Tag Archives: sleet

Messy Winter Storm Monday Night Into Tuesday

Hello everyone!

This evening’s update will focus on an impactful and messy winter storm forecast to move through the area Monday night into Tuesday. It will bring with it copious amounts of all precip types with significant snow in the far north, sleet and freezing rain for most, and heavy rain along the shorelines.

12Z 3km NAM Showing Light Flurries Tomorrow Night. Credit: Weatherbell
12Z 3km NAM Showing Light Flurries Tomorrow Night. Credit: Weatherbell

The event will technically begin tomorrow during the afternoon as shifting winds aloft bring some light moisture into the area. The greatest chance for precip will be across southern areas where some ocean moisture will become entrained in the NE winds and also in the mountains where some upsloping will aid in precip development. Precip will fall as sprinkles of the liquid variety along the southern coast, flurries in the mountains, and pockets of sleet/freezing rain across interior SW NH. No accumulation is expected but some slick spots are possible here or there.

18Z NAM Vertical Slice Compilation Tomorrow Evening. Image Credit: Accuweather
18Z NAM Vertical Slice Compilation Tomorrow Evening. Image Credit: Accuweather

Shown to the left is a series of maps that holds the key to this forecast. The model and time are kept the same with each map displaying a forecast for a different slice of the atmosphere. The top forecast is for about 25,000 feet followed by 10,000, 5,000, 2500, and 0 feet. The feature of interest is a back door cold front moving SW across the area tomorrow evening. Notice how it slopes backward over the cold airmass with the most forward progress of the cold wedge at the surface and the least progress aloft. This sets up a situation where you have a deep cold intrusion at the surface (and a high pressure system over Quebec to lock it in) and an environment only marginally cold aloft. This sets up a situation where warm air can easily flood in aloft but will have a hard time making headway at the surface. This is why we’re in for more freezing rain/sleet than snow for most of the area. The best chance for sizeable snowfall accumulation will be the far NW mountains. The poleward slope of the cold frontal surface illustrated above means that we’ll have an excellent isentropic overrunning surface as warm air is forced to glide up and over the low-level cold dome.

18Z NAM NB-VA Cross Section Showing A Well Defined Poleward Sloping Cold Frontal Surface. Image Credit: Accuweather
18Z NAM NB-VA Cross Section Showing A Well Defined Poleward Sloping Cold Frontal Surface. Image Credit: Accuweather

Here’s a cross section showing another view of the same phenomenon we discussed above. Because of the discrepancy between airmasses, this boundary acts similarly to a material surface along which air will rise. This sets up the arrival of precip Monday evening, initially as snow due to the deep cold air. You can see the warm nose moving in from the SW on the cross-section, it’s the little kink to the right in the purple (0C) line. That’s the warm air riding up and over our cold front. The image is valid 1 AM Monday morning. Also notice the low-level moisture on the cold side of the front. This is why we’ll see some light flurries/sprinkles/drizzle Sunday night and Monday morning.

Now that we’ve established that we’re looking at an elevated warm layer and a near surface cold layer, let’s look at a sounding (vertical profile of the atmosphere at a single point) to determine if we’re looking at inches of sleet or a damaging ice storm.

12Z NAM Sounding For Lewiston At 7AM Tuesday
12Z NAM Sounding For Lewiston At 7AM Tuesday

Thankfully for the power grid, the cold layer near the surface looks deep enough to allow for sleet to be the dominant precip type. While the deep warm layer will melt snowflakes, the deep cold layer near the surface will allow for those raindrops to refreeze into ice pellets rather than freeze on contact with the ground. That’s not to say that some folks won’t see ice accumulation but it likely won’t be heavy enough to cause power outage issues. Don’t worry though, we have winds for that job along the coast. For more on how warm/cold layers impact precip type, check out one of my recent UpPortland columns where I explain various forms hydrometeors make their way to the ground.

NAEFS Ensemble U-Vector Anomaly Tuesday Morning Showing Anomalously Strong East Winds At 850mb. Image Credit: NWS/NOAA
NAEFS Ensemble U-Vector Anomaly Tuesday Morning Showing Anomalously Strong East Winds At 850mb. Image Credit: NWS/NOAA

Here’s a look at the mid level winds which will be very strong out of the east/south east. The map to the left shows the anomaly in the u vector which is the east/west component of the wind. The highly negative u vector means the easterly component of the wind will be exceptionally strong. This will help not only to bring warm air into the region aloft, but it will also help introduce the threat for gusty winds out of the east along the midcoast early Tuesday morning.

18Z NAM Showing Strong Winds For The Midcoast And Southern Shorelines Tuesday Morning. Image Credit: Weatherbell
18Z NAM Showing Strong Winds For The Midcoast And Southern Shorelines Tuesday Morning. Image Credit: Weatherbell

Winds will be an issue along the midcoast and any other shoreline towns that happen to make it into the maritime airmass E of the coastal front. Wind gusts of 40-45mph are likely for a time Tuesday morning as low pressure approaches. On the western side of the coastal front, look for cold but lighter N/NE breezes to keep cold air locked in place at the surface resulting in slippery travel and messy precip types.

12Z NAM Showing Gusty Winds Just Above The Surface In Rockland Tuesday Morning
12Z NAM Showing Gusty Winds Just Above The Surface In Rockland Tuesday Morning

Here’s another view of the wind potential as shown by a vertical cross-section through time above Rockland. Notice the strong low-level jet just off the surface. Any winds below the yellow line are ‘eligible’ to be mixed down to the surface via momentum transfer and as a result, there is fairly high confidence in 40-45mph gusts along the midcoast Tuesday morning. For more on momentum transfer, check out one of my UpPortland columns from a while back where I explain it.

Tide Forecast For Portland Through Wednesday Morning. Image Credit: NWS/NOAA
Tide Forecast For Portland Through Wednesday Morning. Image Credit: NWS/NOAA

All those easterly winds over the Gulf of Maine will push water up along the coast. While thankfully we’re not experiencing astronomically high tides, some splashover is possible as shown by the black total water level forecast above the first red line which is mean higher high water level. The specifics of that value are complicated but you should know the little yellow line (storm surge) will be between 1 and 2 feet and will push water high enough for some minor coastal flooding though no major impacts are expected.

Precip Type Forecast For Monday Night Through Tuesday
Precip Type Forecast For Monday Night Through Tuesday

Here are my thoughts on precip type. Rain will be confined to the midcoast/shorelines and most of the area will see sleet for most of the event after an initial thump of snow. During that initial thump, 2-4″ can be expected for most. An additional few inches up in the northern mountains will likely bring totals to the 4-8″ range in the blue zone on the map above.

18Z GFS Showing Another Round Of Light Precip Wednesday Evening. Image Credit: Weatherbell
18Z GFS Showing Another Round Of Light Precip Wednesday Evening. Image Credit: Weatherbell

Precip moves out Tuesday evening and we’ll be left with a relatively mild airmass and dry weather for about 24 hours before another system approaches from the west. This one will be much weaker and is likely to bring just a brief period of snow/mix to the mountains with rain showers in the south. Little to no accumulation is forecast but some slick spots will once again be likely. Behind this system, colder air will begin working back into the region as winter’s comeback begins.

More tomorrow after I enjoy some turns up at Sunday River. As a result, tomorrow’s update may be a little later in the evening but will contain all the latest analysis.

-Jack

More Messy Weather Tomorrow Into Friday

Hello everyone!

Early spring is in full swing in Maine and this week will be a good reminder that Spring is a battle between warm and cold. In the beginning, cold wins. Slowly but steadily, the warm air wins out but it will take many messy battles before that happens. For now, the advantage is with the cold. We’ll see that in full swing in the next few days as a powerful Colorado low which is currently bringing every type of weather under the sun from Colorado/Nebraska blizzards to Texas tornadoes. The storm will be significantly weaker by the time it gets to us but will still be potent enough to cause some issues tomorrow into Friday.

The Setup: This Evening

Afternoon Observations Showing Our Next Storm Setting Up To Our West. Image Credit: COD
Afternoon Observations Showing Our Next Storm Setting Up To Our West. Image Credit: COD

A cold front is moving through the area currently (blue line on map) and winds behind it are out of the north which is bringing in cold air. Canadian high pressure is diving SE across Eastern Canada and will continue to supply this cold air through most of the event. Low pressure is moving across the Western plains and will be moving NE towards our area tonight into tomorrow. A warm front extends out ahead of this storm and is linked to the cold front bringing us the cold air this evening. This warm front will try to push north tomorrow and Friday but cold, dry air in place will impede its progress significantly.

Round One: Snow Tonight Into Tomorrow Morning

HRRR Showing Snow Moving In Tomorrow Morning Well Ahead Of The Main Storm. Credit: Weatherbell
HRRR Showing Snow Moving In Tomorrow Morning Well Ahead Of The Main Storm. Credit: Weatherbell

Precip starts late tonight and tomorrow morning in the form of snowfall. Initially, everyone is snow and very light accumulations are likely for everyone by the morning commute. Snow will be light though and major issues are not expected. That tapers off tomorrow morning leaving mid-day tomorrow mainly dry but cool. The main system can be seen at the very end of the loop spreading into western PA/NY.

Round Two: Main Storm: Surface Edition Friday

12Z HRDPS Showing Winds Friday Morning At The Surface. Notice The Warm Winds At The Coast And The Cold High Pressure (No Winds) Holding Strong Inland. Image Credit: Weatherbell
12Z HRDPS Showing Winds Friday Morning At The Surface. Notice The Warm Winds At The Coast And The Cold High Pressure (No Winds) Holding Strong Inland. Image Credit: Weatherbell

The warm front mentioned in the setup section will attempt to move north overnight tomorrow into Friday. It will hit a brick wall at around route 1 which will let temps rise above freezing at the immediate coastline but will keep inland areas below freezing. This pattern should continue through mid afternoon Friday before the low passes overhead and the trailing cold front busts up the inversions holding the low level cold in place. This is the surface pattern that is known far and wide for not changing. Guidance says most of the region goes over to rain by 9 AM. I think it will be 3 or 4 in the afternoon before temps rise above freezing in inland/mountain areas.

Round Two: Main Storm: Upper Air Edition Friday

12Z NAM Showing The Upper Air Setup Friday Morning Over Lewiston.
12Z NAM Showing The Upper Air Setup Friday Morning Over Lewiston.

Aloft, a much different story will play out. There is no Canadian high above 3-4 thousand feet. Therefore, there is no source of cold air. Warm air blasting north will have no trouble pushing the cold air in place out of the way. This will result in a classic mixed precip setup where snow forms in the cold layer really high up before melting in the warm mid levels of the atmosphere. It then refreezes close to the surface resulting in sleet and freezing rain depending on the depth of the cold at the surface. With the cold Canadian high just to our north, there will be a continuous feed of cold dry air being funneled down the east side of the mountains. This is a classic Cold Air Damming setup and CAD always lasts longer than you think even if you think it will last longer than you think. That tongue twister boils down to the fact that cold air moves when it’s good and ready too and it’s not usually to motivated to go anywhere.

Round Two: Main Storm: Impact Map Friday

Expected Impacts From This Storm
Expected Impacts From This Storm

Following the initial snow tomorrow morning, this is what I expect for impacts. Everyone starts out with a little mix but strong SE winds should quickly warm the coast up above freezing resulting in mainly rain there. Despite that, do be prepared for slick conditions everywhere as sleet and freezing rain are a dangerous combo especially with some leftover snow around. Inland, even a few miles, cold air will put up a much mightier fight. Look for snow changing to sleet changing to freezing rain. Sleet and freezing rain look to be the dominant precip types through this event. Snow will quickly change over to a mix as warm air blasts in unimpeded aloft but for most areas away from the coast, the surface high will be enough to keep temps below freezing at the surface for a good long time. In terms of accumulation, in the green area, a trace to a tenth of an inch of ice is expected. In the pink area, a tenth to a quarter inch of ice is expected.

Rounds One And Two Combined Snowfall: Tonight Through Friday

Expected Snowfall Before The Change To Mix/Rain
Expected Snowfall Before The Change To Mix/Rain

Here is what I expect for snowfall before we change to a mix or rain depending on location. While I have the Penobscot Bay and York County regions missing out on any accumulations, I wouldn’t be overly surprised to see coatings there tomorrow morning. This all basically is gone Friday afternoon as sleet and freezing rain turn the ground into an icy crust. The March sun angle is still a factor here despite cloudy conditions and sleet/freezing rain could have a hard time accumulating on pavement. However, please use caution especially Friday as any untreated roads will likely be slick. This snowfall map includes precip tonight and into tomorrow morning.

Round Three: Possible Storm: Early Next Week

12Z GEFS Ensembles Showing The Potential For More Stormy Weather Early Next Week. Image Credit: Weatherbell
12Z GEFS Ensembles Showing The Potential For More Stormy Weather Early Next Week. Image Credit: Weatherbell

Following this storm, we have a nice early Spring weekend to look forward too with cool temps and sunny skies. However, tranquil patterns rarely last long in March in Maine and by early next week, another storm threatens. As you can see here, guidance is converging on the idea we see some sort of precip. How much/what type is still yet to be determined. Snow, mixed precip, and rain are all on the table as well as no storm at all though that is becoming less likely. While it is too early to offer details, I just wanted to put that out there as something to watch in the coming days.

-Jack

 

Another Messy Storm Wednesday

Hello everyone!

A quick update tonight on the next messy storm in the lineup which arrives Wednesday. This one looks to be a fairly simple storm with mountain snow/mix, inland snow/mix/rain and coastal mix/rain. The challenge, as always, will be to pinpoint exactly where those transition spots will set up. The actual storm looks to track right over us and any nudge in the track would result in big changes to the forecast.

12Z GFS Showing The Setup Wednesday Morning. Image Credit: Weatherbell
12Z GFS Showing The Setup Wednesday Morning. Image Credit: Weatherbell

Low pressure that passed north of the region today left a cold front behind and that is currently sitting across the region this evening. Low pressure will develop along the front to our SW tomorrow and will move into our area overnight Wednesday. The low currently looks to track right over the area which means that we get the best of both worlds depending on location. The low passes south of the mountains so they get mainly snow with some respectable amounts possible especially the farther NW you go. The low looks to pass over the foothills so they get the full house of snow, sleet, ice, and rain. The low passes NW of the coast so they get the warm rain treatment. The exact lines between these zones are still blurry and will remain that way until things start playing out Wednesday morning.

12Z GFS Showing The Upper Level Setup Wednesday Evening
12Z GFS Showing The Upper Level Setup Wednesday Evening. Image Credit: Accuweather

The trick to this forecast will be temps aloft. The mid level low will track over the mountains which should let them stay mostly snow. Farther south, even the foothills are on the warm side of the low which means that the stage is set for mixed precip likely in the form of freezing rain. Significant accumulations are not expected but there will likely be widespread slick spots away from the coast Wednesday. Should the track of the mid level low shift to the north, even the mountains mix and less snow falls. If it shifts to the south, the mainly snow area could shift down towards the foothills. Both options are on the table at this point.

2-29 Graphic 3

Here is what I’m thinking in terms of accumulation for various precip types. The only area that could get a significant storm looks to be the northern mountains. Everyone else mixes with an assortment of precip types.

A coastal storm misses south late week and then a ridge builds into the east coast which leaves us with building heat heading into next week.

Next winter will be better.

-Jack

Update #2

7:45 pm EST Thursday 2-23-12:
New forecasts coming in now and still trending cooler. This means that the secondary low will develop more quickly and reach a greater intensity before being driven off by approaching high pressure that will be building in for Saturday.

Low will approach the area tonight and snow will start at around 5:30am. Little accumulation before dawn but this thin layer will set the stage for more efficient accumulations with heavy snows later. Heavy snow will come with the 2nd low forming roughly 50 miles NE of Boston. This new low will start out fairly strong and will continue to deepen though cyclogenisis is not expected at this point. The new low will start to pull in sufficient cold air starting around 11:00. Warm air advection (which is warm air interacting with cold air usually overtaking it and produces precipitation) will be halted or significantly slowed by this point due to cool air being wrapped in by this point by the secondary low.

East winds brought on by the secondary low passing south of us will draw in warmer air along the coast and we will see a change to sleet possibly mixing with rain.

Snow amounts: Southern York County: 1-3″
Coast north of Portland to 20 miles inland: 3-5″
Inland and foothills: 4-6″
Mountains: 6-10″

Stay tuned!

-Jack

Wet and unsettled beginning to the workweek

As most of us are enjoying the long weekend ( myself included! ) There will be an unsettled beginning to the workweek. A system from the midwest will move in tonight with snow. Warmer air works in at around 9-11 am and we will see a mix with sleet and freezing rain  and eventually rain at the coast and will work inland from there.

Stay tuned!

-Jack

Tricky forecast for friday

Friday will feature clouding skies with precipitation starting around 3-4pm. But the tricky part is precipitation type. Ice, snow, or rain??

Stay tuned!

-Jack

 

Make your predictions here:

 

Snow wrapping up on Friday active 7 day forecast

 FRIDAY  6:15 am

As I write this, the snow/rain line is bouncing around. It is frusterating to watch the rain.snow line retreating a few miles up the coast, and have it advancing on me. Snow/rain will wrap up around noon today with flurries and showers remaining this afternoon.

5 day forecast as of 6:15 am Friday

Tonight: Few snow showers with temps in the teens.

Saturday: Partly cloudy with highs in the 20s and lows around 10

Christmas: Mostly cloudy with highs in the upper 30s and lows in the lower 20s

Monday: Rain and snow showers with highs in the low to mid 30s and  lows in the mid 20s

Tuesday: Mix of sun and clouds with highs in the upper 30s and lows in the upper 20s

Wednesday: sun mixed with a few clouds with highs in the 30s and lows in the 20s

Enjoy the holidays!

Stay tuned!

-Jack