ITHACA, N.Y. — With moderate to heavy rain continuing through the evening, flood risks are elevated across Tompkins County, with isolated flash flooding and urban/creek flooding being the biggest concerns. This week will be unsettled, cool and rainy, though some (sun)light at the end of the tunnel appears to arrive in time for next weekend.
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This week’s rain maker is deep and large low pressure storm system centered over the Eastern Great Lakes. This cutoff low will be slow to move, and the system is so large that it’s channeling moisture from the Gulf of Mexico into its overall flow. A secondary low in its southeastern flank is currently riding up the larger low’s frontal boundary, creating widespread moderate to heavy rain across New York State this Sunday.
Half an inch has already fallen at the Ithaca-Tompkins County Airport, and another 0.50-1.00″ is likely through the overnight hours tonight. Embedded heavier bands and thunderstorms may result in rainfall amounts as high as 3-4″, basically a month’s worth in less than a day. As a result, a Flood Watch has been issued through 12 AM, and flash flooding will be possible in much of the Southern Tier, as well as ponding and urban/creek flooding in low-lying areas and areas of poor drainage. Use common sense – don’t cross roadways if they’re overrun with flowing water, don’t attempt to cross flooded roads, and be mindful that gutters and storm drains clogged with leaves, flower petals and other stormwater runoff material can easily become plugged and flooded.
The heaviest rain will fall before midnight. By the early AM hours, the rain becoming lighter and more showery, tapering off as we head towards sunrise. Temperatures will fall back from daytime in the upper 50s, to lows in the low to mid 40s as the frontal boundary swings east and cold air enters on northwest winds.
Monday sees a brief, cloudy pause in the rain during the morning, but a shortwave (pulse of instability) rotating around the stalled Great Lakes low. While rain is expected during the afternoon and evening hours as the shortwaves moves eastward through the region, additional rainfall amounts are expected to be light, <0.1″. This system is not that strong and does not have the tap to deep moisture that Sunday’s secondary low has. It will be cool with highs in the mid 50s. Monday night will be overcast with light rain showers through the night, even a few snowflakes on the hilltops. Lows will be around 40.
Tuesday sees the low pressure system weaken. Deep, stacked lows physically weaken themselves when surface and upper-level lows align in the atmosphere, as it cuts off the instability needed to sustain itself. However, the low will be directly overhead, and that cold pool aloft will still drive some instability at surface level. Expect on and off showers Tuesday with about another 0.1″ of rain and cold daytime highs around 50. Tuesday night will see rain/snow showers become less frequent after midnight, but still present, with cloudy skies and lows in the upper 30s.
Wednesday sees the system stall over New England before being shunted southeastward into the Atlantic. This will allow one more persistently rainy day, with light to moderate amounts expected. Highs will be in the low 50s. Showers taper off Wednesday evening with dry conditions towards sunrise, though cloud cover will persist. Lows will be around 40.
Thursday sees the low turn back to the northeast and head for Atlantic Canada. While out of its direct proximity, a few instability showers will still be possible on its rear flank, as well as unseasonably chilly air from the northwest. Expect a few rain showers, mostly cloudy skies, and highs in the mid 50s. Thursday night will see a few showers and mostly cloudy skies with lows around 40.
As the low moves further away Friday, skies will partially clear up, though a weak shortwave may trigger a few showers. Plan for partly sunny skies with highs near 60. Friday night will see a few lingering showers with partly cloudy skies and lows in the upper 30s.
The weekend is looking rather pleasant from this far out. High pressure will likely build in from the Western Great Lakes. It’s looking to be dry and seasonable, with mostly sunny skies, highs in the mid 60s Saturday and upper 60s Sunday, and lows in the low 40s.
Looking into Mid-May and Mother’s Day weekend, the large-scale pattern favors a stark change in the jet stream pattern, shifting to a trough upstream over the Western United States, and a ridge over the Midwest and Northeast. This pattern will help to slow the melt-off out west and give us some welcome warmer temperatures. On the precipitation side, the ridge will allow Gulf of Mexico moisture to slide over the Gulf Coast, while the jet stream transition over the Great Plains will create unsettled conditions over the Central U.S. Locally, precip is expected to me near to slightly below normal, which is fine given that we’ll be running well above normal after this week.