NASA satellite Moderate Resolution Imaging Spectroradiometer (MODIS) image of the Getty Fire on October 28, 2019, shortly after the fire began. Smoke is visible billowing offshore to the south.
“Extremely critical” fire weather conditions are forecast to impact a large part of Southern California, with the strongest Santa Ana wind event of the year possibly occurring Wednesday before some improvement Friday. Affected areas include the entire Los Angeles metro area, where the Getty Fire continues to burn. Wind gusts at or above 70 mph in higher elevations coupled with very dry air (relative humidity less than 10%) will make it incredibly difficult to make any progress towards containing this fire, and presents a high risk for new fires to start.
Weather Prediction Center surface forecast for 5AM PDT Wednesday
Weather Prediction Center surface forecast for 5PM PDT Thursday
Synoptic Set Up Believe it or not, the strength of the Santa Ana winds will be tied directly to the very cold air mass moving into the Great Basin. A low along the leading edge of this cold air has caused a massive ongoing snowstorm across much of Colorado. Behind this, cold, stable air will move in along with a strong area of high pressure with surface pressures forecast above 1040 mb. At the same time, a coastal low will sweep south along the northern and central CA coast along the leading edge of the colder air accompanying this high pressure. This will set up a tight pressure gradient at the coast favoring strong offshore east-northeast winds, with local forecast offices citing model output of as much as 10-12 mb gradient from Barstow to LAX, over a distance of only 200 miles.
Impacts With the tight pressure gradient forecast above, forecasters are calling for the possibility of gusts in excess of 70 mph in the mountain ranges near the coast with, with lower wind gusts of 35-40 mph at lower elevations. The influx of cold air already less capable of holding moisture that will downslope off coastal ranges and towards the ocean will yield relative humidities of 3-8% (as the air dries further during downsloping due to compressional warming). Santa Ana winds of this magnitude along with such dry conditions easily warrant the Storm Prediction Center designation of extremely critical fire weather.
GFS model output forecast sounding for KLAX at 11AM PDT Wednesday. Note the huge gap between the green dew point line and red environmental temperature line at the surface (5°F dew point, 64°F temperature). This will result in extremely low relative humidity values.
Storm Prediction Center fire weather outlook for Wednesday
Timing Peak potential for winds appears to be during the overnight hours through morning and early afternoon Wednesday. This is the time when the pressure gradient will be maximized. The high pressure referenced above is forecast to weaken overnight into Thursday, while the coastal low should also dissipate. The high pressure is forecast to continue weakening into the weekend, thus ending the most dangerous period of fire weather.
This weekend starts off with fair and dry weather. A storm developing along the Gulf Coast of Texas, tracking north along the Mississippi and Ohio Valleys into the Great Lakes, then east towards our area will bring a prolonged period of steady rain on Sunday. As of 11AM today, National Hurricane Center has designated this storm as Tropical Depression Seventeen. This storm should pull out of the area before the start of next week. Temperatures during this period should be at or above average for this time of the year in the low-mid 60s.
Rest of today – partly sunny to mostly cloudy with a cold front weakening, then stalling and returning north as a warm front. High temperatures in the mid-60s. Overnight lows in the low-50s with decreasing clouds as high pressure builds in.
Weather Prediction Center surface forecast for 8AM Saturday
Saturday – high pressure builds briefly and should give us mostly sunny skies with high temperatures in the mid-60s. Overnight lows in the low-50s with increasing clouds and chances for rain.
Sunday – much like last weekend, a storm with tropical origins will bring rain and lots of moisture to the area. The extratropical remnants of Tropical Depression Seventeen will track north towards the Great Lakes during this period. A warm front attached to it will bring a shield of steady stratiform rain over the area. Mostly cloudy with highs in the upper-60s as winds turn to the south. Steady rain continuing into the early overnight hours until the storm’s trailing cold front finally sweeps through and drier air works in. Lows in the mid-50s.
NAM model output for relative humidity and wind at 850 mb for 5PM Sunday. Note the nearly saturated nature of the lower levels of the atmosphere.
NAM model output for wind at 850 mb for 5PM Sunday. Note the high wind speeds at this level, indicating the presence of an 850 mb low-level jet (LLJ)
NAM model output for precipitable water at 2PM Sunday. Note the high values above 1.50″. This makes sense, given the tropical origins of the storm that will impact us Sunday.
Projected track of Tropical Depression Seventeen
Monday – high pressure and calmer conditions return with highs in the mid-60s and mostly sunny skies. Overnight lows in the mid-50s with mostly cloudy skies.
Sunny and seasonable weather with highs in the mid-60s will be punctuated by the passage of a strong frontal system mid-week. The timing of this frontal passage should bring the bulk of the rain through overnight Tuesday, such that Wednesday ends up still being a nice day. Looking ahead, a second cold front is forecast to move through late in the weekend but is not expected to bring significant rain at this time. Temperatures throughout this forecast period and beyond are looking to be at or above normal in the low-60s/
Rest of today – mostly sunny, with highs in the mid-60s. Overnight lows in the low-50s.
Weather Prediction Center surface forecast for 8PM tonight. We will be wedged between the storm that brought steady rain yesterday to the east and an approaching frontal system with a parent low over the Upper Midwest.
Tuesday – increasing clouds with high temperatures in the low-60s. Rain chances increasing especially later in the day. Bulk of the rain accompanying the cold front should arrive overnight. Overnight lows in the mid-50s.
Wednesday – rain should clear the area. Temperatures expected to rebound back into the mid-60s under sunny skies with some downsloping westerly flow behind the front. Overnight lows in the upper-40s with a cooler, drier airmass working in.
Climate Prediction Center temperature outlook for Oct 26-30. We will be in an area with about equal chances of above or below normal temperatures up to 33% for warmer than normal temperatures.
Thursday – another really nice day with high temperatures in the mid-60s and mostly sunny skies. Overnight lows around 50°F.
Soaking rains from Wednesday’s nor’easter have long since exited east, yet we will continue to feel the impact of this low with windy conditions to start the weekend. As the low continues moving east, an area of high pressure will build in and take its place. Winds will relax and we should enjoy a nice, sunny day for Saturday. Clouds are expected to build back in as a potential extratropical remnant low of what could become Subtropical Storm Nestor this weekend pass south of the region. Temperatures during this period are expected to be at or just below normal in the low-60s with a warm up going into next week.
Rest of today – windy conditions continue as the pressure gradient between a building area of high pressure to the west and the low that brought us rain Wednesday which is now over the Canadian Maritimes. High temperatures around 60°F with partly cloudy skies. Overnight lows expected to be quite cool, in the low-40s with skies looking to clear up and winds dying down – conditions that could lead to some strong radiational cooling.
Weather Prediction Center surface forecast for 8AM Saturday
Saturday – high pressure builds in and gives us a sparkling, sunny, fall day with high temperatures in the low-60s. Overnight lows milder around 50°F.
Sunday – although the extratropical remnants of what could be Subtropical Storm Nestor are forecast to pass well south of the area, this storm is expected to have a broad cloud shield to its north, and some outlying rain bands could even result in a couple scattered rain showers for the area. High temperatures should be similar to Saturday in the low-60s, because even with clouds, overall flow will be from the south. Overnight lows around 50°F again.
GOES satellite imagery of Potential Tropical Cyclone Sixteen
National Hurricane Center’s latest forecast track guidance for this storm
Monday – with this low exiting east, we’ll see more southerly flow ahead of the next incoming storm system. High temperatures should respond by warmingin into the upper-60s with mostly sunny skies. Overnight lows in the mid-50s with mostly cloudy skies.
The week starts off with warm temperatures for this time of year, followed by entry of a cooler airmass. A storm system is forecast to bring rain mid-week. Temperatures will cool even more behind this storm with high temperatures dropping to slightly below normal levels in the low-60s by the end of the week.
Rest of today – mostly sunny, with highs in the low-70s. Overnight lows in the low-50s.
Weather Prediction Center surface forecast for 8PM Tuesday
Tuesday – a dry cold front passes over the region later today, leading to cooler high temperatures in the low-60s for Tuesday on the back of colder northwest winds behind the front. It should be a sunny day. Overnight lows in the low-50s.
Wednesday – a low pressure system over the Great Lakes will track east towards the area. Mostly cloudy skies will prevail with highs warming into the mid-60s due to a shift in winds to the south and southeast. Rain should start to overspread the area later in the afternoon and continue overnight. Overnight lows in the low-50s and even cooler possibly in the upper-40s. A secondary coastal low forming off the Carolina coast will become the primary low as energy transfers from the inland storm.
GFS model output for 1000-500 mb thickness and precipitation valid 2PM Wednesday
GFS model output of the same metrics for 2AM Thursday
Thursday – rain should clear out before the start of the day but winds will be breezy from the northwest. This will bring in cooler air again with high temperatures in the upper-50s and partly sunny skies. Overnight lows around 50°F.
The persistent storm off the Northeast US coast finally starts to move east. This storm has defied the odds, increasing in organization and intensity overnight, and has just been named Subtropical Storm Melissa. We will enjoy a spell of warming temperatures (from the low-60s into the low-70s) and dry weather leading into early next week as the region sits between the exiting storm and another strong low over the interior of North America. A couple of frontal boundaries will pass over, however, these will be starved of meaningful moisture and should not result in any rain.
Rest of today – mostly cloudy with high temperatures in the low-60s. Overnight lows in the low-50s as winds start to shift to the north due to Subtropical Storm Melissa continuing to move to the east.
Satellite imagery of the incipient Subtropical Storm Melissa
Saturday – mostly cloudy with high temperatures warming to around 70°F. Winds will diminish as Subtropical Storm Melissa finally starts moving east. Overnight lows in the low-50s.
NAM model output for 500 mb heights and wind at 2PM Saturday. A significant closed upper-low, largely cut off from westerly steering currents, will be over the Upper Midwest. A slow-moving, strong occluded low will accompany this upper low at the surface. East of this, there will be some slight ridging, keeping our weather fair.
Sunday – a weakening cold front moves through, but with lack of appreciable moisture, there shouldn’t be any rain. High temperatures will be similar to Saturday, around 70°F, with m ore sunshine expected. Overnight lows in the mid-60s.
Weather Prediction Center surface forecast for 8AM Sunday
Monday (Columbus Day) – the cold front that moves through overnight into Sunday is expected to stall and become stationary. A surface low is forecast to form and move along this boundary near the coast, leading to increasing clouds with high temperatures in the low-70s. Overnight with lows dropping into the upper-50s.
A distinct fall feel this week with grey skies the norm and spotty rain chances for many of the days. A coastal storm brewing off the Southeast coast is forecast to track north and then northeast. National Hurricane Center is tracking this system as it has some potential to acquire subtropical characteristics. This will be a slow moving storm that will bring a long period of northeasterly winds to the area.
Rest of today – mostly cloudy, with highs in the upper-60s. Overnight lows in the upper-50s.
Weather Prediction Center surface forecast for 8PM Wednesday
The developing coastal storm depicted above.
Showers and thunderstorms over the western Atlantic between the southeastern coast of the United States and Bermuda are associated with a broad, non-tropical area of low pressure. This system is forecast to move northward or northeastward and could acquire some subtropical characteristics off the east coast of the United States by the end of the week.
Wednesday – although the storm referenced is forecast to remain well offshore, outer rain bands from it could bring showers to the area along with persistent northeast winds. These wind are anticipated to be on the strong side, steadily in the mid-teens with gusts in the 25 mph range. Mostly cloudy with highs around 60°F. Overnight lows in the low-50s.
Thursday – rain chances continue as the storm develops and becomes a closed low. Mostly cloudy with highs in the low-60s. Winds will become blustery from the northeast around 15 mph with higher gusts. This will be due to the increasing pressure gradient between the deepening low and high pressure over eastern Quebec. Overnight lows in the low-50s.
GFS model output of 850 mb winds and relative humidity. The coastal storm continues to spin off the Northeast coast, although its center remains well offshore (just above the pivotalweather logo in this frame).
Friday – rain still lingers though the storm starts to finally make some eastward progress as a trough approaches from the west. High temperature remain in the low-60s with mostly cloudy skies. Overnight lows in the upper-50s as warmer southerly flow starts to work into the region.
This Saturday will likely start off with the coldest overnight low temperatures so far this season for NYC. Strong high pressure will be moving in from the west overnight and during the day, the center of this high pressure will be passing almost directly overhead. As a result, we should see a sunny day with diminishing winds, though high temperatures will be much below normal (69°F) with the day starting off pretty chilly. Quite a contrast between this past Wednesday when we set a new daily record high across the city with temperatures peaking at 92-93°F! Autumn is certainly in the air.
My Forecast High: 61°F | Low: 48°F | Max sustained winds: 14 mph | Total precipitation: 0.00″ – verification will come from METAR data for the period between 2AM Saturday and 2AM Sunday (06Z Saturday to 06Z Sunday) at LGA (LaGuardia Airport), and the KLGA Daily Climate Report.
Verification High: 60°F | Low: 46°F | Max sustained winds: 20 mph | Total precipitation: 0.00″ – Temperature forecast turned out to be pretty good, especially high temperatures. Off by 2°F on low temperatures, which ended up 1°F colder than statistical guidance. I believe this was due to slightly stronger cold air advection than expected leading into the forecast period. Off by 6 mph for max sustained winds, which qualifies as a minor bust. The highest wind speed direction was northeast. Judging by METAR data, winds were coming form this direction sometime between 7-8AM Saturday. I think it’s possible that the pressure gradient was tighter than forecast the day before, which would have resulted in the potential for faster winds like these.
Weather Prediction Center surface forecast for 2PM Saturday
Synoptic Set Up A strong area of high pressure is forecast to be the dominant feature at the surface for much of the Northeast, Mid-Atlantic, and Ohio Valley during the forecast period. The center of this high pressure will be moving east during this time and will be nearly overhead for the hours of peak solar heating tomorrow. This high pressure will be accompanied by a dry airmass throughout nearly the entire atmospheric column. Reference the images below, which show NAM model output of relative humidity and winds at 300 mb, 500 mb, and 850 mb respectively. The brown hues shown indicate very dry conditions.
High Temperatures GFS, NAM, and NBM are in good agreement that tomorrow will be a much below average day in terms of high temperatures. These forecast sources depict high temperatures ranging from 58-62°F, which is 7-11ºF below normal for this time of year. They also show winds that are veering from northerly to east-southeast, which makes sense given the forecast position and track of the high pressure center. Although northeasterly and easterly are onshore wind directions, the near surface layer of the atmosphere is forecast to start off so dry that it would take quite a while for moisture off the ocean to make an impact and produce clouds that could eat into high temperatures. Furthermore, sea surface temperatures at this time are actually ranging in the upper-60s, so onshore flow should actually serve to bring warmer air in. EKDMOS 50th percentile for high temperatures is about 60°F. NAM is a touch cooler at 58°F while GFS and NBM call for 62°F. NAM seems to suggest slightly more cloudiness than GFS. I’m going with a high of 61°F, which I think is a reasonable balance that incorporates the data points above.
Low Temperatures Just as is the case with high temperatures, statistical guidance similarly shows that low temperatures could be as much as 8°F below normal for this time of year. These temperatures are more typical of the end of October. This is a result of decent cold air advection leading into the beginning of the forecast period. Clear and dry conditions should carry though the overnight hours. However, winds should be strong enough so as to limit radiational cooling. EKDMOS has 47°F as the 10th percentile, and 50°F as 50th percentile so going with 48°F seems plausible when considering that statistical guidance is nearly unanimous calling for 47°F as the low.
NAM MOS forecast, initialized at 8AM Friday
GFS MOS forecast, initialized at 2PM Friday
Max Sustained Winds Climatologically, winds during October can be quite strong from the northeast, but easterly to southeasterly winds are typically the weakest. Since the center of the high pressure should be moving overhead during the forecast period, the pressure gradient should be decreasing, leading to diminishing winds. Statistical guidance looks on point calling for peak winds at the beginning of forecast period. Even with a well-mixed layer forecast to form during the afternoon tomorrow, winds aloft will be weak, so wind speeds should be subdued. NBM came in with max wind speeds well below the other statistical guidance at only 6 knots. EKDMOS 50th percentile is about 10 knots, thus a forecast of 12 knots here should be OK.
GFS model forecast sounding for 2PM Saturday
Total Precipitation This is the easiest part of the forecast as strong high pressure and very dry air throughout most of the atmospheric column makes it nearly impossible for precipitation to materialize.
Strong high pressure and sunny weather will be the main theme this weekend. Despite the sun, we do have a chance to see the coldest overnight temperatures so far this season tonight into Saturday. High temperatures start to warm from the 60s to the low-70s by the second half of the weekend and to start next week as the high pressure progresses east and we get warmer southerly return flow before the next storm system approaches Monday.
Rest of today – sunny with high temperatures in the mid-60s. Breezy with a refreshing northerly wind, 15-20 mph with higher gusts due to the relatively tight pressure gradient between the high pressure building moving in from the west and the low that brought us rain yesterday continuing to move offshore. Cold overnight, with lows in the upper-40s. Frost advisories and freeze warnings are up for many areas of upstate New York not too far from us.
850 mb winds as indicated by GFS model for 8AM today, indicating the presence of strong winds of 30-40 knots just above the surface.As the day progresses, the near-surface layer up to 850 mb is forecast to become well-mixed, and this will allow the faster winds above to reach the surface.
Saturday – a sparkling, sunny fall day with high temperatures in the low-60s. Wins will calm also. Overnight lows in the mid-50s with increasing clouds.
Weather Prediction Center surface forecast for 8AM Sunday
Sunday – the cloud shield preceding an incoming storm system will continue moving in Sunday resulting in partly sunny skies. High temperatures will warm to around 70°F as winds turn to the south. This is due to the high pressure exiting east (clockwise flow around this) as well as winds ahead of an approaching cold front. Overnight lows in the low-60s.
Monday – mostly cloudy with chances for rain increasing later in the day. High temperatures in the mid-70s. Heavier rain accompanying the passage of a cold front overnight with lows dropping into the upper-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 October.
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: Due southwest (9%). Note: due northeast is basically co-equal most common wind direction, perhaps only off by a fraction of a percentage point.
Directions that are most and least common: Other most common wind directions include due northeast (9%), due northwest (8.75%), and west-northwest (8.25%). Least common wind directions are east-southeast (1.8%), due southeast (2.75%), and due east (3%).
Direction(s) most likely to produce the fastest winds: Winds of 16.5-21.4 knots are most frequently found coming from due northwest. West-northwest, north-northwest, due northeast, east-northeast, and due south directions can also see less frequent winds over 21.4 knots.
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: October’s wind profile is a continuation on the trend established in September where wind frequencies begin to be distributed more evenly across the compass and less focused in the south. Winds from the northwest quadrant continue to increase in frequency, along with the frequency of the fastest winds coming from these directions. Northeasterly winds still figure prominently, though slightly less so than in September. Curiously, while southerly winds generally decreased in frequency, due southwest winds tick up slightly compared to September.
In general, northwesterly winds bring cooler, drier Canadian air into the region following cold fronts. Northwesterly winds will tend to warm slightly because of compressional warming as they 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.
Northeasterly winds, on the other hand, are often 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. Southwesterly winds are still capable of bringing in oppressive heat, as seen in the temperature section below.
Maximum observed two-minute wind speed for the month: 56 knots (64 mph) – this is the fastest recorded two-minute wind speed for any calendar month.
Temperature and Precipitation Averages/Records
Temperature units are in Fahrenheit and precipitation is in inches.
Worth noting: Even though average high temperatures in October fall into the 60s, it’s still possible to see summer-like warmth – you can see this from the record high of 95°F, set anew in 2019, and that record highs can reach into the mid-80s until late in the month. Overnight lows start to fall into the 50s and end up in the 40s by the end of the month!
