tag:blogger.com,1999:blog-4572286363399496963.post1459270428685838870..comments2024-03-28T07:09:59.093-08:00Comments on Deep Cold: Alaska Weather & Climate: Cold And SnowyRickhttp://www.blogger.com/profile/03946704894714514716noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-4572286363399496963.post-68185194405563472552017-01-19T09:49:09.920-09:002017-01-19T09:49:09.920-09:00In case you don't have it, here's the link...In case you don't have it, here's the link where I get the upper-air charts:<br /><br />https://www.weather.gc.ca/analysis/index_e.html<br />Richard Jameshttps://www.blogger.com/profile/08313902028896263276noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-78339797564057469562017-01-19T09:42:58.470-09:002017-01-19T09:42:58.470-09:00Thank you for the explanation...it does make sense...Thank you for the explanation...it does make sense. After I wrote above I read your latest posting and saw the 500 mb trough depicted on #4. So in reality the surface High is weak and an artifact (likely) of the cold air above. I've seen this before and now I grasp the connection.<br /><br />We only saw -46F at home but as usual there was and still is a slight NE breeze along College Road in town. <br /><br />GaryNL7Yhttps://www.blogger.com/profile/15874712728971005352noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-65287305583284214132017-01-19T09:31:07.944-09:002017-01-19T09:31:07.944-09:00Thanks, I see exactly what you mean: there is a we...Thanks, I see exactly what you mean: there is a weak surface high analyzed over the northern interior even while there is a trough aloft. This appears to be a good example of what cold air can do: the very cold air near the surface is raising the pressure slightly over the land area.<br /><br />Consider a back-of-the-envelope calculation: a temperature drop from -20°C to -40°C gives a ~10% density increase, and if this is the average difference in the lowest 2% (20mb, ~150m) of the atmosphere, then the mass of the column would increase by 0.2%, which equates to 2mb. This is about the right order of magnitude for the pressure increase.<br />Richard Jameshttps://www.blogger.com/profile/08313902028896263276noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-92092015558216225692017-01-19T09:03:19.573-09:002017-01-19T09:03:19.573-09:00Here's where I'm uncertain. These are curr...Here's where I'm uncertain. These are current surface analysis charts for 01/19/16 that I looked at:<br /><br />https://www.weather.gov/afc/surface<br />http://www.wpc.ncep.noaa.gov/html/sfc2.shtml<br /><br />I assume for today (maybe better for 1/18/16) that there is/was a trough aloft. It's the combination of the two (forecast surface pressure vs aloft) that's visually confusing.<br /><br />GaryNL7Yhttps://www.blogger.com/profile/15874712728971005352noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-46515575240111048522017-01-19T08:01:30.044-09:002017-01-19T08:01:30.044-09:00Gary, pressure is actually quite low at the surfac...Gary, pressure is actually quite low at the surface currently - are you referring to a forecast for high pressure to build in?<br /><br />One concept to bear in mind here is that the rate of decrease of pressure with height is related to average temperature in the layer - cold air is more dense, so pressure decreases more quickly with height; in other words, the 1000-500mb thickness is lower. If the air mass were warmer, then an upper-level trough as strong as the current one would produce much lower pressure at the surface. But nevertheless, there's only so much cold air can do to raise the pressure - there's no way to have high pressure at the surface with such a strong trough aloft.<br />Richard Jameshttps://www.blogger.com/profile/08313902028896263276noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-66351267932098494292017-01-18T22:23:33.210-09:002017-01-18T22:23:33.210-09:00Richard could you offer an explanation for the cur...Richard could you offer an explanation for the current forecast surface High and an upper level Trough that's apparently providing cold temps in Interior Alaska? How do they function independently or combine together in their temperature regimes? It's confusing.<br /><br />GaryNL7Yhttps://www.blogger.com/profile/15874712728971005352noreply@blogger.comtag:blogger.com,1999:blog-4572286363399496963.post-25979439294555458132017-01-17T15:34:34.255-09:002017-01-17T15:34:34.255-09:00Excellent analysis and review Richard. My only sou...Excellent analysis and review Richard. My only source of knowledge regarding cold surface temps under a similarly deep cold column of air was from flying. Unless we get some mixing wind or insolation (not much of that in January) it tends stay cold at the surface and not vary much. The troughs probably help as noted.<br /><br />We're finally getting some of that "Anthropogenic nucleation of air saturated to ice" stuff known as Ice Fog in Fairbanks. The next few days will be interesting and a first experience for many.<br /><br />GaryNL7Yhttps://www.blogger.com/profile/15874712728971005352noreply@blogger.com