textproduct: Gray - Portland

WHAT HAS CHANGED

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

KEY MESSAGES

1. Unsettled weather is expected through the weekend, but no widespread significant rainfall amounts anticipated.

2. Isolated rain chances Monday-Tuesday with a lingering upper- level low. Tranquil conditions by midweek, and loose signals for increasing humidity late week ahead of another system.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Low pressure south of southern New England will continue to slowly lift northeast and weaken today. As it does so showers will become more likely, especially over western Maine. Save for the Seacoast it is possible most of NH remains dry today. NBM handling the placement of best rain chance fairly I think, so no planned changes there. Despite the relatively high PoP, QPF will be on the low side. Most locations can expect less than a tenth of an inch, but an especially lucky section of town could see up to a quarter.

Overnight we will need to watch and see how marine fog/stratus develops. The long range HRRR brings low visibility into coastal areas, especially for western Maine. The set up would be favorable as a warm front begins to lift into the region by early Sun.

Along that warm front showers and maybe a few thunderstorms are forecast to form and lift north into the local area. This will bring a scattered potential for beneficial rainfall amounts. I do not anticipate this being a widespread soaker, but locations that do see precip could see a decent amount given that this will be more convective in nature. At this time I think significant rainfall amounts will be too isolated to forecast, so I will stick with the NBM QPF amounts, which more closely match ensemble means around a quarter of an inch.

Showery weather may continue into the afternoon and overnight, as upper low begins to move overhead and keep conditions unstable.

KEY MESSAGE 2 DESCRIPTION...

Upper-level low moving out of the Great Lakes will continue to pivot into southern Quebec early week while fully occluding/cutting off from the mean flow. This brings cyclonic westerly flow to New England. Most likely outcome will be falling dew points with diurnal clouds/brief showers Mon-Tue, especially focused in the higher terrain and closer to the upper-level low in the north.

Should see a nice dry punch on Monday especially across NH with very dry mid-levels and dew points mixing down to as low as the 40s! Uncertain how much of this pushes into Maine. Depending on how it all times out there may be an opportunity for some t-storms to develop in a juicy warm sector featuring rather steep lapse rates, MUCAPE values that may be pushing 1000 J/Kg, and close to 50 kts of deep-layer shear. It is possible the mid- level dry punch could be a resistant against robust convection, but will keep a mention of iso to sct showers/thunder in the forecast at this time, with the primary focus from the Kennebec Valley down into the Midcoast.

On Wednesday the low loses its grip with brief height rises bringing tranquil conditions. By late week ensembles show another wave heading our way with possible surface cyclogenesis in the Michigan vicinity. With a developing trough to our west, likely will see southerly flow developing and returning humidity, but details are largely unknown at the 6+ day range.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Through tonight...Mainly VFR conditions prevail today, but by mid to late afternoon CIGs will be lowering and MVFR conditions are anticipated. It is possible that some IFR CIGs work into coastal areas by evening along with some rain showers. Low CIGs and more widespread fog will likely bring IFR to LIFR conditions across much of the area tonight.

Outlook:

Sunday: Fog scatters out as rain showers lift across the area Sun. Some improvement to MVFR and VFR is possible by evening.

Sunday night: Continued improvement in conditions, except local LIFR in valley fog.

Monday: Local MVFR or lower possible in showers.

Monday Night: VFR conditions expected.

Tuesday: Local MVFR or lower possible in showers.

Tuesday Night and Wednesday: VFR conditions expected.

MARINE

Winds and seas are expected to remain below SCA thresholds thru the extended period, despite weak low pressure moving thru the Gulf of Maine today. Will have to watch the overnight window, when areas of fog and low stratus may develop ahead of an approaching warm front. Those foggy conditions are expected to lift out on Sun.

GYX WATCHES/WARNINGS/ADVISORIES

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