Thunderstorm Possible Through This Evening

As expected, showers are popping up in the southerly flow west of the Cascades.  We just had our first lightning strike between Yamhill and Gaston near Highway 47 too.  This shower is headed northeast towards Forest Grove and Cornelius.

The showers die off this evening, but then we’ll see showers return each of the next three afternoons as cooler air moves inland.

Chief Meteorologist Mark Nelsen

37 Responses to Thunderstorm Possible Through This Evening

  1. Kassie97222 says:

    So… nothing but light to moderate rain today… a couple short lived sun/cloud breaks… wheres the action at???

  2. Very heavy shower dumped 0.26″ rain between 4:30 and 5….

  3. pappoose in scappoose says:

    Some Stray Albino Donkeys wandering about!


    SHORT TERM FORECAST…CORRECTED
    NATIONAL WEATHER SERVICE MEDFORD OR
    211 PM PDT WED APR 11 2012

    .NOW…
    AS OF 200 PM PDT ISOLATED THUNDERSTORMS HAVE DEVELOPED ACROSS PORTIONS OF THE AREA. OVER THE NEXT HOUR EXPECT THESE ISOLATED
    THUNDERSTORMS TO CAUSE OCCASIONAL CLOUD TO GROUND LIGHTNING STRIKES…BRIEF HEAVY RAIN…PEA SIZED HAIL OR SMALLER…AND GUSTY WINDS OF 15 TO 25 MPH.

    • pappoose in scappoose says:

      Point Forecast: Portland OR
      Last Update: 2:16 pm PDT Apr 11, 2012
      Forecast Valid: 4pm PDT Apr 11, 2012-6pm PDT Apr 18, 2012
      Late Afternoon: Showers likely and possibly a thunderstorm. Some of the storms could produce small hail

  4. W7ENK says:

    The sky to the South of downtown Portland looks nasty right now!! 😀

  5. weathercrazy82 says:

    Witnessed what I believe was a brief funnel north of Vancouver around 115. Around the same time, my station in BG recorded a peak rain rate of 3.05″ an hour!

  6. W7ENK says:

    Another chance for more laser-guided thunderstorms this afternoon?

    (See photo above for reference)

  7. emcsqrd says:

    Starting at 7am this morning, I received .4 inches of rain in 20 minutes during a very heavy shower; at one point my rainfall rate was 2.67″/hour!

    • emcsqrd says:

      By the way, this is “Dave in SW PDX (235′)”, aka “emcsqrd”… WordPress is being wonky again.

  8. cphatts says:

    How does the NSW calculate the percentage number of “chance of showers” for a given day? I’ve lived in Portland for 15 years, watch the weather religously, and have found that when the NWS gives a percentage number for showers, you can almost always double or triple it. For example, if they say 20% of showers it seems like it actually rains at least 75% of the time (at least some point during the day). How to they calculate this because it always seems way off?

    • W7ENK says:

      Best I can come up with:

      It is not an exact science, but they combine barometer measurements, forecast models, and math equations such as the Percent Mean Absolute Deviation (PMAD) as well as others. See the second link for forcasting accuracy equations.

      Use of forecast models

      An example of 500 mb geopotential height prediction from a numerical weather prediction model: In the past, the human forecaster was responsible for generating the entire weather forecast based upon available observations. Today, human input is generally confined to choosing a model based on various parameters, such as model biases and performance. Using a consensus of forecast models, as well as ensemble members of the various models, can help reduce forecast error. However, regardless how small the average error becomes with any individual system, large errors within any particular piece of guidance are still possible on any given model run. Humans are required to interpret the model data into weather forecasts that are understandable to the end user. Humans can use knowledge of local effects which may be too small in size to be resolved by the model to add information to the forecast. While increasing accuracy of forecast models implies that humans may no longer be needed in the forecast process at some point in the future, there is currently still a need for human intervention.

      Analog technique
      The Analog technique is a complex way of making a forecast, requiring the forecaster to remember a previous weather event which is expected to be mimicked by an upcoming event. What makes it a difficult technique to use is that there is rarely a perfect analog for an event in the future. Some call this type of forecasting pattern recognition. It remains a useful method of observing rainfall over data voids such as oceans, as well as the forecasting of precipitation amounts and distribution in the future. A similar technique is used in medium range forecasting, which is known as teleconnections, when systems in other locations are used to help pin down the location of another system within the surrounding regime. An example of teleconnections are by using El Niño-Southern Oscillation (ENSO) related phenomena.

      Analog model – A model based on similarities between the system under study and another system or process.

      Analytical model – A model that uses classic methods such as calculus or algebra to solve a series of equations.

      Conceptual model – A simplified representation of the system being examined.

      Continuous model – A model that uses continuous simulation, as opposed to a single-event model.

      Deterministic model – A model that produces the same output for a given input without consideration for risk or uncertainty.

      Empirical model – A model represented by simplified processes based on observation, measurements, or practical experience rather than solely on principles or theory. A lumped model is an example.

      Explicit model – A numerical model that uses parameter values or unknown variables at the beginning of a time step in the computational algorithms.

      Implicit model – A numerical model that uses parameter values or unknown variables at the end of a time step in the computational algorithms.

      Mass balance model – A model based on the conservation of mass and focuses on balancing inputs and outputs from the model area. Also known as a zero-dimensional model.

      Numerical model – A model that uses a numerical method to solve a series of equations, as opposed to an analytical model. The results from numerical models are often approximations, while analytic models produce exact solutions.

      One-dimensional model – A model that includes only one space dimension.

      Pseudo-deterministic model – A semi-distributed model.

      Stochastic mathematical model – A model that includes statistical elements and produces a set of outputs for a given set of inputs. The output represents a set of expected values.

      Two-dimensional model – A model that includes two space dimensions, usually horizontal and vertical averaging.

      Public uses
      An example of a two-day weather forecast in the visual style that an American newspaper might use. Temperatures are given in Fahrenheit. Most end users of forecasts are members of the general public. Thunderstorms can create strong winds and dangerous lightning strikes that can lead to deaths, power outages, and widespread hail damage. Heavy snow or rain can bring transportation and commerce to a stand-still, as well as cause flooding in low-lying areas. Excessive heat or cold waves can sicken or kill those with inadequate utilities, and droughts can impact water usage and destroy vegetation.

      Source(s):
      http://en.wikipedia.org/wiki/Weather_for…
      http://en.wikipedia.org/wiki/Forecasting

      ~~ Or ~~

      They flip a coin, roll a 20-sided die, and then use the outcome to determine the number and color of darts to throw at a map. :mrgreen:

    • W7ENK says:

      Another interpretation:

      In Washington, Oregon, and British Columbia, we have a different interpretation of precipitation forecasts. If the weatherman says there’s a 20 percent chance of rain, that means it will rain 20 percent of the day. If there’s a 50 percent chance, it will rain 50 percent of the time, etc., up to 100 percent, which means, of course, a typical January day. This interpretation seems to be quite accurate.

    • cphatts says:

      A classic example is todays forecast calls for “showers likely”. “Likley”? How about showers are GOING to happen!?!

    • pappoose in scappoose says:

      Weather forecasters never say any type of weather is coming for sure. Can’t ever be wrong if you just say it’s likely/possible!

  9. bgb41 says:

    4/10/2012 Oregon (All) Temperature Summary

    Warmest:
    High:78 at Rye Valley(I-84(2230 ft)
    Low: 50 at DW2682 Portland(213 ft) & MORGAN MOUNTAIN(4200 ft) & Cascade Locks St(151 ft) & Fremont Bridge W(270 ft)

    Coldest:
    High:40 at BIGELOW CAMP(5120 ft) & SWAN LAKE MTN(6800 ft)
    Low: 26 at CRANE PRAIRIE (5500 ft ) & Sand Creek (US 9 (4525 ft )

    Largest Diurnal Change: 46 degrees
    Rome (75/29 ) (4049 ft )

    Heaviest Rainfall:
    0.67″ at CW9669 Springfie(462ft)

  10. pappoose in scappoose says:

    Hahaah!

  11. Picked up about a 1/2″ in an hour.

  12. runrain says:

    Activity moving up I205 here. Looks dark to the south. Will keep our eyes and ears in alert!

  13. Darral C says:

    just had a cell move through McMinnville

  14. Kassie97222 says:

    I want some thunder too!!!!!!!!!

  15. pappoose in scappoose says:

    Bring on the Stray Albino Donkeys!

  16. AlohaWeather says:

    I can’t wait to see some of this action 😀

  17. Roman~Snow-Zone-Monmouth, Elv. 223' says:

    Mark we got thunder, gusty winds and rain down here!

  18. W7ENK says:

    YAY!!! \^_^/

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