Tuesday, January 20, 2009

Zonal Flow Ahead Of Next Trough, Snow In The Piedmont

New Poll Added Today

Former poll was do you think the 2009 hurricane season will be bad? 39 votes came in and the results were as follows...

  • Yes, bad as 2005 -- 33%
  • Yes, but not quite as bad as 2005 -- 12%
  • No, but there will be a few big ones -- 48%
  • No, it will be a quiet year -- 5%

    Have you ever heard one of your television weather forecasters talk about zonal flow and wondered what?

    Recall over the past few days we've had a large ridge of high pressure over the western US, and a deep trough of low pressure over the eastern half of the nation.

    As the ridge of high pressure breaks down, or flattens out, so does the trough of low pressure.

    This transition usually results in a zonal flow.

    Think of a roller coaster ride -- with a ridge and trough back to back, upper level winds riding the roller coaster ride along the jet stream (up and over the ridge of high pressure in the west, then down a steep hill to round out the bottom of the trough of low pressure in the east).

    In a zonal flow, the winds pretty much go west to east in a straight line.

    The best illustration of zonal flow is to look at a contoured temperature map, such as the one below.

    With a few exception, you can look from the west coast to the east coast on this map following a straight line, and most all locations along that line are in a similar temperature band.

    It gets a little less defined around the US/Canada border but if you look close you can still draw the line with a slight curve to it in the middle.

    And on this map, that is already done for you with each temperature zone (i.e. 20s, 30s, 40s, 50s, etc.) having a different color.

    The next trough of low pressure (or kink in the zonal flow) will begin the influence the western and northern US early next week as cold air moves down from Canada with a chance of snow.

    Most impacted will be places like Denver, where we are currently in a streak of daytime highs topping out in the 60s and even some lower 70s!

    Early next week we'll be lucky to get above freezing each afternoon here in the Mile High City.


    Snow is falling across much of North and South Carolina, and flakes are expected before sunset in the Virginia Beach vicinity.

    As of this blog posting, up to 4 inches has fallen around the Raleigh/Durham area.

    The CoCoRaHS snow report map will be a sight to see on Wednesday morning, that's for sure!

    We may get some 6 to 12 inch totals in a few spots before all is said and done.

    You can bet it's a heavy, wet snow --- great for making snowmen and having snowball fights!

    The kids (both young and old) are probably having a blast today.

    Blog reader fanghopper left a comment about the blowing of bubbles in sub-zero air over the weekend.

    Dubbed as "hours of entertainment" -- fanghopper says the soap bubbles freeze into a plastic-like consistency, and rather than popping with a burst and a splatter, they sort of collapse on themselves. They also get pretty frost formations on them as they freeze -- the feathery pattern like you see on windows -- that's if you can stay close enough to one to watch it, or capture on on your bubble-maker without popping it.

    And in the comments section of my blog titled "Wild Temperature Swings" -- John has provided some more insight on the throwing hot water into very cold air and watching it vaporize.

    And thanks to BettyAnne for her comments about freezing fog!

    1. I live in Tennessee and we've had snow flurries for the last couple of days. When I check my rain gauge however, this is 0 accumulation of precip. Maybe you could address in a future blog how it could flurry all day and 0 precip accumulate. Thanks.

    2. Greg-

      Are you getting any ground accumulation at all? I can think of two reasons why it might be not showing in your guage, but both require really light and fine snow.

      1) The snow is so light and fine that there's virtually no moisture in it, and it might be sublimating as fast as it's accumulating. But that would probably only occur if it's been bitterly cold, really dry, and also a bit of sun to help the sublimation.

      2) Also with really light and fine snow, and a bit of breeze, it may literally be blowing snow away from, or even out of your guage, depending on how your guage is situated.

    3. I know January has been a pretty dry month for snow in Missouri, and the NOHRSC Snow Analysis site (http://www.nohrsc.noaa.gov/nsa/) shows a lack in other areas.

      Is the whole country experiencing less snow this year?

    4. I am in a western suburb of Raleigh and we ended up with about 6 inches of snow on Tuesday. But, it was so dry that we really had trouble making a snowman bigger than regular sized snowballs. That is really unusal for us here!