textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes for this forecast package.

KEY MESSAGES

1. Low pressure continues to bring soaking rainfall through this morning. While widespread flooding is not expected, embedded heavy rain could lead to some urban and poor drainage issues along the coast and southern NH.

2. Next chance of thunderstorms arrives Friday with a cold frontal passage. This will be followed by fair and warmer weather.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Troughing will remain overhead through Wednesday as the center of an upper low stubbornly drifts from western Quebec over to New Brunswick/Nova Scotia. Widespread showers will remain in place through the morning across western Maine and New Hampshire as a couple of waves move through the flow.

Not much has changed in our thinking regarding totals and the heaviest precipitation is still expected over southern New Hampshire and coastal Maine. Most areas will likely see precipitation move out by late morning but steady rain may continue in the vicinity of the Midcoast through the afternoon. A secondary low may try to ride up the coast in the afternoon, but models continue the trend of keeping most of this precipitation out to sea. Given the cyclonic flow aloft, can't rule out a few afternoon showers over the mountains. Overall, areas across southern New Hampshire and coastal Maine will see the highest totals where the NBM is suggesting high probabilities for an inch or more with only some medium probabilities for 2 inches or more. Seems like these areas will see a fairly widespread 1 to 1.5 inches with localized 2+ inch totals under some of the heavier showers. While these totals will generally remain below flash flood guidance, recent wetting rains could lead to some some urban and poor drainage issues. Areas under the heaviest precipitation could also see some isolated thunder with some weak instability in the forecast.

As we remain in cyclonic flow aloft, another round of afternoon showers will be possible on Wednesday with most of this activity likely in and around the mountains. A rumble or thunder or two can't be ruled out with a couple hundred J/kg of MUCAPE floating around. This activity should diminish with the loss of daytime heating.

High temperatures will be seasonable today, ranging from the upper 60s and lower 70s north, to the mid/upper 70s south. Highs on Wednesday will be similar to today, but maybe a touch cooler in the mountains and a touch warmer outside of the mountains, ranging from the mid to upper 60s north, to the mid to upper 70s south. A few lower 80s will be possible over southeast New Hampshire or coastal Maine.

KEY MESSAGE 2 DESCRIPTION...

Thu will be seasonably warm as south winds ahead of the cold front bring in some more 80s than we have had recently. Not much worry about the sensible weather except for the potential for some marine fog Thu night. Confidence is low in that outcome however.

Otherwise the big weather story in the extended will be our next and maybe only chance for precip in the days 3 thru 8 period. A cold front will cross the forecast area around Fri. It will all come down to timing. If we can get the frontal passage coming thru near peak heating, thunderstorms are more likely. If we can get thunderstorms there will be enough shear to organize storms and give a potential for severe weather. At this long range CSU machine learning does have low probabilities of severe weather, so it will be something to monitor. If the boundary ends up pushing thru overnight it may just be areas of rain working northeastward along the front. And the current rainfall is a good example of what can happen if that convection ends up too far south. We may get rain but not much of it.

Beyond the frontal system high pressure will gradually sink southward and allow for southwesterly flow aloft to bring increasingly warmer temps into the region. At points early next week temps may be pushing the upper 80s to lower 90s again.

AVIATION /06Z TUESDAY THROUGH SUNDAY/

Through tonight...Expect widespread IFR/LIFR ceilings this morning for all sites. Steady rain with pockets of occasional heavy rain will continue to push east. Rain ends away from the coast and southern New Hampshire with ceilings lifting and scattering late morning. All sites likely improve to VFR in the afternoon. VFR conditions will remain likely through tonight, but some valley fog could lead to some local IFR or lower, potentially impacting LEB or HIE.

Outlook...

Wednesday - Wednesday night: VFR conditions expected.

Thursday: VFR conditions expected.

Thursday night: VFR conditions expected, but low chance for IFR or lower in marine fog/stratus ahead of the front.

Friday: Low chance of IFR or lower in marine fog/stratus. Otherwise VFR conditions until frontal passage. Local MVFR or lower possible in showers/thunderstorms.

Friday night - Sunday night: VFR conditions expected.

MARINE

Waves of low pressure will track across southern New England through the early part of today. Early morning winds will see gusts around 20 kts approaching 25 kts along the outer waters. Seas will also build and will generally be 3-4 feet, approaching 5 feet along the outer waters. Light offshore winds develop this afternoon as low pressure exits.

Winds and seas expected to remain below SCA thresholds through the rest of the week. Will have to watch for areas of fog and stratus developing in the warm/moist advection ahead of the cold front. This may begin as early as Thu night.

GYX WATCHES/WARNINGS/ADVISORIES

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