Nov 3, 2010: Rain Entering, Storm Forecast

10:00 PM: Rain is already spreading into the area from the WSW, which is earlier than expected. Some of the rain is virga, meaning that it is evaporating before it can reach the ground, but the rain will eventually be able to reach the ground, likely by later tonight.

There are still a lot of uncertainties on this storm, and there are still significant differences with the models for Thursday night, but I will discuss the potential scenarios of this storm below. Whether the first or second scenarios verify, at least 3/4 to 1 inch of rain is likely for most of the area with amounts potentially a little higher.

Storm Scenario:


Thursday:
The low pressure currently off the Carolinas will move north and intensify tonight, reaching at least 998 mb by tomorrow afternoon SE of New York City. Rain from the storm will spread NE and intensify, with moderate to heavy rain falling from New Jersey to Maine. Some snow may mix in the higher elevations of the northern Northeast.

Moderate to heavy rain will fall in the area for most of the day, mainly in the early afternoon hours, with lighter rain by the late afternoon to evening hours as the first round of rain moves out of the area. High temperatures will be chilly, in the upper 40s inland and lower 50s in the immediate NYC area.

Thursday Night: This time frame is the one that currently has the most uncertainty. There are two model solutions, one of them being the one used in yesterday’s forecast, where the second storm will not see much of a negative tilt and stay to the east of the area, but more models are showing the second solution, where the second low pressure intensifies and becomes the main low pressure, being just SE of NYC on Thursday night with a negative tilt, meaning that the storm would go N or NNW from there instead of moving NE and along the coast, but the heaviest rain would be to the east of the storm.

Looking at the overall set up, I am now leaning more towards this second scenario, which was briefly mentioned in yesterday’s update. As such, moderate to heavy rain is now becoming a good possibility tomorrow night for Long Island/S CT, with moderate rain in NYC and lighter rain inland. Friday’s outlook will be discussed in more details tomorrow. This change, if it verifies, however, has a significant impact on the potential cold spell, which will be discussed in more details below.

Longer Range: Scaled Down Cold Spell?

For Friday, some rain is still expected in parts of the area as the storm exits. The recent trend, which pushed the storm west, also ended up pushing the trough west. The coldest 850 mb temperatures will be further north/west than originally expected, and with the frontal boundary still offshore on Saturday/Sunday, the cold air mass won’t be able to move into the area in full force like originally expected, and should stall just to the west of the area before lifting north and weakening. This would still lead to cold temperatures, but not as cold as yesterday’s forecast expected, rather temperatures similar those of yesterday and 2 days ago.

What could reduce the cold spell even further, however, is if the storm’s negative tilt ends up taking it too far northwest, like the GFS and GGEM are suggesting. The storm would be placed north of the trough, blocking the cold Canadian air from dropping south, and the trough would not have any source of cold air, quickly weakening from that point, with 850 mb temperatures barely dropping below 2c for the area. This would lead to temperatures slightly warmer than those of yesterday.

Tomorrow, I will review the model data and trends and where the storm will likely track, and discuss which solution could be the more likely one. Whether the first or second scenarios verify, however, snow flakes are no longer a possibility for most of the area like they were yesterday, only staying in far NW NJ. Stay tuned for more details on the cold spell.

Longer Range: Warmer Pattern Returns

There is still a lot of uncertainty on the longer range, however one thing that is likely is that the early to mid week time frame will be dry and warmer. There is uncertainty with which scenario verifies, though for now I’ll discuss the scenario currently shown by the models.

At this time, the models remove the cold air mass by Monday, with much warmer temperatures through Wednesday bringing high temperatures into the 60s. A storm is expected to form in the Midwest on Tuesday/Wednesday, and may pull down colder air into the region, but if the models are correct, this may not be the storm that brings down the cold air yet. The GFS model is hinting at another storm forming by Friday and Saturday, affecting the area directly while pushing the ridge offshore and bringing in a much colder air mass.

With this still being in the longer range, these details will likely change, but the overall theme at this time is that the mild pattern may last for at least a week before a colder pattern may return. Stay tuned for more details on this time frame.

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