This blog post is a follow-up to several prior including this one
As of now I DO NOT see any extreme weather for Atlanta the next 10 days.
The change in the jet stream pattern is a gradual evolution not a snap of the finger, but the models continue to suggest the prevailing storm tracks slowly but steadily sinking farther and farther South with time the rest of this month into February, (suppressed jet stream), allowing increasingly polar air masses to move into the lower 48.
This process starts this weekend but then goes away a little bit before trying again in about 10 days and beyond.
But for the foreseeable future the primary major Arctic cold Polar Vortex stays in Eurasia:
Our best odds for snow or ice come when we get a split flow jet stream pattern with cold air established followed by the approach of low pressure from the Southwest U.S. bringing “Over-running” precipitation with a “Miller A” type surface low track. These systems in the weeks ahead will ride more or less along the stalled polar front temperature gradient between the Southern edge of the cold air and the northern edge of the warmer air (blue vs yellow in U.S.)
But first things first. The high pressure aloft blocking ridges suppress the jet stream flow with a broad flat trough across a big part of the country West to East forecast by the GEFS. This allows the Polar Vortex (PV) to shift South and polar air fills the trough...
MID-UPPER LEVEL JET PATTERN EVOLUTION FORECAST GFS ENSEMBLE:
SURFACE TEMPERATURE MEAN DEPARTURE FROM NORMAL GEFS FORECAST:
The Pacific jet stream is loaded with energy for surface low pressure systems and big surges of moisture (atmospheric rivers) to move into the West and Southwest U.S. and then head NE/E within the suppressed jet pattern.
So the FORECAST future synoptic meteorology pattern looks MOSTLY good “on paper” (digital) but we can not take the charts literally at this distance in the future, its numerical weather prediction algorithm projections so no specifics possible for now.
Of the major index measures we look at A0/NAO/WPO/EPO/PNA/MJO, 4 are or are forecast to become favorable for a turn to cold and stormy for much of the country, and 2 are unfavorable. But the 2 are important ones especially for the SE USA...
Models like forecasters are not infallible, especially the further into the future we try to look.
The two hold outs:
MJO PHASE 7 IN JANURARY/FEBRUARY:
PNA NEGATIVE PHASE (-PNA):
So there are signs of polar air getting into the NW U.S. and then sliding East later this month but there is resistance to how far South it can get for now. We have more below-normal temperatures in front of us yes, but nothing frigid, and a warm-up will probably follow before any flip back.
The devil will be in the details which are unknowable that far in the future. But the long and short of it is that the trends are forecast more favorable as we move through the remainder of the month into first week or two of February especially North of I-40.
The big questions are can we get a stretch of cold air to lock in later this month and last into mid February and get at least some of it down to I-20 or I-10? And can we get one or more systems in Georgia with the right temps and moisture together at the same time? We don’t know.
But at least many models are suggesting the table will be set, which has to happen first before there is any hope of anything other than rain (for snow lovers). If it must I want snow, not ice which is also a risk in the model projected pattern.
Rain, snow or ice. The dice will roll.
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