As we finish the clean up from our latest major to historic snow producer in the area, it's time to look ahead to the next potential event. I know many are probably ready for spring at this point, but the pattern currently in place will ensure that any sustained warm weather is at least two weeks down the road. I explained reasoning for the March 3rd event in my post last Monday (feb 22nd), but now that the storm is depicted nearby on modelling, let's examine the synoptic evolution here.
Balancing the pros and the cons of this upcoming Miller A (Gulf-origin) possibility.
Pros:
1) Tropical forcing; MJO will be in phase 8 over the next week, which is a very conducive octet for east coast storminess. This was a note from last week which I'll repeat since it's important -- all of the KU events that impacted the Eastern US this winter, happened in MJO phase 7 or 8. El Nino's love to have their snowstorms coincide with favorable tropical forcing, and that's certainly been the case this winter.
2) Steady rise in AO values as we move into early March, suggests a poleward contraction of the mid latitude jet, thus a higher probability of southern stream short waves moving northward. Additionally, Heather Archambault's great research demonstrates a tendency for heavy precipitation events along the eastern seaboard during times of sharp rises in either the AO or NAO.
3) Strong +PNA ridge in an almost ideal position, with its axis centered over ID/MT. Longitudinal, amplified upper ridges in this part of the country teleconnect to similar magnitude trough amplfication downstream in the Eastern US. And we can see on the following 00z GFS depiction valid Tuesday at 06z, that the Western ridging allows the southern stream short wave energy to dig / acquire a slightly negative tilt, as the SE-ridge attempts to build offshore. However, there is a caveat, which I will explain in the cons section.
Cons:1) I'm sure many of you know from experience that it's fairly rare to receive two big snowstorms back to back, within a week of each other. One of the reasons for this is the fact that the exiting low pressure can aid in blocking subsequent lows from impacting the area. In this particular case, our recent major storm will fight the mid week monster as it tries to push NE up the coast.
Note on the following graphic, I've illustrated on the 00z GFS valid 18z Tuesday afternoon how our current low sits east of New england, creating strong WLY/NWLY confluence across the Northeast - thereby preventing this low from hitting our region. Key in on the wind barbs; the upper flow is southwesterly up to NC/VA, but then changes abruptly westerly by NJ's latitude. If this depiction is correct -- which is the big if -- we won't get a snowstorm. 50-50 blocking lows are good, but this one is positioned too far SW according to the GFS.
The question is - should we trust the GFS? The NAM's 500mb depiction has a stronger SE ridge w/ a greater negative tilt on the southern short wave, hence its surface reflection shows a bombing storm near the VA capes and big snows about to move into our area by 84 hours. The NAM has performed better than the GFS this season, and the trend with Miller A's has been slowly north with time. In addition, the pros outweight the cons.
Conclusion - I'll have to stick with my thinking from last week - get ready for a March lion, as we may have another snowstorm on our hands. If it is a miss, it'll be to the south, so it's a snow or no type of situation. Areas most at risk with this one -- the Mid atlantic states once again, and up through our region.
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