textproduct: Gray - Portland

WHAT HAS CHANGED

Little change to the going forecast for today.

KEY MESSAGES

1. Early morning fog today. A few showers and an isolated thunderstorm possible by early this evening. Thursday should be fair as well, but there is some minor forecast uncertainty.

2. The next chance for rain on a widespread basis arrives for the second half of the weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

After areas of early morning low clouds and fog we should see increasing sunshine, especially on the coastal plain and across southern NH. As a result, temperature will warm into the 80s at most locations. A cold front will approach during the afternoon hours, but the deeper forcing for ascent associated with it will weaken considerably by early evening. Therefore, most showers and any thunderstorms associated with it will probably weaken or fall apart on approach from the west. However, heating of the day may support a couple of convective showers or storms across central and northern NH late in the afternoon and early evening. Areas of fog are again likely later tonight, especially in the CT River Valley and Midcoast of Maine.

The cold front continues to sag southward into southern New England on Thursday. At this time most ensemble guidance indicates that it will sag far enough south so that a developing wave along said front remains well to our south also. This would keep a possible round of showers and thunderstorms well to our south later Thursday as well. However, there are some model outliers that bring the wave farther north and thus a more showery scenario late Thursday to our southern zones. However, the forecast favors the drier majority at this time.

KEY MESSAGE 2 DESCRIPTION...

High pressure then builds in Friday and the first part of Saturday, keeping the weather dry for much of the area. The high does move off to the northeast later Saturday as low pressure emerges off the Mid-Atlantic coast, and moisture will start to increase from south to north over northern New England, potentially enough for a few showers along the coast and southern NH during the day Saturday. But again, most will be dry as the better chances hold off until the second half of the weekend. Highs will in the 70s to low 80s and lows mostly in the 50s, except some embedded upper 40s.

This initial low will keep a chance for showers along the coast and southern NH Saturday night, but rain chances further increase areawide Sunday into Sunday night as a 500mb approaches from the west and encompasses much of the US East Coast. There's a strong signal in the ensemble for most of the area to see measurable rain, although there are timing differences. If the 500 mb trough remains an open wave the rain looks more in the Sunday-Sunday night timeframe, but if it closes off, then a slower onset and end will likely be the result, making the higher rain chances more in the Sunday night and Monday window. By Tuesday, we should see a return to drier conditions, except there may be some upslope showers in the mountains.

AVIATION /08Z WEDNESDAY THROUGH SUNDAY/

Fog may be locally dense early this morning, mainly in the CT River Valley and perhaps even the Midcoast of Maine. Elsewhere 2-5 miles in BR is expected through about 12z. VFR conditions during the day today with fog returning to more or less the same locations tonight. VFR Thursday.

Outlook:

Thursday night-Saturday: Mainly VFR, except nighttime/early morning valley fog could produce IFR to LIFR at HIE and LEB.

Saturday night-Sunday: Increasing chances for rain. IFR to MVFR possible.

MARINE

Winds and seas generally stay below SCA thresholds today through Thursday.

Thursday night-Tuesday...SCA conditions are currently not expected through early next week. A weak front crosses the waters Thursday and will be followed by high pressure building in Friday and the start of the weekend. The high shifts to the north and east as a couple of low pressures approach and cross the waters from the west and southwest during the late Saturday through Monday timeframe. High pressure returns by Tuesday of next week.

GYX WATCHES/WARNINGS/ADVISORIES

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