Apologies for the lack of updates recently. Winter weather has come in full force a few days ahead of the actual Winter Solstice. We’ll see possibly record-tying or record-breaking cold Friday in some parts of the area, our first measurable snowfall in the city this season, all while temperatures swing about 30ºF from now through Sunday. The medium term shows a continuance of average to below-average temperatures in the upper-30s and low-40s.
Rest of today – we had some passing snow showers this morning, and there will be another chance for snow showers this afternoon. The main story will be the wind, cold temperatures, and low wind chills. A wind advisory is in effect for today with a high wind warning in place for tonight. Sustained winds of 20-30mph are expected, with wind gusts between 40mph to as high as 60mph possible later. Combined with high temperatures only in the mid-20s, this will result in wind chills of between 0-10ºF in the city.
Friday – slightly colder than today with highs in the mid-20s, with a very cold start to the morning as overnight lows drop into the teens. Winds will slowly abate through the course of the day as the high pressure center depicted above moves east over us, lessening the pressure gradient. Overnight Friday, a warm front approaches and brings the possibility for 1-2″ of snow.
Saturday – the snow will continue into the first half of Saturday with the possibility of 1-2″ additional inches of accumulation before temperatures warm and winds turn towards the southwest. There is some question as to whether some period of freezing rain will occur before a transition to all rain from south to north in the afternoon hours. High temperatures rebound nicely into the upper-40s in the wake of the warm front passing through.
Sunday – a cold front will follow the passage of the warm front mentioned above, but that shouldn’t happen until late Sunday. Ahead of that cold front passing, temperatures will continue to warm into the low-mid 50s as rain continues to fall. That snow won’t stick around long!
There will be a wet start and end to this week, with some fairly dramatic swings in temperatures in between as two storm systems affect the tangible weather across our region.
Rest of today – rain is tapering off across the region and there should be a slow clearing late in the day. High temperatures in the mid-50s.
Tuesday – the low pressure responsible for the wet weather today will strengthen as it departs to the northeast. The tightening pressure gradient will allow for stiff west winds to sweep across the area, in the 25-30mph range with gusts as high as 50mph. High temperatures will be about average in the low-50s with mostly sunny skies.
Wednesday – winds will diminish overnight Tuesday into Wednesday. With high pressure in place, this will set the stage for excellent radiational cooling that will allow for temperatures to plummet into the mid-30s and below freezing outside of the city. Temperatures should rebound back into the low-mid 50s during the day Wednesday.
Thursday – winds will switch to the southwest and temperatures will warm up into the mid-60s, despite increasing cloud cover. A chance of rain develops later in the afternoon with the approach of a cold front.
Friday – rain is likely for the first half of the day with temperatures about the same as Thursday in the mid-60s.
Periods of rain this afternoon give way to drier weather over the weekend as a cold front passes through late today into the overnight hours. Drier weather prevails this weekend, though with the passage of this cold front, gusty northwest winds will enter the region, bringing in significantly cooler temperatures for Saturday. Temperatures rebound Sunday as we enter another period of slightly above normal temperatures.
Rest of today – showers have moved out of the area at this point, but a few scattered showers may still pop up later today. Otherwise, cloudy with high temperatures already peaking around 60.
Friday – mostly sunny with winds from the west in the 15-20mph range, gusts up to 30mph.
Saturday – winds again in the 15-20mph range with gusts up to 30-35mph. Sunny skies, but temperatures well below normal in the upper-40s, highs may not break 50 in the city. With the winds, it will feel like temperatures are in the upper-30s to low-40s.
Sunday – winds finally start subsiding, and temperatures will rebound back to around normal in the mid-50s with sunny skies.
Monday – as the high pressure depicted above begins moving to our east, southwest flow on its backside will bring temperatures back into the low-60s.
A major nor’easter will be bringing a high impact blizzard throughout the NYC region tonight through Tuesday midday. Beginning this evening, snowfall will increase in coverage from south to north. Periods of heavy snow are expected with snowfall rates of 2-4″ per hour, with thundersnow occurring in the heaviest bands of snow. Extended periods of high winds, with sustained winds at least 35mph and gusts over 40mph (even up to 60mph) will lead to blowing and drifting snow, blizzard conditions, and near-zero visibility. Widespread snowfall totals of between 18″-24″ possible throughout the area, with locally higher amounts.
Snowfall Totals
Since yesterday afternoon, forecast models have backed off a bit on the overall total accumulations. At this point yesterday, the quantitative precipitation forecast (liquid water equivalent total) was as high as 2.7-2.8″ and broadly over 2.5″ across much of the area. As seen below, those liquid water equivalent numbers have gone down by about half an inch.
Liquid water equivalent forecast totals
This decrease in overall precipitable water has led to a corresponding downgrading of the overall snowfall totals. Using a 12:1 snow to water ratio, a drop in precipitable water by half an inch translates to a decrease in snow totals by 6″. Indeed, the National Weather Service has decreased the likely totals from 27″+ for many places to closer to 20-22″.
Snowfall accumulation total forecastHighest probabilities for snowfall totals in excess of 18″ during the 48 hour period ending 7AM Wednesday now rests over Southern New England, with the bullseye setting up right over Boston and immediate suburbs. Here in NYC, we are in the range of 30%-50% probability of receiving over 18″ – notice how abruptly the probability goes up as you go further north and east.
Timing
Light snow has already begun falling over the area, however the heaviest snow will not be occurring until after 8PM tonight. The most intense period of this storm is expected overnight tonight, as a deformation banding feature forms and begins moving slowly inland. Based on the simulated radar loop below from the NAM (North American Model), the peak intensity of snowfall looks like it will occur between 1AM-7AM overnight into Tuesday. Snow appears to taper off over NYC by 1PM tomorrow.
It does appear that a secondary set of banding snow will linger over eastern areas of the metro region throughout the afternoon Tuesday until as late as 4PM tomorrow.
By the way, part of the reason the main area of highest snowfall totals is now shifting to Southern New England and Boston is because it is anticipated that these areas will see moderate to heavy snow for much longer than we will here.
NAM model simulated radar output for this storm
Impacts
Snow, heavy at times, beginning in earnest this evening especially after 8PM. Some thundersnow possible, with the most intense snow occurring overnight. Strong sustained winds up to 35mph with gusts over 40mph and as high as 60mph will lead to blizzard conditions with blowing and drifting snow cutting visibilities down to near zero.
Caveats
Forecasters have been pointing out that there continues to be some slight disagreements between different models even though this storm is imminent. Snowfall total forecasts for storms like this one are notoriously difficult to predict with a high degree of accuracy prior to the event itself. This is due to the fact that the exact placement, movement, and intensity of the deformation banding feature on the northwest flank of the low pressure center is hard to foresee until the storm is ongoing. With snowfall rates as high as 2-4″ per hour within this banding feature, a difference of a couple hours under it could translate to 4-8″ difference in overall accumulation in any one location. Same thing with location, as one location that misses the most intense portion of the banding feature could easily miss out on 6″+ in total accumulation. Furthermore, a slight change in the thermal profiles within this type of storm could alter the snow to water ratio to be higher, and of course, a change from 12:1 to 15:1 would result in a dramatic difference in totals.
This week will be a colder repeat of last week, with a wet mid-week period, but better conditions going into the weekend.
Tuesday – an area of low pressure with an accompanying cold front moving in from the Great Lakes will give us a chance of showers, especially in the afternoon Tuesday. Ahead of the front, temperatures will warm up to the mid-upper 60s under mostly cloudy skies.
Wednesday – the low pressure above will spawn a secondary low off the coast of the Mid-Atlantic. This low pressure center will be the main weather-maker for the mid-week period. Forecast models point to a stubborn storm system that will meander slowly off the Northeast. Multiple bands of rain will rotate around this low. There will be enough instability with the vorticity associated with the low to allow for the possibility of thunderstorms, despite the fact that this low will be a colder core low. Temperatures will only be in the upper 50s with a unpleasant north to northeast wind.
GFS model output for Wednesday, Oct 22, 2014 @ 8PM EDTGFS 500mb vorticity and height – notice the concentric circles indicating a closed low off the coast of the Northeast and New Engalnd. The darker yellows indicate areas of increased vorticity and energy.
Thursday – the rain should subside by around noon Thursday, but before all is said and done, we could get another 1-1.5″ of rain. The rainfall will mainly be concentrated to the east of the Hudson River, including NYC and Long Island. Temperatures will remain cool in the mid-50s with winds diminishing from the north and northwest.
Friday – the low will lift away, it will dry out, and clouds will diminish as temperatures also rebound back into the lower 60s to end the week.
You can feel that cold front has passed, can’t you? A stiff northwest wind is ushering in an unseasonably cool air mass, and temperatures will be quite a bit lower than yesterday, with high temps about 10 degrees less than yesterday in the mid-upper 50s. Cloud cover should continue to diminish throughout the day.
Windy and cool weather persists Thursday – with high temperatures again struggling to hit 60. The breezy conditions and very dry air mass in place will lead to conditions conducive to the spread of wildfires.
GFS model’s output for Friday
Our next shot of rain comes Friday, with a weak low pressure system moving over the Great Lakes and a trailing cold front. Forecast models suggest the system weakens as it approaches, hence lowering the chances for rain. If it rains, only light, showery precipitation is expected. High temperatures Friday will be slightly warmer, in the low 60s.
Saturday & Sunday – So far, we have a nice weekend on tap with mostly sunny skies and temperatures slightly below average in the low-mid 60s both Saturday and Sunday.
