Friday, February 14, 2014

February 15-16 Potential Blizzard

It looks like there is now the potential for a blizzard this Saturday and Sunday.

The GFS model shows extreme wind speeds along the coast of the Northeast as another strong storm system rides up the coast in similar fashion as the storm that just ended for the East Coast. We see 10 meter wind speeds over 44 knots just offshore land, with widespread 25-35 knot wind speed forecasts at the height of this storm.

The GFS model indicates the storm will drop accumulating snow along the coast, as the 984 millibar low comes close to land. Despite the proximity of the low pressure system to the coast, the precipitation here will not be incredibly intense. Accumulation is expected, and the wind will be that of borderline-blizzard conditions, but the accumulation will not be significant.

The real fun begins overnight of Saturday into Sunday, as the GFS projects this storm will rapidly strengthen to drop significant snow accumulation on Maine, and this should continue into the day on Sunday. The system will be moving rather quickly, so while significant amounts are expected, it will not be a prolonged event. This also means good news for those of you who like to watch snow come down at high rates (i.e. 2 inches an hour or higher), as we'll likely see some pretty high snow rates in Maine from this storm.

This 6 hour snowfall forecast shows the intense snowfall overnight Saturday into Sunday, with the GFS depicting amounts as high as 12 to 14 inches of snow falling in that 6 hour period. If you were to average that out, it would be equivalent to 2" of snow falling every hour, but as we all know, snow does not fall in uniform and consistent rates like that. It's more probable that we would see very high snow rates (possibly 4" an hour at best) for a period of time, with lighter rates mixed in (i.e. 1" an hour or lower).

When all is set and done, here is the total snowfall put out by the GFS model. We can see those high amounts in Maine, but also some good totals in coastal portions of Massachusetts and Connecticut. Again, totals aren't looking to be too bad (I'm not so sure we see the GFS' predicted 10" of snow hit those areas in MA/CT), except for in Maine. The wind will certainly make it feel like a big snowstorm for those further south, though.

The NAM model has a different take on this event, bringing heavy snow to only the extreme eastern portion of Massachusetts, with that jackpot in Maine also moved to the east. Considering we saw the snowstorm along the East Coast a few days ago also further east than what model guidance suggested, it's possible we see a solution like this work out.

I'm wrestling with which solution I like better in this case. On one hand, we have the GFS solution, which seems somewhat-reasonable (compared to the NAM) with the slightly-lower inland snow amounts, but on the other hand, the NAM model being to the east may verify, considering the most recent East Coast storm appears to have been further east than modeled. Needless to say, this forecast will see some fine-tuning in the hours ahead.


Sudden Stratospheric Warming Commences in Northern Hemisphere

The winter's most sizable sudden stratospheric warming event to date has commenced.

The animation above shows us temperature anomalies in the 10 millibar level of the atmosphere, which is located way up in the upper stratosphere. We see how the stratosphere has been rumbling since mid-January with attempts at a stratospheric warming event, but it is only as of the last few days that the stratosphere saw a massive warming event, titled a sudden stratospheric warming (SSW) event. To see how big this event is, let's head down to the 30 millibar level, located further down in the atmosphere compared to the 10mb level.

The 30mb temperature anomaly animation above shows how the stratospheric polar vortex has been under attack for a longer period of time compared to the upper stratosphere. We see a large swath of warmth had been developing and manifesting itself in Eurasia in January into February before finally bursting into the upper latitudes. It is now clear that the sudden stratospheric warming event has extended itself into a decent chunk of the stratosphere. Let's check up on the 50 millibar level next.

The 50mb level is also seeing significant warming in the upper latitudes, which only confirms the idea that this is indeed a sudden stratospheric warming event, quite possibly the first one we've seen this whole season.

Why is this a big deal? The sudden stratospheric warming phenomenon allows the polar vortex to weaken, and this enhances the possibility of Arctic cold outbreaks not unlike those we saw earlier in January. I'm not saying we will see January 2014-level cold again, the prospects of cold outbreaks rise roughly 2-4 weeks after the sudden stratospheric warming occurs. This would place cold weather prospects in the February 18-March 4th period. It's already looking like we'll see a cold blast to kick off March, and this could be related.

The ECMWF model sees this intrusion on the stratosphere continuing, forecasting continued elevated geopotential-Wave 1 activity at the 10 day forecast period. We see the elevated values maximized around the 3mb to 30mb levels, with lesser influences downwelling as low as the 500mb level. It is likely that this will be the biggest stratospheric intrusion this season, as we are just about to wrap up the meteorological winter season, and the "final warming" (where polar winds reverse to signal the end of the SSW season) isn't too far away.