Thursday, January 4, 2024

Big Pressure Gradient

There's been a very large pressure gradient across Alaska in the past couple of days, reflecting the contrast between Arctic high pressure to the northeast of Alaska and a very strong storm in the eastern Aleutians.  As of yesterday morning, the difference in central pressure between these two features was 100mb, or about 10%.

Strong winds are the immediate result of big pressure differences, and so it's been very breezy in many places across Alaska; blizzard conditions have been occurring for the eastern Arctic coast.

The 100mb pressure difference led me to wonder about the largest pressure difference ever measured across the state of Alaska.  In the current event, the maximum pressure difference between two land points appears to have been around 90-95mb, judging from model MSLP maps - for example this one from Tuesday night (a range of 944mb to 1036mb).

Using hourly ERA5 reanalysis data back to 1950, I determined that the largest MSLP difference was 103mb, on February 4, 1989.  This was a case with strong high pressure over the interior and southern Alaska (at the tail end of the notorious January 1989 cold spell, with record high MSLP), and only a modest cyclone over the Aleutians.

In contrast, just three years ago the MSLP difference across Alaska exceeded 100mb for only the second time since 1950, with an exceptionally strong western Aleutian cyclone being the culprit rather than a very strong anticyclone over the interior.  This event also saw the lowest MSLP on record at an Alaskan land location, 923mb (according to ERA5 data since 1950).

The time series of annual (winter) peak pressure differences shows no significant long-term trend.  The peak pressure differences of each cold season have occurred in all months from November through April, with December being most common.

There's also no significant overall relationship with El Niño/La Niña, although it's slightly intriguing that the strongest El Niño winters have tended not to produce a high pressure difference.  The current event is therefore a bit unusual in this regard, because we certainly have a strong El Niño in play at the moment.

I'll provide an update with the ERA5 peak MSLP difference for the current event when the data is released in a few days' time.


  1. What is the lowest pressure reading ever recorded at ANC? I saw 28.33 last week.

    1. Wow, that's low.

      Looks like the record is 952.3mb, or 28.12 inHg.

    2. Great thanks!

  2. More storms moving SW---->NE this coming week across Alaska. Wet and warming trend. Plus, the Sun is returning.

    1. El Nino is really flexing its muscles now, in terms of extratropical impacts. Lots to keep us busy in the weather biz.