The “Wedge” has us socked in today. Noon temps in map above.
Once again we will go from below-normal temperatures to above-normal temperatures. Below-normal Friday/Saturday then above-normal Sunday-Thursday.
The January Thaw is a real thing and winter severe weather is hardly unprecedented here in the Southeast, just not common.
Of course, it’s hard to have a true January Thaw when there has not been any long lasting cold. But more warm air is on the way.
I am already seeing the Cheery Trees starting to bud/bloom, they are always the first but its a bit early even for them.
Except for November the prevailing Northern Hemisphere atmosphere has featured a mean prevailing +AO/NAO, +EPO, disruptive MJO, +IOD, a reversing QBO from +West to -East, a -PNA and a weak, non-classic Modoki El Nino near-neutral.
This has resulted in a somewhat zonal flow in the jet stream off the Pacific Ocean with a split flow pattern of a sub-tropical jet stream across the South and the main Polar jet stream across the North, the combo bringing mild Pacific air more than Polar air and keeping most of the true Arctic air bottled up far North.
This combo of indices has not been seen in quite this way before and therefore was not anticipated and has led to a poor winter forecast issued way back in October.
The IOD seems to have changed the MJO which in turn disrupted the rest of the Northern Hemisphere Stratosphere and Troposphere behavior making it do things it normally does not given the general set-up.
Reasons unknown, may be a result of the changing climate background base state and/or the record high positive Indian Ocean Dipole (+IOD).
It may be a factor in the abnormally poor model performance in long-range (weeks to months) model output that we’ve seen for the last year or two.
One thing we have learned is that the EPO/PNA looks to be more important in seeding Eastern North America with truly cold air for any real snow below I-70.
We could easily end up with a top 5-10 warm winter and maybe a top 5 streak of snowless days at the airport.
Most similar past duds have rolled forward into a warmer than normal March.
LOOKING AHEAD...
The numerical weather prediction equations combine with supportive analog (non compute model) history based cases to show a clash of cold and warm air next week, resulting in an energized jet stream and attendant vigorous mid-latitude cyclone (low pressure) system with snow to the North of it’s track and heavy rain and severe weather possible to the South of its track.
There could be a multi day snow-severe threat as a result of this forecast deep mid-level long-wave trough in the jet stream:
GFS MODEL 500MB LEVEL VALID 7PM WEDNESDAY FEB 5:
This winter we’ve seen this play before.
From this distance the severe threat looks rather modest and mostly to the West and South of Metro Atlanta. But that could change.
ANALOG GUIDANCE TEMPERATURE THRESHOLDS AND RAIN (Forecast 168-312 hours):
ANALOGS ON SEVERE WEATHER (Forecast 168-240 hours):
NOAA/NWS STORM PREDICTION CENTER (SPC) GUIDANCE WEDNESDAY/THURSDAY:
EARLY ESTIMATE OF RAINFALL AVERAGE FEB 5-6:
While a real snow or ice system can not yet be ruled out for Metro Atlanta there is still none in the foreseeable future.
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