Category Archives: Storms

NYC Mother’s Day Weekend Weather – May 10, 2019

NYC, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , , , , ,

Mother’s Day weekend here in NYC unfortunately looks to be quite rainy. We start off with the potential for rain later today. Saturday is shaping up to be the sole dry day with high pressure briefly building before giving way to a prolonged period of wet weather Sunday and Monday. So, if you’re making any outdoor plans for mom, consider bumping them up to Saturday!

Rest of today – cloudy, with temperatures around 70°F. We will sit in the warm sector of an elongated low centered over western Quebec as a warm front has already passed overhead. This will allow plenty of mild, moist air to stream northward with southerly winds ahead of the trailing a cold front associated with this low. This cold front will serve as the trigger for some showers and thunderstorms later this evening as it swings through. Overnight lows behind this cold front in the mid-50s.

Weather Prediction Center surface forecast for 8PM Friday

Saturday – high pressure briefly builds in during the day. This will give us the best weather of the weekend with mostly sunny conditions and seasonable high temperatures in the upper-60s. Ideal weather for any outdoor activities. This nice weather doesn’t last with clouds building into the overnight hours and low temperatures dipping to the low-50s

Sunday – another storm system approaches from the south. A warm front at the leading edge of this storm seems likely to stall out. This will bring a prolonged period of chances for showers, cloudy skies, and cooler temperatures with easterly onshore winds. High temperatures in the mid-50s. Overnight lows quite cool in the upper-40s as rain chances continue.

GFS model output for 2PM Sunday

Monday – a coastal low forms along the frontal boundary mentioned above. At this time, it appears this coastal low tracks close enough to make Monday another rainy day with cool temperatures, highs in the mid-50s, 10-15°F below normal for this time of year. Overnight lows looking even colder than Sunday if prolonged rain and a northeasterly wind flow materializes with this coastal low, current forecasts pointing to the mid-40s.

NYC Weekend Weather – May 3, 2019

Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , ,

The unsettled weather pattern this week continues into the weekend. Rain is possible tonight into Saturday, then again overnight Saturday into most of the day Sunday. Entering next week, it appears we get a break from rainy weather, but looking ahead, another period of prolonged chances for rain could occur mid-week next week. Temperatures will alternate between below normal and around average, depending on whether there is rain in the forecast.

Rest of today – cloudy, with temperatures in the upper-50s. A warm front lingers to our south slowly moving north. Eventually, a cold front will push through overnight into Saturday. This could bring a brief period of rain, and maybe a thunderstorm. Overnight lows in the mid-50s.

Weather Prediction Center surface forecast for 8AM Saturday

Saturday – rain chances should end by late morning. High temperatures should be able to reach around 70°F despite cloudy skies. Another storm system will move in overnight going into Sunday. Rain chances will ramp up steadily after midnight. Moderate to heavy rain is possible. Temperatures overnight in the mid-50s.

North American Model (NAM) high resolution simulated radar for 11AM Sunday

Sunday – washout of a day as low pressure moves though. Plenty of moisture available for this system and that could lead to some heavier precipitation. Poor conditions for the Five Borough Bike Tour, with highs around 60°F, as a cool onshore easterly wind accompanies this storm. Overnight lows in the low-50s.

Monday – nice rebound day with high temperatures reaching to around 70°F. Finally should see some sun with high pressure briefly building in the wake of Sunday’s storm and before the next frontal boundary to impact the area. Overnight lows in the mid-50s.

April 19, 2019 KLGA Forecast Post-Mortem

NYC, Post Mortem, Rain, Storms, ,

For reference, here’s the post that triggered the following forecast post-mortem analysis. To start, here’s my forecast and the verified totals.

My Forecast
High: 70°F | Low: 58°F | Max sustained winds: 30 mph | Total precipitation: 0.10″

Verification
High: 76°F | Low: 56°F | Max sustained winds: 24 mph | Total precipitation: 0.16″

Since I did decently at forecasting the low temperature and total precipitation, this analysis will focus primarily on why I missed the mark on the high temperature and maximum sustained winds.

How I Verify Forecasts
For an explanation of how I verify my own forecasts, see the methodology outlined in this prior post-mortem post

Post-Mortem Analysis
On this forecast, I ended up handling total precipitation and low temperatures but missed the mark on the high temperature badly and to some extent the max sustained winds. Let’s look at what happened here.

High Temperature
When I was putting together my forecast on the high temperature, the MOS output for both primary models (GFS and NAM) suggested the day would be largely overcast. Forecast soundings also suggested a deck of low clouds would be present for nearly the entirety of the day before the onset of an initial round of precipitation in the late evening/early overnight hours. Indeed, morning soundings at 8AM seemed to bear out what forecast models were calling for.

Sounding at 8AM from Brookhaven National Laboratory in Long Island, the site of the local National Weather Service forecast office for NYC. Note that the lower atmosphere, below 850 mb, is largely saturated, indicating low clouds and fog

Above the low level clouds, though, there was a noticeable dry layer up to about 500 mb, where high clouds were present. For temperatures, the biggest impact that’s hardest to pick up in advance is a low, thin, but optically thick layer of overcast clouds. Such a layer would suppress temperatures, whereas the lack of such a layer would allow for higher temperatures.

GOES East 1km resolution visible satellite image at 2:56 PM Friday, April 19. Note the relatively small pocket of clear skies right over NYC, western Long Island and Southwestern Connecticut.

In this event, where we were already in the warm sector of a low, any breaks in the clouds allowed for a dramatically warmer high temperature. As it turns out, there was a period of a couple hours in the afternoon during peak heating hours for this time of year that the skies were basically clear over NYC. In the spring, as the angle of the sun’s rays becomes ever more direct, even a small span of time like this with clear skies can result in significantly warmer temperatures. The small geographic scale of this pocket of clear skies, which was largely surrounded by cloudy conditions, shows you how difficult it is to predict something on a small scale like this, even just a day before the event itself!

Max Sustained Winds
On max sustained winds, I was off by 6 mph. That’s not too bad in the grand scheme of things. However, looking back at it, I should have realized that my own forecast calling for a small potential for precipitation would likewise mean a lower possibility for strong winds mixing down from 850 mb to the surface.

NYC Weekend Weather – Apr 19, 2019

Flooding, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , ,

A slow-moving storm system will impact the area with potentially heavy rain that could trigger flash flooding overnight into the first part of Saturday. Precipitation chances die down significantly with the passage of this round of rain as a dry slot works into the area. However, lingering chances for showers still exist as this storm makes a slow exit to the east. Temperatures during this period are forecast to be at or above normal.

Rest of today – cloudy, but still warm with temperatures rising to about 70°F. We will be in the warm sector with the influence of southerly winds during the day. Rain chances increasing during the evening hours. Steady rain is forecast late into the overnight hours with temperatures. Some of the rain could be heavy. Thunderstorms are also possible, and these would increase the risk of flash flooding. Overnight lows around 60°F.

Weather Prediction Center surface forecast for 8AM Saturday

Saturday – the north-south orientation of the cold front that will provide lift for these storms overnight will align well with the prevailing southerly flow through most of the atmosphere. The slow eastward progression of this front will allow storm cells to train leading to more flooding potential as rain continues Saturday morning. The cold front associated with this slow-moving low should push through by the afternoon. A dry slot should cut off any precipitation for a while during this time frame. High temperatures should be in the low-60s. Overnight lows should fall into the low-50s behind the cold front.

GFS model output of 850 mb winds and relative humidity for 2PM Saturday, notice the pronounced area of browns, indicating very dry air. This is what is referred to as a “dry slot“, which can often follow on the heels of cold fronts associated with mature mid-latitude cyclones.

Sunday – the upper low associated with this storm system is expected to cutoff (become detached from primary westerly steering currents), resulting in a system that will meander and take a long while to exit the region. As such, Sunday is expected to remain cloudy, with a chance for some showers. High temperatures should be similar to Saturday in the low-60s. Overnight lows will again be around the low-50s.

Monday – temperatures warming up into the upper-60s, but yes, that cutoff low still lingers! Chance for showers continues in the morning. Clouds finally decreasing later and overnight lows in the mid-50s.

NYC Weather Update – Apr 15, 2019

NYC, Rain, Storms, Weather Update, , , , , , , ,

The same storm system that impacted the Deep South this weekend with severe weather, including several tornadoes that caused fatalities, swept through the area overnight. Some severe wind gusts were reported, and area transit networks experienced some delays due to storm-related damage. As this storm departs east, it will continue deepening, resulting in strong winds the remainder of today. Another storm system is forecast to move in to the region Thursday and going into the weekend. Temperatures during the week are expected to be mostly around normal for this time of year.

Rest of today – windy, with decreasing cloud cover. Steady west winds between 20-30 mph later in the day. This will help bring colder air into the area, with highs already peaking this morning in the low-60s then dropping back to the mid-50s by this afternoon. Overnight lows in the low-40s with partly cloudy skies.

Tuesday – sunny day, with winds calming and seasonable high temperatures in the low-60s. Overnight lows in the mid-40s and mostly cloudy.

Weather Prediction Center surface forecast for 8AM Wednesday

Wednesday – increasing clouds as a backdoor cold front works its way through. High temperatures in the low-60s. Overnight, mostly cloudy with lows in the mid-40s.

Thursday – chance of rain as a low tracks slowly from the Plains to the Great Lakes. East of this low, a slow moving warm front could touch off showers during the day and overnight Thursday. High temperatures around 60°F, overnight lows quite mild due to the influence of the approaching warm front and warm advection, in the low-50s.

GFS model output for 7AM Thursday

NYC Weekend Weather – Apr 12, 2019

NYC, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , ,

Two distinct storms will affect weather in the area this weekend going into next week. The first is the remnant of the once mighty “bomb” cyclone that brought an abrupt return of winter conditions to the northern Plains states and Upper Midwest. The second will be a storm developing over Texas that could be a severe weather threat down South. Neither should result in a washout as the bulk of precipitation associated with these storms is timed to fall later in the day or overnight. Temperatures will be largely above normal during this period.

Rest of today – cloudy with chance of drizzle early. High temperatures around 60°F. Overnight lows in the mid-50s. Winds are forecast to turn to the south ahead of an anticipated cold front and in the wake of a warm front passing. Rain should accompany this frontal passage overnight.

Weather Prediction Center surface forecast for 2AM Saturday

Saturday – warm day in store with highs reaching into the low-70s despite mostly cloudy skies as the cold front passing overnight is forecast to stall and become stationary during the day. Overnight lows in the mid-50s again.

Sunday – shower chances increase as the next storm approaches. Temperatures will be cooler with highs in the low-60s due to clouds and rain. A second, more vigorous cold front is forecast to pass overnight into Monday. Rain, heavy at times, possibly with thunderstorms as overnight lows fall into the mid-50s.

GFS model output for 8PM Sunday

Monday – rain associated with this second storm should clear out around lunchtime. Cloudy day forecast now, but could see more breaks in the clouds and warmer temperatures in the upper-60s.

NYC Weather Update – Apr 9, 2019

NYC, Rain, Storms, Weather Update, , , , ,

Summer-like warmth has given way to more seasonable temperatures for this time of the year. The return to normal temperatures will be accompanied by the possibility of rain. Later in the week, temperatures will climb back up again as we are forecast to be back in the warm sector of another approaching storm. This storm should bring some rain Friday and overnight into Saturday, resulting in what should be a decent weekend

Rest of today – mostly cloudy, temperatures in the upper-50s to around 60ºF. Increasing chance for showers later this evening, around 6PM when a line of showers accompanying a cold front is expected to hit the area. Overnight lows behind this front will be much cooler than last night, in the mid-40s.

High resolution rapid refresh simulated 1-km radar for 6PM tonight

Wednesday – should be a nice day with mostly sunny skies and temperatures in the upper-50s. Overnight lows will be cool, around 40ºF.

Thursday – cool start to the day results in high temperatures around the mid-50s with mostly sunny skies and increasing clouds. Overnight lows climbing into the upper-40s.

Weather Prediction Center surface forecast for 8AM Friday. Note that we’ll be in the warm sector of this storm for a good part of the day.

Friday – warmer, with high temperatures in the mid-50s. Chances for rain increasing later in the day with a cold front forecast to be approaching from the west. Overnight lows in the low-50s.

NYC Weekend Weather – Mar 22, 2019

Cool Images, Noreaster, NYC, Rain, Storms, Weather Update, Weekend, , , , , , , ,

A long duration Nor’easter slowly moves its way eastwards. Conditions improve during the second half of the weekend. A brief warmup to above average temperatures takes place. This doesn’t last, with another cold front passing through to start next week. Tomorrow, keep an eye out on the skies for a possible glimpse at the aurora borealis, typically not visible at these latitudes.

Rest of today – chance for rain shower diminishing as the center of a slow moving Nor’easter continues to progress northeast. High temperatures reaching around 50ºF. Winds will increase on the backside of this departing low overnight. Winds will shift towards the northwest as well, bringing in colder air and overnight lows in the mid-30s.

GOES East satellite loop of the storm system affecting the Northeast
Ocean Prediction Center surface analysis for the Atlantic Basin. A strong blocking high is inhibiting the forward progress of the Nor’easter impacting our area. This is leading to a long duration coastal flooding and wind event.

Saturday – decreasing clouds as the low above continues progressing northeast slowly. Winds will increase as this low continues to deepen and the pressure gradient builds between it and and area of high pressure further west. Steady winds in the 20-25 mph range with gusts as high as 40 mph are forecast. High temperatures will be a bit below normal as a result in the upper-40s. Overnight lows will be cold, in the mid-30s with clear skies.

Weather Prediction Center surface forecast for 8AM Sunday, still showing a tight pressure gradient between a high over the Ohio Valley and the departing Nor’easter

Sunday – temperatures rebound into the mid-50s as an area of high pressure builds and slides off to our southeast, and winds turn towards the southwest bringing in warmer air. Sunny skies – this will be the best day of the weekend.

Monday – another cold front approaches from the west and brings a possibility for rain. Temperatures ahead of this front should reach into the low-50s. Behind this, we’ll get another shot of cold air, with temperatures dropping overnight into the low-30s.

Northern Lights Possibly Visible from NYC

On Tuesday, The Space Weather Prediction Center (it exists!) detected a large Coronal Mass Ejection (CME) associated with a potent solar flare. As a result, they have issued a moderate geomagnetic storm watch for Saturday, March 23. Of note, the belt where the charged particles from this CME would impact the Earth’s upper atmosphere and result in an aurora quite a bit further south than where the northern lights are typically visible. In fact, they may even be visible from NYC, although it may be hard to see them due to light pollution.

NYC Weekend Weather – Mar 15, 2019

NYC, Rain, Storms, Thunderstorms, Weather Update, Weekend, , , , , , , , ,

This weekend will see a warm start but then a cool down into the below normal range going into next week. A rumble of thunder and showers will precede this cool down. Weather looks pleasant for St. Patrick’s Day festivities and the NYC Half Marathon this weekend. 

Rest of today – mostly cloudy with some breaks of sun after a warm front passes over shortly and we sit in the warm sector of the same storm that tore through the central US earlier this week. As the trailing cold front pulls through this evening, it could provide enough lift for some additional showers and possibly a couple thunderstorms. High temperatures will be above average in the low-60s, mid-60s if some sun breaks through while we’re in the warm sector. Overnight lows behind the cold front should be in the low-40s.

Weather Prediction Center surface forecast for 8PM Friday

Saturday – bright, sunny day with high pressure building behind the cold front. Temperatures cooler, around 50°F. Overnight lows much cooler in the low-30s.

Sunday – cold start to the NYC Half Marathon in the low-30s but high temperatures will end up in the mid-40s with lots of sun. Overnight lows again around the freezing mark

Monday – increasing clouds with a possibility for some precipitation but chances are too low now to call. Highs in the mid-40s and overnight lows back down in the low-30s again.  

NYC Weekend Weather – Mar 8, 2019

NYC, Rain, Storms, Weather Update, Weekend, , , , , ,

As we spring forward this Sunday, our weather pattern finally takes a step forwards towards spring as well. Rain will accompany this warmup, then we start next week with temperatures close to average for this time of year. 

Rest of today – Increasing clouds as an area of low pressure moves offshore well to our south. High temperatures in the upper-30s. A 500 mb (upper level) shortwave trough passing through overnight could provide enough lift for some scattered flurries. Lows dipping to around freezing. 

Saturday – High temperatures in the mid-40s with lots of sun as high pressure temporarily exerts its influence. Overnight lows in the mid-30s. Rain starts overnight going into Sunday as a storm system draws near. 

Weather Prediction surface forecast for 8AM Sunday

Sunday – rain during the morning with improving conditions later. Overcast to start with cloud cover decreasing as the storm departs to the east. High temperatures around 50°F. Overnight lows in around 40°F

Monday – sunny and seasonable with highs in the upper-40s. Overnight lows cooler than Sunday in the mid-30s.