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September 2011

SNOW possible in the higher elevations this weekend

A shot of cool air is expected this weekend up and down the eastern U.S., with lows in the 30s possible in the higher elevations and maybe even northern MD. DC looks like it will stay in the low to mid 40s at its coldest point on Sunday morning (and possibly Monday morning).

The 12z GFS is pretty aggressive with the cold, showing widespread 30s and even some 20s in the region Monday morning (similar to Sunday morning, only the 30s reach further east Monday morning as high pressure moves overhead):

On top of the cooler temperatures, some snow showers could develop Saturday morning in the higher elevations, with a flurry or two possible Sunday morning up in the mountains. Some minor accumulation is possible in the highest areas, otherwise the snow that does fall should not accumulate. I wouldn’t rule out seeing a flake or two in the air in northern VA/MD, but it looks unlikely at this point.

Widespread rain event over the next 5-7 days… some severe

An upper-level low is forecast to move into the Midwest tomorrow before cutting off from the main flow, which will allow it to linger over the Midwest and Tennessee Valley regions through around Monday or Tuesday before it lifts out of the eastern U.S. This has a couple of different implications for the region…

The most pronounced threat with the cut-off low is the potential rainfall, with widespread totals of 1-3 inches or more in the Mid-Atlantic and Northeast. Normally 1-3 inches isn’t that critical, but when you add it to the recent record-breaking rainfall in these regions any larger rainfall potential becomes a significant event.

Here’s a look at the total rainfall and the percent of normal rainfall for the period starting August 1st and ending yesterday, September 19th:

With some areas with over 20 inches of rain in the last 45-50 days, anything over a couple of inches will cause some of the rain-soaked areas to flood once again. Right now it looks like the coastal areas are more at risk for heavy rain compared to the inland/mountain areas in the Mid-Atlantic.

In terms of severe weather, strong to severe storms will be possible Thursday through next Monday or Tuesday, depending on the position of the cut-off low. This complex cut-off will have a few pieces of energy floating around it (at least initially… some guidance suggests one of the pieces breaks away before it completely stalls):

Having 2-3 pieces of energy in this cut-off low will make the forecast very difficult as models struggle to resolve the complex mesoscale interactions between the different pieces of energy and what they’ll do in turn at the surface.

Also associated with this energy will be an upper-level jet streak out ahead of the trough, which will help enhance lift. The problems, at least initially, will be the fact that the energy is just a bit too far to the west to have that great of an impact on the Mid-Atlantic, and clouds and rain could inhibit heating and worsen the lapse rates. My main focus for severe is when the trough does finally push eastward over the region… hopefully the timing will be good and it could trigger some afternoon/evening storms over the Mid-Atlantic. Once it progresses into the region, the energy involved with it will cause greater lift and the lapse rates should improve.

Not getting my hopes up on severe yet, but at least it’s something to watch over the next several days.

Summer 2011 forecast verification

Overall I’d give my summer 2011 forecast a B+, a grade worthy of a forecast that used one of the hottest summers on record as its main analog to forecast what ended up being yet another record-setting summer of heat. On a month-to-month scale, I’d give June an A-, July a C and August a B. The one thing that really hurt this forecast was just the sheer extent of the heat, especially over Texas and Oklahoma where extreme drought occurred. Otherwise, the pattern was recognized fairly well, with warm anomalies across the eastern two-thirds of the country and a cooler West Coast.

Summer 2011 (based off of 1971-2000 30-year normals):

The monthly breakdown:

June

July

August

And here’s summer 2010 (left) next to summer 2011 (right)… what I would consider a grade A forecast:

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I also must remember to do something like this for last winter, as I managed to completely forget about doing the winter verification.

TS Maria & Nate named today; seem to be minimal threat to US

While it is still too early to know where Tropical Storm Maria and Tropical Storm Nate will be heading for sure, initial forecasts keep both systems away from U.S. soil. Both became named storms today (Maria at 11am EDT, Nate at 5pm EDT), and both will be fairly interesting to track in the coming days.

TS Maria is expected to stay on the weaker side as it tracks from the central Atlantic up through the Bahamas. The latest model guidance indicates that Maria should recurve before it can make a U.S. landfall. The upper-level pattern does not favor a U.S. landfall at this time.

TS Nate, currently in the Bay of Campeche, is forecast to drift northward into the western Gulf of Mexico before it turns westward and makes a landfall in northern Mexico. Despite growing model consensus on this solution, Nate will be highly sensitive to subtle changes in the steering winds, which means a U.S. landfall is not out of the question (though it seems unlikely at this point).

Lee remnants bring flood problems to the East

The remnants of Tropical Storm Lee combined with a stalled frontal boundary will bring widespread rainfall to the eastern U.S., particularly along the Appalachians. 1-2+ inches of rain is expected from northern Alabama and northern Georgia up through the Northeast over the next few days, with a narrower swath of 2-4 and localized areas of 4+ inches of rain.

Katia, which is now a Category 3 Major Hurricane, should miss the U.S. as it nears late this week. I don’t have any particular concerns with this system. The Canadian Maritimes have small chance of landfall with Katia.

I also need to post more Irene stuff and verify my summer forecast (which did well!).