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U.S. Futures Slip on Rate Fears; KOSPI Opens Tuesday With Mixed Signals — Korea Market Pre-Open, Aug 18, 2026

Tuesday, August 18 (2026): KOSPI and KOSDAQ index closing prices are not yet confirmed at this hour — today’s session has not opened.Overnight, U.S. equities fell — the S&P 500 settled at 7,745.06 (−0.52%) and the Nasdaq at 26,644.91 (−0.32%) on August 17 — while the SOX semiconductor index gained 1

The Silmari
A daily data newsletter on the Korean stock market — silmari, ‘a clue: the loose end that unravels the knot’
① Pre-Open 07:302026.08.18 Tue · No. 15Cautious — crash-precursor score 3/max; sentiment composite not yet computed for Aug 18; ADR and short-surge sub-signals active.
① Pre-Open · published 07:30 KST · before the open
01 · VerdictRegular session confirmed 15:30 KST

Today’s Calls

U.S. Futures Slip on Rate Fears; KOSPI Opens Tuesday With Mixed Signals

Tuesday, August 18 (2026): KOSPI and KOSDAQ index closing prices are not yet confirmed at this hour — today’s session has not opened.Overnight, U.S. equities fell — the S&P 500 settled at 7,745.06 (0.52%) and the Nasdaq at 26,644.91 (0.32%) on August 17 — while the Philadelphia Semiconductor IndexA U.S. index tracking the share prices of major semiconductor design and manufacturing companies.Historically one of the strongest overnight leading indicators for Korean chip stocks such as SK hynix and Samsung Electronics. semiconductor index gained 1.64% to 12,621.0, a split that sets up a divergent open for Korean tech.

Key points
01The 30-year U.S. Treasury yield topped 5.31% overnight (August 17), the move amplified by geopolitical oil pressure — Brent crude back above $90 — pulling broad U.S. equities lower even as semiconductor names held.
02SOX closed +1.64% on August 17; in the 2026 regime (n=139), Korea has followed U.S. semiconductor direction in 39 of 139 sessions outright, with bidirectional follow-through in 46 — context, not a guarantee.
03One-week KOSPI foreign net buying stands at +₩654.7bn; the Tuesday 2026-regime base rate shows foreigners net-selling on 60% of Tuesdays (n=30), a headwind to watch at the open.
04Crash-precursor score is 3 out of a possible higher reading, driven by Advance-Decline RatioThe number of rising stocks divided by the number of falling stocks in a given market on a given day.A sub-component of today’s crash-precursor score; a very high ADR reading can signal overbought breadth, while a very low reading flags broad selling pressure. and a short-selling surge sub-signal; the composite sentiment gauge value for today has not yet been computed.
02 · Prediction2 calls · posted 07:30 KST

Today’s Calls

Where the day’s calls are placed by number — grading starts with the Early Session edition

Today’s Calls: KOSPI +0.5–1.5%, KOSDAQ Flat to +1.0% — Awaiting Verdict at Close

Two calls are on the board for Tuesday, August 18 (2026): KOSPI +0.5%–1.5% (P1) and KOSDAQ 0.0%–+1.0% (P2).These are open predictions — the session has not begun, so no judgment is possible at this hour; scoring will appear in the evening edition.

calls placed today
2 issues
posted 07:30 KST
Direction grading
from the 10:00 Early Session edition
Magnitude grading
settled in the 20:00 Final Edition
Call ① KOSPIThe KOSPI is more likely to rise
Band +0.5~1.5% · full day
Morning rationaleSOX +1.64% current setup: next-day avg +2.15%, 78% upside (n=54) bullish signal; however, foreign investors’ 4th-day final-stretch buying + weekly surge fatigue (+11.49%) + Tuesday gap-reversion pattern limits gains
Call ② KOSDAQKosdaq likely to trade flat to modestly higher
Band 0.0~+1.0% · full day
Morning rationalePast 5 days: foreigners and institutions selling together, individuals buying solo; SOX rally provides tailwind but underperforms vs Kospi

No sector-level or individual-name calls were registered for today’s pre-open edition; the two market-index calls above represent the full prediction set.

03 · OvernightOvernight, confirmed — previous U.S. session

The world overnight — how the US session ended

A window on what happened in the US market overnight

Wall Street Splits: S&P 500 and Nasdaq Fall While SOX Advances 1.64%

Nasdaq26644.91 (−0.32%· as of 2026-08-17)
S&P5007745.06 (−0.52%· as of 2026-08-17)
SOX semiconductors12621.0 (+1.64%· as of 2026-08-17)
Dow53459.78 (−0.51%· as of 2026-08-17)
iShares MSCI South Korea ETFA U.S.-listed ETF tracking a broad index of Korean equities, widely used as a proxy for foreign-investor sentiment toward Korea.EWY’s daily move on the prior U.S. session (August 17: +2.98%) gives an early read on how offshore money views the Korean market before Seoul opens.(Korea ETF)185.1 (+2.98%· as of 2026-08-17)
Dollar index99.58 (−0.09%· as of 2026-08-17)
U.S. 10-year Treasury4.72 (+0.60%· as of 2026-08-17)
Nikkei 225 (prior session)68713.8 (+0.59%· as of 2026-08-14)
USD/KRW (prior Seoul session)1417.0 (−0.23%· as of 2026-08-14)

On August 17, the S&P 500 fell 0.52% to 7,745.06 and the Nasdaq slipped 0.32% to 26,644.91, weighed by a surge in the 30-year Treasury yield to 5.31% and a roughly 2% rise in crude oil on U.S.–Iran negotiation stalemate.SOX bucked the broad decline, gaining 1.64% to 12,621.0; the Wall Street brokerage scorecard across tracked calls stands at 15/28 (54% hit rate) over the three-day horizon — a mixed record that argues against treating any single overnight directional signal as decisive.

04 · Cross-followingMeasured in 2026

Korea–U.S. mutual following — overnight grading

A window on which market followed which

2026 YTD: Korea Followed U.S. Overnight in 39 Sessions, Moved Independently in 24

In 2026 year-to-date data (n=139 sessions), the KOSPI followed the prior night’s SOX direction (|SOX| ≥ 0.5%) in 39 sessions outright and showed bidirectional movement in 46; U.S. markets followed the prior KOSPI direction in 30 sessions.On 24 of 139 sessions there was no meaningful follow-through in either direction — a reminder that overnight SOX gains do not mechanically transmit to Korean semiconductor names, as the August 10 lesson showed when a prior SOX surge did not lift KOSPI semiconductor stocks.

The asymmetry in the 2026 data — Korea following the U.S. more often than the reverse (39 vs. 30) — suggests the directional influence runs predominantly west-to-east at present, but bidirectional days (46) outnumber either one-way category.With SOX up 1.64% on August 17 but U.S. broad futures softer overnight, today’s open is a case where the two signals point in opposite directions — a configuration that historically produces more dispersion within the Korean market rather than a uniform index move.

Days Korea followed the U.S.39 days
Days the U.S. followed Korea30 days
Both ways46 days
Sample139 days

Overnight SOX ↔ same-day KOSPI in the same direction (|SOX| ≥ 0.5%) = Korea following · same-day KOSPI ↔ that night’s SOX in the same direction (|KOSPI| ≥ 0.5%) = the U.S. following

05 · Night windowOvernight indicators

Night window —EWYofficial indicator

A window on what overnight futures foreshadow for the next day’s open

Overnight Futures: S&P 500 Contracts Down 0.69%, Nikkei CME Off 0.40% Before Seoul Open

Nasdaq26644.91 (−0.32%· as of 2026-08-17)
S&P5007745.06 (−0.52%· as of 2026-08-17)
SOX semiconductors12621.0 (+1.64%· as of 2026-08-17)

As of the 05:00 KST snapshot on August 18, U.S. and Japanese futures were all in negative territory: S&P 500 futures (ES) stood at 7,765.5 (0.69% from the August 17 15:00 KST reference), Nasdaq 100 futures (NQ) at 30,078.25 (0.81%), and Nikkei CME-yen futures at 68,985.0 (0.40%).These are CME-linked proxies, not the Korean overnight futures contract; the directional read is indicative only — in 2026 year-to-date data, Korea followed U.S. overnight direction in 39 outright and 46 bidirectional sessions out of 139, leaving 24 sessions of no follow-through.

06 · Pre-openPre-open check

Pre-open08:00~09:00single-price auction (open/close)The single-price auction window (before the open and just before the close), where orders are pooled and matched at once.When large volume crowds into this window, a gap is created.forecast

A window on where the pre-open auction is pulling the opening price

Pre-Open Watch: Long Rates and Oil Versus SOX Rebound — Which Signal Wins at 09:00?

At 07:30, the simultaneous auction (08:30–09:00 KST) has not yet begun; the key question is whether the SOX +1.64% tailwind pulls semiconductor heavyweights (SK hynix, Samsung Electronics) to a positive gap, or whether the broader risk-off from higher long rates and softer S&P 500 / Nasdaq futures (0.69% and 0.81% respectively) pulls the open lower.A secondary watch point is SK Telecom, which appeared among Monday’s KOSPI volume leaders with a notable move — whether that momentum extends or reverses at the open will be one early read on today’s breadth.

KOSPIClose6,977.94· same-day+2.42%
KOSDAQClose864.65· same-day+0.38%
Historical contextTuesday 2026-regime base: KOSPI avg. +0.29%, up on 73% of 30 sessions; foreigners net-sold on 60% of those Tuesdays (avg. −₩133.2bn) — directional tilt modestly positive but foreign supply a recurring drag.
07 · ReviewPrevious trading day (08.14) confirmed

Previous-Day Review

A window that retraces what happened in the previous session

Prior-Session Scorecard: 6/10 Hit on August 14 — Foreign Buying Understated Again

KOSPIClose6,977.94· same-day+2.42%
KOSDAQClose864.65· same-day+0.38%
08 · Fear gaugeStanding gauge8 factors · based on previous trading day (08.14) · percentile: current setup (2026)

The Silmari Fear Gauge

A window measuring market anxiety through volatility, margin lending and short selling

Crash Pre-Signal CompositeA composite score (0–max) combining sub-signals including ADR extremes, short-selling surges, selling acceleration, and sentiment-90+ readings.Today’s score of 3 with two sub-signals active is a background risk indicator — not a prediction but a quantified reminder of tail-risk conditions. Holds at 3 — ADR and Short-Surge Sub-Signals Active

Volatility percentile
93
Silmari Fear Gauge percentile basis — to be stated
Margin balance, 5-day change7.41 — Change in Leveraged Purchases — Larger increases create greater forced liquidation pressure on declines ·As of 08.13
Forced-liquidation share0.5 — Share of Forced Liquidations — Higher ratio signals greater mechanical selling pressure ·As of 08.13
Short-interest surge multiple7.8 — Short bets multiplied how many times in 5 days — Steep surge is a warning signal ·as of 08.12
Retail buying intensity on down days0.0 — N/A — Not a down day (2.42%)
Consecutive no-trigger down days0.0 — N/A — No-trigger declines did not continue
KOSPI 20-day realised volatility5.88 Risk · Top 7%· Recent 1-month volatility size — dashboard’s core metric
Leveraged-ETF share of turnover9.81 Risk · Top 29%· Leveraged product fund concentration — short-term sentiment gauge

The crash-precursor composite scores 3 this morning, with two sub-signals lit: the ADR reading (reference date: August 28 U.S. session, −16.7%) and the short-selling surge sub-signal (reference date: August 12 T+2 settlement).The selling-acceleration and sentiment-90+ sub-signals are both at zero; the composite sentiment gauge value for today has not yet been computed — the most recent gauge reading available is from August 14.

Among recent short-surge events in the data, SK hynix saw surges on August 10 (7.8×, ratio 0.01) and August 11 (12.1×, ratio 0.02); five-day returns after those events were +0.35% and +5.54% at day one respectively, though the sample is small.Across the full 2026-regime cohort (n=108 surge events), the five-day average return after a short surge is −0.55% with a 51% down-probability — essentially coin-flip, and well below the 2026 baseline of +2.87%, giving an excess return of −3.42%.

No scheduled macro trigger (central bank decision, major data release) appears in today’s event calendar data for the Korean session; the main external variable at this hour is the long-rate move in the U.S. overnight — a background pressure rather than a dated event trigger. The judgment is each reader’s own.

09 · FX windowFX window — previous close

The won — the signal is the speed of the move, not its direction

A window on the pressure the won-dollar rate puts on foreign flows

Won at ₩1,417 Per Dollar; DXY — U.S. Dollar IndexA weighted geometric mean of the U.S. dollar’s value against a basket of six major currencies.A rising DXY tends to reduce the won value of dollar-denominated foreign capital flows into Korean equities, increasing mechanical selling pressure from foreign investors. Edges Down to 99.58

USD/KRW₩1,417.0
DXY (Aug 17)99.58 (−0.09%)
JPY/KRW (100 yen)₩888.54
U.S. 10-yr yield (Aug 17)4.72% (+0.60% change)
30-yr Treasury (overnight)5.31%

The won-dollar rate stood at 1,417.0 as of the latest reading, with the DXY dollar index at 99.58 (0.09% on August 17) — a marginally softer dollar that, all else equal, reduces mechanical foreign selling pressure on Korean equities.The yen cross reads 888.54 won per 100 yen; the Nikkei CME futures were off 0.40% overnight, and the August 17 Nikkei 225 cash close was 68,713.8 — yen and regional signals are mildly negative but not sharply so.

10 · KOSDAQ windowKOSDAQ index close for August 18 (2026) not yet determined — session opens at 09:00 KST.

The SilmariDecouplingWhen two markets that used to move together break apart and move separately.The wider the gap, the less any single index can tell you about the market.Gauge

A window on the pattern in the KOSPI–KOSDAQ decoupling

KOSDAQ: Closing Index Not Yet Available — Pre-Open Data Only for Tuesday, August 18

Kospi · Kosdaq close (08.14)6,977.94 · 864.65
Previous session change+2.42% · +0.38%
Previous-session gap (KOSPI − KOSDAQ)+2.04%p
YTD cumulative (through 08.14)+61.92% · −8.56%
Silmari Decoupling Gauge — year-to-date gap+70.47%p
11 · WarningToday’s warning score of 3 = crash alert — thresholds: 3+ crash alert · 2 caution (small sample)

Warning

A window flagging in advance where today’s session calls for caution

Risk Watch: Score-3 Crash Precursor, Short-Surge History, and 30-yr Yield at 5.31%

The crash-precursor score sits at 3 this morning, with the ADR and short-selling surge sub-signals both active; in the 2026-regime short-surge cohort (n=108), the five-day down-probability is 51% and average excess return versus baseline is −3.42% — not a definitive warning but a non-trivial drag.The 30-year U.S. Treasury yield at 5.31% (overnight) and broad futures soft (ES −0.69%, NQ −0.81%) create a higher cost-of-capital backdrop that has historically weighed on high-duration growth names; Tuesday’s 2026 foreign net-selling base rate is 60% (n=30), so a foreign supply overhang at the open cannot be ruled out.Single-Stock Leveraged ETFAn exchange-traded fund designed to deliver a multiple (typically 2×) of the daily return of a single underlying stock.The share of these products in total daily turnover (2.10%–2.81% over Aug 10–14) serves as a daily thermometer of retail speculative activity. turnover ran at 2.10%–2.81% of total market volume over August 10–14, a range that past data associates with elevated intraday volatility; should that share spike today, it would reinforce caution around mid-session swings.

Sources: Korea Exchange · NXT · own measurements · regular session confirmed 15:30 KST · The Silmari editorial desk.
This edition organises and explains publicly available market data. It is not investment advice. Predictions and their scores are preserved without revision — the judgement is yours.