Tag Archives: flooding

NYC Weekend Weather & West Coast Storm – Dec 2, 2014

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It’s been a up and down week for weather in NYC, with Monday starting out in the mid-60s, then a colder mid-week that featured some mixed precipitation and rain. The end of this week will feature rain and slightly warmer temperatures by Saturday, then a return to colder conditions Sunday into next week. I’m also going to point out some of the spectacular weather brought on by a huge Pacific storm that hit California this week.

Thursday – the remainder of today will be pleasant and sunny, though cold with high temps only in the low 40s.

Friday – clouds will begin to build overnight tonight ahead of the a storm system moving in from the Southern Plains to the Ohio Valley. There is a small chance for scattered showers, otherwise expecting a cloudy day with highs in the mid-40s.

Saturday – rain should overspread the area by Friday night into Saturday. This storm system will be drawing on energy and moisture from the Pacific storm that slammed California earlier this week (discussed below). Combined with influx of Gulf moisture, this setup favors a moderate to at times heavy rain event for Saturday. Temperatures will rise steadily ahead of this storm system as it pushes warm air up. High temperatures Saturday should reach into the mid-50s despite rain and clouds.

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GFS model output for overnight Friday into Saturday

Sunday – rain should end overnight Saturday, and high pressure from Canada should quickly build in behind this storm system. The positioning of this high pressure, along with the exiting low, will make for a tight pressure gradient, which should allow for stiff northwest winds perhaps in the 15-25mph range. Temperatures will drop back into the low 40s with the arrival the colder Canadian air.

gfs_namer_084_1000_850_thick
GFS model output for Sunday night

Monday – the storm system from Saturday will move offshore, but it appears from model runs that there’s some chance the storm lingers. As the high pressure from Sunday moves off to the northeast, the clockwise flow behind it may draw this offshore area of low pressure back into the area. This could lead to some rain on Monday. It’ll be a mostly cloudy day otherwise with highs in the low 40s.

Pacific Storm Slams California

Earlier this week, California got slammed by a very strong Pacific low. This storm brought on furious rains that dropped 1″+ in many areas of Northern California, with totals as high as 3-4″ in spots near the Coast Range and Sierra, as well as further south in the mountains east of San Diego. These totals represent more rainfall than had fallen in many of these areas all of last year.

You can see from the map below which overlays drought conditions (the deeper the red, the more extreme the drought, with the darkest red representing extreme/record-breaking drought) with rainfall totals from yesterday. You’ll see that much of the heaviest rain did fall over regions worst affected by drought. Sadly, though this is a case of too much of a good thing, as much of this desperately needed rainfall occurred so quickly, it will simply runoff back into the ocean.

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Map of California with drought condition layer (reds/oranges), and rainfall totals from yesterday

NYC Weather Update – Oct 14, 2014

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Apologies for the lapse in posts last week. There was plenty to talk about with the formation and dissipation of Hurricane Fay, and with Hurricane Gonzalo developing. Gonzalo won’t be a threat to the U.S. mainland, but may wreak havoc in the vicinity of Bermuda as a low end Category 3 storm with 115-120mph sustained winds. This storm has the potential to hit Category 4.

Back to our region:

Today – we get to enjoy a very warm day for this time of the year with highs in the mid-upper 70s and sunny skies! Unfortunately, clouds will begin spreading over the area in a few hours time ahead of a system described in detail below.

Wednesday – there will be a chance of light rain in the morning, with the chance for more substantial rainfall increasing in the afternoon. Temperatures will remain mild in the mid-70s with persistent southeasterly flow channeling in warm, moist air from the south ahead of the cold front and storm system that was responsible for a severe weather outbreak in parts of the Midwest and Southeast earlier this week.

Thursday – will be the main event. Lucky for us, the storm system coming at us won’t be bringing severe weather, however, a thunderstorm or two is not out of the question. The main issue for us will be the risk of flooding from this slow moving system. Forecast models show training of storm cells, meaning the same areas will get hit repeatedly or continuously with moderate rain showers. Rain will likely be falling throughout the entirety of the day Thursday with little or no breaks. Rainfall totals of nearly 2″+ could lead to some minor flooding. However, the rain is welcome since we are nearly 3″ below average for rainfall. Temperatures should again remain on the warm side with highs in the mid-70s.

NAM high resolution model output for Thursday, Oct 16 @5PM
NAM high resolution model output for Thursday, Oct 16 @5PM – note the bright blue and purples stretched over the area, indicating bands of heavier rain
Precipitation total forecast for 8PM Wednesday-8PM Thursday. Nearly 2" for the NYC area.
Precipitation total forecast for 8PM Wednesday-8PM Thursday. Nearly 2″ for the NYC area.

Friday – things settle down quickly as a brief window of calm weather enters the picture. Temperatures will be cooler in the wake of the cold front with west winds and highs in the lower 70s.

NYC Weather Update – Jul 15, 2014

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A correction from yesterday – I had said today may see less potential for severe weather. In fact, the Storm Prediction Center once again has most of the NYC metro area under a slight risk for severe thunderstorms later today.

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Based on current satellite trends, it does appear there will be some breaks in the clouds this morning and afternoon. This will allow sufficient sunshine and daytime warming to fuel strong to severe storms across our region again later today. In the upper atmosphere, largely unidirectional winds from the south-southwest, a favorable jet stream set up, and approaching cold front suggest the potential for storms with damaging wind gusts and even some hail. Flash flooding is again a distinct possibility.

As you see below, portions of our area saw up to 1-1.5″ rain yesterday, and these same areas are in the target zone for severe storms today as well. With the upper level winds lining up from the south-southwest, training (where multiple storms hit the same location over a period of time) of storms is likely. This will enhance the risk for flash flooding.

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A note about the term unidirectional winds: Unlike a hurricane, severe thunderstorms thrive on upper atmospheric energy, and unidirectional winds at all levels are more conducive to imparting a rotation on a rising parcel of air (rotating thunderstorms can produce tornadoes).

Otherwise, expecting a warm, humid day, with highs in the mid 80s and some sun before storms arrive later in the afternoon. It will be cooler and more comfortable tomorrow with this stormy cold front having passed us!

NYC Weather Update – Jul 14, 2014

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The Storm Prediction Center has placed the entire NYC metro area in an area for a slight risk of severe weather today. A strong low pressure center over the Great Lakes and its associated cold front are slowly making their way towards the Eastern Seaboard. Despite the cloudiness today, forecasters are still fairly confident that atmospheric conditions will be favorable for the formation of severe thunderstorms in the region. Based on current radar trends, these storms would most likely not be arriving in the NYC area until later this afternoon. The primary threat to our area will be damaging winds and torrential rain capable of triggering flash floods.
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Tuesday will feature a similar set up for weather over the region, though there is less risk for severe weather tomorrow. However, strong storms are possible throughout the day and the risk of flash flooding is a distinct possibility. High temperatures will be in the mid 80s despite cloud cover, due to the influence of warm, humid air rushing in between the cold front and high pressure offshore over the Atlantic. This same warm, humid air mass is what will feed the storms for today and tomorrow. As you see below, the forecast rainfall total for today and tomorrow is as high as 3.6″ over Northeastern New Jersey, and ranges between 2.5-3″ for most parts of the Tri-State area.Untitled2

Wednesday – we get a reprieve from the stormy weather as the cold front and storm system finally move east of NYC. Expect a cloudy start to the day with gradual clearing and conditions improving markedly. The next weather story for Wednesday through the end of the week is the cool, polar air mass that will be a dominant feature. High pressure will build in behind this storm system and usher in much cooler temperatures, with highs in the low 80s Wednesday-Friday, and overnight lows in the low-mid 60s in the city, and in the 50s north and west!

Thursday & Friday – expecting these two days to be essentially the same weather-wise, with high temperatures in the low 80s in the city (and upper 70s further north). Sunny to mostly clear skies for both days.

NYC Weekend Weather Update – May 16, 2014

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First for weather headline that will be dominating today: the storm system that is set to bring us heavy, potentially flooding rain later today and into the overnight hours. Currently, temperatures in our area are generally in the mid-upper 60s with a strong south to southeasterly wind. This is leading to an influx deep moisture ahead of the approaching cold front. We are firmly entrenched in what meteorologists refer to as a warm sector. This will provide the necessary conditions for heavy rain and some possible embedded thunderstorms to form later.

NOAA NCEP surface analysis as of 9AM EDT. Note the cold front sitting just off to our west with an elongated area of moderate to heavy rain.
NOAA NCEP surface analysis as of 9AM EDT. Note the cold front sitting just off to our west with an elongated area of moderate to heavy rain.

Based on the latest output from GFS and NAM models, it would appear the heaviest of the rain will arrive in our area during the PM rush and last through the evening into the early morning hours. So, if you’re going to be heading out this evening, grab an umbrella and appropriate rain gear.

NCEP's forecast for quantitative precipitation totals over the next 24 hours.
NCEP’s forecast for quantitative precipitation totals over the next 24 hours.

One of the major hazards with this storm is flash flooding and flooding in general. Because a high amount of precipitation is anticipated to fall in a relatively short time window, flash flooding is a real concern especially in urban areas and small streams. This will make for a sloppy and slow evening commute. The flip side of the fast moving nature of this storm system is that it should clear the area fairly quickly, meaning that you runners out there should have slightly better conditions than previously forecast for the start and duration of the Brooklyn Half Marathon.

NAM high resolution model output showing the cold front and storm system to have pushed through our area by about 5AM EDT
NAM high resolution model output showing the cold front and storm system to have pushed through our area by about 5AM EDT

Saturday after the cold front passes through and the rains subside, we should be looking at gradually clearing skies and slightly above average temperatures in the low 70s.

Sunday through Tuesday – we will be compensated for this rainy Friday by a string of days with fair conditions and seasonable temperatures. A high pressure center will form and camp out over our area, preventing any bad weather from impacting us. As such, temperatures should be nearly steady each day during this period in the upper 60s to low 70s with mostly sunny skies.

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NYC Weather Update – Apr 30, 2014

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Are you wondering why today is so cool with highs barely touching 50, but tomorrow is forecast to have high temperatures in the low 70s? It’s because there’s a warm front currently situated to our south. Let me clarify the two most common types of frontal boundaries:

  1. A warm front delineates a boundary where the airmass behind the front is significantly warmer than the airmass ahead of it.
  2. A cold front, not surprisingly, applies to the reverse situation and delineates a boundary where the airmass behind the front is significantly colder than the airmass ahead of it.

Currently, a warm front sits south of us, causing an onshore flow (easterly winds) off the frigid Atlantic Ocean. Why the easterly winds? Looking at the image below, you’ll see yellow contour lines that demarcate isobars of pressure. In the Northern Hemisphere, air flows counterclockwise around a low pressure center and clockwise around a high pressure center. The counterclockwise flow also applies to the frontal boundaries attached to a low pressure center.

In our present situation, the air flows towards the east (counterclockwise) south of the west-east oriented warm front (in red), and then from the east to west north of it. Hence, we are experience very cool conditions, and the moisture being funneled off the Atlantic Ocean into our region is fueling these steady showers.

Current surface analysis from the WPC with my overlay showing movement of the warm front to our south.
Current surface analysis from the WPC with my overlay showing movement of the warm front to our south.

We should actually see temperatures begin to rise overnight as the warm front pushes through the area. Once this occurs, we will be in what is referred to as the “warm sector”, which is an area that sits behind a warm front and ahead of an advancing cold front. This type of setup is favorable for the development of thunderstorms.

Therefore, Thursday will be a warm, cloudy day with high temperatures in the low 70s and a chance of showers and thunderstorms in the morning.

Friday, with the cold front having passed through, conditions will clear up and we’ll have a nice, sunny day, with temperatures near 70. There will be a chance for afternoon showers.

Saturday continues the trend of nice weather with another day in the upper 60s and mostly sunny skies. Again, there will be a chance for afternoon showers, especially inland where daytime heating can produce enough energy (and instability) to induce those showers.

One other note about today and tomorrow, and that’s the whopping headline numbers for how much rain is forecast to fall, with totals ranging from as high as 3″+ in the western portions of the Tristate to 1.5″+ in the east. This could easily cause flooding in poor drainage areas, small streams, and urban areas.Screen Shot 2014-04-30 at 1.50.54 PM

 

 

NYC Weekend Weather Update – Mar 29, 2014

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If you’re getting ready to venture out this evening make sure to bring an umbrella and wear your rain gear as a heavy rain event is in store for the New York City area. This will be an extended rainfall event leading into Monday. temperatures today will peak at around 50, near normal. The heaviest rain will be falling from approximately 8 p.m. tonight into the overnight hours. Winds will be at around 25-35 mph. Parts of the area are forecast to receive between 1.5″-3″ of rain in the next 48 hours, which could lead to some minor flooding in poor drainage urban areas and small creeks.

So, in general expect conditions to gradually deteriorate through the day and the intensity of rain to pick up. Rain will continue on Sunday, albeit with diminished intensity. Temperatures will hold steady around 50.

Refer to the diagram below, which represents the North American models guidance for this evening at around 8 p.m. Note the areas of blue and bright blue that correspond to rainfall rates anywhere between .75″ to 1.5″ per hour.

nam-hires_namer_015_1000_500_thickRain will diminish by Monday afternoon as the low pressure center responsible for the heaviest rains moves off to the northeast.

High pressure will move in Tuesday, with a weak cold front moving through later Tuesday. This frontal boundary is not forecast to produce any precipitation. Ahead of this frontal system, we’ll see temperatures rebound to seasonal levels in the mid-upper 50s and partly cloudy skies. Wednesday will likewise be a seasonable day with mild temps near 60.

Light rain is possible Thursday, Friday, and Saturday of next week, but it’s much to early to be certain. GFS model also shows a possible coastal storm for next Tuesday.

NYC Weather Update, Monday Storm – Mar 1, 2014

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Summary

March is coming in like a lion this year (let’s hope it leaves like a lamb), with yet another snow storm to add to our misery here in the NYC area Sunday night into Monday night.

Background

A strong coastal storm that’s currently pummeling California with heavy rain and snow will be transferring its energy and moisture to the aforementioned storm. For California, the rain and snow is a mixed blessing: with a hundred-year drought gripping the region, moisture is welcome; however, so much rain in such a short time window is leading to flash flooding, mudslides, and other headaches. See the video below:

Forecast

Our local NWS forecast office has issued a winter storm watch for Long Island, NYC, and central NJ on south. The latest snow maker will be two waves of low pressure that will travel along the length of an arctic cold front Sunday and Monday. This cold front will across our area during this period, ensuring that the air will be cold enough for all snow during the strongest part of the storm, although precipitation may start off as a rain/snow mix during the day Sunday with highs expected to be in the mid 30s.

The forecast graphic below depicts probabilities of snowfall accumulations at least 6″ or more across the region from 8PM Sunday through 8PM Monday. As you can see, we are right on the cusp of a high confidence zone for more than 6″. As it stands, 6″ seems to be the going number for the areas under the winter storm watch. A slight northward adjustment of the storm track would increase the chances we get more than 8″.

This will be a prolonged weather event – so, moderate snow for a longer time, but less of the heavy snow that we saw with the last storm.

Screen shot 2014-03-01 at 1.50.16 PMOvernight lows on Sunday will be around 20 in the city, and highs Monday will be in the mid 20s, with the cold air flowing in behind the cold front.

Extended Forecast

Things settle down after the storm passes Monday, with mostly clear and dry conditions Tuesday through Thursday. High pressure will dominate, bringing these clear conditions, but also extending the cold snap well into next week as it continues to pump Canadian air into the area. Highs will continue struggling to reach the mid-upper 20s, with overnight lows in the teens at the coast and single digits in the interior.

Interesting note: some of the GFS (Global Forecast System) models are showing the potential development of a strong coastal storm next weekend. Of course, it’s far too early to talk specifics about precipitation type and amounts as this storm may not materialize. The models are fairly consistent in developing a low over the northern Gulf of Mexico, however, a frontal system also develop to be strong enough to push this storm well offshore as it approaches the region.

psu