June 2013 - Page 2 of 5 - New York Metro Weather

PM Update: Splendid Saturday, but unsettled pattern continues

June 14, 2013/0 Comments/by Doug Simonian

Radar image as of 5:30pm EDT shows numbers showers and thunderstorms in New Jersey, with less activity from NYC and east.

For a lot of the NYC Metro area, today turned out to be quite the nice day. However, the lingering storm system from yesterday and some day-time heating allowed some scattered showers and thunderstorms to develop across much of New Jersey. These storms are not severe, but could provide some locally heavy downpours and lightning. The upper level winds on the backside of the storm are oriented from north to south, so the storms in Jersey will also move from north to south. Thus, I anticipate the eastern parts of NYC and east to remain primarily dry for the rest of the afternoon and evening, whereas western NYC and much of New Jersey can expect some scattered showers and thunderstorms. However, an additional even weaker area of storms may hit central Long Island, producing moderate rain and a rumble of thunder. Not everywhere in Jersey will be hit, but it might be prudent to bring an umbrella if you’re in Jersey, just in case.

Tomorrow, however, looks beautiful. The storm system will finally move out of the way, and a ridge will build in from the west, leading to sunny skies and warm temperatures. Temperatures should sore to around 80, or even low 80s in the warm spots tomorrow, with dry, downsloping northwest winds.

Sunday morning and early afternoon also looks nice, with more warm temperatures. However, the active weather pattern will return for Sunday afternoon, Monday, and Tuesday. An upper level low in SE Canada will force storm systems to track to the south, across the Ohio Valley and Northeast. These storm systems will not be as strong as what we saw yesterday, but will still lead to unsettled weather, and perhaps isolated severe weather as well. The activity may be a bit more scattered on Sunday and Monday, and perhaps more widespread on Tuesday. Though for Tuesday, if the storm stays to our south, heavy rain will be the threat, and if it goes further north, severe weather becomes more likely. The main threat each day would be a line of storms producing strong winds. More detailed and more technical discussions will be issued over the next couple of days, further addressing this potential.

Rest of today and tonight: Partly sunny skies from NYC and east, with the chance for a shower or weak thunderstorm on central Long Island. Mostly cloudy with numerous showers and thunderstorms in New Jersey. Temperatures initially in the upper 60s to around 70 will fall into the mid 50s to around 60 tonight.

Saturday: Mostly sunny skies, with high temperatures around 82. Light northwest winds.

Saturday Night: Clear skies with lows around 60. Light westerly winds.

Sunday: Sunny in the morning, with increasing clouds as the day goes on and a 30% chance for a line of thunderstorms in the afternoon and evening. High temperatures in the upper 70s.

Monday: Mostly cloudy with a chance of scattered showers and thunderstorms. High temperatures in the upper 70s to around 80.

Tuesday: Mostly cloudy, with either widespread rain or the threat for severe storms, depending on the track of this storm system. High temperatures in the upper 70s.

An image showing the time stamp of yesterday morning’s derecho.

In other news, yesterday morning’s squall-line was officially classified as a low-end derecho. It peaked in strength in Ohio, producing a wide swath of severe, damaging winds. It weakened a bit once it got east of the Appalachians, but still produced some severe winds in southern PA and southern NJ. It was not nearly as strong as the derecho that hit the Mid Atlantic on June 29 of last year, but it still packed a decent punch.

It was actually this system being stronger than expected that helped to halter the warm front’s progress northward, and stabilized the atmosphere over much of New Jersey, preventing yesterday’s severe weather outbreak from being as severe as once anticipated. Over the next few days, we will be doing a re-analysis of that event, going over what went right and what went wrong with our forecast.

Live Blog: Severe storms, heavy rain likely

June 13, 2013/0 Comments/by John Homenuk

[alert type=”error”]Moderate Risk of severe thunderstorms for Southern New Jersey. Click for details.[/alert]

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An unusually strong storm system for June will move eastward from the Ohio Valley through the Mid Atlantic states on Thursday, providing the area with several hazardous weather threats. Severe thunderstorms, heavy rain and wind are all likely throughout the area at some point on Thursday as the system moves through. Throughout the day we will be updating this live blog post with the last information, discussion and links. We encourage you to keep reading along with us as we track the system.

5:00pm Update: The initial storm system helped to keep the warm front a tad further south than originally anticipated. Central NJ was originally on the border of the severe weather, but they are now safe from any severe weather threat, as are all areas north of Central NJ. An area of moderately strong (but NOT severe) thunderstorms are approaching northern and central NJ, so Sussex Counties through Flemington may have to watch out soon, and these storms should generally traverse I-80. Moderate to heavy rain, some lightning, and wind gusts up to 40mph can be expected.

However, strong and severe thunderstorms have developed a bit further south in the Mid-Atlantic, with numerous severe wind reports all throughout Virginia and Maryland. There was also a confirmed tornado by law enforecement near Colesville, Maryland, which is 15 miles north of Washington, DC. That tornado has lifted, but potent storms with strong winds still remain. They are heading east and could give southern NJ some wind gusts up to 50mph, and perhaps some exceeding 50mph. The strongest threat for these storms will be in Salem, southern Gloucester, Atlantic counties, and southward…perhaps clipping extreme southern Ocean county. We’ll keep you posted if anything changes and fine-tune things as well.

11:20am Update: Storms have cleared the NJ coast from the initial thunderstorm system. Rain continues over parts of New York, Long Island and Connecticut. Some clearing is expected over New Jersey during the next hour or two. A warm front is expected to push northward with time, with additional storms developing. A severe weather threat is expected over much of New Jersey this evening. Stay tuned.

9:20am Update: Severe Thunderstorm Warning for much of Southwest NJ and the city of Philadelphia. Strong winds, heavy rain and frequent lightning expected with the complex of warned storms. Click here to see the high resolution radar imagery from the time of the warning issuance.

9:00am Update: Heavy rain in association with the decaying thunderstorm complex will approach NYC, NJ, CT and LI over the next 30 minutes and continue through around 11am. A local threat for severe thunderstorms exists over Southern New Jersey through that time frame, with the potential for some hail and strong/damaging winds.

8:05am Update: Severe Thunderstorm Watch #304 remains in effect for Central and Southern NJ. A Moderate Risk for severe thunderstorms from SPC remains over Southern New Jersey through tonight. Our forecasters were tracking a weakening complex of thunderstorms moving through Southeast Pennsylvania. Periods of rain are expected to impact New Jersey, NYC, CT and LI within the hour from the system — with the severe storms impacting Southern and Central NJ. Stay tuned for any potential warnings. Additional severe thunderstorms are expected later today.

Myriad of threats expected from midweek storm

June 12, 2013/0 Comments/by John Homenuk

[alert type=”error”]Storm Prediction Center has placed parts of the area in a Moderate Risk for severe weather on Thursday. Details. [/alert]

A strong storm system traversing the Ohio Valley will strengthen and shift towards the Northeast US on Thursday, bringing the potential for several types of hazardous weather. Forecast models suggest the system may be anomalously strong for this time of year, with pressures dropping to near 990mb as it moves through the Mid Atlantic states. This is absolutely unprecedented for this time of year, as normally the jet stream is too weak this time of year to support such dynamic systems.

A warm front is forecast to lift northward from the Mid Atlantic states to a position near Central New Jersey on Thursday afternoon. The combination of building instability near and south of the warm front, as well as favorable wind fields and forcing for precipitation will lead to the potential for not only heavy rain and strong winds, but severe weather…including the potential for a few tornadoes.

If you have not already, I highly recommend you check out our previous technical discussion, as it will help to explain some concepts that I will talk about in detail for the rest of this post, and give you a pretext as to what is going on.

The exact position and timing of the surface low, cold front, and warm front will be crucial in determining where the tornado risk is, and where the northern boundary of the severe weather can be expected. Latitudes north of the surface low can expect heavy rain of 2-4″ and little in the way of severe weather, areas with the same latitude as the surface low can expect 1-2″ of rain with a chance of being hit by a squall line producing borderline severe winds, and latitudes south of the surface low can expect severe weather and a few tornadoes. The problem is, the exact position of the surface low is still a bit uncertain, but we’ll do our best to warn everyone of the possibilities.

The 00z 6/12 NAM valid for 2 p.m. on Thursday.

Our first two images will illustrate the NAM’s boundaries and its movements throughout the day on Thursday. The NAM, at 2 p.m. on Thursday is forecasting a 990mb surface low in SW PA (top left panel). You can see two distinct temperature gradients — one to the south of the low, and one to the east of the low. I quickly highlighted the approximate warm front position in red and the cold front position in blue, at that time.

As I said in yesterday’s discussion, the cold front often triggers a linear convective mode. But look at how far east the warm front extends away from the front! Areas just south of the warm front and away from the cold front can expect a discrete supercellular convective mode. Thus, at 2 p.m., SE PA, SW NJ, DE, and MD could really be under the gun for a tornado threat, and perhaps severe hail as well.

A very key fact that one must understand for this threat: the slower the cold front advances, the longer the warm front will be the main boundary for thunderstorm initiation in the very favorable tornadic environment, thus discrete supercells. A faster moving cold front means that it would eventually be the dominating player in the favorable tornadic environment, potentially “wasting” the environment and turning the convective mode more linear, since it would more quickly intercept that environment. Linear squall lines can still provide embedded tornadoes, so a squall line does not mean there is no tornado threat, but it would be significantly reduced compared to that of more discrete supercells.

Also note the southeast surface winds that even exist to the south of the warm front in SE PA on the bottom left panel — when you combine that with the potent mid level winds from the WSW associated with this powerful storm, you get strong, deep-layer shear supportive for severe weather and even tornadoes. More will be discussed about the wind profiles later in this post.

Severe Storms Likely for the Mid-Atlantic on Thursday. How Far North Will They Go?

June 11, 2013/1 Comment/by Doug Simonian

As well evidenced by the recent inclement weather, the northeast is under a very active weather pattern, and after a couple of days of general relaxation, the weather looks to turn unsettled again on Thursday.

A potent storm system with lots of vorticity will be the culprit for severe weather on Thursday.

A powerful storm system will quickly traverse the country, giving the Midwest and Ohio Valley a severe weather event on Wednesday. This will head eastward and approach our area for Thursday. At this point, all eyes will turn towards the northern Mid-Atlantic states: in particular, southeastern Pennsylvania, Maryland, Delaware, northeast Virginia, and perhaps central and southern New Jersey as well. This storm system will provide very strong winds — well in excess of 50 knots — at 500mb, coming out of the WSW; generally a very conducive environment for severe weather. In addition, the potent vorticity, among other factors that will be explained shortly, will also be conducive for lift, in order to generate thunderstorms.

What is often true about these powerful storm systems is that they possess strong boundaries, such as cold fronts and warm fronts. It is along these boundaries, and on the warm sides of them, where we pay particularly close attention, because the warm, moist air in the warm sector is lifted near the boundaries themselves, helping to initiate convection, and thus, thunderstorms. Usually, a cold front in itself is a boundary that is only conducive for squall lines, because they are expansive, they favor lots of lift over the entire front (as opposed to a dry-line, where the lift is more localized), and move quickly — so the best lift continually catches up with any storms that form, causing more and more storms to form in close proximity to them, thus quickly favoring congealing into a line. This is what is typical for northeast thunderstorm setups, and one reason why you tend to see large lines of storms, rather than the discrete supercells that you get in the Plains. However, in addition to this cold front, there will also be a warm front extending from west to east, well out ahead of the cold front.

Archive for month: June, 2013