Good morning everyone,
The upper level flow continues to weaken. Look at the map below:
This is the 500 mb map, valid Friday night. 500 mb is around 18,000 feet up. The wind blows parallel to the lines at this level. Each line represents the height at which the pressure is 500 mb. Kansas City is between the 588 line and the 582 line, so our 500 mb height is around 585. These numbers are measured in decameters. So, 585 means 5,850 meters above the surface, or close to 18,000 feet up. There is a 522 upper low near the North Pole. The pressure is 500 mb at the 5,220 meter level way up there. Each line on the map is separated by 60 meters or 6 decameters. The anticyclone is indicated by the highest height areas with the H that I placed over Arizona and off the Florida coast. This upper high has yet to set-up over the middle part of the nation. We will be paying close attention to the flow aloft, as there is a much better chance that some heat will build in near the end of the month.
As you look at the map above, notice that there are only three to four lines across the United States. This is showing how weak the flow has gotten at this level. During the winter months, when the jetstream reaches its peak strength, there can be as many as 15 lines or more across the USA. The flow strengthens in response to temperature contrast, and right now there is very little temperature contrast.
The red arrows show the diffluent flow. When the flow diverges aloft, we will likely have the air below rising to replace the diverging air above. So, conditions will become favorable for thunderstorms near our local area by Friday or Saturday. The very slow moving cold front will be sagging our way, but likely stay to our north Friday and Saturday. Thunderstorms may organize and drift around, but my confidence is still low that we will see rain at any one location, so this is why our precipitation chances will remain low for now. We will up the probability of rain & thunderstorms as the weekend approaches, if it appears more likely. So, watch our weathercasts on NBC Action News and we will go over this set-up as it gets a bit closer.
The flow aloft will continue to weaken during the next two to three weeks, reaching the most likely weakest point of the jet stream, and flow aloft, by early August. After this point, the flow aloft may begin its transition slowly into next falls new weather pattern. So, August, September, and October, are the hardest months to forecast the weather utilizing my theory, the LRC. And, this goes hand in hand with the seasonal forecasts put out by the Climate Prediction Center (CPC). They will tell you that fall is the least reliable time to trust a seasonal forecast. And, this makes complete sense as the new LRC is just evolving at this unreliable time. And, if the 2007-2008 LRC still exists, then there would be a high likelyhood of a cold outbreak sometime in September with an early freeze up north. But, only if the same pattern is in place, and I think it will be in transition by then. Something to pay attention to.
I would like to thank everyone who entered the blogger contest. It is too late to enter. I left the entries at work, but we had more that 150 entries. The average number of 90 degree days forecast between today and August 31st is around 21. The average hottest temperature was right near 100. When I get into our empty NBC Action News studio later today I will get the data and post the entries. The construction of our new set and Forecast Center will begin next week. The floor is now in, and it will be waxed and all shiny by the end of this weekend.
Have a great day!
Gary