I first did a blog last Monday the 23rd on the cause of our heat wave and drought. I did a blog on the prospects for an end to the heat wave on Wednesday the 25th (the first day of autumn). This is an update of both.
It’s the jet stream. It’s always the jet stream. The jet stream is both the result of weather and a mover and shaper of the weather.
It represents a baroclinic zone, the boundary between contrasting air masses as it moves generally from West to East. Simplifying things you generally find the cooler temperatures to the left or poleward of the jet flow and warmer air to the right or equator-ward of the jet stream flow and the wettest storm track in-between.
For this reason across the nation it is typical for opposite weather in opposite parts of the country at the same time. Something we’ve been seeing for a long time now, cool-wet Northwest and hot-dry Southeast.
We have been under a Great Smokies high pressure ridge which is a Westward extension of the subtropical Bermuda high in the Atlantic.
The jet stream does not flow in a straight line though it bends dips curves and swings forming what are known as Rossby Waves forming “high pressure ridges” and “low pressure troughs”. When the pattern becomes amplified or abnormally strong we get extremes of weather and if a jet stream blocking pattern forms, the jet stream configuration can get stuck for extended periods of time making extremes such as floods or drought, heat waves and cold waves last a long time.
The bright colors in the chart below represent upward vertical motion of air that creates precipitation. Notice under the high the colors are muted indicating mostly downward sinking air currents, the opposite of what is needed for precipitation and the downward sinking air currents also add compression heating:
SNOW SO FAR:
MORE SNOW FORECAST:
COLD NW HOT SE trough vs. ridge:
THE GREATEST PRECIPITATION IN-BETWEEN WITH THE “RING OF FIRE” JET STREAM BAROCLINIC ZONE:
Over the next few weeks the jet stream is forecast to finally de-amplify and the heat ridge over the Southeast will break down and the jet stream flow will “flatten out” some becoming more “zonal” West to East and the troughs and ridges begin to move again taking the crazy extremes with them:
In fact the ECMWF Deterministic/operational model suggests a deep trough coming East in 8-10 days. IF, if true that could bring us some real good and badly needed rain around that timeframe early next week:
Until then, only the very lucky get any rain the next 5-7 days:
But with that jet stream change comes cooler temperatures, not cold but much lower despite still being a bit above average for the coming weekend into next week highs in the 80s and lows in the 50s and 60s with low humidity (if we’re lucky maybe some highs only in the 70s later next week--normal high this time of year is 78):
MODEL ENSEMBLES AND BLEND:
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