Jan 22, 2013: Cold Continues; Snow Expected Friday

Forecast Highlights:

Very cold temperatures were observed today with a cold air mass over the region, with daytime highs peaking in the upper 10s inland and the low 20s across the rest of the area. Windy conditions were observed as well with gusts up to 25-35 mph, resulting in wind chills in the single digits across the area. These cold temperatures will continue through the rest of the week into Saturday, while a storm on Friday is expected to produce snow across the area, but with uncertainty regarding accumulations.

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Tonight - Thursday: Strong Cold Continues

Overnight lows will be very cold tonight, dropping into the mid to upper 0s inland and the upper 0s to low 10s for the rest of the area, with low to mid 10s in NYC. Highs on Wednesday will be cold as well, peaking in the upper 10s inland and the low 20s for the rest of the area. Similar temperatures are expected for Thursday but perhaps a few degrees warmer. Breezy conditions are expected for both days, with wind chills again in the single digits across the area and below zero inland.


Friday - Saturday: Less Snow Expected

The main uncertainty in the forecast is regarding the storm expected for Friday and Saturday. As this afternoon's update mentioned, the model guidance became more spread out today, with the GFS, originally showing moderate snow accumulations across the area, now showing a weaker and more suppressed storm with light snowfall, with the UKMET and CMC were further north with more snow for the area. The ECM 0z run last night had a significant snowstorm for the area, with over 10 inches in some spots, while the 12z run did not develop the low pressure until it was offshore, with only minor accumulations at best.

The storm is still about 3 days away; while significant changes are not too likely, additional changes are expected with the model guidance considering that there are still differences with the handling of the shortwave, which is still over the Pacific but is expected to move inland tomorrow night where it will be sampled better, as well as the northern stream and the trough currently over the region. However, there are about 72 hours remaining until the event begins to affect the area, and significant changes as in a major snowstorm like the 0z ECM showed are not expected at this time. The trends on the model guidance throughout the day have been less favorable for a snowstorm, with the northern US shortwave trending towards less digging, which instead of resulting in a strong low pressure developing in the southern Ohio Valley, moving through the Mid Atlantic and as an intensifying coastal with widespread moderate accumulations, ends up resulting in a weak low pressure near the Midwest with a weak low pressure developing near the Mid Atlantic coast, remaining relatively flat and progressive while racing to the ENE and gradually intensifying. This scenario would just result in widespread snow showers across the region with light accumulations at most.

This significant change in the model guidance, especially considering that the storm is now only 3 days out, does suggest there is validity to this idea, with decreasing likelihood of the scenario initially expected with a strong low pressure in the Ohio Valley moving through the region. While at this time, there is not enough confidence to completely dismiss the snowier outlook, the current forecast has been revised downwards to reflect light to potentially moderate accumulations, with light snow developing on Friday afternoon and lasting through the early overnight hours before ending, as this is still expected to be a fast moving system. There is still some uncertainty in the forecast, and while it is not impossible to see a snowier solution than currently expected, the latest model solutions cannot be dismissed either, and it is possible that accumulations may have to be revised downwards again with the next update.

The next update will be posted on Wednesday afternoon regarding the storm and any changes in expectations, with the next full discussion tomorrow evening, when any additional changes to the forecast will be made.


Longer Range Update: Cold temperatures are expected to continue through Saturday, with highs again in the 20s and lows in the 10s for most and possibly single digits inland. By early-mid next week, however, lower 500mb heights are expected in the western US as the PNA temporarily ends up strongly negative, which should result in rising heights in the East. At this time, next week does not appear to be a significantly warmer than average week, although temperatures will be much warmer than they are for this week, with highs likely back into the 30s and 40s. The next chance for rain is likely to be around the 30-31st, with a low pressure likely to track west of the region. More information on next week's outlook, as well as the potential for a cold pattern to return for early-mid February, will be posted throughout the next few days.