textproduct: Gray - Portland

WHAT HAS CHANGED

Rain will continue to diminish through the rest of the evening across much of the forecast area but a few showers will linger, especially near coastal areas. Another round of showers, and some potential thunderstorms, will develop on Sunday. No major changes were needed for this update. Just blended in the latest observations to the going forecast and freshened up the aviation discussion.

KEY MESSAGES

1. Steady rain will continue through this evening. Conditions stay showery overnight.

2. Warmer temperatures Sunday may allow for the development of showers and storms across the interior.

3. Temperatures run a couple degrees below normal this week, featuring a period of mostly dry weather followed by chance of areawide rain mid to late week. Overnight frost will be possible across interior locations Tuesday night.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Current observations and radar imagery currently show a broad swath of light rain over New England. This rain will slowly move northeastward through the day. As the day progresses, some daytime heating may allow for some very weak embedded convection. The embedded convection may include a rumble or two of thunder this evening. This slug of rain should be out of the area by midnight, though some isolated showers are still possible after midnight.

KEY MESSAGE 2 DESCRIPTION... Sunday morning, a decaying cold front from the Great Lakes will move eastward. Some breaks in the clouds during the day Sunday will likely allow for the development of some low-top convection in the afternoon. These storms will not be impressive, as CAPE values are only between 200 and 500J. Lapse rates, while unstable are not steep enough to provide enough buoyancy for more robust storms. Storms look to initiate first across northern New Hampshire in the early afternoon. Most of the storms are over by mid-afternoon but a few isolated storms may continue through the early evening hours. The cold front finally exits the area Sunday evening.

KEY MESSAGE 3 DESCRIPTION...

Cooler temperatures settle across the region behind a cold front early this week. These arrive on breezy northwest winds Monday as the front crosses the Gulf of Maine. There will be some residual moisture in the 700-800mb layer, and this will likely support at least some cu development through the afternoon. Towards the northeastern half of the CWA and the mountains, it could also mean a passing sprinkle.

Daytime highs will run a couple degrees below normal for early May through much of the week. Forecast highs hover in the upper 50s to the lower 60s, where climate norms for this period are usually in the low to mid 60s along the coast, or mid to upper 60s for interior locations. This is mainly due to influence of a passing trough to the north. While there is some mid-week ridging, it will likely occur overnight and see increased daytime cloud cover and our next chance for widespread rain.

High pres moving overhead Tuesday night will shift NW winds S into Wednesday, but do expect a lull during the nighttime. Should moisture advection be weighted more during the day Wed, Tuesday night could get chilly enough for frost development across interior zones to the foothills. Calm winds would allow for a good portion of the area to decouple, but also need to keep an eye on how quickly cirrus arrives from the SW.

Model guidance seems to agree that low pressure will swing through the Great Lakes Wednesday, arriving to New England overnight into Thursday. There are differences in where the low trends after it passes the Great Lakes. This will impact precipitation residence time into late week. The differences via cluster analysis are separated by the strength of pre and post ridging and how far south it forces the low: flatter through northern New England or much further south into the Mid- Atlantic. The flatter solution, popular in the GEFS, is predictably quicker. It lifts greater precip rates through the CWA by Friday morning. Deeper cutting solutions, amid the GEPS and ENS, try to cut the low off. This spirals moisture towards the New England coast through at least the first half of next weekend.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Through Sunday night...Restrictions will remain IFR/LIFR due to rain and low stratus tonight. Restrictions will be slow to improve with more showers on Sunday. A few thunderstorms will also be possible Sunday afternoon but confidence is too low at the moment to include mention at any specific TAF site. For now, will utilize PROB30 groups for showery activity in the afternoon. Ceiling wise, Sunday will likely start with IFR but improve to MVFR with the low stratus mixing out as convection initializes in the afternoon. Most sites return to VFR Sunday night, though some low stratus may keep CIGs low near KRKD.

Outlook:

Monday and Monday night: VFR with daytime NW winds gusting 10 to 15 kts. Can't rule out a VCSH mid afternoon. Winds become VRB overnight.

Tuesday and Tuesday night: VFR. No sig wx under high pressure.

Wednesday and Thursday: Cigs lower through the day as SHRA approach from the west. MVFR to IFR cigs Wed evening through Thursday, though there is low confidence in onset and duration.

MARINE

SCA Conditions are expected this evening with southerly winds and 4-6ft seas. These conditions are likely to continue through Sunday night.

4 to 5 ft waves continue through the day behind a cold front Monday on the coastal and outer waters off of Maine. The offshore wind direction should knock these down by the evening. High pressure pushes across the waters Tuesday night bringing a lull and shifting winds southerly. Low pressure then advances east from the Great Lakes Wednesday into late week. This low could reside off the Mid-Atlantic coast, prolonging onshore flow and building seas.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 2 PM EDT Sunday for ANZ150-152-154.