TGIForecast

Good Morning!

You wake up temps across the region and projected high temps. Lots of mid to upper 30’s with colder spots across the higher terrain. Clear skies to start the day but don’t increasing cloud later this morning ahead of a piece of energy that may cause some areas of scattered sleet and snow showers this afternoon, where these do occur, they will be brief, but might put down a quick trace of precipitation.

Everyone have an amazing Friday!

-Alex

Thursday Update

Be alert for isolated patches of dense fog this morning, especially in areas where snowpack exists.

There are a few scattered showers around the region but the bulk of the precipitation has departed the region, temps are also above freezing almost region wide, so roads are mostly just wet. The exception to that rule is some of the higher terrain areas which look to slip back below 32° this morning as colder air starts to seep back into the region.

It will turn a bit windy later today as that low pressure that was the weaker of the two yesterday goes through rapid cyclogenesis and drops to 968MB’s over Maine. This will result in gusty WNW winds of 20-35 mph across some of the higher terrain. In addition some bands of lake effect squalls off the abnormally warm, and mostly open waters of the Great Lakes, May meander into western and northern counties later today and overnight.

Our next weather maker arrives Sunday PM into Monday and you guessed it, looks like some lower elevation rain and mountain snow is possible, we will dive into that more later. Hope everyone has an amazing day!

-Alex

Image- GFS Monday 1AM Surface Map

Storm Update: Wednesday 11am Radar

It has begun, Hudson Valley…
The front edge of the overrunning snow band pushed into the Hudson Valley between 8:30am and 10am this morning. It took roughly 30 to 45 minutes for the atmosphere to saturate, and for the snow to reach the ground. But once the snow began to fall, it fell moderate to heavy across the majority of the Hudson Valley. Our viewers in Rockland and Westchester counties mostly missed out on the snow thus far… but north of I-287, the snow has been falling.
There were questions about this leading edge of snow, and how far south it would reach this morning. As it happened, the steady snow has reached all the way into the lower Hudson Valley, which may help to get the Hudson Valley into the higher end of the snowfall forecast range. The big question now will be, “where does the snow taper off for a bit, and where does it continue?” We’re seeing the southern edge of the snow shield shift north toward I-84 at this hour… so viewers down toward Warwick, or Peekskill, are likely tapering off after a coating of snow… while the snow continues to fall steadily along and north of I-84. We’re watching the main area of moisture push into NE PA , so we’ll have to see if the snow shield fills back in before it ever tapers off from I-84 on north.
LOOKING FORWARD…
Snow will continue in the Mid & Upper Hudson Valley at light to moderate rates into the early afternoon. As the primary area of moisture pushes into the Hudson Valley, we’ll see snowfall rates intensify again during the early afternoon (1 to 4pm). Temperatures continue to be at or below freezing in most of the valley, which will allow for road conditions to deteriorate as the snow intensifies this afternoon. As we get later in the day, we’ll begin to track the advancing warm air, that will eventually change us over from snow to rain before ending.
SNOW ACCUMULATIONS…
No major changes from our earlier ideas, just minor tweaks…
… Catskills : 4 to 7 inches
… Taconics & elevations over 1000ft : 2 to 5 inches
… Valley north of I-84 : 1 to 4 inches **
… Valley south of I-84 : Coating to 3 inches **
(** = now expecting to be on the higher end of these ranges)
We’ll continue to have updates through the day… stay safe out there!
-Bill

Early.. Way to Early Thoughts on Latest.

Some Way to Early Thoughts-

Small trend in the data is to be weaker and further north with the initial band of precipitation this morning, resulting is more of the region not seeing the short initial period of snowfall this morning.

In addition the lull between the initial warm air advection snow and the larger precipitation shield associated with the storm. Data points to this overspreading the region between Noon and 1pm. This second period of snow is the one that may impact travel the hardest. Bands of moderate to heavy snowfall will impact most the the region through the afternoon commute.

At the same time, a rain/snow line will be marching northward, with the majority of the region, excluding the highest elevations above 2500’, changing over to a heavy rainfall by around 8/9PM. Our southern most parts of Rockland and Westchester may only see a brief burst of snow at the onset before changing over.

How quickly areas change over will determine high end or low end of the forecast, with the initial burst of snow this morning look a bit less in coverage, this may hold things back a bit, although this was always a brief appetizer to the main event. This may also be offset by a period of snowfall where rates may reach 1” per hour before change over. There is a longer more detailed version of this from last nights post as well, if your into that kinda stuff. Speak soon..

-Alex

Images- HRRR and NAM Simulated Radar at Noon

Tuesday Evening Update : Latest Storm Thoughts

The short and long of it…
Forecast remains intact and on track, no real need for any changes of this evening. Wanted to take a moment to explain the current set up and why the forecast is going to evolve the way that it is.
But first let’s get the details out of the way. (Images 1,2,3) are the current hires snowfall projections from three models, the HRRR,NAM and RDPS.
The data all paints a similar picture, a nose of warm air both aloft and at the surface pushing up the river valley and limiting snowfall amounts, more snow in the hill towns east and west of the valley and high elevation snowfall amounts exceeding six inches above 1500’.
Snow May break out as early at 9-11AM in the form of early frontogenesis as the warm front pushes north, this can be funny as they can leave some areas out of the action initially as a band of precip will lift north through the region and some southern zones may see a late morning lull in precipitation. You can kinda see this on (image four) which is the simulated radar for 9AM.
By 12-1PM overrunning precipitation has broken out region wide. This initial burst of precipitation is where the entire region will make or break the snowfall forecast, with the exception of the higher elevations.
Snow may fall heavily along and north of i84 between 11-6PM (image above is 5pm Thursday), all the while warmer air will be pushing north into the region, southern most zones may only see a very brief period of snow resulting in a trace to a coating. As you head further north the duration of snowfall before changeover increases, therefore so do the amounts. The range in our snow forecast for the valley locations (black) should be digested based on your location, further south (lower end), further north (higher end), locations on the valley floor nearest to the river will warm the fastest.
The 9AM initial burst of snow can impact the morning commute, that mid afternoon into late afternoon snow will impact the afternoon commute. Between 4PM and 8pm heavy rain will be pushing into the region from south to north adding to the mess and complexity and erasing earlier snowfall. This is shown in (Images 4,5,6) which is the the HRRR simulated radar for 9AM,4PM and 8PM.
Current Snowfall Forecast:
(Image 7) is our snow forecast which doesn’t differ much from our forecast last night, in a set up like this it’s best to aim low and keep snow amount expectations low, it will be a brief albeit potentially heavy period of snowfall before the change over.
Finally the reason why the forecast and many others have evolved in this manner. (Images 8 and 9.)
While we do have some cold air in place ahead of the system with lows tonight dropping below freezing in many locations, it’s a decaying airmass, and transient cold that is being evicted from the region by a warm front associated with a low pressure cutting to our west.
In the final image I have highlighted both the high pressure responsible for our cold air and marked the the flow around a high pressure is clockwise while the flow around low pressure is counterclockwise. The high pressure is retreating to the east, no longer supplying cold air from Canada into the region the question mark notes the missing high pressure from the previous image. Meanwhile the low pressure tracking to our east is pumping warmer air north into the region. Warm air is light and cold air is heavier and dense, when warm air is forced into cold air, it’s forced up and over it. This lift creates precipitation, otherwise known as overrunning precipitation.
When a cold air mass is not deep and well established the atmosphere eventually warms from the top down and the warm air scours out the colder air. This results in snow changing over to sleet and eventually rain. In the final image you can see that although a secondary low pressure does eventually form offshore it’s weaker than its parent low to our west. If the offshore low was the primary or energy was transferred to it, colder air would be able to rush back into the region, because our flow would no longer be out of the south. This has been a repetitive pattern this season and last, which is another topic for a less busy day!
-Alex

Winter Storm Preview : Wednesday 1/25/22

An active pattern developing as we move straight from one winter weather event to the next. A low pressure will push northeast into the Great Lakes on Wednesday, and it will bring another round of wintry weather to the Hudson Valley.
 
Timing:
– Snow develops between 10am and 2pm Wednesday
– Snow falls steady/heavy late PM early evening
– Snow changes to sleet then rain before ending near/after midnight.
 
Preliminary Snow Accumulations (Subject to change):
– Catskills: 4 to 8 inches
– Mid & Upper Hudson Valley: 2 to 6 inches
– Lower Hudson Valley (south of I-84): 1 to 3 inches
 
Cold air will be in place ahead of this storm, so we’ll all start off as snow. However another storm track where a low pressure moving into the Great Lakes will bring enough warm air in the mid layers of the atmosphere to cause the snow to transition to a wintry mix, and then rain (likely between 7pm and 10pm), before tapering off after midnight as the low pressure pushes the precipitation to our northeast.
Temperatures are projected to be in the upper 20s to around 30° when the snow moves in, and should begin to accumulate on all surfaces. In addition, the timing of the snow arrival appears to be late morning. This will cause have impacts on travel, so school cancellations or early releases appear likely on Wednesday.
 
In terms of accumulations, this system has the potential to spread a blanket of 2 to 6 inches of snow over a wide area. Highest totals will be in the higher elevations like the Catskills and Taconics, where it will take longest to transition to rain. But much of the valley could see several inches of snow as well. Unfortunately for snow lovers, this system is very likely to transition to rain before ending late Wednesday night.
 
We will iron out the details on Tuesday, prior to issuing the formal storm forecast Tuesday evening, but signs of winter are finally appearing in the Hudson Valley.

Monday AM Update

As mentioned in yesterdays update, colder air is not wrapping back into the region, rain is changing back to sleet and eventually snow from NW to SE through the morning. Precipitation is also beginning to redevelop as lift associated with the deepening low pressure begins to increase. Data continue to support the development of banding mid morning thorough early afternoon. A period of moderate to heavy snow is likely this morning between 7am and 1pm, the further NW you are you’ll be on the early side of that time line and our most southern zones on the later side. Snowfall rates may be heavy enough to cover over roadways, especially from i84 north. We will open a new OBS thread so we can track this change over as it happens. Everyone have a safe Monday.

-Alex

Sunday Afternoon Thoughts

Sunday Afternoon Thoughts- Afternoon data has trended a bit more robust with the moisture and the strengthening of the low pressure as it pulls NE. This is a bit different than the models trending colder as they really have not, temps overnight still warm, and temps tomorrow morning are also above freezing in many locations.

So what’s changed? The biggest development is the blossoming moisture field associated with the deepening low pressure, and the timing of the strengthening. Let’s talk through this with the images attached.

First two images are the latest HRRR and NAM modeled snowfall, both very similar but also showing more snow further south across the region. The next series in images are the simulated radar from the NAM and 5pm,8pm,1am,8am,noon.

Let’s talk about those images- precipitation arrives around 5pm, it may start as a brief burst of snow across the lower Hudson Valley but it quickly changes to rain. By 8PM the rain/snow line is pushing north to about i84 and it continues to push north through midnight where snow at that time may only be falling across the higher terrain and parts of Delaware and Greene Counties.

Snow accumulations of a coating to an inch or two is possible and will be highly dependent on who stays snow the longest with the northern most zones likely to see the 1-2” with a coating or less as you get south towards i84 and beyond where change overs occur sooner. The exception to this rule is the higher terrain and counties mentioned above that may stay snow for much of the overnight period, where several inches of snow may accumulate by daybreak.

Now tomorrow morning is where things will need to be watched and where those traveling need to keep their guard up. As the low pressure organizes to our SE, colder air aloft will begin pouring back into the region, this will begin to change rain back to snow during the morning hours. At the 8AM time stamp you can see how the rain/snow line has collapsed southward. So areas seeing rain just before daybreak may be back into the snow during commute times. In addition the low pressure will be deepening, the data shows very good atmospheric lift occurring over the Hudson Valley. This may result in banding developing as the moisture shield begins to backup into the region. You can see this sudden expansion of precip when you compare the 8am and noon radar stamps.

While surface temps will be above freezing, upper air temps will support frozen precipitation, the intensity of the precipitation will be enhanced by the upward motion of the atmosphere as our storm deepens. This will aid in dynamic cooling, and more importantly snowfall rates can overcome warmer surfaces. This could lead to rapidly deteriorating road conditions as heavy snowfall begins to slush over and snow cover roadways. While the data has been inconsistent and only begun catching onto the idea of earlier deepening of the LP in the last few runs. Given the fact it is both a work day, school day, and that conditions may not look “bad” predawn, it’s important to highlight this potential so sound decisions can be made around travel.

Final image is our snow forecast, we have added a circled area where if banding does occur, could result in accumulations on the high end or exceeding the current forecast. In addition it’s worth mentioning that the higher peaks of the Catskills may exceed 8” of snow within that forecast zone. More to follow.

-Alex

Sunday AM Thoughts

Good Morning! Happy Sunday!

Clouds associated with out incoming storm system have overspread the region, our thoughts on the storm remain very much unchanged since Friday and our snow map remains unchanged for now. The data with this system has been doing a lot of waffling, we’ve found it best to not react with every 6-12 hours of data. We’ve seen some track shifts and with that some thermal changes that have resulted in data showing more or less snow across more of the region from run to run.
At this point we nowcast, and look at the real-time data, for example we are closely monitoring actual temps vs what the short range models are initializing temps at for the current hour. If we’re colder or warmer that is an early indicator of how things may evolve. So far since about 4AM we’ve been running 1-3° cooler in most spots with the a significant discrepancy on the colder side across parts of the Catskills, which seeing the fact that more snow is already forecasted in that region, that piece it irrelevant.
I’ve attached the current temps vs latest HRRR temps for the same hour for comparison, as has been the theme this winter and really last winter as well, we have a lot of storms running into weak or decaying cold air masses, with the 32° or less boundary seemingly always setting up across the region. It is true that the atmosphere can get muscle memory, as an example the ice storm last winter was a result of a boundary of colder air just to our north, the persistent severe weather that plagued Ulster and Dutchess Counties over the summer was a result of this pattern and it’s one that has carried into this season as well.

When forecasting these type of events, everything is always on a knifes edge, as a few feet of elevation, or a few miles further north, or a degree or two colder can either bust or boom these systems. When the data shows boom, but the 18 month pattern is meh, we like to stay conservative.

Precipitation arrives around 430-6PM, southern most zones look like rain from the onset, as you get closer to i84, we start as snow but it may be brief in the valley locations. North from there the period of snow before change over is of longer duration, how long it stays snow will determine low end or high end of current snow map. The further west and east away from the valley and higher in elevation, the higher probability of a moderate to heavy snowfall. Western Ulster,Western Greene and Delaware Counties continue to look to be the places to exceed 6”+.

-Alex

Images-
Mesonet- current temps
HRRR-8AM Temps
HRRR-Sim Radar 4PM
Current HVW Snow Map

Storm Forecast : Sunday 1/22/23 – Monday 1/23/23

Timing:
– 4pm to 7pm : Snow develops (mixed with rain in valley)
– 7pm to 6am : Snow/mix/rain falls light to moderate at times
– 6am to 3pm : Rain/Mix changes back to wet snow before ending
 
Impacts:
– Wide range of effects depending on location & elevation
– Mainly wet roads expected in valley, above 1500ft icy roads possible
– Expect some surprises, rain/snow line splitting our area in half
 
Snow Accumulation:
– Catskills & Taconics : 2″ to 6″ (locally up to 8″ above 1500ft)
– Mid & Upper Hudson Valley (north of I-84): Coating to 3″
– Lower Hudson Valley (south of I-84): Coating to 1/2″
 
A difficult forecast as the Hudson Valley is in the crosshairs of the rain/snow line. Precipitation will move into the Hudson Valley as sunset approaches on Sunday. Surface temperatures will be above freezing in the valley, and near freezing in the Catskills. Snow is likely to develop, mixed with rain in the valley areas. The question to monitor Sunday evening is, there will be a ‘warm layer’ of air about 5000 feet up, associated with the coastal low pressure system. Just how far north the warm layer of air pushes, will determine if we see the higher end, or lower end of snowfall ranges.
 
Temps are expected to remain at or just above freezing through the event, so snow accumulation is likely confined to unpaved surfaces. The Monday AM commute is likely to be impacted, but it will depend greatly on where the rain/snow line was overnight, and what conditions are in your area. Even with temps above 32°, some slick spots are possible.
 
The details with this system continue to remain in doubt… so we will have updates on Sunday to try and keep you a step ahead.