January 29-31, 2010 Mid-Atlantic Winter Storm...

Discussion...
Here is the final snow map for the storm. For the folks that saw our scenario map last night, we essentially made no deviations on it and went with the traditional 1-3, 3-6, and 6-12 ranges. Models remain in good agreement with respect to precipitation area placement and QPF. The GEFS and NAM place the heaviest QPF along the NC/VA border, with potential for between 1.25-1.50. It is here we decided to opt for placement of an isolated higher zone of 12-16 (for the potential of a few locations getting over a foot), but overall, still expecting most locations to fall within the range of 6-12.

Potential Issues:
First... Precipitation shield placement and track remains the main issue with respect to northern extent. Our map involves DC on the edge of 1-3 inches, while leaving Baltimore outside this range with the idea they stay under an inch. It continues to be a possibility that the precipitation shield penetrates further north bringing light accumulations north of a line from D.C. to Cape May County NJ, however given the amount of cold and dry air in place, we expect precipitation to have a very hard time reaching the ground with only light QPF forecasted to reach this area. Hence, we think amounts stay under an inch, however, will need to keep an eye today on the high-res models and radar trends.

Second... Another possible issue if the storm does come a bit further north would be dry slotting knocking storm totals down in the southern parts of the accumulation area, as the main deformation axis would set up further north. In addition, this would also increase the potential for some sleet to mix in across the far south, which would also slightly lower amounts. At the present time, think the only area that stands a chance at mixing is across immediate coastal areas near the vicinity of Virginia Beach.

Other than the slight possibility of either of these issues, this continues to be a high confidence forecast by us, with very little change implemented from 24 hours ago.

..GLUNT/EGAN.. 1/29/10

January 7-8, 2010 Clipper Event...

Discussion...
Synoptic Event: Once again, up until the latest runs, models the last several days look to have underestimated QPF amounts for this clipper and that means that we will be going with a more aggressive map. This storm should also feature favorable dendritic growth of the snow so will likely need to factor in the snow ratios which should be above 10:1 for most everyone that sees meaningful snow from this. Back into the higher ground of PA/WV/NY, ratios could be up around 20:1.

The big issue to watch for is the integrity of the snow shield as it gets over the Apps. We still incorporate downsloping but still give a pretty solid 1-3 to folks east of the mountains. If the snow shield holds together well, we could be looking at the solid 3-5 advisory snows continuing eastward to the coast. Given the overall dynamics and strength of this upper level low, it’s something that is plausible.

Accumulations will generally be on the light side to the east of the mountains, with a broad area of 1-3” expected. Further west, higher amounts are likely, especially in the mountains from West Virginia into western Maryland where upwards of 6”is likely, with a general 3-5” expected. Additional Lake Effect Snow is likely Friday Afternoon thru early Saturday, which will bring storm totals over 6” in many places (see below).

Lake Effect Snow Potential: In behind the Clipper and associated Arctic front, Lake Snows will be developing downwind off Lake Erie by Friday Afternoon and Lake Ontario by Friday Evening. Additional significant lake effect snows are likely Saturday into Sunday.

Off Lake Erie... In general, expecting a total of 4-7” downwind from Erie County NY southwest to Cuyahoga County OH. This in combination with an expected 3-5” of synoptic snow Thursday Night into Friday, will bring storm totals to 6-12” by Saturday Morning.

Off Lake Ontario/Finger Lakes... In general, expecting 3-5”Friday Night into early Saturday downwind of Lake Ontario from Southern Oswego southwest along the shoreline to Niagara County, including the Syracuse and Rochester Metro areas. Further south thru the Finger Lakes region and Susquehanna region of Central NY, expecting a multi-band streamers to develop off Cayuga/Seneca Lakes resulting in a general 1-4” Friday Night into early Saturday. Storm Totals thru early Saturday Morning will range from 4-7” Across the Lake Ontario Plain, with 3-7” across the Finger Lakes and Southern Tier.

...GLUNT/EGAN... 1/7/10