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Saturday Briefing: Heavy Rainfall Likely Tonight and Sunday

February 10, 2018/1 Comment/by Miguel Pierre

Good morning, friends! You may have noticed it’s a bit warmer outside – and you are correct, as temperatures have warmed in advance of an approaching storm system in the Northeast states. Temperatures will remain mild for much of the weekend as a southwest flow develops ahead of an approaching cold frontal boundary, with highs reaching into the 50’s in many areas (Away from the high elevations). With this gift will come a curse, as warm air advection ushers in increasing moisture and approaching lift in the atmosphere the that will bring an increasing potential for heavy rain by Saturday afternoon.

Heavy Rain Likely This Weekend, Mild and Unsettled Through Next Week

February 9, 2018/1 Comment/by Steven Copertino

Good evening!

Today has been another cold, but relatively calm day across much of the Northeast and Mid Atlantic. Some weak lift associated with a frontal boundary over the region has spark some patchy areas of light snow and snow flurries, mainly confined to the western parts of New York State as well as southern New York and northern New Jersey. These areas of precipitation will gradually shift north over the rest of the evening as the frontal boundary and lift also begin to gain more latitude. Since precip rates will be rather low and conditions are not ideal for snow accumulations, only a trace is expected for the locations that manage to see more sustained light snow. Otherwise, high pressure retreating off of the Mid Atlantic coast will contribute to more southerly flow this evening, which will begin to bring in a more mild airmass in the mid levels of the atmosphere. Additionally, moisture will begin to increase and this will likely cause the rest of the evening to remain rather cloudy. Lows this evening will come quite early in the evening as the warm air moving into the mid levels of the atmosphere will also help to warm things up tonight after midnight. Most of the area will see lows in the upper 20’s to middle 30’s, but these will rise into the middle to upper 30’s during the overnight hours, with come locations in southern New Jersey likely reaching the 40’s.

This afternoons current surface observations, regional radar mosaic, and high resolution satellite imagery showing a cold day across the region with areas of light snow

Heavy Rain Likely Sunday

Saturday will likely start off rather mild and with substantial overcast as mid to low level warm air and moisture continue to stream in over the region from the south. This surge in mild temperatures and moisture will be thanks to a large, but disorganized area of mid level energy extending from the West coast, all the way into the Great Lakes. Additionally, the sub-tropical jet stream will also be getting involved by pumping moisture-rich air from the Gulf of Mexico into the southeast United States, creating a large area of showers and thunderstorms. These showers and thunderstorms will gradually work their way north during the day on Saturday, likely working their way into the Mid Atlantic and Northeast by the late afternoon hours. Conditions will almost certainly remain unsettled with a chance of showers lasting well into the evening hours. Highs on Saturday will be quite mild, with most of the Mid Atlantic and Northeast likely getting into the lower 40’s, with some locations to the south possibly seeing highs in the lower 50’s! We’ll have the same situation tomorrow night as we did tonight, were temperatures during the overnight hours actually rise, with temperatures likely getting well into the 40’s and even middle 50’s for portions of the Mid Atlantic and southern New Jersey.

Conditions should really deteriorate during the early morning hours of Sunday morning, as warm/moist air surges ahead of semi-stationary frontal boundary out over the Ohio Valley. Early Sunday morning and into the afternoon hours should virtually be a washout, with a threat of heavy downpours across much of the Mid Atlantic and Northeast. The main batch of moderate to heavy rain should gradually push north and east off the coast during the middle afternoon hours, but there will still be a threat of some steady showers ahead of the last concentrated batch of rain. This last batch looks to come into the Northeast around 6-8pm on Sunday, with some locally heavy rainfall likely. This area of showers will also have a chance at producing some gusty winds as the low level jet streak a few thousand feet above the ground begins to strengthen. Rainfall totals should be above an inch for interior sections of the Northeast, with higher amounts around 1.5-2″ closer to the coast. The threat for stream flooding is rather low at this time, but there could be some urban flooding in locations that are prone to poor drainage. However, this will be highly dependent on just how much rain falls over the six to twelve hours or so on Sunday. Highs on Sunday will be quite impressive, with readings likely breaking into the 50’s areawide ahead of the cold front. Some locations to the south may even make a solid run at the 60’s later in the evening on Sunday.

This afternoons NAM model showing the progression of the heavy rain set to impact the region into Sunday night

Unsettled and Mild Next Week

A frontal boundary will move across the Northeast and off the Mid Atlantic coast by Monday afternoon, which should be able to kick most of the moist/unstable airmass out of the region temporarily. Temperatures should moderate back into the upper 30’s to lower 40’s for the most part on Monday and Tuesday, but the large and disorganized area of mid level energy out over the west will begin to undergo a change. This system will gradually drift south and begin to break off from the main upper level flow, causing another period of zonal winds to rage from west to east over the country. As these zonal winds take over, we’ll see more moisture begin to surge northward from the Gulf of Mexico by Wednesday. As this moisture moves over the region, temperatures will once again return to well-above normal across the Northeast. In fact, this afternoon European model even shows the potential for the NYC to get into the 60’s by Thursday, which would likely challenge some records. The best threat for rain appears to be on Thursday as the bulk of the Gulf moisture moves up and over the Northeast. It is too early to say whether or not there will be a heavy rain threat from this system, but we will certainly be monitoring things over the next week or so and provide updates when needed!

The European Ensembles probability of reaching/exceeding 50 degrees by next Thursday-showing a rather high chance over portions of the Mid Atlantic and Northeast

Have a great weekend!

Steve Copertino

Wide Variety of Impacts Likely From Weekend Storm, Warmer Weather On Borrowed Time

January 10, 2018/by Steven Copertino

Good evening!

Today has been another in a series of relatively warm days when compared to the sub-freezing ice-box that the Northeast was stuck in over the past two week. High pressure has been moving off the coast throughout the day today, leaving most of the Northeast with southeasterly winds at the surface which helped to bring in slightly above-normal temperatures for this time of year. Highs were able to reach into the upper 30’s to middle 40’s across much of the NYC metro area this afternoon, with middle to upper 30’s over much of the Lower Hudson Valley. Today started off rather clear, but westerly winds in the mid levels of the atmosphere allowed for some weak mid level energy to pass over the Northeast. This weak mid level energy helped to bring some increasing mid level clouds this afternoon, which likely capped off our high temperatures for the day. As we head later into the evening and the overnight hours tonight, this mid level energy is expected to clear out as the area of high pressure centered off the Mid Atlantic coast begins to head off to sea. This will allow for mid level flow to strengthen from the south and west, which should bring in increasingly warmer mid level temperatures this evening. We may see the early evening temps become our overnight lows as most of the I-95 corridor may warm up a few degrees during the overnight hours. Regardless, lows will likely be in the lower to middle 30’s across the Lower Hudson Valley, with locations in and south of NYC likely getting into the middle to upper 30’s. It may not be all that impossible to see some locations in central and southern New Jersey to see temperatures rise into the 40’s during the overnight hours.

This evenings surface observations, RTMA 2 meter temperatures, and regional radar mosaic showing a rather dreary and cool day across the Northeast with warmer temperatures off to the west

Thursday is likely to start off rather cloudy and cool as winds from the Atlantic continue to bring in a moderately moist airmass in the mid levels. These clouds and even some spots of patchy drizzle will likely continue throughout the majority of the day as a large system centered in the plains continues to drag a more moist/warm airmass over the Mid Atlantic and Northeastern States. Widespread cloudiness through the lower to upper levels should allow highs to rise into the upper 40’s to lower 50’s across much of the area tomorrow, with some locations to the south of NYC likely getting into the lower 50’s. Very strong southerly flow should become well established by the evening and overnight hours, and we may once again see temperatures rise a bit into the upper 40’s and lower 50’s. Moisture content in the atmosphere will also begin to rise rather rapidly ahead of a frontal system over the Ohio Valley, which may begin to kick off some light to moderate rain showers over much of the Mid Atlantic and Northeast.

Friday morning will almost certainly start off very warm and cloudy, with the threat for some steady rain, especially as you head further west into western NJ and PA. As the front gets closer to the Northeast during the afternoon hours, there will be much more available lift in the atmosphere to support more moderate to heavy rain. Moisture content will also be very high (PWATS around 1.4″) for this time of year, so some of the heavier areas of rain may be capable of very heavy downpours that may cause some street flooding. This flooding threat will also be exacerbated by the amount of snow left over the area, with the greatest risk for street flooding in more urban locations with poor drainage. Some of the higher resolution models are also indicating the potential for some thunderstorms to exist, as some very marginal instability looks to be in place around 11am-2pm. Steady rain is likely for the remainder of the day, with the heaviest rain likely occurring over portions of eastern NJ, LI, and CT. Temperatures will be very warm on Friday, with highs likely reaching well into the upper 50’s! This will further help to melt any leftover snow, which will compound any potential flash flooding.

This afternoons NAM model showing the potential for periods of very heavy rainfall over the East on Friday and Saturday

Myriad of Impacts Likely on Saturday

Low pressure will be tracking from the Tennessee valley and into the Mid Atlantic states on Friday evening and into the overnight hours as a large Arctic high pressure system extends from the northern Plain and into portions of southeast Canada. By early Saturday morning the low will likely be located over the Mid Atlantic states, with a large area of moderate to heavy precipitation over the Northeast. This part of the forecast becomes tricky, as some of our more reliable models have been trending weaker and further southeast with this area of low pressure on Saturday. This is very important detail to nail-down in the 24 hours, as the Arctic high pressure extension will be capable of bleeding sub-freezing air into the Northeast, and this could lead to a significant amount of Saturdays precipitation being frozen for portions of New England and potentially locations further south.

If this system is weaker and further south and east, we may see heavy rain over NJ, LI, CT, and eastern New England, with heavy snow over portions of PA, upstate NY and VT/NH. This afternoons European model showed a similar scenario, but with a significant amount of freezing rain and sleet over portions of PA/NJ, extending all the way north and east into Maine. This type of scenario certainly seems possible at the moment, and we may see the NWS issue Winter Weather Advisories or even Winter Storm Warnings in the next 24-36 hours over portions of the Northeast if this trend continues in tonight’s model runs. Computer models often have a tendency to under-model cold air in the low levels of the atmosphere, which is why we are suggesting that you keep a very close eye on the NWS over the next couple of days, as this would be a potentially dangerous situation for portions of the Northeast. Regardless, more heavy rain would be likely on the eastern side of this low, with the brunt of the rain falling once again over eastern NJ, Long Island, and Connecticut. Rainfall totals in that area may reach amounts of 3″ to locally 5″ in some spots, with a general 1-3″ likely for the rest of the region.

Another hazard we must mention will be the potential for a “Flash Freeze” on Saturday as the Arctic front moves through the Northeast. Temps will quite rapidly fall from the middle to upper 50’s in the early morning hours of Saturday, to below-freezing Saturday night. Any residual rain on roadways will freeze quite quickly and could lead to very slippery conditions, with some spots of black ice. This threat does seem more likely as this time, as the Arctic front is almost a guarantee to quickly move from west to east on Saturday. However, we will be very closely monitoring this potentially dangerous storm over the next few days and will continue to provide updates!

This afternoons European model showing a very wide range of impacts on Saturday with the potential for heavy snow, ice, and potentially flooding rains over the Northeast.

Have a great night!

Steve Copertino

Warmer Conditions Finally Take Hold, Watching This Weekend

January 8, 2018/by Steven Copertino

Good Evening!

Today has been quite the interesting day, as we finally saw high temperatures lift above freezing for the first time in almost two weeks for some locations! Many states across the Eastern third of the country saw their coldest first week of January on record, which is a fitting way to bookend this intense Arctic Outbreak that will likely be remembered for years to come. Although some locations to the south and east of the immediate NYC area saw a return to above-freezing, many locations did not and were once again stuck in the middle to upper 20’s. This combinations led to problems, as a weak mid level disturbance moved in from the Ohio Valley this afternoon and brought a mixed bag of precipitation for the majority of the Mid Atlantic and some Northeastern states. Despite having mid level temperatures just slightly above freezing in the lowest 3,000-4000 feet of the atmosphere, low level temperatures were cold enough and were accompanied by enough dry air to have precipitation start off as a mix of freezing rain and sleet for locations mainly to the north of Philadelphia. As this system quickly headed towards the coast during the late afternoon, we were able to see a change to mainly sleet and snow as mid levels once again cooled enough to end the freezing rain threat. Farther south, the freezing rain threat has stuck around longer due to more stubborn mid level warm air and higher temperatures near the surface. No major ice accumulations have been recorded as of this evening, but it would appear that at least some roads have become slick over the past few hours over southern NJ, southeast PA, and portions of MD/DE.

These slippery conditions accompanied by lingering light freezing rain should continue until around 11pm-1am before completely shutting down as dry air begins to take over the mid levels from northwest to southeast. While precipitation may not be all that heavy, freezing rain accumulates the most when rates are light, so please use caution when driving this evening, especially on back-roads and roads that usually are not treated. Otherwise, we should see continued gradual clearing through the overnight hours, with temperatures getting into the lower to upper 20’s over the majority of the Northeast.

This evenings regional radar mosaic, surface observations, and RTMA 2m temperatures showing some light rain, snow, and freezing rain over the Mid Atlantic states.

Tuesday Into Thursday

Any mid to upper level clouds associated with tonight’s system should be out of the region and well off the coast in time for the morning commute on Tuesday. Tomorrow will likely start off quite cool, but clear for the entire area. Winds should generally be from the west for the vast majority of the day tomorrow, with temperatures likely getting into the middle to upper 30’s across much of the area tomorrow, with only locations north of southern New England staying below freezing. Calm conditions can be expected tomorrow as a surface high pressure system builds in over the Northeast by tomorrow evening. Conditions will be quite calm and just right for some good radiational cooling to take place tomorrow night, which should bring lows down into the lower to middle 20’s right around the NYC metro area, with teens likely to the north and west.

Wednesday should see much of the same, with a high pressure system remaining in control of the weather for the day. Mid level temperatures will begin to rise from the southwest during the afternoon hours, and with relatively clear skies, we should see highs mainly in the middle to upper 30’s, with some locations to the south and east likely getting into the 40’s. Clouds should begin to increase during the late evening hours and into the night as a mid level warm front will begin to lift over the region, bringing warmer temperatures in overnight. Lows will likely range in the middle to upper 30’s, with some locations to the north and west stuck in the low 30’s.

Thursday will likely be one of the more noticeably warmer days as low to mid level flow continues to increase and draw up warmer temperatures in the process. A growing system located in the Plains that will impact our area this weekend should provide some moisture early in the morning hours and possibly into the early afternoon, but these should generally be light in nature as the bulk of the lift associated with the system remains a great distance away. High temperatures on Thursday are going to be tricky, but the increased humidity and mid level temperatures should yield highs in the lower to middle 40’s across much of the Northeast, with some locations likely to hit that 50-degree mark . Any meaningful precipitation looks to wait until the early morning hours of Friday to move in, so expect relatively dry conditions until that time.

18z NAM models evolution of the surface temperatures over the Northeast, showing a change to a warmer couple of days.

Plain Rain Or A Mix For The Weekend?

Finally, a large area of energy will be over the southern Plains states by Friday morning, and this will help to pump copious amounts of low level moisture into the East during the day. As of right now, it appears that we may see one heavy burst of rain start to move from the south and over the Mid Atlantic and Northeast early Friday morning and into the afternoon hours. Rain intensity may dwindle a bit in the late afternoon hours and into the evening, but at least some showers are likely during this time. The next batch of steady rain looks to occur right around Saturday morning as the mid level energy begins to strengthen and take on more of a negative tilt over the central US. This kind of setup promotes the development of a primary low pressure system over the Ohio Valley, with moderate precip extending from Illinois from Boston. This will be a large system in nature, so the impacts will already be large, however this afternoons European model has shown a more interesting solution as the surface low pressure system bumps into a strong area of Arctic high pressure located over southern Canada. Such a solution would create the threat for snow/sleet/freezing rain as the more dense cold air runs into the strong warm air advection from the south.

As of this evening, it appears that portions of New England would be at greatest risk from any significant frozen precipitation, but this is still five days out at this moment, and these situations usually continue to change up until the event is occurring. We will be closely monitoring the potential for heavy rain and possibly some frozen precipitation this weekend and will provide numerous updates over the next couple of days!

This afternoons ECMWF model showing a large winter storm centered over the Ohio Valley bringing a wide range of possible impacts.

Have a great evening!

Steve Copertino

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