textproduct: Gray - Portland

WHAT HAS CHANGED

A later shower onset is expected for southern New Hampshire, with precipitation arriving after midnight tonight.

KEY MESSAGES

1. Rain slowly approaches southern New Hampshire tonight, continuing into far southern Maine through Tuesday afternoon. Isolated instances of heavy rain rates in far southern New Hampshire could result in ponding or nuisance flooding of urban or poor drainage areas.

2. Temperatures warm during the latter part of the work week with elevated humidity returning Friday. Chances for showers and thunderstorms will increase on Thursday into Saturday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Fair conditions continue through this evening. Onshore flow will advect moisture into the ME coast and interior as the evening goes on. This will likely result in low stratus and fog developing overnight, with visibility improving come Wednesday morning.

To the south, a heavy rainfall event is underway across portions of southern New England. While the most widespread heavy rain is expected to remain south of the forecast area, environment conditions will still be favorable for isolated instances of heavy rainfall in far southern NH. This is supported by deep warm cloud depths, anomalous PWAT values, and forcing from the low passing south of New England.

The juxtaposition of these elements should move northward into southern NH through the day Tuesday, with the more robust showers within the precip shield containing heavier rainfall rates. Of concern would be the combination of these heavy rates with backbuilding over urban environments where nuisance flooding of poor drainage areas may result.

Lift will slowly consolidate to the east, with the back side of the precip shield exiting the ME/NH coast Tuesday evening. With thick cloud cover and rain Tuesday, cooler temperatures are expected. This will be especially apparent in southern NH where daytime highs may only make it to the mid to upper 60s. Where no precip is expected and clouds will be thinner, highs towards the lower 80s can be expected towards central Maine.

KEY MESSAGE 2 DESCRIPTION...

Skies clear behind the departing system as a ridge builds in Wednesday and full sun should allow temperatures to rebound into the low to mid-80s for many locations. The ridging slowly breaks down Thursday, but not before 850 mb temperatures climb into the +15-17C range. This should be good for temperatures to reach the into the upper 80s and potentially even the low 90s south of the mountains, whereas the north may only reach the low to mid- 80s before clouds begin creeping in. Chances for showers increase, mainly in the north Thursday night as height falls continue and the 500 mb pattern transitions to a broad trough.

Guidance has trended faster with the frontal passage since this time yesterday, now slowly sagging it through on Friday. The Euro was notably slower yesterday, but it now speeding up to join the rest of the models which increases confidence in this solution. However, Friday does continue to look like the more humid day with dewpoints climbing into the upper 60s and low 70s on southwest flow. I'm not ready to fully count out the possibility of Heat Advisories being needed in southern zones as these locations may still push 90 degrees with the southwesterly flow giving that extra bump to warming. Cooler dewpoints and drier air behind the front are going to help making things feel more pleasant over the weekend and into early next week. Broad troughing over the region is going to keep some chances for afternoon showers and thunderstorms in the forecast, but with not much lift advertised in the models most locations stand to spend much of the time dry.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Through 18z Tuesday...VFR through this evening with a few SHRA possible towards HIE. Clouds thicken and lower this evening as RA approaches southern NH terminals overnight into Tuesday morning. This will likely result in MVFR cigs, with some reduction in visibility possible in heavier rainfall into the afternoon. Meanwhile, onshore flow along the ME coast this afternoon will bring in moisture that could result in a low stratus deck and fog tonight into Tues morning. IFR conditions for AUG/RKD/PWM will be possible after midnight local to shortly after sunrise.

Outlook...

Tuesday Night: Can't rule out some IFR cigs across southern NH Tuesday afternoon and evening, but a general improvement trend to VFR is expected through early Wed morning.

Wednesday-Saturday: VFR conditions expected for the latter half of the work week, with TEMPO MVFR conditions possible in afternoon showers and thunderstorms.

MARINE

Low pressure passes south of New England through Tuesday, with onshore flow building winds and waves towards the NH coast. This may lead to SCA conditions, slackening after midnight Tuesday night.

Generally sub-SCA conditions are expected from midweek into early next week as high pressure remains dominant over the Atlantic.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 8 AM Tuesday to 2 AM EDT Wednesday for ANZ154.