Unfortunately I don’t have a ton of time for a full update this evening so I’ll save analysis of this weekend’s rain threat for tomorrow morning’s post. In this post I’ll look at tomorrow’s severe weather threat.
Today’s forecast worked out pretty well. Mostly sunny skies were reported across the area with only some high thin clouds to make a feeble attempt at blocking the sun. Temps soared as forecast into the 90’s almost everywhere. Even behind the sea breeze front, temps were near or over 90. Dew points dropped slightly, as forecast, as the atmosphere mixed out but it still felt quite stifling. Ready to do it again tomorrow except with even more humidity?
The plume of tropical moisture, believe it or not, was sitting just to our south today. The humidity you felt was mostly due to yesterday’s rain. Tomorrow, however, the full force of the tropical airmass will be pointed right at us and dew points will soar into the 70’s and stay there right on through the day (there is simply too much moisture in the air tomorrow to mix out like today). Meanwhile, a cold front will be approaching from the NW and an upper level disturbance will be moving into the area from the west (right black line on W edge of blue). The front and the disturbance will act as a trigger for some storms tomorrow. See those PWATs >2″ (blue colors) over coastal areas? Those PWATs, 3 standard deviations above the mean and in some cases never before seen in GEFS climatology, will provide plenty of fuel for downpours. Will there be any fuel for other severe weather? Absolutely.
As temps soar into the 90’s again tomorrow, the atmosphere will become quite unstable. CAPE values in excess of 1,500 j/kg will support strong storms, some of which could be strong enough for gusty winds. The atmosphere looks far too warm for significant hail but as a result of all the moisture, the atmosphere will be primed for a tornado or two. They look weak at this point but be prepared to seek shelter if you do come under a tornado warning. Also have a plan to be notified of that tornado warning if it’s issued for your area. Again, this is by no means a tornado ‘outbreak’ but one or two spinups are possible.
The final ingredient, the organizer, looks not fantastic but good enough for at least some severe storms. 0-6km shear between 20 and 40 knots isn’t fantastic but it does raise the isolated severe storm red flag. The most important thing to note about tomorrow’s storm setup is that the biggest threats will not be gusty winds or hail or tornadoes. The biggest threat will be intense lightning and very heavy rain that could lead to flash flooding. It’s been so dry that the soil has ‘forgotten’ so to speak how to absorb moisture. This means that any heavy rain that suddenly falls will run right off and into the nearest road/ditch, some of which won’t be able to handle the large volume of water at once. Remember, turn around don’t drown and when thunder roars, go indoors.
I’ll be back tomorrow morning with a full update on both the severe weather threat and the heavy rain threat this weekend.
We have two interesting weather systems coming our way in the next few days. The first will be a cold front dropping south out of Canada tomorrow afternoon. It will bring with it the threat for showers and storms tomorrow afternoon and into the evening. No severe weather is expected. That front will lose steam and stall somewhere just to our south Friday morning at which point a wave of low pressure will try to develop and move NE along the front. Where that low tracks and how strong it is will determine the outcome of our second weather event and how much beneficial rain we receive. Quieter weather is expected to follow that event with mild temps and sunny skies expected into next week.
Let’s do a quick rundown of the three ingredients needed for strong/severe storms. Doing this will explain why some storms are likely but also why severe storms are not. Instability is a go as temps soar into the 80’s and low 90’s while dew points climb as well, into the upper 60’s to low 70’s. Nothing incredible, but certainly enough for some booms.
How about a trigger? An upper level disturbance will be pinwheeling around the base of an upper low over Eastern Canada tomorrow. Meanwhile, a surface cold front will be sagging south across the region tomorrow. Both of these are shown in the image above with the left two panels representing one model forecast and the left two representing another. While there are some differences, the general idea remains the same. The general idea is that there will be enough of a trigger to get at least a few storms going. The big question then becomes, will they become organized enough to produce severe weather?
The short answer to that question is no. While guidance indicates some marginal shear, perhaps enough to trigger an isolated severe storm, there is not enough shear to support widespread severe weather. This means that you can expect your typical garden variety thunderstorms tomorrow with heavy rain, frequent lightning, and possibly some gusty winds. Remember, storms don’t have to be severe to be dangerous. Lightning can strike up to 15 miles from a storm and is just as dangerous as strong winds or large hail. When thunder roars, go indoors.
Putting that all together, here’s the big picture for tomorrow afternoon/evening. Scattered storms look to develop in the early afternoon over the mountains and will slowly move SE through the afternoon and into the evening hours before reaching the coast in a weakened state later in the evening. Storms are most likely in the mountains and least likely along the coast and especially along the midcoast.
Tomorrow’s cold front will stall just off the coast Friday morning and a low pressure area will develop along its southern end over the Mid Atlantic states. The GFS shows this situation well with the map shown depicting conditions at 8:00 Friday morning. Scattered showers are possible during this time but steady rain, if it happens, is likely to occur Friday afternoon/evening. There is still quite a bit of uncertainty in the forecast for Friday as guidance offers several different possibilities. There are two scenarios, the dry scenario, and the wet scenario. I break each down below along with which I think is more likely.
The NAM and GFS models from this afternoon present the two more extreme solutions: almost no rain on the GFS and tons of rain on the NAM. The map above is data-rich and small, so click it to enlarge it so you can see all the details, if you want. The main difference between the models revolves around the amount of upper level energy in the atmosphere and where that energy is located. The NAM has way more energy (lots of red, top right panel) while the GFS has very little (thin stripe of red, top left panel). Also of note is the location of the kicker disturbance. The software I use to get the data for these graphics makes any boundaries very hard to see so I highlighted New England as well as the Quebec/Ontario border to show the differences in location of the kicker disturbance. Notice that the NAM has it farther west, closer to the border while the GFS has it well east of the border. Keep in mind these maps are valid at the same time. By keeping the kicker farther west, the NAM allows for more moisture to stream northward and also gives the low more time to strengthen, bringing more rain. The GFS on the other hand hurries the kicker along, pushing the storm and the moisture offshore quickly.
The difference in moisture can be seen in the Precipitable Water maps which show how much moisture is available. Notice how the blue (super moisture laden air) is much more abundant and closer to the coast on the NAM (right) compared to the GFS (left). Also notice that on both models, SE MA gets in on the action. Heavy rain is likely there but rain chances become more uncertain as you head NW. Notice also how the mountains are in fairly dry air (brown/yellow). Very little rain is expected there. The battleground so to speak will be those areas in between the SE MA coast and the ME/NH mountains.
What do I think will happen? Right now I am leaning towards the GFS’s scenario because the larger scale pattern supports it. This morning’s upper air map shows this well. Winds in the upper atmosphere are overwhelmingly west-east over North America with only shallow ridges and troughs. This “zonal” pattern does not lend itself to troughs digging and amplifying which is what the NAM depicts. Right now, the WNW flow around the heat dome over the SW US looks likely to simply shove the fledgling low off the coast, leaving us with just a few showers or perhaps a brief period of steady rain. SE MA is likely to see the steadiest and heaviest rain with showers making their way all the way up to the base of the mountains. The mountains are likely to stay mostly dry as they are simply too far removed from the deep moisture to our SE. I’ll have more on this tomorrow along with updates on the thunderstorm threat.
Quieter weather is expected through much of next week.
Today will feature slightly cooler temps, less humidity, and another chance for strong/severe thunderstorms. The thunderstorm threat will develop later this morning and continue through the early evening hours. Storms are more likely in SW areas where more energy will be available aloft. While most of the storms are not likely to become severe, some of the stronger cells do have the potential to mix down some strong wind gusts and perhaps some small hail. Frequent lightning and heavy rain are the main threats. Highs will range through the 80’s with dew points in the 60’s which is still warm and certainly not dry but far better than yesterday.
A vigorous disturbance is currently located north of the Great Lakes and is forecast to drop SE and intensify, arriving in our area bu sunset. Storms will form out ahead of it late this morning/early this afternoon. When I talk about forecasting thunderstorms, I talk about the trigger, the organizer, and the fuel. This disturbance will be the trigger for today’s storms.
A band of strong winds and powerful shear will rotate around the disturbance today. The strongest winds will be pointing at Southern New England while Northern Maine sits in the calm aloft associated with the disturbance being to their south. In southern Maine/New Hampshire, we’re a bit on the edge. We likely see enough shear to get some small clusters but large squall lines are unlikely. If that disturbance can intensify enough fast enough, it could pull some of those winds north and we could see a bit more action. If it remains a little weaker, those winds will continue screaming towards SNE. These winds will be our organizer.
The biggest question today is how unstable the air will be. A cold front moved through last night (remember those storms?). That front has moved offshore and has taken the extremely soupy/unstable air with it. We are left with marginal moisture and several areas of clouds to limit surface heating. Model guidance suggests that more unstable air will try to filter in from the west later today but I have to wonder if that will make it in time. Also of note with regard to instability is wind direction. Westerly winds don’t exactly bring in the warm moist air you need for big storms. Regardless, we do still have leftover moisture and dew points remain in the 60’s which is sufficient for at least some storms. Also, wide swaths of clear skies this morning support some solid surface heating which will bring temps up into the 80’s, also plenty sufficient for storms.
All that to say, ingredients are at least sufficient for some storms, a few of which could be severe with strong winds and small hail. However, I do have doubts as to how unstable the atmosphere is. Also, we don’t have optimal winds aloft for organizing storms into lines capable of widespread wind damage. While organized severe storms are not forecast, still do keep an eye to the sky today and be prepared to duck inside for a few minutes if you plan on heading outside.
More storms are possible Monday and Thursday with two more cold fronts.
This week will serve as exhibit A for the old saying “If you don’t like Maine weather, wait a few minutes”. Tomorrow, lazy spring breezes give way to summer showers and storms. By Sunday, the brisk winds of fall usher in the snows of winter which could drop several inches of snow come Tuesday morning. Not a fan of the snow? By late next week, temps in the 60’s are on the table once again along with rain.
Spring/Summer: Warm And Showery Tomorrow
Today’s warm breezes continue tomorrow bringing in warmer and, believe it or not, humid air. Dewpoints will rise to near 60 tomorrow which will feel humid this time of year. Temps will range through the 60’s for most. The warm humid air will fuel afternoon showers and storms with the best chance for rumbles in the mountains where the atmosphere is a tad more juiced. No severe weather is expected tomorrow but when thunder roars, go indoors.
Fall: Brisk Winds Deliver Arctic Air Sunday
After getting Spring and Summer out of the way tomorrow, Fall takes over Sunday as a clipper moves through. Rain showers will change to snow squalls as low pressure develops offshore and races east. Winds will be quite gusty as well. On Monday, temps likely will stay near or below freezing as cold air pours in. This sets the stage for the more sizable snow threat on Tuesday.
Winter: Snow Threat Tuesday
Sunday’s cold front stalls offshore Monday as a clipper blasts SE from Alberta. The clipper will move offshore Monday night and a strengthening, negatively tilting upper level trough will help it to intensify. Uncertainty still remains as to the exact track of this storm and thus the exact impacts though some accumulating snow seems likely along the coast. Snow likely moves in Monday night and lasts through Tuesday afternoon. Guidance is fairly far offshore with this storm at the surface but the upper air pattern is giving strong indications that this is likely to drop at least a couple inches along the coast, perhaps a little more.
Spring Returns: Warming Up Late Next Week
As we head into the latter part of next week, the pattern is likely to modify a bit. The longwave trough in the east is likely to remain but looks to retrograde slightly west and weaken. A flatter pattern out west will allow for the Arctic connection to be cut off and ridging is likely to build over the area. All that jargon translates to a return to normal or above normal temps by the time next weekend rolls around. Current guidance is hinting at heavy rain accompanying this increase in temps but it is far too early to tell specifics. Just know warmer temps are on the way.
A Note On Spring Updates
It’s that time of year again, the sun is out, the birds singing, and the snow flying (sometimes). Spring is here and with it comes Outdoor Track season. Unfortunately, my practice schedule will not allow for evening updates beginning either next week or the week after. I’ll still have morning updates every morning but getting home at 6:30 doesn’t leave a lot of time for forecasting. While I’ve developed a solid system for time management, sometimes high school obligations get in the way.
Thank you all for your patience and continued support, it means a lot.
A jucier than normal morning post today as the forecast for this evening is fascinating and very complicated. Before the snow arrives, look for increasing clouds with highs in the 20’s inland, low 30’s along the coast. Snow should arrive around 4 PM or a little after, then things get interesting.
The setup from yesterday evening’s post remains largely the same this morning. Low pressure currently over Michigan will move E into southern Ontario this afternoon. Secondary low pressure will develop to our SW and move NE east of us. How fast this low develops is the key to the forecast. The general idea is that the combination of tons of upper level energy, warm ocean waters, and a favorable upper level setup (VERY negatively tilted trough for those that understand) will lead to rapid development just offshore.
Intense snow bands will begin to develop along with the low but when and thus where these bands develop is still an unknown. We do now have a slightly better idea of where to look for the heaviest snow, the lightest snow, and where it could go either way. This is a very complicated situation and I mean it when I say there is high bust potential here. With that being said, I doubt York County sees much more than 2-4 or maybe 5″. It looks like things pull together just a little too late down there. The Midcoast and areas NE of Augusta/Auburn are likely to see a solid 6-10/8-12″ snow. It’s the areas in between that are really tricky.
This is what I anticipate snow amounts to look like. Uncertainty is very high especially NE of York County and SE of Augusta.
Even in areas without much accumulation in terms of raw numbers, expect difficult travel as the snow will fall very heavily. There is also the chance that those in the heaviest bands see thundersnow this evening as well.
The immediate coast could mix with rain this evening before the heaviest stuff arrives. If this happens, watch for a rapid refreeze which would cause dangerous travel in those areas. Right now I think the peninsulas are most at risk for this but anyone east of Route 1 should be watchful.
Snow moves out tonight leaving a cold and gusty wind for tomorrow.