textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes needed with this afternoon's forecast package. Guidance remains in good agreement on rainfall totals for the Sunday system.

KEY MESSAGES

1. Low pressure will bring a period of beneficial rain Sunday into Sunday night. Rain may be heavy at times, but no flooding is expected.

2. High pressure brings mostly fair weather Monday through Wednesday with temperatures running below normal. Rain chances increase during the Friday to Sunday timeframe as a possible coastal low develops along the Eastern Seaboard.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... High pressure exits to the east tonight and clouds slowly build in, but we should stay just clear enough for temperatures to drop into the upper 30s and 40s once again.

Clouds are going to be abundant over the area by early Sunday morning, but guidance continues to suggest that dry air stays nosed in just long enough for most of the morning to be dry. Late morning is when rain moves into New Hampshire and spreads eastward across the area into the afternoon. By Sunday evening the bulk of the rain is going to be south of the mountains, and shortly after midnight it is likely to be offshore. Similar to the event that just passed, the highest rainfall totals are expected to be across southern New Hampshire and into the southwest coast of Maine. This is where PWATs are going to be in the 1.25 to 1.50 inch range. While we are going to be too stable for any convection (the early arrival of the clouds and rain are going to limit daytime temperatures to the 50s) soundings suggest warm cloud depths are still going to climb into the 10 to 12 kft range, so rain may be moderately heavy at times. As this is one of the drier areas in our CWA, it should be able to handle this with no threat for flooding. Rainfall amounts look to end up in the 0.50 to 0.75 inch range, with the HREF max suggesting some locations could see upwards of an inch. Northern New Hampshire and the remainder of Western Maine likely see lighter rain through this event, but still stand to pick up a tenth to a quarter of an inch. The only area that may see less is the Upper Kennebec Valley. As clouds clear overnight Sunday into daybreak Monday, temperatures should fall into the upper 30s and 40s once again with valley fog likely forming. Overall this should be a beneficial rain event for our southern areas, but more is needed if we are going to replenish our deficits.

KEY MESSAGE 2 DESCRIPTION...

A strong area of high pressure will build across Quebec on Monday and remain through much of Thursday. This will allow for a prolonged period of mainly dry weather conditions and below average temperatures as negative H5 height anomalies continue. Daytime high temperatures will generally be into the lower to middle 60s most days with overnight lows into the 30s and 40s. Frost will be possible, especially across interior valleys.

Rain chances will then increase during the Friday to Sunday timeframe as a possible coastal low develops and moves northward along the Eastern Seaboard. Forecast confidence at this time range is low and there are significant differences in latest ensemble and deterministic based guidance on timing, placement, and strength of this potential low. If it does manage to form and move far enough north and west, then rain, gusty winds, and high surf would be possible. Forecast details and confidence will hopefully become clearer over the coming days.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18Z Sunday...VFR prevails through tonight with ceilings beginning to thicken and lower Sunday morning. By Sunday afternoon most terminals should be close to, or at, MVFR as rain overspreads the area.

Outlook: Sunday night: MVFR prevails through the evening with IFR visibilities possible at some southern and coastal terminals in briefly heavy rain. IFR is likely at valley terminals overnight, but generally the trend should be toward improving conditions as the rain moves out.

Monday-Thursday: Other than valley FG at LEB and HIE most nights bringing IFR- LIFR restrictions, VFR conditions will prevail through Thursday.

MARINE

Sub-SCA conditions continue through Sunday night as high pressure slides eastward over the waters. Heavy rain is possible at times through Sunday evening. Winds remain generally onshore through Sunday night, but will shift around to northerly by daybreak Monday as a front crosses the waters.

ENE winds will prevail Monday night through Thursday with gusts between 20-25 kts and seas of 1-3 ft. A coastal low may bring increased winds and seas during the Friday to Sunday timeframe but forecast confidence is low.

GYX WATCHES/WARNINGS/ADVISORIES

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