A weakening storm system moving west to east across Quebec Provence in southeastern Canada will push a series of two cold fronts through southern England over the next two days. The first cold front, is weakening as it approaches southern New England and as the front nears CT during the overnight hours this front is expected to wash out. With the front approaching, we can expect some isolated to scattered showers through the overnight hours along with extensive cloud cover. The combination of the front washing out along with extensive cloud cover will allow for overnight temperatures to remain around 60F with dewpoints hovering the 60F mark as well.
As we move into and through the first half of Monday, one of the biggest questions is how much clearing and how much sunshine will we see? There is decent agreement within the computer models, that there will be breaks of sun, along with clearing, moving from west to east during the late morning and early afternoon hours. The greatest likelihood of seeing breaks of sun and sunshine will be along and just west of the CT River Valley. In fact, we may see enough sunshine to where temperatures could reach the mid-80's.
With temperatures, potentially reaching the mid-80's, dewpoints around 60F, and mid-level lapse rates between 6-6.5 C/KM, computer models are indicating we could see Cape values reach anywhere from 500 J/KG to as much as 1500 J/KG along with lifted index values getting to around -2C to even -3C. This is all indicative of an atmosphere that will be marginally unstable tomorrow afternoon. We will have to watch trends tomorrow with sun as any more sun than forecasted could lead to higher values.
A secondary cold front will slide towards CT tomorrow and with the potential for a marginally unstable airmass we will be looking at the threat for showers and t'storms. The lift associated with the cold front is not very strong and the system moving through southern Canada will be weakening so we will not be looking at widespread showers/t'storms but more of the scattered nature.
There will be some pretty impressive wind shear aloft as well with forecast models indicating 0-6km shear values as high as 35-45 knots. These values are supportive for updrafts which can organize and also supportive of updrafts which could slightly rotate.
Given the potential combination of instability/strong wind shear aloft, and a cold front sliding east, we should see some showers/t'storms develop during the early to mid afternoon hours. While activity may not be all widespread, the presence of 35-45 knots of 0-6km shear will allow any activity to potentially organize into a squall line. We will also have to watch out for a few strong to potentially severe t'storms with a threat for strong gusty winds and perhaps even some hail, especially if stronger cores can develop and acquire some weak rotation. While not a major threat, given how much rainfall has occurred the past few weeks, there will be a flash flooding risk with any storms given there will likely be torrential downpours.
The best timeframe for storms should be from 2-8 PM, although activity could persist until past 9 PM or so, however, as the sun goes down, the atmosphere will begin to stabilize.
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