New York City Metro Weather

Four days of comfortable weather on the way

By: NYCvort, 9:01 PM GMT on June 29, 2010

Today we are transitioning from heat and humidity to much cooler and drier weather. In fact, the humidity has already come down a bit across the area as the cold front has moved off to the south and east. A secondary cold front will pass through this evening along with an 850 mb front pushing through. Temperatures at 850 mb will plummet behind this mid level front from 57 degrees this evening all the way down to 47 by tomorrow morning. This will be felt at the surface as temperatures starting out in the mid to upper 80s this afternoon will easily fall into the lower 60s overnight. I have a feeling the MOS guidance may actually be underestimating the effect that such a strong mid level front will have overnight, and temperatures will likely drop off very quickly under a strong northwest flow early tonight. The upper level bowling ball will be closest to us in proximity tomorrow over southern Quebec; however, another round of cold advection, this time more upper level based, will come through Wednesday night at which point the full effects of the trough will be felt. I’m completely discarding the GFS MOS as it doesn’t do well in cold advection situations, and even the NAM MOS looks too high to me. Despite full late June/early July sun, highs will only make it into the low to mid 70s, with perhaps some upper 70s in the urban areas. Lows at night will drop into the 50s with low 60s urban. Plenty of sunshine along with dewpoints in the 40s Wednesday through Friday will make for very pleasant weather. There will be less wind and mixing on Wednesday but 850 temperatures will still be higher; on Thursday, though 850 temps are lower, more mixing will take place. For this reason, I don’t expect a big temperature difference each day, but even with a lot more mixing it will still be slightly cooler on Thursday with 850 temps in the low to mid 40s. High pressure will build down into the Great Lakes region tonight through Thursday before nearing our area on Friday. As a result, less mixing is expected on Friday so highs may be even cooler when combined with the core of the cold 850 mb temps overhead. With an omega block that is slow to break down as additional energy drops into the Gulf of Alaska, this will teleconnect to a ridge moving slowly across the central US and southern Canada, and a trough lingering in the northeast through early Friday. As a result, cool and dry weather will prevail right through the end of the week. Heights will start to rise on Friday as the upper level pattern shifts eastward and a ridge starts to build into the east, beginning a slow warming trend in time for the holiday weekend.

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Heavy rain producing storms slowly approaching

By: NYCvort, 6:41 PM GMT on June 28, 2010

I personally am not that hyped on the idea of widespread severe weather today. We do have close to 2000 J/KG of surface based CAPE forecast across the area this afternoon; however, the mid level CAPE, which I consider to be more important for thunderstorm development, is low because the air at 500 mb is relatively warm. So we don’t have the mid-level buoyancy, and 35-40 kts of shear really isn’t that remarkable. The observed storms currently north/west of the city have not been classified as severe, and I think the factors discussed above are the reason why they haven’t developed into severe status. The precipitable water is very impressive, over 2 inches widespread. For this reason I do expect heavy rainfall with these storms. Shortwave energy and a prefrontal trough/cold front approaching from the west will help to ignite the storms and keep them going.

Also of note this afternoon is a stationary frontal boundary that is evident on the radar showing a coastal air mass dividing line. A marine layer of air has pushed onto the south shore of Nassau and most of Suffolk County on Long Island. The rest of the area including all five boroughs, the remainder of Nassau, and extreme NW Suffolk are under a WNW flow with no ocean influence, so temperatures across the city and NW Long Island are a bit hotter but also a little drier.

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Northeast Longer Range Weather Discussion: Relief from the heat

By: NYCvort, 6:27 PM GMT on June 26, 2010

Temperatures have been well above normal for a while now, but there is the possibility of a pattern change of sorts as we had into the middle of next week. I first recognized this potential on Wednesday when I saw the teleconnections from both ESRL/PSD and NCEP. One particular indication of such a change that caught my eye was that the EPO, which has been positive for some time, was shown by both models as going neural or slightly negative for the start of July. In addition, the NCEP teleconnections showed the possibility of the PNA going from negative to neural, and also of note was that the NAO was forecast to go from negative to either neural or positive. If all of this had actually occurred, I think the idea of a major pattern change would be imminent. However, I doubt the idea of a major pattern change as the models have since altered their tune somewhat. There is also little support for a long-term change, but there is still one feature that I think will win out and reverse the pattern for a few days.

The GFS and European models have been playing a game of hot potato of sorts, passing back and forth the idea of a deep upper trough/embedded closed low developing over the east coast. It’s almost as if the models can sense that for a while now their depiction of deep troughs over the east has rarely panned out as a result of convective feedback error. However, I believe that this trough is different, and I’ll explain why. First, the idea of an upper trough over the northeast is supported by the fact that a ridge is expected to build from the Rockies all the way up into central Canada as an upper low approaches the Gulf of Alaska. Just following the physical properties of a wave, if it bumps up in one place, then the wave must be just as negatively amplified in another. Second, the energy that would create this trough/upper low couplet has its origins in north central Canada, not in an area that would see thunderstorms this time of year and thus eliminates the idea of convective feedback errors generated by the models. Third, the AO oscillation, which is currently neural, is forecast by all of the ensembles to turn negative for the last week of June. As a matter of fact, if the ensembles are correct, the AO will be in the lowest state that it has been for over a month (it wasn’t lower since the end of May). Just as an aside, the NAO is also forecast to plummet, likely to a lower state than it has been for over a month as well, which would support this trough staying locked in for at least a couple of days. The fourth and final reason why I think this situation is different and why the trough/upper low will influence our weather late next week is because although the models have been waffling with its intensity for a while now and continue to do so, the GFS, the European, the European ensemble mean, and the Canadian models all show this intense feature impacting our weather by mid to late week. One thing that the models have been doing is continuously pushing back the time of the upper trough’s arrival, but this is to be expected as we are in an extremely strong negative QBO, especially for this time of year, which slows down all of the longwave weather features.

So to reiterate, I would expect hot and humid conditions to persist through early next week, but a return to a more springlike weather pattern can be anticipated later on in the week as the upper trough and potentially an embedded upper low begin to take hold of our area, at least for a short time. However, the key word there is short because we do, of course, continue to head into a weak La Nina pattern characterized by a ridge whose influence is likely to return to the northeast, as the AO is forecast to go strongly positive for early July. Once this occurs, there will be no support for a deep upper trough/low over the northeast.

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Very hot weather in store for today

By: NYCvort, 2:33 PM GMT on June 24, 2010

Under a WSW flow of about 5-10 mph throughout much of the night, La Guardia airport failed to drop below 83 degrees for an overnight low. In fact, the low of 83 degrees was higher than our normal high temperature for this time of year. Today will only be hotter with temperatures already climbing close to 90 this morning. As of 10 am, it is already 89 at La Guardia and 88 at Farmingdale Republic airport on Western Long Island. The south shore of Suffolk County may be a bit cooler today under a SW flow into early this afternoon. However, the five boroughs, Nassau County, and the north shore of Western Suffolk should see highs reach their full potential under a strong WSW flow. Expect highs in the lower 90s with a chance of strong storms later on this afternoon.

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5.0 Earthquake in Ontario-Quebec Border Region, Canada

By: NYCvort, 8:21 PM GMT on June 23, 2010

Felt across parts of New York and New England:

http://earthquake.usgs.gov/earthquakes/recenteqsus/Quakes/us2010xwa7.php

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Weather discussion for Wednesday: More heat and humidity

By: NYCvort, 8:01 PM GMT on June 23, 2010

Anomalous upper ridge persists across the south central/southeast with jet stream near US/Canadian border. WNW flow at the surface and aloft will continue the unseasonably warm spell of weather today. Shortwave ridging is currently providing plenty of sunshine along with hot and moderately humid conditions. Light winds and partly cloudy skies tonight will preclude temperatures from getting close to the dew points, which are pretty high anyway. Lows will be uncomfortably warm with mid and upper 70s urban areas to lower 70s elsewhere. Parts of northern Queens may even struggle to get below 80! A shortwave/associated cold front will move through Thursday afternoon providing a little bit of much needed relief from the oppressive heat and humidity for Friday. However, in the meantime ahead of the front, Thursday will feature sun and clouds once again but with rising humidity levels. Temperatures will start out warm and only get hotter as the day progresses. With good mixing and very warm 850 mb temperatures in the mid 60s, that will likely translate to afternoon highs in the mid 90s in much of the five boroughs and lower 90s elsewhere, with little ocean influence as winds will be strong out of the WSW turning WNW late.

In terms of thunderstorms Thursday afternoon, I certainly think the potential exists. The shortwave looks good (especially the mid-level one, and it's close by when the front approaches), the jet dynamics are good, and there is a well-defined surface front providing the necessary lift to get things going. CAPE (providing the buoyancy) values are pretty good (around 1500 J/KJ), and I like the amount of shear that I see present on the vertical profiles (although winds at the surface are pretty strong, so even though winds aloft are strong there isn’t as much shear as there could be). There’s quite a bit of mid-level dry air, which is a plus for thunderstorm development. The LI is below –4, which just shows how unstable the air will be. To be honest, my main concern is that even though all of the factors listed above will be present, the cold front will be moving through late in the afternoon so it may come through too early before things can get going. Let’s just say, if any strong/severe thunderstorms are going to develop, it’s probably going to have to happen earlier rather than later. Once the front moves through, all bets are off in my book. Taking all of this into account, I would say that for Thursday we’ll have a chance of thunderstorms later on in the afternoon. I think the chances actually increase further to the east of the city as the front will pass through there later with greater time for the atmosphere to become more unstable.

Updated: 8:09 PM GMT on June 23, 2010

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About NYCvort

I am a meteorologist from New York who has been studying and forecasting the local weather for years. I especially enjoy tracking winter storms.

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