Monday, December 3, 2012

No Change in Outlook: Central U.S. Moisture Prospects Improving!

Here is the forecast moisture for the next 5 days ending at 6pm Saturday evening:
That is some nice moisture for the Ohio and southern Mississippi River Valleys.

On Friday, I wrote a posting, Is This the Long-Awaited Pattern Change? which described my analysis of what appeared to be a good chance of significant moisture in the Plains and Midwest the middle third of December. That forecast still looks good.

This is the new (00Z) NWS GFS model valid at 9pm next Monday evening. It shows a strong upper atmospheric low near Lubbock (arrow) which is an excellent pattern for moisture in the central and southern Plains.

Here is the forecast moisture through 9am Tuesday morning (11th).
The same color scale is in use here as in the map at top. Moderate to heavy snow accumulates over the eastern half of Kansas (in the unlikely event this is a perfect forecast) and an additional 2 to 2.5 inches falls from central Arkansas to western Kentucky which is in addition to the 1.5" forecast during the first five days (top map). The cumulative effect of the two storms is for some areas to get 4 to 5" inches of moisture.

And, the good news doesn't stop here. There is at least one more storm that will cause additional rain and/or snow in the drought areas of the Plains and Midwest before the middle third of the month is over!

Just remember: You heard it here first!

4 comments:

  1. I'd like your opinion on how much effort goes into historical model validation. I'm also curious on how often the models themselves are modified.

    Reason I ask is that when one reads the technical weather discussions issued by the local NWS offices, the following phrases pop up quite a bit:

    "Model X tends wet."
    "Model Y tends not to forecast open waves well."
    "Model Z does not do well in progressive weather patterns."
    "Model Q has a warm bias, especially when there is deep snowpack."

    Hope the forecasted pattern change validates. Snowpack in the CO Rockies is abysmal (~50% of normal) which is compounded by the fact that last year's snowpack was also quite a bit below normal.

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  2. Brian, excellent question but I can't give a comprehensive answer in a blog comment.

    The validation is done objectively (principally through root mean square error and other metrics) and through experience.

    For example, the European model handles hurricanes on a consistently better basis than the US GFS.

    The European tends to "dig" low pressure systems moving into the Southwest too far to the south.

    Both models usually (more than five days out) start convective precipitation too far east.

    In this and other ways human forecasters can add value and provide an optimal forecast given the state-of-the art.

    Thanks for the question.

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  3. Mike, love the blog...especially the behind the curtain weather/forecasting discussions. I'm a structural engineer by trade but have a keen interest in all things 'science'.

    Any chance you could do a daily update on this system? Hopefully the moisture pans out because we sorely need it throughout the Great Plains.

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  4. Hi Seth, I did an update about an hour ago. The forecast looks about the same...which is good news.

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