Massive Cold Blast Forecast for New England around Jan 5

PIN!!!

Thursday, December 27, 2012January 3-6 Potential Winter Storm
By Andrew at 10:13 AM

It looks like the potential is arising for a winter storm to hit the Midwest and Ohio Valley at the end of the first week of January. This possibility is being shown by the two major models (ECMWF and GFS) which we will review right now.

The above image is the ECMWF's 500mb height forecast for the evening of January 4th. Depressions in these isobars (lines of constant pressure) signify low pressure systems, while arcing formations depict high pressure systems. The ECMWF shows the storm system in the southern Midwest at this time. Typically, this would be a good snow maker for many in these two regions. However, the jet stream is aligned in something called a split flow pattern.

The split flow pattern involves high pressure stationed in the Pacific Northwest, leading to a literal split in the jet stream, and thus two branches of energy form: what I call the Southern Jet stream and the Northern Jet Stream. In this ECMWF Forecast, the Northern jet stream is stationed in Canada, and is shown by several isobars very close together. The Southern jet stream goes through Baja California, Mexico and the Southeast in a situation that could easily provoke severe weather. This split flow pattern keeps the cold too far north for these types of systems to access.

The GFS forecast for this storm system has the system further north, into the Midwest at this point. The GFS later brings the system down south into Kentucky like the ECMWF, but there are still big timing differences. The ECMWF and GFS do seem to be in good agreement as far as showing a common track, but the key thing is timing. It may just be 24 hours between the two forecasts, but that 24 hours can and will dramatically alter forecasts for this system, as demonstrated by these two models.

I think the ECMWF's forecast is more realistic. I find the split flow regime more likely at this point in time after a temporary Rex Block gives way.

Andrew [link to theweathercentre.blogspot.de]

January 11-14 Potential Winter Storm
By Andrew at 9:17 AM
The slim potential there is for a storm in this timeframe appears to be rising. Let's take a look.

This is the 0z GFS forecast for this timeframe, the evening of January 12th. We see a strong storm system lifting northeast, producing a good swath of snow across the Midwest and central/eastern Great Lakes. Heavy rain is ongoing in the Ohio Valley and Mid-Atlantic regions with this system, and a severe threat may be evolving on the Gulf Coast if this is a linear storm formation. A quick look at snowfall forecasts reveals a nice 6''+ swath of snow from Iowa to Illinois to Michigan. Behind this system, cold air stretches as far south as Corpus Christi, Texas, as shown by the solid blue freezing line (32 degrees F).

I would not post this if it were just a single GFS run. It has now been at least 4 model runs of the GFS that a storm has been shown to go through the Ohio Valley and bring accumulating snow to either the Midwest, Ohio Valley or both. Each image is a different model forecast.

I'm the sort of person that needs to know why things happen; I can't just see a forecast and accept it, I need to know what would make that forecast work. I'll do the same here.

This is the GFS Ensemble 500mb height anomaly forecast for Hour 384, the furthest the GFS model and ensembles can go. We see lower heights over much of the United States, as well as high pressure in the Gulf of Alaska and low heights in the Bering Sea.

The lower heights in the Bering Sea creates a positive West Pacific Oscillation (WPO). In response to these lower heights, high pressure then forms in the Gulf of Alaska, and in response to that, low pressure forms in the West US. This West US low pressure causes a negative Pacific-North American index (PNA) to form, which typically diverts storms to the Gulf Coast and North Plains. But the big thing is how low pressure is not confined to the West US, but is present across the entire nation. This then results in higher heights (high pressure) to form further out in the Atlantic. In a typical -PNA, the ridge sets up in the East US. This high pressure in the Atlantic then tries to propagate down into the waters off the Southeast US, meaning the infamous Southeast Ridge could set up. If this happens, the storm track would greatly favor the Midwest and Ohio Valley for snow, and that's what I think will happen going into the end of the second week of January. It should also be noted that many individual GFS Ensemble members project this Southeast ridge to form at Hour 384:

This massive low pressure will emerge in the United States by the splitting of the polar vortex. Not collapse, but a split. This will send pieces of the vortex into lower latitudes, and in this case possibly the US.

Andrew [link to theweathercentre.blogspot.de]

Weather Underground‏@wunderground

Another storm set to renew snow in the East. Find out the details. [link to www.wunderground.com] …

Jim Cantore‏@JimCantore

At 64% #snow coverage we have one of the largest snowpacks since winter 10/11: [link to www.nohrsc.noaa.gov] …

Abby Crock‏@AbbyCrock1

Winter wonderland! #ohwx #seohio @jimcantore bryanwx [link to instagr.am]

3 hNWS Louisville‏@NWSLouisville

Highest snow amount so far is from Paoli Indiana with 7 inches. #kywx #inwx #lmkwx

3 hJim Cantore‏@JimCantore

Here comes the #snow: [link to www.intellicast.com] … #nyc