ITHACA, N.Y. — The calendar says late February, but you could be forgiven for thinking that spring has already arrived. Enjoy it while you can, though, because more seasonable cold is expected to make a return later this week.

Monday’s high temperatures. Image courtesy of the NWS National Digital Forecast Database.

Your Weekly Weather

One of the major drivers for our weather in the first half of the week will be a large area of high pressure parked over the Atlantic between the Carolinas and Bermuda. With its clockwise flow, the ridge in the jet stream will be reinforced, allowing mild air to take hold and stay in place for the next few days. The jet stream itself has been pushed far enough north that a passing storm on Monday will be unable to penetrate southward. The first major change to our weather won’t occur until Tuesday, when a developing storm over Oklahoma and Texas rides up along the western side of the jet stream ridge and presses into the Southern Tier from the southwest.

As a result, tonight’s forecast for the next couple of days is fairly boring, and there is nothing wrong with that. Tonight will be mostly clear skies, and with southwesterly winds, overnight lows will be fairly mild for February, in the low 30s for most of Tompkins County, with perhaps a few upper 20s in the higher elevations.

Monday is looking fairly pleasant, a mild winter day. Expect partly cloudy skies with a low in the low 50s. Skies will progressively cloud over during the afternoon hours, with mostly cloudy skies by sunset as the low pressure storm system approaches. Monday night will see mostly cloudy skies turn overcast by midnight, a perhaps a few showers develop ahead of the main body of precipitation during the early hours of Tuesday morning. With lows in the mid 30s, these will most likely be in the form of rain.

Tuesday is looking like a mostly or all rain event, with little in the way of snow. The low’s counterclockwise flow will maintain the southwest winds and keep temperatures on the mild side, and with the ridge, it may actually retrograde a bit and turn around, lodging itself into Michigan. Expect periods of light rain during the day Tuesday and cloudy skies, with temperatures in the mid 40s. Tuesday night will see scattered light rain showers as the bulk of precipitation moves northward, with mostly cloudy skies and lows around 40°F. Rainfall amounts will be about one-tenth of an inch.

The low pressure system begins to slowly move northeastward from Michigan into Canada Wednesday, and the southwest flow will keep temperatures mild, but a second wave of moisture will make for another rainy day. Plan for periods of light rain and highs around 50 °F with cloudy skies. Rainfall amounts will be one-tenth and one-quarter of an inch, mostly in the afternoon.

The most intense rain with this second wave of moisture will push through between 7 PM and 12 AM Wednesday night, as the moisture lines up with favorable jet stream dynamics (to go technical in brief, it’ll be the left exit region of a more intense jet streak in the greater jet stream flow, which creates divergent air flow aloft that pulls up air from the surface and enhances instability). This is going to be a moderate to heavy rain, a quarter of an inch to one-half of an inch. The rain begins to lighten up after midnight, and eventually transitioning to a light snow before daybreak. Temperatures will slide into the mid 30s as colder air on the backside of the low begins to make its way into the Southern Tier.

Thursday will be a much cooler day. A second low developing off the coast will take energy from the first low, making that the stronger of the two systems (according to forecast models, it doesn’t look like it will fully absorb the first low, which is somewhat unusual). This will place us on the backside of the new low, allowing cold air to stream in from the north. The new low will also have abundant oceanic moisture, so light snow is likely during the morning and early afternoon hours. The only thing really stopping a real snowstorm from happening is that the storm will be too far east. Plan for mostly cloudy skies by afternoon after the inch or two of snow, with highs in the mid 30s. Thursday night will see a chance of snow showers as the lows move north and northeast respectively, and lows in the low 20s.

A cold regime sets in for the rest of the week as the two lows draw in enough cold air to build a trough in the jet stream over the Eastern United States. It’s not going to be frigid, but it will be a few degrees below average, and unsettled as those northerly winds cross Ontario and stir up lake-enhanced snow showers. Friday will be cold and cloudy, with a few scattered light snow showers and a high in the mid 20s. Friday night’s forecast is for cloudy skies and light snow showers, and a low in the mid to upper teens.

Saturday and Sunday will also be on the cold side as the jet stream troughs through the weekend; a cold start to March is on tap. Both days will be mostly cloudy with scattered lake-enhanced snow showers, with highs in the mid 20s. Lows overnight will be in the mid teens.

Extended Outlook

Looking further ahead into March, after that initial weekend cold, temperatures should begin to rebound Monday, and medium-range forecast models are supportive of temperatures being back above normal by Tuesday, well into the 40s in most areas. A fairly warm pattern will remain in place, if also a bit on the wet side, as the jet stream ridge builds back as part of a low-wavenumber pattern (meaning long-length ridges and troughs) where the ridge covers most of the continental United States. A cooler and dry pattern is expected to set in later in March, but it’s too early to make any explicit statements, and we’ll see what happens as we get closer to the start of spring.

Brian Crandall

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at bcrandall@ithacavoice.com.