Tuesday, February 12, 2013

Stormy Pattern Evolves in Next 7-14 Days

The stormy pattern we recently began with that historic Northeast snowstorm will continue in the next 7-14 days. For those wondering, I am not changing my forecast of the pattern becoming less favorable with time for snow and persistent cold.

Shown above is the 500 millibar forecast from the GFS Ensembles over the Northern Hemisphere. We see pressure contours clumped very close together in the Pacific Ocean, with low pressure anomalies in the Bering Sea and very weak/nonexistent high pressure anomalies off the coast of East Asia. These two factors will act to tighten the Pacific jet stream and really pump up storm systems that cross the northern Pacific. The persistent low pressure in the Bering Sea will shed off pieces of energy that will then crash into the Pacific Northwest region of the United States, or into southwestern Canada. Due to the already-active subtropical jet stream (another, weaker jet stream that is present in the South US, does lead to Nor'easters when storms go in that path), I anticipate the Pacific Jet Stream to drop south into the southern Plains and have the two jet streams merge in that region at least once in the next 7 to 14 days. When this merging happens, the storm itself will strengthen and we will see at least a modest chance of severe weather along the Gulf Coast, depending on where the system goes. If the subtropical jet stream captures that piece of energy, it could become a Nor'easter. If the polar jet stream catches it, the Midwest and Ohio Valley could benefit.

The forecasted Madden-Julian Oscillation (MJO) shows Phases 2-4 in the next several days, possibly into Phase 5 towards the end of this two week period. Phases 3 and 4 actually support high pressure across the eastern US, so that could diminish the chances for storms in the East US. Instead, these storms may be more provoked to go into the Plains, like they have most of the winter. However, going to back to the top image, if we see that arc of pressure contours over Greenland work out, the Midwest would benefit. You see, that arching pattern is a negative North Atlantic Oscillation (NAO), and when it's negative it enhances the chances for a high-amplitude pattern and storms for parts of the central and eastern US. If the highest pressure is based to the east of Greenland, it is an east-based negative NAO. This is more conducive for storms in the Midwest, A west-based negative NAO implies highest pressures are west of Greenland and thus favors storms in the Northeast. Based on that GFS Ensemble forecast and the Madden-Julian Oscillation forecast (along with a few other factors), I think the Midwest will get at least one fair snowstorm, but the Northeast and Plains (possibly the Midwest as well, if they're lucky) will need to watch out for lots of disturbances that could form some good snow-producers.


1 comment:

Anonymous said...

Ok... I understand I will get some flak for stating this..but I do not consider the Midwest (at least where I live, Iowa) lucky to get snow. Nope, I want Spring! Spring, with a nice gentle warm rain on a Sunday evening! No need for drought! Birds, flowers, pools, green grass…Spring! Bring it on!