Sunday, January 24, 2010

Significant Storm For Tonight & Monday

The tranquil weather of the past week or so across Eastern New York State and Western New England will be coming to an end over the next 24 to 36 hours. As a multihazard storm system will affect the region.

A complex storm system moving north and east from the middle of the country will threaten Eastern New York (ENY) State and Western New England (WNE) with the following adverse weather:

Primary Threats
- Heavy Rain causing possible flooding especially in poor drainage areas
- Stream and River Flooding due to heavy rainfall PLUS mild air causing snowmelt (in areas where snowpack exists) adding to the runoff
- Ice Jam flooding potential also due to the mild temperatures that could cause ice to break up and shift/move on streams.

Secondary Threats

- Precipitation may start as a brief period of sleet and/or snow or freezing rain (along and north of I-90) in ENY and WNE

- Possible strong winds later tonight and Monday, especially across higher terrain of ENY and WNE where gusts in excess of 45 mph could occur, especially AOA (At Or Above) elevations of 1500 feet

The complex storm system that will affect us extends from the Western Great Lakes (Wisconsin) south-southeast to the Southeast U.S. (SEUS). Over Wisconsin one storm is located and it moving north-northeast across the U.P. of Michigan. A second storm is developing over the Lower MS Valley Region.

It is this low that will move N-NNE along or just west of the Appalachians with some moderate deepening (strengthening) enroute to Lake Ontario by tomorrow afternoon.

Numerical Weather Data indicates the high likelihood that ENY and WNE will receive 1-2 inches of rain with most of this precipitation falling during the morning through early afternoon of Monday 25 Jan. There will also be locally enhanced rainfall especially over favored upslope areas of the Adirondacks in NYS and across the Taconics and Berkshires where amounts of 3-4 inches are possible.

With the low over the Lower MS Valley this afternoon moving across SE Canada Monday night, its associated cold front will sweep east. Ahead of this front very mild air will surge north followed by a return of seasonably cold air towards Tuesday Morning. As this colder air returns it is possible that there could be a period of snow late Monday night through early Tuesday morning, especially across west facing slopes of the Catskills, Western Adirondacks and more so across the higher terrain east of the Capital District. For locations here there could be some accumulations.

Now we can look at some data for this upcoming event.

The data that we are looking at will be time sections (TSEC) for various locations across ENY and WNE. The TSECS show the following: along the X-axis is the time (increasing from RIGHT to LEFT from 0 hour to 72 hours). The Y-axis is height decreasing UP. Relative humidity is contoured, temperatures in degrees Celsius, wind speed and direction is indicated along each vertical axis. Speed is indicated by barbs and pennants; a full barb is 10 knots of wind, a half barb is five knots; pennants equal 50 knots of wind. Yellow dash lines indicate forecast lift, or vertical motion (called vertical velocity [VVEL] or Upwards Vertical Motion [UVM])

Here is a TSEC for Albany, NY from the 24 Jan 12Z NAM model:

The strongest UVM is centered approximately between approx 5am and 4pm 25 Jan and it is during this time that the heaviest precipitation is expected to fall.

Also note on the TSEC chart during the forecast hours of 42 through 48 hours (1am through 7am Tuesday 26 Jan) another "maximum" of UVM move through with moderate and nearly uniform W-WSW winds from the surface up to just below 700 millibars. This is the cold front moving through with another burst of precipitation possible. With temperatures expected to be decreasing/lowering this few hour period of precip could fall as snow.

Now onto a TSEC for Mount Equinox VT in the Taconics (Manchester, VT):

Mt.Equinox (elevation 3816 feet) has the potential for experiencing strong SSE-S winds from about 9p-10p 24 Jan through 1pm 25 Jan in advance of both the northward moving cold front and the eastward advancing occluded front. Sustained speeds of 20-28 kts are possible across the higher terrain of WNE and extreme ENY. Note the forecast winds centered around 850 millibars - note the barbs and pennants at this height level and during this time period. Using the 85 rule: take the 85% of the 850 millibar wind speeds to get "expected" gusts thus gusts of 50kts or more are possible over the higher terrain.

TSEC for Speculator, NY:

Similarly the TSEC for Speculator indicates the potential for strong SSE-S winds both sustained winds (20-25 kts) with gust potential for 50kts or more.

In both the Speculator and Mt. Equinox TSEC data the best chance or time period when strongest winds occur will probably be in advance of the occluded frontal passage during the afternoon hours of Monday 25 Jan.