Month: March 2014

Winter Storm Possible Sunday Night into Monday

Miguel Pierre Uncategorized

Fri evening update: Latest guidance now keeps accumulating snow south of NYC. Due the less interaction between northern and southern streams. As well as a stronger high pressure over the Great Lakes/Northeast. My confidence is increasing that this will occur. But will continue to monitor for any changes. Look at 7-day forecast for updates.

Guidance shows another winter storm possibly for late Sunday night into Monday. What complicates this winter storm threat, are models handling of another system coming into Pacific NW and flattening heights over the Western US. Each model has slight differently 500mb pattern that results in different impacts in our area.

The 0z ECMWF and 6z GFS hangs back more southern stream energy over Gulf coast. While also showing a little northern stream interaction. This more strung out area of low pressure with two waves that remain weak and farther east. The reason for this because Pacific system has already moving into Northern Rockies.  These solutions would keeper is colder and drier.give a light to moderate snowfall for the tri-state area:

0zEC96hr

6zGFS84hrThe 0z CMC model is showing  more southern stream energy coming out and interacting with northern stream energy. This results in a stronger first wave and the second wave coming further north. The reason this can happen here, is that Pacific system is little slower coming into the Northern Rockies. Strong high pressure will also be supply us with cold air and enhance a thermal gradient just to our south.. This solution would result in moderate to significant snowfall for much of the tri-state area.

0zCMC84hrThe 6z NAM has more phasing between northern and southern streams. Therefore has more consolidated storm, tracking further west. The reason it is able to do this, is because Pacific system is much slower coming into NW coast and heights remain stronger over Northern Rockies. This solution would actually cause more warmer air to surge aloft, changing many of us over from heavy snow to sleet or freezing rain:

6zNAMf786zNAMf84 ECMWF,GFS, GGEM all have support form their ensemble means. The ECMWF and GFS , have a little more support from the current progressive pattern, as well. However, the GGEM has been most consistent with ejection of more southern stream energy. So it’s solutions should be strongly weighed here. The NAM at this range is unreliable for winter storms. So I would be wary of it, without any other model support. Models will get a better on all this energy as it comes onshore the next few days. I will have another update this evening, with new set of models runs.

Mild Today, Rain Wednesday, Bitter Cold Thursday

Miguel Pierre Severe Wx, Winter Wx

In my last post, I discussed hot the models where show temping the low and middle 50s. Temperatures actually soared into 60s today in many with west downslope winds. JFK set new record at 65. Beautiful late winter day to enjoy some outdoor activities. Tonight will see increasing clouds late with temperatures falling into upper 30s inland and lower 40s for the coast.

With this very mild airmass in place, the storm for Wednesday has trended warmer, deeper and further northwest. It now appears this will be a mostly rain event for even parts of Hudson Valley and Interior CT.  If fact, these could steadier and heaviest rainfall. Many of us will be in warm sector, with periods of light rain and drizzle with temperatures rising into 50s over NYC and lower 60s over Central and Southern NJ.  A strong 500mb shortwave and cold front, likely to produce a forced low-topped squall with some gusty winds later tomorrow afternoon or evening. With some elevated instability in the form steep mid-level lapse rates,TTs in the 50s and MUCAPE, some elevated thunderstorms are also likely. Any surface-based instability will be based on any clearing that takes place, tomorrow afternoon. This will enhance the threat for isolated severe wind gusts. Most-likely south and west of NYC.

12zNAMf3912zNAMrad36Behind this cold front, it will turn windy with temperatures will rapidly fall back into 20s and teens later tomorrow night. Any wet roadways could see some black ice form. Some snow showers that could coat the ground, are also possible with the upper-level trough with swinging through tomorrow night. Especially north and west of NYC.  Thursday will be big change from the last few days. It will be windy with temperatures only slowly climbing out of the teens into lower 20s. This arctic blast will not last longer, however. After a cold Friday morning, temperatures will rise into upper 30s and lower 40s in the afternoon.

March 12-13 Storm Looking More Wet than White

Miguel Pierre Winter Wx

There’s been much discussion in the media and weather forums about another winter storm next week. I haven’t posted too much about it here, because model guidance haven’t shown alot of consistency or agreement. Particularly, on amount of cold air/confluence over the Northeast and the handling northern and southern stream energy. However, the models now appear to be converging on solutions, that doesn’t support a major snowfall for much of the Tri-State Area, at least.

First let’s discuss, what we have ahead of this storm.  We have temperatures several degrees above average for early March, next few days. Highs will be near 50 degrees on Monday. Then models show temperatures in the low or middle 50s on for NYC and south on Tuesday.  So unlike other winter storm this seasons, we don’t have cold air mass in already in place to begin with. Which is not a good sign for major snowfall in our area.

12z NAM showing high temperatures 40s and 50s on Tuesday:

12zNAMf57

During Tuesday night, a disturbance rotating around the polar vortex over Canada, will be dragging an cold front into Upstate NY and New England. Behind this is colder airmass,  that will support snow in those areas. However, this cold front shown by the guidance stay north of the NYC area. This front, also marks leading of edge of the confluence zone, that will be too far north to suppress this storm to the south.

Now let’s discuss at what we have coming together for this storm. We have northern stream energy coming out Pacific and around the Polar Vortex, out of Canada. The issue with the model guidance, has been how much of the Pacific energy comes out and begins interacting with energy coming from Canada. The latest guidance now brings out a little more this Pacific energy east. However, the phasing between disturbances, is somewhat sloppy and trough remains broad. This happens because the ridge over the West Coast is flattening east. Energy has difficult time consolidating and phasing more cleanly along the the trough axis. The result is storm that only slowly deepens and organizes as it moves east.  Development of a strong cold-conveyor belt or deformation band behind this low, occurs too late for us. Especially for the coastal plain. Some dry-slotting near the low track will also be a concern.

The 12z GFS showing a broad trough over Eastern US and a shortwave flattening the ridge over Western US:12zGFSf90Based on latest guidance, this storm would be mostly rain for much of New Jersey, NYC, Long Island and Coastal Connecticut. As the low moves offshore and intensifies Wednesday night, it might pull down enough cold air for rain to change to snow before ending or cause a flash freeze. For the Lower Hudson Valley, and Interior CT,  precipitation types are less certain. If the low tracks far enough south,  we could possible see more snow or a wintry mix throughout most of the storm. If low tracks farther north, there would likely be a wintry mix changing to rain, before ending as snow. The specifics here on precipitation types and amounts will become clearer the next few days.

That all being said, there is still enough time for some changes here, that could affect the outcome of this storm. The Pacific shortwave energy won’t be onshore until tomorrow. So the models have start having better grasp on he amplitude of that energy coming east. If the models today are flattening the Western US ridge too much,  this will result in more Pacific energy ejecting east and more southern stream energy involved. Also the disturbances rotating around the Polar Vortex are always difficult for the models handle. If any of these disturbances are stronger, than confluence will be ahead of this storm. That would result in a colder or further south solution. I will be watching for these changes on future model runs and post more blog updates here accordingly.

The 12z ECMWF today at 72hrs:
12zEC72hr