Wednesday, November 13, 2013

Record Moisture Over Bethel

This morning's 3 am balloon sounding from Bethel measured an atmospheric profile with higher precipitable water (total column moisture) than ever observed before in November (1.10" vs 0.98" in 1991 and 1970).  Remarkably, today's precipitable water measurement also matches the record for October (1.10" in 1970).  The chart below shows the lower atmosphere profile: note the extremely warm saturated layer up to 6000 feet and freezing level above 10000 feet.


The eastward-moving surge of warm moist air is bad news for the interior, as it translates into a freezing rain event for some.  Freezing rain is already being reported as mixing with snow at Fairbanks airport, though it's not clear if this is correct as the 3 am sounding showed temperatures still far below freezing throughout the column.

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9 comments:

  1. NL7YNovember 13, 2013 at 9:22 AM

    Just walked the dog at 8:30 am...raining as reported at +15F. Everything's covered with ice at valley level in town. Good day for a pot of beans and a good book.

    Gary

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    1. Richard JamesNovember 13, 2013 at 10:11 AM

      Thanks Gary, that's helpful and remarkable. There must have been a heck of a lot of warming in the Fairbanks sounding between 12 and 14 UTC.

      I see freezing drizzle - not rain - is being reported at locations from Tanana to Kotzebue. According to conventional thinking, the difference is FZDZ can occur with a column completely below freezing, whereas FZRA is melted snow and requires above-freezing temps aloft.

      Would be interesting to hear Rick's comments on today's cloud microphysics.

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    2. NL7YNovember 13, 2013 at 10:35 AM

      Thanks for the info Richard as I'm not an obs expert like the NWS folks. The precip may have properly been FZDZ given the temps involved...all I know is that it was still wet when it hit my clothing and wasn't snow or frozen droplets.

      I'd call it rime ice if I were flying due to its coarse opaque nature on the coated substrate, which today would be ill advised. Now (10:20 am) it's snowing.

      Maybe this would be a good info topic for a future Blog...FZDZ vs FZRA. I looked up the difference but it's still somewhat confusing.

      Gary

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    3. Richard JamesNovember 13, 2013 at 11:08 AM

      Thanks Gary. Perhaps it was FZDZ after all, although the airport reported FZRA for hours. Are you able to estimate how big the drops were from their diameter on your clothing? 1 mm or greater would certainly be considered rain by most.

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    4. NL7YNovember 13, 2013 at 11:39 AM

      They were small...1-2 mm I'd guess, and certainly not abundant as in the typical rain events I've seen cover a parked aircraft or power lines in winter. Coarse opaque rime ice formed with a low rate of accretion on surfaces at home.

      Local Fairbanks PAFA METAR obs at that time:

      PAFA MP 13 1725Z OVC010 2 ZRS-F 18 12 00003 994 77% 18

      Pilot report over PAFA @ 1751 during climb after departure. FZ RA noted surface to 8K MSL. Moderate icing surface to 11K:

      FAI UA /OV FAI/TM 1751/FLUNKN/TP DH8A/SK TOP110/WX FZ RA SFC 080/TA M08 AT 110/IC MOD SFC 110/RM DURC ZAN

      So, whatever it was should be definable via soundings if available. Note that despite the reported icing above by the Dash 8, it wasn't called as clear ice, so I suspect it was heavy rime or whatever the ZRS-F was as reported at the surface.

      Gary


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    5. Richard JamesNovember 13, 2013 at 12:08 PM

      Thanks, that is very helpful. Definitely rain, and Rick confirms this.

      Rick also notes there was an 18Z sounding from Fairbanks! This link will show it for the next few hours:

      http://weather.rap.ucar.edu/upper/pafa.gif

      I agree this is worthy of a blog post soon.

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    6. NL7YNovember 13, 2013 at 12:44 PM

      Excellent info re 18Z PAFA Skew-T. It'd be helpful to expand on this event and how to best interpret the sounding data relative to the surface obs. Winds at altitude are brisk from the west.

      Now for the coming backside of the Occlusion and the forecast wind event soon to follow. With the icing holding the pre-existing snow cover and new snow loads on the way trees and power lines are sure to suffer.

      I've got my backup genset ready to power the heaters if required.

      Gary

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  2. Climatologist49November 13, 2013 at 10:56 AM

    I once saw a METAR from Dalhart, TX (KDHT) where the precipitation was FZDZ+; i.e., heavy freezing drizzle.

    Here's an article that discusses a freezing rain event with the entire column below freezing: Rauber R., M. Ramamurthy and A. Tokay, June 1994: Synoptic and Mesoscale Structure of a Severe Freezing Rain Event: The St Valentine's Day Ice Storm, Weather and Forecasting, 9, 183-208.

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    1. Richard JamesNovember 13, 2013 at 11:11 AM

      Thanks Brian, I'll have to look at that paper carefully.

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