Meteorologists are in agreement that forecast skills drops off the further one predicts into the future. In fact, according to an American Meteorological Society policy statement, “The current skill in forecasting daily weather conditions beyond eight days is relatively low. However, products designed to highlight significant trends (e.g., warmer than normal, wetter than normal), such as 6–10 day and 8–14 day temperature and precipitation probability outlooks, often have useful skill.”
Note that the use of “normal” (in a mathematical / statistical sense) is bothersome, because weather conditions are rarely “normal.” Instead, the term “average” would be better suited in the above description, for improved public understanding.
The National Oceanic and Atmospheric Administration’s (NOAA) National Weather Service (NWS) runs computer models out to two weeks or more in order to detect trends and address 6- to 10-day and longer “outlooks.” The use of the term “outlook” brings with it it’s own hints at uncertainty.
Note that there are also shorter-term “outlooks” that address more short-fuse problems such as severe weather, winter storms and flooding, situations in which more pinpoint forecasts are required.
With this framework in mind, it’s now time to look ahead to the next two weeks through the latest GFS (Global Forecast System) computer model. The model output should generate sufficient concern for anyone fed up with the winter to date. That’s because the upper-level western ridge and the upper-level eastern trough that have persisted across the U.S. for much of the past three months are expected to continue. However, storminess is likely to increase, especially across parts of the East Coast from New England southward to the Carolinas.
Take a look at the surface weather forecasts for the period Feb. 22 – Mar. 9, 2014 (slightly more than a 2-week period) shown in Figures 1 to 6. It is easy to see many large, intense low-pressure systems (with central pressures similar to those found in some intense hurricanes), along with large, intense high-pressure systems. On some days, according to the GFS model, there could be as much as an 80 to 100 millibar (2.36 inches to 2.95 inches of mercury) pressure difference across North America and nearby ocean areas. Since average global sea level pressure is around 1013.2 millibars (29.92 inches of mercury), this pressure gradient translates into about 10 percent of the average global pressure value.
While many winter storms are expected to appear during the upcoming two-week period, perhaps the most significant is the one that should develop off the Carolina coast on Feb. 26, 2014 (Fig. 3). During each of the ensuing 24-hour periods, this winter storm’s central pressure drops more 24 millibars (Figs. 3 – 5). This yields two successive 24-hour periods in which the storm satisfies, “meteorological bomb” criteria. This would make it a meteorological bomb squared!
During the upcoming week, a series of arctic high-pressure systems moves southward from Canada, gradually allowing temperatures to fall across the northern Rockies and much of the eastern two-thirds of the U.S. Look for below or much below average temperatures for most places east of the Rockies. Only the southern tier from California to Florida will escape the onslaught of these chilly air masses. For the following week, the cold air will remain across much of the east (Fig. 7).
Out west, storms affect Pacific Northwest, but, for the most part, graze only northern California. It does not appear that there will be much, if any, rainfall for drought-stricken and water-starved areas of the southwest U.S.
Again, just to reaffirm, this story involves a two-week weather outlook. It should not be used to forecast site-specific winter weather conditions on any particular day in any particular place.
© 2014 H. Michael Mogil