textproduct: Gray - Portland

WHAT HAS CHANGED

Minor update to the Aviation section for the 12Z TAFs.

KEY MESSAGES

1. After several dry days, we return to wet weather through Thursday. Dreary onshore winds today will give way to steady, soaking rains by Thursday.

2. A cool pattern settles in for the end of the week through the weekend with chances for light showers.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Wet weather is set to return this morning. It will begin with a gradually moistening as winds turn northeast. Clouds will lower thru sunrise and by then some drizzle is possible for the immediate coast. CAM guidance is also insistent that showers will develop in the onshore flow. Forecast soundings are largely dry in the snow growth zone, so I tend think any showers will be widely scattered. That being said, some elevated CAPE is present, so any showers that do form may be briefly moderate to heavy. Showers will become more likely thru the day as southerly flow increases and moisture depth increases with it. As dewpoints climb, areas of fog will also be possible tonight into Thu. The main front and steady rain will move into the forecast area early Thu, sweeping east of the area around midday. Much like today there will be more than enough elevated instability for occasional heavy rainfall rates. This will contribute to the overall 1 to 2 inches average QPF over the two days. This will be a beneficial rainfall, helping to ease drought conditions, alleviate fire weather concerns, and push green up farther along.

KEY MESSAGE 2 DESCRIPTION...

As the Thursday system departs New England, a trough deepens across Quebec and the Northeast. The trough then lingers across the region through the weekend, and likely remains in the place through at least early next week.

This brings an extended period of seasonably cool conditions with northwesterly to westerly flow. Highs are mostly expected to top out in the 50s each day downwind of the mountains, with 40s more likely across the higher terrain and northern areas. Along the coast, the westerly flow will actually yield highs near average most days before any late day sea breeze.

With the trough in place and cold air aloft, any daytime heating will lead to an increase in cloud cover and the chance for scattered afternoon showers. The best chance for these will be across the higher terrain. A more organized round of rain looks most likely to track offshore on Sunday. The next chance for more widespread showers would likely be on Tuesday as a cold front approaches from the west.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

IFR CIGs have arrived at PWM ans PSM with LIFR CIGs at RKD. These should hold steady through today and will drop lower tonight. Farther inland is more likely to remain MVFR, and may even scatter out to VFR again during the day. The exception will be AUG where CIGs will lower to IFR. Across the Connecticut River Valley conditions are most likely to stay VFR thru the day. This morning into the afternoon occasional showers or drizzle are possible at AUG, RKD, and PWM in the onshore flow. As moisture increases tonight more widespread showers, fog, and low CIGs will bring widespread IFR to LIFR conditions.

Outlook:

Thursday: IFR or lower conditions possible. Widespread rain/showers, occasionally heavy with reduced VIS. Some fog is possible along and near the coast. Some LLWS possible for PWM/AUG/RKD first half of the day.

Thursday Night: MVFR likely improves to VFR at most terminals overnight.

Friday-Monday: Mainly VFR, with some periods MVFR and showers possible, especially during the afternoon.

MARINE

Persistent onshore winds are forecast to build seas above 5 feet on the coastal waters this morning. Thru this evening northeast winds will be breezy with some marginal SCA wind gusts at times possible. Gradually winds turn more southerly by Thu and SCA gusts will become more frequent. Drizzle and fog will also develop beginning this morning, but continuing thru Thu. Rain/showers will also be heavy at times and reduce visibility thru Thu.

Seas likely settle below 5ft Friday night. Broad high pressure builds across the waters on Friday and Saturday. A deepening low pressure system likely tracks outside the Gulf of Maine on Sunday. Southerly flow then freshens early next week with SCA conditions possible ahead of an approaching cold front.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ150-152- 154. Small Craft Advisory from 2 PM this afternoon to 8 AM EDT Thursday for ANZ153.