ITHACA, N.Y. — As early summer weather goes, it’ll be a bit of a roller coaster week temperature-wise. Today’s mild if climatologically cool temperatures will give way to a heat wave likely into the low 90s for mid-week, with a cooling trend just in time for your weekend activities. Thunderstorms are likely Wednesday, but no severe weather is expected this week.
Looking at the month of May courtesy of the Northeast Regional Climate Center’s data, it was really a tale of two months, with an extremely cold first half and a more mild second half. All in all, this resulted in a modestly cooler-than-normal month, with an average temperature of 54.0 °F, 1.4 °F below average. That’s cold, but not especially so, ranking 36th out of 128 years of Cornell-NRCC recordkeeping. But if you were to limit it to the first half of the month (1st-16th), it was the third-coldest on record.
The story was much the same through the Northeast and Mid-Atlantic, with New England being the only region to see a substantial number of stations with above normal temperatures, and that was because it was further downstream from the deepest part of the jet stream trough that dominated our weather pattern in that first half of May. On the flip side, the ridge that was overhead by Memorial Day was intense enough to give Scranton, PA and Burlington, VT their warmest May temperatures ever (95 °F and 93 °F respectively).
On the precipitation side of our local climatology, May 2020’s 4.00″ was marginally higher than the average of 3.19″, and that four inches included the meltwater from 0.1″ of snow on the morning of May 9th. That’s the latest date with measurable snowfall since 1977, and only the 8th time snow has occurred on or after that date in Ithaca’s climate record. Tompkins County and the Twin Tiers were something of a wet spot in what was otherwise a fairly dry month across much of the Northeast and Mid-Atlantic.
According to the NRCC, June has started off on the cool and dry side, and this week ahead will likely be on the warm and dry side, though it seems like we’ll be receiving our share of humid air in the coming days.
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At the moment, the defining feature of our weather is an area of high pressure currently centered over the southern tip of Hudson’s Bay Canada. Located well to our northwest, the clockwise circulation of the high is streaming cooler air into our region on a northerly wind. This is also creating some instability as the June sun heats the land beneath, and the heat radiated from the earth destabilizes the lower levels of the atmosphere enough to produce widespread cloud cover. However, the initial stability of the air is substantial enough that rising air parcels can’t build momentum, so cloud cover is about all we’re seeing on this pleasant Sunday afternoon.
As this high shifts eastward over the next day or so, we’ll find ourselves on the backside of its clockwise flow, and as the winds turn to the south, we’ll see temperatures warm up considerably in the next couple of days. Also playing a factor will be Tropical Storm Cristobal, which after making landfall in Louisiana today will maintain its circulation and move northward. Models show Cristobal transitioning to a more typical mid-latitude low, but maintaining a broad area of low pressure all the way into the Western Great Lakes and Canada. Its counterclockwise flow will amplify southerly winds over Tompkins County, resulting in an even warmer and tropically humid air mass my the middle of the week.
For the rest of today, expect a fairly pleasant evening with dry conditions, partly cloudy skies and temperatures slowing receding through the 60s, into the 50s after sunset and settling to a low in the mid to upper 40s prior to Monday’s sunrise, with just a few passing clouds during the overnight hours.
Monday will be a fairly quiet day, and somewhat warmer as the northerlies slacken with the eastward movement of the Canadian high pressure system. Expect mostly sunny skies with temperatures in the mid 70s. Monday night will host mostly clear skies with lows in the mid 50s.
The transition to southerlies and the movement of the remnants of Tropical Storm Cristobal should usher in a much warmer day for Tuesday, as daytime highs top out around 90 °F with mostly sunny skies. The humidity will be fairly limited at first, because the air initially tapped by the high will be drier than usual. During the day, it will be a touch humid, but not muggy. However, by evening, as that tropical airmass is trucked northward by the large circulation of Cristobal, the humidity will rise substantially. The cloud cover will build overnight as we see a warm, muggy overnight Tuesday into Wednesday, with lows in the upper 60s.
Wednesday will be about the same temperature as Tuesday, with highs around 90 °F, but with dewpoints into the low 70s, it will be much stickier, downright oppressive with a heat index close to 100 °F. Heat advisories may need to be posted, and if the National Weather Service issues advisories or warnings, a weather update will be issued accordingly.
With Cristobal transitioning to a mid-latitude low, it will developing a cold front to its southeast, and that will sweep through during the overnight hours Wednesday into Thursday. This in combination with naturally more unstable humid air (humid air is more buoyant) will lead to numerous pop-up showers and some thunderstorms during the afternoon hours, and especially in the late evening around and after sunset as the approaching cold front shunts the warm, moist air upward and destabilizes the atmosphere ahead of it. The atmosphere will have plenty of energy stored within, but the dynamics are not expected to be favorable for severe thunderstorm development. Expect mostly cloudy skies with some rain or rumbles of thunder, maybe some downpours due to the sheer amount of moisture-laden air, and lows in the mid 60s.
Thursday will feel more comfortable, if still a touch on the humid side as a modestly cooler and drier air mass is ushered into the Southern Tier. Plan for a few lingering showers in the morning, but otherwise it will be mostly sunny with highs in the mid 80s. Thursday night will be partly cloudy with lows around 60 °F.
By Friday, the remnants of Cristobal will stall around Hudson’s Bay, and its large, counerclockwise circulation will drag ample amounts of cool Canadian air down through the Great Lakes and into the northeast. With that, we’ll see cooler conditions across our region, though generally we’ll be far enough south of the low to avoid most of the potential rain showers it will generate. It will be mostly sunny with highs around 80 °F. Friday nice will see a chance for a few isolated showers, and lows in the upper 50s.
Next weekend is looking seasonably warm and generally pleasant, though the stalled remnants of Cristobal will continue to generate a few showers to the north, and they may occasionally work into Tompkins County with the heat of the day providing a bit more instability. Generally though, it will be partly cloudy with highs in the upper 70s for Saturday and mid 70s for Sunday, with lows in the mid 50s.
Looking through the middle of the month, it’s looking it will be a little on the cool side as a narrow ridge, likely enhanced by Cristobal’s lingering remnants, builds over the Great Plains, with troughs over the Eastern United States and Pacific Northwest. Precipitation for late June is expected to be near-normal to modestly dry, but nothing that should set off any alarm bells as we approach the first day of astronomical summer.