Nov 11, 2013: Rain/Snow Showers Tonight, Then Cold

Revised on Monday afternoon to include latest information

Forecast Highlights:

snow_graphicTemperatures will slightly cool down today, but will only continue to trend downward as a strong cold front moves through tonight into Tuesday, producing snow showers across the area into early Tuesday morning. Cold temps will follow for the midweek, with highs struggling to reach 40 degrees, but will be quickly followed by a late week warmup with highs returning well into the 50s and 60s by next week.




Today – Wednesday Night: Rain, Snow Showers Tonight, Then Widespread Cold

snow_graphicBehind yesterday’s cold front, which brought an unexpected round of light rain showers, a cool air mass moved in for last night, but with the progressive flow aloft has already exited the region this morning, with a light southwest wind and highs reaching the low to mid 50s. More significant changes begin tonight, however, as a strong arctic air mass enters the region with 850 millibar temperatures as low as -10C reaching the area. A cold front will move through this evening, bringing a line of light to moderate precipitation, but the precipitation will be lagging behind the cold front, which along with strong cold air advection taking place overnight as temperatures quickly fall into the 30s, is expected to support a changeover to snow across most of the area, including Long Island and locations near and south of NYC.

Below is the 0z NAM modeled precipitation type graphic for 9z Tuesday (4 AM). Afterwards, the snow spreads further southeast (image credit: PSU e-Wall).

cld33Rain showers are expected to develop late tonight, with a changeover to snow likely during 4-6 AM north/west of NYC, and 6-9 AM south and east of NYC. With precipitation intensifying as it enters the area, the highest likelihood of snow is expected to the east and south of NYC, although some snow showers are likely across the rest of the area as well. Surface temperatures are expected to be marginally warm for accumulations, although locations under locally heavier snowfall, especially east and south of NYC, could pick up a coating of snow with locally higher amounts not out of the question.

Following the frontal passage, much colder temperatures are expected on Tuesday and Wednesday, peaking in the upper 30s inland and low 40s for the rest of the area. Windy conditions are expected on Tuesday, with a NW wind at 10-20 mph, gusting to 30-35 mph at times. The coldest temperatures are expected on Tuesday and Wednesday nights, falling into the low 30s in NYC and 20s elsewhere, and as low as the upper 10s in the typical cold spots in interior areas.


Thursday – Monday: Warming Up

As the trough axis quickly moves out of the region, remaining positively tilted, the surface high pressure that brought the cold temperatures will spread east, becoming stationed south of the area as ridging quickly builds aloft over the region with troughing returning to the western half of the US. This will lead to a warming trend starting on Thursday, with widespread above average temperatures expected to return. Temperatures initially will be slow to warm up, peaking in the mid to upper 40s on Thursday, but will accelerate afterwards, reaching the mid 50s on Friday and the mid to upper 50s for next weekend. Mostly sunny skies are likely through Saturday, but with an increase in cloud cover likely towards Sunday and Monday. The warmest temperatures are currently likely to be towards next Monday, with temperatures possibly reaching the 60s in the immediate NYC area. There is some uncertainty towards Sunday and Monday, however, with the possibility of scattered showers and slightly cooler temperatures from a potential system developing to the south of the area.


Tuesday – Beyond: Widespread Rain Possibly Returns; Colder Temps Likely

The main uncertainty in the longer range outlook at this time is the setup of northeast Pacific ridging and a dropping cold air mass from northern Canada. The ECMWF is currently the most aggressive in dropping this cold air mass south into the US with a widespread cold outbreak, although it is currently an outlier as it pulls too much energy to the west with significant trough amplification in the western US, as opposed to the rest of the model guidance, which keep the trough more progressive and bring a quick cool air mass on Tuesday and Wednesday followed by another warm up as ridging in the northeast Pacific expands into the US with troughing returning to the west. The ECM displayed the same bias of holding back too much energy with exaggerated medium range amplification just a few days ago, when it showed a major storm for this coming Wednesday where it ended up as a significant outlier, and at this time given recent trends I am siding towards a somewhat more progressive scenario than the ECM. In this case, however, a more progressive scenario would favor the cold air mass directed towards the eastern half of the US as opposed to the western US, with a strong frontal passage likely around Monday or Tuesday, bringing the next potential for widespread rain over the area, followed by a transient but potentially strong cool down for the middle of next week and a warm up by the end of the week or next weekend. Stay tuned for more information on next week’s outlook.

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