ITHACA, N.Y. — With last week’s record-breaking heat confined to memories and data sets, a cooler week is in store for Ithaca and its environs. Lake effect rain will create enhanced cloudiness and showers well to the north and west of Ithaca, with a decaying but large low controlling our weather for the first half of the week. While some sun and milder weather will be on tap to close out the week, another storm system looks to make for a wet weekend to follow.
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A large storm system, comprised of both the mid-latitude storm system that ushered in this colder air, as well as the tropically-moist remnants of Tropical Storm Philippe, is current retrograding northwestward from the St. Lawrence River Valley to the southern tip of Canada’s Hudson Bay (retrograding meaning that it’s moving contrary to the typical west to east flow we see at this latitude). The system is drawing down ample cold, subpolar air in its counterclockwise flow; however it’s also becoming vertically stacked with low pressure near-surface and aloft, which weakens storm systems.
From a practical standpoint, what this all means is that westerly winds will be dominant across the region for the next few days as the system decays and is eventually weak enough to be swept away by the usual west-to-east mid-latitude flow. The storm’s circulation will usher in cooler-than-seasonable air, though the winds will keep temperatures from falling low enough overnight to produce widespread frost. A few hilltops have an off-chance of seeing a hard or “killing” frost, but most areas will see the growing season continue for a little while yet with overnight lows in the upper 30s to mid 40s over the next week.
Secondly, this cold westerly wind will generate lake-effect rain downwind of Lake Erie and Lake Ontario; while areas directly east of the lakes get a soaking, the biggest impact to Tompkins County will be enhanced cloud cover. A weak short wave (pulse of instability) rotating around the larger low will generate a few showers this evening, but new rainfall will be limited and light.
For the rest of your Sunday, expect a stiff WSW breeze and increasing clouds as the short wave enters the area and enhances cloud cover already being provided by the lake effect bands to the north and west. A few showers around sunset are likely, but once again, new rainfall amounts will be light, <0.10″. Highs will be in the upper 50s in urban Ithaca and along the lakeshore, mid 50s in the outlying towns. Tonight will see showers end before midnight as the shortwave continues ENE and away from the area, resulting in decreasing clouds towards sunrise Monday. Lows will be in the low 40s in Ithaca, upper 30s in the outlying areas; south winds and warm, moist soils will keep temperatures above freezing.
Monday will be fairly similar as that large storm system weakens to the north. Expect WSW winds and partly to mostly cloudy skies, with highs in the upper 50s. No precip is expected in Tompkins County for Monday, as the rain bands are oriented away from the area. Monday night will see mostly cloudy skies and light south winds with lows around 40.
The low continues to weaken Tuesday, which will result in more abundant sunshine, and slightly milder temperatures as winds slacken, resulting in highs around 60. Tuesday night will see partly to mostly cloudy skies and lows in the low 40s.
Wednesday may be a little windier as the weakened low is shunted ESE since it’s now able to be pushed around by the mid-latitude flow, but otherwise expect another partly cloudy day with highs around 60. Wednesday night will be partly cloudy with lows in the low 40s.
The system moves ENE Thursday, and the upper-air cold pool looks to stay well to the north of Ithaca. A short wave along the south flank of the system may bring a few rain showers, but those look to be light. It will be mostly cloudy with highs in the low 60s. Thursday night will see a few showers and mostly cloudy skies with lows in the mid 40s.
It gets a little warmer Friday with enhanced southerly flow ahead of the next storm system winding up over the Ohio River Valley. A few scattered showers are possible, particularly later in the day, with mostly cloudy skies and highs in the mid 60s. Friday night will see steadier rains arrive, with lows in the mid to upper 40s.
At this point, it’s looking like a cool and wet weekend. Rain is likely Saturday, and more showery weather Sunday. Highs will be in the upper 50s Saturday and mid 50s Sunday, with lows in the mid to upper 40s.
Looking into the second half of the month, the large-scale pattern calls for a jet stream ridge in the Western U.S., and a trough in the east. However, it would be incorrect to think of this orientation as straight up-and-down. In fact, it’s expected to be more like a backwards “S” shape – Ƨ – with the ridge bending towards the northeast, and the trough forming a pocket of particularly cool air over the Southeast U.S. The result for Tompkins County is near-normal temperature and precipitation, as the air drawn in would be moist, inherently more unstable air from the Atlantic, but without storm systems to really trigger hefty rains.