Monday, April 7, 2014

April 13-15 Potential Late-Season Snowstorm

WARNING: The chances of a significant snowstorm in April are VERY low. This post is only showing one model's output, and is made to alert people that there could be some snow in this timeframe. I do NOT expect we see these amounts verify exactly.

I'm watching the April 13-15 timeframe for what could be a strong storm system resulting in, yes, snow.

Shown above is an image depicting the most recent ECMWF model snowfall forecast for a potential April 13-15 snowstorm. The exact image showing the ECMWF snowfall output cannot be displayed for copyright purposes. In this most recent forecast, we saw a swath of 2 to 6 inches of snow stretching from northern Missouri into western Iowa and central Illinois, before moving northeast into both land masses of Michigan. Inside that accumulating snow swath, we then see a rather large area of 6 to 12 inches-plus of snow from western Iowa and northern Illinois into southeastern Wisconsin, before continuing into the northern LP of Michigan. As I mentioned above, I do not expect we see these snow amounts hitting for this timeframe; this post is merely to alert people about the potential for snow.

Tropical Tidbits
There is some merit to the idea that we may see a strong storm system, as the ECMWF is suggesting. Shown above was the observed 500mb height anomaly chart over the Western Pacific, where cool colors depict negative height anomalies/stormy weather, and warm colors represent quiet, warm weather. On the morning of April 6th, we saw a trough moving through Japan, possessing a pretty decent strength. This is significant, as it directly relates to what we may see in this April 13-15 timeframe .There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Thus, we can expect a storm in the US on an April 12-16 period, and the April 13-15 ECMWF snowstorm falls right within this timeframe. Additionally, this trough in Japan brought along some pretty cold weather, which COULD contribute to additional chances for snow in this potential storm system.

Looking at the raw ECMWF surface pressure forecast for the morning of April 14th, we see the storm system at a pretty low minimum central pressure, likely below 1000 millibars, in the middle of Missouri. The ECMWF model may be locked on to this snowstorm idea, but its ensembles are much more uncertain.

The image above shows the projected mean surface pressure by the ECMWF ensembles, as well as the spread among all ECMWF ensemble members in the shown colors. We first observe how the ensembles are much less enthusiastic about the idea of a storm system for this timeframe, only bringing a minimum 1006 millibar swath of low pressure over an area just to the east of the ECMWF model. This sort of weaker projection is to be expected, as these ensemble means take the average of 52 ensemble members, unlike the ECMWF model, which only shows one solution. The next item we observe is the swath of oranges and yellows over the Plains and Midwest. These warmer colors indicate a higher spread in the ensembles; in other words, the ensemble members are in higher disagreement with one another over this higher spread envelope, thus indicating increased uncertainty. While this would initially disprove the idea of a storm system in this timeframe, note how the highest spread is located further west of the ensemble low pressure alignment, more in line with the ECMWF model. All in all, this means that the ensembles are seeing this idea of a storm, but aren't biting yet.

To summarize:
• A potentially major storm system is expected in the April 12-16 timeframe.
• Colder than normal weather may arrive with this storm system.
• Model guidance is hinting at a snowfall event during the April 13-15 timeframe, in conjunction with this potentially major storm system.
• There is high uncertainty with this potential event. Caution must be used.



Anonymous said...

Part of me hopes you're wrong but the other part..... I would so bring the sleds back out.

Anonymous said...

Large April snows are not that uncommon. Look at 2013 and the major snow event that took place in early May-2013. Like last year, there's plenty of cold air on the N. American side of the hemisphere and with the large snowpack in Canada this year, there's still plenty of cold available to drain into the US.

Andrew Ditch said...

Your winter was right on with my forecasts. I give both of us an A-. Next winter will be warmer in the Northeast but wetter.

Anonymous said...

These is an absolute awful forecast. How can you say that much snow on your map if you have high uncertainty. You are making people worried mad, sad. That is what i call an alarmist. In my area next week is going to be 40s and 50s and rain according to major stations and I'm in the snow. I did not know where you are getting this but i take it as alarming people in the wrong way by putting 6-12+ and even any snow will put people over the edge. If i were you i would check next weeks forecast for those areas before you make these forecasts.

Ps. It wouldn't even stick because the ground is warming now so your are wrong about any accumulation, at least in my area. This is also long range so don't make people dread over next week.

I would like an apology set out on your website for alarming people including me. I am not happy cause now this makes me really worried and I want warmth and your wrong.

Andrew said...

Anonymous at 3:11: If you read closer into the map, you would see it is an interpreted ECMWF model snow map, not mine. No apologies will be issued, because no apologies are needed. I stand by my forecast.
If anything, you should be making an apology for the incorrect interpretation and rush to judgement of this still-valid forecast, in addition to the less-than-necessary remarks about the forecast's integrity.

Anonymous said...

In regards to the potential snow during the 13th-15th, my area is forecasting snow. Mind you, I am on the Canadian side of this swath of snow and it is quite common to have snow all the way into May. I wouldn't be surprised one bit to see more snow.

Anonymous said...

Andrew at 3:11.

I still stand by my opinion. It will not snow in 40-50 degrees and I am a weather expert. I have been studying the weather for years and I love it. I did look at your maps but if your writing other things in your own words then it's your forecast. I still stand by my opinion that it's a bad forecast. Sorry if I offended you.


- anonymous

Anonymous said...

Anonymous at 3:11pm,
I feel your pain! I understand the frustration, I hate cold, snowy weather also!
I say we all in our minds (as the mind is very powerful) see highs in the mid 70's to 80's, sun shinning, flowers blooming, grass green, & the sky blue! Doing all kinds of summer fun things! It only take 5 mins per day thinking on the above & it will happen! Oh, did I forget to mention all the above really helps when your on a high does of me! And a sun lamp helps to! Anything to get thru it, (legal) I'm all on it!!
Take care,

Anonymous said...

Anonymous at 3:11, You are a jerk! You deserve NO apology whatsoever. It's idiots like you that make this world a bad place to live when you open your mouth.
Andrew, I'm sorry. I just couldn't help it.

unknown said...

I'm anonymous at 3:11.

Thank you Bree. Someone that understands.