Ramblings of a Graduate Student

Last night I mentioned the persistent upper-level high (referred to as an upper-level ridge) that was redeveloping across the western United States.  In that post I mentioned that one result of this upper-level high would be warmer than normal temperatures across portions of the west.  Another impact is a lack of precipitation.

The image above displays the current “Drought Monitor” for the United States, including Alaska and Hawaii, produced by the National Drought Mitigation Center.  Areas shaded in yellow (bad) to red (worst) indicate areas where there is an ongoing drought.  Notice how for most of the country, little to no drought is found – including places in southern Texas that were experiencing an extreme drought just last summer.  One place where drought is a developing concern is the western United States, which has been under the west coast ridge for a good portion of the winter. This west coast ridge extends all the way up into Alaska, and the beginnings of a drought are observed there as well.

Another place that is experiencing a drought is Hawaii.  This is the result of a different upper-level high (also the result of an El Nino winter).  This upper-level high over Hawaii made my Snow Shot of America project “interesting” as the lack of Hawaiian precipitation has resulted in less snow on the peaks than is normally expected.

As we enter February, one of the world’s biggest sporting events is about to take center stage – the Olympics.  This year’s winter Olympics are being held in Vancouver, British Columbia (Canada) – about 120 miles north of Seattle, Washington.  This part of North America typically experiences a cool and rainy winter, allowing for a lot of snow to fall in the higher elevations – perfect for winter sports.  In fact, the National Severe Storms Laboratory (NSSL) has one of their experimental mobile radars in Canada to provide additional radar support.  (You can view this radar data by clicking here!).  Unfortunately, this year has not been typical.  We are currently in the El Nino phase of the El Nino Southern Oscillation which usually results in a more southern track for low pressure systems and storms across the United States.  For places in the Pacific Northwest, the weather tends to be warmer and drier than normal, and places in the southern United States tend to be cooler and wetter than normal.

The warm temperatures in the Pacific Northwest have resulted in a lack of falling snow, and a melting of snow that has previously fallen.  As you can imagine, this is causing all sorts of headaches for the Olympic Games organizers.  Recent news reports state that the Olympic organizers have resorted to trucking snow in from other mountains to ensure the Games will continue as planned.  Since the Olympic Games start in less than two weeks, I thought we’d take a look at the official National Weather Service forecast (provided by the Climate Prediction Center, [CPC]) for the northwestern portion of the United States.

The image above is the current 8-14 day (10-16 February) temperature probability outlook from the CPC.  Areas shaded in red indicate a greater than 33% chance that temperatures will be above normal during the 7 day period, areas shaded in blue indicate a greater than 33% change the temperature will be cooler than normal, and areas in white indicate equal chances that the temperature will be above, below, or near normal.  As you can see, the CPC does not forecast explicitly for British Columbia, but if we connect the Pacific Northwest forecast with the Alaskan forecast, we can assume that the forecast would be for a greater than 50% chance of above normal temperatures for the start of the Olympic Games.  This certainly is not good for the events requiring snow!

What if the temperature forecast is wrong and temperatures are near or below normal – which would support snow to fall?  Well, the image above is the CPC forecast precipitation probability outlook from the CPC.  It’s similar to the temperature outlook, except green implies a greater than 33% chance of being wetter than normal and brown indicates a greater than a 33% chance of being drier than normal.  Once again assuming what the CPC forecast would be for British Columbia, we see that there appears to be greater than a 40% chance that it will be drier than normal for the start of the Olympic Games.

What about for the entire month of February?  Well, the CPC is once again forecasting a greater than 50% chance of temperatures being above normal…

… and a greater than 40% chance of being drier than normal.

It is important to understand that these are probability forecasts, and not guarantees.  A 40% chance of being drier than normal means that there is a 60% chance of being normal or wetter than normal.  Furthermore, just because an area is drier than normal doesn’t mean that there won’t be any precipitation.  It just means that precipitation will probably be lighter than normal when it does occur and that you may go longer between precipitation events.  The same can also be said of the temperature.

So, if the Pacific Northwest is forecast to have temperatures that are above normal, and precipitation that is below normal, one might think that the chances of a drought occurring should also increase.  Well, in the figure above, you can see that the CPC is forecasting drought conditions to either develop or persist across a good portion of eastern Washington, northern Idaho, and fast western Montana.

The flip side to the drier than normal Pacific Northwest is that southern California and the southwestern United States should be slightly wetter than normal.  This should help with the ongoing droughts there and hopefully help restore water tables to near their normal levels.

Over the past week, a series of storm systems have walloped the west coast of the United States with wind, rain, and even a rare southern California tornado!  So much rain has fallen in such a short amount of time, mudslides are becoming a worry.  Today’s set of  images attempts to put into context just how much rain has fallen in southern California in terms of the last six months rainfall total.  Please note that today’s rain is *not* included in these totals!

Also, continuing with the tornado watch theme from yesterday, a rare tornado watch for southeastern California and southern Arizona was issued by the Storm Prediction Center earlier today.  This is the eighth tornado watch this year (also the eighth tornado watch issued in the last 36 hours!).

The image above displays the “normal” expected rainfall for 14-21 January.

The image above displays the observed rainfall for 14-21 January of this year.

The image above displays the departure from normal rainfall for 14-21 January 2010 in terms of inches.  Several places have received more than 8 inches more than normal.

The image above displays the departure from normal rainfall for 14-21 January 2010 in terms of percent of “normal”.  Several places have received more than 600 percent of their normal rainfall.

The image above displays the departure from normal rainfall for the past 180 days, ending 21 January in terms of inches.  Even with the heavy rains of the last week, most places in the desert southwest still remain several inches below normal.  Places that are not significantly below normal are typically within 2 inches of normal.  When you consider how much rain has fallen over the past week, one begins to appreciate the drought that was plaguing the southwest.

The image above displays the departure from normal rainfall for the past 180 days, ending 21 January in terms of percent of normal.  Even though a lot of places are within 2 inches of normal, they have received only about half to maybe three-quarters of their normal rainfall.  This goes to show just how little rain the southwest receives – they can be within two inches of normal and still only have 50% of what they would expect.

Also, not everywhere in the last two images have below average rainfall over the last 180 days.  Places along the coasts and in the higher elevations of California are above normal – however, a significant portion of that has fallen this week!

And last, but not least, the outline and (color-filled) counties included in the desert southwest tornado watch!