Radiation fog and Mount Saint Helens blowing off steam on October 4 and 5, 2004

What happened?

On the morning of October 4, 2004, a dense fog blanketed an area including the entire Puget Sound of Washington State and the straits of Juan de Fuca and Georgia.
The fog was caused by a layer of warm, sinking air sitting atop a layer of cool, moist air. This temperature inversion prevented the boundary layer from becoming deeper through convective mixing. The fog dissipated in a very classical manner, dissipating from the outside towards the inside. This is attained by heating the ground (and thus the air) near the edges of the fog, mixing the moisture through a larger and larger depth. The fog dissipates and allows the ground underneath where it had been to heat up, continuing the process until all the fog has dissipated or until the sun goes down.
The other reason for showing these satellite image animations isn't weather-related, but it's cool anyhow. On October 4 at around 17:00Z, Mount Saint Helens let off some steam. The satellite animation of this is presented here.
The next day, on October 5, the same thing happened; the satellite animation of that day's steam release is also presented here.

Satellite images

Click here to see the satellite animation of October 4.
Click here to see the satellite animation of October 5.

Fog observations

Vancouver, BC:

METAR CYVR 041500Z 08003KT 1/2SM FG VV002 10/09 A3013 RMK FG8 SLP204
SPECI CYVR 041508Z 11004KT 3/8SM FG VV001 RMK FG8
SPECI CYVR 041524Z 10004KT 1/8SM FG VV001 RMK FG8
METAR CYVR 041600Z 11004KT 1/8SM FG VV001 10/10 A3014 RMK FG8 SLP208
SPECI CYVR 041653Z 10004KT 1/4SM FG VV002 RMK FG8
METAR CYVR 041700Z 11004KT 3/8SM FG VV002 11/10 A3014 RMK FG8 SLP208
SPECI CYVR 041704Z 10004KT 1/2SM FG VV003 RMK FG8


Victoria, BC:

METAR CYYJ 041100Z 00000KT 1/8SM FG VV001 07/06 A3013 RMK FG8 SLP204
METAR CYYJ 041200Z 00000KT 1/8SM FG VV001 07/06 A3013 RMK FG8 SLP202
METAR CYYJ 041300Z 00000KT 1/4SM FG VV001 08/07 A3013 RMK FG8 SLP203
METAR CYYJ 041400Z 00000KT 1/8SM FG VV001 09/08 A3013 RMK FG8 SLP202
METAR CYYJ 041500Z 00000KT 0SM FG VV001 09/09 A3013 RMK FG8 SLP204
METAR CYYJ 041600Z 00000KT 0SM FG VV001 09/09 A3014 RMK FG8 SLP206
SPECI CYYJ 041610Z 00000KT 1/8SM FG VV001 RMK FG8
METAR CYYJ 041700Z 00000KT 1/8SM FG VV001 09/09 A3014 RMK FG8 SLP208

(The fog persisted at CYYJ for 24 hours after this.)


Seattle, WA:

METAR KSEA 051156Z 00000KT 1/4SM FG VV001 08/08 A3001 RMK AO2 SLP167 60001 70001 T00830083 10111 20072 56005 RVRNO
SPECI KSEA 051225Z 00000KT M1/4SM FG OVC001 08/08 A3000 RMK AO2 RVRNO
METAR KSEA 051256Z 00000KT M1/4SM FG VV001 08/08 A3000 RMK AO2 SLP164 T00830083 RVRNO
SPECI KSEA 051317Z 00000KT 1/4SM FG VV001 08/08 A3000 RMK AO2 RVRNO
METAR KSEA 051356Z 00000KT 1/4SM FG VV001 08/08 A2999 RMK AO2 SLP164 T00830083 RVRNO
SPECI KSEA 051434Z 23003KT M1/4SM FG VV001 08/08 A3000
METAR KSEA 051456Z 17006KT M1/4SM FG VV001 09/09 A3000 RMK AO2 SLP164 T00890089 55004 RVRNO
METAR KSEA 051556Z 17005KT 1/4SM FG VV001 09/09 A2999 RMK AO2 SLP163 T00890089 RVRNO
SPECI KSEA 051626Z 21004KT M1/4SM FG VV001 09/09 A3001 RMK AO2 RVRNO
METAR KSEA 051656Z 18006KT 1/4SM FG VV001 09/09 A3001 RMK AO2 SLP169 SFC VIS 1/4 T00890089 RVRNO

(M1/4SM means that the visibility was less than 1/4 statute mile.)


Tacoma, WA:

METAR KTCM 050555Z 00000KT 1/4SM R34/3500V4500FT FG SCT000 BKN001 08/08 A3002 RMK FG SCT000 SLP170 WR// 57007
METAR KTCM 050655Z 00000KT 1/16SM R34/3500V5000FT FG VV001 09/09 A3002 RMK SLP168 WR//
METAR KTCM 050755Z 00000KT 1/16SM R34/2400V2600FT FG VV001 09/09 A3002 RMK SLP168 WR//
METAR KTCM 050855Z 17002KT 1/16SM R34/2400V2600FT FG VV001 09/09 A3002 RMK SLP168 WR// 56002
METAR KTCM 050955Z 00000KT 1/16SM R34/2400V2600FT FG VV001 08/08 A3001 RMK SLP167 WR//
METAR KTCM 051055Z 23003KT 1/16SM R34/2400V3000FT FG VV001 08/08 A3001 RMK SLP165 WR//
METAR KTCM 051155Z 00000KT 1/16SM R34/2200V2400FT FG VV001 08/08 A3000 RMK SLP163 WR// 57005

(It's fairly rare to see visibilities reported in 16ths of a statute mile.)

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