The weather story for the first part of this week will be a prolonged heavy rain event occurring Tuesday, delivering parts of the region some much needed precipitation. Temperatures will remain slightly below normal through Thursday, first because of the rain and clouds and then due to the influence of high pressure to our west.
Rest of today – NYC remains under mostly sunny skies, however, cloud cover is building to our west, so we could end up with more clouds later this afternoon. It will be a noticeably more humid day, although temperatures will still only top out in the low-80s.
Tuesday – rain should begin falling in the early overnight hours, and looks to persist through the morning and into the early afternoon hours. The heaviest rain seems likely to fall during the morning hours. Thunderstorms cannot be ruled out, and while the atmospheric conditions will not be very favorable (timing of the strongest lift will occur early in the day before any substantial daytime heating, which will be diminished due to cloud cover anyway), a few strong storms could still pop up in the morning. Some areas could see some isolated flash flooding if storm cells end up training over the same spots. Under the cloud cover and rain, high temperatures should be limited again to the low-80s.
North American Model High Resolution simulated radar for 11AM EDT Tuesday
Wednesday – rain will have cleared out after the passage of the cold front responsible for Tuesday’s storms. Behind this cold front, high pressure will set up over the Ohio Valley, bringing in cool, dry air. Temperatures will be quite comfortable in the low-mid 80s with low humidity.
Thursday – the pattern of cool, dry weather continues with another day of sunny skies and high temperatures slightly below normal in the low-80s.
Drought Relief
A slight/moderate drought continues to cling to areas of Long Island and costal Connecticut, as you can see from the map below. It does appear that this upcoming Tuesday storm will bring some much needed rain to these particular areas. As you’ll also note from the map of forecast precipitation totals for Tuesday, some of the highest totals are expected precisely in the areas that need them the most.
Weather Prediction Center’s Quantitative Precipitation Forecast for total precipitation between 8AM EDT Tuesday and 8AM EDT Wednesday
It certainly does feel as though Memorial Day 2015 has been the unofficial start of summer, given the warm and humid temperatures we’ve had from Sunday onwards. The warm, late-June like temperature trend continues through mid-week, with some chance for thunderstorms. Rain in any form would be most welcome, given that the region has been placed in a region of moderate drought as of this week.
Rest of today – the Bermuda high, more typical of mid-summer, brings us very warm and humid high temperatures in the mid-upper 80s, more than 15ºF above average for this time of year. If you like the heat, go out and enjoy it because we might see showers and thunderstorms both Wednesday and Thursday afternoons.
Wednesday – a weak cold front approaches from the west, bringing with it a chance for showers and thunderstorms. The critical question for NYC will be how long organized storms can stay together as they enter into influence of cooler, maritime air nearer to the coast. Temperatures will remain warm in the low-mid 80s with clouds and some breaks of sun. As is generally the case in these setups, the more sun we can get in the afternoon ahead of the frontal bou
North American Model high resolution simulated radar image for 8PM EST Wednesday
Thursday – we get another shot at thunderstorms Thursday afternoon and evening, with highs likely topping out around 80 under mostly cloudy skies.
Moderate Drought for the Region Forecast to Persist
We’ve had an remarkable run of sunny, rain-free days, and above average temperatures for much of May (and indeed even going back a couple of months), and while that’s translated to pleasant weather for outdoor activities, it also has meant that we’ve entered into a stretch of moderate drought. We had a stretch of no rain for 23 consecutive days, earlier this month, which definitely didn’t help things. According to the USDA Drought Monitor, Central Park recorded 7.12″ of rain from March 1st through May 19th, which is only about 63% of average for this time of year.
While we are only in the lowest tier of drought and were just added to this category this week, these drought conditions bear watching. We hope to get some rain out of this week, and it looks like more storms are on the way this weekend, however, the drought forecast for our region looks to have the drought persist through this summer.
As many of you woke up this morning, you were probably wondering, what happened here? This storm seemed like a dud. True, the snowfall totals in and around NYC were lower than initially forecast, but portions of the area did get slammed with over 20″ of snow. To put it simply – as I had laid out in the caveats from the last post, slight changes in track of this storm dramatically altered the placement of mesoscale banding features, hence leading to a sharp cutoff in snowfall totals from east to west.
Snowfall Totals
Looking at this snowfall totals map, you can easily make out the line that demarcates where the heaviest snow bands stopped their westward march. We got what appears to be around 6-8″ in the city, but just east of us in Nassau the totals jump to 12″ and then just east of that in Suffolk we see 20″+ totals.
Snowfall total map
On a larger scale, you can see the areas that got the highest snowfall totals, corresponding to where the heaviest bands of snow were able to pass over.
Forecasters are saying that the storm tracked further east than they expected by about 50-75 miles, which literally would have meant the difference from us having 6-8″ snowfall totals here in the city to easily 12-18″+. Now before we all go blaming them for a dud forecast (that some are already saying wasted taxpayer money), there are a couple things to consider:
Forecasters utilize a suite of different computer models to come up with these forecasts, in this case they favored the NAM (North American Mesoscale) and ECMWF (European Center for Medium Range Weather Forecasts) over the GFS (Global Forecast System), UKMET (United Kingdom Meteorology), and Canadian models. There were specific reasons for doing so, one of which is based on forecasters’ experience with these types of systems and which models have historically done a better job with them. ECMWF often does a very good job of modeling strong cyclonic systems like this (and is often favored in forecasting tropical cyclones). In this case, the NAM and ECMWF had the storm moving just far west enough to put us on the cusp of those high snowfall totals.
Mesoscale (medium scale) banding features are notoriously difficult to forecast in these types of storms. The exact position, orientation, and movement of these banding features is often not known until the storm is already ongoing. This is due to a number of complex atmospheric interactions that are responsible for these features forming. To take another example, the Storm Prediction Center can forecast that severe thunderstorms are likely over a certain area 2-3 days out. However, it is exceedingly difficult even the day of to know which towns will get hit by individual storm cells/tornadoes, etc. Despite advances in supercomputing power, forecast skill and accuracy, and understanding of meteorology, these mesoscale events remain challenging to get right even for the most experienced forecaster. So while the general public can say, “I told you so”, I’d challenge any one of them to forecast the next Nor’easter, and the one after that, and so on, and get them right with more skill than a straight up guess.
Anyway, since we all got the day off (the political response to this storm is a whole other debate beyond the scope of this blog), forget about the forecast being a dud and go out to take advantage of a day off!
Yesterday’s Nor’easter will seem downright quaint by the time Tuesday morning rolls around. Just a couple of days ago, forecasters were not even clear if we’d get any precipitation Monday going into Tuesday. Now, words like “historic” are being used to describe what will undoubtedly be the biggest snowstorm of the season so far. When all is said and done, we could be looking at widespread snow totals on Tuesday of 18″ to as much as two feet of snow. During the peak of this much stronger Nor’easter, high winds and blowing snow could lead to an extended period of blizzard conditions near the coast.
The Setup
Forecast models that up to just 2 days ago were displaying significant differences as to how this system would transpire are now in close agreement on a classic setup for a strong Nor’easter, and a powerful, high-impact blizzard for the Northeast.
A relatively weak clipper-type low will be moving across the Midwest during the day today. By Monday evening, a secondary low will form from the remnants of this first system. This second low will rapidly intensify as it tracks on or just west of the 40ºN 70ºW benchmark early Tuesday morning.
NAM model output for the next couple of days
As the low bombs out (dropping more 30mb in less than a day), its forward progress will be slowed by a high pressure to the north. This high pressure over Quebec is a key difference between the setup of the storm on Saturday and this coming Nor’easter. In contrast to Saturday’s storm, this high pressure will allow a relatively deep layer of cold air to take hold prior to the arrival of this storm. As the low pressure continues moving northeast, the pressure gradient between the rapidly intensifying low and this high pressure will allow for strong winds to affect the area from first from the east, then northeast and finally north.
This combination of a slow moving, strong low pressure with ample cold air and moisture available will translate to widespread snowfall totals of over a foot, and close to 2 feet, primarily for the Hudson Valley and points east. This will primarily be due to the influence of a mesoscale deformation banding feature is expected to form north of the storm center, then slowly wrap around the storm as it moves northeast. Because the forward motion of the storm will be so slow, the banding feature (which could contain snowfall rates of 2-4″ per hour) could be sitting nearly stationary over large portions of the region for a prolonged period of time – thus leading to what could be record breaking totals.
With the wind expected to pick up during this event, there is a blizzard watch in effect for coastal areas of the region, where wind sustained winds (25-35mph) could lead to near zero visibilities while heavy snow falls.
Snowfall Totals
As you can see from below, almost the entire region is expected to pick up more than 12″, with eastern areas possibly picking up near 2 feet!
Looking at probabilities of snowfall totals below, you can see that there’s now at least a 70-80% chance a good portion of the NYC region receiving more than 8″ of snow.
This storm will also have ample moisture to draw off of, with the liquid water equivalent of between 1.5″ to over 2″ across a good part of the region. Using the standard 10-1 ratio of snow to liquid water, this would translate to between 15-20″.
Quantitative precipitation total forecasts from the Weather Prediction Center
Timing
Snow will begin Monday, with increasing intensity through the day. Winds from the northeast will also pick up during the day Monday with high temperatures only in the mid-upper 20s. Anywhere between 1-3″ of snow could fall across NYC.
The heaviest snow will be taking place overnight Monday into Tuesday morning, where parts of the area could pick up another 9-13″. Again, the heaviest snow will be occurring within the mesoscale banding feature, where intense snowfall rates of 2-4″ an hour for a prolonged period of time could even be accompanied by thundersnow. Winds will probably peak during this overnight period.
Snow will continue to fall during the day Tuesday, with another 4-8″ of snow possible. High temperatures will again only be in the upper 20s.
Rest of the Week
Wednesday – snow finally ends Tuesday night with conditions clearing by Wednesday, but high temperatures again struggling to reach the upper 20s.
Thursday – a slightly warmer day with high temperatures in the low 30s.
Friday – there’s a chance at some more precipitation (but much lighter) from a weak low pressure system moving through Friday.
You can feel the chill in the air now. This cold will continue Saturday, but we’ll get a slight warmup Sunday and Monday ahead of a low pressure system moving in from the southwest. Behind that low pressure system, we get a reinforcing blast of arctic air that will be entrenched through the rest of next week. I’m also monitoring the potential for a Nor’easter just in time for the busy travel day Wednesday and through Thanksgiving.
Saturday – a cold day on tap despite ample sunshine. High temperatures will be generally in the lower 40s. There’ll be a noticeable northwest wind making it feel like it’s in the 30s.
Sunday – a milder day with warm air flowing in ahead of a low pressure system, but by warm, I mean highs only around 50. Clouds will increase throughout the day and there could be some rain Sunday night.
Monday – rain will be falling for the majority of the day, with highs in the city in the mid-40s. Monday night gets interesting with the potential for a rain/snow mix in the city, and all snow in interior regions north and west. Depending on the timing of the main slug of precipitation with this system, we could actually get some accumulating snow in the city also (the later in the night the main body of precipitation falls, the colder it will be, and the better the conditions for snow).Tuesday – cold air rushes back in behind this storm on Monday and we drop back into high temperatures hovering in the low 40s.
Potential Thanksgiving Nor’easter?
In looking ahead at the long-term GFS model output, I’m noting the possibility for a possible high-impact Nor’easter that would be timed to coincide with the busiest travel day right before and then during Thanksgiving. Of course, this far out, there’s still considerable uncertainty to the forecast, so this scenario could not pan out, or the storm track could be nowhere close to where it needs to be to produce a high-impact Nor’easter. Still, it’s worth watching, as it could be a major headache for folks if it does materialize.
A gloomy looking Friday will give way to a sunny though cool weekend. Next week starts off with near normal temperatures and dry conditions, but get ready for a blast of Arctic air later in the week with high temperatures falling into the mid-40s by the end of next week.
Saturday – cool but sunny to start. High temperatures will be in the low 50s. Clouds build in advance of a passing cold front Saturday night into Sunday morning.
Sunday – a moisture starved cold front will approach from the west, and precipitation is not expected in NYC, though could see some spotty showers in interior regions. High temperatures will be slightly warmer in the mid-50s.
Monday – high temperatures again in the mid-50s with partly cloudy skies.
Tuesday – another good day weather-wise with highs in the mid-upper 50s and mostly sunny skies.
We will feel the effects of a strong cold front next Wednesday. A Canadian Arctic airmass will work its way into the region following this frontal passage, leading temperatures to plummet down into the 40s!
Although the passage of a cold front yesterday didn’t bring any precipitation with it, you can definitely feel its impact in the form of much cooler and drier air today. Temperatures will be in the low 70s today with crisp, clear skies above.
Saturday – cloud cover will build tonight as an area of low pressure originating from the Tennessee Valley area slides along the frontal boundary that’s now located offshore to our east. This low pressure system will bring a solid chance at rain tomorrow especially later in the day into the evening hours. High temperatures will be cool, around 70, under cloudy skies.
NAM high resolution model output for Saturday evening at 8PM
Sunday – luckily, this storm system will exit rather quickly to our east, making Sunday an excellent day for outdoor activity of all varieties. Temperatures will be on the cool side, with highs in the low 70s under partly cloudy skies.
Monday – this week begins a trend towards cooler, fall-like temperatures as an upper air pattern favoring the intrusion of a cool, Canadian airmass takes hold. Highs on Monday will again only be in the low-70s, about 5 degrees cooler than average for this time of the year.
Tuesday – brings us our next shot at rain, as a weak impulse of energy passes through. The rest of the week after Tuesday looks like it will be uneventful, albeit on the cool side with the aforementioned arrival of a Canadian airmass and high pressure.
GFS 500mb vorticity and height model output. Note the two areas of very strong vorticity and closed heights in the Atlantic and Eastern Pacific corresponding to two tropical systems.
A correction from yesterday – I had said today may see less potential for severe weather. In fact, the Storm Prediction Center once again has most of the NYC metro area under a slight risk for severe thunderstorms later today.
Based on current satellite trends, it does appear there will be some breaks in the clouds this morning and afternoon. This will allow sufficient sunshine and daytime warming to fuel strong to severe storms across our region again later today. In the upper atmosphere, largely unidirectional winds from the south-southwest, a favorable jet stream set up, and approaching cold front suggest the potential for storms with damaging wind gusts and even some hail. Flash flooding is again a distinct possibility.
As you see below, portions of our area saw up to 1-1.5″ rain yesterday, and these same areas are in the target zone for severe storms today as well. With the upper level winds lining up from the south-southwest, training (where multiple storms hit the same location over a period of time) of storms is likely. This will enhance the risk for flash flooding.
A note about the term unidirectional winds: Unlike a hurricane, severe thunderstorms thrive on upper atmospheric energy, and unidirectional winds at all levels are more conducive to imparting a rotation on a rising parcel of air (rotating thunderstorms can produce tornadoes).
Otherwise, expecting a warm, humid day, with highs in the mid 80s and some sun before storms arrive later in the afternoon. It will be cooler and more comfortable tomorrow with this stormy cold front having passed us!
You may have heard from media reports that the dreaded polar vortex is set to make a return to the Eastern US during the middle of the coming week. I’ll discuss that in detail below. First, for the weekend forecast:
Today & Saturday – a very pleasant couple of days in the wake of the cold front that finally pushed through our area yesterday. You can feel a marked drop in humidity, and temperatures are much more comfortable. Saturday, high temperatures should top out in the mid 80s in NYC.
Sunday – a chance for afternoon thunderstorms and a high in the mid 80s, chance of rain increasing through out the day into the overnight hours.
Polar Vortex?
Forecast models are in good agreement that beginning Tuesday into most of the rest of next week, an upper air vortex (see below, the trough with an inclosed region surrounded by the blue arrows) will drop into the Midwest and Northeast from the northern regions of Canada. This vortex can be technically referred to as a polar vortex, a term that instantly revives media hype about how cold it will be. But keep in mind, during the summer, polar regions heat up as well, so even the coldest polar airmass and vortexes are much milder than their winter counterparts. Furthermore, the influence of the sun is quite strong as we just passed the summer solstice, so the sun is sitting at a very high angle each day and is highly effective at heating the air quickly. Hence, temperatures are expected to be much below normal for some areas, but we’re not talking about snow or ice.
Upper air forecast from GFS for Monday, 8PM EDT, 500mb absolute vorticity.
Next Week
There will be a good deal of energy traveling with the polar vortex, so we’re expecting a somewhat disturbed pattern of weather for the beginning of next week. Tuesday & Wednesday will see the best chances for rain and thunderstorms with a cold front approaching us from the west. Before the cold front, we’ll still see temperatures in the mid to upper 80s with a chance for thunderstorms Monday. Once the cold front passes, we’ll be right in the mix with the “polar” air mass, so our high temperatures will drop into the low 80s, and overnight lows will drop into the upper 60s for the latter part of the week.
Severe thunderstorms are approaching the area from our west. Several distinct bowing segments of severe thunderstorms have been making their way steadily towards our area from Central Pennsylvania since earlier this afternoon.
These storms have a history of producing damaging wind gusts and even a few tornadoes. Sundown over some of the areas under the current Severe Thunderstorm Watch areas in our region may weaken these storms, however, overall atmospheric conditions are quite favorable to the forward propagation of this line.
