Oct 23, 2012: Showers Tonight; Next Week Update

Forecast Highlights:

• Some showers expected tonight, Wednesday; light rain totals
• Temperatures start in 60s, warm up to 70s by weekend
• Update on storm potential for early next week

Cloud cover and some showers will continue through Wednesday and Thursday before a warm up during the weekend. Attention then turns to Tropical Storm Sandy, which as a non-tropical system is increasingly likely to affect the region. Click below to read the full post for the latest information.

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Tonight - Saturday: Clouds, Some Rain, Cooler

Temperatures today ended up busting too warm for parts of the area, with actual highs in the mid to upper 50s inland, mid 60s in the immediate NYC area, and the mid to upper 60s for most of Long Island and southern CT. The latest regional radar, at the top of this post, shows scattered showers affecting the area. The area currently remains near a stalled frontal boundary, with the front dropping south of the area later on Wednesday, with expected highs in the upper 50s to low 60s in southern CT, Long Island and interior SE NY, low to mid 60s in NYC and interior northern NJ, and mid to upper 60s west and southwest of NYC. As with today, bust potential remains higher than usual with the temperatures as the area is near a temperature gradient.

Similar temperatures are expected on Thursday as well with mostly cloudy skies. As a high pressure drops south of the area with more of a SSW flow developing, a brief surge of warmth will reach the area with highs warming up on Friday along with partly to mostly cloudy skies. Highs will reach the mid 60s to low 70s across the area, with the warmest highs in the immediate NYC area and coolest highs near coastal Long Island and the interior N/W parts of the area. These warmer temperatures will continue into Saturday as well with more sunshine.


Next Weekend - Early Next Week: Watching Sandy, Potential Storm

The highlight of the forecast in the medium range remains the same as the last few days, with the potential for a storm to affect the region with moderate or possibly significant impact, coincidentally landing on the same date as last year's record shattering October snowstorm. As the storm is still 6-7 days out, it is very important to note that it is too early to come to a high confidence conclusion, and there will continue to be changes with the forecasts and the model guidance. Regardless of what will happen with the storm, however, this time period is shaping up to be a very interesting one for the region, far more anomalous than anything observed over the last year.

Potential Set-Up: This storm potential comes from a result of several key factors, also shown with the GFS posted to the left. The first factor is Tropical Storm Sandy, currently in the Caribbean. Sandy is currently a 50 mph tropical storm with a minimum pressure of 993 mb, and will intensify while moving NNE, making landfall over Jamaica and eastern Cuba. From there, it will track into the Bahamas before turning NE, moving parallel to the East Coast. The track and speed of Sandy in the western Atlantic will help to determine the outcome. Another factor involved in this set up is an approaching shortwave from the central United States. This shortwave has the potential to phase with Sandy while in the western Atlantic, preventing her from moving offshore and instead pulling her into the Northeast US while Sandy becomes non-tropical and intensifies. Another key part of this set up is a low in the northern Atlantic, southeast of Newfoundland, along with an anomalous block over Greenland. The low in the Atlantic will prevent Sandy from simply moving well offshore, although how far east or west this ends up will also help to determine how far west or east Sandy ends up. If Sandy is too far east, chances for a significant impact in the region will be lower, even if there is a phase.


Model Review: As mentioned over the last few days, the CMC and ECM have been showing Sandy phasing with the shortwave and being pulled inland, while the GFS missed the phase and kept Sandy well offshore with little to no impact in the area. While the ECM remained consistent with a significant storm in the region today, the CMC and UKMET are now siding with an offshore scenario, along with the GFS, although Sandy is still blocked from moving out of the North Atlantic on the GFS and CMC and still retrogrades close to New England. The model ensembles are also important, however, and are sometimes considered to be "red flags" to the operational models if the majority of a model's ensemble members show a different outcome than the model. This is what we are seeing in this case; the majority of the CMC, UKMET and the GFS individual ensemble members are showing Sandy phasing and moving straight NW into the region, despite the operational models showing an offshore scenario. The main issue with relying too heavily on the models is the time range, as the models will continue to change with the set up, especially with the incoming shortwave, which will be sampled better once moving into the United States later on Wednesday. Despite the uncertainty, I would not be surprised if the GFS is currently too far east, and ends up trending towards the rest of the model guidance with more phasing and a larger impact in the region.

Looking at past examples of difficulty with model guidance, this is where predicting exactly which scenario happens becomes complicated. Interestingly, some of the more high impact events in the region in the last few years have been modeled well in advance, such as hurricane Irene, the December 26, 2010 blizzard, and the October 29, 2011 snowstorm. With the 12/26/10 and 10/29/11 examples, the models showed the storm in the long range, but lost the storm for a period of time in the medium range (about 3-5 days out), before suddenly reaching a consensus for a strong storm again in the short range. With both of these cases, the ECMWF was consistent with showing a high impact event, while the GFS was persistently weaker and further away from the area. Considering that the storm is still 6-7 days away, there is plenty of time for the models to change around, and even if there are more models not showing the big storm over the next few days than there were today, it does not guarantee that the storm will miss the area; neither does it ensure that the big storm will certainly verify.


Summary: As with yesterday, it is still too early to make any high confidence call for the storm, especially as it is still 6-7 days in the longer range and there is still plenty with the set up that can change and result in a less significant storm affecting the region. Despite these uncertainties, the potential is clearly there for a moderate to potentially significant storm to affect the region, including the NYC area, on Monday and Tuesday of next week. While some models are still well offshore, recent trends suggest that the possibility of the storm entirely missing the region are decreasing with the probability of phasing and direct impact in the Northeast US much higher, even if the phase is to the east of the Northeast.

At this time, I do expect to see direct impact in the region, with the GFS likely the eastern outlier, although the full magnitude of the impacts remain uncertain, and most options remain on the table, including a significant storm affecting the area. Once the storm enters into the more reliable shorter range, there will be a better idea of exactly what the storm does and to what extent it will affect the region. While it is too early to forecast the exact impact from this storm, should the stronger case scenario verify, the storm would be capable of producing significant impacts in the region, including very heavy rain totals, strong to possibly damaging wind gusts, and coastal flooding. Stay tuned for more information on the storm over the next few days.