textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this update.

KEY MESSAGES

1. High pressure maintains dry weather today.

2. Rain accompanies a passing system tonight into Monday morning. A period of moderate to heavy rainfall after midnight and early Monday morning could result in nuisance flooding or ponding in poor drainage areas for the morning commute.

3. A fairly tranquil week beyond Monday with near-seasonable temperatures. Slightly warmer and wetter conditions may be present midweek.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Similar to last night/yesterday morning, valley fog is could be locally dense in some areas along the CT River, but fog should lift by 8 to 9AM.

For the rest of the day, low pressure crossing through the Great Lakes will shift the high pressure currently overhead to the east. We'll see increasing clouds as the day goes on, mostly in the high and mid variety as moisture increases, but the airmass will remain too dry for any rain during the daylight hours today. High will be mostly in the 70s, except closer to 80 in parts of southern NH.

KEY MESSAGE 2 DESCRIPTION...

Clouds further lower and thicken this evening as low pressure system tracks along the Canadian border and continues to draw in higher moisture from the south. Latest guidance indicates showers moving into NH in the evening while the higher coverage of shower activity along with an area of stratiform rainfall overspreads the area from west to east overnight and into Monday morning.

Rainfall rates could be efficient at times late tonight and into Monday morning as PWATS increase to 1.50-1.80" across much of the area along with increasing warm clouds depths and better lift, which could create some ponding of water on roadways for commute time. Beyond Monday morning, lingering low-level moisture and weak lift remain in place for much of the day, keeping skies mostly cloudy with instances of light rain and drizzle possible.

There seems to be decent consensus in latest guidance with another slight northward shift in where the higher rainfall totals may fall along with a somewhat downward trend for southern areas on average. Rainfall amounts across northern areas are forecast to be mostly to be in the 0.50-0.75" range, although a stripe higher amounts of 1.00-1.50" is possible somewhere across northern NH extending into the western ME mountains. Based on latest guidance, average amounts of less than 0.25" are possible for southern NH and southwest ME, but given the airmass, showers could produce localized amounts higher than this.

KEY MESSAGE 3 DESCRIPTION...

Overall mixed signals on Tuesday as the global guidance keeps the disturbance just offshore, while the hi-res guidance that has arrived in range shows a dry day as the wave departs quicker. What does seem consistent among guidance however is elevated humidity continuing with dew points in the 60s. Global guidance shows a diurnal convective precip signal, but am skeptical given shallow moisture and subsidence.

Continuing to Wednesday, current indications are it will be the warmest day of the week with some widespread 80s likely with southwest surface flow. A trough will swing into the region late Wednesday, bringing another chance for precipitation. There will be more forcing for ascent with some decent 500 mb jet dynamics, however with the core of the trough up near Hudson Bay, a more glancing blow over New England will keep rain chances scattered rather than widespread.

By late week the signals begin to diverge on model guidance. There are generally two camps at this range between the trough lingering and quickly exiting with high pressure filling back in, which will dictate how dry it will be come late week. What generally is in agreement at this range however is falling 500 mb heights and 850 mb temperatures, suggesting temperatures will trend a bit on the cooler side, albeit nothing looks anomalous.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12Z Monday...Patchy dense fog and LIFR ceilings will continue over HIE and LEB for the next hour or two before lifting. Otherwise, VFR conditions should prevail through the day. An approaching system will lead to lowering ceilings and increasing rain chances after 06z Monday, resulting in widespread LIFR/IFR restrictions. A few thunderstorms may also be possible late tonight or early Monday morning but uncertainty is too high to include mention at any specific site for now.

Outlook:

Monday: MVFR to LIFR likely due to low ceilings and rain or drizzle. Ceilings across western ME may be as low as LIFR.

Monday night: LIFR to IFR ceilings and fog may linger, but improvement is possible overnight.

Tuesday-Wednesday: VFR expected.

Thursday: MVFR due to showers and thunderstorms.

MARINE

Through Monday...Winds will be light and out of the north this morning before switching around to southerly this afternoon ahead of an approaching low pressure system and frontal boundary to the west. Winds stay out of the south and increase this evening through Monday with gusts possibly approaching 25 kt at times. Seas may also briefly approach 5 ft during the day Monday. However, and SCA is currently not expected due to short duration.

Monday night-Saturday...SCA conditions are not expected. Low pressure passes south and east of the waters Monday night and Tuesday with another frontal boundary approaching toward midweek. High pressure builds across the waters late in the week and the start of next weekend.

GYX WATCHES/WARNINGS/ADVISORIES

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