ITHACA, N.Y. — April showers bring…May showers, apparently. The recent wet spell is set to continue this week, with a moisture-laden storm system crossing the region today into tomorrow, and an inch of rain or more is likely in many communities south and west of Ithaca. For what it’s worth, it does appear drier and milder conditions will arrive towards the weekend, though most if not all of the week will continue to see below normal temperatures.
Weather Recap
With all of April 2021’s meteorological data in the record books, it was a fairly uneventful month for Ithaca and Tompkins County, a little on the mild side and a little on the wet side, but nothing to write home about. With an average temperature of 44.8°F, the Northeast Regional Climate Center’s site on Dryden’s Game Farm Road was 1.1°F above average, which is a tie for 55th warmest in 123 years of valid local records – or in other words, the warm side of near-normal.
Regionally, the pattern was much the same, with 30 of the 35 first-order climate stations reporting warmer-than-normal temperatures for April. The exceptions were the four West Virginia stations and Albany, which has had a well-documented cold bias (it reads artificially low temperatures) ever since the sensor was replaced back in July 2020. Only the two Maine stations, Caribou and Portland, reported top-ten warmest Aprils.
On the precipitation side, April was wetter than usual, and that’s a good thing, given that early in the month much of Upstate was heading into mild and moderate drought conditions. 3.88″ of liquid and liquid-equivalent was received at Game Farm Road, including the meltwater from 4.1″ of snow. The typical figures for April are 3.40″ of precipitation and 2.8″ of snow respectively. Precipitation doesn’t follow normal statistical distributions (instead of the Bell curve, it follows a gamma distribution), so 3.88″ is actually wet enough for 20th place in the 120+ years of valid local records.
Regionally, however, most of the Northeast and Mid-Atlantic was on the dry side. 28 of the 35 first-order climate stations were drier than usual, with Allentown, Pennsylvania having its fifth-driest April on record. In contrast, Binghamton, the closest first-order site to Ithaca, had its tenth-wettest April on record. Precipitation tends to be more variable than temperature, as a line of thunderstorms and downpours hitting the right place can make the difference between a wet and dry month. With precipitation data, it’s generally better to look over longer-term periods for seasonal trends.
On the topic of those seasonal trends, we still have a modest precipitation deficit at the moment (about 1.4″ or so ), but the next day and a half will make substantial progress to bringing Ithaca and Tompkins County closer to normal as we head continue into the prime growing season and the thirstier part of the year.
Your Weekly Weather
Of focus this cloudy Sunday afternoon is a broad area of low pressure trekking east-northeastward across the Ohio River Valley on a trajectory that takes it across Pennsylvania, downstate New York and Southern New England. This system has a tap into the Gulf of Mexico and its moisture-heavy air, which will allow for significant amounts of precipitation starting this evening and carrying through the overnight hours and into Monday. The primary shield of precipitation will fall from about mid-evening (5 PM) through about 5 AM Monday morning, with lighter, scattered showers past sunrise and into the later morning hours.
This is a rather tricky system to forecast because small changes in storm track and strength will have significant impacts. The further northeast it goes, the more heavy rain there will be. If it intensifies and the counterclockwise-rotating circulation deepens, a stronger low will wrap in more cold air on its backside and that will up the chances for measurable snow at higher elevations (inversely, a weaker storm results in lower chances).
The model runs coming out suggest Tompkins County is situated far enough east to avoid the coldest air passing through in the middle of the night, and therefore that snow risk. However, it’s going to be a wet evening and overnight Sunday into Monday. Highs in the mid 50s will fall back into the low 40s in Ithaca and along the lake, and upper 30s in the outlying areas as overcast skies with moderate to heavy rain deposit a tenth of an inch to a quarter-inch of rain by sunset. Overnight, the rain will continue with another quarter-inch to half-inch of rain, with higher amounts south and west of Ithaca, and temperatures holding steady in the upper 30s and lower 40s. The rain should begin to taper off after about 2 AM, with periods of light to moderate rain through sunrise Monday, finally winding down between 9 AM and 12 PM.
Once those showers taper of Monday, skies will clear up to partly cloudy conditions by afternoon, though with a northwest breeze behind the low, it’ll be on the cool side for mid-May, with highs only in the upper 50s to around 60°F. With the clockwise floe of a Canadian high to the northwest, it’ll be a chilly night Monday, especially in places where the clouds manage to clear out; Ithaca will be in the upper 30s, and mid 30s are more likely up on the hills, with some patchy frost possible.
Tuesday will be a brisk day for Tompkins County, as the Canadian high and a low pressure system aloft to the northeast create an enhanced flow of cool air from the north. It will be mostly sunny early, with partly to mostly cloudy skies by afternoon as that upper-level low retrogrades southwestward into Northern New York, and it may provide enough instability aloft for a few showers as well as cloudier skies. Highs will be in the mid 50s. The low will begin to move back eastward again by evening, which will reduce the risk for rain, though mostly cloudy skies will continue into Wednesday morning. Lows will be in the upper 30s.
Wednesday is looking a little milder and sunnier as the low’s departure means a weaker northwesterly flow as that Canadian high still sits off to the northwest. It will be mostly sunny with highs around 60 °F. Wednesday night will see clear or near-clear skies, which allow temperatures to slide back into the upper 30s for overnight lows across Tompkins County.
Thursday sees the high move southeastward, which will cause the northwest flow to slacken even more. Close proximity to the Southern Tier will result in a stable atmosphere and generous amounts of sunshine. Highs will be in the mid 60s with partly cloudy skies. Thursday night will see somewhat cloudier skies as a weak shortwave (pulse of atmospheric instability) develops to the south, but it will remain dry with lows in the mid 40s.
Friday will see the risk for a few rain showers south of Ithaca as that shortwave develops and moves northeastward with a coastal low, but generally it should remain dry. Plan for partly cloudy skies and highs in the mid 60s. Friday night will have a chance for a few light rain showers, primarily south and east of Ithaca, with lows in the mid 40s.
For your weekend, a cold front will pass to the north, and there’s the possibility it may channel enough instability into the Southern Tier to trigger some rain showers, but those that develop will be light and generally north of Ithaca. Highs both days will be in the upper 60s with partly to mostly cloudy skies, with lows in the upper 40s.
Extended Outlook
Look into the second half of the month, medium-range models favor a regime change with a broad ridge in the jet stream over the Great Lakes and a trough along the West Coast. The edges of the ridge would be far enough from the Northeast to support a drier-than-normal period to go along with the warmer-than-normal temperatures expected for the week of the 17th – good signs for a meteorologically pleasant graduation season, and early indicators suggest the warm, dry pattern will continue into Memorial Day weekend.