Cool Trends Persist

Cooler than normal temperatures have persisted recently in both southern and northern Alaska, and a quick glance at UAF's statewide temperature index confirms the decidedly chilly nature of this month for the state overall.  Indeed, the month-to-date average of the UAF index suggests this is the coolest May since 2012, and it might be the coolest since 2001 when the final numbers come in.

It's rather notable that Utqiaġvik hasn't yet reached 32°F this year, and if it happens today or tomorrow it will be the latest since 2001 or 2000.  If Utqiaġvik manages to get into June without a 32°F reading, it will be the latest since 1955.

Here's a map view of the temperature anomaly in the past 30 days, as estimated by ERA5 and ECMWF model data:

Note that the anomaly is expressed in terms of standard deviations, which gives a good sense of how unusual the situation has been: for example, 1.5-2 standard deviations cooler than normal in the vicinity of Cook Inlet.  The standard deviation is calculated for the same 30-day window as the anomaly calculation.

Here's the 500mb height anomaly from the same perspective:

Here's the link to view these graphics for yourself: it's a page that I put together recently.

https://s2s.worldclimateservice.com/wcs/era5_monitoring/

Clicking on the 2m temperature map near Utqiaġvik produces a similar chart to the first one above (confirming the veracity of the model data), but the chart also appends the latest (00UTC initialized) ECMWF ensemble forecast.  Cooler than normal conditions appear likely to persist on the North Slope in the next week or two.

Interestingly, the forecast suggests the 30-day temperature anomaly is likely to become rather strongly statistically significant to the north of Alaska in the coming days:

A caveat is in order, however: part of this anomaly could reflect a discrepancy between ECMWF's current forecast model and the much older model version that is used for the ERA5 reanalysis (historical baseline).  Many tweaks and upgrades have been made by ECMWF since the ERA5 version was implemented, and the new model may have cooler 2m temperatures over Arctic sea ice at this time of year.  We'll find out in a few weeks when the ERA5 data includes these dates and we can do the apples-to-apples historical comparison.

Nevertheless, the forecast does show a robust trough over the Arctic waters to the north and northeast of Alaska, so persistently below-normal temperatures are certainly plausible.