Pleasant start to the work week, then unsettled
We remain in a well-defined negative NAO pattern that is currently almost 2 standard deviations below normal.
This is in a sense protecting us from the heat as trough energy continues to pool in southeastern Canada and over the Canadian Maritimes.
As such, an upper low pinwheeled over Quebec and brushed northern New England today. This upper level feature pushed a cold front through last night and allowed for a dry air mass to move into the region with high pressure nosing down from Canada.
It also brought a stable air mass into the area. LIs will be nearing +10 by Monday evening, which denotes very stable air, while all of the instability and associated thunderstorm activity remains well suppressed.
After a comfortably cool morning, with light onshore flow, highs on Monday will be in the upper 70s along with another day of low humidity levels making it very pleasant. There will likely be an increase in high clouds midday as a mid-level disturbance passes to our south, but we will remain dry.
Winds will back around to the southwest on Tuesday. The change in surface flow pattern combined with slightly warmer 850mb temperatures will send highs back into the 80s. With the air gradually becoming more unstable, we will have to put back in the chance for a thunderstorm, especially north and west of the city where instability will be greater. A warm front will approach on Wednesday. There is some indication that the front will get caught up and could remain the focus for periods of showers and thunderstorms from mid to late week as an upper level trough, now located over the western US, approaches and sends moisture up the eastern seaboard.
This will need to be monitored as the week progresses.
Updated: 5:24 AM GMT on June 20, 2011
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Negative AO/NAO helps to send down some relief from the heat
The entire New York metro area experienced scorching early June heat this week. Northeast New Jersey has already recorded its first heat wave of 2011, with the mercury at Newark topping out at 102 degrees on Thursday. LaGuardia Airport recorded a high of 97 both Wednesday and Thursday, with Central Park reaching 95 degrees on Thursday and heat indices over 100.
The oppressive heat was ended abruptly Thursday evening as a line of thunderstorms came though. The temperature at LaGuardia plummeted 20 degrees, from 95 to 75 in merely one hour.
Despite the fact that a cold front has drifted to the south of the area, heights were still high Friday and mid-level temperatures remained warm. This resulted in another warm day. High pressure to our north moves off the coast on Saturday, which will shift winds to the east. In the meantime, a frontal system will be cutting up through the Lakes, with moisture streaming out ahead of it providing clouds. The combination of cloudy skies and an onshore flow will make for cooler temperatures with highs struggling to get out of the upper 60s. The overrunning of moisture ahead of the warm front will also lead to showers.
The associated cold front will pass through on Sunday with the potential for showers and maybe a thunderstorm. It will be a lot milder on Sunday in the warm sector.
An upper low is expected to form over eastern Ontario later in the weekend. The low will slide to our north on Monday.
This time around cold advection really gets going behind the front with 850mb temperatures dropping and highs on Monday only in the low 70s along with low humidity. Dry air wrapped around on the southern side of the upper low will allow for morning sunshine followed by increasing clouds. It will be a very pleasant start to the new work week with the heat suppressed to the south.
Energy rotating around the upper low may spark some showers late Monday or Tuesday. There is still some question as to what actually happens with the upper low after this point. Latest model runs appear to be trending toward keeping a more intact closed low and thus slower to depart. The GFS and especially the GGEM still has the low/trough weaker and more open which allows it to depart quicker, while the ECMWF (which has support from its ensemble mean) actually deepens it further as it heads off the New England coast and has a closed low meander in the Gulf of Maine through Thursday.
The GFS/GGEM solution would suggest a gradual warming trend during the week as ridging embedded within the Pacific jet stream slides in and heights rise, with temperatures back to near normal levels by Wednesday, with highs the upper 70s to low 80s. On the other hand, the ECMWF solution would keep us very cool in the upper 60s both Tuesday and Wednesday and in the 70s through the remainder of the week. There is support for a more extreme solution in regards to the low with strong positive anomalies over the higher latitudes potentially allowing for something to remain closed off underneath.
Regardless, it will remain comfortable and fairly dry with dewpoints expected to stay in the 50s with high pressure coming down from the Great Lakes and Canada.
Taking a brief look at some teleconnections, we are now in a negative AO/NAO pattern.
As a result, the jet stream will likely stay more suppressed to the south than it has been lately with high latitude blocking over northern Canada and Greenland remaining into next weekend.
I expect this will act to keep temperatures reasonably mild in the extended with no extreme heat expected, at least for a while.
Updated: 1:45 AM GMT on June 11, 2011
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Strong to severe thunderstorms possible thru 10pm
SPC has placed the entire area under a severe thunderstorm watch. Thunderstorms continue to develop, triggered by a prefrontal trough. There is plenty of CAPE or energy available (2000-4000 J/kg) for these storms to intensify and maintain themselves in the highly unstable airmass:
The shear values are marginal (30-40 kts), but so far have proven to be enough:
(All images above update automatically on reload)
Updated: 8:26 PM GMT on June 09, 2011
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