Temperatures cool off after a warm holiday weekend. A frontal boundary will linger in the area this week allowing multiple disturbances to move along it. This will result in multiple chances for rain but with generally mild temperatures except today. Looking into the weekend, it does appear that high pressure takes over and gives us a nice Saturday at the least.
Rest of today – mostly cloudy, temperatures cool, in the upper-60s. Showers early should give way to a period of dry weather, however, stronger showers and thunderstorms could hit later this evening around 8PM ahead of an approaching low sliding along a warm front just to our south. We are just outside Storm Prediction Center’s slight risk area for severe thunderstorms, and these storms should weaken as they near the more stable marine layer, in particular if clouds hold and no sun peaks through. Overnight lows staying steady in the upper-60s.
Weather Prediction Center surface forecast for 8PM Tuesday
Wednesday – a cold front is forecast to push through and allow for some drying out on Wednesday with partly sunny skies. High temperatures should rise into the upper-70s. Dry weather doesn’t last because yet another warm front pushes through later in the evening with more showers and thunderstorms possible. Overnight lows in the low-60s.
Thursday – another impulse of low pressure and warm front moves through the area bringing continued chances for rain. High temperatures in the upper-70s under mostly cloudy skies. Overnight lows again in the low-60s and with more chances for rain.
GFS model output for surface pressure, precipitation, 500 mb thickness at 6AM Friday
Friday – cold front sweeps through and allows for sunny skies to return, this should be a really nice day with high temperatures in the upper-70s. Overnight lows about 60°F.
The long holiday weekend appears to be mainly dry, and even features a day that could make for a good beach getaway. We do have a chance for rain overnight Saturday into Sunday but this shouldn’t be a damper on anyone’s plans. Sunday’s shaping up to be the warmest day of the weekend although Memorial Day itself may end up being the nicest all around day.
Rest of today – breezy and sunny with high temperatures in the mid-70s. The strong pressure gradient between a departing surface low and a high pressure center moving east from the Great Lakes is what’s causing these breezy conditions. Winds should die down overnight as the high moves overhead and the pressure gradient relaxes. Overnight lows in the upper-50s.
Weather Prediction Center surface forecast for 8PM Friday
Saturday – as the high pressure continues moving east, clouds will increase due to the influence of an advancing warm front. This frontal boundary may serve as the focus for some showers and thunderstorms overnight Saturday into Sunday. High temperatures Saturday expected to be in the low-70s due to increasing cloud cover. Overnight lows in low-60s.
GFS model output for surface pressure, precipitation, 500 mb thickness valid 4PM Sunday
Sunday – we’ll be in the warm sector this day. Clouds and rain are expected to subside early and allow for temperatures to warm into the mid-80s and possibly higher. This will be the best day of the weekend to hit the beach though it’s not a lock for sunny weather all day. Overnight lows in the mid-60s.
Monday (Memorial Day) – anticipating this will be the best day of the weekend with sunny skies and mild temperatures in the upper-70s. Overnight lows in the low-60s.
This week kicked off with high temperatures yesterday that were more typical of the mid-summer. Things have cooled off noticeably this morning in the wake of a cold front that brought some showers and thunderstorms to parts of the region last night. The remainder of the week should see temperatures around normal for this time of year, with the next chance for rain Thursday. Looking ahead to Memorial Day weekend, it seems there could be some rain chances especially late Saturday into Sunday.
Rest of today – sunny conditions with high pressure in control today. Fresh northwesterly breezes calming down later in the afternoon. High temperatures in the low-70s. Overnight lows in the mid-50s.
Weather Prediction Center surface forecast for 8AM Wednesday
Wednesday – high pressure remains in place, yielding another great day with lots of sun and seasonable high temperatures in the low-70s. Overnight lows in the upper-50s as a warm front approaches from the southwest.
Thursday – chance for showers, on the light side developing ahead of this approaching warm front. High temperatures in the low-70s with partly sunny skies. Rain chances increase going into the overnight hours as the parent low of the warm front nears, lows in the low-60s.
GFS model output fro surface pressure, 500 mb temperature and height valid 10PM Thursday
Friday – mostly sunny behind Thursday’s quick-moving storm. High temperatures in the mid-70s. Overnight lows around 60°F
This weekend is shaping up to be similar to last weekend in some respects, with Saturday being a nearly ideal day with plenty of sun, while Sunday is cloudier with some chance for rain. The big difference is unlike last weekend, we’re not anticipating a coastal storm or record-breaking cold! In fact, we should see our first 80°F+ day in some time by Monday before a chance for showers and thunderstorms cools things off.
Rest of today – current visible satellite observations show clouds moving in from the west, so the sunny start to the day will give way to mostly cloudy conditions later. Temperatures will be mild with the influence of warm southwesterly winds, topping out in the mid-70s. Later in the evening, a cold front will push through, bringing a chance for scattered showers and possibly a thunderstorm or two. Overnight lows expected in the mid-50s.
Weather Prediction Center surface forecast for 2PM today
Saturday – even though we’ll have a cold front push through, sinking air behind the cold front and downsloping winds from higher terrain in the north should keep things around average for this time of year in the low-70s with mostly sunny skies. Overnight lows continue to be in the mid-50s.
NAM output for 500 mb height and vorticity, valid for 8AM Saturday. A noticeable reversal of the upper air pattern from earlier this week is visible with a deep longwave trough over the Western US, and ridging over the Eastern US. This will result in great weather for us tomorrow, while areas of the Plains downstream of the trough picture above see the potential for severe weather.
Sunday – warm front approaching from the south during the day Sunday will result in more clouds than sun, and perhaps a scattered rain shower. High temperatures still around average for this time of year in the low-70s. Overnight lows warm up into the low-60s as we enter the warm sector of the storm system approaching us from the west that’s expected to bring severe weather to parts of the Central US this weekend.
Monday – with the region forecast to be in the warm sector of the parent low shown below, and a prolonged period of southwesterly surface winds bringing warm air into the area, temperatures are expected to warm up into the low-80s. This day will have a summery feel, with some humidity to the air and a chance for showers and thunderstorms later in the day as a cold front approaches from the west. Overnight lows should remain mild around 60°F.
Weather Prediction Center surface forecast for 8AM Monday
After a very cool, wet start to the week, temperatures should moderate and conditions will gradually improve as we approach the weekend. A pattern change at mid and upper levels is apparent in forecast models going into this weekend. We finally break free of persistent troughing that brought the cold, rainy weather this weekend going into the beginning of this week. Instead, we’ll get to look forward to sunnier, warmer weather more in line with the calendar.
Rest of today – if we don’t reach 55°F, today will be the second day in a row we set a new record low and record low maximum at KLGA. High temperatures are forecast to be in the low-50s with lots of clouds. Needless to say, it’s been quite cold and below average for this time of year. The noreaster that brought us miserable conditions yesterday is steadily moving east. However, a surface trough and moisture is forecast to rotate around its back side as it keeps retreating east. This could result in scattered showers later in the afternoon and evening. Overnight lows are expected to be quite cool again, in the mid-40s.
Weather Prediction Center surface forecast for 2PM today
Wednesday – temperatures should rebound nicely out of the gate as we finally get some clearing skies. High temperatures should reach into the mid-60s. Chance for showers overnight going into Thursday as a cold front approaches from the north. Overnight lows much warmer in the mid-50s.
Thursday – the warm up continues despite cloud cover associated with this approaching cold front. High temperatures expected to touch 70°F for the first time in a while. This passing (and slowing) cold front could continue to touch off a couple showers going into Friday. Overnight lows slightly cooler in the low-50s.
Weather Prediction Center surface forecast for 8AM Thursday
Friday – cooler with high temperatures in the upper-60s and partly sunny skies. Overnight lows into Saturday in the mid-50s. Pattern change is coming with large scale troughing forecast for the western US while a ridge builds east, essentially the opposite of the pattern we’ve had the past few days.
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.
During my time taking classes as part of Penn State University’s Undergraduate Certificate in Weather Forecasting, we were taught that understanding the climatology of the location you are interested in is an important prerequisite for making accurate forecasts. This post continues on this theme, adding a climatology for May.
City Name / Station ID: New York, NY (LaGuardia Airport – KLGA)
Local Geography and Topography
Station Elevation: 10 feet above sea level.
Station Location: LaGuardia Airport (KLGA) is situated on the north shore of Queens along the East River, approximately 6 miles east-northeast of Midtown Manhattan.
KLGA’s location within the broader NYC area, as seen in a Google Maps terrain view
Important Topographical Features: New York City is located in the extreme southeastern corner of New York State, bordering suburban New Jersey and Connecticut. These suburban regions combined with those in Long Island comprise the Greater New York City Metropolitan Area, which is the most populous urban agglomeration in the United States and one of the populous urbanized areas in the world with an estimated population of 18 million. New York City itself sprawls across the coastal plain around the Hudson River estuary. The terminal moraine formed by glaciers of the last Ice Age result in a ridge of higher terrain that cuts a swath from southwest to northeast across the boroughs from northern Staten Island, northern Brooklyn, southwestern through central and northeastern Queens. Otherwise, the city itself is low lying. This ridge varies in height between 200-400 feet, rising sharply from south to north, but tapering more gently north. North and west of the city (about 30-50 miles away), lie significant elevations of the Catskills (north), Poconos (west), Taconics that are part of the broader Appalachian Mountain Range. The elevations of the lower foothills can range from 1000-1500 feet. Some of the elevations in the Poconos and Catskills, west and north of KLGA respectively, peak between 2000-3000 feet. The open expanse of the Atlantic Ocean lies south of KLGA and New York City. Long Island Sound also lies east-northeast. The vast urbanized area of the NYC metropolitan region has significant effects on local microclimates via differential heating (urban heat island effect). KLGA is in a low-lying area sensitive to UHI effects and marine influences.
On winter mornings, ocean temperatures which are warm relative to the land reinforce the effect of the city heat island and low temperatures are often 10-20 degrees lower in the inland suburbs than in the central city. The relatively warm water temperatures also delay the advent of winter snows. Conversely, the lag in warming of water temperatures keeps spring temperatures relatively cool. One year-round measure of the ocean influence is the small average daily variation in temperature.
National Weather Service – NYC Office
Wind Patterns
Below is a wind rose – you can read more about how to interpret this chart here.
Frequency (percentage) of the single most common wind direction: The most common wind direction for this month by frequency of occurrence is due south (~13%).
Directions that are most and least common: Due northeast (11.5%) winds present a second maximum of most frequent winds. The least common wind direction is east-southeast (~2%), followed by due east (~2.25%).
Direction(s) most likely to produce the fastest winds: Due northwest winds have a slim possibility of generating winds over 21.5 knots. No other wind direction seems to have a measurable occurrence of winds exceeding this speed. This is a marked difference from the previous two months when wind speeds of this magnitude were much more common. Winds of 16.5-21.4 knots are most frequently found coming from the west-northwest, due northwest, north-northwest, and due south.
Direction(s) least likely to produce the fastest winds: Due east, east-southeast, and due southeast winds rarely exceed 16.4 knots.
Impacts of wind direction on local weather: The most common wind directions in May differ from the previous two months, with northwesterly winds becoming less frequent, while southerly and northeasterly winds become more prominent. In fact, winds from the southern semicircle are generally more common than previous months. Cold air advection from northwest winds continue to influence temperatures in the wake of cold fronts approaching from the west, however, the effect should be dramatic than in prior spring months. Winds from the northeast can be associated to backdoor cold fronts arriving from the Canadian Maritimes, bringing a moist, cool maritime polar air mass; the advance of coastal Nor’easter type storms; or a warm front approaching from the south. The difference between sea surface temperatures and temperatures over land widens during May as daily normal highs increase. This increases the chances for sea breezes during periods of overall weak synoptic winds, though generally, southerly winds would allow for advection of warmer, more moist airmasses into the area. This would often be the case when the NYC region is in the warm sector of mid-latitude lows, preceding the passage of a typical cold front attached such lows.
Maximum observed two-minute wind speed for the month: 36 (41 mph)
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Worth Noting: Average temperatures climb above 70ºF in May for the first time during the spring months. In 2019, new record lows were set for the 13th and 14th of May, at 42ºF and 44ºF respectively. In 2020, an all-time monthly record low of 36ºF was set on May 9th. In 2021, record lowest max temperatures were set for the 29th and 30th (52ºF, brrr), and record lows were set for the 29th-31st (48ºF, 48ºF, and 50ºF respectively)!
We have a beautiful, sunny start to the week for a change. This will be short-lived though, as a cold front will arrive late Tuesday and bring the first chance for rain this week. More rain arrives later this week with a storm system moving in. Looking ahead to the weekend, we should see a decent Mother’s Day weekend, but chances for rain do show up on Sunday.
Rest of today – mostly sunny, high temperatures in the upper-60s. High pressure in control today will give us a pleasant, spring day, right about average for this time of year. Overnight lows in the low-50s.
Weather Prediction Center surface forecast for 2PM today
Tuesday – most of the day should be dry with high temperatures in the low-70s. Partly cloudy but increasing clouds late as a cold front moves into the area. This frontal boundary will be the focus for any rain that develops in the evening and overnight hours. Overnight lows in the low-50s.
Weather Prediction Center surface forecast for 8PM Tuesday
Wednesday – should have another decent day after the rain moves through overnight. High temperatures in the mid-60s with partly sunny skies. Overnight lows going into Thursday in the low-50s with increasing clouds.
Thursday – mostly cloudy, chance for showers as a warm/stationary front approaches from the south. High temperatures cooler, around 60°F with overnight lows in the mid-50s.
A cool start to the week will lead into a period of extended unsettled weather, with multiple disturbances bringing chances for rain throughout the remainder of the week. During this period, temperatures will remain generally below normal under the influence of these cloudy conditions and rain, though not by much.
Rest of today – increasing clouds with high temperatures rebounding into the upper-50s from a cool start in the mid-40s. The first of several quick-hitting storm systems should move in overnight, bringing generally light precipitation leading into early tomorrow morning. Overnight lows are expected to be warmer in the upper-40s with clouds staving off radiational cooling as occurred overnight into today.
Weather Prediction Center surface forecast for 8AM Tuesday
Tuesday – brief period of dry weather Tuesday as a ridge of high pressure builds in. If more sun than clouds materializes during the afternoon, we could see temperatures nearing 70°F, though temperatures could end up in the low-60s if clouds linger all day. Rain chances increase into the overnight hours with overnight lows near 50°F.
Wednesday – mostly cloudy and cooler with a stationary front setting up near or just south of NYC. This will bring easterly onshore flow and keep temperatures in the mid-50s. As another low develops west of us and slides up along this stationary frontal boundary, rain chances will increase through Wednesday. Overnight lows in the low-50s.
Weather Prediction Center surface forecast for 8AM Thursday
Thursday – temperatures expected to rebound into the mid-60s with the stationary front changing into a warm front and slowly pushing north. Clouds and rain yet again. Mild overnight lows in the low-50s.
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.
