The first half of this first full week of the summer felt very much like mid-summer, with hot, humid conditions and even some severe thunderstorms. The second half of this week, along with the weekend will feel a lot more like late spring, with Saturday afternoon into Sunday morning shaping up to be a washout.
Rest of today – pleasant, sunny skies, with a wind from the northwest, will yield comfortable high temperatures in the mid-80s.
Friday – an area of low pressure will be tracking eastward from the Midwest along a nearly stationary frontal boundary that will be positioned over southern New Jersey. The timing of this wave of low pressure will be overnight Thursday into Friday morning. Rain should end by noon Friday. With mostly cloudy skies, high temperatures will only top out in the mid-70s.
North American Model high resolution simulated radar image for Friday at 8AM EDT
Saturday – the respite from the rain will be short-lived. Saturday morning into the early afternoon should remain rain-free, though temperatures will again be suppressed in the low-mid 70s. Another, more potent area of low pressure will make its approach from the west during the day Saturday. The precipitation shield associated with this low should begin to fill in over the area beginning in the mid-afternoon hours. Periods of showers will continue falling, with moderate to heavy rain at times, throughout the remainder of the day and overnight Saturday.
North American Model high resolution simulated radar for Saturday at 2PM EDT
Sunday – rain begins to taper off on Sunday from south to north as the center of the low pressure responsible for this storm moves to our northeast. Rain should end in the early afternoon hours. Mostly cloudy skies are expected with temperatures in the mid-70s. Rain from last week has put a dent in drought conditions across New York state, but areas of Central upstate New York and eastern Long Island could still use this rain. The downside is that it will put a damper on many outdoor plans for the first full weekend of the summer, and the first weekend after school ends here.
Monday – conditions improve on Monday as the low pressure continues to pull away. High temperatures should remain in the mid-70s with cloud cover decreasingly steadily.
We got a bit of a (cold) respite during the weekend from any precipitation, but all that is about to change in a big way tonight and into tomorrow. A complex storm system that is set to bring snow across a wide swath of the Midwest will be approaching the area tonight and into tomorrow. Various factors make this storm even harder to forecast than the Nor’easter last week, including a still uncertain storm track and a very tight temperature gradient leading to the potential for a mixed bag of all precipitation types in the NYC region.
Impacts
This storm is set to make Monday a downright nasty day to be out. Snow is forecast to begin falling tonight, with areas to the north of the city expected to pick up the most snow through this storm. During the AM rush, temperatures are expected to rise just enough in the lower atmosphere to allow for the possibility of sleet, ice pellets, and a period of freezing rain along the coast near the city, with rain possible further east in Long Island. Then, to close out the day, temperatures will drop rapidly below freezing, such that any slush or melted snow or wet surfaces could flash freeze. Because the temperature gradient is so tightly packed, it will again literally be a matter of miles between a spot that picks up mostly snow and perhaps 8″+, and another location that picks up almost no snow, but gets a significant coating of ice.
Ice accumulation forecast – anything over 0.10″ can cause serious problems.Snowfall total forecast – note the similarity with the last storm as to how dramatically snow totals range across a very small geographic area.
Below are some probabilistic forecast graphics that will give you a good sense of the degree of uncertainty within this storm forecast. First, with respect to snowfall totals over the next 48 hours.
Probabilities of greater than 2″ of snowProbabilities of snow accumulation greater than 4″Probabilities of greater than 8″ of snow
Here’s the same time window, but with probabilities for ice accumulation.
Probability of ice accumulation greater than .10″Probability of greater than .25″ of ice accumulation
In the snowfall probability maps, you can see just how tightly packed the different bands of probability for snowfall are. A matter of 50 miles means the difference between being in an area of 40%-50% probability of receiving more than 4″ of snow, and an area with a greater than 80% chance of receiving the same total.
Timing
Snow will begin to fall later this evening and pick up in intensity overnight. Depending on the area you’re living in, you could see between 3″-8″ overnight, with the highest totals most likely north of the city, and the lowest totals along the coast and in eastern Long Island. Around the morning rush, areas along the coast and eastern Long Island should begin to see a transition from snow to freezing rain, or some type of wintry mix of ice pellets and sleet. Some parts along the coast may even see a changeover from rain/snow to plain rain. In the afternoon, temperatures will drop quickly below freezing, allowing for flash freezing of slush and other wet surfaces. Winds will begin from the east initially before turning northeast and then north through the day.
Why the Uncertainty?
The reason behind the complexity of this storm with respect to precipitation types, uncertainty of total snowfall amounts, rests with storm’s track and the dynamics in the lower atmosphere accompanying this storm. This storm, unlike a Nor’easter, has its genesis over the Central Plains. However, as it approaches the coast, it will still be able to pick up a good amount of moisture off the ocean and from points south.
Recalling that air around a low pressure center in the northern hemisphere in a flows in a counterclockwise motion, you can better understand what is going on here. The low pressure center is forecast to pass just to our south. To the north of the storm center, colder air will dominate, since the cyclonic flow would be pulling air from north to south. Meanwhile, on the south side of the storm center, warmer air is being wrapped into the storm from the south and east. This onshore flow bringing relatively warmer air in close proximity to colder (sub-freezing) air is the reason why there is such a dramatic range in forecast snowfall totals across the area, and also the reason why there is a possibility for a range of different precipitation types.
Above is a forecast map that shows the forecast position and track of the storm. The colored points represent the individual forecast ensemble members (different forecast models with slightly different inputs) predictions for the storm. Notice that there is still a nontrivial spread between these ensemble members. You may also observe that they seem to cluster to the north of the official forecast track (the black line). Indeed, forecasters have been making slight northward adjustments in response to this trend. Should this bear out, and the low pressure center does move a bit further north, we would end up with less snow, more chance for mixed precipitation and even rain. On the opposite end, if the storm track deviates south, we would get more snow, and less chance for mixed precipitation. A very tricky forecast indeed!
Election Day features temperatures much above normal for this time of year, with high temperatures in the mid-60s under mostly sunny skies. Wednesday continues the warm trend but with increasing clouds. We’ll see another stormy end to the week before conditions improve this weekend.
Tuesday – the remainder of the day will feature high temperatures in the mid-60s reminiscent of early October and not November. This is all thanks to a warm front that passed through (you can see this in the diagram below for Wednesday, up and to the right of NYC demarcated by the red line). Go out and enjoy this while you can, and don’t forget to vote!
Wednesday – we’ll see an even warmer day despite the increase in cloud cover ahead of an approaching cold front. Southwesterly flow will allow warm, tropical air to surge into the area from the Gulf. This plume of warmth and moisture will also prime the atmosphere ahead of Thursday’s storm. The cold front itself will weaken as it passes, so we’re not anticipating any rainfall. High temperatures will be generally in the upper 60s.
Thursday – a storm system with its origins in the Great Lakes/Ohio Valley area will form a secondary low near the offshore waters of the Northeast. Despite being only 2 days out, there’s still some uncertainty to the ultimate track of this storm system. The general pattern will be somewhat similar to last week, with the coastal storm forming and then slowly making its way northeast. The availability of deep moisture suggests the possibility of bouts of heavy rain during the day Thursday into Thursday night. When all is said and done, we could be looking at rainfall totals in the 1.5″-2″ range across the area, depending on the final track of the storm. The further west the track, the further west the highest impact areas will be, and the inverse for tracks further east. High temperatures will remain mild until after the storm departs to the northeast, with high temperatures in the low 60s.
GFS model output for Thursday
Friday – rain should end early Friday as the low lifts to the northeast. Winds will pick up and shift towards the north, resulting in much cooler high temperatures only in the mid-50s.
We get a  cool but sunny Saturday before another chance of rain Sunday.
Wednesday is shaping up to be a stormy, rainy day. Low pressure center currently located over Nebraska and Oklahoma will slide to the northeast into the Ohio valley while continuing to strengthen.
Current forecasts point to the storm center tracking just north of the NYC area. This should ensure that most of the region receives all rain for this storm. As the storm center draws closer, a nearly stationary frontal boundary will slowly push through to just north of the NYC area. This will allow the area to be entrenched in the warm sector, this means temperatures will stay relatively mild with highs in the mid-50s. It also raises the possibility for some weak thunderstorms in the afternoon hours as the cold front trailing the storm center pushes through.
In fact, the Storm Prediction Center has placed the DC-PHL metro areas as well as parts of southern Pennsylvania, northern Virginia, Maryland (see diagram below) under a slight risk for severe thunderstorms. The same cold front could trigger stronger storms down to the south due to the likelihood of warmer temperatures, more unstable air, and favorable conditions for thunderstorm initiation.
Behind the cold front, temperatures will plummet during the evening and overnight hours. The departing low will continue to strengthen into Thursday, with increasing northwest winds ushering in this colder air as well as a chance for snow showers (negligible accumulation expected). Highs will only barely hit the mid-20s.
Conditions will improve later in Thursday and Friday as an area of high pressure moves over the region. Temps will climb back into the low 40s Friday just below average, and rise to near 50 Saturday. Next chance of significant precipitation looks to be Sunday into Sunday night – with the potential for a snow storm!
