Wednesday 10 a.m.
Temperatures a mile overhead in the Northeast today would support afternoon ground-level temperatures well up in the 80s today... if this were July. In July, the sun climbs high in the sky. Mornings warm quickly; soon it is very warm or hot. Not so fast in October, though. The longer nights allow more time for the temperature to drop to the saturation point, and soon fog forms.
The fog prevents much solar energy from the reaching the ground to cause warming. If there are higher clouds around like there are at many places today. the warming process is delayed further... and before we know it the sun is sinking back toward the horizon. The changing amounts of clouds and fog can wreak havoc on temperature forecasts. Despite this, we can say confidently that temperatures in Middle and North Atlantic states will run higher than the long-term averages for this time of year.
Fog may redevelop late tonight and longer tomorrow morning. On Friday, however, slightly drier air will advance from the west and southwest... and with the breeze picking up, it could turn out to be the warmest day of the week. A cold front will arrive and be followed by noticeably cooler air for the weekend. The cold front is associated with a low pressure area that will cause heavy snow across parts of the far North Central states and adjacent Canada. This video shows the expected progression of events:
Dense fog has often proven to be very challenging for painters and photographers. You can see why with this image from a webcam overlooking the area between the Statue of Liberty and the buildings of Manhattan.
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.