Heavy Rain & Strong Winds Expected Tonight & Fri; A “Flash Freeze" Expected Late Fri Afternoon/Eve

There aren’t a whole lot of changes to the forecast, except for some minor refinements to when the rain begins this evening and also to when I’m expecting a “flash freeze” across the region late Friday afternoon into Friday evening. A strong storm system now located over the central Great Lakes region is still expected to move into the eastern Great Lakes region by late tonight and Friday morning. That storm system is still anticipated to move into eastern Ontario and southern Quebec provinces by late Friday. This storm system is going to bring multiple hazardous weather types across the region, including strong winds, heavy rain and then a “flash freeze” at the very end of the storm. Let’s try to detail each hazard individually: Strong Winds: The pressure gradient between the strong low pressure system moving into Ontario and Quebec provinces and a strong high pressure system over Newfoundland and Labrador will lead to strong winds to be a real concern with this storm system. Current data indicates that the strongest winds will occur from about mid-morning Friday until about midnight Friday night. During this time, wind gusts of up to 50 to 60 mph are expected, especially when the Arctic front moves through during the late afternoon and early evening hours of Friday. These strong winds during the day Friday into Friday evening will lead to downed trees, downed power lines and power outages. Heavy Rainfall: Heavy rain is expected to occur throughout tonight and Friday morning before there’s a brief break early Friday afternoon. This will likely be followed by a line of heavy showers that will accompany the front during the mid and late afternoon hours of Friday. It’s possible that the rain will change to a brief period of snow late Friday afternoon and Friday evening before it ends towards midnight Friday night. Total rainfall amounts tonight and Friday will be around 2 inches with local amounts of up to 3 inches possible. The heavy rainfall tonight and Friday will lead to widespread ponding of water on streets, highways and areas that have poor drainage. In addition, there’s also the possibility for minor river and stream flooding. It appears likely that this rainfall will push a majority of the rivers and streams across the region to near flood stage with some seeing minor flooding. Any flooding of rivers and streams may occur this weekend when they reach their crests. A “Flash Freeze” With Very Icy Conditions Expected From Mid To Late Friday Afternoon Through Friday Evening: A rush of Arctic air will push into the area from southwest to northeast leading to an almost immediate 10 to 20 degree fall in temperatures. The biggest uncertainty is when exactly will the Arctic front move through. This is extremely important as we need to know exactly when streets, highways, parking lots and driveways will become icy and hazardous for travel. Some of the high resolution weather forecast guidance shows the rapid fall in temperatures to well below freezing by 3 to 4 pm Friday afternoon. Other high resolution weather forecast guidance delays the rapid temperature fall to well below freezing to about 5 to 6 pm or so Friday. This minor time difference in when the Arctic front moves through is actually extremely important. This is because if we see the “flash freeze” occur around the 3-4 pm time frame, it’s going to lead to a very difficult and hazardous afternoon and evening commute. On the other hand, a 5-6 pm Arctic push would allow most people to get home from work and school safely, but Friday evening travel is still going to be extremely hazardous. Based on all of the data that I’ve looked at, I think that we’ll see the rush of Arctic air push into Western Mass between 3 and 4 pm Friday afternoon leading to “flash freezes” across the region & conditions will be very icy by 4 pm across Western Mass. Across Central Mass, it appears that the push of Arctic air with a rapid fall in temperatures to well below freezing will occur between 4 and 5 pm Friday afternoon. “Flash freezes” and very icy conditions are likely to develop across Central Mass during that 4 to 5 pm time period. One thing that I want to emphasize is that “flash freezes” do not happen very often and because of this forecasting them are very difficult. These sort of flash freeze events only happen once or twice every 5 years or so. That said, my best educated guess right now is that there will be icy streets, highways, parking lots and driveways. The temperature drops with this Arctic front have already been insanely dramatic and many locations over the Central United States have recorded 40 to 50 degree temperature drops in one hour! While the temperature drop across Western and Central Mass will be dramatic, it will not be that dramatic. At this point, I think we’re looking at a 10 to 20 degree temperature drop in about an hour when the Arctic front moves through. One thing that is going to be important in determining how icy it may get is the time difference between the rain ending and the Arctic air arriving. If it’s still raining when the Arctic front arrives, then road surfaces will not have any time at all to dry out and thus they will ice up for sure. On the other hand, if we see the rain end for a while, even up to an hour before the Arctic front arrives, the strong winds may be able to “blow dry” the roads leading to just lingering puddles to freeze up and prevent widespread icy conditions. Unfortunately, current indications are that there may be very little time, if any, between the rain ending and the Arctic air arriving. Because of this, I’m very, very concerned that water on streets, highways, parking lots and driveways will freeze up leading to very icy and very dangerous travel conditions across Western Mass by 3 to 4 pm Friday and across Central Mass by 4-5 pm Friday. These very icy conditions are expected to continue through Friday evening. My blunt and to the point recommendation to you is to be off of the roads, if you can avoid it, by 3 pm Friday across Western Mass and by 4 pm Friday across Central Mass. It’s going to take time for DPW crews to respond and for treatments to take effect and thus icy and dangerous travel conditions are likely for several hours late Friday afternoon and Friday evening. So, Let’s Break It Down Even More: For The Rest Of This Afternoon & Tonight: Rain is expected to rapidly overspread the entire area during the 6 to 7 pm hour and it will be raining everywhere shortly after 8 pm this evening. The rain is then expected to become heavy at times across the entire area by midnight. Heavy rain is then expected after midnight tonight. Temperatures will remain between 35 and 40 Degrees the rest of this afternoon and this evening and then rise to the mid to upper 40s very late tonight. Winds the rest of this afternoon will be East at 10 to 20 mph. Winds tonight will be East at 10 to 20 mph with gusts to 30 mph before midnight and East to Southeast at 20 to 30 mph with gusts to 40-45 mph after midnight. Friday: Heavy rain is expected throughout the morning, which will become more showery in nature during the afternoon. A line of heavy showers is expected to push across Western Mass by mid-afternoon and then across Central Mass during the mid and late afternoon hours. This line of heavy rain will be the Arctic front and will bring with it wind gusts of up to 50-60 mph, the potential for a quick change to snow, a rapid temperature drop of up to 10 to 20 degrees to readings well below freezing and a “flash freeze” leading to very icy and dangerous travel. As I already mentioned, I expect this to occur across Western Mass by 3 to 4 pm Friday and across Central Mass by 4 to 5 pm Friday. To make things even more icy, any snow that falls on ice will lead to even more slippery conditions during late Friday afternoon and Friday evening. Any snow looks to come to an end by about midnight Friday night with a dusting of snow expected. It’s also expected to be very windy throughout Friday and Friday night. During the day Friday, South to Southeast winds of 20 to 30 mph with gusts to 50 mph are expected. An enhanced period where wind gusts of up to 60 mph is expected when the Arctic front moves through during the mid and late afternoon hours on Friday. On Friday night, Southwest winds of 20 to 30 mph with gusts to 40 to 50 mph are expected during the evening and Southwest winds of 15 to 25 mph with gusts to 40 mph are expected after midnight. The strong winds on Friday and Friday night could lead to downed trees, downed power lines and power outages. High temperatures during the day Friday will be near 55 Degrees with temperatures rapidly falling to 25 to 30 Degrees by 4 pm Friday across Western Mass and by 5 pm Friday across Central Mass. Low temperatures Friday night will be between 10 and 15 Degrees. This means that everything will be frozen solid by sunrise Christmas Eve morning. Bottom Line Is That this is NOT your typical December wind and rain storm & this is a storm that means business. I will be continually updating you on the latest regarding this storm, which is going to have many different impacts from heavy rain to strong winds and very icy & dangerous travel conditions. Be safe out there!! Merry Christmas & Happy Holidays everyone!