Category Archives: Rain

NYC Detailed Forecast for Apr 19, 2019

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It’s been four months (!!) since I’ve done one of these detailed forecasts. I’m a bit out of practice but trying to get back into the groove. Lucky for me, I picked a day to forecast that has a decent bust potential for precipitation. I’ll discuss that below.

Friday is going to start off decently enough. It should end up being the warmest day of the week. However, it’s also going to be the start of a protracted period of unsettled weather that will affect the weekend. A flash flood watch is in effect late overnight Friday going into Saturday for this reason.

My Forecast
High: 70°F | Low: 58°F | Max sustained winds: 30 mph | Total precipitation: 0.10″ – verification for temperatures and precipitation will come from METAR data for the period between 2AM Friday and 2AM Saturday (06Z Friday to 06Z Saturday) at LGA. Wind speed verification will draw on the daily climate summary from the National Weather Service.

Verification
High: 76°F | Low: 56°F | Max sustained winds: 24 mph | Total precipitation: 0.16″ – I did decently forecasting the low, and the total precipitation. Hedging way down on precipitation totals towards the NAM solution on a slower moving storm was a good idea. On the low temperature, I think a 2°F margin is acceptable here. Being off by 6°F on the high temperature here constitutes a forecast bust that I’ll put a post-mortem together for – as it turns out the bust happened here and not with precipitation. Winds were also not as strong as anticipated. I should have hedged a bit down too with less intense precipitation anticipated.

Weather Prediction Center surface forecast for 8PM Friday

Synoptic Set Up
We begin the period in the warm sector of a low with a center forecast to sit over southwestern Quebec. A secondary surface low is forecast to form over the OH valley and strengthens as it briefly moves northeast. This low is then forecast to stall out and retrograde northwest as it matures and occludes. This will lead to a protracted period of precipitation, with the primary focus being along a cold front moving through Sat morning. This may result in the best chance for heavy rain being outside the forecast period.

At the 850 mb level, a strong low-level jet will provide efficient moisture transport. At 500 mb we’ll be downstream of a longwave trough, with an embedded closed low that becomes cutoff (this mid-level cutoff low will be tied to why the secondary surface low retrogrades). The best vorticity and divergence (lift) associated with this upper low seems to move through after forecast period according to NAM forecast model. GFS has a bit earlier timing, and hence brings precipitation in earlier Friday. Finally, at the 300 mb, there’s not much evidence of enhanced divergence and lift at this level since, we’ll be east of any favorable entrance/exit regions of a 300 mb jet streak.

NAM forecast model’s depiction of the 500 mb layer at 11PM Friday. The cut off low referenced above is circled in green. The shades of yellow-purple indicate increasingly strong vorticity, which is linked to divergence and enhanced lift.

High Temperatures
GFS and NAM MOS are in pretty close agreement here. It should be warmer than average, since we’ll be in the breezy warm sector of a low as mentioned above. Limitations on warmth will be evaporational cooling due to precipitation, but this doesn’t appear to be a factor until late in the forecast period, past normal times for peak temperatures. The other factor is thick cloud cover. However, temperatures will largely be driven by warm advection tomorrow and not necessarily solar heating. EKDMOS suggests a temperature over 70ºF. In deference to this ensemble model, I’ve sided with the warmer GFS and EKDMOS (as well as National Blend of Models) and call for a high temperature of 70ºF.

  • GFS MOS output
  • NAM MOS output

Low Temperatures
NAM and GFS MOS are again in close agreement. With warm advection happening during the course of the overnight hours (strong winds at large angles to isotherms, southerly flow), have no reason to disagree that temperatures could actually go up early then back down a touch before rising again with daybreak, and I’m going with an overnight “low” of 58ºF that is well above average for this time of year.

NAM showing temperature contours and wind direction/speed for 2AM Friday. Note the direction of the wind barbs (pointing from south) is crossing at large angles of relatively closely packed isotherms. This is a set up favorable for warm advection (transport of warm air).

Max Sustained Winds
NAM is lower on winds than GFS, but the ensemble EKDMOS skews towards faster GFS solution. This makes sense with heavy rain possible and downward momentum transfer. Winds are forecast to back from south-southwest to south-southeast during the period. These directions don’t typically produce the strongest winds climatologically. However, a strong 45-60 knot low-level jet aloft mixing down with precipitation could easily top 20 knots, especially if elevated convection and thunderstorms materialize. I’m going with the EKDMOS 50th percentile range and going with 25 knots.

  • The NAM forecast sounding at 5PM tomorrow shows considerably drier low-mid levels.
  • In contrast, the GFS forecast sounding shows a deep saturated layer indicative of ongoing precipitation by 5PM tomorrow.

Total Precipitation
There’s a large spread between NAM and GFS on forecast totals (more than 0.50″) because the GFS is coming in with precipitation starting much earlier in the forecast period than the NAM. The local forecast office seems to buy more into the NAM solution due to its consistency with slower onset of heaviest precipitation. There is some indication as well of MUCAPE present in SREF plumes, could result in some elevated convection that would boost precipitation totals. Any faster timing and/or burst of elevated convection could cause heavier rain to fall earlier, resulting in a forecast bust.

Counting against that, I don’t see any strong signal for frontogenesis at the 850 mb level enhancing lift. SREF doesn’t show too much in the way of strong lift either. Still, the fact that SREF ensemble shows much heavier precipitation totals are not far off to the west during this forecast period makes me a bit nervous.

Lastly, moisture isn’t a total lock, and there’s some evidence of drier air offshore and pockets of dry air moving through from the west at times. NAM is notably drier than GFS at both outset of the forecast and throughout the forecast period, as seen in the comparison forecast soundings above. Training of storm cells possible with steering currents set up parallel to the forecast orientation of the cold front.


NYC Weather Update – Apr 15, 2019

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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

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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

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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 – Apr 5, 2019

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A cool start to the weekend should give way to a nice couple of days before another storm moves in to start next week. During this period, high temperatures will start well below normal, then rise above average before finally settling around average. Looking ahead, another storm system appears to impact the area late next week, bringing a colder weekend next week in its wake.

Rest of today – cool, cloudy with high temperatures only in the mid-40s. Increasing rain chances towards the evening and overnight hours. Rain should taper off overnight then we should see overnight lows stabilize in the low-40s as warm advection takes hold. 

Saturday – clouds diminishing as the low responsible for the rain moves over the Atlantic to our south. High temperatures in the mid-60s, maybe a touch warmer if we see clouds break earlier than forecast. Overnight lows milder in the upper-40s.

Weather Prediction surface forecast for 8AM Sunday

Sunday – high pressure stays in control and gives us a pleasant, mild day with high temperatures in the low-60s. The high pressure and nice weather doesn’t stick around long though, with another storm system approaching during the overnight hours going into Monday. Overnight lows should hold around 50ºF as rain starts to fall.

Monday – despite clouds and rain sticking around, temperatures will surge to about 70°F with a warm front forecast to pass through.

NYC Weather Update – Apr 2, 2019

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High pressure gives way to a be coastal storm that will sideswipe the area. Following this, we’ll see a brief warm up, but temperatures will cool off towards the end of the week. We have rain chances overnight into tomorrow and Friday night.

Rest of today – high temperatures around 50°F. Increasing clouds ahead of a coastal approaching from the south. Overnight, chance of rain with low temperatures around 40°F.

Weather Prediction Center surface forecast for 8AM Wednesday, depicting a coastal storm passing us to the southeast.

Wednesday – winds increasing to 15-20 mph in the afternoon. High temperatures warming into the low-60s be with clouds dissipating and winds shifting to the southwest. Overnight lows drop back into the low-40s behind the passage of a dry cold front. Winds will shift to a colder northwesterly direction. 

Thursday – cooler with partly sunny skies and high temperatures in the mid-50s. Low temperatures colder in the upper-30s. 

Friday – another low approaches from the southwest. High temperatures below average in the mid-40s, rain chances increase later in the day with the low pressure drawing closer. Rain chances continue into the overnight hours with lows in the low-40s.

NYC Weekend Weather – Mar 29, 2018

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We will have a warm though not too sunny start to the weekend. A solid chance for rain hits Sunday with the passage of a cold front. After that, temperatures will drop to below normal levels again. Looking ahead into next week, there should be a dry start to the week but a coastal storm may impact the area mid-week. There’s some outside chances for snow with this storm.

Rest of today – cloudy, with some chance of light rain though most rain should remain over interior. With southwesterly flow, despite clouds we should still reach into the upper-50s to 60°F. A cold front approaching from the west is forecast to stall out and acquire semi-stationary characteristics. Thanks to the continued influence of high pressure off to our east, we should stay mostly dry today. Overnight lows should be warm, near 50ºF.

Saturday – the warmth continues, with high temperatures forecast to reach well into the upper-60s though clouds will still linger around with the stationary front to our west. Overnight lows will be similar to tonight around 50ºF.

Weather Prediction Center surface forecast for 8AM Sunday

Sunday – the stalled frontal boundary finally picks up forward momentum and pushes through the area as a cold front. Ahead of it, temperatures will still be mild in the mid-50s. A line of showers is expected with this front during the day. Overnight lows behind this cold front will be considerably colder, in the low-30s.

Monday – dry, sunny weather, but with a chilly start to the day, temperatures are expected to only be in the upper-40s to near 50ºF, slightly below normal. Overnight lows are expected in the mid-30s.

NYC Weekend Weather – Mar 22, 2019

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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 Weather Update – Mar 18, 2019

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Much above average warmth last Friday resulted in a spectacular light show from passing thunderstorms. In the wake of this, temperatures have dropped into a below average range, considerably cooler than this weekend. There will be a warm up later in the week though, along with some rain chances.

Rest of today – mostly sunny with high pressure in control. High temperatures in the mid-40s, overnight lows dropping into the mid-30s.

Tuesday – not too much of a difference between these two days. High pressure remains in control. High temperatures maybe a little warmer in the upper-40s, overnight lows again in the mid-30s.

Weather Prediction Center surface forecast for 8AM Wednesday

Wednesday – as high pressure shifts eastward, we should see a shift in winds to the west, allowing temperatures to warm into the low-50s. Overnight lows around 40°F.

Thursday – chance for showers with a frontal boundary moving through. High temperatures in the low-50s with mostly cloudy skies. Lows in the low-40s.

NYC Weekend Weather – Mar 15, 2019

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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.