Hello everyone!

We have an absolute mess of a storm on the way tomorrow night through Tuesday evening. A powerful storm system will move through the Mid Atlantic states tonight and redevelop offshore tomorrow before heading our direction tomorrow night. I discussed each threat as well as some of the dynamics behind the storm in yesterday’s update. Because I’m short on time, I want to spend this update on explaining why we’re likely to see more freezing rain/sleet than snow.

The short reason that we won’t have all/mostly snow is that the mid levels will be too warm. The GFS 700mb plot shows this perfectly with a deep stream of S/SE winds coming all the way from the tropics. This warmth will easily displace the weak cold airmass in place now. Remember from last night’s discussion that the cold front in the mid levels did not make nearly as much southerly progress as the surface front.

The type of precipitation forecast to fall at the ground is often most easily forecast through analysis of a vertical profile like the one shown to the right. This is what the atmosphere directly over Gray is forecast to look like on Tuesday morning at 9 AM. Notice the deep warm layer between 5 and 10 thousand feet (850 and 700mb). This will allow for any snowflakes to melt into rain. Now notice the deep (5000 foot) layer of cold air near the surface. This will allow for all those raindrops (and there will be plenty) to refreeze into delightful (not really) little pellets of ice. These ice pellets are NOT hail! What they are, though, is annoying, slippery, heavy, and unfortunately for the Tuesday morning commute, abundantly plentiful.

I also highlighted locations of latent heat transfer on the sounding. At the top of the warm layer, melting will occur which requires outside energy to change from a solid to a liquid, cooling the environment. The opposite will happen at the bottom of the warm layer where rain refreezes into sleet. This process is how the warm layer will gradually descend to a point low enough to the ground to allow for freezing rain. Finally, as temps approach freezing at the surface, some melting may try to occur but as we discussed above, melting requires outside environmental energy which will cool the environment overall thus favoring a continuation of the cold air through most of the event, even along the coast.

Here’s the forecast for all the various things that will fall from the sky. We’ll start with a burst of snow that will quickly change to rain in the light pink areas along the immediate coastline of York County, SE NH, and the midcoast. The snow will stick around and pile up a little longer inland and most of the event will feature snow for places in the far NW mountains. The timeframe for this segment of the event will be from midnight Tuesday morning through around 6AM Tuesday morning.

After a little snow, the warm air aloft will begin to invade changing everyone over to sleet (abbreviated commonly as IP for Ice Pellets). The sleet will fall on top of the snow, compacting it and making it extra heavy/icy. The rain snow line will move a little inland during this time but won’t make a lot of meaningful headway. This phase of the storm will last from around 6AM to around noon.

Then, warm air will sink towards the ground due to latent heat transfer in the refreezing zone and as a result, some areas are likely to see a change to freezing rain. This will be most impactful in the foothills where up to a quarter-inch of ice is possible. For the mountains, snow will begin to mix with sleet and for the coast, the rain line will continue to inch its way inland. This phase of the storm will last from around noon to around 4/5 PM.

The final phase of the storm will see a change to sleet across even the most NW parts of the mountains and a change to freezing rain/freezing drizzle for the foothills. The coastal plain will change to rain as the cooling influences of upward motion, falling precip, and partial melting at the surface will ease. This phase of the storm will last from around 4 or 5 PM through the end of precip in the predawn hours Wednesday.

For more info about winds, coastal issues, and some exploration of isentropic dynamics driving the event, check out last night’s update. The stuff there is still relevant.

More info tomorrow.

-Jack

Hello everyone!

Today will feature mainly cloudy skies as a cold front sinks southward across the region. Look for this front to touch off a few patches of drizzle along with some flurries or sprinkles. No accumulation is expected though a few slick spots are possible. Highs will range from 30 in the mountains to 40 along the southern coastline.

Our next storm arrives tomorrow night. For my latest forecast and analysis, check out last evening’s update. I’ll have another one later this evening.

-Jack

Hello everyone!

Today will feature mild temps and mainly cloudy skies as weak disturbances drift around the area. Look for highs a little above freezing in the north and right around 40 along the southern coastline. No precip is expected though some drizzle offshore may work its way onto the midcoast at some point this afternoon.

I’ll work on having a more in-depth analysis of the storm Monday into Tuesday this evening.

-Jack

Hello everyone!

Today will feature more clouds than sun along with mild temps as a weak front drifts around the area with no particular purpose. Expect high temps to range from right around or a little below freezing in the north to the upper 30’s in the south. Skies will be cloudiest in the mountains where some upsloping may squeeze out a flurry or two. The frontal system that brings the rest of the region clouds may also provide enough forcing for a shower of rain, snow, or sleet, depending on location. These showers will be very light and are not expected to cause any significant issues.

What is expected to cause a significant issue is the storm riding up the east coast early next week. While I won’t be able to get an update out on that today, I’ll have all the details tomorrow. For now, just know that substantial impacts to travel are likely Monday and Tuesday with exact timing still to be determined.

-Jack

Hello everyone!

Our mild (ish) pattern has a few more days left in existence before winter reminds us all we live in Maine. Today will feature mild temps, more clouds than sun, and light snow this morning. Highs will range from a few degrees below freezing up in the mountains to a few degrees above freezing along the coastline and across southern NH. Light snow is falling across parts of the area this morning and will move out by the mid morning hours leaving behind an inch or two of accumulation at most. Skies will see more clouds than sun but bright spots are certainly not to be ruled out especially across western areas.

-Jack

Hello everyone!

Today will feature cloudy skies along with light to occasionally moderate snow. Low pressure dragged its feet in developing south of Cape Cod last night so snowfall totals are going to be on the lower side of the forecast but roads are still slick nonetheless. Snow will taper to flurries and then move out of the mountains this morning and areas NE of Lewiston will likely also fall in that same boat. The foothills will keep things rolling for another few hours but it’s the coast that’s going to see the most snow today as maritime air laden with moisture 

Here’s the HRRR model showing how precip dissipates for most except the immediate coast by mid day. While the model shows mainly dry conditions across inland areas today, I would be prepared for areas of freezing drizzle which will create continued slick travel conditions. More snow is expected tonight with a general coating-2″ expected. More is possible in the favored upslope areas in the mountains.

Temps today will range from the low 20’s in the mountains to the mid 30’s along the York County coastline.

-Jack

Hello everyone!

All our players are in place for a moderate snow event for most of the area tomorrow. Snow is already falling across SW NH, as was forecast last evening, and is making slow but steady progress NE. By midnight, everyone in the area should be seeing flakes (or raindrops along the York County coastline, far SE NH, and the tips of the midcoast peninsulas) with snow beginning in the Portland area around or a little after 9.

We have all the players on the field so to speak with cold air streaming south out of the north ahead of the storm. Our primary low is dissipating over the Great Lakes while the secondary low begins to emerge over northern Virginia. As the secondary low slides ENE, the coastal front along the ME and NH coastlines will sharpen up, changing any raindrops at the onset over to flakes fairly quickly. Wet bulbing will also help with this as latent heat energy is lost from the atmosphere during evaporation. Notice also the relatively warm airmass following the storm. This is part of the ‘winter halftime’ and while temps for most will be below freezing, there’s no punishing cold behind this system. We’ll save that for the pattern change that’s been widely advertised for February. I talked a little about that last evening.

Here’s a visualization of that coastal front. Warm marine air will attempt to push inland and will run into strong cold air damming associated with high pressure to the north. This high will feed cold air south and will be the driving force behind the mainly snow nature of this event. The exact placement of the front will determine who sees rain and who sees snow but I think the model has a pretty good handle on its placement. The NH seacoast, the coastline of York County, and the tips of the Midcoast peninsulas will be at greatest risk for raindrops though some snow accumulation is likely there too.

The other important factor the coastal front brings to the table is a focus for lift and enhancement of precip. The warm marine air being forced to rise over the low-level cold dome will produce lift and will help to wring out the moisture in an otherwise weak system. In terms of overall QPF (quantitative precipitation forecast), about .5 to .75″ of liquid is expected across most of SW ME (areas in blue are where the model thinks >.5″ will fall). Farther NE, amounts will drop off as less moisture is available. How much snow does that equate to? The answer will lie in the snow to liquid ratios, to be determined by lift and moisture within the dendritic growth zone.

Note the two different areas of lift in the vertical profile of upward motion (z component to the wind). The component that will produce the best snow growth will be associated with a burst of warm air advection in the mid levels. This is a process driven by the weakening primary low and thus won’t be super strong. The stronger lift will be closer to the surface and driven more by the coastal front dynamics. This process will not be co-located with the DGZ. As a result of the modest snow growth and fairly warm surface/near surface temps (just below freezing), look for this to be a heavier/wetter low ratio snow rather than the fluffy stuff that piles up much more efficiently. Look for snow:water ratios of right around 10:1 compared to the usual 12:1 or the fluffy 20:1 we sometimes see.

Here’s the latest snowfall forecast. Most areas will see 3-6″ with rain holding down accumulations along the seacoast of NH, coastal York County, and the midcoast peninsula tips. A lack of lift/moisture will keep accumulations down to the NE while the jackpot is likely to be across NH and extreme western Maine.

Here’s a look at how things evolve tonight and tomorrow. Snow will be light to moderate for most and will taper off to flurries for most by tomorrow mid morning. The steadier snow will hang on the longest at the coast where the coastal front will continue to enhance lift as discussed above. After the snow moves out mid day, residual moisture in the low levels will create a freezing drizzle hazard through the evening hours. As a result, use caution traveling tomorrow even if the flakes aren’t actively falling.

More snow is expected as a disturbance passes overhead Thursday morning. The best chance for a couple of inches will be in the mountains though some ocean moisture could enhance things just enough along the coast to squeeze out an inch or two. The rest of the area will see flurries with a dusting possible.

More precip is likely by the time we get to the upcoming weekend but it’s too soon to say if we’ll see rain, snow, or a mix of both.

-Jack

Hello everyone!

Today will feature in increase in clouds and a decrease in temps as our storm for tomorrow moves closer. Temps will range from 25 in the north to 34 along the southern coast with only the coastline seeing above freezing temps. Everyone except the coast south of Portland and the peninsulas of the midcoast (Boothbay, Rockland, etc.) will be below freezing and ready for snow by the time precip arrives tonight.

Here’s a visual on the storm’s approach, most areas will see some sun this morning but as the sun approaches the horizon this evening, clouds will begin to move in. Snow should begin in the 4 PM hour across far SW NH and will slowly move NE reaching Portland between 8 and 9 PM. Snow will continue through the night before tapering off to flurries and freezing drizzle tomorrow afternoon. For more details on the storm as well as other chances for flakes in the 7 day plus a look at why winter’s comeback is coming, check out the update from last evening.

Hopefully my schedule will permit another update tonight.

-Jack