Kyle heads to Nova Scotia – KY rain chances fizzle

Model trends show that Tropical Storm Kyle appears to be headed for Nova Scotia rather than New England, which will set a chain of events in motion that will diminish the chance for rain in the Mid-South next week. However, chilly air is still expected to arrive in time for Fall Break next week.

Here is the current synoptic set-up as of Friday afternoon. My last post suggested that if Kyle made landfall in New England, a highly amplified pattern would emerge the middle of next week that would result in a cut-off low over the Midwest that would bring a good chance of rain and temperatures in the 60s to the Mid-South. With Kyle now trending eastward, that can’t happen. Instead, as it moves northward, Kyle will raise heights and pump up the ridge further east in the western Atlantic. Since the upstream ridge over the Rockies hasn’t moved, the wavelength will be increased, which acts to de-amplify the jet stream. With the jet stream de-amplified, the vort max associated with the arctic air mass will take a trajectory towards southern Ontario rather than the Midwestern U.S early next week. This means no rain for the Mid-South next week with temperatures in the 70s.

The interesting part of this change in the jet stream is that with a less-amplified pattern, the second vort max mentioned in my last post will then be able to follow the new quasi-zonal baroclinic zone and bring some true arctic air into the northern Great Lakes and New England late next week. Whereas I originally thought the more meridional pattern would bring a short burst of very chilly air to the Mid-South, this more zonal pattern will keep the very cold (for the season) air primarily north of I-80. With 850 temperatures of -9 C and thicknesses of 526 dm, this is an airmass capable of the first flurries of the season for the Arrowhead region of Minnesota and the northern Great Lakes. I concerned that the GFS is overdoing this early-season cold air, especially considering the ECMWF is not as cold as the GFS.

In the long range, the models have consistently shown the Pacific jet increasing in intensity, with 110kt (and greater) jet streaks common fur the 8-14 day period. This is a good sign for the Mid-South, considering that an active Pacific Jet typically is associated with increased winter season precipitation for KY and TN. Many of the long-range winter forecasts I have been studying are showing a La Nina-like pattern even though La Nina has been replaced by neutral ENSO conditions in the tropical Pacific.

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