Mar 16, 2013: More Snow, Rain For Monday Night

Forecast Highlights:

A late season light snow event affected the area today, with minimal accumulations under 1 inch observed for some locations. Since then, snow has ended across the area, with chilly temperatures expected to continue on Sunday. This is not the last snow event of the winter yet, however, as another storm affects the region on Monday and Tuesday, producing heavy rain as well as accumulating snow across the interior regions and parts of the area.



Saturday, March 16 Observations:

A weak low pressure moved through the Mid Atlantic, with widespread snow showers observed on Saturday. A steady period of moderate snow took place in the afternoon hours especially west of NYC, with light snow persisting through the early night hours. Temperatures peaked early in the day for most of the area around midnight in the upper 30s to low 40s across the area. During the day, temperatures peaked in the mid to upper 30s for most.





Short Term Update: Clearing skies are expected tonight behind the departing storm, with lows dropping into the 20s across the area. Mostly sunny skies are expected for Sunday with highs peaking in the upper 30s to mid 40s.

Monday – Tuesday: Storm To Produce Rain, Snow

The next storm to affect the region has its origins from two areas of precipitation in the western US; a broad area of rain and some snow in the Plains and lower Ohio Valley, and more rain/snow with an organized low pressure in the northwestern US. Both will continue to track east, reaching the region on Monday night. The primary low is expected to track into the northern Great Lakes and southern Canada, with widespread front end snow falling across Pennsylvania, New Jersey and the southern Northeast region. A secondary low is then expected to form near the area, intensifying as it tracks into New England, resulting in a significant snowstorm across the Northeast, to the north of the NYC area.

The main areas of uncertainty at this time with the forecast are regarding how much snow initially falls in the area prior to the changeover to rain and the timing of the heavier precipitation. Temperatures during the day on Monday are expected to peak in the mid to upper 30s inland and upper 30s to low 40s across the rest of the area, dropping as precipitation begins to fall in the mid to late afternoon hours. Initially, temperatures aloft and at the surface are expected to be cold enough to support precipitation starting as snow in northern NJ, SE NY and southern CT, with a brief start of snow possible in NYC and Long Island as well. A strengthening easterly flow is expected during this time, which should result in a quick changeover to rain for coastal areas on Monday evening while interior locations are slower to warm up and thus take longer to fully change over to rain, perhaps seeing some sleet/freezing rain in the process. Currently, the ECM is among the colder models and slower to warm temperatures up, although it has had several cases this winter where it underestimated the warming of temperatures both at the surface and aloft with east/SE flow events, such as 12/26 and 2/27.

The next question to consider is the timing of heaviest precipitation, as significant precipitation over 1 inch is expected but with the timing uncertain. The ECM has a period of heavy rain on Tuesday morning, while the rest of the models show some sort of a dry slot on Tuesday morning in between periods of moderate-heavy precipitation on Monday night and Tuesday late morning-early noon. At this time, I am siding with a compromise with spread out moderate to locally heavy rain, although this is subject to some changes.

Forecast for the area: The current outlook is for increasing clouds on Monday, with precipitation developing in the mid to late afternoon hours. Precipitation is initially expected to start out as snow north and west of NYC with a rain/snow mix for NYC and Long Island. With increasing easterly winds, NYC and LI should quickly change over to rain by the evening, while the north and western suburbs hold on to snow long enough for at least minor accumulations. The interior parts of the area should hold on to snow the longest, currently expected until at least 12-2 AM, with some sleet and freezing rain potentially mixing. Temperatures then continue to rise overnight, enough to change the interior areas to rain as well. Steady rain is then expected to continue through Tuesday afternoon, with drier conditions for the rest of the evening and overnight hours.

At least 1 to 1.5 inch of precipitation is expected to fall across the area. Snow amounts are more uncertain at this time and subject to some changes, although light to moderate accumulations are expected north and west of NYC, especially into NW NJ and interior SE NY. Stay tuned for more information on this storm over the next few days.

Longer Range: Still Chilly, Drier

The Tuesday storm won’t completely depart the region, but is expected to stall near Maine with the upper level low stalling over the region, forming a rex block configuration with the strong blocking in Greenland shifting south, which will keep the area under a trough for the rest of the week into next weekend with chilly temperatures. Temperatures on Tuesday and Wednesday are expected to peak in the upper 30s to low 40s inland and the low to mid 40s for the rest of the area, with overnight lows in the 20s for most places and the upper 10s for interior northwestern areas. Towards the late week and the weekend, the air mass is expected to become increasingly stale, with high temperatures slightly warming up. A few days ago, some of the long range models showed a storm potential for Saturday, but have since trended much more suppressed, with a weak low pressure over the southeastern US while the region stays chilly and dry. Given the upper level low over the region, some suppression is expected with this storm and it is not expected to track nearly as far north as the midweek storm, although it is not out of the question it could end up far north enough to affect at least parts of the region, which is a possibility that needs to be watched as medium range model guidance on some occasions can overdo suppression. More information will be posted on the long range over the next few days.

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