Forecasts

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.

Snowfall Map and Discussion for 2/18/14 Winter Storm

Miguel Pierre Forecasts ,

 

130am Snowfall map***Updated snowfall map, based latest guidance and observation and radar trends. It appears this system moving faster, and less snowfall will fall for areas NW of NYC. Still anyone visibilities may reduced to 1/4 mile for a couple hours, in heavy bands of snow.***

Cold high pressure will slide to the east tonight. Winds will turn more southeasterly. Temps will probably not drop much this evening and the may rise after midnight, near the coast. A 500mb shortwave will phases into closed low over Great Lakes region than open up as it heads east. At the surface, a small but robust area of low pressure will into Ontario and weaken. A secondary low will form near NJ/DE coasts and track into New England. This will set the area up for another moderate winter storm.

Precipitation with this system should arrive late tonight. There will be enough cold air in place, for everyone to start as accumulating snow. However, a  low-level southeast flow increases, enough warm air arrive to change coastal sections to rain or drizzle before ending tomorrow afternoon. Exactly when this happens and how snow fall before it, is problematic as mesocale models such as the NAM and RGEM are showing more liquid amounts than the global models. As they develop secondary low faster. Dynamics may also come into playing in keep boundary level temps cooler. The NAM model shows strong upward vertical velocities and mid-level instability (H5-7 lapse rates 7.1 C/km and total totals in upper 40s) that would result in band producing 2-3″ per  snowfall rates tomorrow morning with perhaps some thunder, before any changeover. The shortwave energy with system is also very potent. At this time, I will stay under the NAM’s totals. But if the NAM is correct, or the changeover is delayed, snowfall totals could be a few inches higher than on snowfall map.

namNE_500_avort_021Areas that see the least snowfall on the map, are south and east face shores that will most influenced by 15-30kt SE winds off the ocean and changeover to rain quickly. Just little farther inland over north side of NYC and north shore of LI snow will last longer, and come down moderate to heavy at times. Before changeover to rain and ending after 1-3 hours. Further NW in NNJ and theLower Hudson Valley, should remain mostly snow (perhaps ending as light rain and drizzle).

I might update this forecast map this evening or tonight, if more guidance comes in supporting a bigger/smaller snowfall. Tomorrow morning, I will be nowcasting here.

Snowstorm 2/15/14

Miguel Pierre Forecasts, Winter Wx

Models have been trending stronger and NW this system. Particularly with closing off 700mb and 850mb lows near our area. The GFS has been leading way in these trends. The 0z run tonight back a little bit from it’s 18z run. Which would given NYC around 6″ of snow and  LI and CT 6-12″ of snow. But it still more amplified than the 12z run. The 0z UKMET and ECMWF has also come in further west tonight. So my forecast will follow the 0z GFS closely. Note that initially BL temps may be warm enough for some mixing or melting at the start. Especially over LI. So this may cut-down to the low-end of these ranges.


Snowfallmap21514