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  1. USCAPEWEATHERAF
    Latest Entry

    The title is "A Wild Weekend to remember, a love story" there will be a continuation of Marie and Walter's weekend in the second short story and then a continuation of the story.

     

    James Warren Nichols, written by

    A couple, a love story.docx

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    April is seen as a transition month during the severe weather season, as the frequency of tornadoes typically picks up rather quickly through the month. Despite what the calendar has to say, tornado activity has been fairly lackluster so far this month. In fact, after moving well above the average to-date tornado count in late February, the U.S. has steadily been losing ground. As it stands now, through April 18, the U.S. is near average this year for tornadoes, but with a relatively quiet rest of the week forecast, it looks like the country will fall below average for the first time since February. (The 1986-2015 climate period of 30 years is used for this average)

     

    The month of April started with the “dreaded” trough of low pressure across the Northeast. Locally, it was cold and snowy after a winter that was relatively mild and snowless. Likewise, after an active winter season for tornadoes, severe activity has been sporadic over the past several weeks. With all of this said, a pattern change is finally on the not-to-distant horizon, with troughiness returning to the West and the welcomed return to ridging across the Southeast U.S. This pattern will broadly support a more active period of weather across the central states, including an uptick in tornado potential.

     

    If we’re keeping track, a pattern change was slated for mid-April a long time ago, back as early as mid-March. That pattern change has been delayed somewhat as pesky troughing across southeastern Canada hangs on and the models display a glaring ridge (positive height) bias. This past week saw a shuffling of the pattern, but an omega block led to a messy setup and only a few isolated tornado reports in parts of the High Plains. The models often have issues handling larger scale pattern changes, but now that such a change is effectively inside of a week, confidence is increasing and the models are getting into good agreement.

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    By this weekend, the first in a series of troughs is likely to swing across the western half of the country with some modest ridging to the east. Watch for lee-side cyclogenesis in the central High Plains vicinity between Sunday and Monday. While this is encouraging, the setup is not without flaws. This first trough ejection and evolution of the system is kind of junky (for the lack of a better word) in terms of tornado potential. There’s some instability as early as Saturday progged in the north-central states, but shear is forecast to be lackluster. The similar is the case for Sunday and Monday from the Plains into the Upper Midwest – generally marginal overlays between modest shear and favorable instability as a frontal system slides east. This is subject to change, but the trends are not particularly impressive. It’s the middle and latter portion of next week that really bears watching, figuring that this first system may at least get the gears turning for building a warm, moist air-mass over the Plains.

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    With the Euro and GFS in good agreement (including the ensembles), it’s fair to use the GEFS analogs as a baseline for what type of setup we could be looking at, somewhere in the Tuesday to Saturday (April 26-30th) time-frame. Even before looking at specific dates, the string of digging troughs in the West with increasing moisture return in the central states sets the stage for a classic period of near-peak/peak tornado season activity. This does not necessarily mean we will have a massive number of tornadoes or that there will be a high-end setup, but at the very least, it is probable that tornado activity will markedly pick up as the week wears on. Now speaking of those analogs, there are some big dates and periods that show up, in order from ranking:

    1. 5/10/1953: A couple of days removed from the day 6-10 analog, but this date featured a localized outbreak of strong tornadoes in the Upper Midwest.
    2. 4/25 – 4/29/1994: 124 tornadoes in five days, including an outbreak from the 25th into the 26th.
    3. 5/12 – 5/13/1980: Not an outbreak, but strong tornadoes in Missouri followed by a pair of EF-3 tornadoes in Michigan the next day.
    4. 4/17/1995: AR/OK/TX outbreak with 21 tornadoes.
    5. 4/26/1991: Plains outbreak with 53 tornadoes, including the Andover, KS EF-5 tornado.
    6. 5/2/1994: The only analog in this bunch that didn’t have notable tornado activity.
    7. 5/7 – 5/11/2008: 122 tornadoes in five days. (2008 has been an analog on the radar for a while, also one of the busiest spring seasons of this century)
    8. 5/8/1979: 21 tornadoes, though mostly in Florida, two were reported in Iowa, including an EF-3.
    9. 4/30/1978: 15 tornadoes in the southern Plains, including 6 strong tornadoes and a mile-wide EF-4 on the northwest side of Oklahoma City.
    10. 5/4 – 5/6/1960: 71 tornadoes in three days from the Plains into the Midwest, including a long-track EF-5 tornado in eastern Oklahoma.
    11. If the pattern unfolds closely to what is modeled, it would appear that April certainly has the potential to go out with a bang.

     

    Through some of the research I’ve done with a May tornado outlook for USTornadoes.com, I noticed that the analogs have things in common. Without giving away too many of the details, one of the common themes in the analog was for the potential for violent tornado events in May. It could be the case that we’re just getting warmed up next week…

  3. For far western areas along I-81 between I-64 and OKV

    An area of low pressure will move out of the northern Gulf of Mexico and up the east coast tomorrow and Wednesday. As it does, light precipitation will begin to overspread the area early tomorrow morning and will increase in intensity throughout the day … before beginning to taper during the overnight and possibly end as a period of snow Wednesday.

    Initially, there will be just enough cold air in place for some spotty flurries during the predawn hours Tuesday morning. Precipitation type will quickly shift towards freezing rain and sleet by 7:30am. As warmer air continues to move in with heavier precipitation through the day, freezing rain will transition to a plain cold rain. As typical, deeper and sheltered valleys will hold to freezing rain the longest … possibly into the late morning hours.

    Steady rain will decrease in intensity after midnight Tuesday night as colder air begins to filter in on the back side of the storm. Any leftover precipitation will begin to mix with sleet and snow again early Wednesday morning and eventually end as light snow/snow showers, as precipitation fully shuts off Wednesday afternoon.

    Wintry accumulations Tuesday will likely not amount to much at all … up to a coating of snow/sleet and up to 0.1” of ice accretion in the very coldest valleys (where freezing rain will hold on the longest). I do not expect roads to be that much of a problem tomorrow … icy spots should be limited to bridges and overpasses I think. This is not a great setup for a high impact freezing rain event … but that does not mean that slick spots cannot develop.

    Snow/sleet accumulations that occur Wednesday will likely total an inch or less for most. This part of the storm remains the most uncertain in terms of sensible weather. If colder air filters in more quickly than expected, then we will see a change over to snow earlier. There is also a question as to how much moisture will still be available and how efficient snowflake production will be aloft … both factors will have a big impact on the end result.

  4. The Quasi-Biennial Oscillation (QBO) is a cycle of zonal wind in the equatorial stratosphere with a period that varies between 24 and 30 months. This oscillation is a product of downward propagating alternating wind regimes. The current method of monitoring this oscillation is through an index, calculated by the zonal wind anomaly at 30hPa averaged along the equator. This method excludes information on the vertical structure of winds in the stratosphere, and presents the QBO as a one-dimensional temporal oscillation.

    Presented here is a new framework for monitoring the QBO. This framework incorporates both the oscillation in time and in space. The two leading principle components (PCs) of equatorial stratospheric zonal winds are calculated from NCEP/NCAR reanalysis monthly mean data. These PCs are then standardized and used as X and Y coordinates in a 2-dimensional phase space. A phase angle can then be calculated from the coordinates, forming a new index that is much more representative of the state of the stratosphere. The results show a very clear pattern of zonal wind and temperature regimes in the stratosphere.

    Furthermore, from each of these phases, there are physical connections to characteristics in the troposphere on a monthly to seasonal basis. These include the distribution of tropical cyclone activity, the El Niño / Southern Oscillation (ENSO), and the extratropical pattern. This new framework for monitoring the QBO is shown to be much more applicable to seasonal forecasting.

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    Compare the EOF-constructed oscillation to a 52-month reanalysis segment

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  5. Same general theme, with a slight shift south along the southern edges and a more pronounced southern shift towards the upper part of the map. Risks are generally to the higher side on the southern fringe areas if the models are to be believed (especially if the overnight front-end thump is fairly wet).

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  6. Wow
    Latest Entry

    By Wow,

    Some non-mets have asked for blogs recently and we're aware there are plenty of members here who are just as informative as a degreed meteorologist. Therefore, we'll allow access to blogs for non-mets by request and allowed on a case-by-case basis. We're stilling figuring exactly how to go about doing this but you can still reserve your place once we get a plan in place. Just PM one of the admins.

    Thanks.

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