textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the going forecast at this time. With NW flow in the low levels today, convergence will not be enough to support thunderstorms other than one or two isolated ones.

KEY MESSAGES

1. Temperatures becoming more seasonable with the threat for showers and thunderstorms moving south of the forecast area.

2. Mostly dry to start next week with increasing temperatures and humidity before the chance for showers and storms returning mid week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

The surface cold front will struggle to make much headway overnight, and so I do not expect temps to be all that cool by sunrise. However the front looks like it will have pushed into southern parts of the forecast area by morning. Across the southern half of the forecast area model guidance is only getting 850 mb temps into the +14 to +15C range. At those temps it will hard to get surface readings too much above the mid 80s, which is a bit cooler than the NBM which has some near 90 highs and brings that all the way up the coast. So I will include some MOS guidance to knock them back. Then going into the weekend should generally be in the low to mid 80s typical of a warm not hot summer pattern.

The chance for showers and storms has diminished quite a bit for today as well. With the front pushing south, all the forcing for storms will be across southern New England or into the Mid Atlantic. Isolated convection may still be possible, but forecast soundings have a lot of dry air aloft and dry air at the surface enough to make convective initiation look tough. Machine learning severe weather guidance has also shifted the threat south of the forecast area. NBM slight chance PoP looks fine to cover any limited potential, but I think it will mainly be dry. That will also be the trend into the weekend with both Sat and Sun looking dry.

KEY MESSAGE 2 DESCRIPTION...

Looking ahead to next week, high pressure will stick around at least until Tuesday morning. As such, heat looks to be building starting Monday with temperatures in the upper 80s with humidity on the lower side. Tuesday onward, however, the heat and humidity look to build, with some models indicating temperatures in the middle of next week approaching the low to mid 90s away from the immediate coastline, with humidity levels making temperatures feel like the upper 90s as dewpoints approach the upper 60s to low 70s. There will be some opportunities for convection too, although details are largely unknown at this time. Interestingly, some global and ensemble guidance suggests northwest flow aloft as an anomalous ridge develops over the Midwest.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Mainly VFR tonight with rain crossing the area with local MVFR or lower embedded heavier showers. I cannot rule out some patchy valley fog in areas that area able to clear out, but cloud cover should hang tough across the northern half of the forecast area. Marine fog and stratus is forecast to develop thru morning, but at this time I only expect that to move into RKD before daytime heating helps mix it today. There may also be isolated showers or storms during the afternoon, but confidence is quite low and not enough to include in the TAFs.

Outlook... Friday night: VFR conditions expected. Patchy valley fog possible, especially HIE and LEB.

Saturday: VFR conditions expected.

Saturday Night: VFR conditions expected. Patchy valley fog may be more widespread.

Sunday - Monday: VFR conditions expected.

Tuesday: Scattered showers and thunderstorms possible in the afternoon that may bring local MVFR or IFR restrictions.

MARINE

Winds and seas expected to remain below SCA thresholds. Areas of fog are forecast to develop tonight on the coastal waters, but generally clear out south and east of the waters by afternoon.

This weekend high pressure will keep winds and seas below SCA thresholds. By early next week increasing south to southwesterly winds may approach SCA thresholds as a cold front nears the area. That front is forecast to cross the waters Tue or Wed, with showers and thunderstorms possible.

GYX WATCHES/WARNINGS/ADVISORIES

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