ITHACA, N.Y. — As we go through the second half of April, it’s a mostly quiet week ahead. Temperatures will be on the cool side of seasonable, and most of the week will be fairly quiet weather-wise. However, a storm system passing through Wednesday and Thursday will bring some rain into Tompkins County, and there might be some snow on the ground, however briefly, when you wake up Thursday morning.

Your Weekly Weather

It’s a cloudy and seasonably cool Sunday as moderate instability and a moist ground surface are providing for a fairly broad amount of cloud cover across the Northeast and Mid-Atlantic. You might notice in the satellite imagery above that the odd areas out appear to be Lake Huron, Lake Ontario and the Mohawk Valley from Oswego through Syracuse all the way to Albany. This is likely due to lake effect (really, “oasis effect“). Just as snowbands develop when cold air moves over warm water and is jolted and destabilized with surface heat energy from water to air, when shallow warmer air passes over the colder lake surface, you get an energy flux from air to water, a stabilizing effect that inhibits cloud formation. Erie doesn’t show it because as a shallower lake, it may not have the necessary volume of cool water to stabilize the low-level air overhead. In this case, the Mohawk Valley provides an outward channel for that more stable air, producing a relatively cloudless tendril all the way to the Capital Region 150 miles away. With that, folks, is your meteorology lesson for the day.

Anyway, to the forecast at hand. The area of low pressure that resulted in cold, unpleasant weather for the second half of last week is now east of Nova Scotia and we’re on the fringe of its influence – the moderate instability is due to a weak shortwave (pulse of instability) that passed southeastward across the Southern Tier earlier today. With that moving on out, weak high pressure is building from the southwest. Expect variable partly to mostly cloudy conditions for the rest of the day, maybe a lingering rain shower or two courtesy of the shortwave, with highs in the upper 50s. Tonight will be mostly cloudy and dry, with lows in the low 40s.

Monday will be a little warmer, with southwesterly flow enhanced by a developing area of low pressure over the Western Great Lakes; as air flows counterclockwise around lows, this should amplify the flow of milder air out ahead of the low, so temperatures will climb into the mid 60s. Another weak shortwave is likely to cross the Southern Tier, but there’s little energy for it to tap into so a few pop-up showers are the extent of its impacts, as well as partly cloudy skies. This will move on out by evening, leaving partly cloudy skies for Monday night with lows in the mid 40s.

Tuesday sees the Great Lakes pass well to the north, but the cold frontal boundary extending from its core will be enough to knock a few degrees off the temperature as it crosses our longitude. But this far from its core and with not much moisture to tap into, rain is unlikely, though there will be some partly to cloudy skies as temperatures top out in the upper 50s. Of greater concern will be a second storm system developing in the Ohio River Valley and crossing northeastward through the Catskills and into New England Wednesday. We’ll start off in the warm sector Tuesday night as the precipitation shield moves in. Rain will begin to move in shortly after sunset, and be fairly widespread by midnight through Wednesday morning. Lows will be in the low 40s.

Wednesday will be just a gray, wet day, and turning more unpleasant after 12 PM. At about time, the system passes Ithaca’s heading northeastward, which will shift Tompkins County into the cold sector of the storm. Winds will kick up from the northwest, 20-25 MPH gusts, through the evening. An early high temperature in the low 50s will steadily fall back through the 40s. All the while, light to moderate rain will persist all day long with overcast skies – expect around one-quarter of an inch of new rainfall. Temperatures will continue to fall Wednesday night, and rain showers will change over to snow showers by late evening as the precipitation winds down and cloudcover breaks up a little; lows in Ithaca and along the lakeshore will be in the low 30s, and a few degrees colder out on the hills. Don’t be surprised if there’s a coating of snow on the ground Thursday morning.

Thursday’s going to be a rather raw day. Some lingering snow showers and then rain showers will persist through the day, and gusty northwest winds of up to 30 MPH will persist as the storm intensifies to the east and tightens its pressure gradient (which is largely what drives those stronger winds). Skies will brighten to at least partly cloudy conditions later in the day, but with those northwest gusts, highs will only be in the mid 40s. The winds will slacken somewhat overnight Thursday as the system pulls away. Skies will clear further and any remnant rain showers will wither away before midnight. Lows will be in the mid 30s.

Friday will be an improvement as high pressure begins to build in from the Central United States. The northwest winds will still be present but lighter as it’s basically a weak combination of the low’s extended influence and the high’s clockwise flow. Skies will be largely clear with highs in the upper 50s. Friday night will see a few passing clouds as the high continues to build in, with lows in the upper 30s.

Next weekend is likely to have some showery conditions as the high quickly shifts eastward and a storm system passes to the north; while this will create some instability, the high to the east will counteract the colder air driven by the low, so it’s looking like partly cloudy with a few showers both Saturday and Sunday, with highs in the low 60s Saturday and upper 50s Sunday, with lows in the low 40s.

Graphics courtesy of the NOAA Climate Prediction Center.

Extended Outlook

Looking towards the end of the month, it’s a “western ridge / eastern trough” scenario with the jet stream. In the winter, this usually portends frigid, stormy conditions, but seeing as it’s late April, here it’s just cooler-than-usual with some elevated precipitation amounts possible as coastal storms ride up the western side of the next ridge, which will be over the Atlantic (you can see the tip of it over South Florida as it begins to curve back up). Drier than normal conditions will continue over the Plains and parts of the Southwest along with pronounced warmth over the Four Corners, which is not good as their drought situation worsens and water supplies from the Colorado River have dropped so low an official water shortage, with potential restrictions, is likely to be declared this summer.

Brian Crandall

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