March 2013 Archives - New York Metro Weather

Fair weather on the way in wake of nor’easter

March 25, 2013/0 Comments/by John Homenuk

Water vapor satellite imagery early Tuesday morning, showing the strong coastal system moving away to the Northeast and calmer, drier weather approaching.

A late season winter storm impacted the area on Monday, with less flair than originally expected. Warm ground temperatures (and warm air temperatures during the day) combined with light precipitation rates to keep it mainly a non accumulating snow event in Northern NJ and New York City. Dry air won the battle over precipitation farther north over Connecticut and Southeast New York. Farther south, over Central and Southern NJ, a few inches of snow were observed through Monday evening. The brunt of the storm (as far as heavy banding and the low pressure center), however, remained barely offshore. In the end, the storm system will likely be remembered as a “near miss for the area”. As we move forward into the week, a moderating trend in temperatures and dry weather are in the forecast — and it should at least begin to feel a bit more like Spring.

Cool air will hang on initially, with some clouds and a slight chance of showers on Tuesday. High temperatures in the upper 40’s, approaching 50, are expected. Cool nights will still be present with lows in the 20’s and 30’s — so don’t put away the coats just yet. Additionally, the cold air is still present to our north (owing to the big blocking and historically negative AO we experienced last week), so that could take a while to shake. By late this week into the weekend, high temperatures are expected to reach into the 50’s. I think it’s safe to say we are all looking forward to it.

Tuesday: Partly sunny with a high in the mid to upper 40′s. Northwest winds around 10 miles per hour. A slight chance of showers in the afternoon.

Tuesday Night: Mostly clear and cool with lows in the upper 20′s to middle 30′s. Northwest winds 1o to 15 miles per hour.

Wednesday: Mostly sunny with a high in the mid to upper 40′s. West winds around 10 miles per hour.

Thursday: Mostly sunny and feeling warmer with a high in the mid to upper 40′s to near 50. Overnight low in the mid 30′s.

Week begins with late season winter storm

March 25, 2013/0 Comments/by John Homenuk

NAM model forecast precipitation totals through Tuesday. Notice the sharp cutoff in precipitation totals from North to South near New York City.

Historically strong blocking, incredibly low Arctic Oscillation values, and a strong negative NAO have been in place for over 7 days. It was only a matter of time. A strong disturbance moving through the Central United States will move eastward towards the Mid Atlantic Coast, and eventually offshore. The surface low, which initially develops towards the Ohio Valley, will be forced to transfer and redevelop off the coast. However, the northward extent of precipitation will be extremely limited with a sharp cutoff likely. This will throw a serious wrench into the forecast — with a large discrepancy in snow possible over small areas.

Our Storm Total Snowfall Forecast, valid through Tuesday PM.

Forecast models have been inconsistent with the developing gradient. As of Sunday evening, the GFS is the “wetter” of the model guidance — and farthest north with the precipitation shield. The NAM (which had previously shown extreme precipitation totals), Euro and SREF remain farther south. The precipitation amounts and intensity become an increasingly important issue due to the time of year. The warm ground and marginally cold low levels of the atmosphere suggest that light precipitation will not accumulate — and may even fall as rain in some locations on Monday.

Accordingly, the forecast remains highly uncertain as we move forward. We have laid out the expected snowfall totals in our Storm Total Snowfall map, but confidence remains extremely low. It is possible that many locations see light snowfall accumulations but only on grassy surfaces. The best chance for solid light to moderate snowfall totals appears to be over Interior Central and Southern New Jersey, where more persistent heavy precipitation is expected.

A Winter Storm Warning from the NWS remains in effect for Southern New Jersey, while a Winter Weather Advisory remains in effect for the remainder of the area.

The periods of snow, which will begin Monday, could linger into Tuesday throughout much of the area. For up to the minute updates on the upcoming storm system, stay tuned to our Facebook and Twitter accounts.

Cool and dry weekend, snowstorm threat looms

March 22, 2013/0 Comments/by John Homenuk

Canadian model (CMC) showing a significant snowstorm impacting the area on Monday. The CMC remains one of the farther north models within the envelope of guidance.

Not only is March madness taking place in the college basketball world, but it’s also taking place in our world of meteorology. Cooler than normal air remains well settled into the region to begin the weekend, as historically strong blocking near Greenland and the North Pole as well as a historically negative Arctic Oscillation (AO) has led to a late-March pattern that feels more like mid-February. High temperatures in the 40’s and cold westerly winds have been a staple in the area weather the past few days. Much of the same is expected through the first half of the weekend, with cooler and dry conditions prevailing. Attention will then turn to a potential snowstorm (yes, snowstorm) on Monday. Forecast models are struggling with the track and intensity of the system as well as the resulting impacts on our area. We’ve detailed the entire threat below.

SREF ensemble mean showing a significant snowstorm on Monday.

It’s Spring. What is causing the threat for the snowstorm? Historically strong blocking over the high latitudes (extending from Greenland to the Pole) is displacing unseasonably cold air into the Northern 1/3 of the US. At the same time, a strong disturbance is ejecting out of the Pacific Northwest into the Central United States. Such a storm track could occasionally cause a rain storm in our area, especially this time of year, with the surface low tracking to our west. However, the presence of the unusually strong blocking is forcing the system farther south, to redevelop off the East Coast. The presence of cold air to the north and throughout our area is increasing the likelihood of snowfall if precipitation makes it to our area.

What are the uncertainties with the system? One reason why blocking patterns can be so unseasonably cold is the fact that they force powerful Upper Level Low (ULL) pressure systems to meander at latitudes just to our north and northeast, which are a great source of cold air. However, when an ULL is too powerful and too close to our area, it can compress the height field out ahead of our storm and force it drift eastward instead of turning the corner and heading up the coastline. We do know that eventually, the storm will run into a brick wall and be forced to drift eastward. However, will it do this after it gets to only Ocean City Maryland’s latitude, south Central Jersey’s, or somewhere in between? This is the difference between a graze, a moderate rain to snow event, and a major snowstorm.

AO Falls to lowest value ever for Mid March

March 20, 2013/0 Comments/by John Homenuk

The Arctic Oscillation readings over the last several months show the dramatic and unrivaled drop in readings during mid March 2013.

The Arctic Oscillation (AO) has fallen off the cliff in the last week, as incredible high latitude blocking ridges have developed both north of Alaska and over Greenland. The AO fell below -5.0 to -5.632 on March 20th, 2013 — making it by far the lowest reading after March 15th in the history of the AO’s recorded values. It also remains, historically, the lowest AO after March 6th.

GFS Model observed (black) and forecast (red) AO values

The Arctic Oscillation, or AO, refers to the generally opposing pattern between pressure in the northern-middle latitudes and the Arctic. It is a climate pattern, that is characterized by counterclockwise winds which circulate around the Arctic near 55°N. The phase and degree of amplitude of the Arctic Oscillation can be a very useful forecasting tool, especially in the winter season. During a positive phase AO, a belt of strong winds circulating around the pole often acts to keep cold air confined to our north. But a negative AO opens the proverbial flood gates for the arctic air to penetrate much farther south.

It should come as no surprise, then, that this strongly negative AO phase has been accompanied by the presence of unseasonably cold air. The forecast, holds the potential for cold air through the next 7 days with chances for snow. The GFS ensemble and most medium range global models forecast the AO to rise over the next 7 days. Although it is typical for the AO to rise and fall rather consistently, the dramatically low values are being accompanied by rather high return values to normal, and in some cases a positive phase of the AO. Regardless, It remains to be seen if the wintry weather threats will work out Still, one thing is for sure: we are in uncharted territory as far as the Arctic Oscillation goes, for this late in the season.

For more on the Arctic Oscilation check out this article, which details the different phases and amplitudes.

Tag Archive for: March 2013

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