Significant Rain and Wind Event Possible Early Next Week

While most of the weather interest this time of year revolves around snowstorms, we are simply not in a pattern favorable for any in the next ten days or so. Instead, we have a very fast, active Pacific Jet with a plethora of disturbances running into the West Coast. Any one of these can theoretically bring rain to our area as they traverse the country, but that is largely dependent on the pattern downstream. As we head into this weekend, the pattern will become very “blocked up”, which means that any storm that moves east will be forced to slow down and amplify before it has any chance to move north and eastward towards our area. Essentially, the Pacific Jet serves as a highway, and the blocking pattern serves as a traffic jam that forces everything to slow down. When several shortwaves are forced to slow down, the traffic increases and backs up more with time, which forces the slowing down to move much further southwest with time. This means that several potent shortwaves are forced to interact with each other well to our southwest and turn into a monster storm system that has to slow down, and tap into plenty of Gulf of Mexico moisture.

This weekend is when we see this beginning to occur. A large, extremely anomalous ridge in SE Canada bends back to the west and forces the entire pattern to slow down. This forces two closed off 500mb lows to its southwest, which eventually phase together into a monster storm.

Often times, a blocking ridge southwest of Greenland forces the storm to track off the coast, and that may eventually happen. But the block is not completely disconnected from the ridging along the East Coast, so the storm is able to slowly gain latitude. But because of how slowly it tracks, along with how powerful the storm becomes, it has ample time — several days — to gather a plethora of moisture from both the Gulf of Mexico and the Atlantic. This creates a very unique situation where precipitable water values, which essentially represents the total amount of moisture in the atmospheric column, may shatter late January records. This means that if the storm takes the right track, several inches of rain is possible on Monday through Wednesday.

Precipitable water values of around 1.4″ are typical in a summer thunderstorm, and the fact that we are getting this with a storm that is nearly stalling to our southwest means we could have multiple days of consistent periods of heavy downpours. The mean column winds are also very fast and surging from the Atlantic and the Gulf Stream, adding even more warm, moist fuel into the atmosphere. This means that multiple squall lines may back in from the Atlantic into the region.

As far as the wind threat goes, there is certainly the potential for 50-60mph wind gusts, particularly along the coast, as the low-level jet will be coming in straight from the Atlantic and be fast and filled with moisture. This may add just enough low-level instability to get the 50-60 knot winds at 925mb to mix down to the surface. The ECMWF model in fact does this, which would be a very high-impact scenario when combined with the several inches of rain, as with the saturated soil, trees could be susceptible to being uprooted.

But what may ultimately prevent these winds from mixing down to the surface is that there may be an inversion aloft via very warm air being advected just above the ground more strongly than it is at the immediate surface. It is still way too early to determine whether this inversion will win out here, but it’s certainly something to consider. Regardless, coastal flooding could also be a major issue with this storm as water gets piled up in the Atlantic.

The timeframe for the rain as of right now looks to be late Sunday night through Tuesday, though the GFS actually keeps rain into the area through Wednesday. We will be posting plenty more details on this storm as we get closer and confidence increases.