​Good evening from SCW!
 
Well, it’s quite the roller coaster of weather this week, as we move from record highs yesterday to a winter storm tomorrow. While the impacts will differ across the state depending on where you are, one thing is clear; tomorrow will be a nasty day (or at least morning) of weather, and we expect impacts to travel, schools, and businesses. Let’s dive in.
 
The Setup
 
Energy currently moving over the Midwest will eventually hit blocking high pressure to the north, forcing the surface low to move to the east and transfer to a secondary low, currently projected to form just south of Long Island. This will help lock in some low level cold air at the surface, however, as the primary low continues northeast into central New England, it will bring warm air further north in the mid-levels. This sets up a wintry mix scenario for areas that are far enough north for cold air to hold on while not far enough north to be free of the mid-level warmth. Unfortunately, that zone will encompass most of our state.

Above is a loop of the 18z Regional Canadian model. You can see how most areas start out as a period of snow, but the warm air quickly works in aloft and changes most spots over to sleet by the early hours of the morning, and eventually brings some plain rain to the shoreline by mid-day. When that changeover happens, along with how far north the warm air can intrude, will be the primary contributor to our accumulations of snow vs. sleet/ice vs. plain rain. Let’s take a look at some of the modeled outcomes for gradients.

Above are snapshots from the GFS, NAM, RGEM, and high-res FV3 models for 7 AM tomorrow morning. You can see that the extent of the mixing varies fairly significantly across the guidance, with the RGEM (warmest solution) bringing the mix line nearly to the MA border (and shortly after crossing it). The colder FV3 and GFS are still mostly snow in the state, while the NAM is somewhere in the middle. By this time, we’ve seen about a half of an inch of liquid across the state; if it remains all snow, we would already have 5-6” of snow on the ground by sunrise, but those areas that see mixing will see those totals reduced.
 
At the end of the day, model consensus is fairly strong for about an inch of liquid, meaning double digit totals are likely for those who stay all snow. That said, those areas will likely be to our north, in northern MA and into VT/NH, and I do expect our state to completely mix with sleet/freezing rain, with the potential of plain rain along the shoreline.
 
So how much snow will we get? Depends on the solution you believe. The warmer solutions, like the RGEM, keep most significant snow to our north, and only bring a few inches to most of our state down to little to nothing on the shoreline. The colder solutions, like the Euro, bring a warning level snowfall to our northern zones, and a solid plowable snowfall for all. Those maps are shown below – keep in mind that these are algorithms, not forecasts, but should give you an idea of the differences between the solutions.
 
The Forecast
 
This is a tricky one, since as we just saw, the small differences in modeled temperature have a substantial difference in sensible impact. While we can’t know for sure if one is more correct than the other, we can use some logic to try to come to a conclusion. Here’s what we know:
 
-These sorts of systems, known as South West Flow Events (SWFE’s) are routinely underestimated by the models as far as the extent of lower level cold air.
-Similarly, they often under-do the extent of the warm tongue.
-The trend over the last few cycles has gradually been warmer, though by small amounts.
-We’re expecting a fairly heavy band of snowfall to kick off the storm, which will serve to put down some quick accumulations and cool the column. If heavy rates persist, this will help to temporarily hold off mid-level warming.
 
Given all of that, I think a blend of the models, biasing a bit towards a warmer mid-level and a colder surface, is the sensible approach. That yields something like the map below.

​Along the immediate shoreline, I’m expecting two to four inches of snow and sleet, with a glaze to perhaps a tenth of an inch of ice, and an eventual changeover to plain rain. I’d expect that by the morning commute, most folks here are seeing an icy mix, which will make for slow travel, even if it’s not snowing. The cold air on the shoreline will probably hold on longer than modeled, but I would suspect that by lunchtime or so, we will be over to a cold rain in this area. 
 
Across the interior, however, it’s a different story. The extra latitude, combined with the lack of marine influence, should keep temps colder, and allow precipitation to be mostly if not completely frozen. The further north you go, the more snow and less ice you’ll get, but the idea is the same – it’s a mess. Splitting the difference between the model camps generally suggests a solid advisory snowfall across the state, with the chance for warning level (6”+) most likely north of Hartford.
 
As such, I’ve gone with a general three to six inches of snow for most, followed by sleet and a glaze of ice, and have added a five to ten inch zone for the far north where I think confidence of remaining mostly snow throughout the heavy precipitation is highest. I would generally expect most in that zone to stay in the 5-8” range, but I am leaving some wiggle room up to 10” in case of either an overperforming band or colder than expected temperatures.
 
Winter Storm Warnings are in effect from the NWS for our northern four counties, while Winter Weather Advisories are in effect for the southern counties.
 
Timing
 
We should see snow arrive late tonight, with the leading edge of precipitation reaching the state by midnight. I’d expect snow to come in quickly once it arrives, as mesoscale guidance is in good agreement that we’ll see a heavy band to kick this event off. Snow will continue through the overnight hours, and towards sunrise, we should start to see a shift from snow to sleet and ultimately to freezing rain begin across the south. The morning commute will be messy for all areas, with snowy and icy roads in the south giving way to heavier snow up north. As the morning progresses, the mix line will move north, and plain rain will eventually make its way to the south coast. Mesoscale guidance suggests that the precipitation exits most of the state by early afternoon, and it’ll be a race between the warm air and the back of the precipitation to see if far northern areas will hang onto all snow or flip to sleet/freezing rain at the end of the storm. The evening commute should be improved from the morning one, though with cold air streaming back in after the system, expect roads (especially secondary and tertiary) to be icy and slow going throughout the evening as any melt/liquid refreezes.
 
Impacts
 
I got a new computer and don’t have the fancy impact scale graphic right now, so we’ll have to do this the old fashioned way…
 
Snowfall Accumulation: Moderate. Most of the state should end up with a solidly plowable snowfall, but don’t think we’ll see anything too crazy here.
 
Snowfall Rate: High. We should see an inch an hour or more during the heaviest snow, which for many areas, will be during peak commuting hours.
 
Wind: Low. Luckily, we aren’t expecting any significant winds with this event.
 
Power Outages: Low. If we get more freezing rain than expected, we could see some isolated outages, but I’d expect those to be few and far between.
 
Timing: High. With the heaviest precipitation coming during the morning commute, I expect significant impacts to schools and businesses tomorrow AM.
 
Road Conditions: High (Moderate on the immediate shoreline). Ice is never a good thing for the roads, and when you add heavy snow, it makes a real mess.
 
Overall: Moderate/High. While the totals won’t be spectacular with this storm, and it’s over quickly, the conditions tomorrow morning won’t be pretty, and we’ll likely see larger impacts to commutes and travel than we’d otherwise expect with these totals.
 
Bust Potential/Confidence
 
Overall, this is an average confidence forecast. I think we understand the storm well, and the overall model consensus on liquid is excellent. No sharp cutoffs or screw zones here, for the most part. The challenge will be determining temperature gradients both at the mid-levels and at the surface, as that is always what will ultimately determine precipitation types and thus accumulations. These systems tend to be fairly predictable, so I think I’m confident with our forecast, but I can’t help but notice the swings in outcomes still shown on the models and the resulting changes to our outcomes. I think the areas of highest bust potential are on the immediate shoreline (in both directions – could see things tick warm and see little to no snow, or a tick colder would bring 3-6” right to the coast) and far northern CT (if we see the transition quicker than expected, we’ll be closer to the 3-6” range there vs. 5-10”). I feel pretty good about the middle portion of the state, but we’ll just have to wait and see what happens!
 
As always, please like, share, and ask questions – I’ll be keeping an eye on our FB comments for the next few hours, so drop your questions there and I’ll do my best to get back to you. Please also send us your observations tomorrow morning, as they’re critical in knowing where the mix line is setting up and how we’re tracking vs. models and the forecast.
 
Thank you for trusting SCW, and enjoy the snow!
-SA

'Tis the season for rapidly changing wx conditions! Near record warmth today will leave the region quickly and lead us into yet another winter storm threat.

Currently: The cold front that will herald our rapid wx change was currently stretching from the Lehigh Valley to Eastern NY state.  Temps will fall very rapidly behind that front.

Tonight: Temps fall rapidly behind the cold front.  Guidance is in pretty good agreement w/overall thermals.  No reason to bicker w/guidance on temps at that range.  Low temps generally in the mid 20s, except maybe upper 20s along the SE coast.

Tomorrow: Morning sun leads to increasing clouds.  An area of light pcpn, mainly snow, could break out during the day near the Mason-Dixon line.  However, dry air from the high pressure sys overhead should allow that snow to break apart before it gets near our area.  Once again, guidance is an excellent agreement and generally accepted.  Highs should be in the mid to upper 30s throughout the state.

Tomorrow Night/Fri:
...A WINTER STORM WATCH HAS BEEN ISSUED BY THE 3 NWS OFFICES THAT SERVE OUR STATE FOR EVERYWHERE EXCEPT THE IMMEDIATE S COAST...

Here's where the winter wx occurs.  Pcpn probably arrives in our area around midnight, give or take a few hrs.  Initially, all levels are cold enough to support snow.  However, a transition to other forms of pcpn will migrate S to N as  the event continues.  Snow should accumulate an inch or two along the immediate SE coast before changing to other ptypes.  As one migrates N thru the state, accums will be higher, with up to 6" possible in the NW and NE parts of the state, esp over 1000 feet.  Most areas will see somewhere between 2 and 5 inches of snow.  

After we change over, we do not change directly to rain, as the mid-levels of the atmosphere warm before the sfc.  We will change to sleet probably everywhere, then freezing rain at least in the southern half of the state.  The exact timing of these changeovers is uncertain right now.  The later the changeover to freezing rain the better, as that is by far the most dangerous winter p-type.  My thinking is that we do make a complete changeover to rain along the immediate S coast, up to about the Merritt Pkwy.  N of there, temps may very well stay below freezing for the duration.  Even in areas that do change to rain, most of the pcpn may be done before we changeover.  I went several deg under guidance for temps, and have highs of 30-35.  These systems have a tendency to keep cold air in at the sfc longer than progged.
Stay tuned for our snowmap highlighting this system.

Long Term (The weekend and beyond): Generally below to much below norm temps are expected during this time, w/Clipper systems/Arctic fronts producing occasional bursts of snow.

For Sat: A cold day behind our departing sys.  Went a bit below guidance on temps, w/some snowcover and fresh cold air advection.  Highs generally around freezing.  Winds gusting to 30-35 MPH will make it feel even colder!

For Sun: Temps moderate, as high press moves overhead.  Guidance temps generally accepted.  Highs generally around 40, except low 40s along the I 91 corridor.  An Arctic front approaches Sun night.  This front looks similar to the one last Sat and could produce snow squalls again.  This time, with the nighttime passage, temps could be lower and we won't have to deal w/sun angle, so we could see more widespread brief accums.

For Mon: Bitter cold, esp for the time of yr, behind the fropa.  Went a bit below guidance w/fresh cold air advection.  Highs only in the mid to upper 20s.  Wind gusts up to 30 MPH will make it feel even colder!

For Tue: An Alberta Clipper sys approaches.  This sys has trended stronger and further S w/last model runs.  So there could be minor accumulations up to an inch or two w/this, as it has the potential to produce a burst of steady snow.  Also, because of this trend, I went well below temp guidance, and I have highs generally in the mid 30s.

For Wed: Clearing skies but still cold.  I feel there's one more good shot of cold air advection behind the sys that is not being modeled well right now.  For this reason, I took a big risk at this range and totally ignored temp guidance.  My temp fcst is based on thermal profiles, using a top-down approach.  Highs should be 30-35 across the state.

The long range does not look all that atypical for the time of yr.  Highly variable conditions day to day, esp regarding temps, will lead to high uncertainty with the actual fcst.  There is the potential for a very warm day like today at times, but there is also the potential for more winter storms, if a storm lines up at the right time w/a burst of cold air.  Stay tuned!

A couple of production notes: I did not add any graphics today, since my cohorts will likely be working on a map.  I may add a quick line or two update to this later today or tomorrow, as NWS headlines and model runs change (if I have the time)!

Take care and see all next week!

-GP!

The pattern is going to first turn more stormy, which is often indicative of big changes.  Then it will turn much colder, but the next week or so is mostly warm (with a cold shot over the weekend).

Currently: High pressure has moved offshore, allowing temps to turn much warmer today.

Tonight: Temps don't move much.  We have increasing Southerly flow, combined w/cloudy skies.  This is not a recipe for temps to fall.  Guidance is always stuck on everything being diurnal, so I went above guidance w/temps.  Basically, whatever your temp is now, expect a similar temp tomorrow morn.

Tomorrow: Despite cloudy skies, warm air advection surging ahead of our storm sys will allow temps to reach very warm levels.  I went very close to guidance temps, which are in the mid to upper 50s.  Because of southerly winds ahead of the next sys, the S coast will see winds blowing off the LI Sound, so that will be the coldest part of the state.  Any pcpn ahead of the next sys holds off until night, so I kept the day pd dry.

Tomorrow Night/Fri: This is the first interesting part of the fcst pd coming up.  Rainfall/flooding is not a real concern, as the ground is now only partially frozen, and rainfall amounts will be under an inch.  The main concern is wind.  Numerical guidance, as well as superens products, all point to wind gusts over 50 MPH W of I 91 and over 60 MPH E of I 91.  That doesn't really make all that much diff anyway, but either way, winds will be a concern.  There is the potential for downed trees and power lines w/this wind.  I will post a graphic about this further down.  The other interesting aspect of this storm will be the roller coaster temps.  Temps will stay steady or even rise a few more deg Thu night.  A few spots in the state could hit 60 degrees! Then, after the strong cold frontal passage, temps will plummet right thru the day on Fri, w/temps in the 30s everywhere by sundown! Because of the extreme, non-diurnal range of temps, guidance was completely ignored.  Temps were calculated using a blend of 850 MB temps and gridded data.  Winds will stay gusty Fri.  Although they will not be as strong, some gusts to 40-50 MPH will still be possible.  This could hamper any cleanup efforts.


Long Term: (Sat and beyond):

For Sat, once again the main concern will be wind.  An Arctic front will arrive from midday to early afternoon.  This front could contain wind gusts between 40 and 50 MPH along it.  Again, while not necessarily in the "damaging" category, isolated damage is possible, and this could once again hamper ongoing cleanup efforts.  The cold front should not have much moisture with it.  However, because of steep lapse rates, I did include a 40 POP for snow showers over NW CT (basically N of the Merritt and W of 91) and a chance for a localized squall.  I included a 20 POP for snow showers E of 91 away from the coast.  Near the coast, I just have a chance of a flurry.  Any squalls could produce whiteout conditions.  However, none should last more than 5-10 mins.  As for Sat's temps, I went near guidance everywhere, except a smidge above along I 91.  So highs generally near 40, except maybe 40-45 along I 91.

For Sun, after a cold start, as high press moves overhead, temps should rise fairly rapidly.  Highs statewide should be near 40, which is right in line with guidance.

For Mon, w/high press moving offshore, it should once again turn much warmer.  Even though clouds should increase, temps should make the low 50s in most places, except cooler along the S coast, where the southerly flow will be blowing off the LI sound.

The next sys effects the state Tue.  For now, I am going pretty generic w/the wording and p-type.  I will just call for rain across the entire state, and do my normal thing of going a bit below temp guidance due to clouds and precip.  It should be noted, however, that there has been a trend toward colder solutions w/this sys.  Later crews may need to watch for the potential for mixed pcpn across our northern 3 counties (Tolland, Windham, and Litchfield).  But w/the sys still being six days out and still trending, I am not going to go crazy w/that yet.  As mentioned, I went a few deg blo temp guidance, and then trended it even colder than that to try to compensate for trends.   I have highs mostly in the mid to upper 40s, but already lowered that to the low 40s in the northern 3 counties.

For Wed, we should be in between systems.  So we'll call it mostly cloudy, as clouds leave from one sys as soon as they arrive from the next one.  It should be very warm, but went just under guidance, since it's so far out, just out of an abundance of caution.  Even so, expect most highs in the low 50s, except possibly cooler along the S coast, once again owing to winds off the LI Sound.

In the longer range, the Alaskan Ridge is going to become a bigger player in our wx.  As this happens, you'll see more high press across Southern Canada, which forces more cold air into the Eastern CONUS.  This will result in a colder pattern overall.

Now, let's look at a couple graphical images displaying this week's wx.  First is a map showing wind potential overnight Thu night into Fri morn.  Anywhere in or along the purple coloring would have a high probability of damaging winds, while the greener shades are lighter, but still gusty.

Finally, this last map shows the rain for Tue.  It is a general, widespread rain- just a gloomy, late winter's rainy day for now, nothing extreme.

Anyway, that's all for now! See you next week!

​-GP!

As you can feel outside today, the pattern is slowly beginning to change as seasonal climo changes and we leave the "dead of winter".

A couple very near term notes first: Wind gusts need to be increased thru this afternoon, as frequent gusts in the 30-35 MPH range are occurring with a fropa.  In addition, some sprinkles will occur, esp N of the Merritt Pkwy, but really could occur anywhere in the state w/this feature.  This front is of Pac origin, so other than a chilly night, cold temps are really not expected w/this feature.

That cold front is currently over the Lehigh Valley and just W of the NYS Thruway, so it should enter the state this afternoon and be clear by dinner time.

Tonight: Went a little below guidance on temps tonight, w/fresh cold air advection.  Lows generally near 30, except upper 20s in the NW Hills.  Sheltered valleys could cool more, but that will all depend on when/how much winds decouple.

Tomorrow: Another sunny and pleasant day for the area.  As I mentioned, any cold air advection is very brief and only tonight.  So followed guidance very closely for highs tomorrow.  Look for highs generally in the upper 40s.

Tomorrow night/Sat: Sat will be warm, but exactly how warm is the big ? and temps are a bit tricky.  There are two reasons temps are a bit tricky.  First is timing of a strong Arctic fropa.  This is the biggest question.  The earlier the fropa, the less warm it will be.  The second big ? is temps along the S coast.  Winds will likely have a southerly component ahead of the front, which would be blowing off a frigid LI Sound.  This could hamper temps significantly along the S coast, esp the further E u are, where the Sound is wider.  For now, I have most highs in the upper 40s, with low to mid 50s in the I 91 corridor, which means I went under guidance most places, but close to guidance along I 91.  Similar to today, that front does not have a lot of moisture to work with.  A sprinkle is possible (maybe even transitioning to sleet and snow showers), but I do not have enough confid to add to the fcst right now.

Long Term Summary- The two main events in the long term are a possible coastal low Sun and a big Great Lakes low on Thu-Fri, w/fair wx in between.

For Sunday, this coastal low will likely be pretty far out to sea, if latest model consensus is correct.  But it is still close enough to watch, and even as is, could bring some light snow to the S coast.  For now, low POPs (30%) will be in the fcst for the S coast, w/no mention anywhere else.  Will also mention that any accums would be 1" or less.  We are close enough now.  For high temps, I went a few deg below guidance due to clouds, and any potential light snow along the S coast.  Highs will generally be near 30, except upper 20s in the NW Hills.  If the coastal low trends further W, then these temps may be too warm.

For Monday, went close to guidance on temps.  For now, w/the coastal low progged to be too far offshore to produce widespread snow, I did not incorporate snow cover into the temp fcst.  Cold either way, w/highs only 20-25!

For Tuesday, went right w/guidance again, w/no discernable reason that it would be wrong.  High pressure more overhead, so temps moderate a bit.  Highs generally 30-35.

For Wednesday, once again riding the temp guidance pretty closely, without any real reason to go against it.  We continue to warm up, with highs 40-45, except cooler in the NW hills.

For Thursday, clouds increase ahead of the next sys.  However, we should stay dry, esp during the day, so no pcpn was included in the fcst at this time.  W/increasing clouds and southerly flow off the Sound, I went a bit lower than guidance, with high temps mostly in the upper 40s, although it could be colder than that along the S coast and warmer than that inland.  I just didn't want to get too cute on day 7 temps.

Only one graphic is needed today, since the late-week sys is just outside our fcst period.  This is the GFSm valid Sun morn.  You can see that the storm is too far out to sea for anything appreciable here, but it wouldn't take a whole lot to bring measurable snow into parts of the state.

Anyway, that's all for now! See you next week!

-GP!

No, major snows are not coming, but tomorrow, especially in the afternoon and evening, much of the state will have to deal with ice.

Currently: A cold front was over Central PA, with many waves of low pressure along it.  This will be the focal pt of our wx today and tomorrow.

Tonight: Went slightly above guidance on temps.  Temps prob rise to about midnight, then fall.  The freezing line at dawn should be somewhere near or just N of the Merritt Pkwy.  Lows generally 30-35.  In this setup, the 35 vs 30 will be a big difference.  Pcpn typ is all liquid, so those places where the temp is AOB freezing will begin to ice up.

Tomorrow: The NBM insists that just because it is daytime, temps must rise.  However, when you have strong northerly flow and heavy pcpn falling in early Feb, that isn't the case.  I went about 10 deg lower than NBM guidance, which allows for steady or slowly falling temps thru the day.  Ptyp transitions to frz rain everywhere, then sleet from N to S.  The entire state is under a winter wx advisory for icing.  Pay attn to any products from NWS for possible upgrade to Ice Storm Warnings or changes to the advisories for portions of the state.  If anything significant chgs during the aftn updts from NWS, I may do a quick updt.  Please use extreme caution if you must travel tomorrow, since ice can be much worse than snow! Winds should not be overly significant, but there could be decent breezes.  If enough ice accumulates on trees, w/gusts to 25-30 MPH, limbs can blow down and cause power probs.

Tomorrow Night/Sat: Icy tomorrow night.  Pcpn is over by midnight, but it might be prudent to allow road crews several hrs to clean up afterwards.  Breezy and cold Sun.  Guidance reflects this pretty well, so followed pretty closely.  Look for highs in the mid to upper 20s.

Long Term: Pretty quiet thru this pd.  Sunday is sunny and cold.  Temp guidance looks fine, w/advection near zero.  Highs near 30 degrees.

Monday: Warmer, as high press shifts offshore.  I did go a bit under guidance, just a deg or two, as I think the guidance may be overly aggressive w/warming us up as it won't be totally sunny.  Highs generally in the upper 30s.

Tuesday: This is the only small concern of the pd.  I inserted a 20-30 POP S coast only.  A "coastal scraper" low has begun to show up on the models, and comes close enough to possibly graze the S coast with some light pcpn.  GFS and GGEM models both agree on this.  Any trends closer would bring a more sig pcpn event to the area, while any further would be just sunny wx.  Right now, pcpn would be all snow and centered on the AM.  Obviously a chg in storm track would result in chgs to the fcst.  For highs, once again, I went just a bit below guidance, w/upper 30s for most, and maybe near 40 along I 91.  These could be lowered if the storm does a closer approach.

Wednesday: We clear out behind any storm sys/front.  Aloft we're cold, but it's sunny and the sfc flow is W/SW, so that limits how cold we can be.  Guidance reflects this well, so followed closely.  Look for highs in the low 40s.

Thursday: Air mass is cooler aloft, the same at the sfc, but for some reason the NBM is 2 deg warmer.  Therefore, I went ahead and subtracted that 2 deg from guidance.  Basically, the same wx expected as Wed, with highs in the low 40s and generally fair skies.

A cold front could approach Fri w/some snow and rain showers, and much cooler air behind it.

For our graphics today, here's a good one.  Very simple: the entire state is purple on the NWS map, indicating a winter wx advisory.  

Anyway, that's all for now! See you next week!

​-GP!