Winter Wx

New Snowfall Map for 3/02-3/03

Miguel Pierre Forecasts, Winter Wx , ,

FinalSnwofallmap0303

This morning’s 6z and 12z NAM, RGEM, GFS guidance today has trended further south this storm. The latest HRRR runs also supports this trend. Total qpf totals for Northern NYC are now in .10″ -. 25″ range. With less north and more south. Current radar, water vapor imagery, and observations, don’t give me much reason doubt these solutions. Also some warmer temperatures, may support more wet snow,sleet, rain at onset. Especially over Southern New Jersey. The cause for the continue trend further south, is the lobe of the PV, dropping down faster into Great Lakes and Northeast regions and suppressing this
southern stream wave.

Along with the south trend, is also a trend to end the storm faster everyone. For NNJ,NYC, LI snow may tapering off to flurries by sunrise tomorrow morning. While steadier snow continues further south into late morning or early afternoon hours tomorrow.

So for all those reasons, snowfall totals have been adjusted downward everywhere. And it’s possible this is still too high for some areas. Just to note, the ranges in general, are from lowest to highest; from north to south. For example: Staten Island, is more likely to see 3″ or 4″ than 5″ or 6″. While Philadelphia is likely to see at or either side close to 6″.

Snowfall Map for Winter Storm Sunday Night and Monday

Miguel Pierre Forecasts, Winter Wx

 

FirstSnowfallmap0303Latest guidance over the past couple days has trended farther south with this storm for Sunday and Monday. Models now show stronger confluence, behind a lobe of the polar vortex, swinging over the Great Lakes. This is shearing and suppressing the southern stream disturbance to the south and creating a sharp cut-off of northern fringe of area of overrunning precipitation with this system. There will be heavier banding just north of the thermal gradient. Where it stronger frontogenesis will be occurring. Which currently appears to be over Southern New Jersey and DE and SE PA.

12zECf48The NAM is also slowest push the artic boundary to the south of the area tomorrow. So there may be some light rain,sleet, and/or wet snow at the onset. Especially for the coastal sections. But this should quickly changeover to snow tomorrow night. With surface temperatures falling through the 20s and teens. Liquid totals are expected between .25″ to .50″ over NYC/LI/NNJ. Less to north. As much as 1″ of liquid in SNJ. The column with warmer air aloft, support snow ratios to average between 12 and 15 to 1 for much the area. Strong upward vertical motion by might support higher ratios south of NYC.

Check back for more updates. If they are any changes handling the lobe of the polar vortex or the southern stream disturbance, there could be some north or south adjustment to snowfall totals tonight or tomorrow.

Major Winter Storm More Likely for Sunday Night and Monday

Miguel Pierre Winter Wx

The potential for major winter storm over Eastern US is increasing for Sunday night and Monday  A Pacific storm will move inland over California and weaken on Saturday. The remaining  energy from this system will track into the Southern Plains on Sunday. Where new area of  low pressure will from along a strong baroclinic zone.

This afternoon’s water vapor of the storm now in the Pacific:

wv-animated

Overrunning precipitation will developing well ahead of this system on Sunday evening, over the tri-state area, What form this precipitation take depends on timing and placement artic boundary moves through the area. At this time, most of guidance pushes this boundary through to south late Sunday night, with low-level and mid-level temperatures falling behind it. So precipitation could start of mix of rain,sleet, and snow early Sunday night before changing over to all snow.

A strong thermal gradient form between along the artic boundary, as the Southern Plains low being to track NE and push warmer air over a very cold airmass support by a polar vortex over Southeast Canada and large, strong high pressure system to north. Just north this gradient, is where snowfall rates will be higher due to isentropic lifting. This is important for significant snowfall to occur, especially during the daylight hours on Monday. Surface temperatures will also lower 20s and teens throughout the region. So there will be some accumulation, despite the stronger sun angle in early March. Anywhere, south of this gradient, snow changes over to sleet, freezing rain, or plain rain near the coast. These details will be fined tuned as get closer.

Today’s 12z GFS forecasting heavy snowfall just north of thermal gradient over the tri-state area on Monday :

12zGFSf102The evolution of the polar vortex, will be a determining factor on far north and amplified this storm system will be and the placement of thermal gradient in our region. A stronger vortex over all of SE Canada will shear out this system and keep us north of the gradient. A weaker vortex would allow this storm to amplify more and pushing the thermal gradient to our north.

500mb heights and 850mb temperatures from today’s 12z ECMWF (right) and ECMWF Ensemble Mean (left):

12zECENS500mb12zECENS850mbOn the extreme sides, of possible scenarios, is one that leads to complete suppression by a very strong Polar vortex. The other scenario is that this is mostly rain with weaker Polar Vortex, allowing more warm air to surge northward. Based today’s guidance, for stronger polar vortex and more organized system, these scenarios appear, very unlikely at this time.

A couple more notes on this system. First one, is that there is a 150kt+ upper-level jet streak running to north of it. Underneath this jet streak is alot of divergence (forcing). This will cause an expansion of snow well north of the low track.

Today’s 12z ECMWF 200mb jet forecast:

ecmwfUS_200_spd_096

Second note, is that s stronger/organized storm, would increase warm-air advection into very cold airmass already in place. This results in strong frontogenesis.  An example is from the 2/13/14 winter storm, where many of saw snowfall rates of 2-4″ per hour, during the early morning. In this case, this may not be as extreme. But it potential, that would have evaluated, as we get closer.

NAM frontogenesis forecast for the morning of 2/13/14:

18zfrontb20Check back for more posts on this system here over the next few days!