Mar 17, 2013: Rain, Snow, Ice Tomorrow Night

Forecast Highlights:

The colder than average pattern continues across the region with no sign of falling apart anytime soon, as the area observed another day with highs in the 30s to low 40s. A storm is expected to affect the region on Monday into early Tuesday, producing snow, ice and rain across the area with accumulations expected north and west of NYC, followed by continued cold temperatures for the rest of the week.


Sunday, March 17 Observations:

Unseasonably chilly temperatures continued across the region on Sunday, with high temperatures over 10 degrees below average for parts of the area. High temperatures peaked in the mid to upper 30s west of NYC, and in the upper 30s east of NYC with New Haven, CT peaking at 40 degrees. Partly to mostly cloudy skies were generally observed with a N/NW wind gusting up to 20-25 mph for parts of the area.



Monday – Tuesday: Storm Produces Rain, Snow, Ice

Throughout the day, a narrow band of rain and snow spread east through the Ohio Valley into Virginia, while a low pressure continued to track east through the northern US, currently near North Dakota. These two areas of precipitation will continue to track east, affecting the region on Monday and Tuesday. Widespread front end snow and ice is expected to develop over Pennsylvania on Monday afternoon, which later extends into the NYC area and New England. A secondary coastal low is expected to begin developing south of the area, which later intensifies and enhances precipitation over New England, where a widespread significant snowstorm is expected.

Forecast Discussion: As with yesterday, the main question for the area remains how much snow and ice fall prior to the changeover to rain. The ECMWF was initially among the colder models, but last night’s update pointed out to other cases this year where the ECM was too cold with E/SE flow events, and today’s runs were closer to some of the other models. Precipitation is expected to develop around 3-6 PM west of NYC and 5-8 PM east of NYC. Temperatures aloft are expected to be cold enough to support snow at the onset for most of the area, with surface temperatures dropping by the late afternoon into the upper 20s to low 30s inland, low to mid 30s for the immediate NYC area and southern CT, and the mid 30s in Long Island. Due to an easterly flow, coastal locations should quickly change over to rain, with NYC also changing over later in the evening hours, with little to no accumulations expected.

North and west of NYC, including southern CT, temperatures are expected to be cold enough for a more prolonged period of snow before the changeover to rain, which is expected to take place towards 8-11 PM for most of the area except for far NW NJ, SE NY and interior southern CT. Some freezing rain and sleet is likely to mix in during this process as well. Some of the issues in the snow forecast include the timing of the day, as the snow develops during the mid afternoon hours, meaning some of the precipitation falling as snow is not expected to accumulate due to initially warm surface temperatures and especially depending on precipitation rates, with locations seeing bursts of moderate-heavy snow likely to have snow accumulate earlier than other areas. Regarding snow totals, I am currently siding close to the model guidance for interior parts of the area and more conservative for locations closer to NYC, although the snow outlook is still subject to change.

Forecast for the area: Snow is expected to spread into locations west of NYC from 3-6 PM, and east of NYC from 5-8 PM. Most locations are expected to start out with snow, but with coastal locations and NYC quickly changing over to rain by the evening. Through the overnight hours, steady moderate rain is expected in NYC and Long Island, while locations north and west of NYC and southern CT observe moderate snow, which starts to change over to rain from south to north, mixing with sleet/freezing rain for interior areas in the process. Most of the area should change over by 8-11 PM, with interior locations changing over by 12-2 AM. Moderate rain will continue falling through the late morning or early afternoon hours from NYC and further west and into the mid afternoon hours east of NYC, with clearing skies expected afterwards as high temperatures rise into the 40s.

Most of the area is expected to see a total of at least 1 to 1.5 inch of precipitation. Regarding snow totals, little to no accumulations are expected in NYC, with up to 1″ in the immediate suburbs, 1-3 inches in the interior suburbs, and 2-5″ further inland. The snow outlook is still subject to some revisions. New experimental forecast precipitation and snow maps can be found in the Weather Hazards page. Storm updates will be posted on the blog and on Twitter during Monday afternoon and evening.

Wednesday – Beyond: Chilly Pattern Continues

Cold temperatures are expected to return by Tuesday night with lows in the 20s across the area. Partly sunny skies are expected for Wednesday with a strong west wind and highs peaking in the mid to upper 30s inland and upper 30s to low 40s across the rest of the area. A weak low pressure is likely to develop offshore overnight, quickly racing northeast until it reaches Atlantic Canada on Thursday. There is some uncertainty with this feature, although scattered snow showers are possible especially for eastern parts of the area on Wednesday night. Partly sunny skies are expected to continue for Thursday and Friday with highs again in the mid to upper 30s inland and upper 30s to low 40s for the rest of the area.

As of today, a strong block is developing over Greenland, the strongest since early June 2012, with 500mb geopotential heights as high as 558-564dm, nearly 48-60dm above average. Along with this blocking, a strongly negative AO is expected, falling to -5 or -6 SD, which along with several other factors ensures that a persistent spring pattern remains nowhere in sight through at least early April as temperatures remain generally colder than average across the region. Late this week, the block will shift south, briefly forming a rex block setup with the upper level low from the midweek storm to the south, over the Northeast US, with the block then likely to shift west into central Canada by the weekend as the ULL begins to drift east and another trough digs into the region. Most models show a coastal storm developing by next weekend or early next week, but with the storm staying south of the area. Given the pattern in place, any storm that develops in this time frame is unlikely to track too far north, with a stale cool air mass in place but still cold enough to support the potential for a wet snowstorm. This is still nearly a week out, with additional changes expected with the models, and this time period will continue to be watched for the possibility of a storm affecting parts of the region, potentially with snow. More information will be posted on this time period as details become clearer.

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