textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the forecast early this morning other than to adjust temperatures for this morning slightly and to add fog in some areas.

KEY MESSAGES

1. A front will drift through the region late today through Monday. Rain showers and thunderstorms are likely, but heavier rainfall amounts will be more localized.

2. Humid conditions persist through the remainder of the week with chances for scattered afternoon thunderstorms.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A warm front continues to push towards the forecast area this morning. To the north some marine fog has lingered thru the day and is now pushing towards the Maine coastline. I anticipate it will creep into the lower Kennebec Valley by early morning. After sunrise some scattering out of the stratus is expected, but it should more or less hang out offshore all day.

Today I also cannot rule out some showers or thunderstorms, but the bulk of precip looks like it will hold off even thru the overnight. So fog moves in again towards sunset and will be more widespread tonight.

Then showers and thunderstorms approach the region and try to move thru the area early Mon. Model guidance is all over the place with the heaviest rainfall, but the highest probabilities for something greater than a half inch of QPF is over the southern half of NH. In addition the ECWMF EFI has continued to get more robust with rainfall thru the end of Mon. This includes most of NH with 80 percent or more of the ensemble members with a seasonably heavy rainfall. I believe that the best chances for some appreciable rainfall will be over far southern NH as well as the North Country, both of which may see some convection before the frontal precip on Mon. The least likely spot for significant rainfall at this time looks like it will be west central Maine. Overall the NBM is generally below 1 inch QPF, with most areas closer to a half inch or less. That seams reasonable than some of the more bullish recent rainfall events.

We will also have to keep an eye out for some stronger storms Mon. With the slowing down of the system overall, the frontal passage is more favorably aligned with peak heating. As a result some long range CAM guidance is now initiation quite a bit of thunderstorm activity along the boundary. Machine learning guidance shows the possibility of severe weather, and SPC has added a portion of the forecast area to a marginal risk for severe thunderstorms. Given the low confidence in heating with plenty of fog and low cloud cover possible, I do not see any reason to include enhanced wording at this time. However NBM thunder probabilities in the scattered range seem on target.

KEY MESSAGE 2 DESCRIPTION...

Some showers may linger Monday night as the upper trough and cold front clear the area. Abundant clouds are going to bring about another night with temperatures only managing to drop into the low to mid 60s. By Tuesday we start to feel the influence of the Bermuda high once again as we end up dry with temperatures in the low to mid 80s. Ridging aloft continues into Wednesday, but the ridge axis moves east of the area kicking off an extended period of southwest flow. This will bring about humid conditions as it continues through at least Saturday. Heat builds somewhat as well, but with the ridge mainly off to the east it won't be quite as dramatic as this time last month. We likely see temperatures approach the 90F degree mark by the end of the week with the elevated humidity making it feel a bit warmer, but nothing suggests major heat.

As far as precipitation chances, it looks like we are going to be relying on diurnal instability and the potential for frontal boundaries to be stalled in the vicinity and/or shortwaves moving through the broader trough to our west. Either way, widespread rainfall is not looking likely and many locations may continue their dry streaks.

AVIATION /10Z SUNDAY THROUGH THURSDAY/

Through tonight: Cannot rule out an isolated warm advection shower thru morning, but overall expecting a dry night. VFR conditions fairly widespread tonight. Patchy valley fog will be possible once again, especially at LEB and HIE. However high cloud cover may delay the onset. Along the Midcoast some marine fog/stratus will continue to slowly creep inland, having already reached RKD. Eventually I bring some low CIGs into AUG as well. Some lingering low cloud is possible around Penobscot Bay in the morning but a return to VFR is expected for all terminals. More widespread IFR or lower conditions are expected tonight as warm/moist advection continues.

Outlook...

Monday: Some improvement to MVFR or VFR possible during the day. Showers and thunderstorms will bring local MVFR or lower conditions in both the morning and afternoon. Monday night-Thursday: Generally VFR conditions during the day with potential for IFR fog at some terminals during the night as we enter a period of increasing humidity through next week.

MARINE

Winds and seas expected to remain below SCA thresholds today. However, an increase in winds and seas are likely Monday afternoon and night resulting in possibly SCA conditions. Areas of fog early this morning will linger thru today and then expand again tonight and be locally dense at times.

GYX WATCHES/WARNINGS/ADVISORIES

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