An amplifying trough will continue to strengthen as we move towards the weekend and slide a cold front east. Once the cold front pushes east of the region we will usher in some "cooler" (in a sense of more seasonable temperatures) and drier air into the region as the pattern changes from ridge dominated to more trough dominated through much of next week. Before this cooler and drier air works in though we will have to deal with the threat for t'storms and the potential exists for several t'storms to become quite strong to severe.
While isolated t'storms are possible both Thursday and Friday, Saturday is the day of greater concern for widespread t'storms along with an enhanced threat for some severe weather. Saturday will not be a washout by any means, however, we may have some shower/t'storms activity around in the AM before we see a break. This is when we see sun and lots of surface heating which will help to fuel the atmosphere for storms later on in the day.
A strong piece of energy moving through southern Canada along with the approaching trough/front will help to really tighten the pressure gradient over our region given the Bermuda High is centered to our south. In response, the winds aloft will really begin to strengthen. Forecast computer models show winds in the lower levels of the atmosphere to strengthen to 20-30 knots with winds in the mid levels of the atmosphere strengthening to 35-45 knots. The region will also be in the right entrance region of a very strong upper-level jet which will really help to increase lift/forcing. Given the strong mid-level winds, we are looking at vertical shear values to be in excess of 35-40 knots across the region.
At the surface, temperatures are expected to reach the mid 80's to around 90F with dewpoints right around 70F. A piece of computer model guidance is showing mid-level lapse rates around 6.5 C/KM on Saturday which is pretty decent. The combination of high temperatures, high dewpoints, and steep mid-level lapse rates should lead to moderate amounts of instability region wide. We are looking at the potential for SBcape values in excess of 2500-4000 J/KG, MLcape values 1500-2000 J/KG, and LI values in the -6C to -8C range.
As the cold front slides east on Saturday, there are some hints that a pre-frontal trough may develop out ahead of the cold front. If this does come true, we could be looking at t'storms firing as early as 1-2 PM across western sections and then sliding east. If a pre-frontal does not develop, storms may not fire until 2-3 or even 4 PM. Typically, we almost always see pre-frontal troughs develop so I believe we will see action early on in the day along/ahead of the pre-frontal trough and then quite possibly again later on just ahead of the cold front.
Given the potential for moderate instability coupled with fairly strong winds aloft, and strong forcing from the front and/or pre-frontal trough and enhanced forcing from the right front quadrant of the upper-level jet, we are looking at numerous t'storms Saturday afternoon and quite possibly multiple lines of t'storms. Any t'storms that develop will have the potential to become quite strong very rapidly and approach severe limits. The main threat with any storms will be damaging winds in excess of 60 mph. Small hail is also a possibility, however, the freezing levels appear to be rather high but if any supercells develop, which is a possibility if we can achieve 3000+ Capes, then there could be a secondary threat for large hail. Torrential downpours are very likely with any storms so flash flooding will be a possibility.
This potential will continued to be closely monitored.
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