March Climate Data

March was another warmer-than-average month for most of Alaska, although not excessively so; it was the 15th warmest March in the NOAA/NCEI history since 1925.  The only region that wasn't warmer than the 30-year normal was the west, and the Bering Strait region was actually significantly colder than normal.  Here are my usual "percentile rank" maps, showing how the month compared to the same month in the past 30 years. 

The monthly average mid-atmosphere circulation pattern isn't what we would usually think of as producing a warm month for the state as a whole: a ridge to the north and a trough over the Gulf of Alaska tends to be a colder pattern in the cold season.

However, there were tremendous changes in the flow orientation through the month.  The first 10 days were very warm owing to a Bering/Aleutian trough (a typical warm pattern), but this reversed to an Aleutian ridge by late in the month.  Here are 500mb height anomaly maps for one-third portions of the month:

It seems that the northern Bering Sea and Bering Strait region managed to remain north of a frontal zone for much of the month, and so Arctic air dominated that region and kept temperatures relatively low.  The persistent frontal zone can be seen on a map of solar radiation, which was below normal (i.e. above-normal cloudiness) from the central Bering Sea to Bristol Bay:

March precipitation was below normal for more of Alaska than it was above normal, and according to NCEI both the Northeast Interior and Northeast Gulf divisions were significantly drier than normal for the second month in a row.

Given that March is typically a dry month, the precipitation anomalies made relatively little difference to the snowpack, which remains quite similar to a month earlier - although the positive anomalies have generally diminished in the western and northern interior.

Snowpack remains seriously lacking in the southwest, parts of South-Central, and the Seward Peninsula, according to ERA data:

Winds were lighter than normal for large parts of the state in March, which makes sense in view of the overall circulation anomaly (ridge to the north, trough to the south).

The extended winter period of November through March ended up as the sixth warmest on record - not as anomalous as December through February (third warmest).  November was the coolest month relative to normal (although still not cooler than normal), and January was by far the warmest and wettest.

The North Slope climate division had its third warmest November-March, trailing only 2017-18 and 2018-19, and the Northwest Gulf was fourth warmest on record.  In the case of southern Alaska, it's worth considering again how remarkable it is that this kind of warmth can prevail with a significantly negative PDO phase, although admittedly the PDO index did rise to neutral by the end of March.  Here's a chart of the PDO index for the last decade or so (click to enlarge).

Precipitation for the extended winter season was above normal for most of the state except the Panhandle, largely because of January; but as noted above, this generally only produced a good snowpack to the north of the Alaska Range, because of all the warmth (again, especially in January).

More on Persistence

I suspect that not everyone finds this as interesting as I do, but nevertheless here's a follow-up on seasonal temperature persistence in and around Alaska, this time from a map perspective.  Using ERA5 reanalysis data, I calculated the correlation of consecutive monthly temperature anomalies from 1950 through 2020, with the linear trend (specific to each month) removed.  A positive correlation means that the sign of the anomaly (i.e. above or below trend) tends to persist from one month to the next, but a negative correlation indicates that it tends to reverse.

It is usually a safe rule of thumb that weather and climate anomalies tend to be "persistent" even over land - there is a positive autocorrelation - so it's a surprise to see that the overall correlation is slightly negative for a portion of east-central Alaska and an adjacent zone in northwestern Canada.

This is actually the only place on the planet that has a negative month-to-month correlation, according to ERA5 data for this particular historical period.  There are plenty of regions with very low correlations, but this small region just to the north of Eagle is the only place with inverse persistence.  Here's a map for the Northern Hemisphere extratropics.

The tendency for temperature anomalies to reverse sign is mostly found in the winter for interior and eastern Alaska.  Here's the December-January correlation:

The rest of the year is added below.  The maps confirm the observation I made in the previous post: for the state as a whole, persistence is very much heightened in April-May and in July-August.  One might say those pairs of months are temperature twins: they tend to resemble each other in terms of departure from normal.

The other striking point is how much higher persistence is in summer than in winter for the maritime southern regions, and for late summer and early autumn near the Arctic Ocean.  Clearly the warm season temperature anomalies are dominated by slowly-varying ocean temperature regimes in locations close to open water, whereas relatively chaotic atmospheric flow patterns tend to control the month-to-month temperature changes during winter or over ice-covered ocean.