Does it seem like the Spring and Summer have been somewhat cooler than normal? More cloudy than usual? More humid than normal? More wet than usual?

That’s only because for most of the area it has been on all points.

Blame the jet stream as usual. I’ve blogged and tweeted about hot dry high pressure ridges and cool wet low pressure troughs many times in the past. Often the jet stream will get stuck in a pattern, or a pattern will repeat. That has been the story of the past 4 months and it looks to continue TFN with only occasional variation.

The news making heat and drought out West occurs under an upper level high pressure ridge (H). When there is a ridge out West there’s usually a trough in the East. When there is a trough out West there is usually a ridge over the East. The patterns called Rossby Waves work in tandem across the entire hemisphere and therefore across North America.

Usually we get highs of 90 or above for many weeks in a row once the 500mb jet stream height gets to 588 or above. But that won’t happen if the moisture levels of the atmosphere are high under those heights because we get more humidity, clouds, and showers and thunderstorms than normal. That in turn holds down the temperatures during the day.

This has been the recent story and looks to go on with just a few day to day or week to week variations.

Dew Points in the 60s to 70s represent tropical air. And the Southerly air flow between the Bermuda High to our East and a low pressure trough to our West keeps the high humidity coming in from the Caribbean and Gulf of Mexico. The upper low will fade away with time but not disappear entirely.

So far the Spring and Summer are playing out as forecast in the long-range outlook many months ago.

We are in the Dog Days of Summer, but with the Dog Day heat MIA.

Look at all the moisture (humidity, dew point, precipitable water anomaly charts):

DEW POINT AND COMFORT LEVEL:

And all that moisture when activated by the sun (daytime heating in the diurnal pattern) the atmosphere becomes unstable and the high dew points are fuel for clouds and pop-up showers and thunderstorms peaking in coverage during the late afternoons.

Slow moving July and August storms are known as prolific lightning producers and torrential downpours with large raindrops.

DOPPLER RADAR EARLY MONDAY AFTERNOON 7/12:

“Air mass” thunderstorms are NOT caused by a front or low pressure system but rather from a moist air mass heated by the sun to the point the atmosphere becomes unstable. (high CAPE, low negative Lifted Index)

UNLIKE other types of forecasts, some thunderstorm forecasts must be updated roughly every couple of hours.

“Every dark cloud has a silver lining”

The upside of this pattern is an increase in beautiful sunrises and sunsets and more rainbows. I’ve seen three rainbows including a double in just the past couple days.

For more follow me on Twitter @MellishMeterWSB.

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