A rain-snow transition event occurred from March 21 into the early hours of March 22, which was an excellent example of this transition. This event coincided with the presence of a weak, cold-core low pressure system with a central pressure of approximately 1006 mb. Rain began to fall at the KES site around 18-19 UTC, with a rain-snow line at 600-800 m on Mount Kidd around 21-22 UTC. Just before 2230 UTC, some snowflakes started to fall, as the rain-snow line collapsed from approximately 600 m to the surface within a half-hour. Mixed precipitation (with rain and snow alternating in terms of dominant type) occurred from just prior to 2230 UTC to approximately 23 UTC. Temperatures during the initial occurrence of rain were > 9°C and decreased to just above 3°C within the same half-hour the rain-snow line descended toward the surface.
Cloud cover was inconsistent. For some periods during precipitation occurrence, cloud cover was total, but for others, nearly half of the sky was clear and the Sun was shining on some of the mountains to the north. Visibilities were also highly variable, with Mount Kidd completely obscured by clouds and possibly fog at some instances. Winds were generally light (< 5 m/s), although variable in direction.
The MRR was fully operational during this event. The instrument detected reflectivity values > 20 dBZ within the lowest 2 km during some periods of precipitation, mirroring reflectivity values from the Strathmore radar, which were also > 20 dBZ at some instances. The MRR also detected changes to the velocity of falling precipitation which clearly showed the transition region from snow to rain, which increased from 1-2 m/s to approximately 4-6 m/s between the 600-800 m layer and the 200-400 m layer. The instrument also detected this increase occurring just above the surface-200 m layer.
Later in the evening, sporadic periods of light snow flurries occurred and continued beyond 09 UTC. However, they were too sparsely distributed to obtain photographs prior to them melting on warmer surfaces, as temperatures at that time were no colder than -2°C. Particle sizes were very small, and some were heavily rimed.
The following imagery are presented for the event (from left to right): infrared satellite from 00 UTC on March 22, upper-air analyses from 00 UTC on March 22, surface analysis from 21 UTC on March 21, and snow precipitation radar from Strathmore at 2220 UTC on March 21.
Ida, Juris, and Stephen performed field duties during this event.
Instruments working during that event: MRR, Parsivel, manual obs, some snow photos.
-Stephen Berg
Cloud cover was inconsistent. For some periods during precipitation occurrence, cloud cover was total, but for others, nearly half of the sky was clear and the Sun was shining on some of the mountains to the north. Visibilities were also highly variable, with Mount Kidd completely obscured by clouds and possibly fog at some instances. Winds were generally light (< 5 m/s), although variable in direction.
The MRR was fully operational during this event. The instrument detected reflectivity values > 20 dBZ within the lowest 2 km during some periods of precipitation, mirroring reflectivity values from the Strathmore radar, which were also > 20 dBZ at some instances. The MRR also detected changes to the velocity of falling precipitation which clearly showed the transition region from snow to rain, which increased from 1-2 m/s to approximately 4-6 m/s between the 600-800 m layer and the 200-400 m layer. The instrument also detected this increase occurring just above the surface-200 m layer.
Later in the evening, sporadic periods of light snow flurries occurred and continued beyond 09 UTC. However, they were too sparsely distributed to obtain photographs prior to them melting on warmer surfaces, as temperatures at that time were no colder than -2°C. Particle sizes were very small, and some were heavily rimed.
The following imagery are presented for the event (from left to right): infrared satellite from 00 UTC on March 22, upper-air analyses from 00 UTC on March 22, surface analysis from 21 UTC on March 21, and snow precipitation radar from Strathmore at 2220 UTC on March 21.
Ida, Juris, and Stephen performed field duties during this event.
Instruments working during that event: MRR, Parsivel, manual obs, some snow photos.
-Stephen Berg
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