Good morning all,
Following on from OldMetMan's comments regarding the NWS discussion, i'd like to add some further information.
I'll try and keep this as simple as possible.
Firstly though, the current weather situation we have here in the United Kingdom, or "reliable timeframe" as it's commonly known as.
This week, Monday to Thursday is looking rather benign, dry, some sunshine and feeling chilly, especially at night time, where frosts may accumilate in favourable places.
We can see this from the following charts: (I'll be using the GFS to illustrate in the reliable time frame, as most models agree unanimously)
Tuesday
Wednesday
Thursday
So, we can see from the above charts (MAX Temperatures) that it will feel rather chilly, especially after the mild(ish) weather we have been accustomed to as of late.
The 500-1000hPa charts are of good use, these measure how warm, or how cold a layer is in the atmosphere. Thickness charts are a good way to measure the probability of snow, or other prospects like warm/cold air.
The change is coming in from our North West of the United Kingdom, and we can see by Thursday night.
We can see on the T850 chart, which measures the upper air temperature's and becomes instrumental to what we recieve on the ground, so to speak. It's also another good tool to use for deciding if you will get snow or not, and the general rule is:
(Maritime flow)
Sea Level: -7c
150m: -6c
300m: -5c
450m: -4c
600m: -3c
I say "General Rule" as it can be different depending on what else is happening weather wise.
So, anyways, we can see from the following thickness chart on Friday there is potential for snow, albeit mainly at elevated levels.
The above chart is the 500-1000hPa. What we are looking for here is the "528 DAM Line" or 528 Dacameters. We want this to be as south as possible if you are looking for cold/snow.
The 850's are showing at -5C.
Using the rule we learnt earlier, places above 300-400m could see some snow.
We can see from the Snow Risk chart below as the front pushes in, NW Scotland and higher ground 400m + is ideal for snowfall.
After this time frame, we are really getting into the unreliable time frame, but it's always nice to check what the charts are showing within the reliable timeframe, as people tend to get carried away with silly posts like:
"No cold for the next 4 weeks"
"No mild weather for the next 4 weeks"
"No snow in December"
"Charts are crap"
Etc etc, you get my point. If anyone can tell you with 100% confidence what the weather will be like in 4 weeks time, then they should be working for NASA/UK Met and running the company. Oh, and placing lottery numbers too.
As I mentioned at the start of the post to go on from what OldMetMan was talking about, we can see as per comment from NWS:
We can see where the Jet is at the moment in Mexico which attributes to the post above, it usually isn't their at the moment.
Maybe this does mean a large pattern distruption, I am not sure, but will have a good look at the charts and data available to us and decide from there.
If we look at the forecast for the Jet we can see it remains very strong for 14/12
But after this is where the NWS discussion and what OldMetMan was talking about might change, around the 17th as we see a strong surge from the Jet over Mexico at 180 hours.
Which looks on course for Central USA & should start to impact upstream around the 17th.
Remembering the Jet Stream from earlier, and how powerful it was, we can see around the time of impact C.USA we have a slack Jet coming from Canada and southerly digging:
I am unsure if this is related, but will post again when I have done some research.
Another thing to keep an eye out on is the potential storm, at the moment it's hitting Scotland, and Western Isles, but needs an eye kept on to track and see how it unfolds, but that's for another post, maybe.
Regards,
Dr. Astro