Today's video includes a time-lapse movie with cumulus clouds as well as the forecast through the coming weekend. Around the Great Lakes, stubbornly cool air aloft contributes to the chance of daily afternoon showers or thunderstorms. However, at most times and most places, the vast majority of the time will be dry.
Some of the cool air aloft moves over the Northeast as well, and that can lead to spotty afternoon showers and thunderstorms... mainly west and north of I95. This weekend, a switch to more southerly flow aloft can bring very moist air toward the region, leading to widespread showers from the Appalachians to the Atlantic. In areas where clouds and showers are most numerous, daytime temperatures will not get out of the 70s (rare for the first weekend of August).
On the following map, we see the upper air flow around 3.5 miles overhead. I also highlighted the temperatures at two spots. The site in Michigan had a temperature of -18 C, which is just below zero degrees Fahrenheit. Near Las Vegas, the temperature at the 500 mb level was -4 C, which is 25 degrees F. In a trough, the 500 mb height is lower than it is in a ridge.
It is interesting to contemplate that even when Death Valley, California, has a temperature of 110 or 120 degrees, you only have to go up a little more than 3.5 miles to find temperatures at or below freezing.
The cold front is embedded in a large area of clouds, showers and thunderstorms covering the middle of the country. It will advance past the Northeast coast by the end of the day Sunday. The frontal zone is shown on this picture from late morning Friday.
When weather systems are relatively weak, small scale variations cause forecast uncertainty because several different weather types (such as showers, sunshine, cloudiness, etc.) can coexist in the same region and change constantly. This map shows such a pattern:
Some of the thunderstorms can become severe, with damaging wind and brief cloudbursts of rain. The greatest chance for locally severe storms should be in the "S" areas highlighted on this map (based on the NWS Storm Prediction Center's guidance).
There is a slight risk for severe thunderstorms later today from north-central Tennessee up across Indiana and Ohio to Michigan and eastern Wisconsin (shown by the "S" area on the map below. Thunderstorms are not predicted for areas near the coast from Delaware to New England.
It is not going to snow any time soon, but in any type of weather the flag is a symbol of freedom. This holiday weekend we celebrate the contributions of those who were there to defend the freedoms we enjoy in these times.
Once again, the rain will miss much of central and northern New England. The region has been in a dry spell, as evidenced by its appearance on this U.S Drought Monitor map.