Halloween Day Features A Strong Baroclinic Low For Much Of The Northeast

Halloween 2019, unfortunately, will not go as hoped for much of the Ohio Valley and Northeast. A rapidly strengthening low pressure system will make its way northeast from the Mississippi Valley, the Ohio Valley and Southern Ontario. It will bring a significant wind and rain threat right around the time trick or treating will begin in the northeast. In addition to the wind and rain threat, the reach of the system will be felt along the east coast as well. A severe thunderstorm risk is a concern for eastern Pennsylvania down to North Carolina. It will be an active Halloween day.


Earlier in the week, there was significant disagreement among the GFS and Euro (as well as ensembles) as to both the formation and intensity of the low pressure system. The Euro had a prominent low forming, while the GFS was not in agreement; keeping flow more zonal in nature. This is no longer the case. 

Stratiform rain will likely begin around 12z (8am) for Windsor and push east, with the rest of Southern Ontario being hit by 15z (11am). It will likely be sustained for much of the day. The heaviest precipitation will be before the cold front coming through between 21z and 00z (5-8pm). Current estimates range from 30-50 mm with potentially more west of Hamilton due to rainfall currently ongoing (6:30pm Wednesday). There is a chance that parts of Southern Ontario get into the low's "dry slot", which gives an opening around trick or treat time, but there will still likely be the wind threat to deal with (more on that in a minute). This may lead to localized flooding of areas with the plentiful amount of leaves in eaves troughs and sewers, so monitor those throughout the day tomorrow. 

The greater concern is the wind threat with this system.

The sounding to the left (subject to timing changes) shows the strongest winds above an inversion. This is pre-cold front. You can see the southeasterly winds still ongoing at the surface. The strongest winds are not likely to be mixed down to the surface at this point despite the low continuing to deepen.







The second sounding, about 3 hours later, shows a well mixed layer up to about 875 mb. At this height, there are 50 kt winds ongoing, which may get mixed down with precipitation in addition to the mixed layer itself. This is the most significant threat the system poses. Gusts could end up exceeding 100 km/hr; especially with winds coming off Lake Erie with a lack of friction to slow them down.

The entire system will have winds ranging from 70 to 90 km/hr, but north shore Lake Erie will be the most at risk area. Shoreline areas were hit by another strong low on Sunday, so water levels are already above normal. Long Point, Turkey Point, Port Colborne, and Crystal Beach will likely be hit quite hard by strong winds and waves potentially exceeding 10 feet at some points. Coastal properties should be quite vigilant of this threat especially because it happens overnight and into the morning.

The wind threat will begin on Thursday night and continue into Friday afternoon, with less of a threat to the coast lines beyond Friday morning due to the low pushing to the NE out of the Great Lakes area (this means the wind direction will shift from SE, to E/NE (parallel to shoreline) and finally as the pressure gradient becomes weaker, stronger winds will begin to subside by Friday night. Coastal areas around Buffalo, as the winds turn more easterly in the morning, look to be hit significantly by a surge of lake water.

Special weather statements have already been issued by Environment Canada and I think an upgrade to a watch/warning is highly likely by morning. If you have any loose items in the yard, or even Halloween decorations outside, make sure they are well fastened down, or just take them inside unless you want to unintentionally decorate the neighbor's yard. 

This isn't the best case for the kids looking to trick or treat, but the high winds may just be spooky enough throughout the night.

July 19th/20th Severe Weather Threat For Southern Ontario

Very Hot

If you're reading this and don't live in Ontario, southern Ontario is in the midst of an intense short term heat wave; temperatures from Thursday to Saturday are projected to reach the mid 30 Celsius mark (86+F) with Friday and Saturday being the peak. Dew points with this very moist air mass will also be very high; current surface analysis station readings (11pm EST) are showing a 77/70 F Temperature/Dew Point spread in Windsor, with 10 knot SW flow pushing more of that humid air into Ontario... yeah, it's hot and very humid, and it will continue to get worse. It may even approach record territory for many cities this weekend across the province. 

If that wasn't enough of a concern, as you'd expect with this air mass like this, severe weather is also a threat throughout the entire weekend. There is a lot of uncertainty tied to these storms, however; storms that form late in the day in Wisconsin/Michigan will make their way into the Ontario area in the early morning hours nearly every day of the severe threat. Whether they survive long enough to reach Ontario, make it into Ontario and take away some of the instability needed for Ontario storms to becoming explosive, or become explosive themselves, will have a influence on what Ontario will see this weekend. In addition, there's plenty of model disagreement; both in solutions per model, and run-to-run consistency. I'll break down the environment the storms will head into, however.

Severe Threat Analysis- Friday

Near Chatham, Ontario. 18z

Strong ridging will continue to hold its ground across the SE US. As a result,the strongest upper level winds, and the strong jet streak, will be kept into northern Ontario. Most of southern Ontario will have only mid 20 knots of upper level speed shear. The same holds for the 500 mb flow: mid 20 knot winds. The strongest winds, located at the 700 mb level (~35kts) seems to come through S ON at the worst time if you want storms: around 18z. They're also maximized a bit north of the strongest storm risk area. That being said, models disagree on the bulk shear values: the GFS paints a meager picture, and the NAM is more bullish on stronger values.

In general, this means that the best speed/directional shear will not lie over the strongest areas of instability. Storms are likely to be strong due to the extreme instability, but more pulse style in nature; as opposed to discrete, long track supercells. This doesn't mean supercells can't/won't form (especially if one forms further north of the Kitchener/Waterloo region), but the further south in Ontario you go, the less shear storms will have to work with to reach max intensity.


I do think, with the extreme instability the area is due to see, that there's a chance that storms that do fire (especially along lake breeze boundaries due to lack of strong trigger) will upscale quickly (merge and continue to explode along the boundary). The entire 401 corridor should be paying attention to the possibility of torrential rain, hail, and damaging winds. It could get quite messy. An isolated tornado can't be ruled out if storms can avoid hitting each other and merging quickly, and can do so before running into Lake Erie.

If chasing (I'll likely be out), I think the safest bet to see storms will be from the Grand Bend area and south to Windsor/Chatham. That said, there is absolutely a chance that storms could fire along the 401 corridor, and I'll bet that the chances of it increase the longer that storms don't fire throughout the day, or if the air mass isn't influenced by early convection, but that's a morning observation. Some runs even had stronger storms entering the Hamilton/Burlington area by 18z. We'll see about that tomorrow. If that lake breeze boundary gets to set up to prominence, or the Lake Huron/Erie breezes collide with this brutal air mass, storms will explode to life. As discussed, there's a lot to determine first before that may/may not become a reality.

Photography wise, I'll see what I get to work with. If the relatively weak deep layer shear is what verifies, I can see these storms being VERY high precip style, which means structure and lightning may be problematic to get. If a tornado does form, it'll likely be rain wrapped, so if you're driving around the storms as they fire, think twice before driving into them.

Either way, stay cool, drink lots of water, and be on alert for some potentially strong storms this weekend. 


Update Verdict (1:30 am Saturday morning):

I wish I took more screenshots of the radar while out chasing to prove my points, but I was driving around an awful lot and it slipped my mind. Ideally I'll pay more attention for future blogs.

CAMs did not do a good job of picking up ongoing storms heading into western Ontario in the am. They figured the storms would have been dying crossing Lake Huron, or would have already been dead by then, but with the extremely unstable air mass in place, they had too much fuel to die out completely. As a result, any storm energy north of the 401 area had most of their energy consumed by the early morning storms. Additionally, the outflow from these storms collided with a W-E lake breeze boundary already established by the Woodstock/Burlington area and we were off to the races. 

Storms did fire along the 403/401 corridor; nearly exactly where I expected and mentioned above. I had them nearly form on top of me as I pushed west around 12:30 pm. I was tempted to stick around and see if a strong line of storms (with high winds and lots of lightning) formed, but I liked my original target a bit southwest of London.

Though I did allude to storms possibly being tornadic if they stood a chance at being discrete, truthfully, I did not expect the 2nd wave of storms to the NE of London to have so much rotation, or be as long lived; considering they were passing through an area that had already been hit by storms twice earlier in the day. I guess that's just a testament to how intense this air mass really is. It can make recover in very little time. I was in the notch of the first tornado warned storm that passed right over the city of London, but thankfully it didn't produce anything that caused any major issues. It became outflow dominant shortly after as it pushed SE towards Lake Erie. The 2nd wave of storms to the NE of London that tracked SE towards Woodstock were likely cells that spawned and followed the outflow boundary of the previously mentioned storm. Both had rotation on them for hours. I tracked the one cell further to the NE as it tracked towards Embro because I thought it had the best chance of staying discrete longer than the south one did. I'll be reviewing the pics and time lapse footage shortly.

Overall, I was content with my forecast. Definitely some room for improvement, but I did cover the areas that were hit today. I was just taken back with the timing and how quick the boundary layer recovered after the earlier storms. I did also think it would upscale faster than it did. It's a testament to this brutal, unstable, air mass.


Severe Threat Analysis- Saturday

Very, very muggy

Not an awful lot will change in terms of the synoptics on Saturday when compared to Friday. The ridge in the SE US will remain in place, so, again, the best upper level and mid level winds will not be located over the areas in southern Ontario with the most unstable air.  As we saw on Friday, however, outflow boundary/lake breeze interactions, when mixed with an extremely unstable air mass, can still produce strong, relatively long lived storms; even with marginal deep layer shear.

Saturday (today) has a chance to have an EVEN MORE unstable air mass compared to Friday. Temperatures are expected to be a bit hotter, and dew points are expected to climb higher than Friday. Areas across southern Ontario may see temperature/dew point spreads of 92/80F- that is just unbelievable for Ontario. PWAT (precipitable water) values, in some areas, are about 2.5 inches (!!!).

Just absurd amounts of MLCAPE

CAMs, once again, show convection from Michigan dying before reaching Ontario in the early morning. We already have evidence from Friday that this trend is not to be taken as gospel. The morning will tell you whether or not these storms can stay alive with the fuel from the air mass in place. If they do track into Ontario, their timing and placement will be key on where, or if, ouflow boundaries are placed. With the lack of a surefire trigger to ignite storms, such as a cold front, they will need a bit of help to get going. Early morning convection, if it does make it into Ontario, could make Saturday seem quite similar to Friday.

So, not much changes for Saturday from Friday's forecast: the 401/403 corridor could get subjected to more high wind, torrential rain, and frequent lightning anywhere the lake breeze sets up. These volatile air masses make lake breeze boundaries good starting points; especially with a lack of a definitive trigger. Outflow boundaries from preexisting storms (if applicable) may also be factors. I still think early morning storms, whether they're modeled well, or horrifically (like Friday), may play a key role in shaping how Saturday unfolds. Storms could also be going up early again; early afternoon, as opposed to later in the day. There could be multiple rounds as well, especially as you go further southwest.

London area, 18z

I think the best areas, once again, for severe thunderstorm (and slight tornado chance depending on how discrete storms remain and how they interact with surroundings) ends up being in the Grand Bend, London, Windsor triangle area, with another chance at more of the same storms along the 401/403 corridor. Area wise, it doesn't look like much has changed from yesterday, but if morning runs show something different, I'll make sure to cover it.

Stay cool, stay hydrated and stay weather aware tomorrow. For those that loathe this kind of air mass, relief is on the way on Sunday.


12z Update:

Model consensus in the morning has shown quite a bit of change. They've been showing a nasty line of storms heading into Ontario along eastern Lake Huron around 00z instead of having semi-discrete storms that the previous 00z runs had shown, which would have been similar to yesterday. The expectation is that the weak cap will hold with little to no triggers (especially as no storms came through earlier in the day laying down outflow boundaries). If this were to be the case, brutal rain and very strong winds will be the primary threats for as long as the bow echo tracks southeast. This can, and likely will, include the area mentioned in the forecast above, and anywhere from Guelph, Hamilton, Burlington and south.