textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the previous forecast with this update.

KEY MESSAGES

1. Seasonable and largely dry weather continues into early next week. While winds will be on the lighter side, relative humidity may drop below 30 percent at times.

2. Unsettled weather makes a return after a dry start to the week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Thru the weekend high pressure continues to build south towards New England. This will help to keep precip largely at bay beyond a stray cold pool shower over parts of western Maine. This will be most likely this afternoon as a secondary spoke of cold temps aloft pinwheels down across Maine. I am not super confident that showers will even wet the ground, so I opted for sprinkles instead. Otherwise winds will be breezy during the afternoon but become substantially weaker this weekend into Mon. The biggest forecast concern will be the model tendency to under-represent mixing and resulting temps/dewpoints. My preference was to mix down dewpoints from aloft and blend those with NBM/NBM 10th percentile thru Sun. That brings sub-30 percent RH values to southern NH today, much of NH and adjacent western Maine Sat, and western NH Sun. However the day with the best chance for elevated fire weather concerns will be this afternoon because of the aforementioned breezy conditions. The relatively clear and calm conditions will help overnight temps fall quickly and allow surface fuels to recover well in most cases.

KEY MESSAGE 2 DESCRIPTION...

An interesting upper-air configuration is setting up for next week. Upstream across the CONUS, an active dual-jet stream structure will be in place. Riding this brisk upper-level flow will be a rather strong surface cyclone coming out of the Plains. However with some high latitude blocking over the Canadian Maritimes, the surface low track is likely to slow and deflect to the north, with some uncertainty how close it gets to our forecast area/what the impacts are. Another uncertainty is the lingering coastal low off the New England coast. Guidance varies significantly on the placement of this feature by next week, and if there is any interaction between the coastal low and land-based low coming out of the Plains.

At minimum, would expect the second half of next week to be on the cloudy and damp side, but notable uncertainty remains on precipitation chances. Could see a range of scenarios from 1.) the forecast area is split between the two features, with just scattered/light precipitation chances for a brief period to 2.) a widespread soaking rain for multiple days. Worth noting that for the wetter solutions, some deterministic members are suggesting coastal redevelopment which could enhance precipitation given the rather stagnant flow pattern that looks to be in place. But in any case, confidence in timing/impacts is just not high at this range yet given a rather blocky pattern. Stay tuned.

AVIATION /03Z FRIDAY THROUGH TUESDAY/

Through 06z Saturday...VFR conditions expected to prevail thru the overnight, with MVFR cigs nearing HIE late. Some clouds develop again across west central Maine, and stray showers are possible, but chances are too low to include any CIG or VIS restriction in the TAFs at AUG and RKD. Late afternoon should see winds shift from offshore to onshore near the coast, mainly PWM and PSM.

Outlook:

Saturday - Monday: VFR conditions expected.

Tuesday-Thursday: At least beginning VFR, but chances for MVFR or lower conditions will increase towards the latter half of the week as the next storm approaches and winds become largely onshore.

MARINE

Winds and seas are expected to remain below SCA thresholds. With a fairly weak pressure gradient, afternoon sea breezes should dominate the wind direction. Northeast winds will become more common starting around midweek and gradually increase thru the end of the work week. While SCA conditions do not appear likely, areas of fog and low clouds may develop over the latter half of the week with the approach of a warm front.

GYX WATCHES/WARNINGS/ADVISORIES

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