Final Storm Forecast : Sunday 12/1 – Monday 12/2

As we turn the calendar to December, we’ll kick off the 19/20 winter season with a bang.  A 2 part storm system that has the potential to deliver well over a foot of snow to some parts of the viewing area.  Because of the structure of this storm, it will start around noon on Sunday, and likely won’t end until after midnight Monday night.  The complex structure of this storm will also mean some inevitable surprises.  So here are the forecast details as we see them…

Storm Timeline:
– 10am to 1pm : Snow begins from west to east
– 1pm to 5pm : Snow, mixes with sleet near I-84 corridor, changes to sleet south of I-84
– 5pm to 10pm : Snow mixing with sleet north of I-84, sleet near I-84, sleet/rain near I-287
– 10pm to 6am : Precip tapers… snow showers upper HV, light sleet Mid HV, light rain showers Lower HV
– 6am to 12pm Monday : Snow redevelops over HV, becomes steady to moderate at times
– 12pm to 12am Tuesday : Snow… gradually tapering near midnight

Impact: High Impact
– Long Duration Event, 24 to 36 hours possible
– Significant snowfall in northern HV, travel extremely hazardous
– Icing possible late Sunday Mid and Lower HV, treacherous travel likely
– First widespread school delays and cancellations likely
– Monday commutes likely very hazardous

Snowfall Accumulations
– Catskills (Zone 1 & 2): 10″ to 20″
– Southern & Eastern Catskills (Zone 5 & 6): 8″ to 14″
– Mid and Upper HV (Zone 3, 4 & 7): 6″ to 12″
– Lower HV (Zone 8): 4″ to 9″
– Extreme Lower HV (Zone 9): 2″ to 6″

Additional Highlights:

The precise details that we have highlighted over the past several days, continue to be major factors in the forecast.  We’ll have additional discussions both here and on Facebook to try and clarify the significance of these uncertainties.

  • Dynamic Cooling along Warm Advection precipitation band
  • Precise location of Upper Level Low on Monday

We’re seeing some data just in the last hour, that suggests that precipitation falls heavily enough Sunday afternoon, that instead of the sleet we have anticipated advancing all the way up the HV… that snow falls for a longer period of time.  To put it simply… in the battle between snow and sleet, it looks like snow may hold ground for longer than expected, especially north of I-84.  If this happens, snow totals will be on the higher end of the ranges.

Also, with regard to the Upper Level Low… the snows on Monday are a product of the upper level energy moving by to our south.  These features are NOTORIOUSLY DIFFICULT to forecast, because they produce areas of heavy snow… but those bands of heavy snow are rather narrow.  So a shift by 50 to 100 miles can be the difference from 8″ of snow… and 2″ of snow.  So no matter how precise we try to get… if this feature provides any surprises on Monday, it will either mean higher than forecasted… or lower than forecasted snowfall amounts.

Expect more commentary as often as possible through Sunday and into Monday.  Thank you for all your continued support!

Preliminary Storm Forecast : Sun 12/1 – Mon 12/2

We are now officially in storm mode as we are within 24 hours of the beginning of this two phase storm system. Confidence is high with Sunday phase and medium with Sunday Night into Monday. Because confidence of the second phase is still moderate our prelim snow map remains the going forecast until the final is posted.
 
So what can go wrong with the forecast? If the secondary low forms further north the axis of heavier snow shifts further into the capital region.  If low forms further south we can expect high totals shifting into the mid and lower Hudson Valley. If colder air is deeper and first round over performs with more snow than sleet in some locations or vice versa.
 
Finally the notoriously impossible to forecast location of quasi stationary, mesoscale banding and pivot points of precipitation as coastal low moves NE. These bands combined with orographic enhancement in the Eastern Catskills will cause some localized heavier totals that may exceed 2’. These same uncertainties have caused the NWS to withhold warnings in their morning updates. We will monitor the hires short range data throughout the day and have final snow map late afternoon/eve.
 
Below we have also included snowfall forecasts from all three of the National Weather Service offices that serve our forecast region for your digesting in combination with our on-going forecast from yesterday.
 
Storm Timeline:
– 9am to 12pm Sunday : Snow/sleet begins from west to east
– 12pm to 5pm Sunday : Snow/mixes with sleet and freezing rain
– 5pm to 9pm Sunday : Wintry mix slowly tapers from west to east
– 9pm Sunday to 3am Monday : Cloudy, scattered snow/sleet/rain showers
– 12am to 6am Monday : Snow redevelops, falls moderate at times
– 6pm Monday to 12am Tuesday : Snow gradually tapers off
 
Precipitation Types– Snow, Sleet, Freezing Rain,Rain
 
Impacts– High Impact (Long Duration,High Snowfall Totals, Ranging conditions over short distances, Work/School day)
 
Travel-Difficult/Impassable
 
Snowfall Accumulations:
8-16″ (Zone 2,3,4&6) Mostly snow with sleet possible across southern parts of this zone Sunday afternoon and Night.

5″-10″ (Zone 1,5,7,N8) Snow… with sleet Accumulations likely. Possibly mixing with freezing rain, before changing back to all snow by sunrise Monday. Accumulations highest across northern parts of this zone where localized amount may exceed 10″.

2″-6″ (Zone 9 & S8) Snow to sleet, and freezing rain, and possibly rain. Highest accumulations Northern part of area. Change to all snow Monday morning.

Snow Consistency- Light and Dry to start, transitions to heavier and wet Sunday afternoon, especially where sleet mixes in, and begins to transition back to lighter and drier on Monday.
 
Additional Hazards- Blowing and Drifting across higher terrain. Sporadic power outages.
We will try to have additional discussions as the day progresses, but our previous discussion on this really has a good line on our current ideas.  We will have conversation and lesser discussion on Facebook today, and will have the Final Storm Forecast issued tonight.  Once again, this storm is 24 hours away from starting (as of this post)… and over 60 hours away from completion.  Have a great Saturday!

Winter Storm Discussion : Potential Huge Kickoff to Winter Season

With every passing hour, the likelihood of our 1st significant winter storm of the season increases.  The computer guidance is getting a better and better handle on the basic structure of this storm system, and how it will unfold.  Because of the complexity of this storm’s structure… we will continue to have details to iron out, right up until the start of the storm.  This will make pinpointing snow totals, timing, and impacts a bit tricky.  So lets start digging in…

Estimated Timeline:
– 8am to 12pm Sunday : Snow/sleet begins
– 5pm to 9pm Sunday : Snow/Mix tapers
– Sunday Evening : Cloudy, scattered snow/sleet/rain showers
– 12am to 6am Monday : Snow redevelops
– 6pm Monday to 12am Tuesday : Snow tapers off

Total Snow Accumulation Probability:
– Over 1 inch : 95%
– Over 3 inches : 75%
– Over 6 inches : 65%
– Over 8 inches : 60%
(*probabilities based off Poughkeepsie area and Mid Hudson Valley. Chances increase as you go north and up in elevations, and chances decrease as you go further south)

Precipitation Types:
– Zone 1,2,5&6: Snow… mixing with sleet Sunday afternoon.  Mostly snow Monday
– Zone 3&4: Mostly snow on Sunday, some sleet possible… best chance for heaviest snow on Monday
– Zone 7&8: Snow… mixing with sleet and freezing rain Sunday afternoon.  Mostly snow Monday
– Zone 9: Wintry mix, possibly light rain late Sunday. Changing to snow on Monday

Confidence : Medium
– Good handle on the basic structure of the storm
– Confident about timing for the first half of the storm
– Timing and location of Monday portion is lower confidence

Synopsis

The first half of this storm, the Sunday portion, we have a good handle on.  It’s the 2nd half of the storm, on Monday, that could give us some unexpected surprises.  But lets go through Sunday first.

The moisture likely arrives from mid to late morning from west to east.  You can see the purple on the map is indicative of sleet… not snow.  The reason is because there could be a thin layer of mild air in the atmosphere, that melts the snowflakes before they refreeze on their way to the ground.  We will have to see how thick that layer of warmth is, and if it stays further south.  But this could result in some parts of the region seeing a burst of snow, quickly change to a snow/sleet mix by late morning.  It’s one of the details that we’ll be monitoring.

As the storm moves in, the entire region should be seeing snow and/or sleet falling by lunchtime on Sunday.  Surface temperatures are expected to hold in the mid to upper 20s all day Sunday, plenty cold enough for frozen precipitation.  The major question that we will be focusing on, is how much mild air at the mid levels of the atmosphere we get.  That will determine whether we see snow, sleet or freezing rain.  But as we look at the progress of the storm, you can see that the first half of this system begins to taper off late Sunday afternoon and early Sunday evening…

Futurecast Radar Loop : 7am Sunday – 1am Monday

 

The bulk of the moisture associated with the warm front moves through by around 7pm.  This will result in most of the precipitation tapering off Sunday evening, and the Hudson Valley is left with scattered light snow, sleet and freezing rain showers.  A rather icy Sunday night lined up for anyone with travel plans.  But there should be a low pressure developing off the NJ coast, that will stall out south of Long Island.  So just at the end of this radar loop, you can see some of the wintry mix changing back to snow, and the snow beginning to fill in a bit on the radar image.  So when considering the first part of the storm (Sunday)… we’re leaning on the lighter side of accumulations.  When considering total snowfall amounts… what falls on Sunday will likely be about 25% to 30% of the total snowfall accumulations this storm brings.  

This leads us to the most uncertain part of the forecast.

Futurecast Radar: 1am Monday – 1am Tuesday

This is a futurecast loop of the final 24 hours of this storm, from 1am Monday morning.  Notice how disorganized this storm system becomes.  A coastal low pressure system develops as the Upper Level Low pressure moves to the coast.  It results in the redevelopment of a steady moderate snow across much of NY and the Hudson Valley.  This is easily the lowest confidence portion of our forecast.  Because if the position of the upper level low is further south or north… the band of moderate snow could be outside of our area.  If the coastal storm develops too late, the snow could be east of the Hudson Valley.  There are a lot of tricky pieces here… and Upper Level Low pressure systems are notoriously difficult to forecast.

So when we talk about snowfall accumulations, if things play out just right, over 12″ of snow is certainly possible.  At the same time, if the details are different from what we currently project… snowfall amounts could be significantly less than what you’re seeing and hearing.  So this is something to keep in mind when thinking about this storm’s forecast… even as we roll out our preliminary snowfall forecast tonight.  Remember… the 1st half of this storm… the Sunday portion… we have a moderately good level of confidence.  It’s the Monday portion… that remains more of a wildcard.  While a lot of guidance suggests the Hudson Valley is in the focal point of heaviest snow… like the GIF images above… we all need to take this into consideration.

Any way you slice it… this should be a wild start to the winter season!  Thanks for your support!!

Sunday/Monday Winter Storm

A complex and long duration winter storm to potentially impact the region Sunday into Monday……

Timeline– Sunday 2PM-5PM  thru Monday 8PM-Midnight

Precipitation Types-  Snow, Sleet, Rain (Depending on Locations)

Accumulations By Probability %- 

6″+ 50%
4″-6″- 65%
2″-4″- 70%
1″-2″- 80%

(Probabilities are dependent on North vs South in region and elevation)

Confidence- Medium Confidence

Synopsis- There are a lot of moving parts to this upcoming winter storm, lets try to explain some of the details, a warm southerly flow ahead of an incoming upper level low will help create warm air advection over colder air in place across the region, we are not dealing with a deep arctic air mass but more of a shallow and stale cold air mass. Precipitation will overspread the region Sunday afternoon or evening, which will be heavily dependent on how much dry air is on place ahead of the storm. Precipitation will become more widespread and steady overnight, but warmer air will also be slowly eroding the cold air across the region, this will result in the potential mixing of sleet and rain across parts of the region. This is one of the unknowns at this time frame, if the colder air is deeper we may see more snow than mixed precipitation.

The plot thickens, as warm air advection begins to weaken Sunday overnight, we may see a lull in the precipitation, at this time a surface low will be forming off the coast of the Mid Atlantic, this will help to reignite precipitation by Monday AM, at this time we may still be dealing with some warmer layers of atmosphere and therefore the exact precipitation types are questionable. Now if this didn’t all seem complicated enough, the upper level low mentioned earlier will be sweeping in from the west, this will not only cool down the atmosphere but slow down the surface low from escaping and help to persist the precipitation throughout the day Monday into the evening.

As you can see there are a lot of moving parts to this system we need to iron out but there is now a high probability that we will be dealing with a period of winter weather in this timeframe that will have impacts on travel. Here are the GFS and European model take on this scenario..

Lets start with the European, a few things to point out here the european model has only in its most recent run shifted the axis of snow fairly far south vs all other guidance, while it can’t be discounted we are viewing it as somewhat of an outlier at the moment, as always the snow map isn’t to be taken verbatim. Next is the probability of 6″ or more as per the European, it helps highlight where it thinks the bullseye may be. The next two images are the Ensembles, this is the euro model running 50 additional solutions, these are useful to look for trends and also to see what the majority of models are projecting, as you can see there aren’t many that leave us unscathed from the storm at this point with a lot of members showing the bullseye further North, which is why we take the first image with a grain of salt….

Next up is the GFS model, now the first thing that stands out here is the GFS is taking a more northern approach to the axis of heaviest snow, which is a plausible outcome given the current setup, you can see that the accumulations and probabilities are all much further North than the European model.. With all of this said, at this timeframe we are simply beginning to discuss some of the probable outcomes of this upcoming storm. We will continue to monitor the data as it comes in and we will dial in the details throughout the day tomorrow into the weekend, but it’s best to continue to factor impacts to your Sunday and Monday plans with the upcoming storm.

Tuesday Discussion : Gorgeous Change of Pace

A frosty start in some locations this morning will actually work into a fairly mild day, one of the warmest in awhile with temps breaking into the 50’s. The warm air advection is an early indicator of a storm system advancing towards the region, this will spread rain into our area by tomorrow.

Tomorrow night into Thanksgiving morning a strong high pressure will begin to build into the region, the right pressure gradient between our departing storm and building high pressure will result in some gusty NW winds. The good news is high pressure! As the winds subside we will be left with a beautiful Thanksgiving day with highs starting out in the 40’s but sliding down as those NW winds usher in colder air.

Cue Friday morning, cold start for shoppers but another great day of weather across the region, this tranquil weather should carry us straight into Saturday.

Beyond Saturday things begin to look potentially stormy. We are now monitoring the potential for a winter storm Sunday PM into Monday AM. This period has had a strong signal for a storm for quite a long time and the data is beginning to show that potential. Please remain steady in ignoring the plethora of click bait articles a 0% chance of verification snowfall maps that will flood your feeds in an attempt to boost clicks and followers. At this point know there is a potential for a storm, it has the potential to be mostly snow and plowable, low confidence due to be in longer range.

Monday Discussion : Looking Ahead

In the wake of a soaking Sunday around the Hudson Valley, things will dry out to start the work week.  But not before we saw widespread 1 to 2 inches of rain around the region.

Rainfall Totals
– Cairo 1.80″
– Poughkeepsie 1.58″
– Catskill 1.54″
– Red Hook 1.28″

In addition to the rain, our higher elevations had measurable snowfall, and quite a bit in the Catskills, where 3 to 6 inches fell in parts of Greene and Columbia counties, as the back edge of the storm funneled in colder air.  But now we’ll see a shift to warmer air to start the week.

Temperatures will begin to climb on Monday into the upper 40s for highs under mostly sunny skies.  Those sunny skies will see some increasing high clouds filter in ahead of our next system.  But still, we’ll see highs climb into the mid and upper 50s on Tuesday

Tuesday’s Highs

Then on Wednesday our next storm system will approach and spread some scattered rain showers into the region.

Futurecast Radar : Wednesday into Thursday

The low pressure system passes by to our north, and spreads some scattered showers late Wednesday and into Wednesday evening.  But the real story will likely be the howling winds.  We’ll see winds out of the south on Wednesday gusting over 25mph… then behind the system, winds out of the NW will gust over 35mph

Thursday Afternoon Wind Gusts

So a blustery and chilly Thanksgiving appears likely this year.  But on the positive side, we won’t be talking about snow or icy travel as a concern.  So holiday travel should be decent.  But lets not ignore the potential hazardous travel from strong winds.

Looking beyond this week, we’re seeing signs that the seasons are preparing to change from autumn to winter.  Our first major Sudden Stratospheric Warming event for this season appears likely to occur in the beginning of December.

Northern Hemisphere Stratosphere Temperatures: Dec 1 – Dec 10

This graphic shows temperatures compared to normal at the top of the atmosphere.  You’ll notice the standout feature is the warming that develops at the top of the image, and slowly pushes southward.  This is the visual interpretation of what is expected to occur in the stratosphere the first 10 days of December.  A “Sudden Stratospheric Warming” event or SSW, is usually the precursor to an outbreak of arctic air.  The rapid warming of the stratosphere forces the coldest air in the arctic region to push to lower latitudes, and leads to a weakening, and possibly splitting of the polar vortex (you likely remember the term ‘polar vortex’ from previous winters).  The major question with these events, is where the cold air will be focused.  The location of the development and the transition of the event is believed to be crucial to determine where the arctic air is felt.  We’ll have to see if the arctic air makes its way to the eastern US about 10 to 15 days after the event has concluded.  As of this post… which is still extremely early in the forecasting of this event… we think that this event could bring a colder than average 2nd half of December to the region… but we’ll have to wait and see.

Nonetheless, things are looking more and more interesting.  Chances for snow will be in the region before this event peaks… but this is just another sign of the changes that should be coming our way as we get closer to winter.  Have a great Monday!

Sunday Discussion : Raw Rain Showers

So close, snow lovers… so close.  But not this time.

Precipitation moved in before midnight Saturday night, and with temperatures in the mid 30s, that meant a cold rain.  Well, there was enough cold air in the atmosphere to lead to a brief period of sleet and wet snow in some areas on the front edge of the rain.  But once the air mixed a bit with the falling precipitation, most areas became a steady cold rain.

As we look at Sunday, the rain showers should become more intermittent during the morning at first… before possibly intensifying by late morning.  As the low pressure pushes east, the back edge of precipitation could produce enough lift to cool the air enough for a change back over to snow.  The chances of this occurring are best the further north you go.  But any accumulation should be confined to areas above 1000ft.  For the majority of us, the rain showers could end as a mix of rain and wet snow around mid day… or early afternoon.  Skies will remain mainly cloudy, before gradually clearing overnight.

Looking into the start of the week, sunshine returns for Monday and Tuesday.  We’ll see a SW flow return, which will bring temps back up near to above average for late November.  Something we haven’t seen in what feels like forever.

We’re tracking our next storm for Wednesday, which promises to bring a lot of wind to the region, and some colder air into Thanksgiving day.  We’ll touch more on that later today.  Have a great Sunday!

Friday Discussion : Breezy and Unsettled

We’ll end our work week with a changeable day around the Hudson Valley.  SW winds during the morning will keep it rather mild around the region, with mostly cloudy skies and temps quickly jumping into the mid and upper 40s by mid day.  But a cold front pushes through during the late morning and early afternoon, causing winds to shift out of the NW.  This will cause temps to drop a few degrees in the afternoon hours with a blustery NW wind.  So the morning may have a mild feel to it… while the afternoon will feel a bit more brisk.

Through the day, expect mostly cloudy skies with a scattered rain shower or two possible.  We could see wet snow showers in the Catskills, and even mixing in across the valley during the mid afternoon.  They should be few and far between for most locations… but a coating can’t be ruled out in the Catskills.

Things will then quiet down for the region Saturday, with mostly sunny skies and chilly conditions in the low 40s… ahead of our next system for Saturday night and Sunday.  If you’re a snow lover, this one is gonna sting a bit.  If it were late December or early January, this would be a snow event.  However, with a Pacific air mass in place, the air won’t be a truly cold air mass… so the moisture coming for Saturday night and Sunday morning should fall mostly in the form of a cold rain.  Temps in the mid 30s are expected through the event, and some of our colder northern valleys could see patchy freezing rain.  We’ll have to watch and see how well the cold air dams from the northeast Saturday night ahead of the system.

Sunday afternoon should try to improve slowly… but it looks mostly cloudy with highs in the low to mid 40s.  So the first half of the weekend is definitely the better half.  Hope everyone has a great Friday!

Monday Night Update : Wintry Suprise Possible

We continue to track a rather interesting weather situation overnight, that surprisingly could provide the first accumulating snowfall to parts of the Hudson Valley.  Now, before anyone begins to panic, this is NOT expected to cause widespread problems for the Tuesday morning commute.
 
The coastal storm that led to patchy areas of drizzle on Monday, is exiting to the northeast.  Behind the storm, upper level energy will pass across the Hudson Valley tonight.  The result is the futurecast radar loop you see here. 
Futurecast Radar : 9pm Mon – 10am Tue
This projects from 9pm Monday night, to 10am Tuesday morning.  The considerable upward motion in the atmosphere should generate a rather large area of moderate to heavy precipitation over the Hudson Valley between 9pm and 12am.  At the same time, colder air will be pulled down as a result of the falling precipitation, and this could cool the column of air in the Hudson Valley to change the rain over to a period of wet snow.  The snow could fall heavy for a time between 1am and 6am in some places… especially in the Catskills and the eastern Taconics of northern Dutchess and Columbia counties.  The higher elevations will be the places most likely to see the rain change over to a wet snow.
 
Temperatures across the entire Hudson Valley are expected to remain between 32° and 36°… meaning that any accumulation is likely to be confined to grassy and unpaved surfaces.  Above 800 feet, it’s possible that some slush covered roadways.  But even there, widespread travel problems are not expected for the Tuesday AM commute.  In the lower elevations, a slushy coating to a half inch is possible on unpaved surfaces… with the chances increasing the further away from the river valley that you get.
 
In summary:
Timing:
– 9pm to 12am – cold rain develops
– 12am to 5am – rain mixes with (changes to) wet snow
– 5am to 10am – rain/wet snow mix tapers off
 
Accumulation/Impact:
– Zone 1, 2 & 4 (Catskills & Taconics) : coating to 2″
– Rest of the Hudson Valley : slushy coating to 1/2 inch
– roads mainly wet, temps above 32°
 
We’ll have more discussion as possible this evening.

Monday Discussion : Icy Commute Thoughts

The winter weather advisory continues to be in effect for all counties except Putnam, Rockland and Westchester.  The reason for this advisories, as we’ve discussed in previous posts… is the threat for freezing drizzle prior to sunrise on Monday.  So as of late night… lets look at the current conditions:

3am Temperatures:
– 30° to 33° (Sullivan, Delaware, Greene, W Ulster)
– 32° to 36° (Orange, E Ulster, Dutchess, Columbia, Putnam, Rockland, Westchester)

The radar is quiet, not showing any precipitation over the last 3 hours.  Here is the computer guidance showing the total preciptation through the Monday morning commute:

Total Precipitation through Noon Monday

Notice that there is some light moisture, maybe up to 0.05″… or some spotty drizzle.  Where you see the gray on the map, it’s suggesting enough precipitation to dampen the roads.  So if temperatures are near or below freezing, those damp roadways could freeze and become black ice.  So let’s take a look at the low temperatures between now and noon on Monday…

You can see that most locations hover just a degree or two above freezing.  HOWEVER… there are some colder spots on this map, where you see pinkish coloring, that are at or below freezing… 31° or 32°.  If those colder locations also see the trace amounts of precipitation… we could have some icy conditions on untreated surfaces.  Sidewalks, driveways, and potentially roadways… could be icy in spots.

This will be a potential problem… because it won’t “rain” in any location… but a light mist is possible.  This will make it more difficult for some people to realize that the surfaces may be damp, and potentially icy… increasing the odds someone is caught off guard.  Ultimately, we’ll all have to take extra caution on Monday morning… and see how the situation unfolds.  As you see… it’s VERY Little moisture, and VERY marginal (near freezing) temperatures… but it’s enough that some localized icing could occur.  Be alert Monday morning.