Joe’s Weather World: Tipping the weather ever so slowly into Spring (TUE-4/2)
During this time of the year…as we still fight a weather pattern that wants to have some winter elements and some spring elements to it…can be very challenging to a meteorologist. The April sun angle…essentially the equivalent of the 1st week of September sun angle should help warm things up every day…but there are issues sometimes. Cold fronts, clouds, rain, and a bevy of other things can sometimes remind folks that it’s still winter. Remember last April? 3 straight Sunday’s with snow! Remember last winter…our 2nd coldest. It can be a somewhat strange month too…especially the 1st half or so. Then again…severe weather is always possible thins month…and really warm windy days are possible too…it will keep us on our toes I think.
I don’t think this will be in the top 10 of cold Aprils…but I do have concerns that the 10 day period from roughly the 10th-20th could be rather chilly for this part of the country or at least biased cold with a few milder days mixed in. So if you’re a gardener you may want to take note of that.
Today: Variable clouds and cool with highs in the 55° range…could be a few degrees warmer farther south with more sunshine.
Tonight: Partly cloudy and cool with lows closer to 40°
Tomorrow: There may be a few showers scattered around but overall not too bad and milder with highs into the mid 60s…breezy too. Variable clouds.
Thursday: Turning cooler again with some scattered showers around, especially in the morning hours…highs in the 50s
I wanted to touch on the forecast for the middle of the month at the beginning of the blog today…I do have concerns for some chilly days setting up towards the 10th or there after. There are several reasons…by then we should be almost into the mid 60s for highs…so it’s “easier” for us to be a bit below average (or more) with shots of cold air. 2) there is a pattern that may be setting up that would be more favorable for colder air shots moving through the central and eastern US. This is still a bit tentative because when the models have suggested this in the past there hasn’t been the verification that I’d like to see.
The pattern that is being “suggested” are tanking NAO and AO indices. The NAO refers to the North Atlantic Oscillation and the AO refers to the Arctic Oscillation.
0 is considered a “base” state and for most of the winter these values have been positive. It should be noted that this winter was cold locally and regionally with values that would not necessarily suggest the cold…so these indices are to be taken as just a factor and not necessarily a “put all my forecast eggs in this basket” type situation.
With all of that out of the way…let me show you the “forecast” values…again just a model forecast.
Let’s start with the AO…and I’ll explain what these indicators are in a minute. Note the open circles forecast…and see how it dips at the end of this week into the negative and keeps going down.
Now the NAO
That tanks even more so.
Also important to note that there is a lag between the tanking and the weather effects…
Now an explanation. The AO or Arctic Oscillation has been talked about before but not for awhile. When it’s negative, especially substantially negative we’re vulnerable to a southwards trend in the jet stream. This allows a farther south push of colder air from the northern latitudes.
When the NAO is negative, especially when these two indicators are in tandem…there is a tendency(!) for cold air to be drained from Canada.
The above graphics are via the NC Climate Office and here is a good explainer of what’s happening.
Now there have been more than a few model busts with these indices over the past 6 months…so I’m not putting everything into this “basket” right now…but I sort of see how the models are forecasting this cold biased pattern to develop. There have been about a handful of days this year that the values have been in the negative so again…let’s see how this plays out.
I seem to remember, and maybe I’m wrong with this, that these values went negative last early Spring too…and we know how that turned out. I’m trying to verify.
Anyway…it’s NOT a great recipe for prolonged warmth and the model data this morning is showing a 5+ day run of chillier weather heading towards the mid month period. Take a look at the EURO ensemble forecast for the 5 day period leading up to the 15th or so. This map shows the anomalies up at 5,000 feet or so.
Those values are in °C…so about double that for °F…and that’s almost 10° or so below average up above us…that should mean at least cooler than average weather in the Plains.
How wet it will be remains to be seen…there are some rain chances WED>THU then again later SAT into SUN…and also later next week it appears…so the pattern isn’t dry for any length of time. This will affect the farmers and the fields and potentially slow down field work in the Plains I think.
The good thing about that set-up is the reduced severe weather risk (if it happens) locally. Colder than average temperatures isn’t a good ingredient in many cases for severe weather risks in the Plains.
Let’s see how this all pans out. I’ve been watching the soil temperatures a bit more as a result of last weeks crabgrass lesson from TJ…and those soil temperatures are still pretty chilly. I did notice in my yard a pretty decent henbit outbreak in progress. This is going to be a bad year I think for my yard…I lost a lot of grass for whatever reason last season and I tried to get my front yard back to respectability with limited success.
Our feature photo comes from Austin Hamilton up in IA…