Tonight’s images come from the Climate Prediction Center (CPC) and are forecasts for the next 6-10 days (above) and 8-14 days (below). These are forecasts of temperature relative to normal. As I mentioned in the last few days, the ridge in the east that was responsible for the extremely hot temperatures along the east coast last week is now redeveloping over the central United States. As such, expect above normal temperatures in the near term.
Today is day 18 of VORTEX II and the armada once again deployed on thunderstorms in eastern New Mexico. These thunderstorms posed a low risk of tornadoes, but did give the armada a chance to practice deployment strategies in preparation for what appears to be another active pattern. More on this below.
How did the VORTEX II armada fair today? Well, at least five separate vehicles will need to replace windshields after today’s adventures. We probably won’t have a final count until sometime late tonight or tomorrow morning. The broken windshields were the result of hail up to the size of baseballs falling repeatedly on portions of the armada. If you are curious as to what this might look or sound like, then take a look at this video of the Oklahoma City hail storm that occurred yesterday. Warning, while the hail sound is loud, if you listen close enough you may hear some foul language.
So, above I mentioned the fact that we appear to be heading into a fairly active severe weather pattern. Above is a temperature forecast for the next 6-10 day. Instead of actually predicting what the high temperatures might be, this is a probability that a given location will experience a high temperature greater than normal for this time of year. In general, cool temperature indicates upper-level troughing and warmer temperatures indicate upper-level ridging.
If one were to translate the temperature forecast above into a forecast for mid-troposphere trough/ridge forecasts (below), we see that a trough is forecast for most of the western United States and a ridge is forecast for the eastern United States. This kind of pattern is conducive for extremely warm, moist air originating over the Caribbean Sea to move northwestward into the central United States. (For the more technical readers, this occurs because the persistent southwest flow at mid-levels results in a lee trough on the eastern slopes of the mountains that allows southeasterly winds to develop from the western Caribbean Sea into the northern plains.)
The warm, moist air is just one of the necessarily ingredients for severe thunderstorm development. We still need something to lift this warm, moist air into the troposphere to develop thunderstorms.
Typically on the east side of a large trough (such as the one forecast to develop over the western United States), minor shortwave troughs “eject” northeastward from the base of the trough to the crest of the ridge to the east. Ahead of each of these shortwave troughs rising motion is found. Without going into all the details, this rising motion that can act to lift the warm, moist air into the troposphere. Now, it is almost impossible to predict the exact timing of these shortwave troughs, but it is almost a sure bet to they will be there.
Like I discussed on 8 May 2010 (Day 128) for model forecasts, it is possible to construct analogs to previous events based on the forecasts above produced by the Climate Prediction Center (CPC). In the bottom right of the image below, analogs for this predicted pattern can be found. For convenience, I’ll post them below the image.
The analogs (click on the red ones to see the storm reports) are:
11 June 2005
17 May 1962
04 June 2005
27 May 1978
15 May 1999
23 May 1975
21 May 1991
07 June 2004
08 June 1984
14 May 1998
Most of these dates are either severe weather outbreaks themselves or are dates very near severe weather outbreaks. Like I said previously about analogs, you can’t take an analog as a specific forecast of what is going to happen. It should be used as a piece of guidance; it is merely one piece of information regarding a particular pattern’s potential. It’s a form of pattern recognition, and in this case the pattern appears to be an active one.
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.
