Dec 14, 2013 Storm Updates

Frequent updates will be posted below on the heavy snow, ice and rain event affecting the region today and tonight. Radar images are from the Pennsylvania State University e-Wall.

Links: Yesterday’s forecast | 8-Day Forecast | Twitter | Facebook

 


Final storm snow totals in NYC:

Central Park – 5.0″  |  LaGuardia – 4.7″  |  JFK Airport – 3.2″


 

1:35 AM: Storm Starting to End

nerad257As of 1 AM, the primary low is over NW PA with a minimum pressure near 1004 mb. The secondary low pressure is over southern NJ with a minimum pressure near 1001 mb, and is tracking steadily to the NNE. The two lows will merge tonight as the coastal low tracks over NYC, then through southeast New England before exiting offshore.

Precipitation types generally remain the same since the last update, with the rain/freezing rain line shifting slightly north into the immediate north/west suburbs of NYC as temperatures have warmed slightly above freezing. No ice reports have been posted by the National Weather Service yet, although unofficial reports suggest up to 0.15 to 0.25 inch of freezing rain has accumulated in parts of the area inland of NYC. The back end of the storm is entering far southwestern parts of the area, and will gradually spread northeast between 2-4am for most locations.

This is the final storm update for tonight. The next update will be posted on Sunday morning.

 

12:20 AM: Heavy Freezing Rain North & West of NYC

12.15_0500As of 12 AM, the primary low is entering NW PA with a minimum pressure of 1004 mb. The secondary low is over central Delaware with a minimum pressure of 1003 mb, and is tracking NNE.

The mid level low is currently placed near Toronto with a southerly flow over the region, supporting the warm air advection occurring aloft. Meanwhile, a surface high pressure remains over northern New England with surface winds generally out of the east. For most of the area, this is preventing a significant warm up, with locations north and west of NYC still in the 20s, along with upper 10s for interior locations. Closer to the coast, however, the strong easterly winds led to a quick rise in temperatures, currently in the mid 30s in NYC and mid 40s in Long Island. Heavy rain will continue through 2-4 AM in these locations, but north and west of NYC, where surface temperatures remain below freezing, precipitation type is expected to remain frozen for the remainder of the event except for the immediate north/west suburbs of NYC.

Current observations show that northeast NJ and Rockland/Westchester counties have changed over to moderate/heavy freezing rain, while coastal Connecticut remains with snow but will shortly change to sleet/rain. Further inland towards NW NJ and Orange county, where the warm layer aloft is more shallow, sleet is the main precipitation type. Freezing rain will continue to fall in the former locations, heavy at times; the intensity of precipitation will help to limit ice accretion due to runoff, although totals of at least 0.15 to 0.30 inch of freezing rain are likely, locally higher. Temperatures on Sunday are expected to peak in the low to mid 30s inland and upper 30s for the rest of the area, which will help to melt some of the ice but with hazardous road conditions expected for Sunday morning.

 

11:15 PM: Sleet, Ice, Rain Spreading North

12.15_0345As of 11 PM, the primary low pressure is located over far northeast Ohio, with a minimum pressure of 1005 mb and is tracking northeast. The secondary low pressure is located over east central Virginia, with a minimum pressure of 1006 mb and is tracking NNE. The secondary low pressure is developing slightly west of the forecast, and looks to track over NYC later tonight.

Since the previous update, a combination of increasing easterly winds over Long Island/NYC and warming temperatures aloft due to the mid level low to the west advecting warmer temperatures from the south has resulted in a changeover to rain in Long Island and NYC, with sleet and freezing rain over northern NJ. Interior NW NJ, SE NY and southern CT remain with snow at this time, but will also gradually change over to sleet to the west and freezing rain to the east, including rain in coastal CT, by 12am as temperatures aloft continue to warm up. Surface temperatures will be slower to warm up, however, gradually moderating towards freezing north and west of NYC. NYC is likely to reach the mid to upper 30s, while Long Island surges into the 40s later tonight with 50 degrees possible towards eastern Long Island. Precipitation is expected to end between 1:30-4am from SW to NE.

The latest Public Information Statement posted by the National Weather Service shows current snow totals are generally between 4-7 inches over southern CT and SE NY, 3-7 inches over northeast NJ and NYC, and 1-4 inches over Long Island with localized reports of 5-6 inches in Nassau county.

 

9:10 PM: Rain, Sleet Slowly Entering

nerad256As of 9 PM, the primary low pressure is located over northeast Ohio. Minimum pressure is near 1005 mb, and the low is steadily tracking northeast. The secondary low is located over southeast VA, with a minimum pressure near 1009 mb and is tracking to the NNE. The secondary low will continue to intensify, merging with the primary low later tonight as it tracks just east of NYC.

Over the last hour, there have been increasingly frequent reports of rain in eastern and southern Long Island, and sleet in NYC and central NJ. Surface temperatures have been colder than expected, currently only near 14 degrees in NW NJ and SE NY, but as the secondary low continues to intensify, surface winds will shift to the east and strengthen, leading to temperatures surging into the 30s in Long Island, likely reaching the 40s by 12am. NYC, meanwhile, will continue to slowly warm up until at least 10pm when more widespread sleet and rain are expected to mix in.

Further inland, however, despite surface temperatures remaining below freezing, temperatures aloft will warm above freezing as the mid level low takes longer to transfer to the coast, with a changeover to sleet and freezing rain expected after 10pm from south to north. Freezing rain of at least 0.1 to 0.25 inch is likely across north NJ, SE NY and western CT.

 

7:30 PM: Moderate-Heavy Snow Covering The Area

nerad255As of 7 PM, the primary low pressure is located over central Ohio. Minimum pressure is near 1006 mb, and the low is steadily tracking northeast. The secondary low will soon take shape over coastal Virginia, tracking NNE and then NE up the coast, merging with the primary low as it reaches western Pennsylvania.

Temperatures so far have been colder than expected across the area, generally in the mid to upper 10s north and west of NYC and in the low-mid 20s in NYC and into Long Island, while snow rates have been slightly lighter than expected. More widespread heavy bands are spreading into the area from the southwest, however, and precipitation is beginning to develop over central Virginia as the secondary low begins to develop near the southeast Mid Atlantic coast. With surface temperatures colder than expected, the changeover to rain is likely to be delayed by at least an hour, with most of Long Island and NYC expected to change over to rain by 10pm, possibly a bit later towards northern NYC. After that time, temperatures are expected to surge into the 40s over Long Island with a strong easterly wind, and may approach 50 degrees towards Montauk. The rest of the area will continue to gradually change over to sleet and freezing rain as temperatures aloft warm up above freezing generally after 11pm. Ice will be a concern tonight especially north/west of NYC, with temperatures likely to fail warming up above freezing until the precipitation ends after 2-4am.

Snow totals of at least 2 to 5 inches are expected in Long Island, 4 to 6 inches in NYC, and 5 to 10 inches over northern NJ, SE NY and southern CT away from the immediate coast. Ice totals of at least 0.10 to 0.25 inches are likely over northern NJ, SE NY and western CT.

 

5:40 PM: Peak of Snow Approaching

nerad254As of 5 PM, the primary low pressure is located over southwestern Ohio. Minimum pressure is near 1006 mb, and the low continues to track to the northeast. The secondary low is near central North Carolina, with a minimum pressure near 1009 mb, and is tracking to the northeast. The secondary low will begin to track more to the NNE as it interacts with the primary low, which will track into western Pennsylvania before merging with the deepening coastal low later tonight.

Moderate snow is covering most of the area except for Long Island and southern CT, where moderate snow is gradually spreading in. Temperatures remain cold as well, generally in the mid-upper 10s inland and low-mid 20s for the rest of the area. There has been isolated reports of heavy snow so far, such at Central Park. A band of locally heavy snow is currently over NE NJ, and will spread into SE NY and SW CT, while a dry slot over central NJ will push northeast while filling in, with a temporary decrease in snow rates expected over NE NJ and NYC before intensifying again after 6 or 6:10pm. The outlook remains unchanged at this time, with a gradual changeover to rain in Long Island and NYC between 7-9pm from south to north as winds turn easterly near the surface and temperatures quickly rise into the 30s, and the rest of the area changing over to sleet/freezing rain after 10-11pm with low-mid level temperatures above the surface warming up above freezing as surface temperatures take longer to warm up.

 

3:30 PM: Moderate Snow Spreading In

nerad253As of 3 PM, the latest analysis from the Weather Prediction Center (WPC) places the low pressure near southeast Indiana. Minimum pressure is near 1007 mb, and the low is tracking northeast towards central Ohio and western Pennsylvania. The secondary low pressure is taking shape over South Carolina, with a minimum pressure just under 1012 mb.

Accumulation reports across the area so far are generally between 1-2 inches, with locally higher totals up to 3″ over southeast NY and western CT. The latest radar shows a band of moderate snow spreading into the I-80 corridor and NYC, tracking northeast, which should lead to moderate snow developing across most of the area within the next hour. The dry slot over southern NJ has largely filled in as expected, and steady light to moderate snow will continue through at least 7-8pm, when heavy snow is likely to develop over some areas north/west of NYC with snow rates up to 1-2 inch/hour expected. The forecast for the remainder of the right is unchanged at this time, with a changeover to rain in Long Island/NYC after 8-9pm, and the rest of northern NJ, SE NY and south CT changing to sleet inland and freezing rain closer to NYC after 10pm-12am with 0.10 to 0.25 inch of ice likely.

 

2:30 PM: Snow Intensifying; More To Come

nerad252As of 2 PM, the low pressure was centered near south central Indiana. Minimum pressure is near 1008 mb, and the low pressure is slowly tracking northeast. Signs of a secondary surface low pressure are emerging over South Carolina, which will continue into North Carolina as the surface low pressure intensifies, and the primary low merges with the coastal low pressure near NYC’s latitude this evening.

Snow has continued to steadily fall over the last 1-2 hours, falling moderately at times north of NYC. A stronger band of moderate snow is currently located over central-northern NJ, and will continue to spread through the rest of the area over the next 1-2 hours as a steady light to moderate snow continues to fall. A dry slot currently over southeastern PA is forecast to mostly fill, although a temporary decrease in snow rates may be possible behind the current band before moderate to heavy snow develops this evening after 7-8pm, with snow rates up to 1-2 inch per hour expected.

 

12:30 PM: Steady Light Snow Falling

nerad25As of 12 PM, the low pressure was centered near extreme southern Indiana. Minimum pressure is near 1010 mb, and the low pressure is steadily tracking northeast. It will continue to track into Ohio as a secondary low pressure develops off the Delmarva coast, then intensifies as it tracks northeast along the coastline.

Steady light snow has fell across the area since early this morning, with light accumulations of at least up to 1 inch reported so far, locally higher north of NYC where New Canaan, CT has already reported 2.5″ as of 11am, according to storm reports sent to the National Weather Service. The latest radar to the left shows the snow rate has become lighter since the morning, with a large dry slot present over eastern Maryland. This dry slot is expected to fill in within the next 2-4 hours, although the HRRR and RGEM short range models appear to be filling it in too quickly.

Forecast Update: After the dry slot fills and the coastal low begins to form, heavier precipitation will develop over New Jersey and eastern Pennsylvania, with moderate snow expected to develop towards 3-5pm, becoming heavy at times over northern NJ, SE NY and CT towards 7-8pm. By that time frame, the coastal low will begin to strengthen, but with the mid level low still positioned over Ohio and taking longer to transfer to the coast, mid level temperatures will warm up, leading to a gradual change to rain in NYC and Long Island by 10pm, and sleet/freezing rain elsewhere towards 11pm-12am.

Yesterday’s update noted an uncertainty was how fast mid level temperatures warm; current observations show the primary surface low is stronger than modeled yesterday, and the mid level low is both stronger and further north, which support a slightly faster surge of mid level warmth aloft and a further north extent of warming, bringing mixing with sleet up to the central-northern Hudson Valley and Massachusetts, locations that were previously forecast to remain with plain snow. At this time, I opted to keep the snow outlook the same as moderate to heavy snowfall rates are still anticipated later this evening, along with current snow reports and the forecast duration of snow, although it is possible the snow outlook may be revised slightly downwards for parts of Long Island. Yesterday’s forecast snow map has been re-posted below.

 

NYCSnow

Leave a Reply