Fickle Fairbanks

I forecast balmy breezes for Fairbanks, and after warming a bit, Fairbanks whirled around and stabbed me in the heart with an icicle:

Well, part of the mystery is solved. Regarding what happened to the warm weather, the answer is that it arrived on schedule. At 850 mb levels, 4,000 feet above Fairbanks, temperatures are currently close to freezing. But that warmer air is "decoupled" from the surface - it's just sailing over, and past Fairbanks.

When the warmer air first arrived, it had sufficient momentum to push the cold surface air out of the way, and surface temperatures warmed up to just above 0 F. But drainage flows, continued radiational cooling, and simple thermal inertia of the cold surface soon reintroduced cold air into Fairbanks, and the southerly air flow does not have enough speed and turbulence to dislodge the colder air. So, temperatures at the surface remain cold.

Wind speeds should remain low, until Saturday and Sunday, when they should pick up. Unfortunately, the wind direction will be from the east, so it's unlikely to be a warming wind (but it just might be if it forces the breakdown of the wedge of cold air at the surface).

The National Digital Forecast database forecast looks warmer, but that depends on the warmer weather actually getting there.

Nevertheless, if skies should cloud up in preparation for precipitation, temperatures should rise, since radiational cooling will be stymied. The FNMOC forecasts suggest that no such precipitation is in the forecast, however, in conflict with the National Weather Service's forecast of Wednesday and Thursday ppt. So, will it snow, or not?

There is a little band of negative vorticity (500 mb) scheduled to pass over Fairbanks on Thursday evening, so it's possible it will snow a bit then. Nevertheless, it doesn't look like a lot of ppt. So, maybe temperatures will rise briefly on Thursday, then fall backwards again.

Here is that current Alaska weather map, with pop-ups. Delta Jctn/Ft. Greeley (at higher elevation) is at +18 F: Eielson is at -16 F.

So close, yet so far away.....

Right now I'm thinking: cold, Wed.; warmer Thurs. evening; cold Friday, warmer Saturday, etc. Just a real schizophrenic forecast, driven by the whirl of vortices around a common center over the Bering Sea, whether the vortices are retreating or advancing, whether or not it's cloudy, whether or not it's windy, and where the arm/cold air interface happens to be (and it's very close!)

There is an inevitable political function to weather forecasting, and people bring all kinds of hidden assumptions into the process. Nevertheless, weather forecasters are subject to public abuse when they get things wrong, and bad forecasts can endanger lives, so they have considerable incentive to do their best.

Forecasting for Fairbanks is just hard, I think. Instead of receiving direct hits from weather fronts it often receives glancing blows, with difficult-to-predict consequences. Cold air "sticks" rather than moves aside. Counterintuitive things happen (e.g., cold breezes can increase the temperature, because of either turbulence, or Chinook effects, or both). There are local effects too.

With today's forecast, I knew there was a possibility that the warm air might sail over Fairbanks, at least at first, but counted on the southerly air flow to carry the day. And it did, at first. That southerly air flow flagged, though, and the cold air reasserted itself. Forecasting that weakness, and its possible consequences, was the problem.