Nov 23, 2013: Frigid Week Ahead; Rain Tuesday Night

Forecast Highlights:

temp36An arctic front moved through the area this evening, bringing scattered snow squalls across the area with low visibility and a coating of snow in some locations. Behind this arctic front, highly anomalous cold temperatures will move in for tomorrow, with high temperatures over 20 degrees below average and record cold temperatures possible for the area. The cold will moderate by the mid week as a storm affects the area with heavy rain, followed by another strong cold surge for the late week with high temperatures struggling to rise into the low 30s again (Image credit: PSU e-Wall).



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Friday, November 22 Observations:

11.22.13A weak system quickly moved through the region on Friday, bringing two rounds of light rain. The first round took place in the morning with steady light rain mostly north of NYC, with rain totals less than 0.1 inch. The rain ended by the late morning, with mostly cloudy to cloudy skies and occasional fog in the afternoon and high temperatures reaching average, peaking in the low to mid 50s. The highest temperature was 58 degrees in Somerville, NJ and Newark, NJ, and the coolest high temperature was 51 degrees in Yorktown Heights, NY.

 


 

Tonight – Monday: Highly Anomalous Arctic Blast; Frigid, Windy Conditions

Forecast high temperatures for Sunday from the 0z run of the 4k NAM, showing temperatures in the mid 20s inland and upper 20s for the rest of the area. This is over 20 degrees below average (image credit: PSU e-Wall).

temp19The next 7 days will feature a much more active pattern than the relative inactivity of the last 2 months, starting with a near record arctic cold blast currently moving into the region associated with an unseasonably cold air mass, with 850mb temperatures near -14C to -18C more typical of a January cold surge, and an anomalously deep upper level low with 500mb heights near 522dm, or about 48 decameters lower than average. High temperatures on Sunday are likely to peak at midnight in the mid-upper 20s inland and the upper 20s-low 30s for the rest of the area, but will only continue to fall from there into the low-mid 20s by the morning. During the day, partly sunny skies are expected with a strong NW wind at 20-30 mph, gusting up to 45 mph, and daytime highs peaking in the mid 20s inland and upper 20s elsewhere. Along with the strong wind gusts, wind chill values are expected to remain in the 10s throughout the day.

For comparison purposes, temperatures often peak in the mid-upper 20s during strong cold surges in the middle of the winter, as opposed to November. The average high temperature in NYC is 50 degrees and the average low is 38 degrees; this would place Sunday’s temperatures over 20 degrees below the average high temperature, and even 8+ degrees below the average low temperature. Since 2000, the coldest November maximum temperature in Central Park was 32 degrees in 2008; for the date of November 24, the record low maximum temperature is 30 degrees, set in 1880, which is likely to be challenged. Other locations in the area where records do not go as far back as Central Park, such as Newark, Bridgeport and LaGuardia airport, have record low maximum temperatures in the mid 30s, which should easily be broken on Sunday.

Frigid temperatures are expected again overnight, with clearing skies, decreasing winds, and lows falling into the low 10s for interior NW NJ/SE NY, mid to upper 10s in the north/west suburbs of NYC, southern CT and Long Island, and upper 10s to low 20s in NYC and the immediate coast. Along with windy conditions, wind chills are expected to fall into the single digits for most of the area, with sub-zero wind chills possible for interior areas. Record lows are likely to be approached or possibly surpassed in parts of the area; a list of record lows for the date of November 25 has been included below. The air mass will begin to moderate on Monday with winds shifting to the southwest and highs warming up into the low to mid 30s across the area, which will be slightly warmer than Sunday but still 15-20 degrees below average.

Central Park, NY – 19 degrees (1880)
Newark, NJ – 19 degrees (1938)
Bridgeport, CT – 22 degrees (2005)
LaGuardia, NY – 23 degrees (2005)
JFK airport, NY – 22 degrees (2005)
Islip, NY – 18 degrees (1989)

 

Tuesday – Wednesday: Monitoring Storm Potential; Uncertainty Continues

Storm Analysis: As the anomalous cold air mass exits the region, another weather event may affect the region by the mid week. An upper level low is currently slowly drifting onshore near the coast of southern California, with a ridge placed to its north and another system currently over the northeast Pacific, entering western Canada. With the ridge persisting over the western US, the southern system will track east into the Gulf of Mexico coast by late Monday into early Tuesday, around the same time that the northern shortwave will dive southeast into the north central US. From there, uncertainty increases regarding the interaction of these two systems which will determine the weather conditions for the area on Tuesday night into Wednesday.

Comparison of the 18z GFS (left) and 12z ECMWF (right) for 12z Wednesday, at hours 90 and 96, respectively (image credit: PSU e-Wall).

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The model guidance remains inconsistent with the setup, with even more significant differences than yesterday. The GFS model yesterday showed a cleaner phase compared with the other models, with a consolidated low pressure intensifying over the region while having support from its ensemble members. Today’s runs, however, were much more suppressed while showing two separate low pressures, as the southern shortwave trended slower and the GFS placed more emphasis on another northern stream shortwave dropping into the Midwest on Wednesday, which resulted in the storm being entirely suppressed south of the area. While the GFS ensemble members originally continued to show a consolidated storm, however, this evening’s GEFS came in more similar to the operational run. The other models have not placed as much of an emphasis on this scenario, however, continuing to depict a messier phase with an elongated area of low pressure tracking near the area, bringing widespread heavy rain with 1-3 inches, along with widespread warmth in the mid levels which results in rain across most of the region and limited snowfall in the far north/west ends of the storm. The ECMWF, which continues to show a heavy rain event for the area, still has support from its ensemble members.

The southern upper level low is now mostly onshore, and should be better sampled for the model runs, although additional difficulty is likely with its handling of the amplification of the north stream and timing of the south steam. At this time, I am considering today’s GFS scenario as an outlier based on its handling of the interaction of the northern and southern streams, and I continue to side with a more significant system affecting the region. The main uncertainty remains the track and exact phasing setup, however, as this would also have an implication on the precipitation type, temperatures and wind across the region; an elongated low pressure moving through similarly to the 12z ECMWF would lead to a spike in temperatures into the 50s and 60s, along with strong winds and widespread heavy rain across the region, with mid level warmth limiting the extent of snowfall, while a more consolidated low pressure with cleaner phasing would keep temperatures in the 40s and 30s with significant snowfall north/west of the area and keep the strongest winds to the east. At this time, I maintained some continuity with yesterday’s forecast, increasing probability of rain to 80% west of NYC and 90% east of NYC, while slightly raising temperatures, although the outlook is still subject to some changes over the next 1-2 days as the model guidance gains a better handle on the setup; I am currently siding with a storm track near or slightly west of NYC, although an even more amplified solution cannot be ruled out.

Forecast for NYC Area: While confidence slightly increases on the more significant storm scenario, there is still no 100% certainty in the forecast currently, and some changes are still possible. At this time, the forecast is for rain to develop on Tuesday evening, intensifying overnight with moderate to heavy rain on Tuesday night into Wednesday morning or afternoon. Temperatures are likely to remain in the low to upper 40s range, but as previously mentioned, could be much warmer than currently forecast should the storm track west of the area. Rain is likely to taper off by the evening hours as a high pressure moves in.

At this time, preferred precipitation type for the NYC area is rain, with any snow likely to stay north/west of the area boundaries. Rain totals are still uncertain, but should the scenario verify as currently expected, rain totals of 1-2 inches with locally higher totals up to 3 inches would be expected, which would help to ease but not completely break the drought conditions. As previously mentioned, however, there remains uncertainty regarding the exact solution; at this time, I am siding towards more significant impacts from the storm, although it is possible it remains further south with less phasing, in which case rain totals would be significantly lower with most of the precipitation that falls limited to NYC and further south/east. Stay tuned for more information on the storm with tomorrow’s update.

 

Late Week: 2nd Cold Surge; Cool Pattern Likely Continues Into December

As the storm exits the region, another cold air mass is expected to enter with a broad high pressure covering the region for Thursday; with 850mb temperatures near -10C, mostly clear skies and light winds, well below average temperatures are expected to return again, struggling to warm up into the low to possibly mid 30s on Thursday while falling overnight into the 10s for most of the area. The duration and intensity of the secondary cold surge, however, appears slightly less than previously thought with the second shortwave trough coming in behind the midweek system, although temperatures for Friday and Saturday are expected to remain moderately colder than average with highs generally in the 30s.

Going forward beyond the weekend, a brief moderation in temperatures is possible to start December, but unlike the last 2 years, a sustained warm pattern is unlikely to develop. With a continued -EPO pattern along with an east based -NAO, which has been hinted by some of the longer range models as a possible transient west based -NAO, occasional surges of cold air are likely to continue into the first 1-2 weeks of December, along with additional storm opportunities for the region, one potentially in the December 3-5 time frame; along with likely near-below average temperatures, some of these storm potentials may feature snow for parts of the region, perhaps including the area. More information will be posted on the longer range outlook as details become clearer.

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