Cut-off lows commonly occur when the upper level winds shift to a higher latitude and leave a circulating low pressure behind. The basic pattern of the cut-off low is shown in this link.

Though this upper-level map is from September of last year, it’s quite similar to the situation from about last Thursday. The jet stream dropped off a low pressure system over the Rocky Mountains…then abandoned to meander eastward on its own!

I’ve drawn an arrow to represent the general movement of the low over about 5 days time. We had warm, rainy weather from Friday through early Saturday. Then as the cut-off low moved off the VA coast and stalled off the Jersey Shore, we ended up with cooler, occasionally showery weather while New England had lots and lots of rain pumped in off the Atlantic. As of Tuesday afternoon, the low finally dropped south and southeastward far enough to loosen its effects for our area.

These cut-off lows are somewhat typical for springtime weather. They’re also a real “pain” to forecast! Remember that I wrote that they “meander”. Well, we might add the word, “aimlessly” to that. They’re usually slow-moving and since they’re cut off from any major upper wind flow, they don’t have any substantial steering currents to adequately predict where they’ll go!

We’ll likely see 2 or 3 more of these cut-off lows in the next couple of months. They look pretty impressive and sprawling on satellite pictures, but they’re usually relatively benign. At least, these cut-off lows are a sign of a springtime weather pattern rather than the winter pattern we’ve endured for so long.

-Don

Heavier rain on Saturday morning.

Rainfall is likely to be widespread from late Thursday night into Friday morning. Most of the rain should be fairly light; around .25″ to .50″ with a few isolated spots receiving a bit more. Rain could hang on into the early morning rush hour.

A few showers can be expected during the day Friday, but we are by no means looking for a full day “wash-out”. Highs on Friday should be in the low to mid 60s. If we see any sunshine at all, there could be a quick temperature rise into the upper 60s in inland areas. Winds from the east should hold the temperature down along the water. By mid-afternoon, we’ll see easterly winds at 15-25.

Winds should drop off a bit Friday night into Saturday morning. Rainfall should again be widely scattered for most of the nighttime hours. However, we could see heavier rain in the form of thunderstorms as we move toward dawn. The heaviest rain should arrive roughly between 5:00 & 8:00 on Saturday morning. The remainder of the day should be relatively rain-free. Same goes for Sunday.

Highs in the 60s Friday & Saturday…50s Sunday.

It’s starting to feel like Spring!

At 1:20 PM, Wednesday, the temperature reached 74°.

Now, that’s big news in itself. Especially since we’re all more than a bit weary from winter weather. But the really big news on this took me  through the past to October 31st, 2009.

Immediately upon seeing that we hit 74°, I searched back through daily records to find the last time we saw a day with 74° or greater. I went through February and there were absolutely no days anywhere near 70° there. In January and December, there were a few days in the 70° range-and one day (12/9/09) when we hit 73°-but no days of 74° or above. November fared no better when looking for a warmer day; again, a few 70° days, but nothing above that.

Finally, I found the last time we hit 74° or greater. It was Halloween Day last year when we hit 80°!

So is the cold weather over for the season? Not likely. The average date of the last frost for the area is around April 15th. The good news though, is that we’ll continue to see the ups and downs of temperatures…going generally up for the next few months. Then we’ll complain about the heat. But no complaints today!

On our 6:00 newscast, I pointed out an area of heavy rain that was likely to move north out of North Carolina and into S.E. Virginia. And that was exactly what happened. Except that area of heavy rain dragged down some freezing air from above…and we ended up with an hour-long burst of heavy snow!

I had predicted that snow would not likely be a big problem and there it was…BIG snow and the possibility of a totally blown forecast! Add to that the fact that some of the 18Z models went with a wacky heavy snow over the top of us (I didn’t buy into it). I was sweating bullets for a while, thinking that I’d really given you a bum forecast! But we’re back on track now and the forecast is looking pretty solid.

For most areas, the snow only accumulated on the grass and parked cars. But for some of us, there was a light slushy mess on the roads in the middle of the evening. As the heavy snow burst ended, we’ve gone back to a mixture of rain and snow. Most of the snow on the ground is melting…when you add that rain/snow mix, coupled with wet ground, soil above freezing, and air temperatures recovering into the mid to upper 30s.

We could still see a shot of heavy rain turn into brief heavy snow overnight, but chances are good that it’ll change back into a wintry mix. With all of that in mind, most of us will likely wake up with little or no snow on the ground Wednesday morning.

Now on to the bigger picture. Northeast winds are increasing as of this hour and will continue to increase to 30-40 mph by around 4:00 AM. That kind of northeast wind pushing tides up pretty much defines a Nor’easter. Tidal flooding will be our next concern. The next high tide (around 9:00 AM to Noon) will likely be slightly higher than the Tuesday evening high tide. The high tide Wednesday evening (9:00 PM to midnight) will be an inch or two higher than the morning tide. So far, these tides are likely to fall into the “minor tidal flooding” category…about 2 feet lower than the November Nor’easter. So move your car if you’re on a flood-prone street. Otherwise, I don’t think that we’ll see evacuations or anything other than traffic headaches from tidal flooding.

Wind should shift from the northeast to north during the morning. Wind speeds will continue in the 30 to 40 mph range through around noon, then only gradually begin to diminish into the evening hours.

That wintry mix will also likely continue into the morning hours…and occasionally come down as just snow. But little further accumulation is expected at this time. For Wednesday afternoon and evening, those rain and/or snow showers will continue to diminish.

By the weekend, we’re likely to see temperatures in the low to mid 50s. And we could even break 60° by early next week! But let’s all get through Wednesday first.

Be safe out there!

-Don

UPDATE at 2:00 AM: Scattered bursts of heavy snow have redeveloped. Mainly from Newport News southward to Isle of Wight County to near Franklin…then on into North Carolina in Hertford and Northampton Counties. These bursts could produce a shot of heavy, wet snow in the range of 1″-2″. That’s enough to produce a slushy mess on the roads. Check out the rain-snow line on our radar and that rain-snow line appears to be close to the area of heaviest precipitation. You’ll also notice an area of darker blue (heavier snow) just southeast of Rocky Mount, N.C.

Take care on the roads…some of this stuff is sticking as a slushy mess! And this may yet be a (slightly?) blown forecast!

UPDATE AGAIN at 3:00 AM: A “confluence zone” set up around 1:00 AM from north to south roughly from the Middle Peninsula southward through Newport News, then through Suffolk and into Hertford County, NC. This north-south line is the area where we are seeing the greatest “snow burst” activity. Heavy rain along this rough line drags down colder air from aloft and turns it into heavy, wet snow. As much as 1″-3″ of snow could fall from some of these snow bursts. Most of that snow will likely accumulate on grassy areas, decks, and parked vehicles. However, that heavy an amount of snow can result in a slushy accumulation on the roads. We’ve been saying for several days now that most snow should melt on contact except if a burst of snow would be heavy enough to overcome the effects of warm soil and above-freezing temperatures. And that is happening in that confluence zone.

The center of the storm (at least, on the surface) is just off of Cape Hatteras at this hour. However, there’s an upper level low to the southwest of that surface low offshore. That upper level low will be moving out to sea within the next few hours. As it does so, winds should increase further and become more northerly. Also, that north-south “confluence zone” should start shifting eastward through the rest of SE Virginia and North Carolina. It remains to be seen if the confluence zone is still capable of producing snow bursts as it moves closer to the coast. Once the confluence zone moves out, the precipitation should get lighter, colder air from aloft shuts down, and we revert back to the lighter wintry mix of rain and snow. That wind-driven wintry mix should tend to melt at least some of the existing snow on the ground. Snow amounts remain uncertain with all of the above noted.

What is certain? Pockets of heavy rain, increasing winds, and minor to moderate tidal flooding. It’s gonna’ be a nasty morning commute!

Just to follow up a bit on what Jeremy posted earlier. The info from the evening model runs have been trickling in. Data isn’t totally complete yet, but I’ve gotten a first look at things. The NAM, Canadian, & GFS runs are complete enough to get a good feel for the upcoming storm.

The NAM and Canadian models bring the low (storm center) very slowly toward Cape Hatteras on Tuesday night into Wednesday morning. So slowly in fact, that the storm tends to linger & intensify near Hatteras from around 4:00 AM through almost noon on Wednesday…before moving it east-northeastward and out to sea. This scenario would mean a prolonged time with the storm at full force. Also, this 4:00 AM to noon time frame would be the “height” of the storm. It would mean more precipitation, more wind, and more tidal flooding (esp. Wednesday)…and for a bit longer time. Snowfall amounts are still highly questionable because of the existing ground temperatures. Additionally, the air temperature during the above time frame is likely to drop to around 33° to 36°; cold enough to snow, but is it cold enough for snow to “stick”?? Close call! Of course, a burst of heavy snow could overpower the effects of soil temperatures.

The evening run of the GFS model is complete…except for some of the “bells & whistles” (extra stuff that gives us a better idea as to snow). Regardless, it’s showing a much faster passage of the storm and slightly farther out to sea. Obviously, this would mean lesser effects and for a lesser amount of time.

When all is said and done with this storm, most of the miserable weather will be overnight Tuesday into early Wednesday while most of us are asleep. Snow actually on the ground will not be likely for much of the area. So what will be remembered as it winds down on Wednesday evening? The wind and the tidal flooding might just be the most uncomfortable and inconvenient things that we encounter. Tides are not likely to rival the November nor’easter, but flooding could be moderate on Wednesday during the late morning. High tides are generally between 9:00 & 11:30 (AM & PM) for Tuesday night through Wednesday night. This tidal flooding event should be mostly for the south side cities and southward into North Carolina. Tidal flooding should be more minor for the Peninsula and areas northward.

Again, the models haven’t reached a good consensus yet. So this storm may yet have some “tricks up its sleeve.” So far though, this doesn’t look like it’ll be a major nor’easter. Stay tuned!

-Don

Strong westerly winds have picked up during the evening hours and are likely to get just a little stronger into Friday.

As usual, strongest winds are likely near the coast & Bay…25 to 30 mph with gusts to near 45 mph. Winds along Virginia’s Eastern Shore could gust to near 50 mph.

Those strong westerly winds could push up the tides sound side along the Outer Banks Friday.

Temperatures will be chilly on Friday, but not horrendously cold. Afternoon high temperatures should be in the mid 40s. But with the wind, it’ll feel like around 28°!

-Don

Computer models are widely divergent in snow expected for the region. And right now, this storm is not behaving exactly like any of the computer models have predicted.

When you add it up, the coldest air will not likely coincide with the heaviest precipitation over the area. By the time the coldest air arrives, the heaviest precipitation will be mostly out to sea. So if the cold air doesn’t have as much moisture to work with…less snow. However, we’re still very likely to see some areas with snow on the ground Thursday morning.

As of this hour, the coldest air is moving eastward out of the mountains. The heaviest precipitation is within about 40-50 miles of the Virginia/North Carolina coast. The storm itself is rapidly developing near Cape Hatteras and will likely push northeastward…dragging the heaviest precipitation out to sea before the near-freezing air arrives. Additionally, a dry “punch” of air is likely to move northeastward in the wee hours. All of this should serve to shorten the amount of time that snow falls in the area overnight.

The warm, wet ground is another effect that will somewhat lessen the amount of snow remaining on the ground by morning. Temperatures have not dropped below freezing very often over the past several days, so the soil and pavement are nowhere near freezing. So the snow that does fall should melt on contact for much of the area. Certainly, we’ll end up with snow on grassy surfaces, but less to even none on the pavement. The only exception to this would be the possibility of “snow bursts” of heavier stuff which could overpower the effect of warmer soil. I do want to mention that temperatures are not likely to drop much below freezing by dawn, so water freezing on the roads is not very likely at all.

With all that being said…it’s gonna’ snow! In fact, it is snowing across much of the region at this hour. We’re likely to end up with half an inch to an inch across the Hampton Roads cities, 2″-3″ from Williamsburg through the Middle Peninsula, and 3″-5″ for the Northern Neck (& perhaps, northern Accomack county).

Jon Cash will be in for WAVY News 10 at Sunrise. He’ll be with you on-air for the latest updates.

Rain should begin in the area late Wednesday afternoon through the evening hours. Around midnight or so, some of that rain should mix with or change to light snow. That light snow should continue off and on during the overnight hours…tapering off by around 8:00 or 9:00 AM. We could still see a stray flurry or two during the day Thursday, but most areas will not see further accumulation. The exception to this could be the Northern Neck and Accomack County on the Eastern Shore. These areas are closer to the center of the storm (Jersey) and could see slightly more snow.

Most of us will just end up with a light dusting for Wednesday night into early Thursday. Half an inch to an inch accumulation could possibly fall out of the sky. It’s questionable though, how much of that snow will stick!

We’ve had enough warmer weather over the past few days to keep the pavement temperatures above freezing. In fact, most areas won’t see solidly freezing temperatures overnight and into Wednesday morning. These warm ground temperatures mean that when snow does fall, it’s likely to melt on contact…at least, for a while. When (and if) snow does get heavy enough to start sticking, it will tend to stick to the grass, but not as much to the roads.

We should be able to fine tune the snow amount forecast as we draw closer to the event. Stay tuned!

In the now time frame, fog is the immediate concern. While widespread fog is likely, I don’t think that widespread dense fog is likely. Actual dense fog will likely be a bit more patchy. However, that’s still a problem and sometimes more of a problem. For example, we’ve all been driving in a relatively light fog and then-in an instant- we’ve driven into zero visibility. Drive carefully out there. Low beam headlights, a prudent speed, and a good distance between the vehicle ahead of you!

Then we turn our attention to late Wednesday night and early Thursday. It is entirely possible that we could see some snow mix in with some rain late Wednesday night. In fact, it could be all snow for a while in the pre-dawn hours. However, the amounts are expected to be light…on the order of a half inch to an inch. Additionally, it is expected that whatever snow we get will likely revert to all rain, thus melting whatever snow we get. Again, I’m not too concerned about snow amounts as of this time. But it’s a little early to really nail it down. Stay tuned!

Very quiet, slightly warmer weather for us into the weekend

Relatively quiet, but very unusually warm weather continues for the Vancouver Olympics. Mostly sunny skies should continue through the weekend. Those clear skies are both good and bad for snow conditions. During the daytime, sunshine tends to melt the snow (duh!). But nighttime clear skies tend to make those nights colder, re-freezing existing snow and allowing new snow to be artificially created for the next day’s events. Of course, temperatures vary hugely from near sea-level in Vancouver to the higher-elevation venues like Whistler.

The Canadian national weather service, Environment Canada, is a terrific site  to see the forecasts for all of the specific olympic venues. Of course, all the temperatures are in Celsius. To get the temperatures in fahrenheit, just click on the “°C” colored link…and it’ll automatically translate into fahrenheit.