Most winter weather enthusiast are at the point where if they do not see snow in the near future they're ready to give up and look forward to spring. The frustration is warranted after the record warm December and 60-degree day yesterday. I still think this will be a tale of two seasons - I've been consistent on this since my Winter Outlook. December was forecasted to be above normal, January is transition with mild and cold stretches, and February will be the cold / snowy month possibly lasting into March.
In the 2nd full week of January we could see snow showers late Tuesday or early Wednesday from a weak arctic front that forms ahead of a Clipper. As the Clipper tracks northeast into Canada it will phase with another piece of energy and deepen into a powerful low pressure system. This eventually turns into a closed low and becomes our 50-50 Low for a possible winter storm to effect our area between January 17th-18th. A 50-50 Low is located around 50N latitude and 50W longitude. Its purpose in winter storm setups is to keep cold air in place by preventing High Pressure systems from escaping east and keeping winds in a NW direction.
The next series of images will be the Sunday 12z runs of the GFS and EURO OP models looking at the 17th-18th time frame. The images on the left are the GFS and right will be the EURO. There are 4 key features that I will be comparing and contrasting between both sets of models:
1. The 50/50 Low
2. Northern ULL
3. Southern Energy
4. Western Ridge
Valid 7am Thursday
1. The 50/50 Low: Both models have it located over SE Canada
2. Northern ULL: Both models have it located SW of Hudson Bay
3. Southern Energy: Both models have the southern s/w (short wave) located over SW U.S.
4. Western Ridge: Both models do NOT show a western ridge at this time. The flow is fast.
Summary:
By 7am Thursday we see both models have the location of the Wednesday Clipper over SE Canada. SW of Hudson Bay there is an Upper Level Low that is trying to detach itself from the northern jet. Over in the Pacific there are two short waves entering the west coast. The GFS is a little faster with the second short wave over the eastern Pacific compared to the EURO. Overall, both models have a similar look Thursday morning.
Valid 7pm Friday
1. The 50/50 Low: Both models maintain the same location of the 50/50 Low since Thurs. morning
2. Northern ULL: Both models bring the ULL further south.
3. Southern Energy: The GFS has 3 separate s/w's from the Rockies to Atlanta, GA. The EURO attempts to consolidate these short waves into the base of a trough.
4. Western Ridge: The GFS shows a muted ridge. The EURO shows an amplifying ridge.
Summary:
The GFS and EURO begin to differ as we fast forward to Friday evening. The GFS has a less defined / weaker western ridge because it shows another piece of Pacific energy getting ready to crash into the west coast. On the other hand, the EURO has an amplifying western ridge because of the location and strength of the NPAC trough helping to pump heights. Furthermore, the GFS keeps the 3 southern s/w's separated while the EURO tries to consolidate them into the base of a trough. This makes sense since the amplifying western ridge allows Pacific energy to dig deeper into the U.S.
Valid 7am Sunday 01/17
1. The 50/50 Low: Both models begin to shift the 50-50 Low N&E.
2. Northern ULL: The GFS has the ULL in southern CA while the EURO digs into the eastern U.S.
3. Southern Energy: The GFS has nice consolidation of southern energy at base of trough while EURO has the vorticity elongated along the trough.
4. Western Ridge: The GFS loses the ridge while EURO shifts it east.
Summary:
The GFS has a nice looking trough even though it collapsed the western ridge. The problem is the northern ULL did not dig into the CONUS so the air mass is too mild to promote wintry weather. On the EURO, the ULL is digging further than the GFS but the western ridge is not poleward enough to force the ULL to phase with the southern energy. The end result on both models is a weak surface low off the coast with marginal cold in place.
GFS and EURO Ensembles Valid 7am Saturday
The 500mb height anomalies bring to light the upper air features a little better. The Ensembles suggest the ingredients to getting an east coast snowstorm are very close to coming together. I think the biggest problem is the western ridge. The GEFS show the NPAC trough closer to the west coast compared to the EPS but both sets are not enthused with maintaining amplification of the ridge. This means the northern ULL stays around the Great Lakes and fails to phase with the southern energy, thus keeping our air mass mild and preventing cyclogenesis from occurring. Also of concern is the 50-50 low tries to depart the 50-50 region too quickly. This suggests the -NAO block is transient and the overall flow across the U.S. stays progressive. The only way to combat the transient -NAO block is for the western ridge to amplify so both northern and southern jets can phase. This is how we've gotten storm systems off the coast the last two winters. NOT relying on a -NAO block, rather on a +PNA/-EPO couplet.
Final Thoughts
I think we're still far off from seeing the final solution on the models. Sampling with the Pacific energies is very poor and the 50-50 Low does not even exist. That said, I do not like the trends I saw from models over the weekend. The -NAO block is either weaker or shown to dissipate, the western ridge amplifies for a short period of time before collapsing, and the northern energy is closing off in southern Canada (south of the block). I highly prefer an open wave of northern energy because it has a better chance of digging into the CONUS and replenishing our air mass with arctic cold and phasing with southern energy. If we can reverse the trends on those 3 features, we'll begin to see solutions on models showing an east coast snowstorm. Does the overall pattern favor those 3 features to reverse or stay as currently modeled? Well, 200hPa anomalies are forecasted to go negative around 160W in the Equatorial Pacific. This should keep the NPAC trough further west than where models show it, which in turn should keep the western ridge amplified. There is a lot to track over the next few days. We'll see where this goes...
Have a great week!
Best,
Francesco Paparatto
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