We’ll enjoy a prolonged period of calm weather that should take us through the week of Christmas. Temperatures should warm from below average in the 30s to above average near 50°F by the start of next week. The above average temperature trend looks like it will extend through the week. No white Christmas this year. I’ll be taking some time off and won’t have another update until closer to the new year unless something significant shapes up.
Rest of today – clear conditions with high temperatures already peaking around the low-30s. Overnight lows in the low-20s with an Arctic air mass still hanging around.
Weather Prediction Center surface forecast for 7AM Saturday
Saturday – the high pressure responsible for the cold, but calm and sunny conditions progresses east and return flow should start taking hold, with winds veering south later in the day. High temperatures should be similar to today in the low-30s. Overnight lows will be warmer than tonight in the upper-20s with milder westerly downsloping flow.
Sunday – high temperatures continue to climb into the mid-40s as more southwesterly flow takes hold. Overnight lows likewise continue a warming trend to about the freezing mark.
GFS model output for 500 mb vorticity, wind and heights valid 6AM Tuesday, showing a flat, zonal flow set up
Climate Prediction Center temperature outlook for December 25-29, calling for warmer than average temps over much of the Eastern US.
Monday– the warming continues with high temperatures forecast in the upper-40s to near 50°F. Overnight lows in the mid-30s.
Next week, it appears that we’ll be in a mostly zonal (flat westerly flow) regime at the upper-levels. That should help keep things calm and uneventful.
A soggy and messy start to the week will give way to a blast of Arctic air, leading to an extended period of below normal high temperatures only in the 30s for the most part. Temperatures do look to rebound over the weekend towards more seasonable levels. The next chance for precipitation happens Wednesday as an arctic front, harbinger of these much colder temperatures, crosses the area and brings possible snow squalls.
Rest of today – periods of rain during the day with high temperatures in the mid-30s. Rain tapers off and ends early this evening as the low pressure responsible for the stormy conditions moves off to the east. Overnight lows drop to around 30°F.
GFS model 500 mb height anomalies for Wednesday at 7PM, note the strong negative height anomaly over the Northeastern US and St. Lawrence Valley
Wednesday – should be a mostly sunny day, though as an arctic front hits us late in the day and in the early evening, a few snow squalls/snow bands could hit. These would be brief in nature but could impinge on visibility, making travel difficult. High temperatures should be similar to today in the mid-30s. Overnight lows will plummet quickly into the upper-teens with an Arctic air mass and northwesterly flow.
Thursday – northwesterly flow continues as strong Arctic high pressure builds. This will keep temperatures only in the upper-20s for highs under mostly sunny skies. Overnight lows in the low-20s.
Weather Prediction Center surface forecast for 7AM Friday
Friday – temperatures moderate a little bit, with highs in the low-30s as the high starts moving east. Overnight lows in the low-20s.
Mild temperatures in the mid-50s are on the way along with long duration drenching rains to start the weekend. Rain tapers off Saturday evening and conditions improve Sunday with a return to more seasonable temperatures in the 40s. A chance of wintry mix or snow is possible late Monday.
Rest of today – mostly cloudy with chances for rain increasing by the afternoon. Steady rain expected overnight. High temperatures around 50°F. Temperatures actually rise overnight with southeasterly onshore flow aiding warm advection.
NAM 2-meter temperature and 10-meter winds at 11PM Friday
NAM precipitable water for 7AM Saturday
Saturday – rain continues through the day Saturday with high temperatures peaking in the mid-50s as a warm front passes and persistent onshore flow from the southeast, backing briefly to the northeast then veering south continuously advects warmer air off the ocean to the area. Overnight lows are a different picture dropping into low-40s as winds turn to the west behind a cold front.
Sunday – as the parent low bringing this rain moves north of the area and continues gathering strength, winds will pick up from the west. This will bring cooler air to the area resulting in highs in the mid-40s under partly sunny skies. Overnight lows continue a cooling trend to about the freezing mark.
Weather Prediction Center surface forecast for 7AM Sunday
Monday– another storm system will impact the area starting late in the day. Temperatures will be cold, topping out in the mid-30s. Precipitation starting late on Monday should begin as snow or a wintry mix given the currently forecast temperature profile. As is the case going into Saturday, a change in wind direction accompanying a warm front should help temperatures actually rise overnight into the upper-30s, allowing precipitation to transition to rain.
Very mild air at the start of the week gives way to a much colder air mass as a cold front finally sweeps through later today. Drenching rains from yesterday should give way to lighter precipitation today, however, with temperatures dropping we could see some light accumulating snow by Wednesday morning. Temperatures will rebound into normal to above normal ranges after a dip into high temperatures in the 30s mid-week.
Rest of today – mostly cloudy with high temperatures peaking in the upper-50s. Long duration southerly flow ahead of an slow moving cold front has brought in a much warmer air mass to the region. Rain chances pick up in the afternoon with the front nearing and continues into the overnight hours with a couple breaks. Behind this front, much colder air rushes in with overnight lows dropping to near freezing. With precipitation continuing, this should allow for a transition to all snow. Light accumulation of around 1″ is possible, though not a lock since the ground has been quite warm for a couple days now with all the rain.
Weather Prediction Center probabilistic forecast for 1″+ accumulation of snow by 7AM Wednesday
Wednesday – snow winding down in the morning. High temperatures in the upper-30s, about 10°F below normal for this time of year. Skies clearing later in the day with overnight lows in the mid-20s.
Thursday – with a chilly start to the day, high temperatures will have a tough time getting out of the low-30s. Mostly sunny otherwise. Overnight lows in the upper-20s.
Friday – high pressure that fills in behind the cold front passing Tuesday and giving us the sunny weather Thursday eventually moves off to the northeast. Onshore flow should help moderate highs into the upper-40s. Rain chances increase with the next storm system – a possible coastal low – moving up overnight. Overnight lows in the mid-40s.
An arctic front swings through today, bringing a blast of cold air behind it going into the weekend. Temperatures will rebound dramatically going into the start of next week with an approaching storm system turning winds to the south. We’ll see high temperatures going from the upper-30s to the mid-50s by Monday.
Rest of today – mostly cloudy with a high temperature in the upper-40s. Chance of rain this evening with the passage of an arctic front. Overnight lows cooling into the low-30s with clearing skies.
Weather Prediction Center surface forecast for 7AM Saturday
Saturday – high pressure builds behind the arctic front bringing sunny skies but a much colder polar airmass with high temperatures struggling to hit 40ºF. Overnight lows drop into the mid-20s.
Sunday – high pressure center moves off to the east, allowing for warmer return flow from the south. This should allow temperatures to be a touch warmer than Saturday, in the low-40s. Overnight lows are expected to bottom out around 40ºF before actually rising due to an incoming storm system turning winds to the south.
GFS model output for 1PM Monday, a low-level jet at 850 mb with winds in excess of 40 knots is evident, along with pretty high values of relative humidity.
Monday– high temperatures continue to climb into the mid-50s with deep layer south-southwesterly winds. Increasing chances for rain as a cold front approaches from the west. Heavy rain is possible given a possible tropical moisture connection. Overnight lows barely moving into the low-50s.
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 December.
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: West-northwest (13.75%).
Directions that are most and least common: Other most common wind directions include due northwest (13.5%), due west (11%), and due southwest (8%). Least common wind directions are east-southeast (1%), due southeast (1.25%), and south-southeast (1.5%).
Direction(s) most likely to produce the fastest winds: As is the case with November, winds in excess of 21.4 knots (~25 mph) are most frequently found coming from due northwest. West-northwest, north-northwest, due northeast winds can also produce winds over 21.4 knots though less frequently.
Direction(s) least likely to produce the fastest winds: As is the case with several other months, the least common wind directions of due east, east-southeast, and due southeast also rarely seen winds in excess of 16.4 knots.
Impacts of wind direction on local weather: December’s winds build on a pattern first seen in November, where winds from the northwestern quadrant become prominent. In December, winds from due west to northwest become markedly more common, while the frequency of winds from the southwesterly quadrant continues to decrease. In addition, the frequency of winds in excess of ~25 mph (21.4 knots) from the northwesterly quadrant also increases.
Northwesterly winds bring cooler, drier Canadian air into the region following cold fronts. Winds from this direction also occur on the backside of departing coastal lows. Winds from these directions downslope coming off the higher terrain of the Catskills, and Poconos outside of the city. This can sometimes lead to warmer temperatures than would normally be expected for this wind direction as well as faster wind speeds. As with other months, northeasterly winds are usually related to backdoor cold fronts sweeping from the Canadian Maritimes, the onshore flow ahead of an advancing warm front, or a passing coastal storm to the south.
Maximum observed two-minute wind speed for the month: 38 knots (44 mph).
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Worth noting: December average high temperatures drop into the 40s. It’s the first month of the winter where record lows have historically dipped below 0°F at times.
A quiet, though colder than normal week lies ahead after the departure of Monday’s storm. This storm ended up not bringing the city much of any accumulating snow, though the story was quite different further north. High pressure settles in briefly before a weaker disturbance affects the area later in the week. An arctic front passes Friday, bringing a reinforcing shot of cold. Temperatures during this time will range in the low-40s.
Rest of today – mostly sunny with high temperatures in the low-40s. Winds diminishing as the low that hit us yesterday continues to pull away to the northeast. Overnight lows around the freezing mark.
Weather Prediction Center surface forecast for 7PM Wednesday
Wednesday – partly sunny with high temperatures in the low-40s. Overnight lows in the mid-30s.
Thursday – mostly sunny with high temperatures in the low-40s, and overnight lows in the low-30s.
Climate Prediction Center temperature outlook for next week. A warm up is coming after this week of below normal cold.
Friday – mostly sunny with high temperatures in the low-40s and overnight lows in the mid-20s behind the passage of a dry Arctic front.
Thanksgiving week starts off with warmer than average temperatures largely in the mid-50s ahead of an approaching storm that should impact the area Wednesday. Behind this storm, temperatures are forecast to drop back into the 40s. Thanksgiving Day will be dry, however, the low responsible for the mid-week storm will deepen as it exits the region, resulting in winds possibly strong enough to ground the Macy’s Thanksgiving Day Parade balloons.
Rest of today – partly sunny with high temperatures in the low-50s. Overnight lows heading down into the low-40s with mostly clear skies overnight.
GFS model 500 mb height anomalies, showing positive anomalies over much of the Northeast on Tuesday
Tuesday – southwesterly flow ahead of an approaching cold front/storm system should allow temperatures to warm into the mid-50s. Overnight lows in the mid-40s.
Wednesday – cloudy with high temperatures in the mid-50s. Chance of showers during the day and into the early overnight hours. Decreasing clouds overnight, with lows in the mid-40s and increasing winds.
GFS model output for 1000-500 mb heights, surface pressure, and precipitation
Thursday – mostly sunny with high temperatures around 50°F, winds should be quite breezy with a tight pressure gradient forming around the deepening and exiting low pressure center. Overnight lows in the mid-30s.
Thursday will probably end up being the best day of the week. High pressure will be in control from most of the period allowing for a sunny day with seasonable temperatures. Winds may be stiff overnight as well as late Thursday night into Friday. Rain associated with a low pressure system moving in will hold off until Friday.
My Forecast High: 50°F | Low: 38°F | Max sustained winds: 20 mph | Total precipitation: 0.00″ – verification will come from METAR data for the period between 1AM Thursday and 1AM Friday (06Z Thursday to 06Z Friday) at LGA (LaGuardia Airport), and the KLGA Daily Climate Report.
Verification High: 53°F | Low: 39°F | Max sustained winds: 14 mph | Total precipitation: 0.00″ – high temperatures ended up being a bit warmer than expected, more towards the EKDMOS 90th percentile range. I think this had to do with the fact that overnight lows were warmer (did a good job edging up on that), and because northwesterly winds backing to the west introduced an element of downsloping. Compressional warming from this was not offset by any other temperature advection, and allowed for temperatures to hit exactly the average high for this time of year. The other aspect I missed on was max wind speed. Here, looking at surface analyses from yesterday compared to the forecast models, there was a larger distance between the center of high pressure and the departing coastal low, leading to a weaker than expected pressure gradient early. The fastest winds ended up being clocked from the southwest as a result, ahead of the approaching cold front.
Weather Prediction Surface forecast for 7AM Thursday
Synoptic Set Up The forecast period starts with a north-south elongated high pressure over much of the Eastern US, centered over the Ohio Valley. The coastal low that impacted the area Monday is still forecast to linger southeast of Nova Scotia. A decent pressure gradient will be in place at the beginning of the forecast period as a result (high pressure measuring ~1025 mb, low ~998 mb). An approaching low pressure center will travel northeast from the Midwest across the Great Lakes into Southwestern Quebec during the forecast period. The low will continue intensifying and will erode the northern part of the high pressure center. Precipitation associated with this low won’t reach NYC until Friday, though. The primary influence of this low for the forecast period will be in shifting winds from the northwest to the southwest.
Above the surface, at 850 mb winds are forecast to start off northerly, between 20-25 knots. Wind speeds ease as they continue backing from north to west, then pick up in intensity to 30 knots from the southwest. Dry air, though moistening, will prevail at the 850 mb level throughout the forecast period. At 500 mb, slight ridging takes place during the day, then increased vorticity starts to pivot through ahead of the primary shortwave axis associated with the maturing surface low over the Great Lakes. Finally, at 300 mb we’ll start in the entrance region of a jet streak, then followed by a period of calm before the exit region of another jet streak approaches from the west.
GFS 2-meter (surface temperatures) in contours, and 10-meter wind barbs, valid 1AM Thursday. This shows a decent environment for cold air advection with winds at almost perpendicular angles to the temperature contours, pointing from colder to warmer temperatures. However, wind speeds are modest so the strength of an CAA would not be strong.
By 1AM Friday, GFS 850 mb height, moisture, and winds show depict winds shifting to the southwest, but the air above the surface will still be quite dry.
High Temperatures Statistical models (GFS, NAM, NBM) are good agreement, within a degree or two of 50°F. EKDMOS at 12Z similarly showed a tight band around 50°F, though this widened a bit at 18Z. 50°F is just a touch below climatological norms. I’m not seeing too many surprises here. Moisture is lacking for clouds to form until late in the period after the sun goes down. As winds shift to the southwest later in the day, they will largely parallel local isotherms so there won’t be appreciable warm air advection to look at either. I think 50°F is a good bet here.
Low Temperatures Stiff winds from the northwest will offset relatively clear conditions in terms of radiational cooling. Cold air advection (CAA) is looking modest. While the wind direction is looking to cut at almost perpendicularly across temperature contours from cold to warmer temperatures, wind speeds aren’t going to be sustained at strong speeds for too long. I think 38°F is reasonable because statistical guidance is only a degree cooler or so, with EKDMOS showing this temperature at about the 50th percentile.
GFS MOS forecast
NAM MOS forecast
Max Sustained Winds 850 mb winds have two peaks and so do surface winds in EKDMOS: one early, then one late in the forecast period. I tend to concur the fastest winds will come early in the forecast period, since northwest winds are climatologically favored to produce fast high speeds. However, I also don’t see evidence to support mixing of strong winds aloft down to the surface. One wrinkle is if the pressure gradient ends up being tighter between the lows and the high pressure, as that would drive stronger than anticipated winds. 20 mph is above statistical guidance, but not that much higher.
NAM forecast sounding for KLGA valid 7PM Thursday. Distinct moistening of the mid and upper levels is evident with the dew points (green line) nearly overlapping the environmental temperature (red line). Lower levels are still markedly drier.
Total Precipitation This is the easiest part of the forecast as strong high pressure and dry air throughout most of the atmospheric column for most of the day makes it nearly impossible for precipitation to materialize.
Spells of rain will bookend what should otherwise be a pleasant week of mostly dry weather. Temperatures will trend slightly below normal for this time of year, however, we will avoid any dramatic swings in temperature. Record cold will not be on the table either. All in all, it should shape up to be a fairly typical mid-November week.
Rest of today – windy, mostly cloudy, with chances for scattered rain showers as a slow moving coastal low continues spinning off of the coast of New England. High temperatures should only hit the mid-40s with the cooling influence of clouds and persistently northeasterly flow. Chances for rain continue overnight with lows dropping into the upper-30s.
Weather Prediction Center surface forecast for 7PM Monday
Tuesday – rain chances should finally end as the coastal low affecting us finally pulls away to the northeast. Clouds should break up leading to a decent day with high temperatures in the low-50s. Overnight lows should be around 40°F.
Wednesday – partly sunny with highs around 50°F. Overnight lows in the mid-30s.
GFS 500 mb height, relative vorticity for 1PM Friday. We can see a distinct shortwave trough approaching from the west. Enhanced vorticity around the base of this trough should help touch of some precipitation at the surface as a cold front sweeps through.
Thursday – best day of the week with high pressure briefly building in. High temperatures again around 50°F, with overnight lows in the mid-40s.
