Monday, January 19, 2015

Short Range Outlook (Made January 19, 2015)

This is the introductory Short Range Outlook post of our new posting plan, where the pattern for the next 0-7 days is addressed. This forecast is valid for January 19th to January 26th.

500mb geopotential height anomalies (right panel) and means (left panel) over the last 7 days show a general ridging pattern across the western portion of North America, extending a bit into the Central US. A separate ridge was also observed in the East US. The former ridge permitted the movement of an upper level low further to the south, which gave the Great Lakes and Northeast a somewhat-cool pattern, if not average.

Satellite analysis of the Northeast Pacific shows a healthy storm system moving onshore in southwestern Canada. Abundant moisture from this particular system is being spread across southern Canada, before additional moisture is seen across the Rockies. We can pick out a few more storm systems in this satellite shot, but the main concern will be with that system crossing into Canada.

Model guidance sees the aforementioned piece of energy sliding southeast-ward as a weak snow-producing system. From the most recent NAM model, the heaviest snow would appear to fall in southwest Michigan, with scattered snow also showing up in Wisconsin, Minnesota, Iowa, Illinois, and points east. This will then introduce a period of cooler than normal temperatures.

After this weak system moves eastward, model guidance allows the storm to strengthen quickly along the East Coast, which may drop accumulating snow in the Northeast and parts of the Mid-Atlantic. Amounts are still in question, but this high-resolution model indicates amounts in excess of 6" may impact the region.

To summarize:

- The cool pattern we have observed the last seven days is currently being broken by warmth, but should return in the next week.
- A weak system will drop out of Canada to produce snow in the Great Lakes, re-introducing cool weather.
- Scattered storms can be expected across the Gulf Coast.
- Accumulating, possibly significant snow may impact the Northeast.
- Generally wet and warm conditions may be expected for most of the West.