Marine Weather and Tide Forecast for Rochester, NH

NEAR TERM /UNTIL 6 PM THIS EVENING/
After some brief clearing this morning clouds will gradually increase thru the day as the next storm system approaches. High temps will be pretty close to readings yesterday. Precip will come in quickly late this afternoon or early this evening...but overall most of the daytime should be dry for most of the area.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/
Impacts and Key Messages: * Slippery travel possible tonight and early Tuesday morning as light snow and light freezing rain accumulate on surfaces.

WAA precip rapidly overspreads the forecast area in the evening hours. For the majority of the area precip should start as snow.
The exception may be over southeastern NH from the MHT-ASH corridor eastward. Temps may be a little too warm for snow in that area. Otherwise there will be a several hour period for snow accumulation...generally another 1 to 3 inches.

Around or after midnight things become interesting with both sustained WAA and mid level drying. Temps in the mid level may spike above freezing and precip may change to sleet or freezing rain. More likely is that mid levels dry out and we transition to drizzle. What is also notable is that as surface low slips south of the forecast area...hi-res guidance suggests a nice cold tuck occurs. So cold air dammed against the mtns surges back south towards MA. I have gone with the coldest solutions thru the day Tue. So the combination of drizzle plus sub- freezing air surging back into most of the forecast area should lead to some icing and slippery conditions. This could extend past sunrise as cold air is typically quite stubborn to dislodge. I have issued winter weather advisories mainly for that threat of freezing precip around the commute Tue...but did include the snow this evening and overnight in the headline.
There should be a break in precip Tue afternoon before the next and much stronger wave works its way north along the baroclinic zone. So for the time being I am treating them as two distinct systems.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
Long Term Update:

No significant changes to the long range portion of the forecast late this evening. 00Z operational guidance and latest available ensemble solutions suggest we will remain in between and exiting system Tuesday evening as a stable wave remains over the Gulf of Maine, keeping low level cold air in place across northern New England. Meanwhile, a large scale, vigorous system will approach from the south later Tuesday night, spreading precipitation well to the north in a strong warm air advection pattern. This will allow for freezing rain to develop across portions of the forecast area, mainly over the interior with atmospheric profiles currently indicating mainly rain right along the coastline.

On Wednesday, low pressure will race poleward from the Mid Atlantic region with plenty of moisture involved, partly aided by a low level jet off the Atlantic. PWats now forecast to reach 1.5 inches over southernmost areas during the night, with high PWats continuing northward to the mountains reading over one inch which is very high for the elevated terrain as we approach mid December. Very windy conditions can be expected along the coastline, with the current track and suggesting mostly rain over the region. Model solutions suggest this rain could potentially be very heavy with the added effects of snowmelt across the region. Flooding is possible and will need to be monitored closely for this late season heavy rain event.

Moving forward, will continue to monitor model to model solutions for any shift of track, either to the east or west of the main surface low.

Previous overview...

A cold air dam set up brings cool conditions with periods of light freezing rain at times through the day on Tuesday across the interior. A deepening low pressure center moves up the Eastern Seaboard on Wednesday and Wednesday night, bringing the potential for strong winds and heavy rainfall. Cooler conditions return for the end of the week and next weekend as high pressure builds into the Northeast.

Details...

The cold air dam likely begins to erode Tuesday night as low pressure deepens across the Mid Atlantic and a southeasterly flow begins to increase. Temps rise above freezing along the coast overnight, with the push of warmer temps inland waiting until the daytime on Wednesday. Temps warm considerably along the coastline on Wednesday, with highs in the upper 50s to near 60 degrees. There is likely to be a fairly sharp line with cooler temps on the other side of the coastal front across the interior, but exactly where this sets up remains somewhat uncertain.

Rain overspreads the area by early Wednesday and continues through the day and into Wednesday night. Pockets of freezing rain are still likely across the northern valleys Wednesday morning, but this cooler air will also be eroded as temps warm above freezing. Rainfall amounts look to be pretty heavy, with a widespread 2-3" across much of the area on the table, with locally higher amounts. The question that remains is how far inland the warmer air and dew points reach, and for how long. A warmer period for longer brings a greater risk for higher snowmelt and flooding into the mountains and foothills, while a shorter window limits the snowmelt and flooding potential. Right now it's looking more likely that the melt window looks too short to bring significant melting to the mountains, though not out of the question, while the foothills are at a greater risk of seeing this. Snow across the coastal plain is fully expected to melt out completely, with heavy rainfall on frozen ground bringing the risk for flash flooding by Wednesday afternoon and Wednesday night. The WPC continues to keep up the forecast area in a slight risk for excessive rainfall with these concerns.
We'll continue to iron out the extent of the flood concerns over the next few days, but slight variations in storm track and duration of dew points above freezing will be major factors.

Strong winds are another concern with this system along the coast, and particularly along the MidCoast. Should the storm trend slightly further west, Central Maine would also be at risk of getting into potentially damaging winds. Conversely, should the storm track just slightly further east, the bulk of the stronger winds would stay east of the forecast area. We'll continue to watch trends in the track over the next few days, but the latest runs from this afternoon showed not much change from the Euro ensembles, while the GEFS and Canadian Ensemble trended farther west.

The storm exits overnight Wednesday night, with cooler air returning on a gusty westerly flow. Upslope snow showers would be expected across the north, with highs returning to the 20s and 30s by Friday and through the weekend as high pressure builds into New England.

AVIATION /08Z MONDAY THROUGH FRIDAY/
Short Term...VFR conditions are expected thru around midday.
Then -SN will overspread the area from west to east and widespread IFR or lower conditions are anticipated. Pattern is conducive to keeping low CIGs right thru Tue as WAA continues.
Overnight -SN will likely change to -FZRA or FZDZ and will linger into Tue until temps can creep up above freezing.

Long Term...Coastal terminals improve first Tuesday night, with interior terminals seeing improvement on Wednesday. Heavy rain is likely at all terminals on Wednesday and Wednesday night, with strong southerly winds over 30kt likely along the coast Wednesday and Wednesday night. Drier conditions return Thursday, with MVFR ceilings possible at HIE in upslope flow. High pressure brings mainly VFR conditions by the end of the week.

MARINE
Short Term...Winds will continue to shift to easterly today and increase this evening. SCA conditions are expected into Tue outside of the bays.

Long Term...Southeasterly flow increases Tuesday night and Wednesday as a developing storm center moves up the East Coast.
Gale to storm force conditions are possible Wednesday afternoon and Wednesday night. Westerly gales are possible behind the storm into Thursday, with high pressure building across the waters by late in the week.

GYX WATCHES/WARNINGS/ADVISORIES
ME...Winter Weather Advisory from 7 PM this evening to 4 PM EST Tuesday for MEZ007>009-012>014-018>022-033.
Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Tuesday for MEZ023>028.
NH...Winter Weather Advisory from 7 PM this evening to 4 PM EST Tuesday for NHZ004-006-009.
Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Tuesday for NHZ001>003-005-007-008-010-011-015.
MARINE...Small Craft Advisory from 7 PM this evening to noon EST Tuesday for ANZ150-152-154.