Monday 10 a.m.
Cooler air advanced from the Great Lakes to the Middle and North Atlantic states during the weekend. The high pressure area marking the center of the cool air mass is moving toward the Carolinas now, and a return southwesterly flow will sponsor a warmup until the next cold front arrives. That flow should be on a line from central New England to southern Illinois on Wednesday, and it will drift southward and stall on a line from North Carolina to southern Missouri on Thursday.
Some showers will accompany the front, and some rain may break out on the north side of it later in the week. At the end of the week and into the weekend, there is quite a variation in model solutions, with some suggesting rain spreads across the Middle Atlantic states then into New England during the weekend.
The dominant cloud type in the summertime is the cumulus. Cumulus clouds can still grow in the fall and winter, but there is less solar heating, and thus less fuel to get these clouds to grow. The clouds in this picture are not associated just with fall, but in summer the same situation would lead clouds with greater vertical development.
We always look back at our previous forecasts to try to learn from episodes in which we believe we could have done better. The following satellite picture shows dry weather today in just the area that originally looked like it would have more rain.
In other words, while late summers in Phoenix have gotten wetter during the last few years, Boston has become drier. Is there anything more momentous or general that we can say about this?
This enhanced infrared satellite picture shows the cold front in the Northeast and the moisture wrapping around Odille on the southwest part of the map.
Across the Central and Northern states, thunderstorms are less common at this time of year than in late spring and summer. One area that has had more thunderstorms than usual recently is across the Desert Southwest.
Last week, I mentioned that longer range computer models were suggesting a major warmup by next weekend. More recent runs have backed off on the that idea. However, there is extreme uncertainty beyond the next 7-10 days. This can be seen by looking at the following map.
n the forecast office, we often track cold fronts with pressure maps like these. The examples are from 4AM and 10 AM today. You can see that the northern part of the front is moving more quickly than the southern end. The arrival of the front signals the start of the cooling trend that is spreading east.