textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast update.

KEY MESSAGES

1. Cool Canadian high pressure continues mostly dry weather through mid week.

2. High pressure remains in control of the weather pattern across northern New England through midweek, while a coastal storm develops off the Carolinas.

3. The coastal storm tracks toward New England late in the week and this weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Broad high pressure centered south of Hudson Bay will slide east through mid week. Latest satellite data shows ample cloud cover across the upper Ohio Valley associated with a subtle short wave tracking east. The 12Z model suite is in good agreement that this cloud cover will overspread the area tonight leading to mostly cloudy skies. This will limit radiational cooling while some patchy frost across the north and valley fog cannot be ruled out tonight. Lows tonight will range from the mid 30s north to mid 40s south. Skies will transition to mostly clear Tuesday with highs mainly in the 60s. While skies look to remain mostly clear Tuesday night northeast flow will be on the increase and could hamper radiational cooling. This has the potential to limit frost across remaining active growing zones south of the mountains. Wednesday will be similar to Tuesday with mostly sunny skies and highs in the 60s. Winds and skies may be more favorable for radiational cooling Wednesday night that could lead to frost in active growing zones south of the mountains.

KEY MESSAGE 2 DESCRIPTION...

An anomalously strong high pressure center builds across Eastern Canada and New England on Wednesday and Thursday. This brings with it mainly sunny skies and seasonably cool conditions.

At the same time, a coastal storm begins to organize off the Carolinas by Wednesday, and continue to organize on Thursday. The high pressure center will keep the storm well to our south through at least Thursday. The one impact we'll start to notice from this system will be building surf starting by Wednesday. The interaction between the high pressure center and the developing storm produces an expansive easterly fetch across the North Atlantic, with surf building on Wednesday and Thursday. A northeasterly flow will also become more distinguishable along the coast by Thursday.

KEY MESSAGE 3 DESCRIPTION...

By Friday, the ridge of high pressure begins to break down, allowing the storm to track further northward toward New England. Clouds increase through the day, and the northeasterly flow steadily strengthens along the coast as well. Seas continue to build, with surf approaching 10 feet by late Friday.

The exact track of the system remains in question, with models and ensembles waffling between a track looping near Cape Cod, closer to New Jersey, or mostly remaining out to sea. The track has the biggest implications for rainfall amounts, with these different solutions ranging from virtually no rainfall to several inches. It's worth noting that the most skillful model suites, the Euro and AIFS, show the stronger storm with a closer track near Cape Cod, which would be the highest impact solution for northern New England. However, these Northwest Atlantic Lows also tend to be the kind of systems that these models can over-amplify with the system.

So at this point we have time to continue to monitor the model trends, with any land based impacts unlikely to be felt before late Friday. Surf begins building on Wednesday, and is likely large for Friday through Sunday regardless of the storm track.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Through 18z Tuesday: Mainly VFR is expected through tonight. Increasing clouds tonight will have a shot at limiting valley fog so have gone with 1SM at LEB and north flow could lead to brief LIFR CIGs at HIE. VFR expect Tuesday.

Outlook:

Tuesday night-Thusday Night: Mainly VFR, outside of nighttime valley fog.

Friday-Friday Night: Increasing chance of showers and restriction along coastal sites.

Saturday - Saturday Night: Greatest chance for rain, gusty northeasterly winds, and restrictions.

MARINE

Northeast flow will prevail over the waters through mid week as high pressure remains northwest of the waters. NE winds could occasionally gust to 25 kts along the outer waters tonight and again Tuesday night with seas generally below 5 feet.

High pressure builds across the waters this week, remaining centered across Quebec. A storm center begins to develop off the Carolinas on Wednesday and Thursday, and then tracks toward the Gulf of Maine on Friday and Saturday. SCA conditions are possible by Wednesday, with seas continuing to build into Saturday. Northeasterly gales are possible by Friday, but remain highly dependent on the track of the storm center.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.