textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes needed to the forecast as the near term remains quiet, and trends for the upcoming system remain steady.

KEY MESSAGES

1. Moisture increases tonight with areas of drizzle developing Wednesday, especially in the coastal plain.

2. A coastal low arrives in the area Wednesday night, with soaking rain likely on Thursday.

3. Unsettled and chilly conditions continue into the weekend with daily rain shower chances.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... As funny as it sounds, onshore flow is actually in the process of pushing dry air into the region this afternoon, continuing elevated fire weather concerns into this evening. However, onshore flow will begin to advect moisture into the region tonight with a low cloud deck developing over the coastal plain. This will keep temperatures a few degrees warmer than last night (mid to upper 30s), with similar-to-last-night low to mid-30s for the remainder of the area. A 500 mb shortwave ridge moves overhead on Wednesday which will keep the majority of the column dry, but continued onshore flow is going to saturate the lower levels and lead to areas of drizzle developing. I would expect this to be most prevalent along the coast, but could see some patchy drizzle develop inland as well. This is going to make for a raw day with high temperatures in the coastal plain and most of western Maine topping out in the low 50s. For much of New Hampshire and the Western Maine Mountains where clouds will be slower to thicken, there is a better chance of seeing temperatures make it into the upper 50s and low 60s.

KEY MESSAGE 2 DESCRIPTION... A negatively-tilted trough develops Wednesday night over the Northeast, allowing for the development of low pressure over upstate New York. This low will move to the north-northeast by Thursday morning, and looks to occlude. The occluded low will bring a cold front through northern New England during the day, with a quick initial 0.5-1 inch of rain or so across the area. Over the Gulf of Maine, a coastal low looks to develop over the Midcoast as the mid- level trough continues to tilt further negatively. This should allow for more prolonged rainfall across at least central Maine and the midcoast Thursday evening, with some of the extra rainfall potentially reaching the Western Maine Mountains as well. While this does appear to be an ideal storm track to bring a lot of rainfall to the Midcoast, temperatures will be quite cold with highs in the upper 40s on Thursday. This limits how much moisture can be advected, as shown by PWAT values in the area of 1.0". This is only 1 standard deviation above average and when compared to previously high rainfall events, is actually extremely dry. So rainfall is likely to be pretty inefficient which means that less rain is forecast compared to what guidance has initially.

Across the far north and along the Connecticut River Valley, around 3/4 to 1 inch of rain is forecast, with more rain closer to the coast and further south and east. Across the midcoast, coastal plain and foothills, a little over 2 inches of rain is likely with some local totals nearing 2.5 inches possible in and around Rockland and Camden. Some uncertainty does remain on exactly where this QPF "bullseye" sets up, and there is a chance that the highest QPF ends up a little further to the east, over southern Hancock county. However, more ensemble guidance plus the little bit of hi-res guidance available show a stronger signal for this bullseye to be over the Midcoast at this time.

KEY MESSAGE 3 DESCRIPTION... An upper-level low looks to remain over the northeast this weekend, and will allow for cooler and more showery weather to persist. Low freezing levels may allow for some precipitation to fall as snow in higher elevations. A system may arrive early next week and bring another round of widespread rain to the area in the Tuesday / Wednesday timeframe.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Through 18Z Wednesday...Generally VFR conditions through 03Z Wednesday. MVFR ceilings encroach on coastal terminals around 03Z and may make it inland to MHT and CON by 05Z. Ceilings will continue to lower at coastal terminals to IFR after 09Z with some drizzle developing as well. MHT and CON will see early improvement back to VFR, while coastal terminals likely stay at least IFR through the TAF period. LEB and HIE are anticipated to remain VFR.

Outlook: Wednesday night: MVFR/IFR conditions expected as rain moves into the area.

Thursday: MVFR expected due to rain.

Friday-Sunday: VFR with some MVFR possible due to showers.

MARINE

Persistent onshore flow is going to build wave heights 6-8 feet beginning tonight in the coastal waters and at the mouth of Casco Bay by Wednesday afternoon. Winds are going to remain easterly through at least the day Wednesday, with gusts generally 15-20 knots.

Southeasterly SCA level winds are expected Thursday. 5-8ft seas expected. Winds go below SCA levels Thursday night and shift to westerlies. Seas lower to 4-6ft Friday morning. Sub-SCA westerly winds are likely to prevail through the remainder of the weekend, with 2-4ft seas.

GYX WATCHES/WARNINGS/ADVISORIES

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