Copious Moisture

Flood watches are in effect from the Alaska Range eastward to the Canadian border, as a strong storm system drops moisture from a southwesterly flow originating in the tropics.  Here's a surface analysis from 4am today: note the storm tracking into southwestern Alaska from the central North Pacific (click to enlarge):

This morning's sounding from Anchorage measured nearly 1.5" of precipitable water (total vertical water content), which is extremely high by historical standards.  Here's the sounding: note the very deep saturation (dewpoint nearly equal to temperature) and strong southwest winds through most of the column.

Yesterday afternoon's sounding at Kodiak had even a bit more moisture, as is typical.

The highest precipitable water (PW) ever recorded by an Alaska sounding was 1.90" out at Shemya, on the other side of the Date Line, last August.  This is according to the IGRA database, which calculates PW from the surface up to the mid-atmosphere level of 500mb (the air above that level typically holds very little moisture because of its low temperature and pressure).  The western Aleutians are relatively far south, at less than 53°N latitude, and are often exposed to typhoon remnants with high moisture levels.

Excluding data from Shemya, Cold Bay holds the record for highest PW: 1.75" in July 2016.  I'm ignoring data from before 1960 because of low confidence in the measurements.

It's interesting to look at the history of annual maximum PW for each of Alaska's 14 currently-operational sounding sites.  There's a clear trend towards higher annual extremes at the northernmost sites, as we might expect with amplified Arctic warming.  (Note that the charts below use only June-September data so that I could require less than 10% of days missing in each year plotted.  Virtually all of the annual maxima occur in June-September.)

Sites farther south don't show a pronounced trend, but it's interesting to see that the mid-August 2019 rain event involved the all-time record PW at Anchorage and Bethel, and second-highest at Fairbanks:

Results for Cold Bay and Kodiak:

Yakutat and Annette Island both set new post-1960 PW records in late July last year, and the data from Annette shows very high PW in both 2021 and 2022.  This is very likely related to extreme North Pacific warmth in both summers, leading to higher moisture content in the air masses coming off the ocean.