Big Temperature Contrast

Stormy and active weather patterns usually involve strong temperature contrasts (except in the tropics), so it's been no surprise to observe larger than normal temperature differences across Alaska in the past couple of days.  A strong cold front swept east across the state Thursday night and yesterday, so that by yesterday afternoon most of the west and interior was much cooler than normal, while extremely warm conditions persisted in Southeast Alaska.  Here's a map of the 850mb temperature departure from normal at 4pm yesterday:

The warmth in the Southeast has been remarkable, and I think it's safe to say that locations from Juneau southward are experiencing their warmest last-ten-days of August since 1963 (longer in some locations), at least in terms of daily maximum temperatures.  Including today, Ketchikan has reached or exceeded 70°F for 9 consecutive days, and that would be an unusually lengthy warm spell even in the height of summer.  Juneau has seen 4 days in the mid-70s (74° or 75°) since the 23rd, and the only other time that happened so late in the year was back in 1941.

Perhaps most remarkably, Sitka airport appears to have reached 70°F for the 5th consecutive day today, and that has only happened once at any time of year: August 8-12, 2005.  [Update August 31: the high was actually 69°F, so four consecutive days of 70°+.  Still a rare occurrence even in high summer, and not previously observed this late in the season.]

Of course the magnitude and persistence of the warmth in Southeast is being boosted by the very warm water temperatures across the North Pacific.  Even though the northeastern Pacific isn't as absurdly warm as the northwestern Pacific, sea surface temperatures are still well above normal near the Gulf Coast.

On the flip side, the influx of cold air along with cloud and rain yesterday brought very chilly temperatures to the central interior by early afternoon; here are the observations from 2pm yesterday (click to enlarge).  Munson Ridge (3100' elevation) had dropped to the freezing point by noon, and with nearly half an inch of precipitation falling in the afternoon, there was presumably some snow up there.  Notice the warmth hanging on in the east: it was still 70°F in Chicken at that time.

The temperature then proceeded to plummet overnight in Chicken, apparently reaching an astonishing 14°F at the co-op site this morning.  Given that the RAWS thermometer reached only 25°F, the co-op observation seems slightly difficult to believe, although the RAWS site is up on the hillside, so naturally warmer.  If correct, it's the earliest on record for such cold in Chicken by more than a week (13°F on September 7, 2004), although the period of record only goes back to 1997.

Finally, I'll just note the hydrological situation: all the rain (including recently in South-Central) has produced minor to moderate flooding on several rivers, and there's a record flood on the Yentna River, a lower tributary of the Susitna.  The Tanana River near Fairbanks and Nenana is high, but not expected to reach flood stage in the immediate future.