Published: July 28,2017
The final full week of July has featured several unusual weather events, and there may be more to come in the days ahead.
Among them are several rainfall extremes, strange tropical cyclone interactions and out-of-season conditions.
Here's a look at what we've seen so far and what's to come.
1. A Rain Event That Had a 0.1-Percent Chance of Happening
The orange and red area illustrates the very localized nature of the heavy rain near the Harrisburg International Airport. Locations shaded green saw far less rainfall.Abundant tropical moisture fueled a rare rain event in Harrisburg, Pennsylvania, on Sunday evening.
Harrisburg International Airport received 4.27 inches of rain in a single hour, from 5:56 to 6:56 p.m. EDT. A rainfall event of this magnitude in Harrisburg has just a 0.1-percent chance of happening in a given year, according to data from NOAA.
The total rain for the day at Harrisburg International Airport tallied up at 4.71 inches. This now stands as the wettest July day on record, and the fifth-wettest day overall for any month of the year at that location.
This downpour was extremely localized. Harrisburg's Capital City Airport, just a few miles to the northwest, saw less than a half-inch of rain during the same evening.
2. A Rarity in 140 Years of RecordsA trace of rain was recorded in downtown Los Angeles on July 24, which is a rare event for that calendar day and the month of July in general. Only three other times in history has any rain been observed there on July 24. A trace was also recorded on July 24 in 1954, 1941 and 1910.
July is the driest month of the year in Los Angeles. A vast majority of Julys since the late 1870s have gone without any measurable rain in the nation's second most-populated city.
The reason Los Angeles is so dry this time of year is that the jet stream moves far to the north, taking the storm track away from California.
3. Fujiwhara x 2
ECMWF (European) model forecast from July 27, 2017, of the expected Fujiwhara effect of tropical cyclones Irwin and Hilary. Lower pressure is denoted by the deeper orange and red contours. Higher pressure is shown by the brighter teal, aqua colors.This week we've been discussing the Fujiwhara effect in the Pacific Ocean. It's an uncommon event where two areas of low pressure interact due to their close proximity and then rotate about each other.
Typhoon Noru and now former Tropical Storm Kulap have already done the Fujiwhara dance in the western Pacific earlier this week.
Now, the Fujiwhara effect is forecast to take place in the eastern Pacific between Irwin and Hilary through this weekend.
Observing a single Fujiwhara event is a rarity in a given year, so having this occur twice in a matter of days is exceptional. For more details, see the link below.
(MORE: The Rare Fujiwhara Effect)
4. Dry Month in Seattle?Wet days are not a common occurrence in Seattle during July since it's typically the driest month of the year.
The dryness this month, however, has a chance to enter the record books for Sea-Tac airport. No measurable rain has been observed there through July 28, and none is in the forecast through Wednesday, August 2.
Seattle is in the midst of its fifth-longest dry streak on record at 41 days through Friday, but this comes with a bit of an asterisk.
Many Seattleites saw drizzle on Thursday, but these tiny rain drops only accumulated to a 'trace of rainfall'. This is not considered measurable rainfall, which means that Sea-Tac – the official measurement site for Seattle – continues its dry streak.
That's quite a flip from the record-wet conditions observed during the past rainy season.
5. Raw July Afternoon in New England
Radar, temperatures and winds at 1:40 p.m. EDT July 24 in New England.The weather in New England on Monday afternoon resembled something you might imagine occurring in fall or spring.
At 1 p.m. EDT, Boston was just 58 degrees with light rain and winds gusting to 26 mph. That temperature was only four degrees warmer than the daily record low for July 24, which is 54 degrees.
Many other cities in New England endured a raw, cool July day, as well. At one point Monday afternoon, the temperature in Worcester, Massachusetts, was 53 degrees with light rain and gusty winds.
6. A Rare July Cold Front in the SouthThe South will have a late-July treat this weekend as a cold front sweeps away the typical summer humidity that's currently in place.
The green shading represents less moisture in the atmosphere which means low humidity, including in parts of the Southeast.Cold front passages are a fairly rare occurrence in the South during mid-summer. That is because the jet stream is usually bottled up near the Canadian border and rarely takes the sharp dive southward that is needed for a cold front to penetrate into the southern states.
Dew points in the 70s are typical in the Southeast during July, which means the air is full of moisture and very humid. This weekend, dew points in parts of the Southeast will drop into the 50s and 60s, providing a pleasant change.
Air temperatures will also retreat into the 80s for a few days this weekend into early next week.
7. Absurdly Warm July in South FloridaFloridians in south Florida know it has been stifling hot, even with the above average rainfall this summer. This month is on track to be the warmest month on record.
In Miami, temperatures have had a rough time dropping below the 80 degree mark with dew points often getting stuck in the mid to upper 70s. The number of nights that Miami has failed to fall below 81 degrees stands at 22 through July 28.
The afternoons have been boiling hot too. With the exception of one day, every day in July has peaked over 91 degrees even with rainfall being nearly twice the average for the month.
Selected heat records for Miami, Florida.Here are a few more heat records for the Miami area compiled by Eric Blake.
(Applied Climate Information System/NOAA)
(Applied Climate Information System/NOAA)
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