All posts by Lei Zhao

New Meteor Shower (!!) & Memorial Day Weekend Special Weather Update – May 21, 2014

May 21, 2014NYC, Outside of NYC, Rain, Thunderstorms, Weather Update, Weekendastronomy, atlantic ocean, big dipper, camelopardalis, clouds, cold front, comet 209P/LINEAR, comets, high pressure, LINEAR, low pressure, meteor shower, meteorites, new york, night sky, north atlantic, north star, nyc, oberlin, ocean, ohio, omega high, polaris, rain, skywatch, thunderstorms, virginia, warm front, washington dc, weatherLei Zhao

Memorial Day Weekend Forecast

Weather conditions will gradually deteriorate through the course of the day today as an approaching storm system draws closer to our area. Cloud coverage, scattered showers, and possible thunderstorms associated with a warm front should increase in coverage during the course of the day. High temperatures should be on the mild side in the mid-70s.

Thursday – as of now, the National Weather Service calls for the aforementioned warm front to approach but not clear our region by Thursday morning. As such, cooler southeast and easterly winds off the ocean will keep temperatures on the cool side with highs only in the mid-upper 60s. There will be a persistence chance for showers and thunderstorms as multiple impulses of energy ride up and along the frontal system, with a break probably occurring between early Thursday morning and later Thursday afternoon/evening.

Friday – in NYC, although the warm and cold fronts associated with this latest storm are forecast to have cleared through the area by Friday, an upper level low situated over the Canadian Maritimes will continue to allow impulses of energy (shortwaves) to rotate into our area providing the spark for a continued chance of showers and thunderstorms, especially Friday afternoon and evening. This upper low will be slow to move east due to a strong blocking “omega” high pressure center located over the central North Atlantic. High temperatures will again be around the upper 60s.

For Oberlin, conditions will begin to improve earlier with the chance of rain ending by Thursday, partly sunny skies Friday with gradual clearing and highs in the upper 60s.

NAM output simulated radar image for Friday at 2PM EDT

GFS model output of 500 mb heights and absolute vorticity for Friday at 2PM EDT

Saturday – we’ll see an tenuous area of high pressure trying to build in from our west. However, there may still be a marginal chance of PM showers. Otherwise, expect gradually improving conditions with temperatures climbing back up into the low 70s.

Sunday and Monday (Memorial Day) – These will be the best days of the weekend with dry, mostly sunny, and warm conditions. High temperatures will continue to climb into the mid-upper 70s Sunday and possibly topping 80 Monday (this applies to both Oberlin and NYC). Next chance at rain will be Tuesday.

A New and Spectacular May Meteor Shower? – About Comet 209P/LINEAR & Camelopardalis

A friend of mine brought to my attention that a newly discovered and possibly brilliant meteor shower is forecast to take place in the early morning hours of Saturday, May 24th.

In brief, Earth is forecast to pass through the debris trail of a comet “Comet 209P/LINEAR” (discovered in 2004) during the overnight hours Friday into Saturday. Researchers are forecasting that the debris trail Earth passes through is one that has accumulated dust from as early as 1800 to 1924. As such, expectations are that we could see about an average of 200-400 meteors an hour (some estimates call for a meteor storm of 1000 meteors an hour!), i.e. between about 3-7 meteors per minute. Furthermore, the setup for this event is such that Southern Canada and the East Coast of the U.S. are ideally positioned to view this event. In the image below, the red line represents the forecast position of the radiant line (point from which meteors appear to emanate and where you would see the highest number of meteors), note that this line runs almost direct over Washington DC. Also, notice that the moon is in waxing gibbous phase, reducing its potential to overpower the meteor shower.

Timing and Visibility

The forecast zenith of this meteor shower is between 2AM-4AM Eastern Daylight Savings Time on Saturday, May 24th. Right now, the forecast for this time window calls for mostly cloudy skies over NYC as well as points east and north (i.e. New England). Partly cloudy skies are forecast the points further south and west (i.e. along the Jersey Shore, Washington DC/Northern, Eastern Virginia, Western Pennsylvania), with the best viewing conditions being in the DC metro area and Eastern Virginia where mostly clear skies are forecast. A word of caution: cloud cover forecasts even this close to the day of are notoriously difficult to pin down due to the fact that even small changes in initial conditions can lead to large shifts in a forecast. However, with high pressure building over the east coast throughout the course of the weekend, we should have generally good chances to view this shower.

My recommendation is that you go check this out in an area with minimal light pollution if you can. I think we’re in for a what I hope will be a good show!

Where to Look

The radiant point for this forecast meteor shower will be situated in the relatively obscure constellation Camelopardalis (named by the Romans for a hybrid animal that looks like both a camel and leopard, now known as a giraffe). As you’ll see below, this constellation is located slightly below the North Star (Polaris), and a bit to the right of the Big Dipper.

You can read a more in-depth analysis of this meteor shower here. I’ve grabbed and edited a couple images from this entry.

NYC Weather Update | First Look @ Memorial Day Weekend – May 19, 2014

May 19, 2014NYC, Outside of NYC, Rain, Storms, Thunderstorms, Weather Update, Weekendhigh pressure, low pressure, memorial day, nyc, oberlin, ohio, thunderstorms, warm front, weather, wxLei Zhao

All preliminary indications are that this Memorial Day weekend should see fairly good weather, as you can read in the detailed discussion below. First, for your work week forecast:

For the remainder of the day today, there is a slight chance of a pop up shower or thunderstorm as cumulus clouds continue to build. This risk will cease as the sun begins to go down, and cuts off the heat source for these clouds. Overnight lows will fall into the low 50s in the city (not as cold as last night, as some clouds are expected to stick around early and stunt the potential for good radiational cooling), with 40s in the interior.

Tuesday will be the best day of the week, with high pressure briefly building in from the west. This will lead to mostly clear skies and warm temperatures in the upper 70s (also partially due to an incoming warm front).

Beginning Wednesday, we will see a period of unsettled weather as a relatively slow moving storm system approaches. This system will develop over the Great Lakes, and a warm front is forecast to be approaching our area during the day Wednesday. There will be an increasing chance of showers throughout the day as the warm front nears, with the best chance for precipitation in the late evening and overnight hours. Temperatures will be slightly lower than Tuesday in the mid-70s.

HPC's Day 3 forecast for the US — HPC’s Day 3 forecast for the US

Thursday there is a bit of uncertainty regarding the eastward progression of the warm front mentioned above. If the warm front has already passed over us, then we’ll be in the warm sector between the warm front and approaching cold front. This would lead to favorable conditions for some thunderstorms. Otherwise, we would expect mostly cloudy skies and a chance for more showery precipitation. High temperatures will be similar to Wednesday.

Friday, with the cold front Thursday having moved through and high pressure slowly building in, we would expect a good day weather-wise. However, as you see in the following image, the center of the now occluded low pressure is forecast to remain nearly stationary off the coast of New England. This is due to a blocking high over the North Atlantic (not pictured). Therefore, a chance of showers is forecast for both Friday and Saturday, with skies gradually clearing from mostly cloudy to mostly sunny Saturday. High temperatures Friday is forecast to be in the low 70s.

Now, the all important initial weekend forecast: as depicted above, high pressure building over the Great Lakes should progress generally southeast towards the Carolinas during the weekend. This should translate into improving weather each day during the weekend and increasing temperatures. Saturday, Sunday, and Monday should see high temperatures climbing from the low to mid 70s, and skies clearing to become mostly sunny.

For those of you reading this forecast who are traveling towards Oberlin and points west, the forecast for those parts is actually even better than for New York City in terms of sunshine, although, as you know temperatures will be slightly cooler in Ohio than here.

NYC Weekend Weather Update – May 16, 2014

May 16, 2014Flooding, NYC, Rain, Thunderstorms, Weather Update, Weekendbk half, brooklyn half, brooklyn half marathon, flash flood, flooding, friday, nyc, nyrr, rain, weather, weekend, wxLei Zhao

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.

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

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.

NYC Weather Update & BK Half Marathon – May 14, 2014

May 14, 2014Flooding, NYC, Rain, Storms, Thunderstorms, Weather Update, Weekendbk half, brooklyn, brooklyn half marathon, gfs, nam, nyc, nyrr, rain, thunderstorms, tstorms, weather, weekend, wxLei Zhao

We’ve been fortunate that a persistent high pressure off of Nova Scotia has been stalling the arrive of a storm system earlier forecast to bring showers during the midweek period.

Our luck is about to run out, however, as the low pressure center and associated frontal boundaries will finally make their approach over the NYC area.

Thursday – overnight, a warm front is projected to pass through our area, bringing along a chance of drizzle, and the possibility for dense fog tomorrow morning as lower levels of the atmosphere become saturated with the coming southerly flow. Once the warm front passes over us, we will see a noticeable increase in temperatures, with highs forecast to be in the mid-upper 70s and possibly low 80s in interior portions of the region. Although the probability is low, there could be a couple showers and stray thunderstorms as well.

Friday – as the cold front associated with the low pressure center below draws closer, chance of precipitation will increase steadily during the course of the day. To start off, lighter showery precipitation should move in during the morning and early afternoon hours. Thereafter, heavier precipitation, and possibly thunderstorms, will move in especially during the evening and overnight hours. Due to the ground being somewhat saturated from the last round of rain we got, there could be some flash flooding in the heaviest down pours. Temperatures will be a bit cooler than Thursday in the upper 60s to around 70.

L and H correspond to approximate locations of surface low and high pressure centers. Notice the strength (high amplitude) of the associated upper trough and ridge

Saturday (BK Half Marathon Race Day) – good news for you runners out there as it appears the weather will cooperate for race day. The pesky slow-moving frontal boundary responsible for the rain on Friday will finally clear the area early Saturday morning, just in time for the start of the race. There may be some light showers early, but once the front clears conditions should start to improve. I would estimate start time temperature to be in the low 60s, with a high temperature forecast to be in the low 70s.

Simulated radar image from the North American Model (NAM) for Saturday at 8AM EDT

Sunday – a return to nice weather as the cold front has passed through and high pressure builds in temporarily. Partly cloudy with a high in the low 70s.

NYC Weather Update – May 11, 2014 – BK Half Marathon

May 11, 2014NYC, Rain, Thunderstorms, Weather Updatebrooklyn, brooklyn half marathon, new york road runners, nyc, nyrr, weather, wxLei Zhao

Hey folks, I got a special request to provide an weather analysis for the Brooklyn Half Marathon, which is scheduled for next Saturday, May 17th. A friend at the Road Runners informs me there are also pre-race activities going on at Brooklyn Bridge Park Pier 2 starting Wednesday.

Synopsis

First, in brief, I believe that Race Day itself should be dry, perhaps with a slight chance of showers but later in the day (as per the National Weather Service’s current forecast). Unfortunately, the mid-week pre-race activities won’t be quite as lucky as I’ll explain shortly. It is also worth noting that 6 days out, this forecast can still change, but I’ll be posting again Wednesday with a more up to date analysis.

Your Week

Moms are going to be thrilled that Mother’s Day today will be a spectacular day weather-wise. Subsequent to the passage of the cold front last night, today will feature clear conditions with warm temperatures in the upper 70s to low 80s and comfortable humidity.

Monday will be another nice day with summer like weather, temperatures right around 80 and increasing humidity due to the influence of the Bermuda High (which slowly shifts westward through the course of the spring into the summer, when it begins to dominate our weather with hot, humid air blasting from the southwest).

Tuesday a nearly stationary front will slowly push into our area, sparking the potential for some thunderstorms Monday night, and periods of showers during the day Tuesday (around 30% chance each of the following 3 days). Temperatures will be much cooler than Monday only in the low 70s.

Wednesday the stationary front above turns into a backdoor cold front (retrograde, progressing from east to west as opposed to the general pattern of west to east), continuing the potential for unsettled weather with periods of showers and a cooler day in the mid 60s.

Thursday brings another day of unsettled weather, with a series of weak impulses moving along a nearly stationary cold front just to our west. Temperatures will be slightly higher in the upper 60s.

Friday is the last day we’re stuck in this pattern of unsettled weather. The reason behind this prolonged period of unpleasant weather is the strong ridge of high pressure you see off the coast of Nova Scotia in the following upper air forecast from the Global Forecast Model. This strong high pressure will set up a blocking pattern on the trough of low pressure depicted. As this trough finally passes through our area, the best chance for steady showers and thunderstorms this week will occur. Temperatures will range in the mid-upper 60s.

Screen Shot 2014-05-11 at 10.01.29 AM — Note the strong ridge that corresponds to an area of high pressure, and the trough that denotes low pressure to the west of the high

Saturday (Race Day) – at this stage, models seem to suggest that the cold front and low pressure system will have cleared New York just around start time on Saturday. Clouds should diminish during the day as the frontal boundary pulls away, however, can’t rule out a few spot showers lingering.

NYC Nowcast – May 10, 2014 @ 5:05PM EDT

May 10, 2014Nowcast, NYC, Rain, Storms, Thunderstorms, WeekendLei Zhao

NYC Nowcast – May 10 @ 2:40PM EST

May 10, 2014Nowcast, NYC, Rain, Severe Weather, Thunderstorms, Weather Update, Weekendcold front, nowcast, nyc, thunder, thunderstorms, tstorms, warm, warm sector, weather, wxLei Zhao

A batch of strong showers with some rumbles of thunder is approaching the NYC area. For the remainder of the afternoon and evening, strong to possibly marginally severe thunderstorms may pass through ahead of an advancing cold front. Damaging wind gusts and small hail are the primary threats.

Otherwise, expect broken clouds to cloudy skies and nice warm afternoon in the upper 70s to low 80s across the area. A line of thunderstorms is likely to fire up again later this afternoon into the evening hours as the cold front actually approaches.

Atmospheric instability is continuing to increase as we are in the warm sector ahead of the advancing cold front. Low level lapse rates and shear profiles are marginally conducive to the growth of some strong to severe thunderstorms.

NYC Weather Update – May 8, 2014

May 8, 2014NYC, Rain, Storms, Thunderstorms, Weather Update, Weekendgfs, mothers day, nyc, rain, thunderstorms, weather, wxLei Zhao

We have a similar setup as last week that’s bringing overcast and rainy conditions to the region. A warm front well to our south is causing southeasterly/easterly winds off the cold Atlantic to stream in and saturate the atmosphere. Today, temperatures will be cooler with highs in the upper 50s.

Another mature cyclone with areas of precipitation and associated frontal boundaries

Unsettled weather conditions will continue Friday with the approach and passage of the aforementioned warm front. Temperatures will be warmer in the upper 60s, with a chance for showers and thunderstorms throughout the day.

Saturday looks like a warmer copy of Friday, again with the chance for showers and thunderstorms during the day and with increasing chance for precipitation in the evening/night hours as the cold front depicted above makes its way through. High temperatures will be in the mid 70s despite the cloud cover.

Sunday should be the best day of the weekend (just in time for Mother’s Day), with the frontal boundaries having passed over, skies should clear and allow for temperatures to top out near 80 in the city.

Monday the period of good weather continues to start the next work week, with high temperatures again possibly hitting 80 and mostly sunny skies.

NYC Weekend Weather – May 2, 2014

May 2, 2014NYC, Outside of NYC, Rain, Severe Weather, Thunderstorms, Tornadoes, Weather Update, Weekendnyc, rain, severe weather, spring, thunderstorms, tornado outbreak, warm, weather, weather update, weekend, wxLei Zhao

It’s been a wild weather week that started with a tornado outbreak across half a dozen states in the South, and torrential rain fall that dropped as much as 2 feet in Florida, and as much as 6-8″ across the Northeast (resulting in incredible scenes like this landslide in Baltimore).

Fortunately, the weather has taken a turn for the better and will remain that way much of the coming week. This weekend is shaping up to be a nice one with temperatures on Saturday and Sunday reaching into the upper 60s to the low 70s across the region. There is a chance on both days of popup showers or thunderstorms in the afternoon, especially in inland areas with better daytime heating.

GFS model output for this coming Wednesday. Note the strong trough out west (dip in the contour lines), and a ridge over our region (bulge towards the north of contour lines) — GFS model upper air (500mb absolute vorticity) output for this coming Wednesday. Note the strong trough out west (dip in the contour lines), and a ridge over our region (bulge towards the north of contour lines). Ridges correspond with high pressure and good weather while troughs denote low pressure and poor weather.

We’re finally turning the corner on warmer spring temperatures as the start to next week Monday-Wednesday will continue to feature high temperatures consistently in the low-mid 60s (about average). Dry and mostly sunny skies should also predominate as a ridge of high pressure (see above) builds in over our region.

NYC Weather Update – Apr 30, 2014

April 30, 2014Flooding, NYC, Rain, Storms, Thunderstorms, Weather Update, Weekendcold front, flooding, heavy rain, low pressure, nyc, rain, thunderstorms, warm front, weatherLei Zhao

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:

A warm front delineates a boundary where the airmass behind the front is significantly warmer than the airmass ahead of it.
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.

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.

LZ | Weather

Weather updates & posts for NYC region