HOT AND SPICY...COMING UP
You would never know it by the weather we'll experience the next couple of days but a late summer heat surge is on the way. It's arsenal includes the following ingredients.
Multiple days with highs in the low to mid 90s (perhaps a single day in the upper 90s).
High humidity
Heat Index values of 100 to 110 degrees
Overnight lows in the low to mid 70s
Little if any relief from rain
The heat gets underway this weekend, especially Sunday. Before then, we've got a couple of fine August days to enjoy thanks to a cold front which is racing through the Midwest as we speak. For some, especially in the north widely scattered showers and isolated storms were noted overnight ahead of the front. Amounts in most spots were barely enough to wet the pavement. What's left of those are on the way out and slightly cooler and definitely drier air is moving in. Wednesday's gusty SW winds will be replaced with a brisk WNW breeze that at times could reach 30mph. Here's some of the 10 meter wind gusts indicated by the EURO.
Below you can see the packed isobars in black that deliver the gusty winds.
A band of clouds will exit the south early in the day allowing ample sunshine through the morning. However, some fair weather cumulus will likely dot the afternoon skies. Temperatures will be comfortable in the low to mid 70s and thanks to dew points only in the low to mid 50s, it will be a fine day (aside from the wind).
Thursday night fair skies, diminishing winds, and dry air will allow temperatures to effectively fall. Friday morning will have a September feel with lows in the upper 40s in my northern counties. Note the upper 30s showing up in NC Wisconsin. Fall is waking up.
Friday will be a chamber of commerce day with full sunshine, light winds, no humidity and highs in the mid to upper 70s, A picture perfect day.
HERE COMES SUMMER...
Saturday it's game on for the coming heat as winds return to the south and temperatures begin to climb. What's new from yesterday is that the GFS has come around to the EURO's thinking that the heat dome is strong enough to last through at least Thursday of next week. Yesterday the GFS was very suspicious breaking the heat Monday with a surface high and cold front suppressing the ridge SW. That seemed unlikely and is definitely off the table now.
What you can see in the animation below is the development of the heat dome. A 600dm height contour is very hard to achieve, especially this late in the summer. Yet, you can see it indicated and feeding on itself as it oscillates over Iowa and Missouri for days before breaking down late next week.
Near and underneath of the ridge circulation, the air is being compressed and is forced to sink. When that happens to a gas such as air, it heats up and that is the driving force behind the heat wave. Unfortunately as I've mentioned numerous times, the mixing ratios on the GFS are flawed during the summer which renders the model useless when it come to using it for temperature guidance. At times since last summer the model has been off by 15-20 degrees. Here you can see it has highs next Thursday around 114 degrees. Those would be all-time heat records. No way that is happening!
The EURO generally keeps highs in the low to mid 90s, although Tuesday it does show readings pushing 100. It's depiction of the heat seems far more in line with reality and will be my benchmark for where highs ultimately max out. Also, because of its issues, the GFS is far to low on dew points keeping them in the 50s while the EURO is in the low to mid 70s. The lower water vapor on the GFS is the primary reason it is inaccurately depicting highs in the105 to 115 range. Again, leaning on the higher water vapor of the EURO highs remain in the 90s but with 70+ dew points it will feel more like105-110 degrees on several days. Heat advisories or warnings are on the table.
Since we are still several days away from the advent of the heat, it's hard to pinpoint the hottest days and those refinements will come as we get closer to the event. That said, the potential is there for highs in the low to mid 90s (locally higher a day or two) Sunday-Thursday of next week. That's assuming the heat dome remains in place as shown.
Despite multiple days with significant instability, the warm air aloft will keep a stout CAP in place keeping thunderstorms out of the picture until the heat can shift further south later next week. This is the rainfall forecast on the GFS through next Thursday. Notice how the sinking air under the heat dome diverts showers and storms in a circular pattern around it. That is a classic example of the ring of fire!
Below are the rainfall departures for the same period. In theory, it all fits neatly into the big picture.
With that, I will tie this up in a neat little bow. Until next time, roll weather...TS
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