Looking like spring?

2019-03-29 12:16:48.000 – Adam Gill, Weather Observer/IT Specialist

 

So far this spring it has been a cold one across the higher summits and much of New England. This has largely been due to a big ridge over Alaska that has been pushing the cold air in the arctic down into the eastern half of the continental US. We have only had one large melt out this season so far and temperatures did not even get much above freezing. Now that we are getting close to the end of the month, it is looking like we will be about 4 degrees below average. With the warm weather expected for the last few days of March we may raise average up to about 3 degrees below average. For precipitation, we are currently sitting at about 3.30 inches of liquid water, which is well below our March average of 7.67 and with not much precipitation expected, this will remain well below average. Snowfall has actually been just about average. Without many rain events and many of the snow storms that we got were cold so the snow to liquid rations were low. We are sitting at 42.9 inches and the average is about 45 inches.

Now that we are starting to see warmer weather, will it be sticking around? In the short term, we will be getting back into a cooler weather pattern with the possibility of more snow mid-week next week. Beyond that, it is starting to look like warmer weather will be making a much stronger appearance. Since it is a ways out, I will be taking a look at some of the indicators that show a warmer weather pattern rather than looking at what the specific weather would be.

In the near term, looking at next week, the ridge in Alaska is holding strong with cold air over New England. Below is the 500 mb (millibar) height anomalies for next Monday, April 1st. The warmer colors indicate chances of above normal temperatures at the surface and the cooler colors indicate below average temperatures at the surface. There are two anomalously high heights over Alaska and in the North Pacific, with lower heights over New England and this pattern is conducive to the formation of Nor’easters. Many models are showing a Nor’easter forming during this time frame but the track of the low is still very uncertain.

Short Range 500 mb height map
500 mb height map for Monday April 1st. Indicates height anomalies at the 500 mb level. Large ridge over Alaska shows where the warm air is and the cold air is being displaced downstream into the eastern half of the United States.

Below are the model runs of the European and then the United State’s GFS model. They both have a storm but the location is vastly different.

European's model Nor'easter location
Location that the European model indicates for the center of the low pressure system on Wednesday April 3rd. This is just one run and there is still a lot of uncertainty for the exact path of this storm
Location that the Global Forecast System (GFS) model indicates for the center of the low pressure system on Wednesday April 3rd. This is just one run and there is still a lot of uncertainty for the exact path of this storm

This will have to be a storm to watch. There is cold air just north of the boarder that could be pulled into the backside of the storm, leading to snow all the way to valley floors. At the elevation of the summit here though, we will be cold enough for snow even if the cold air does not slide south. As that storm moves up into the Canadian Maritimes, cold air will move into New England before warm air starts to return.

This is when more consistent warm air is expected. The first indicator is the Jet stream over the pacific will become stronger and more zonal, aimed in a west to east orientation aimed at the west coast. This pattern aids in the development of low pressure systems downwind of the Rocky Mountains in the central plains. Due to the counter clockwise rotation of low pressure system, that sets up for a more southerly low level atmospheric flow over New England. Now that we are headed into April, the sun is strong and most locations south and west of us do not have much snow cover. This will allow for the sun to heat the lower atmosphere more efficiently rather than the suns energy going into melting the snow.

Below is the forecasted 300 mb (about 36,000 feet above the surface) wind map for Friday April 5th and you can see the strong jet of air just off the west coast that extends into the central Pacific.

The strength in knots of the Jet stream. Usually strong jet max’s aimed at the west coast with the energy stretching into the central pacific results in a warmer then average temperatures in the eastern US

The ridge over Alaska finally starts to break down and with the jet stream further south in the Pacific will allow for warmer air to move north out ahead of it in the eastern US. Below is the 500 mb map for April 5th, the warmer colors are starting to settle over New England with the lower heights well off to the north.

What the 500 mb height anomalies look like on April 5th. Good indication of warming on the east coast

This pattern is expected to continue into mid-April with above average temperatures expected. It will be a nice change of pace to start to see some more spring like conditions for a little while. Many areas in the valley will see quite a bit of their snow melt during this time. Once all the snow melts, the sun will do a better job of warming up the surface in New England with more frequent 50 and 60 degree days in the White Mountain Region soon!

 

Adam Gill, Weather Observer/IT Specialist

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