Posts

Steven Copertino

Unsettled Period Taking Shape With Multiple Rain Threats

/by

Good Evening! 

Today was a rather beautiful day across the entire Northeast, as a elongated area of high pressure centered off the New England coast remains in control. Dry air in the mid levels of the atmosphere associated with subtle mid level height rises over the Mid Atlantic allowed for a mostly clear start to the day across the area, which allowed temperatures to gradually rise into the low to mid 80’s. Today also features some refreshingly low dewpoints courtesy of the high pressure system, and when coupled with light and variable winds, conditions were near perfect for enjoying the outdoors. These conditions lasted throughout the entire afternoon hours and into the evenings hours, and should prevail after dark as well. A weak mid level system passing just to the north of Michigan may be able to create some upper level cirrus clouds to develop late this evening, but no shower activity is expected with this unimpressive system. As the evening progresses, this cirrus activity may actually wind up putting a cap on the potential for radiational cooling as all the other factors are quite favorable, however the increased cloud cover may limit just how much temperatures can fall. Regardless, overnight lows should be able to drop down into the upper 50’s to lower 60’s area-wide, with some inland locations possibly dropping to the lower 50’s.

This evenings latest high resolution 500m GOES 16 visible satellite imagery, regional radar mosaic, and surface observations, showing a very pleasant and calm evening across the entire Northeastern region. (Courtesy of Simuawips.com GOES-16 data is preliminary and non-operational)

This evenings latest high resolution 500m GOES 16 visible satellite imagery, regional radar mosaic, and surface observations, showing a very pleasant and calm evening across the entire Northeastern region. (Courtesy of Simuawips.com GOES-16 data is preliminary and non-operational)

Thursday Into Friday 

Thursday will likely start off with a few high clouds due to the aforementioned weak disturbance gradually moving off to our north. Although with the elongated area of high pressure moving off to our south and east, enough mid level dry air should remain in place so that as the morning hours progress, these high clouds will gradually dissipate, giving way to mostly sunny skies. Another positively tilted mid level trof out over the Great Lakes region will help to build an area of ridging overhead during the day tomorrow, which should advect warmer temperatures into the area once again. With winds out of the south over much of the area, clear skies, and warm mid level temps, expect high temperatures to once again reach into the low to middle 80’s by tomorrow afternoon. A weak wave of low pressure may try to pass to the south of our area tomorrow afternoon, which would potentially bend winds back to the southeast along coastal portions of NJ/LI/CT. This would allow some cooler air via a sea-breeze to work its way inland, but the degree to which this cooler air penetrates the coasts will be something that will need to be monitored tomorrow in real-time. Skies will remain mostly clear up until the evening hours before some thicker high level cirrus clouds begin to move into the area just in time for sunset. Depending on the degree of the southeasterly winds tomorrow, some localized patches of fog may be possible, though this should likely remain patchy in nature. Overnight lows will likely once again drop into the upper 50’s to lower 60’s-with some locations inland seeing slightly lower temperatures.

On Friday, we finally lose our support from the broad area of high pressure, and a large mid level trough from the Great Lakes region will begin to move in early Friday morning. As this trough approaches, the southwesterly flow will begin to advect a moist airmass with higher dew points into the area, which should also increase cloudiness quite a bit during the day. The entire region will likely see more clouds than sun during the day on Friday, and this will also put a cap on just how warm it will be able to get. With mid level temperature remaining rather steady during the day, there won’t be too much of difference, but highs will likely remain in the low to middle 80’s across the area. The increased dewpoints and clouds cover will also make Friday seem much more dreary than the previous two days as well. Any shower activity on Friday will likely remain to the west of the area, as the best mid level forcing and jet stream dynamics will be placed off to our north and west. Cloudy conditions should preside over the rest of the day, lasting into the evening hours as well. With cloudy conditions, warm mid level temps, and increased humidity, temperatures will likely only be able to fall a few degrees, with lows likely reaching into the low to middle 60’s Friday evening.

This evenings NAM model showing the progression of a mid level trough that has the potential to brings some rain to portions of the Northeast Friday and into the weekend (Courtesy of College of DuPage)

This evenings NAM model showing the progression of a mid level trough that has the potential to brings some rain to portions of the Northeast Friday and into the weekend (Courtesy of College of DuPage)

This Weekend and Beyond 

Cloudy conditions should continue to dominate the area on Saturday as a frontal system associated with the mid level trough continues to march eastward and over our area. As this system heads east, better forcing and upper level dynamics will also begin to move over the area on Saturday, so showers and possibly a thunderstorm appear likely during the day. With increasing moisture and a strengthening upper level jet streak providing divergence over the area, some of these showers and isolated thunderstorms may have the potential to produce some locally heavy downpours, but a lack of instability and weak vertical wind shear should mitigate any severe threat during the day on Saturday. Highs during the day on Saturday should once again be limited to the low to middle 80’s due to the threat of showers and enhanced cloud cover over the area. The frontal system will then approach the area late Saturday afternoon and into the evening, but any additional shower activity associated with this frontal system will be highly dependent of the overall strength of the remaining forcing with this wave. At this time, it appears that forcing should not be overly impressive and the jet dynamics may be disjointed just enough to keep the bulk of the heavier showers and potential storms to the north and west of the NYC metro area Saturday evening.

Conditions may briefly clear up on Sunday, but this should be rather short lived as another area of low pressure associated with a mid level trof begins to move out of the central US. The next threat for widespread rainfall appears to be on Monday when a wave of low pressure along a frontal boundary begins to push just to our south. Current model guidance has a very expansive and favorable upper level jetstreak overhead, with deep tropical moisture feeding in from the south. Confidence in this scenario is very low at this time due to the models potentially putting too much emphasis on a tropical area of low pressure interaction with this front and enhancing rainfall. This will likely have to be revisited later in the week when details become more clear. Overall, expect an unsettled and potentially rainy start to work week next week, with temperatures around average for this time of year.

This afternoons European model showing the potential for unsettled conditions starting early next week over the area (Courtesy of Accuweather Pro)

This afternoons European model showing the potential for unsettled conditions starting early next week over the area (Courtesy of Accuweather Pro)

For more information and posts like this one, make sure you sign up for Premium 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 great evening!

Steve Copertino

John Homenuk

Cooler risks likely to continue into medium and long range

/1 Comment/by

Much has been made over the past week or two in regards to a gradual warmup across the United States as we approach the middle of the month of August. With seven days of the month gone by, a notable breadth of cooler than normal air has spread throughout the United States. Despite the persistent forecasts for ridging and higher pressure to develop, an active and progressive pattern has remained in place, keeping things cooler and wetter on average.

As we approach the middle of the month of August, medium range forecast models continue to indicate that the risks for cooler than normal air will continue. Understanding exactly how and why these risks are developing will be a critical component to the forecast moving forward; both in terms of understanding the risk itself, and timing exactly when it will end and a transition to warmth will occur.

Read more

Miguel Pierre

What the QBO and the sun can tell us about the winter ahead

/1 Comment/by

Take a deep breath — sit back, and relax. You are about to read our first post detailing some early thoughts for the Winter of 2017-2018. August is a bit of an odd time for it, we know. Not every year offers the opportunity to discuss the road to the winter ahead during the month of August. Some years require patience until September or October before we can start discussing early signals with confidence. This year, however, we’re seeing important signs for the cold season already as we speak.

This afternoon, we’re going to take a very early look at some of the significant changes that have occurred all around us since the end of last winter. It’s true — in the time between the day the last snowflake fell in the Northeast states and today, there have been significant changes throughout the atmosphere, in the oceans, and even in the patterns of energy emanating from the sun. All of these things will impact the winter ahead — so lets dive in to what we’re observing so far.

Read more

Steven Copertino

Severe Weather Possible This Afternoon, Yet Another Unstable Pattern Next Week

/1 Comment/by

Good Afternoon! 

Despite some heavy showers and thunderstorms that moved through the immediate New York metro area this morning, most of the area was able to clear out quite significantly this afternoon. With high humidity in place and full sunshine, we saw the development of numerous cumulus clouds, especially to the north and west of the city. With instability rising gradually through the early afternoon hours, shear kicking in, and forcing from an approaching upper level trough all coming together, we have seen numerous showers and thunderstorms go up over portions of the Mid Atlantic and Northeast regions. Given rather unimpressive lapse rates, unidirectional shear vectors, and a general broad area of forcing, this activity has mainly been limited to multi-cellular and pulse-cell storms. These storms will mainly be capable of damaging winds and possibly a wet micro burst or two, as the weak mid level lapse rates will fail to sustain any significant updrafts over much of the region. As these updrafts collapse over time, they may do so rather quickly, leading to winds up to 60 mph and torrential downpours, which may cause localized flooding.

However, as we head deeper into western Pennsylvania and New York state, the vertical wind shear profile becomes a little more favorable for more organized convection, and we have seen some embedded supercell structures form within larger convective masses. These storms will have a much higher threat of damaging winds, large hail, and even a brief tornado or two. This stronger activity will likely remain exclusive to this region, as the severe parameters quickly become less supportive for anything too strong the further east you head.

Regardless, the rest of the afternoon should remain quite nice for a typical August day, with highs deep into the 80’s-possibly getting to that 90 degree mark in some locations. As we mentioned before, humidity will be increasing ahead of the front located off to our east, so it will feel quite muggy out, and any locations that saw some of the heaviest rains this morning will have the added moisture in the air from evapotranspiration.

As we head into the evening hours, we should see the development of more showers and thunderstorms over the Northeast, as the previous cells begin to collapse and leave convergent boundaries as to which new thunderstorms can form along. Winds from the south will continue to pump moisture/instability into the area, with CAPE values remaining in the 1200-2800j/kg^2 range until sunset. In addition to the instability in place, a very weak warm front will be passing through the region, and this may work to locally improve wind fields, but only to a small extent. At this time, it appears that the best chance for showers and thunderstorms this evening will be over portions of southern New York, eastern Pennsylvania, and possibly far northwest New Jersey. These showers and thunderstorms should mainly be capable of producing gusty winds and small hail, with heavy rain likely as well.

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

Saturday and Sunday 

Saturday may start off cloudy and with a few showers and an isolated thunderstorm in spots as the large upper level trough to our west finally begins to move through. This shower and thunderstorm activity should move rather quickly through the northern portions of the metro area, but brief heavy rain, gusty winds, and small hail may all be possible with any stronger areas of activity.

Afterwards, a cold front associated with the large upper level trough will finally move through the Northeast during the afternoon hours, and will likely clear any residual showers out. Behind this front will be some refreshing Canadian air that will also be packing much lower humidity with it as well, so there should be a noticeable change in airmasses by lunchtime tomorrow. With clearing skies, low humidity, and light westerly winds behind the front, highs should be able to get into the low to middle 80s tomorrow, which is right around normal for this time of year. Tomorrow evening will be a very pleasant one, as the skies begin to clear out and winds out of the north and west continue to usher in cooler air. Conditions will be in place for radiational cooling to take place over the entire Northeast, which is somewhat uncommon for this time of year. This will allow for lows to fall into the upper 50’s to low 60’s across our area-with some locations to the far north and west possibly seeing low 50’s tomorrow evening!

Sunday looks to be the “gem” in this forecast period as light winds, low humidity, and warm temperatures in the 80’s will dominate the day region-wide. Clouds may begin to increase later in the evening, but overall Sunday should be an excellent day for any outdoor activities!

CLICK TO ANIMATE This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

CLICK TO ANIMATE
This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

Next Week

Our eyes will once again shift to the west, as yet another northern stream disturbance begins to approach our area. As this system approaches, it will begin to dig up a serious amount of warm air and moisture from the south and west and direct it towards the Mid Atlantic and Northeastern states. As the mid to upper level system draws closer, a frontal boundary will likely set up. Below this boundary there will be very warm and muggy conditions, while locations to the north experience more seasonable conditions. Above the surface, a large and very impressive upper level jet streak will be nosing in, which is a tell-tale indicator of potential heavy rain for this area. the questions that remain to be answered at this time are where does this frontal boundary set up, how much instability will be in place, and will these ingredients come together at the right time to produce widespread heavy rain? If these conditions do come together on Monday in the correct manner, then we may have to watch for potential flooding rains and much cooler temperatures to start off the week. We will likely have to revisit this system as more data becomes available.

This system should exit the coast late Monday, and an area of high pressure should begin to take over for Tuesday and into Wednesday. However, we may have another rain chance later in the week as the active northern stream regime shows up once more.

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

For more information and posts like this one, make sure you sign up for Premium 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 great evening!

Steve Copertino