Your Fourth-Cast

Good morning all, and happy 4th of July weekend!

The holiday typically brings to mind swimming pools and barbecues, corn hole and fireworks. For many, tomorrow will see the type of summer weather necessary for these activities to be enjoyable, but the experience won’t be universal.

A look at the midlevels shows a pretty bipolar pattern over the CONUS, with moderate ridging centered over the four corners region and a longwave trough positively tilted from the northeast through the south-central US. The longwave is sort of split into two regimes, an intense closed low over New England and a far more diffuse and poorly defined trough axis that digs as deep as the western Gulf.


The way I see it, the two things worth worrying about for the 4th are showers and cool temperatures. We can start with trying to pinpoint negative thermal anomalies, but remember- a -5ºF anomaly in northern Mississippi does not a bad Fourth make. Rather, it is anomalies either substantially negative or in places that aren’t that hot in the summer that require focus.

The big ole’ midlevel low in the northeast will deliver both, as suppressed heights and an offshore surface low pull temperatures down to 20ºF below average. Brrr!

Across the southeast and south central US, troughing will also be associated with near to below average temperatures, but it’s so warm normally this time of year that the thermometer shouldn’t inhibit BBQ activities.

The Southwest will also see negative temperature anomalies, which alone shouldn’t be enough to make the fourth messy. But the reason for these cool temps may: the longwave’s transport of Gulf moisture towards the northwest, which will incite monsoon season storms south and east of the Four Corners. These storms should be scattered, but they could inhibit fireworks where they occur.


Showers will also be possible under the closed low in the southern Northeast, as cool midlevel temps there could destabilize the atmosphere enough to allow popup storms to develop. These showers will be quick moving, but could scatter Fourth plans where they occur. Small hail and brief downpours could occur! To the north, across Maine, a more steady, stratiform rain threat will be likely, which will really mess with plans. Sorry!

Isolated thunderstorms will also be possible in a belt from S. Texas to N. Minnesota, as an unstable airmass advected north from the Gulf will evolve to the east of a broad surface high.

There it is, folks! Enjoy your Fourth!