Tag Archive for: Variable

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Saturday’s Rain Threat Gives Way To More Variable Conditions Next Week

August 11, 2017/1 Comment/by Steven Copertino

Good evening!

Today started off rather pleasant with clear skies, light winds, and rather moderate temperatures. However, as the broad area of high pressure that remained in control for the past few days began to gradually shift offshore and into the west Atlantic, a broad mid level trough began to edge into the Northeast this afternoon. As this trough gradually progressed east, the airmass change could be felt as dewpoints rose into the middle to upper 60’s across the area, which made for a much more “muggy” feel to the afternoon than the past couple of days. On the lee side of this disturbance, mid levels winds are coming from the southwest, which is acting to advect a good deal of moisture from the south. This moisture has continued to overspread the Northeast this afternoon as a weak warm front moved from north to south across the metro area. With some weak ascent and forcing associated with the front, some showers and thunderstorms have popped up over portions of the Mid Atlantic and portions of Pennsylvania, where severe parameters are supportive of locally severe weather. In fact, an isolated supercell has developed over northern Virginia this past hour, and may eventually reach the DC metro area.

Closer to the NYC metro, the atmosphere remains much more stable than our surroundings (as has been the case this entire year so far). Instead of thunderstorms developing this afternoon, we’ve seen widespread cloudiness take over. Some residual showers from dissipating thunderstorms over Pennsylvania are currently making their way into western New Jersey, but no hazardous weather is expected as any showers/thunderstorms encounter the stable airmass overhead.

As the evening marches on, more leftover showers may entire from the west and bring some brief heavy downpours and occasional lightning, but generally cloudy conditions are likely for the remainder of the night. The combination of the higher dewpoints, southerly winds behind the warm front, and cloudy conditions will almost ensure that raditional cooling will be non-existent this evening. Lows should unanimously mild, reaching the middle 60’s to lower 70’s across the region.

This evenings latest high resolution GOES-16 visible satellite imagery, regional radar mosaic, surface observations, and frontal postilions-showing showers and thunderstorms mainly concentrated to the west of the area this evening (Courtesy of Simuawips)

Saturday Into Saturday

Tomorrow morning will likely start off quite unsettled as the mid level warm front to our south and west begins to move over the area with deep tropical moisture entrenched within. Precipitable water values will also increase markedly, into the 1.5-2″ range, so any showers and thunderstorms that develop early Saturday morning have the potential to produce very heavy rainfall in a short period of time. Though, with weak mid level lapse rates, any updrafts that do go up tomorrow morning will be extremely short-lived, and will likely form and die over the same location. Later in the morning, the warm front should lift through the region, possibly clearing out any residual showers and weak thunderstorms out of the area, and allowing for a brief period of sun poking through the clouds. Depending on how much sun the area sees late tomorrow morning and early afternoon will determine just how much the area can destabilize, which will have implications on the rest of the day. Model guidance suggests that the western portion of the New York metro area does in fact clear out enough during the afternoon hours that instability on the order of around 1000-1500j/kg^2 develops. By this time, it appears likely that a mid level trough will begin to nose into the Northeast, with a favorable upper level jet streak also making an appearance.

The combination of these factors could possibly lead to the development of some scattered showers and thunderstorms-some of which may be strong to severe. As of this evening, it appears locations west of NYC will have the best potential to see any robust thunderstorms, with the main threats being gusty winds, sub-severe hail, frequent lightning, and very heavy rains. This activity will be highly dependent on the timing of the best forcing arriving from the west, as well as just how much we can clear up and destabilize tomorrow after the initial batch of rain in the morning. Overall, widespread severe thunderstorm development does not appear likely tomorrow.

As we head into the evening, any residual showers and thunderstorms should gradually head east and weaken as the frontal system associated with the mid level trough begins to push over and out of the area. Behind the front we should have a less humid airmass, but with the risk of cloud cover, temperatures are not that likely to fall all that much-with lows generally in the low to middle 60’s.

Sunday looks to be a huge improvement over today and Saturday, as the shortwave trough that moves through on Saturday heads to our east and begins to usher in a cold front. This cold front not only looks to clear out any substantial cloudiness that may linger over the area, but should also be quite efficient at greatly reducing dewpoints from the 70’s, to lower 60’s over the entire area. With sunny skies, light winds, and low humidity, Sunday will be near-perfect for any outdoor activities , though there may be a risk of rip-current’s along the coasts, so please make sure to monitor beach conditions if you are planning a beach day. Highs will likely be comfortable-with temperatures reaching into the upper 70’s to lower 80’s, and lows getting down to the low to middle 60’s.

This evenings RPM model showing the progression/development of showers and thunderstorms later this evening and into tomorrow afternoon, followed by an eventual clearing on Sunday (Courtesy of WSI)

Monday and Beyond

Previous model guidance runs had Monday being the next potential period for heavy rain, but have since backed off this idea quite a bit. This is due in part to the models incorrectly handling a weak tropical system that has been tormenting forecasters for the better part of the last nine days or so. This low was originally forecast to interact with a stalled frontal boundary located to the south of the region on Monday, which would in turn spawn another wave of low pressure. The tropical low pressure system has once again failed to develop, and this had lead to some significant changes in the model guidance for next week. It now appears that the same frontal boundary will not be able to push as far north as previously thought, mainly due to a lack of a surge in precipitable water values/moisture associated with the tropical system. So in short, this means that any precipitation on Monday will likely be much more spotty in nature than previously thought, with very meager amounts of instability and lift to work with over our area. At this time, we would not be surprised at all if this rain threat continued to deteriorate over time and does not amount to much of anything north of the Mason-Dixon line.

Otherwise, it appears that the northern stream will remain quite active for this time of year and could potentially lead another disturbance down our way by the middle of next week, with moisture surging ahead of this disturbance as we have seen many times before. However, at this time it seems that these rain threats will be transient in nature, with ridges likely building in behind-leading to a brief period of calm weather before the next rain chance.

This afternoons European ensembles, showing another unsettled period shaping up next week, with a trough over the central part of the US, and a ridge positioned over the south. This would lead to multiple disturbances rolling over the ridge, and into the Northeast.

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Have a great evening!

Steve Copertino

Public Analysis: Beautiful and Warm Easter Weekend, More Variations Next Week

April 14, 2017/by Steven Copertino

Good afternoon and Happy Friday!

The end of the work week will come to a very nice close today as high pressure dropping down from Canada is now in control of our weather for at least the next two days. With mostly sunny skies. low humidity, and light winds, this afternoon has been rather pleasant with highs reaching into the upper 50’s and low 60’s across the entire region as of 2pm. Even though it feels much cooler than the previous 80 degree days we’ve had earlier this week, these temperatures are still 5-10 degrees above normal for this time of year.

Some mid-high level clouds were noted on the latest visible satellite imagery this afternoon, streaming from the northwest, to southeast. This is mainly due to the cooler mid-level air from Canada interacting with the ever-so-slightly warmer air in the lower levels of the atmosphere that is situated over northeast Pennsylvania and portions of New Jersey. As the afternoon continues on, these clouds should begin to diminish and mostly sunny skies should continue until sunset across the area. There is a chance that some localized cloud cover may become established later today as a sea breeze begins to set up over coastal sections of New Jersey and Long Island. This may also in turn work to cool temperatures a little, possibly working them back into the mid 50’s.

With the aforementioned high pressure directly overhead this evening, winds will be calm, humidity will be low, and the skies should be relatively cloud-free. This will set the stage for what is known as radiational cooling to take place. Due to the absence of clouds to block outgoing heat from the Sun, any heat absorbed by the surface will easily be able to radiate back into the upper atmosphere and space. This will allow temperatures this evening to drop quite a bit this evening. The immediate New York metro area should be able to hold onto lows around the mid to upper 40’s this evening, but inland locations may see lows drop down into the low 40’s to even mid-upper 30’s in far northern NJ and portions of Upstate New York.

Latest visible satellite imagery, regional radar composite, and surface temperatures this afternoon showing a relatively cool, but pleasant end to the work week (Courtesy of GREarth)

Saturday and Easter Sunday

As we move into the morning on Saturday, the area of high pressure currently situated over our area will begin to feel the effects of an incoming area of low pressure and will begin to slowly move off the Mid-Atlantic coast. As this high moves off the coast, winds will begin to change from light and variable to light southwesterly/southerly winds during the early afternoon hours. These southerly winds will introduce more moisture into the lower levels of the atmosphere that will likely be accompanied by some cloudier weather tomorrow afternoon, especially as a mid-level warm front begins to push through the area.

As this warm front moves through during the late afternoon, there is a very slight chance at some showers across the area, but at this time any widespread activity centred over this NYC metro area seems unlikely. Regardless of clouds, the deep southerly flow will allow for temperatures to reach into the low to middle 60’s across the entire area, except for south-facing shorelines, which may experience more marine influence which would work to keep temperatures in the 50’s tomorrow. Any areas of showers that may be moving through the area should be gone by tomorrow evening as the best forcing associated with the warm front lifts to the north and east.

Again, the best chance for any rain of substance should be limited to central and northern sections or New York state as well as a more isolated chance of showers over Pennsylvania. Deeper southerly flow tomorrow night should keep temperatures relatively mild, with lows staying in the 50’s for the entire region as the high pressure system continues to pump more warm air into the mid levels of the atmosphere, which should help insulate our temperatures.

Sunday should be a much more “pleasant” day, as broken clouds in the morning hours give way to mostly sunny skies by early afternoon. With full sunshine, southerly winds, and warm low-mid levels of the atmosphere all present on Sunday, Easter is shaping up to be another much-above normal day with regards to high temperatures. As we progress throughout the afternoon, temperatures should easily climb into the upper 70’s across the entire area, with areas of low to mid 80’s possible over sections of southeast PA, NJ, southern NY, and Connecticut. Once again, these southerly winds may introduce a sea breeze feature for south-facing shores, so high may be limited to the 70’s for those locations. Regardless, temperatures should be anywhere from 20-32 degrees above normal during the day Sunday, so it will actually feel more like Summer than Spring!

The very warm temperatures and light winds may make for some very unfavorable conditions for those who suffer from allergies, so make sure to take your necessary precautions in order to enjoy the beautiful weather this weekend!

This afternoons 3km NAM showing temperatures in the upper 70’s to mid 80’s across the entire area for Easter Sunday

A cold front associated with an area of low pressure centered over southern portions of Canada and far northern New England will begin to work its way through the area late Sunday evening, bringing another chance of some isolated or scattered showers and thunderstorms. Some thunderstorms could still contain heavy rainfall and gusty winds to the north and west, but today’s model guidance has been suggesting this activity should be centered away from our region and will likely wait until after dark to pass through the NYC metro area-if at all.

Monday and Beyond

As we head back into the work week, Monday should be rather calm and dry behind the cold front, with winds out of the northwest from Canada. As we get later into the Spring, these cold fronts begin to lose their potential to really drag in colder air masses from Canada, and it looks like this will be the case with this next front as temperatures should be able to rise into the upper 60’s to low 70’s on Monday across the entire area, which should once again be above normal for this time of year.

On Tuesday, some cooler air may sink down from Canada ahead of a system passing through the Great Lakes, and this should be the beginning of a more unsettled period of weather for our area again as more storm systems should begin to take shape out over the Central US later in the week. This upcoming pattern may be quite similar to the pattern we saw during late March and earlier this month with backdoor cold fronts as well as numerous chances for precipitation. Temperatures will once again be highly dependant on how these frontal systems shape up, so make sure to check back next week for further updates on this potentially more active period!

12z GFS model showing a potentially stormier pattern setting up for later in the week next week (Image credit Tomer Burg)

With the Holiday Weekend just around the corner and the threat for some showers and thunderstorms on Easter, make sure to check back for further updates!

For more information and posts like this one, make sure you sign up for Zone Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a weekend!

Steve Copertino