Saturday, March 1, 2014

Major Snowstorm Coming Soon...

This one will be different. In fact, it has already been unique for this winter due to its track and size. The storm that will impact the Mid-Atlantic Sunday through Monday originated as a massive storm tracking through the Pacific with an eye-like structure. Take a look....
Circle #1 is the storm, ignore #2
The storm will emerge from the western U.S. into Texas overnight and track ENE from there. Due to the extremely cold air mass in place, the our system will be strung-out in nature, much less impressive than the storm depicted above. Due to the strung-out nature, the storm will come through our area in a series of lows. The first wave will occur Sunday night. This is likely the part of the storm that areas north and west of Philly will receive the majority of their snow. In southern areas (Philly-DC corridor), precipitation will start as rain and transition to mixed and then snow overnight Sunday into Monday. 

The second wave, which will occur during the day on Monday, will hit the southern Mid-Atlantic hardest. This includes the northern half of VA, all of MD, and east into DE and southern NJ. A general 8-12 inches is likely for this area, with up to 18 inches possible in the higher elevations. The storm will wind down from west to east by Monday evening. 

The reason why this storm won't go far enough north to give upstate PA and New England significant snow is that Polar Vortex situated up in Canada will flatten out the 500 mb winds, causing them to blow straight west to east. This sets up a progressive pattern, forcing low pressure to stay further south. 

Snow map coming later tonight....

Thursday, February 20, 2014

Update on Blog Status

Unless there's a major storm upcoming, I will be posting weather updates daily on my Facebook page....

Wednesday, February 12, 2014

Second Half of Event

As mentioned in the previous post, this will likely be a two-part event for eastern PA and NJ. As the storm starts to really bomb out near Long Island on Thursday evening, it will wrap precipitation around and setup a strong band from Philadelphia to NYC and eastward. This band will likely bring 3-6" of additional snowfall for the area before winding down from south to north after midnight on Friday.

Heavy Snowstorm Wednesday Night through Thursday

A very strong low pressure system will affect the area with snow, sleet, freezing rain, and wind on Wednesday night through Thursday.

A disastrous freezing rain and snow event is ongoing across the south currently with some place already receiving in excess of a half inch of ice with much more to come. The heaviest icing will take place across northern GA and throughout SC. Farther north into NC will have a better chance of seeing more snow, but icing is likely in those areas as well even down near the coast.

Impacts on the Mid-Atlantic up into New England will mostly involve snow, with the exception being areas east of the I-95 corridor.

For the Mid-Atlantic, this storm will likely be a two-part event. The first thump starts during the evening hours in the southern Mid-Atlantic and closer to 10 pm or later as you go from DC and to the northeast. This initial round of snow will fall heavily at times and begin to taper off around mid-morning for the in the northern areas. Totals through the morning hours in the southern areas (especially the interior) will range from 6-10" while the I-95 corridor and NW will receive 5-8".

The difference between the I-95 corridor and areas just to the NW is how long precipitation will stay as snow. While the big cities may turn to all rain for a period late Thursday morning and early afternoon, areas to the NW will likely stay snow for longer and then changeover to some form of frozen precipitation (sleet/freezing rain). The reason for this is due to the track of the low. As the storm winds up off the coast, it will retrograde slightly towards the coast, bringing some slightly milder air with it. The key to this part of the storm may lie in the sea surface temperatures near the coast. Currently, they are in the upper 30s off NJ. This means that while the shore is guaranteed to changeover to rain due warm air advection, if winds remain out of the northeast (which they will since the center of low pressure will likely stay off the coast), a colder solution may unfold due to the very cold air already in place ahead of the system.

Progression of the Storm on Simulated Radar

Very early morning hours

Early morning

Late morning

Most likely track (in black) with ensemble members (in brown). This shows that the track could be further east, allowing for the potential for more wintry precip 

More about the second part to come....

Sunday, February 9, 2014

Snowstorm Potential Wed-Thurs

An interesting setup is taking shape for next week. It's a very complex situation, but the result may be a major winter storm for the Mid-Atlantic up into New England. Model guidance indicates that a weak wave of low pressure will emerge into the Plains states in the next 24 hours. This system will crawl along the Gulf coast line, sparking off showers and thunderstorms in the deep south. Meanwhile, up in the northern Pacific, a large area of low pressure, known as the Aleutian Low, will hit the Canadian coast by Tuesday evening. The exact track of this low, thousands of miles away from the storm at hand, will play a major role in what makes or breaks this storm's impact on our area. If this massive low pressure system tracks further south, it will break down the PNA ridge, creating a ripple effect such that the pattern becomes more progressive. This would likely cause the Gulf storm to go out to sea.

Another key to this storm is a broad, weak wave of low pressure that will emerge into the Canadian plains down into the upper Midwest. The timing of the phase between this system and the Gulf system is of the utmost importance when it comes to whom this storm will impact the greatest. If the storms phase late, only Canada will experience a major winter storm. However, if the systems phase earlier, the northeastern U.S. will be in play as well. Even if there is an early phase, the location of high pressure to the northeast will determine the track and duration of the event.

The key to know with this setup is that it is very fragile and is very much dependent on timing. I like to call these kinds of events "low percentage." This means that at this point, there is a threat, but don't be making plans around the potential for late this week just yet.

Tuesday, February 4, 2014

Heavy Snow and Ice Storm Tonight and Tomorrow

This post is very late, but trust me, I have been tracking it. Heavy icing should be expected in southwestern PA and throughout the southern half of PA and into central NJ. The icing in these location should be in the order of 0.25" to 0.75" with locally higher amounts possible in the heaviest banding.

Accumulating snow should fall on the front end as far south as Philly-eastward and westward into the higher elevations of Maryland. In those areas, a general 1-3" is likely, with amounts increasing as you go north. The jackpot will be in northern PA to southern NY eastward into interior New England, with some areas receiving nearly 18".

Snow will generally start from southwest to northeast tonight. Central PA will starting to in on the action at around to 10:00 pm with areas further east into NJ waiting until 12:00 am or 1:00 am. The reason I didn't mention NY is that a band is already set up across southern NY from Jamestown to just west of Ithaca.

Some of the short-range models have been trending colder, leaving room still for the possibility that areas north of Philly do not change over to plain rain during the day tomorrow. However, this outcome remains unlikely. A changeover to plain rain should occur from southwest to northeast starting at around 10:00 am.

For areas that go to rain....
Due to the wet nature of the snow from the previous storm and the layer of ice that will be on top of it by the time the changeover occurs, rain will have a tendency to run off the snow pack and to a low-lying locations. For this reason, areas with poor or snow-covered drainage may experience some street flooding.

Simulated radar by 10:00 am tomorrow morning. Pink and purple is mixed/ice and blue is snow

Sunday, February 2, 2014

Snowstorm Tomorrow

A large and moisture-laden storm is taking shape across the south today as thunderstorms continue to fire south of the system and move north.

Interestingly, this storm in drawing in moisture not only from the Gulf of Mexico, but all the way from the Pacific Ocean...

Because of the convective nature of the storm, the short-range models should be used over the GFS and Euro. A general 3-6" should be expected across the Mid-Atlantic, excluding northern areas of central and western PA. Highest amounts should fall near the Mason-Dixon line and as far north as the Allentown-NYC corridor. Somewhere in this area, where ever the heaviest banding sets up, upwards of 8" will fall. Some of the short-range models like the RGEM and RUC hint that these bands could be capable of producing 2" per hour snowfall rates. A sharp cutoff to the north and to the south of the heaviest snow band should be expected.

Timing and Impacts
In general, precipitation should start from SW to NE during the overnight hours and early tomorrow morning. From Philly-southward, precipitation will likely start as rain or sleet before changing over when the heaviest banding moves into the area. Due to the warmth over the weekend along with surfaces and marginal 2m temps, snow will have a hard sticking on paved surfaces at the onset even in areas that due to receive snow. As the surface cools down and temps fall to around 30 throughout the regions north of Philly, snow will begin to accumulate on back roads and eventually even main roads.
Heaviest snowfall will likely occur from early morning hours until late morning before wrapping up in the early to mid afternoon.