Wet Weather Patterns

Unusually wet weather has shifted from western to interior Alaska in the past 10 days, with upwards of 2 inches falling from the vicinity of McGrath to the hills north of Fairbanks.  A 30-day estimate shows 6-8 inches over most of the western interior, and that's over 3 times the normal amount for the time of year across the mid-Yukon region in the vicinity of Galena.

Fairbanks saw over an inch of rain late last week, and the Friday-Saturday two-day total was the greatest in September since 2016.

The 500mb height map for Wednesday through Sunday last week shows the same westerly flow regime that I highlighted previously, driven by unusual ridging (high pressure) to the south of Alaska.

Above-normal pressure to the south of Alaska is a key ingredient for wet weather in Fairbanks; here is a composite of the 500mb height maps for the 5 wettest 7-day periods in September from 1981-2025.

The composite analysis also shows that unusually low pressure from the Beaufort Sea to Arctic Canada tends to be involved when Fairbanks is very wet at this time of year.

The figure below shows the same Fairbanks-focused analysis for all 12 months of the year (click to enlarge).  The wettest weather in Fairbanks is associated with a North Pacific ridge in all months of the year except June and July, which are distinctly different; the wettest weather in high summer is instead linked to an Arctic trough axis extending all the way down to the Gulf of Alaska.

How about unusually dry weather?  Measuring this on a monthly basis (rather than 7-day periods), we see more variety in the flow patterns, but in general low pressure over the North Pacific favors dry weather in Fairbanks from September through April, whereas warm-season dryness (May through August) is particularly associated with a ridge axis over interior Alaska.