A series of low pressure areas, each with a warm front ahead of it and a cold front following, will move from northwestern Canada to the northern or central Plains, then over to the East between now and early next week. Places north of each storm's track will have an episode of accumulating snow with cold winds, whereas places south of each track will have little or no precipitation of any kind. On the north side, there will be some temperature variation, but for the most part it will quite cold. South of each track, there will be wild swings in temperature as mild air sweeps in as the storm approaches, then cold winds erase any hints of mildness once the storm goes by. In this video, the GFS sequence is shown.
This week, a fascinating conference on weather and climate is taking place at Boulder, Colo. Reports from the scene yesterday marveled at a presentation by Dr. Howard Bluestein, where stunning imagery from severe weather events revealed much more detail than is currently seen by most operational forecasters.
Another presentation included a look at a new scheme for depicting and describing the risk of severe weather. The previous scheme included slight, moderate and high. As long as you remembered that slight was to be thought of as comparative term (more slight than moderate, but more serious than a depiction of no risk), you could relate to it. On the radio, however, if you say the risk of something is slight, I think many people take it as meaning there is not much to worry about. However, slight actually was the first level of enhanced risk.
The new idea has five categories of risk. The lowest is called marginal, then the more familiar slight, followed by a new classification of "enhanced." Enhanced is between slight and moderate. When you see all the terms together, there is some logic to the progression. However, when taken by itself, the term "enhanced" could be confusing. On the radio, you might hear, "There is an enhanced risk of severe thunderstorms today." Will people remember there are two additional levels of enhancement called "moderate" and "high"? I cannot confirm that the new scheme is actually in effect, but that was my impression from seeing a tweet from the Boulder conference. These maps show the old and new schemes.
The second concern is Erika. The map below shows what many different models area saying. While there is a good agreement in the short range, the longer-range spread is quite larger, with tracks ...
This picture shows where Erika is. The various models show a track toward Florida with a lot of uncertainty after that. If it does make it to land, then moves slowly (steering forces look weak), it could be a major rain producer.
It is way too early to be definitive about these storms, but the many models being used in predicting the track have closer agreement than many storms have at this point.
On this satellite picture, you can see a cold front approaching the Appalachians. That front helped produce thunderstorms in the Midwest yesterday, but that activity died out overnight. It is likely to reactivate today, with...
...shows a north-south trough line over New England. Moist air will approach this line from the southeast while northerly breezes bring in dry weather west of the line. As the front stalls then slowly backs up, some moisture can spread westward later in the weekend.
A cold front advancing eastward from the Great Lakes and Ohio Valley is sponsoring showers and thunderstorms from Lake Erie to West Virginia. The setup favors even more moisture getting involved, as suggested by the surface pressure map: