Wednesday, September 29, 2021

Finishing on schedule with timely rainfall

 In the previous posting on the 15th (read it here) I discussed the transition period from the previous pattern to the new one.  I discussed the "maybe" there would be a few opportunities for rainfall as the month ended.  The "maybe" was because of this transition but if the same pattern was still dominating then that would boost confidence.  That appears to be the case.  Looking at this mornings upper air (jetstream) chart....

The red X over the Great Basin has been in place for a couple of days and is poised to to deepen into an upper low dropping south into New Mexico.  But before that happens, a cold front will slide into the central plains and set up a zone of showers and thunderstorms.  Gulf moisture was returning robustly (late September standards) and the interaction with upper level dynamics, the front and the surging moisture should bring widespread precipitation to the plains tonight (Wednesday) and tomorrow.  A second round of more general rains will overspread the area as the aforementioned upper low lifts out into the central U.S., and the most likely time for that will be late Friday and Saturday.  After that storm departs, it appears that it will be primarily dry for about a week.

Now, don't be misled.  Not everyone will get a ton of rainfall through the weekend.  The following map provided by the Weather Prediction Center gives an idea of where the heavier rain will be centered. 

I think that almost everyone across the central and southern high plains will get at least 1/2 of an inch but there will likely will quite a few reports of 1  to 1 1/2 inches and a few locations over 3 inches. 

Also in that previous posting, I had talked about the first cold snap during the first of the week of the 20th.  That happened with low temperatures falling well into the 30s at many locations.  I never saw a freezing report but a local event of freezing occurred it would have been very brief.  Then later in the blog post I threw out the date of October 10 as a possible date of another cold snap but probably not a "killing" freeze.   There is some support that date may be good.

Later into October - I'm not seeing much indication of a BIG cold blast.   BUT - the new pattern is in the process of setting up and rapid changes can take place.  More later....

I'll end this one with this graphic....

That zone between colder than normal and warmer than normal Pacific Ocean waters "MAY" be a big contributor in at least the fall and early winter cold shots.  I'll try and address that in the next posting or two.

Wednesday, September 15, 2021

A transition time for the atmosphere!

For those that have heard my presentations or have read this blog, you know that an entirely new weather pattern starts to form in the fall - centered on about October 1.  What has transpired this first half of September is more than likely entirely the previous pattern but we may be seeing bits and pieces of a new pattern this second half of the month.  In the previous post I did on the 26th of August (click here) I thought there would an increased probability of at least a  couple of "wet" events.  for the second half of September.  More than likely that first chance was the past 36-48 hours and here is what occurred across the area....

But since it appears that "a tiny bit" of the new pattern is showing up, the likelihood of another opportunity for rainfall for the high plains is somewhat in question.  It's not a zero chance, but there is some strong hints that there may not be much for the next 10 days which takes us into late September.  I'm not totally confident of another chance or two, but it would be surprising if we didn't have another system, at least before September is out. 

In addition, a "real" cold front may make an appearance by the first of next week.  The driving force of that "cold" weather is likely a western Pacific tropical storm/typhoon which often causes amplification in the jetstream.   Now I'm not talking about a freeze, but for a couple of days high temperatures may be in the 60s or 70s and lows a couple of mornings next week may briefly fall into the upper 30s (for a minimum) across the high plains.  That period of cooler weather should not last more than a couple of days.

Then as we get towards the end of the month, maybe, just maybe there could be a couple of opportunities for precipitation.  I'll evaluate that during this next week.

As far as the first freeze of the fall?  My gut feeling is it will occur earlier than normal by perhaps a week or so.  If I was to give a date - the guess would be centered on October 10 give a day or two.  As far as a killing freeze?  Probably not yet.  

I'll finish this short post with the outlook for rainfall from the Weather Prediction Center or the next 7 days (into the 23rd), again not much.

Let's hope for that last week of September.