Strong temperature gradients and a strong jet over the US

A large polar airmass is sagging south across the Central US today, bringing with it decently below average temperatures juxtaposed against the above-average temperatures currently along the Gulf coast and the Eastern Seaboard.

That's a fairly strong gradient in the 850 hPa temperatures running from the Texas panhandle up through the Kansas City area and towards the east-northeast. This setup with cold air surging east of the Rockies as easterly flow runs up against the foothills and is forced south is a typical look for cold air outbreaks across central CONUS.

Taking a cross section across this temperature gradient, we can see an impressive vertical gradient in theta-e, with characteristically high static stability within the frontal zone. 

Just looking along the 850 hPa level, there's probably about a 1K/10km theta-e gradient along that transect. Thermal wind balance tells us that where there's strong horizontal temperature gradients, there's bound to be strong cross-gradient shear, and sure enough, check out the magnitude of those winds normal to that transect!

That's a tremendously large expanse of strong westerlies aloft, but that's just about what we'd expect given the sagging cold airmass that's producing behind strong meridional temperature gradients. Both the polar and subtropical jet cores are evident here. That subtropical jet is really high up, straddling the tropopause region and maybe even poking in the stratosphere. Models indicate intensification of that jet, which should deposit energy downstream and result in an zonally-extending jet core across the Pacific, as we see depicted on the GFS:

With how strong that jet core is, that signals oodles of synoptically-forced ascent in the left exit region over the North Atlantic west of the British Isles. This entire portion of the jet will take about a week to propagate past the Atlantic, so there could be several days of repeated cyclonic development over the North Atlantic with tracks into Western Europe. That could result in a prolonged period of onshore flow with significant fetch which could lead to very high waves in the Bay of Biscay and surrounding environs:

Sting jet-like feature in Hurricane Tammy's extratropical phase

The National Hurricane Center declared Hurricane Tammy extratropical early on the morning of October 26 following a roughly week-long trek across the western tropical Atlantic, Barbuda, and the open Atlantic. Thermal and kinematic fields from the global and hurricane guidance suggest that Tammy may fully or partially re-acquire tropical characteristics this weekend, and personally I think the odds of that occurring are higher than what the NHC has been implying.

Anyhow, GOES-16 imagery from this morning showed what appeared to be a fast-moving swath of sharply-marked subsidence to the south and southeast of Tammy's center of circulation, not too unlike that of a sting jet.

Of course, Tammy does not appear to be rapidly deepening, and the banded scorpion-tail cloud head structure typically ascribed to sting jets is notably absent, but there does to be some implication of descent originating from near the convective region to the west. Water vapor-band brightness temperatures were also elevated in this apparently subsident region. Unfortunately, METOP-B and METOP-C missed this region in their morning passes, so we don't have an estimate of the winds there. However, SSMIS-derived wind data indicated a zone of stronger winds in the subsidence region.

The CIMSS meso-AMV product also suggested winds on the order of 50-70 kt within this sting jet feature at the 701-1000 hPa level.

The HWRF appears to have replicated this feature in its 06z run from this morning, showing a strong region of rapid descent (>3 Pa/s) in this area of the storm in tandem with a tangential isotach tail in the horizontal near-surface wind field:

HAFS-A also illustrated expansive descent:

As did HAFS-B:

If we consider strictly isentropic motions along the theta-e contours depicted, we may be seeing the transport of air from 600-700 hPa down to near the surface.

 

2017 Atlantic hurricane season montage

The 2017 Atlantic hurricane season, ultimately a hyperactive one, officially ends today, November 30. Thank goodness. The season finished with 18 tropical depressions, 17 tropical storms, 10 hurricanes, and 6 major hurricanes. All 10 hurricanes came consecutively, one after the other, beginning with Franklin and ending with Ophelia. I'm fairly certain that is by far the record. I lucked out here from devastating impacts here in Austin several hundred miles from the coast, but I did end up with quite a bit of steady rainfall from Harvey.

Here's a hand-drawn montage that sums the season up. I've been working on this throughout the season as storms came and went. The storms themselves are hand-drawn, while some of the background clouds come from a GOES infrared satellite image composite from July 13. All rights reserved, but feel free to use it as a desktop wallpaper. It's 16:9, after all. I'll have a link to more image sizes over at Flickr once I upload this there.