textproduct: Gray - Portland

WHAT HAS CHANGED

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

KEY MESSAGES

1. Much more comfortable weather for today.

2. Precipitation chances centered on Tuesday. Greatest chance for soaking rains will be across southern New Hampshire.

3. Warming up by late week with hot and humid conditions returning.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A cold front that moved through the region is delivering a much drier air mass. While it will remain seasonably warm (highs in the 80s), dewpoints in the 50s will make for low heat indices. An afternoon seabreeze will cool off the coast.

High pressure should remain in control for tonight with only a very low prob of a shower across southern NH late as a system moves across southern New England.

KEY MESSAGE 2 DESCRIPTION...

Yesterday's sagging cold front will stall across the Mid Atlantic, before progressing slightly northward Monday-Tuesday. As this occurs, a surface low will ride east along the front. Ensemble guidance largely shows a track well south of the region, but some members get close to the south coast of New England. As such, we are expected to stay on the cool and stable side of the system, as opposed to what was the cast last week.

Right now guidance is indicating a roughly 30% chance for rainfall to exceed an inch in the Concord-Manchester-Portsmouth corridor, while probabilities drop significantly across interior NH and much of Maine. Meanwhile for 2", values reach 20% across the MA/NH border. There still remains the potential for a soaking rain, and models are quite bullish across the Mid Atlantic and southern New England. WPC clips southern NH in a day 3 ERO, so it is worth keeping tabs on early next week. Working against a heavier rain threat will be stable air north of the front, meaning precipitation should be more steady and stratiform rather than locally heavy/convective. There also will be Canadian high pressure to our north fighting to suppress precipitation to the south. This should do work to keep us dry through at least Monday. It still remains to be seen how far north rain will reach Tuesday, as north-side rainfall gradients can be notoriously tricky. In any case, at a minimum, northern NH/interior Maine are likely to see only limited to zero precipitation, with the highest totals near the Massachusetts border.

KEY MESSAGE 3 DESCRIPTION...

High pressure is expected to return by mid week, signaling a warming and drying trend. This high then shifts offshore into the classic "Bermuda high" position, which should bring a warm southwest flow to the region by late week. 850 mb temperatures rise from +12C on Tuesday to +17C by Thursday night. Combined with surface heating and warm air advection, it may be very warm again by the end of the week. Highs should solidly be in the 80s Wednesday-Friday, but there is upside for low 90s if it all comes together right given a rather warm airmass. Finally, with a trough swinging southeast out of Canada, may have a thunder threat to close the week. At a glance, dew points surge towards 70 by Friday, but lapse rates/CAPE currently look much tamer with no sign of an EML nearby

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12z Monday...LIFR cigs at LEB likely scatter shortly after 12Z. VFR is expected today with a seabreeze expected on the coastal plain this afternoon switching winds to onshore. Valley fog cannot be ruled out tonight at LEB and HIE.

Outlook:

Monday: Increasing rain chances and clouds south to north in the afternoon. Patchy MVFR cigs across southern NH possible, otherwise VFR.

Monday Night: Continued rain chances across southern NH. MVFR possible.

Tuesday: Rain departs east late, with improving cig in the late afternoon. VFR likely.

Wednesday: VFR likely under high pressure in the region.

Thursday: SHRA arrives from the NW, otherwise VFR.

MARINE

Below SCA conditions are anticipated through midweek. Weak wind fields will promote some onshore breeze today and Monday as broad low pressure moves east from the Ohio Valley and passes towards the Delmarva region Tues. Winds then shift east Tues, with building waves into Wed 4 to 5 ft.

GYX WATCHES/WARNINGS/ADVISORIES

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