Nov 25, 2013: Significant Storm Tomorrow, Wednesday

Forecast Highlights:

NovStormSetup2The frigid air mass that spread into the region on Saturday and Sunday began to moderate today, with cold morning temperatures in the 10s and low 20s warming up into the low-mid 30s by the afternoon, which is still at least 15 degrees below average. Attention now turns to the southern US, where a low pressure will form and track NNE along the East Coast on Tuesday into Wednesday, resulting in the first major storm in 2 months with widespread heavy rain and strong wind gusts, followed by the return of cold temperatures to end the month.

<< November 23 | November 24 | November 25 >>

Sunday, November 24 Observations:

11.24.13After Saturday’s arctic front moved through, producing scattered snow squalls in the evening, windy conditions continued through the overnight hours with a tight pressure gradient as temperatures fell into the 10s and 20s for lows. With partly cloudy skies and an unseasonably strong cold air mass overhead, high temperatures only peaked in the upper 20s to low 30s, more typical of a January cold surge than late November. Strong NW winds of 15-30 mph were observed with gusts up to 40-50 mph, keeping wind chills in the 10s for most of the area and single digits inland. Central Park reached a high of 30 degrees, nearly 20 degrees below the average high temperature and tying the record for the coldest max temperature for 11/24, previously set in 1880; the rest of the NWS stations in the area easily broke their previous records for the coldest max temperature, which were previously in the mid 30s. The highest temperature was 32 degrees in multiple locations, and the coldest high temperature was 25 degrees in Port Jervis, NY.



Tonight – Wednesday Night: Storm Produces Heavy Rain, Wind, Flooding

0118zThe latest surface analysis from the Weather Prediction Center (WPC), posted to the left, shows a low pressure area in the northwestern Gulf of Mexico, associated with a southern stream upper level low tracking east, and a cold front moving through the north central US associated with a northern stream shortwave moving northeast out of the region, producing scattered rain/snow showers north of the area tonight, as another shortwave trough to its west gains more of a neutral tilt as it digs southeast into the central US. These systems will interact and phase on Tuesday into Wednesday as the northern stream shortwave picks up the southern system, bringing the southern low pressure up the East Coast as it intensifies and resulting in the most widespread storm to affect the region since late September. The main uncertainty until this point has been the exact development and track of the low pressure, although this uncertainty has decreased with the expectation for a more consolidated system to move through, with some separation between two waves of heavy precipitation but with a single yet elongated low pressure area as opposed to two low pressure centers moving through at separate times.


NovStormSetup2Regional Forecast: Precipitation from the storm will begin to enter the Mid Atlantic region on Tuesday morning, continuing to spread northeast as the front end of the precipitation shield reaches the NYC area in the early afternoon and the rest of the Northeast by the mid-late afternoon and evening hours. With the mid level low to the west of the region, strong warm air advection is expected in the mid levels, but with enough low level cold air initially in place to support light snow and sleet developing first in the mountains of West Virginia and Maryland, then into central/NE PA, most of NY state, and central-northern New England, with freezing rain developing in West Virginia and into parts of Pennsylvania and interior NW NJ. Snow accumulations with the front end of the storm are expected to remain minimal for most, generally under 1-2 inches. As temperatures begin to warm up in the lower levels, a changeover to rain is expected in Pennsylvania in the evening, with the changeover to rain spreading northeast through most of region overnight while western PA and western/northern NY continue to see moderate to heavy snow and sleet.

Heavy rain is expected to spread into the Mid Atlantic up to Pennsylvania, NJ and the NYC area by 3 AM on Wednesday ahead of the low pressure, which is likely to be in the lower Mid Atlantic, then continue to spread across the rest of the Northeast as the low pressure tracks NNE, reaching western New Jersey by Wednesday morning. As it does so, most of the NYC area and southern New England will enter the warm sector, with temperatures surging into the upper 50s-low 60s with a strong southerly wind and a strong low level jet, producing wind gusts up to 50-60 mph. By this point, phasing will be underway as the vorticity from the south catches up with the surface low, with the low pressure likely to reform just west of NYC by Wednesday afternoon, bringing the second wave of the storm with it. Occasional periods of rain are expected to continue in the NYC area into New England, while Pennsylvania and New York change over to snow from west to east as colder air filters into the region aloft. The storm will then end from south to north by Wednesday late afternoon and evening as the low pressure quickly tracks NNE through Vermont and into Canada as it rapidly intensifies, with a tightening pressure gradient and a widespread strong west-NW wind developing across the region.

The storm will be the first significant rain event to affect the region since September 21-22, and will produce the highest precipitation totals since the remnants of Tropical Storm Andrea in early June. Widespread rain amounts of 2-3 inches, locally up to or over 4 inches, are expected from Virginia into eastern PA and New Jersey, the NYC area, and New England, which will help to partially ease the recent drought conditions caused by the lack of rainfall. Towards the western Northeast, moderate to heavy snow, sleet and freezing rain are expected, with 6 to 12 inches of snow expected from West Virginia into the western half of PA, and western and northern NY. Towards parts of West Virginia/western VA, Maryland, Pennsylvania and northern New England, freezing rain is expected with ice accumulations up to 0.1 inch likely, possibly higher.


Forecast for NYC Area: Showers are expected to develop across the area towards 2-5 PM on Tuesday; this may initially mix with snow and sleet in northwest NJ and SE NY. By the evening hours, light rain is expected to cover most of the area, with rain/freezing rain falling in the high elevations of NW NJ/SE NY. The entire area is expected to change over to rain by 9-10pm, with heavy rain spreading in after 12-3 AM; a dry slot is possible in the morning hours, with otherwise moderate rain resuming through the afternoon hours on Wednesday. By the late overnight hours, most of the area will enter the warm sector, with temperatures surging into the upper 50s-low 60s and a strong SE wind at 20-30 mph sustained; while an inversion will prevent the strongest winds from mixing down to the surface, wind gusts up to 40-50 mph are likely in the immediate NYC area, locally up to 55 mph, and 50-55 mph in Long Island and Connecticut, locally up to 60 mph. As the low pressure center redevelops near northern NJ and continues to track NNE, rain is expected to end between 3-5 PM, with dry conditions for the evening, along with much colder temperatures in the 30s/low 40s and a developing west wind at 10-20 mph, gusting up to 30-40 mph.

Rain totals of at least 2 to 3 inches are expected, locally up to 4 inches, making this the most significant rain event to affect the area since the remnants of tropical storm Andrea in early June, which is expected to result in areas of flooding. Strong wind gusts are also a risk especially from NYC and further east, with gusts up to or locally over 55 mph likely which will be capable of producing wind damage and power outages. Towards interior NW NJ and SE NY, light snow, sleet and freezing rain are possible in the late afternoon and evening, but with little to no accumulations expected.

This is the final forecast discussion for this storm. Storm updates will be posted occasionally throughout Wednesday and Thursday, both on the blog and on Twitter.


Beyond The Storm: Cold End to November, Warmer Start to Winter

Behind the storm, cold and windy conditions will return for Thursday with partly sunny skies, highs in the upper 20s inland and low-mid 30s for the rest of the area, with a NW wind up to 15-25 mph with gusts up to 40 mph possible. Temperatures will slightly warm up into the low-mid 30s inland and mid-upper 30s elsewhere for Friday and Saturday, with overnight lows in the 10s inland and 20s closer to NYC. While November will end with December-like temperatures, December will start with more November-like temperatures as the trough departs the region, and along with a strong trough entering the western US region, a warming trend is likely for the region for the first few days or first week of December with highs back into the 40s, or possibly the 50s in the warmer case scenario although an anomalous warm pattern similar to the last 2 Decembers is not anticipated to develop. The next storm potential appears to be towards the December 2-5 time frame, but with impacts, if any, still uncertain.

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