Morning Briefing — Sunday 15 March 2026

Synoptic overview

Source: Estonian Environment Agency

Charts: lennuilm.ee (Estonian Aviation Weather)

Sounding — Tallinn-Harku 00Z

Launch time2026-03-14 ~23:30 UTC

Surface temperature9.0 °C

Lapse rate 0–2 km5.8 °C/km

Lapse rate 0–3 km5.7 °C/km

Thermal ceiling (AGL)458 m

Inversion base (AGL)458 m

Lifted index—

K-index—

CAPEn/a (not computed for this station)

CINn/a

Thermal Index (TI)8.2 (strong thermals)

Wind 500 m AGLSSW 10.6 m/s

Wind 1000 m AGLSW 9 m/s

Source: University of Wyoming, station 26038

Airmass classification (2026-03-13)

SSC typeMT

DescriptionMoist Tropical — warm, humid

Source: SSC v3.0 (Kent State University), station TLL

Current conditions — Tallinn-Harku

Temperature5.5 °C

Relative humidity57 %

Pressure1010.2 mbar

WindS 3.5 m/s

PhenomenaClear

Obs time (UTC)2026-03-15 05:00:15

Source: Ilmateenistus (Estonian Weather Service)

Kuusiku XC forecast

VerdictMARGINAL

BLH max (08–15 UTC)1140 m

Temperature (13 UTC)11.8 °C

Precipitation (08–15 UTC)0.0 mm

Cloud cover mean61%

CAPE max0 J/kg

Wind (13 UTC)S 4.9 m/s

✓ No precipitation

● BLH borderline: 1140 m (target >1400)

● Temp: 11.8 C (target >16)

✓ Cloud: 61%

Source: Open-Meteo forecast API (59.0°N, 24.8°E). Thresholds calibrated on 53 top-100 Rapla XC flights.

Metric reference

Lapse rate	Temperature decrease per km altitude. >6 °C/km = active thermals; >9.8 = superadiabatic (turbulent).
Thermal ceiling	Height where lapse drops below moist adiabatic — approximate top of usable lift.
Inversion	Layer where temperature increases with height, blocking thermals. Common overnight; often breaks by midday.
Lifted Index (LI)	Stability of a lifted surface parcel at 500 hPa. Negative = unstable; < −3 = strong thermals; < −6 = storm risk.
K-index	Thunderstorm potential from temperature and humidity profile. >25 = showers likely; >35 = widespread storms.
CAPE	Convective Available Potential Energy (J/kg). Higher = stronger updrafts. >1500 = overdevelopment risk. Not computed by Wyoming for Tallinn-Harku — shown in Kuusiku section from forecast model.
CIN	Convective Inhibition (J/kg). Energy barrier thermals must overcome. > −50 = weak cap (easy trigger); < −200 = strong cap.
Thermal Index (TI)	Forecast noon surface temp minus 850 hPa sounding temp. Positive = thermals likely; higher = stronger.
BLH	Boundary Layer Height — mixing depth where thermals operate. >1400 m for good XC; >2000 m for excellent.

00Z sounding reflects pre-dawn atmosphere (~23:30 UTC previous day). Surface inversions typically break by mid-morning. Kuusiku forecast uses 13 UTC (16:00 EEST / 15:00 EET) for peak thermal metrics — this hour was calibrated against the top-100 Rapla XC flight dates (2018–2025).

Disclaimer: Content generated using AI under guidance of an amateur paraglider pilot. Always check actual weather conditions before flying. No responsibility is assumed for decisions made based on this data.

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