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.
This year, the "slight" category has been divided in two: slight and enhanced. When seen together on an SPC map, the progression makes sense. When the term "enhanced" is used alone, it can be a challenge, at least until we get used to it.
This map shows the pressure analysis and locations of fronts and low pressure areas at 9 a.m. EDT today. Places from Philadelphia northeastward will only warm up if and when the warm front in Delaware passes any given spot. Chill air follows the front in Indiana.
This map shows the GFS forecast for Monday at 2 p.m. ET. If correct, rain will hold off for the Boston Marathon. However, you can see that any speedup of the rain would prove that idea to be wrong.
Another high pressure area will build over the Northeast during the weekend, so sunshine with mild afternoons can be expected. However, this forecast map for next Monday evening shows how extensive and wide ranging the next storm may be.
These maps show how the US model handles the disturbance now causing rain in Tennessee. On the 1st map (for tomorrow), it is embedded in a southwesterly flow. However the 2nd map (for late tomorrow night) shows it turning more toward the course that would take it out to sea.
In the middle of Pennsylvania, rain ended before daybreak, but rolls of sullen clouds presided during the first hours of daylight. A robin takes in the scene.