No Flooding? Pass the Salt Please.

By -

The Wall Street Journal has an article quoting NOAA's annual spring flooding forecast as calling for a lower than normal chance for flooding this year. Take it with a grain of salt. 


It is important to understand what is being forecast: The likelihood of snowmelt-driven flooding. I agree, the chance of that is lower than normal since snowfall across the contiguous 48 states is much below normal in most areas.


However, this forecast does not speak to the likelihood of flooding from recurring complexes of thunderstorms, so let's address that.  Take a look at the map below. The blues are areas of heavier than normal rainfall the last 90 days.


[caption id="attachment_7839" align="aligncenter" width="727" caption="NOAA data."][/caption]

In and of itself, this is little cause for worry. But, take a look at the forecast rainfall the next five days:


[caption id="attachment_7840" align="aligncenter" width="247" caption="NWS forecast."][/caption]

More heavy rain in some of the areas that are already too wet.  Again, this by itself, is not a major problem. But, when you take the forecast out an additional days, things start to rise to the level of concern:


[caption id="attachment_7841" align="aligncenter" width="955" caption="Ten day forecast rainfall from the ECMWF model. Courtesy of AccuWeather.com's Professional web site."][/caption]

That is a forecast of a huge area of rainfalls of five inches or more. Is this likely to be a perfect forecast? No, it is not. But, that is not the point. We've been seeing a trend recently for heavy rains to develop in the south central U.S. If it continues, spring flooding from the southern Plains into the Ohio Valley (which has also been wet recently) becomes a distinct possibility.


It is far too soon to explicitly forecast flooding. I just want to make sure readers of this blog are not mislead inadvertently by the WSJ story on spring flooding. 

Comments

Post a Comment

Popular posts from this blog

Hilary's Forecast Path Shifts West; Updated 9:20am PDT

By -
Image
The forecast path of the center of Hilary has shifted a bit to the west. This increases the threat to the Southland, especially in terms of flooding.  Rainfall Note the heavy rains are forecast for Los Angeles County. Serious flash flooding may result. Because the forecast path has shifted to the west, that increases the threat of serious flooding in Los Angeles County north into Yosemite and the southern Sierra. It lessens the threat in Utah and western Arizona. While the threat of widespread flooding in Utah and Arizona lessens, note that some thunderstorms with localized heavy rain show up on the map.  In Nevada, the more western path increases the risk of serious flooding around Mt Charleston and into the central part of the state.  Here is the updated  (9am PDT) flash flood risk map. Wind There are already about 40,000 people without power in California, mostly in the center of the state.  The maps above are the peak gusts forecasted with the storm. The highest winds, in general,
Read more

Dangerous Travel Conditions - People Reportedly Stranded

By -
Image
-- Note, more current info available. Scroll up. --- Updated Information as of 8am PDT You are risking your life if you attempt to travel through the purple area.  While the rain has not begun in coastal California, I would urge you to use this time to make any preparations. Power outages have occurred already in southeast California. Here is the latest radar as of 7:55am PDT. As of 6:40am PDT , the radar indicates moderate to heavy rain falling over desert areas of Southern California and far western Arizona (click to enlarge).  Rainfall amounts for the 24 hours ending at 7am PDT show more than two inches have already fallen. There are reports from reliable sources that roads are already washed out and that people are stranded in isolated parts of the desert.  Below is a high-resolution computer model's rainfall forecast from 5am PDT to 11pm PDT Sunday. More than a foot of additional rain is forecast to fall. This will lead to catastrophic flooding.  Here is a map of current watc
Read more

Update on Tornado and Wind Potential; 12 Noon PDT

By -
Image
There was at least one tornado and at least one funnel cloud yesterday.  --- original forecast --- Hilary (the swirly symbol) continues to move NNW paralleling the coast of Baja California, Mexico. The area outlined in red has a significant risk of tornadoe s the rest of the afternoon.  Below is a list of peak wind gusts so far.  Peak winds may increase farther north as the afternoon progresses.  Addition at 12 noon PDT: Sure enough, winds have increased.  Note: If you are in the San Diego area, I recommend not  traveling east on I-8. Heavy rains may cause flash flooding that will involve the highway. 
Read more