Special Update (Tuesday, January 27 at 12:11 am EST): At midnight, snowfall rates in excess of 2 inches per hour were moving west toward New York City. This band has been showing a decrease in intensity over the past couple of hours as the storm intensifies offshore and both the atmospheric energy and mesoscale forcing contract around the storm. In our previous forecast (below this radar image) we discussed the use of the 50th percentile for our snowfall forecast, and we are not expecting a “historic” snowfall in New York City proper. If you want, you can skip the technical discussion and go straight to the accumulation map.
This radar image focuses on the NYC area only.
Previous Forecast Discussion
An area of low pressure currently off the coast of Virginia will continue to move northward through the day as it begins a period of rapid deepening and intensification. This system will bring heavy snow to portions of the Northeast through Tuesday. The main area of low pressure should remain just offshore with precipitation northwest of the low. Winter Storm and Blizzard Warnings are in effect for many of the coastal areas of New England. Heavy snow and winds to 60 miles per hour will be possible, especially along the coastal regions of Massachusetts.
On Sunday evening (January, 25, 2015 at 8 pm CST), we noted an intense jet streak rounding the base of the positively-tilted upper-level trough. A positively-tilted trough is typically more of a nuisance when it comes to weather. However, this incredible jet streak will will force the trough axis into a negative tilt (NW to SE) through the day on Monday, opening up the upper levels east of the trough axis into a highly divergent configuration. These sequence of events will initiate rapid vertical motions leading to very rapid deepening of the surface low off the East Coast through Tuesday. The surface low may deepen as much as 30mb in just 24 hours, which is astounding.
The first two images below are snapshots of the atmospheric dynamics at the onset of a potentially historic and crippling blizzard (valid Sunday night). The third image is the water vapor image just 18 hours later indicated that the upper-level trough has changed orientation, as predicted, and rapid deepening of the evolving coastal storm is underway. /Robbins
The first water vapor image above corresponds to the 300-mb chart at the same time. Note the positive (NE-SW) tilt to the upper-level trough. As the strong speed maximum (jet streak) rounds the base of the trough, it forces the entire pattern into a negative tilt (NW-SE orientation). As expected, the upper-level pattern east of the trough axis becomes violently divergent with enormous vertical velocities. As of the time of the second water vapor image (3 pm EST 1/25/15), rapid deepening of the surface low is beginning. The surface low may deepen as much as 30 mb in a 24-hour period, as previously stated. These are rare events.
What is a Blizzard?
According to official NOAA/NWS guidelines, the term “blizzard” is limited to a snowstorm that contains the following:
- 35+ mph winds (or frequent gusts exceeding that speed)
- Heavy snow and/or blowing snow
- Visibility 1/4 mile or less
All of the conditions above occurring for three hours or more. These will create whiteout conditions, which will make it difficult to see in front of you, causing disorientation.
Analyses and Forecast
By tonight, the main system will be just off the East Coast. As it continues to move along the coast, heavy snow will develop to the northwest of the center of the low where frontogenesis and conditional symmetric instability (CSI) will be the greatest. The strongest frontogenesis will likely be roughly from Long Island to Boston.
The NAM model has a band of frontogenesis extending from New York City into South Central Massachusetts. It is near this band where the highest snow totals will be expected. To the northwest of this band, snowfall amounts will drop off drastically.
Within these frontogenetical bands, snowfall rates will be 2-4 inches per hour with snowfall totals as high as 30 inches along the coastal areas, especially across Eastern Massachusetts. Further inland, 8-12 inches will be common.
Total Accumulations Using the 50th Percentile
The following map shows the snowfall amounts that we are forecasting over the next 72 hours (by Thursday, January 29, 2015 at 6 am EST). The amounts shown lie within the 50th percentile, which is a more realistic approach to winter storm prediction. The 95th percentile would represent a “worst case” scenario, and we are not forecasting amounts that high; in fact, even accumulations within the 75th percentile seem too large, particularly on the western/southwestern periphery. New York City, for example, may not receive more than 15 inches. For these reasons, we have opted to go with a more conservative forecast, using the 50th percentile. Note: The highest amounts will remain east of New York City, and we are NOT forecasting a storm of historic proportions for NYC proper. The coastal areas northeast of NYC will receive the brunt of this storm.
A Few Tips
1) If you live in the impacted areas, please heed the forecasts.
2) If you have friends or relatives in the impacted area, please check on them periodically over the next few days. It’s unlikely that they would be unaware of the forecasts at this point; however, with tropical-storm force winds and heavy snow, many people will lose power.
3) Air travel to this part of the country is now nearly impossible as airlines have canceled thousands of flights. The flight cancellations and delays will eventually impact other parts of the country.
4) If you are traveling anywhere, irrespective of where you may live in the United States, please call ahead to check on your flight’s status.
5) If at all possible, and as conditions allow, please check on the elderly in the impacted area.
6) If you are in the impacted area, do the following TODAY while you still have power:
- Charge all laptops (laptop battery power can be used to charge dead cell phones)
- Charge all mobile devices
- Keep all devices charging, especially while in use, in the event that you lose power
- If you lose power, turn off all laptops (save the battery power until you need it)
- If you lose power, use your mobile devices sparingly. Switch to airplane mode, or power them down when not needed.
- If you power off your mobile devices, tell your family and friends that you are doing so (they may worry if they can’t reach you)
- If you lose power and your cell phone dies, you can use your laptop (or your car battery) to recharge
*I offer point #6 from personal experience. I lost power for 28 hours during the historic snowstorm in North Texas back in February of 2010. If you have any tips that you want to submit for this page, please use the contact form. The tips will not post immediately, but we will add them in moderation. They will also be used as a repository for future events. /Robbins