHART
Thirty-six years of NOAA NCLIMDIV 3-month SPI for Illinois + Iowa, polarity-inverted.
The signal has been in NORMAL for 102 consecutive trading days. Signature episodes: EXTREME_POS firings during the 2012 drought (July SP03 for IL + IA reached deep drought territory), the 1988 drought (historical US corn yield loss of 30+ percent), and the 2000-2001 Midwest moisture deficit. EXTREME_NEG firings during the 1993 Midwest flooding, the 2010 wet spring, and the 2019 flood-driven planting delay windows.
COMPOSITE
+0.076 / tanh
STATE
Normal
PHASE
0
FWD 60d
+3.19% (baseline +2.31%)
SAMPLE N
9,039 days
TODAY’S PLAYBOOK READING
STATE
NORMAL
STATE AND PERCENTILE
NORMAL, 102 consecutive days. Composite at plus 0.0765 is at the 66.3 percentile.
WHY THE SIGNAL IS HERE
Illinois + Iowa 3-month cumulative precipitation is modestly below the 36-year normal for the equivalent fall window.
POSTURE FOR THE WEEKS AHEAD
NORMAL delivers near-baseline corn fwd 60d. A move above plus 0.2 would flip into MODERATE_POS (-0.66 percent, not statistically significant). A move above plus 0.5 would flip into EXTREME_POS (+2.33 percent HAC t +1.44, near 10 percent significance).
WHAT THE CHART SHOWS
The composite sits at +0.08 in the IL/IA Neutral band. The 3-month SPI for Illinois and Iowa reads near-baseline. Note: the rolling 252-day IC vs CBOT corn fwd 60d is -0.640 at p=1.5e-23, strongly CONTRARIAN in the recent regime — SPI drought readings have pre-staged corn weakness rather than strength over the past year, likely because fundamentals have been dominated by abundant 2025 supply. CBOT front-month corn (orange, right axis) sits near $4.48/bu.
TOP INPUTS FIRING
- Primary composite +0.08 State IL/IA Neutral band. 3-month SPI for Illinois + Iowa reads near-baseline after the 2026 growing season.
- 3-month Standardized Precipitation Index, Illinois + Iowa aggregated SPI from NOAA climate data for Illinois and Iowa, 3-month lookback, inverted (drought = positive composite). The two states combined grow approximately 31% of US corn.
- Rolling 252d IC vs CBOT corn fwd 60d: -0.640, p=1.5e-23 (CONTRARIAN recent regime) The recent regime is strongly contrarian: drought readings have pre-staged corn weakness, not strength. Likely reflects abundant 2025 supply dominating the price picture despite isolated-drought firings.
THE TAKEAWAY
What this means for you today
WHAT THE SPI IS TELLING YOU
The Standardized Precipitation Index integrates precipitation over a defined window and normalizes it against the climatological distribution for that location and time of year. A 3-month SPI reading of minus 1.0 means the trailing 3 months of precipitation were 1 standard deviation below the historical same-period average; minus 1.5 is deep drought; minus 2.0 is extreme drought. The current reading for Illinois + Iowa integrates August through October 2026 precipitation and compares against 36 years of August-October history. The reading is mildly dry but not statistically unusual.
WHY ILLINOIS + IOWA MATTER DISPROPORTIONATELY
Illinois and Iowa combined produce approximately 34 percent of US corn , 19 percent from Iowa, 15 percent from Illinois (based on USDA NASS 2020-2024 5-year production shares). Weather conditions in these two states have statistically higher explanatory power for US corn yield outcomes than conditions in minor-producer states. The LightGBM feature-selection in Truthsayer y_proposer picked IL + IA SP03 as the single highest-weight input to ML Auto Corn Composite V9 , a reflection of the empirical fact that these two states’ drought conditions carry outsized market information.
THE HONEST CAVEAT
The signal’s standalone state-conditional corn fwd 60d statistics are DIRECTIONAL but WEAK at state significance. Only the MODERATE_NEG tail reaches near-10-percent HAC-t significance (minus 1.72); other tails are not individually significant. The signal’s value in ML Auto Corn Composite V9 comes from COMBINATION with the other 14 members in the LightGBM-weighted composite, not from standalone edge. Readers should NOT trade this signal as a standalone drought-detector; its role is as the highest-weight contributor to a 15-member ML composite. Additionally, NCLIMDIV monthly data has an approximately 10-day publication lag that the current engine does not explicitly apply , a minor look-ahead per the persona code review 2026-10-25 §6.1.
THE REGIME MAP
The three Illinois+Iowa 3-month SPI regime states, forward returns and sample share
Behavior across the 3-month Standardized Precipitation Index for Illinois and Iowa (the two highest-production US corn states, combined ~31% of US corn), inverted so drought reads positive composite. The highest-weighted input in the ML Auto Corn Composite V9. CBOT corn benchmark.
| State | Phase | Share | Fwd 60d | HAC t | Edge vs baseline | Last firings |
|---|---|---|---|---|---|---|
| IL/IA Surplus | – | 0.0% (0 d) | n/a | n/a | none | |
| IL/IA Neutral | 0 | 0.0% (0 d) | n/a | n/a | none | |
| IL/IA Drought | + | 0.0% (0 d) | n/a | n/a | none |
The historical pattern
Why it matters
THE TRACK RECORD
State changes
| State | Start | End | Duration | Fwd 60d SPY |
|---|---|---|---|---|
| Normal | 10/23/2024 | 10/30/2024 | 6d | +4.92% |
| Extreme Neg | 10/31/2024 | 02/27/2025 | 81d | +6.40% |
| Normal | 02/28/2025 | 05/30/2025 | 64d | -0.51% |
| Extreme Pos | 06/02/2025 | 07/30/2025 | 41d | +9.10% |
| Normal | 07/31/2025 | 08/29/2025 | 22d | +7.15% |
| Extreme Neg | 09/02/2025 | 10/30/2025 | 43d | +5.43% |
| Normal | 10/31/2025 | 01/30/2026 | 62d | +1.76% |
| Extreme Neg | 02/02/2026 | 05/29/2026 | 82d | +2.33% |
| Normal | 06/01/2026 | 10/23/2026 | 102d | +0.99% |
Scroll inside the table for the full history. Forward 60-day SPY is measured from each run’s start date; a reader cannot trade off a start-date they only identify in hindsight, so this is a transparency log, not an alpha claim. Asterisked (*) returns are partial. The run is less than 60 trading days old. The full 60-day comparable fills in as more data arrives.
What this measures
The engine queries NOAA NCLIMDIV monthly SP03 (3-month Standardized Precipitation Index) data for Illinois (state_fips 17) and Iowa (state_fips 19) from the estate weather database. Averages the per-state SP03 values with equal weight. Forward-fills daily. Applies tanh/2.0 clipping (SPI is already a standardized index, no additional z-score). Polarity-inverts (negative SPI = drought = positive signal). Five-state machine on the final the primary composite.
GO DEEPER
Want the full depth?
The full research brief adds methodology detail on the Standardized Precipitation Index computation, the Illinois+Iowa state weighting (31% of US corn combined), the 3-month lookback choice, and the integration into the ML Auto Corn Composite V9. Includes historical case studies anchored to actual IL/IA weather regimes, the three-regime state-conditional table, and the methodology for pairing with Silking Pace, Condition WoW, Nino 3.4, and the Corn Cycle DNA playbook.
Alert drafts
Not investment advice · The analysis on this page is informational and educational. Signal readings, historical case figures, and empirical statistics are derived from publicly available data and are provided without warranty. Hypothetical performance results have inherent limitations, including the benefit of hindsight. Readers who intend to trade should consult a licensed investment professional and see the research brief for the full disclaimer.
Last refreshed Nov 02, 2026 01:40 PM ET