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Close Call Tonight, Another Snow Threat Possible Later This Week

Good Evening!

Today started off with a mix of sun and clouds over much of the Northeast, but quickly turned mostly cloudy as a broad mid level disturbance began to move in from the west. Despite the cloudy conditions, today has been above-normal for this time of year, but still reasonably chilly. Highs were mainly in the upper 30’s to middle 40’s region-wide, as a stale mid level airmass worked into the Northeast. As we move into the late evening and overnight hours, the broad mid level disturbance centered over the Ohio Valley will continue to gradually move eastward. As it does so, it will bring very meager amounts of moisture from the south over portions of the Mid Atlantic and Northeast. If you take a look at the raw radar reflectivity over the Northeast, you may think that most of the region would be under light to moderate rain, however the moisture in place is not deep enough to overcome all of the dry air which is causing most of this precipitation to dissipate before it even reaches the ground. This is the same system that we talked about last week, and since that time the more conservative scenario has indeed played out, with the trough axis remaining too broad and disorganized to tap the impressive tropical moisture feed off of the East Coast. Regardless, an impressive upper level jet streak over the Northeast in excess of 170 mph will aid in the development of more mid level moisture later tonight that should be able to moisten the atmosphere enough so that we see some light to moderate rain along portions of MD/DE/NJ/CT/LI.

Temperatures will likely remain too mild for any pure snow to fall before midnight, however a very light mix of rain/snow may be possible over the farther NW locations of New Jersey and Connecticut. As we move past midnight and into the overnight hours, colder temperatures in the mid to lower levels of the atmosphere will begin to filter into the region, and this is when the best potential for some light snow will exist for the area. However, the vast majority of the precipitation will be centered well-offshore and thus precip rates will be very light. Given the light precip rates, mild temperatures, and meager overall moisture, no significant accumulations are expected for the immediate New York Metro area. Some locations over eastern Long Island and portions of New England will have a better shot at some light snow, but trends with this system will have to be monitored overnight.

This evenings latest RTMA 2m temperatures, surface observations, and regional radar mosaic. Note that despite all of the rain showing up, only stations south of the Mason-Dixon line are actually reporting any rain. This is due to dry air in the mid levels of the atmosphere.

This evenings latest RTMA 2m temperatures, surface observations, and regional radar mosaic. Note that despite all of the rain showing up, only stations south of the Mason-Dixon line are actually reporting any rain. This is due to dry air in the mid levels of the atmosphere.

Tuesday Through Thursday

Tomorrow looks to be an interesting day across portions of the Northeast as the mid to upper level trough associated with this weak coastal system begins to swing eastward and over the region. Some remaining light snow will likely be over portions of Long Island and eastern New England by the morning commute tomorrow, but a more interesting situation will be taking place over PA. As the bulk of the upper level energy moves over upstate NY and PA, lower to mid level forcing will become very strong and we should see at least one band of intense snow squalls develop over central PA. This band will be aided by very steep mid level lapse rates (change of temperature with height) which should allow any squalls to be quite heavy in nature around 8-10 am. As this band head eastward over Pennsylvania, some locations may see brief whiteout conditions with gusty winds and very heavy snow rates capable of dropping a quick 1-3″ locally. As we head into the early afternoon hours, this area of convective snows should be located over far eastern PA and perhaps over portions of Western NJ. This will all depend on how long the mid level energy is able to support this area of snow, but the general brief burst of heavy snow will be possible. Things look to calm down later in the afternoon as the temperature differential begins to even out, so expect any remaining snows to gradually dissipate just to the east or over the NYC metro area. Please use caution if driving through these heavy bands tomorrow, as visibility could drop to around-zero within a few minutes or so!

Evolution of the weak coastal storm as well as the convective snows tomorrow on the latest RPM model (courtesy of WSI)

Evolution of the weak coastal storm as well as the convective snows tomorrow on the latest RPM model (courtesy of WSI)

Wednesday looks to be a generally dry day across much of the Northeast as a weak area of high pressure looks to setup over the Mid Atlantic states. Wednesday looks to be much colder than the past few days as a brief shot of Canadian air makes its way into the Northeast. There may be some high clouds during the afternoon, but high temperatures look to get into the lower to middle 30’s. Later in the evening a weak area of energy will be moving well to the north of the area, with a chance at some snow showers possible for upstate New York and portions of New England. This weak system will help to bring in some warmer air aloft along a frontal boundary, but lows look to stay in the lower to middle 20’s due to radiational cooling.

Thursday is going to likely be a decent warmup from the previous day as stout southwesterly flow works in during the morning hours. This will work to greatly increase the amount of mid level moisture available, which should create a rather cloudy day overall. Some weak mid level energy associated with the Polar jet will also work into the Northeast during the day, which should work to enhance cloudiness and potentially a rain shower or two ahead of a frontal boundary that will be located over the Ohio Valley by Thursday afternoon. This frontal boundary will be the main focus for Thursday night into Friday, as the temperature differential along the front will support at least some moderate precipitation to breakout as it heads east and into the Northeast by Thursday evening. This afternoons model guidance is not in good agreement with regards to just how strong/how much precip this frontal boundary will have, but any light precipitation should begin to work its way into portions of Pennsylvania by late Thursday early Friday.

This afternoons European model showing light to moderate mix precipitation breaking out over portions of the Mid Atlantic and Northeast on Thursday night.

This afternoons European model showing light to moderate mix precipitation breaking out over portions of the Mid Atlantic and Northeast on Thursday night.

Some Snow Possible Into Friday Morning 

The threat for light snow will continue into the morning commute on Friday as the frontal boundary will likely be located right over the I-95 corridor. A strong upper level jet streak will be accompanying this system, so it would not be all that unlikely to see the models become more bullish with the amount of precipitation that develops over the area Thursday and Friday. At this time, this does not appear to be an all-snow event, but rather a mix of rain and snow to start, with light to moderate snow until the front clears. Accumulations looks generally light at this time, but this could change in either direction over the next couple of days, so make sure to check back for further updates!

Much colder and drier air looks to blast into the Northeast Friday afternoon and evening as the front begins to move offshore. Strong zonal flow looks to dominate the country for the majority of the weekend, but we may have to keep an eye on yet another progressive system moving across the country late Sunday and into Monday for the potential for some additional light snow.

This afternoons European Ensembles showing a rather cool, but progressive pattern taking shape over North America with a strong tropospheric vortex centered over Canada.

This afternoons European Ensembles showing a rather cool, but progressive pattern taking shape over North America with a strong tropospheric vortex centered over Canada.

Have a great evening!

Steve Copertino 

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