textproduct: Gray - Portland

WHAT HAS CHANGED

Little has changed with the forecast for the rest of the evening and into the overnight hours. Main theme will be watching for areas of dense fog as higher dewpoint values advect in over the colder snowpack. Otherwise, line of convective showers over upstate NY should continue to weaken this evening but we do expect some later on.

Have also added isold thunder to southern zones for the next few hours with very steep mid level lapse rates in place and a good amount of elevated instability.

KEY MESSAGES

1. Shower activity increases again tonight as a warm front approaches the area. Temperatures will be well above freezing so all rain is expected. A rumble of thunder can not be ruled out.

2. Spring-like warmth to start next week, inducing a significant but controlled snow melt but with only a low chance for river flooding.

3. The next chance for widespread precipitation returns the second half of next week with temperatures returning closer to seasonal normals.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Low pressure moves out of the Great Lakes Region and skirts along the International Border tonight. This will drag a warm front through the area accompanied by an area of rain. Temperatures remain well above freezing overnight with the warm front even helping to spike them up a couple degrees from where we end up this evening, so there is no threat for mixed precipitation with this round. As the warm front pushes in and lifts all this moist air over it, it will produce some instability (models suggest around 100-150 J/kg of MUCAPE), enough that a rumble of thunder can't be ruled out, but also not enough to include it in the forecast with confidence. If it does happen it looks like southern New Hampshire and coastal areas have the best chance of hearing it. QPF is light for this event as well with it being more showery in nature, so this won't lead to any significant river rises.

A trailing cold front begins to sweep through Sunday eventually clearing skies in time for peak heating hours in the afternoon. As a result this looks to be the first of a few days that are going to feel spring-like with highs climbing into the low to mid-50s. Breezy westerly winds can also be expected behind the front, gusting around 20-25 mph. With the warm air in place, and maybe some clouds in the mix as a shortwave passes overhead, Sunday night will be on the mild side as well with temperatures barely dropping below the freezing mark.

KEY MESSAGE 2 DESCRIPTION...

Low-level high pressure becomes centered well to the south and east of New England to start out next week while a low pressure tracks across Quebec that may send a weak frontal boundary into the area from the north by later Tuesday. This brings in a deep layer of west to southwest flow that will continue to usher in a much warmer and spring-like airmass with temperatures likely reaching at least the 50s...and possibly 60s in some areas. However, I'm hesitant to go as warm as the NBM from the Midcoast/Kennebec valley areas with the winds coming off the very chilly Gulf of Maine, and northern areas may not quite as warm on Tuesday depending on the front. So temps may need to be eventually lowered for these areas. No precipitation is expected with the dry airmass.

To continue the messaging from yesterday's discussion: significant reductions in snowpack are likely from the warmth with some movement in river ice. However, the melt is expected to be controlled with only a low risk of any river flooding.

KEY MESSAGE 3 DESCRIPTION...

The pattern turns back to active for the second half of the week and the start of next weekend. The first system of interest is a low pressure that will track across the Great Lakes, likely lifting a warm front through the area on Wednesday, and then ensembles favor the track of the low roughly along the St. Lawrence Valley that will send a sharp cold front through the region sometime on Thursday. Based on the favored track of the low and the warmer airmass, this would be a mostly rain event, but the last couple runs of the operational GFS run are not lifting the warm front as far north and even try to develop a secondary low near the coast, which would bring in cooler temps and potential for wintry weather. However, the majority of the individual GFS ensemble member are more in line with the northern track.

Not only would this bring the next chance for widespread precipitation Weds-Thurs (possibly as early as Tuesday night), but with the warmer airmass and increasing moisture will probably see fog over portions of the area too, which would further eat into the snowpack. The 12Z operational ECMWF from today is hinting at dewpoints around 50F ahead of the front, which could result in a more rapid melt. So we'll have to be mindful of additional river rises a ice movement if we do end up seeing fog and mostly rain.

While not as warm as Mon-Tues, Wednesday should again be above normal with 40-50s for highs with more clouds/precip (unless the cooler GFS solution is onto something), and Thursday should be as well but also depends on what time of day the cold front crosses. There may also be a brief changeover to snow behind the front on Thursday. By Thursday night and Friday, the front is likely to be east of the area with cooler and drier air moving in and highs Friday returning closer to seasonal normals...mid 30s to lower 40s.

Another system quickly follows for late Friday or Saturday but features much more uncertainty.

AVIATION /02Z SUNDAY THROUGH THURSDAY/

Through 18Z Sunday...Widespread LIFR/IFR conditions continue through tonight as moist flow and increased shower activity keep ceilings and visibilities low. Some improvement will be seen toward daybreak Sunday as a cold front approaches and begins mixing things out to MVFR. Toward the tail end of the TAF period some terminals may even be VFR. Low level windshear is expected at all terminals beginning around 21Z and through tonight as a warm front lifts through the area.

Outlook:

Sunday Afternoon-Tuesday: VFR expected.

Tuesday night-Thursday: Increasing chances for widespread precipitation and flight restrictions as low pressure approaches. Mostly rain is favored at the moment, but uncertainty remains.

MARINE

SCA winds and waves continue through Sunday morning. Wind gusts fall below 25 kts Sunday afternoon, but wave heights will be slow to settle and likely remain above 5ft until at least Monday. Winds will be primarily southwesterly through Sunday night.

Monday-Saturday...SCA conditions are likely Monday-Monday night as southwesterly flow strengthens, but winds should ease going into Tuesday and Tuesday night.

Low pressure crosses the Great Lakes Wednesday with a track then favoring near the St. Lawrence River Valley on Thursday that will drag a cold front across the waters sometime on Thursday...although timing is still in question. The southerly flow ahead of and the westerly winds behind the front will likely produce at least SCA conditions through Friday, but gales are possible as well. Another low may quickly follow either late Friday or Saturday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EST Monday for ANZ150-152-154. Small Craft Advisory until 2 AM EST Monday for ANZ151-153.