ITHACA, N.Y. — Some folks like to get the bad news before the good news. Weather-wise, this week is something like that. A dreary, rainy Monday will be followed by days of sunshine and mild temperatures for the remainder of the work week.
First, let’s take a look at the final September statistics. Temperature-wise, the data is about as unexciting as one can get. With an average temperature of 59.7 °F, September finished -0.3 °F below normal, near normal for all practical purposes. Cayuga Lake was a cooler spot in a region that otherwise experienced above-normal temperatures to varying degrees. Warmer-than-normal high temperatures were slightly offset by cooler-than-normal overnight lows, the type of data one might expect for a fairly dry month.
That, ladies and gentlemen, is probably the bigger story for September, as the total precipitation received (all rain, snow hasn’t been recorded in September since 1930) was a piddly 1.78″, less than half of the normal of 3.69″, the 16th driest in the 127-year record for Ithaca, and the driest September since 1983.
That was actually one of the less-impressive dry notes for the month. Several stations further south, like Islip on Long Island, had the driest Septembers they had ever recorded. One station in West Virginia (Beckley) had the driest month it’s ever recorded. That prolonged ridge of hot air from our south-southwest prevented storms from following their customary Ohio Valley track and forced them to route north into Canada, and that shows up in the data in the dry to less-dry precipitation gradient from south to north.
October has already shown itself to be more variable with the first substantially cool air mass of the season late last week. Temperatures got down to as low as 30 °F at the Ithaca Tompkins Airport between 6 and 7 AM Saturday morning, just before sunrise, and 31 °F at Cornell Orchards. This is a touch too warm for a killing frost in Ithaca’s valley and near-lake areas, but it’s highly likely that, once the data is finalized Monday morning for the weekend observations, a hard/killing frost took place in the hills and less urbanized parts of Tompkins County.
For those who escaped it this time around, there’s no sign of temperatures getting nearly as cold over the next week, so those tender annuals will be hanging around for just a little while longer, and enjoy a few days of that ever-decreasing October sun before their demise.
Rain arrives by tonight and turns steadier through Monday. Over an inch of rain is expected. Only minor river responses are forecast as much of the area has been dry for the past 3 months. pic.twitter.com/RJavseDFyN
— NWS Binghamton (@NWSBinghamton) October 6, 2019
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We’ll be starting off this week with a cold front coming in from the west; while the air mass behind it isn’t really cold (the drop in daytime highs will only be a few degrees), it will stall out over the Southern Tier, keeping persistent batches of rain going late tonight and into Monday. The front will finally push out late Monday and give a chance for high-pressure to build in for Tuesday onward.
Rain won’t start in earnest until later tonight, around midnight. As the front will extend deep into the southern United States and be able to tap into moisture from the Gulf of Mexico, there will be plenty of water vapor on hand to feed a moderate but long-lasting rainfall through the overnight and first half of the day Monday.
Tonight, overcast skies precede periods of moderate rain that will continue through to the morning hours. Lows will be mild thanks to the rain and cloudy skies, only pulling back into the mid 50s. Rainfall amounts will be between 0.5″ and 1″.
For Monday, it will be rainy early, with rain beginning to wind down during the early afternoon and tapering off completely by sunset as the front slowly shuffles eastward. It will be an overcast day with highs around 60 °F, with an addition 0.25″ to 0.5″ of rain. Monday night will see overcast skies give way to mostly cloudy skies, with temperatures sliding back into the mid 40s. Some patchy fog will be possible Tuesday morning in the usual valley locations, so use caution if out on the roads late Monday night or early Tuesday morning.
Tuesday will be a fairly pleasant fall day as high pressure works its way into the region from the western Great Lakes. Highs will be in the low to mid 60s with partly cloudy skies and a light north wind. Tuesday night will be partly cloudy with a low in the low 40s close to the lake, and around 40 °F for communities further out, with some valley fog once again in the usual suspect areas.
Wednesday will be a littler warmer as the north winds subside to calm air with the approach of the core of the high pressure system. Temperatures will top out in the mid 60s with mostly sunny skies. Wednesday night will be partly cloudy with a low in the low to mid 40s.
Thursday will be another pleasant today as the high pressure systems moved further east and stalls out due as an omega block develops over New England and Atlantic Canada. An omega block is when a very large amplitude loop in the jet stream is enmeshed between two deep troughs, giving the jet a shape like the Greek letter omega (Ω). These systems are hard to dislodge, and at a glance we luck out by being under the influence of the high and associated jet stream ridge. However, a coastal low below the omega block may strengthen and direct its moisture out the sides of the omega, and into the Mid-Atlantic states. In that case, our weather could turn stormy. But for now, plan for things to be on the dry side, with partly cloudy skies and highs in the mid 60s. Thursday night will be partly cloudy with lows in the mid 40s.
Friday will be another nice day with the high pressure system stalled out and still in control of our weather. Plan for partly cloudy skies and a high in the mid 60s. Friday night will be partly cloudy with a low in the mid 40s.
A large and rather potent low pressure system will be developing over the Upper Midwest later this week, potentially leading to snow in places such as Denver, Omaha, and Des Moines. Models suggest that this storm will move north-northeast, staying well to our east and limiting the flow of colder air into the Southern Tier. However, there will be some cooler air in the vicinity as the low develops a large frontal boundary that will pass through over the weekend.
Saturday is looking mostly cloudy as the front approaches, with a chance for pre-frontal showers and a high in the low 60s. Saturday night will be mostly cloudy with a chance for showers and a low around 40 °F as the front passes and cooler air filters in, and Sunday will be sunnier with highs in the upper 50s.
Looking into the middle of the month, that powerful storm system that will be developing over the Northern Great Plains will draw down massive amounts of cold air from Canada and the polar regions, leading to much cooler than normal conditions over the eastern two-thirds of the countries as it slowly treks to the north-northeast. Since the core of the low will pass well to the north and be significant weakened by the time it does around the 14th, cold air intrusion will be limited in severity and geographic scope in the Northeast. On the bright side, the omega block will maintain a ridge of warm air ahead of the storm system and in fact the ridge will be enhanced by the storm’s counter-clockwise flow. Being on the the edge of that ridge, things are looking slightly above normal temperature-wise for us, even as much of the nation will be suffering through an early and severe cold snap. Precipitation will be about normal for the period.