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Feb 16

Feb 16, 2014: Short Break From Snow & Cold Ahead

Forecast Highlights:

gfs_namer_045_850_temp_mslp_precipYesterday’s snowstorm, having produced snow totals from 1 inch near NYC to as much as 7-8 inches in eastern locations, was only the latest addition to what is one of the snowiest months on record, with 2013-14 now the 8th snowiest winter on record in Central Park. While the peak of the snow has likely passed, this winter’s cold and snow are still not over; 1-3 inches of snow are likely on Tuesday, followed by a temporary late week-weekend warm up only to be followed by a widespread cold surge to close the month.

 

 


 

Tonight – Monday: Still Cold, Few Snow Showers

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Posted above from left to right are the latest surface analysis and radar composite from WPC, and the initialized NAM 500 millibar heights and vorticity from NCEP MAG; both are valid at 18z (1pm). Yesterday’s storm, which produced light to moderate snow across the area, has rapidly deepened last night and is now a very deep 964mb low pressure just northeast of Nova Scotia. With the low pressure departing the region, the pressure gradient has decreased, leading to lighter winds compared with last night and this morning, although another feature to note is a weak low pressure over western Pennsylvania associated with a weakening clipper system; most of the precipitation associated with this system is drying out but with mostly cloudy skies to continue with isolated snow showers possible this evening.

The high pressure behind the clipper will build into the region tonight into Monday; a few days ago this high pressure was forecast to be positioned overhead tonight, but with the pattern slower than previously expected, this high will remain west of the area overnight, not moving overhead until during the day on Tuesday. This will keep cloud cover in place for tonight with a decreasing northwesterly winds, which are not ideal conditions for strong radiational cooling as observed last week when interior locations fell below -10 degrees for lows. Temperatures tonight are expected to fall into the upper 0s in interior NW NJ/SE NY, upper 10s in NYC, and the low-mid 10s elsewhere. Mostly sunny skies are expected for Monday with highs in the upper 20s to low 30s.

 

Tuesday: Snow To Rain, 1-4 Inches Expected

18z GFS at hour 42, valid at 12z Tuesday (7am), depicting light snow covering the area. The low pressure near western NY later transfers to a coastal low with heavier snow near New England (image credit: PSU e-Wall).

f42The next snowstorm will affect the area late on Monday night into Tuesday afternoon, bringing another round of light to moderate snow accumulations. A strong but relatively flat shortwave trough will race east through the northern US, supporting moderate snow reaching the region on Monday night, developing in the area around 2-4am. As this will be a fairly fast moving system with a southwesterly flow setting up behind it, temperatures will gradually warm up throughout the event, with a changeover to rain likely near Long Island and coastal areas into Tuesday morning before precipitation ends in the late morning or early afternoon. The model guidance has varied regarding the location of the transfer to a coastal low pressure, which will also determine whether the steadier snow rates develop near the area or to the northeast. Yesterday’s models were particularly indicating the former scenario, with the ECMWF supporting as much as 4-6 inches of snow in the area, but with the models having since backed down on precipitation totals. At this time, I am expecting snow accumulations to end up in the 1-3 inch range for most locations, with totals over 3 inches possible northeast of NYC into Connecticut, where totals up to 4-5 inches are possible. The outlook is subject to slight changes over the next day as the model guidance gains a better handle on the development of the low pressure. The snow from this system, albeit relatively minor, will further help to ensure a full month of snow cover for most of the area by Friday, 2/21.

Through today, Central Park has recorded 55.6 inches of snow to date this winter, and 27.3 inches during February. If at least 2.2 inches of snow accumulate on Tuesday, this season will be placed as the 6th snowiest winter on record. The snowiest month on record is February 2010 with 36.9 inches of snow; while this storm alone will not lead to such totals, Central Park is at least 3.5 inches away from the 3rd snowiest month on record, behind February 2010 and January 2011.

 

Wednesday – Saturday: “February Thaw” Expected, Highs in 50s Possible

With the strong cold air mass having retreated back into northern Canada, along with a more zonal flow in the upper levels, there will be no strong cold air source for the incoming systems to tap into and to pull into the region, which along with the low pressures tracking north of the area leading to a southwesterly flow in the lower levels, the most prolonged warm period since mid January is expected starting on Tuesday with highs in the upper 30s to low 40s following the light snow event. With the upcoming warmer temperatures and rainstorm, along with the deep snow pack currently over 12-18 inches deep for many locations, the potential for flooding exists as the snow pack gradually melts.

Another shortwave will pass through the region on Wednesday but further north than Tuesday’s system, leading to mostly cloudy skies, isolated showers, and high temperatures mostly in the low to mid 40s, possibly reaching the upper 40s near and south of NYC. Slightly cooler temperatures are expected on Thursday in the low to mid 40s along with increasing cloud cover. The next storm system is expected to affect the region on Friday as a deepening low pressure tracks through the Great Lakes into Canada, leading to a surge of warm air from the south and supporting temperatures increasing on Thursday night into at least the mid 40s. A brief spike into the 50s is possible on Thursday morning depending on the timing of the cold front, with a line of moderate rain likely between the morning and early afternoon hours. A slow cool down is expected on Saturday and Sunday with highs still likely in the 40s; the ECMWF currently suggest a moderate rain event on Sunday, although currently it does not have any model support; only the latest 18z GFS run hints at a similar outcome, and while uncertainty remains, a chance of rain has been added for Saturday night.

 

Next Week – Beyond: Winter Not Over Yet

500mb heights and anomalies from the GEFS at hour 192, on February 24, depicting the redevelopment of strong ridging over the northeast Pacific (image credit: PSU e-Wall).

f192Despite the relatively long lasting warm up late in the week, with highs in the 50s possible, there are strong indications suggesting winter is not over yet. A strong upper level low has recently been positioned over the Gulf of Alaska, supporting a positive EPO teleconnection index which often correlates to above average temperatures in the majority of the US. This feature marks a departure from the pattern which has dominated the northern Pacific for the majority of the winter, with a strongly negative EPO as a result of significant high latitude ridging and blocking alternating between the north central Pacific and the northeast Pacific. The Pacific ridging was the main driver of this winter’s pattern, which was able to override other factors which are not indicative of cold and snowy patterns, such as a lack of blocking near Greenland, which often serves to slow the upper level flow and displace cold into the northern US, and the -EPO pattern partially aided in the displacement of frigid temperatures earlier in the winter over southern-central Canada, leading to colder than average temperatures in the region with the region more often under the influence of moderated polar air masses rather than moderated Pacific air masses. A warm pool of sea surface temperatures remains in the northeast Pacific, however, which is often indicative of a negative EPO index, and unlike December 2012 and the winter of 2011-12, which were dominated by a +EPO pattern with an upper level low frequently positioned near Alaska, this winter’s patterns have not been conductive for such upper level lows to remain in place.

Along with support from tropical forcing as the Madden-Julian Oscillation (MJO) propagates eastward to phase 8, which is often indicative of a greater probability of colder temperatures in the eastern half of the US, these signals suggest that ridging in the western US and northeast Pacific is expected to redevelop by late next week, supporting strong cold air gradually draining towards central Canada again, and by the last few days of February into early March lead to a potentially significant surge of cold air with widespread below average temperatures. Depending on the positioning of the trough axis and the storm track, the potential for additional snow cannot be ruled out as well, although the peak of the frequency and intensity of snowstorms has likely already been reached earlier this month. The latest long range model guidance has shown recurring signals of a potential storm towards the very end of the month, which will continue to be monitored over the next few days. More information will be posted on the specific details of the upcoming pattern as this time frame enters the medium range.

5 comments

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  1. Anonymous

    Sir, is March in NYC expected to have even more snow and cold than last year?

    1. NYC Area Weather

      March does not appear to feature as much cold and snow as last year, although relative to average, at least near to slightly below average temperatures are likely overall for the month, with some snow but perhaps not to the extent of last year’s March.

  2. Eduardo Berroa

    Good morning sir, would you mind if I start discussing about thunderstorm possibility with you? Because the possibility for thunderstorms on Friday does appears unusually interesting.

    On Friday, will potential chance of general t’storms or possible isolated severe t’storms may exist in NYC (New York City) forecasts?

    According to the 4-8 Day Outlook Forecast from SPC (Storm Prediction Center), D5 highlighted almost near NYC and extreme lower Long Island so only general thunderstorms may only be display on forecast outlook or slight risk of strong-to-severe thunderstorms may remain the possibility for being highlighted on the forecast outlook. If D5 has been edited and highlights NYC, we’ll expect strong-to-severe thunderstorms may eventually convert into convective linear/bowing segments to linger across the Atlantic Coastal States after the development occur along the strong cold front. Within the linear/bowing segments, damaging thunderstorm winds to 60-70 mph (52-61 kts) remains as the main threat and it’s expected relatively widespread across the Atlantic Coastal States. In addition, we won’t expect couple of brief tornadoes remains the probability of becoming a second threat, predicting the threat may be embedded in vortices within the convective linear/bowing segments but the threat for tornadoes may be possible across the Mid-Atlantic States, mainly Virginia, Maryland, North Carolina and South Carolina, including Northwestern Georgia.

    Write me soon and please give comments to respond..

    Seen you soon.

    1. NYC Area Weather

      Good catch on the thunderstorm potential – it is a subject I have analyzed and will discuss in today’s forecast discussion. SPC’s latest outlook places a Day 5 enhanced risk very close to NYC and to the south, which is unusual for February. SPC does note the potential for isolated tornadoes and widespread severe thunderstorms, but places this risk over the central US rather than the eastern US, as weakening forcing and less instability will decrease the risk of severe thunderstorms over the region, but will still support a line of rain, strong wind gusts and potentially thunderstorms with the frontal passage during Friday. I currently think SPC extended their 30% enhanced risk area too far north, although the potential does exist for strong to perhaps damaging wind gusts which will be the main highlight for the region on Friday.

  3. Eduardo Berroa

    By the way, the first time I have experienced unusual embedded, elevated thunderstorms on the evening of February 13th.

    Ahead of the cold front, the convective linear/bowing segments may at least re-intensify across the Northeastern States on Friday morning while the strength of the flow field aloft might support damaging thunderstorm wind threat within the linear/bowing segments.

    Have a question — Is the convective linear/bowing segments might gonna contain rumbles of thunder and cloud-to-ground lightning flashes and strikes?

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