Nov 15, 2013: Progressive, Dry Pattern Continues

Forecast Highlights:

gfs_namer_060_850_temp_mslp_precipThe progressive and abnormally dry pattern that has been present throughout the majority of the fall continues through the upcoming period, as a strong cool down with well below normal temperatures earlier this week quickly exited the region, with temperatures again quickly warming up into the low 60s by Monday as a weakening cold front moves through the area, bringing showers up to 1/4″ to locally 1/2″ inland, followed by another transient cool down and warm up.

 

 


<< November 13 | November 14 | November 15 >>

Thursday, November 14 Observations:

11.14.13Following Wednesday’s unseasonable cold, the strong cold air mass quickly exited the region with strong warm air advection aloft bringing a much warmer air mass into the region. Mostly sunny skies continued, with temperatures, having failed to drop much after midnight, surging into the low to mid 50s across the area. The highest temperature was 56 degrees in Montgomery, NY, and the lowest high temperature was 49 degrees in Westhampton Beach, NY.

 

 


 

Tonight – Monday: Warming Up, Another Quick Rain Event

Storm Analysis: The current upper level pattern consists of a broad ridge over the eastern half of the US and trough over the western half of the US, with an overall progressive flow in place. As anomalously strong ridging over the northeast Pacific breaks down with a zonal flow pushing into the western US, the trough currently over the western US will become negatively tilted while rapidly tracking to the east and northeast. A surface low pressure will develop in the central US, leading to a late-year severe weather event, which will rapidly deepen as it quickly tracks northeast into Canada. The upper level trough will quickly lift to the north, leaving the best forcing once again to the north and west of the area, resulting in a weakening cold front reaching the area on Monday.

Modeled 500 millibar heights and vorticity on the 0z GFS for Monday morning at 7 AM (12z) – image credit NCEP Model Anaylses and Guidance.

gfs_namer_060_500_vort_htWarm air advection ahead of the approaching cold front will lead to temperatures gradually warming up, peaking in the mid to upper 50s this weekend and the low 60s on Monday. As the surface pressure gradient becomes more tightly packed, breezy winds are expected on Sunday night into Monday with a south wind up to 10-20 mph, gusting up to 30 mph or locally higher towards Long Island/southern CT. With a breezy southerly wind and clouds/rain on Sunday night, overnight lows will remain much warmer than average, remaining in the low-mid 50s early before rising into the low 60s by the early morning. The frontal passage is currently likely to occur on Monday morning, with isolated showers on Saturday and Sunday but with the bulk of the rain likely to fall between 12-8 AM. Given recent trends this fall and the expected setup, I am siding with lower rain totals than modeled, with up to 1/4 inch for most of the area, locally higher up to 1/2 inch towards SE NY and interior CT where stronger forcing is expected with a heavier line of rain. Should Central Park reach 1/4 inch of rain as currently predicted, it would be the 3rd biggest rain event of this fall, but would have little impact on the lack of recent precipitation with the latest update of the US Drought Monitor placing almost the entire area under an expanding moderate drought.

Forecast for NYC Area: Mainly cloudy skies are expected tonight with isolated showers, mainly near or south of NYC, with partly cloudy skies on Saturday, a light south wind and highs reaching the mid to upper 50s. Mostly cloudy to cloudy skies are expected overnight into Sunday with scattered showers and highs in the upper 50s to low 60s. Temperatures will remain steady in the evening before rising by Monday morning as a southerly wind increases to 10-20 mph sustained, gusting up to 30 mph or locally higher, with showers expected to fall mainly between 12-8 AM from NYC and further west, and 4-10 AM east of NYC. Rain totals of at least 1/4 inch are expected across the area, with totals locally up to 1/2 inch north of NYC. Clearing skies are expected on Monday after the rain ends with highs peaking in the low to mid 60s across the area.

 

Tuesday – Beyond: Colder Mid-Week, Then Warming Up

The setup for the rest of next week has some similarities to that of the last few days, with several changes such as the midweek air mass not being as cold as the last one. Behind Monday’s cold front, a colder air mass will enter the region with 850 millibar temperatures near -6 to -10C, with mostly sunny skies, highs expected to peak in the low to mid 40s, and lows in the low to mid 20s inland and mid 20s to low 30s elsewhere. As with this week, this cold air mass will be quick to move out of the region as a progressive, zonal flow extends into the eastern half of the US, with temperatures likely warming back into the low to mid 50s by late next week as weak ridging builds over the eastern US with a broad trough over the western half of the US.

By late next week, however, another cold air mass is likely to slide south towards the northwestern US. Some changes in the upper level pattern are expected by this time period with signals for east based -NAO ridging, along with a +PNA/-EPO signaling ridging near and off the western US coast. By next Friday and/or weekend, this cold air mass is likely to enter the northern US, but with uncertainty regarding the setup of the cold front or potential low pressure near the region by this time frame, as well as how far south the colder air drops. More information will be posted on next weekend’s outlook as details become clearer.

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