Pyeongchang Weather Update

I could talk about the snow potential for this next system, but it isn't that great, so I'm going to say nothing and hope that might allow Mother Nature to give us better blessings than she has for much of the winter.

Instead, let's turn our attention to the Korean Peninsula and the weather leading up to the Pyeongchang Games.

The loop below shows analyses and GFS forecasts from 1200 UTC 3 February (9 PM KST 3 February) through 1200 UTC 7 February (9 PM KST 7 February), which is the first day of outdoor competitions (qualifiers for Biathalon, Luge, and Ski Jumping).  Opening Ceremonies are 8 PM KST Friday 9 February as the first competitions with medals are the following day.

That run-up period is characterized by a pattern very typical of the Asian Winter Monsoon, with northwesterly flow spreading cold air from interior Asia over the Yellow Sea, Korean Peninsula, and East Sea (a.k.a, Sea of Japan — given that South Korea is hosting the games, I am using their preferred name for that body of water).  Also evident are strong "mesolows", low pressure systems that are relatively small in scale, but develop frequently due to the transfer of heat and moisture from the water to the atmosphere over the Yellow Sea (forms near the end of the loop) and East Sea (evident for the first portion of the loop).  At times, one can also see a strong band of precipitation just offshore of Korea over the East Sea.

All but the mesolow that forms over the Yellow Sea late in the loop can be seen in the GFS forecast below, valid 1500 UTC 5 February (0000 KST 6 February).  Note the mesolow just off the southern tip of Hokkaido Island, with a trailing trough and associated precipitation band and the convergence zone off the east coast of Korea.  One can also see here one of the reasons why the Korean Peninsula is so much drier during winter than the west coast of Japan as it is often in a dry airflow that does not traverse a large water body.  This also results in colder temperatures.  At this time 925-mb temperatures (contours above and below, equivalent to about 750 meters above sea level, near the top of the higher alpine venues) are around -15ºC/5ºF.

This is very common for the region.  Chaos all around the Korean Peninsula, which remains relatively dry.

For the skiers out there, the convergence zone off the east coast of Korea is known in Japan as the Japan sea Polar-airmass Convergence Zone (JPCZ) and it can produce heavy snowfall along the western coast and mountains of central Honshu.  You can see that's what the forecast is going for above.  Note, however, that it's not the only game in town and what happens locally in that region is strongly dependent on both the direction and strength of the incident flow and its interaction with the terrain.

In terms of the current competition schedule, I have my eyes on the Men's and Ladies' Downhills, scheduled for 11 AM KST 11 February and 11 AM 21 February, respectively.  These typically have high weather sensitivity and are more prone to postponements than the other alpine events (although the Super-G is also sensitive).  We'll take a closer look at the forecast for these events as they approach.  Of course all outdoor events are affected by weather, so I'm looking forward to binge watching during the next month.

It is worth noting that a best case scenario for Olympic competitions is clear skies, no snow, little wind, and temperatures below freezing.  Many people are surprised to hear that no snow is good for the games, but snow is more trouble than it is worth, except from an aesthetics perspective.  It complicates transportation and venue preparations.  It creates uneven competitions.  Even a little snow can cause problems.  In this regard, the Korean peninsula has some advantages.  On the other hand, they can get snow under the right pattern, and I suspect something interesting will happen during the course of the Games.