Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Record-Challenging Warmth on Halloween.. and Election Day? *

7:00 p.m. Tuesday, October 29, 2024:

All four weekends this month ended up featuring lots of sunshine, no rain, and rather comfortable conditions. Despite cooler weather on Sunday with highs in the mid-to-upper 50s, an area of high pressure over the Commonwealth promoted sunshine and light winds. Due to the clear skies, light winds, and very dry air mass in place, temperatures "tanked" quickly Sunday night, and the first widespread freeze of the season occurred early Monday morning with lows in the upper 20s to low 30s across northern MD and the Lower Susquehanna Valley (see below). However, temperatures rebounded quickly after sunrise and topped out in the low-to-mid 60s Monday afternoon. On the backside of the high pressure system, winds turned southerly today and boosted highs back into the mid-to-upper 60s.. about 5-10°F above average for late October.. after a seasonably chilly start. 

A warm front will move through the mid-Atlantic States from southwest-to-northeast tonight, but any brief showers will remain north and east of Pennsylvania. Behind the front, southwesterly winds will usher unseasonably warm air into the Commonwealth on Wednesday and Thursday. Low temperatures will still drop into the mid-to-upper 40s tonight and low-to-mid 50s Wednesday night, but the mercury will be "off to the races" by 9 or 10 a.m. each morning. In fact, high temperatures will be around 15-20°F above normal both afternoons, or generally in the upper 70s to low 80s. At Millersville, the October 31st record high of 81°F from 1946 should be challenged or tied on Halloween. The odds are low, but a new record high could even be set with enough sunshine throughout the day. How thick and persistent a layer of cirrus clouds are on Thursday will ultimately play a key role in determining the eventual high temperature. Regardless of the exact outcome, this Halloween will undoubtedly rank among the top 3 warmest on record.. not only at Millersville but also across much of central PA. Temperatures will still be in the upper 60s to low 70s for trick-or-treating festivities, so light costumes will feel far more comfortable than heavier ones this year. A massive ridge, or northward bulge in the Jet Stream, will flare up along the Eastern Seaboard over the next 48 hours in response to a deep trough across the West (see below). This ridge will be the culprit for the unusual warmth and take until later Friday into Saturday to break down. 

The persistent, southwesterly flow will also direct more humid air into the mid-Atlantic States. As a result, dewpoints should reach the low 50s by tomorrow afternoon and max out in the mid-to-upper 50s later Thursday through early Friday morning. Despite the uptick in moisture, only a few scattered showers are expected ahead of a cold front later Thursday night into Friday morning. Rainfall amounts will be negligible (less than one tenth of an inch) in most spots, and showers should already be east of the I-95 corridor by 9-10 a.m. Friday. Speaking of rain, not one more drop will fall through Halloween evening. Thus, October 2024 will indeed conclude as the 2nd-driest on record at Millersville with just 0.04" of rain. Only October 1963 was drier due to there being no measurable precipitation that month. Due to the recent absence of rainfall, Lancaster County and the rest of southeastern PA were upgraded to "moderate-to-severe drought" on last week's U.S. Drought Monitor. With very little rain in sight through Election Day, drought conditions will only expand and worsen in the coming weeks (see below).

The aforementioned cold front will lag behind Friday's early-AM showers by several hours, so temperatures should still be way above normal Friday afternoon. Thursday night's lows will be in the balmy low 60s.. more typical of late August or early September than the first day of November.. so highs on Friday should have no problem reaching the upper 60s north/west of Route 11/I-81 to the mid-to-upper 70s along the I-95 corridor. Despite wind gusts up to 30 mph Friday afternoon, it's going to be a great end to the week for outdoor activities with plenty of sunshine on tap after midday. Winds will then shift to the northwest Friday night and usher much cooler and drier air into the region. Dewpoints are expected to fall some 20-25°F in just 24 hours, and temperatures will "fall off the cliff" Friday evening. They'll bottom out in the upper 30s (outlying areas) to mid 40s (urban centers) early Saturday morning, and a Canadian high pressure system will then settle over the Northeast and mid-Atlantic States this weekend and prevent afternoon highs from exceeding the low 60s. Fortunately, the high will promote mostly sunny skies and light winds both days, so that will help mitigate the chill and create a pleasantly cool setting for outdoor activities. I expect widespread frost early Sunday morning, but jackets and coats being worn to Sunday morning church services will be able to be shed by the late-morning hours.

Looking ahead into next week and Election Day, all indications point toward the development of another anomalous ridge along the East Coast. The Jet Stream will take a pronounced dive southward across the Intermountain West and Four Corners region early next week, and this large-scale pattern configuration favors more incredibly warm conditions at a time of year known for cold nights and crisp afternoons. A warm front is expected to move through the Commonwealth from southwest-to-northeast on Sunday night or Monday, and the air mass behind it will be comparable to the one tomorrow and Thursday. Monday may turn out to be a "transition day" featuring mostly cloudy skies, isolated showers, and highs in the 60s to perhaps 70°F, but southwesterly flow will return by Election Day and push temperatures back into record-challenging territory. The mind-boggling warmth will stick around on Wednesday, as well, and be accompanied by partly-to-mostly sunny skies both days. The record highs on November 5th and 6th are 78°F and 77°F from 1975 and 1978, respectively, at Millersville. Quite frankly, I expect one or both of them to be tied or broken. I know this is a "bold call" with these days being a week or more away, but I'm comfortable with it given the remarkable agreement on its occurrence between various computer models. Since 1914, on only one occurrence has the mercury reached or exceeded 80°F at Millersville after November 4th (81°F on November 18, 1928), but that might change next week. A potent cold front will likely move through the region next Wednesday night or Thursday and slash temperatures by 10-20 degrees. However, there are no signs of any downstream blocking developing over northern Canada and Greenland in the coming weeks, so I anticipate the warm-biased and abnormally dry pattern to persist into mid-November. Next month's weather will simply be a continuation of this one's.. at least for awhile. Considering we desperately need rain, this isn't good news.. -- Elliott


Friday, May 31, 2024:

2024 Atlantic Hurricane season outlook:

Meteorological spring is wrapping up on a sunny and pleasant note today, but I expect plenty of heat and tropical activity this summer. Not only does June 1st mark the beginning of meteorological summer, but it's also the start of the 2024 Atlantic Hurricane Season. El Niño, or the phase of ENSO defined by above-average sea surface temperatures (SSTs) in the equatorial Pacific, has been present since June 2023. However, its death is imminent, and La Niña conditions (below-average SSTs in the equatorial Pacific) should return by July or August. Due to this rapid transition from El Niño to La Niña, wind shear.. or the change in wind direction and speed with height above the ground.. should be lower than normal in both the Atlantic and Pacific Basins this season. During El Niño, the southern branch of the Jet Stream typically becomes dominant over the northern branch. As a result, easterly trade winds in the tropics weaken and can even become westerly in the mid- and upper-levels of the atmosphere. During La Niña, the opposite is true, with an enhancement in easterly trade winds and weakening of the Jet Stream's southern branch. Unlike severe thunderstorms, wind shear is detrimental to tropical storm and hurricane formation. So, less shear and stronger easterly trade winds support more tropical activity and an above-average number of named tropical cyclones.

The atmospheric response to El Niño and La Niña is often delayed by several months, but that may not be the case this go around. Over the last year, the atmospheric response to El Niño was relatively weak, perhaps on account of 3-straight years of La Niña conditions prior to summer 2023. Thus, the atmosphere could exhibit an almost-immediate response to the developing La Niña. Things may get off to a relatively slow start through the July 4th holiday due to the lingering effects of El Niño (more wind shear) and dry air from the Sahara Desert over the main development region (MDL) of the tropical Atlantic. However, I expect that to change in a big way during the second half of summer, and the Atlantic Basin will likely be littered with tropical cyclones during the season's peak (September-October). La Niña is expected to strengthen throughout the fall, so I anticipate at least a few more named storms in November as well. In addition, SSTs as of May 31st were well above normal across the Gulf of Mexico, Caribbean Sea, and MDL (see below). Hurricanes behave like giant heat engines that use warm, moist air as fuel. Warmer-than-normal SSTs provide the additional fuel necessary for frequent storms and rapid intensification.

SSTs May 31 2024

Due to the factors outlined above, I expect the 2024 Atlantic Hurricane Season to be incredibly active and perhaps challenge the record for most named storms in a year (28 in 2005). Of no coincidence is that 2005 is one of my "analog years" for this summer. Anyhow, I am predicting:

  • 21-27 NAMED STORMS
  • 10-14 HURRICANES
  • 4-7 MAJOR HURRICANES (Category 3 or higher)

Unfortunately, I expect at least several of those storms to make a direct landfall in the United States with a higher-than-normal chance of catastrophic impacts. Residents along the Gulf Coast from Texas to Florida appear most at risk this season and should prepare now for the worst-case scenario of a direct impact. For information on hurricane preparedness, visit the National Hurricane Center's website, your local National Weather Service Forecast Office's website, or other emergency management resources. I don't have a good feeling about this one.. 

2024 summer outlook:

As for my 2024 summer outlook, searing heat could become quite common across the Northeast and mid-Atlantic States, especially in July and August. Historical analogs.. or years with similar, large-scale patterns or pattern transitions.. support the idea of a "backloaded summer". In the past 25 years, 1998, 2005, 2007, 2010, and 2016 featured a transition from El Niño to La Niña conditions between the spring and autumn months. Thus, those 5 summers are my "analog years" for summer 2024. Much like the Atlantic Hurricane Season, things may get off to a slow start (in terms of heat) in June. There is often a correlation between drought/soil moisture and extreme heat in the summer months. As of May 28th, the only parts of the nation experiencing significant drought were the Florida Peninsula, northern Rockies, southern Plains, and New Mexico. However, soil moisture was most below normal across the Midwest, Central States, Ohio Valley, and South Texas as of May 30th (see below). Thus, I expect the core of the heat in June to be across the southern Plains and northern Rockies with "near-normal" temperatures across the center of the nation, Great Lakes region, Northeast, and mid-Atlantic States.

soil moisture and drought

However, I expect things to change around or shortly after July 4th. As La Niña develops and the southern branch of the Jet Stream weakens, storms systems and cold frontal passages should become more infrequent. After an active start to the summer in terms of showers, thunderstorms, and severe weather, I expect drier-than-normal conditions to develop in July and persist through August and perhaps September. Thus, the core of the heat should progressively shift farther east each month from June-August. Both branches of the Jet Stream might be very weak from mid-July through at least mid-September, allowing a semi-permanent "heat dome" to develop across the Central and Eastern States. If so, then air conditioners could be working overtime and cooling demands "through the roof" starting sometime in early-to-mid July. High humidity may very well accompany some of this summer's heatwaves, so follow heat preparedness tips and advice given in my Special Weather Discussions (SWDs) and on Twitter (@MUweather) throughout the summer. In terms of 90-degree days, I expect an above-average number (30-40) of them with the possibility of a 100-degree day or two during the second half of July or August. Relative to average, the "coolest and wettest" month of the summer should be June with August being the "hottest and driest." In aggregate, I expect temperatures from June through August to average 1-3°F above normal, but with a near-normal (-1 to +1) June and sweltering (+2 to +4) August. As a whole, rainfall might average "near- to slightly-below normal" for the summer on account of a relatively wet June and bone-dry August.

summer 2024 analog blend

As an FYI, I'll keep these outlooks available until November 1st below my bi-weekly SWDs. Let's see how I do! -- Elliott