El Nino delays winter

Stage = 39cm, Ta = 2.0C, Tw = 3.3C

Heavy snows over the last couple of days signaled the start of mid-winter conditions and seasonal snowpack at all elevations in the basin. The formation of low elevation snowpack is about a month later than an average winter, mainly due to the strong El Nino effect and unseasonably warm temperatures at the start of this winter season.

Larch forest lysimeter site - checking and cleaning drainage

Snow survey at the larch forest lysimeter site showed there to be about 67cm depth of snow, with a snow density of about 0.25 giving a snow water equivalent of 16.5cm. Typically there would be more than a metre of snow depth by the end of January, with a density of more than 0.3 for an older snowpack. The snowpack was temporarily removed around the lysimeter tray drains to clean and confirm free drainage of the trays. For the larch site and tributary cedar site free drainage was confirmed, while at the lower cedar site I found 2 of the 3 trays to be blocked. Unfortunately a blocked drain means the runoff cannot be determined accurately up to that date, but after cleaning the lysimeter should drain freely for the rest of the winter season.

Free drainage condition confirmed in one of the trays

Snow depths at the upper (100m higher elevation) tributary cedar site were similar to the larch site, while the snow depths at the lower cedar site were the least at about 46cm due to snow interception (sublimation and melt-drip loss) in the mature canopy.

The stage hydrograph below shows a moderate peak around early New Year due to heavy rain. With continued cold and snowy conditions we expect the flow to decrease steadily towards a winter low-flow condition. However, ground-melt at the base of the snowpack and minimal evaporation loss will keep the flow level higher than the summer low-flow condition.