After being in a blocking pattern for much of the summer, the jet stream has flattened. This will allow the hot weather that has been building to New England's west and south to spread east and north. The chances of a heat wave for Wednesday through Friday (and maybe Saturday for some) have increased. A heat wave is at least three days at or above 90 for a high. Here's a look at what to expect:
WEDNESDAY
High pressure takes over for Wednesday, leading to a mainly dry and sunny day. I only write mainly dry since far northern areas could see a spot shower in the afternoon. Temperatures and humidity will be building across the region. While much of northern New England will be held to the 80s, southern New England will be shooting to the upper 80s to low 90s.
Since humidity will still be building, heat index values are looking to remain in the low to mid 90s for the day, near the actual air temperature. With a strong offshore flow, the heat will make it all the way to the coast. This will help Boston possibly get to 90 and potentially log their first heat wave of the season (most of New England has already experienced at least one).
THURSDAY
Thursday will likely see heat increase to at least heat advisory levels across southern New England. For a heat advisory to be issued, heat index values must be expected to reach at least 95° for two days or 100-104°over one day. Right now, it certainly looks like these values will hit 95° on Thursday and Friday for much of southern New England. Temperatures may only be a degree or two hotter, but humidity will be increased, leading to higher heat index values.
In a rather significant shift in model trends, thunderstorms are now looking potentially widespread on Thursday. With ample heat and instability to work with, these storms could become strong to severe. The storm prediction Center currently has the southern two thirds of New England in the "slight" category for severe weather. This is the second level of five on their severe weather outlook. At this time, all potential hazards (wind, hail and tornadoes) are on the table, but these threats will be refined over the next 24 hours or so.
This potential for severe thunderstorms may steal Thursday's weather headlines from the intense heat. Exact timing of the storms remains to be determined, but depending on when storms come through and how widespread they are, they could put a bit of a damper on afternoon temperatures, especially in northern New England. Again, depending on timing and magnitude, the northern third of northern New England may get held in the low 80s or even upper 70s. While southern New England has the better chance for severe weather, temperatures are still looking to shoot well into the 80s to low 90s as mentioned in the first paragraph of this day for the southern two thirds of New England.
FRIDAY
Friday is looking to be the peak of the heat across New England. Even far northern areas are looking to get in on the heat with highs into the mid 80s to mid 90s region wide. As mentioned in yesterday's post, energy from northern low pressure systems could drop into these areas, causing more clouds and storms during the day. The latest trends have pointed toward lower coverage of storms and a later arrival time. Both of these factors would allow northern areas to get in on the heat.
As for southern New England, morning lows will likely only drop into the low to even mid 70s, so the day will get a head start on heating. Highs will be in the low to mid 90s with dew points in the low to mid 70s. This will create heat index values of 95-103°. An excessive heat warning is when heat index values are expected to hit 105°, so that will be something to watch as temperatures are refined throughout this week. There is a chance for an isolated storm to slide south in the evening.
WEEKEND
A cold front will bring an end to this heat and humidity over the weekend. As of now, it looks like much of southern New England will have one more hot day on Saturday. How hot it gets on Saturday will depend entirely on the timing of the front. This front has been trending toward a later arrival time, which would allow southern areas to heat to the upper 80s to low 90s once again.
Since the front is dropping in from the north, northern areas won't heat up as much on Saturday since the front will reach them first. Highs there may top out in the mid to upper 70s. The best chance at 90s on Saturday will be across Connecticut.
Saturday will very likely be unsettled as the front passes through. At this time, scattered to numerous thunderstorms and downpours are looking increasingly likely. Timing on all of this will be hammered down later this week.
Euro model showing scattered to numerous showers and storm Saturday afternoon:
The front is looking to clear New England by Sunday, bringing a major change in weather. Temperatures will be looking to top out in the mid 70s to low 80s with dew points nosediving into the 50s. Dew points may even drop into the 40s for northern areas. This will be a very refreshing change in pace from dew points in the mid 70s.
BEYOND
Next week is looking to be very different from this week as cooler temperatures are looking increasingly likely to prevail. This may also come with an increase in unsettled weather once again.
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