Area Forecast Discussion

WHAT HAS CHANGED

Continuing to monitor expected rainfall amounts into mid to late week. Deviation from previous forecast was primarily focusing precipitation chances for Tuesday during the afternoon, and tweaking Wednesday/Thursday highs lower with expected widespread rainfall.

KEY MESSAGES

1. Pleasant weather continues through Monday under high pressure.

2. Unsettled weather returns midweek with rain expected. There exists the potential for periods of heavy rainfall, with the low probability of localized flash flooding Wednesday into Thursday. This threat is mainly focused across the southern third of the forecast area.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... A pleasant and cool summer day continues with quiet weather continuing right through Monday, although MOnday should be a touch warmer with temperatures climbing into the low 80s. A shortwave approaches this afternoon which may squeeze a few drops out of the developing cumulus field along the International Border, but otherwise the dry air in place will hold steady. Temperatures tonight should once again fall quickly as mostly clear skies and calm winds allow for efficient radiational cooling. I would expect another night with widespread low 50s, with mid to upper 40s in the usual better radiating locations and have blended in some cooler MOS guidance to the NBM to reflect that.

A cold front begins moving eastward toward the region Monday, but it doesn't look like it is going to make much progress. The 26/12Z CAMs all depict any prefrontal showers losing the battle to the dry air that will remain overhead. Most of the area is going to end up dry, but I could see a few showers making it into southwestern New Hampshire tomorrow afternoon and evening. An isolated rumble of thunder is not out of the question either as daytime heating and slowly increasing dewpoints create just enough instability. Clouds move in Monday night ahead of the next system, so nighttime temperatures are going to end up warmer than the previous nights, only dropping into the mid- to upper 50s.

KEY MESSAGE 2 DESCRIPTION...

Closed low moves towards southern New England Tuesday. The upper trough is deep, and will gradually work towards cutting off through late week. For Tuesday, this will force the development of showers with a few thunderstorms through the afternoon and early evening mostly across New Hampshire. Heavy precip parameters aren't excessive, but flow is weak. This could result in stronger showers or storms featuring slow storm motion if updrafts can persist. Morning RRFS runs do depict some points of enhanced QPF through the afternoon hours across NH, but these remain fairly isolated as they eventually rain themselves out. Coverage of these heavier showers is expected to lessen through the early evening hours.

Progressing into midweek, more widespread rainfall is likely Wed/Thurs. Trends have been somewhat stubborn for this system, but closed lows are often a scenario that sees greater than normal uncertainty in the medium range. The incoming low will tend to deform a pool of moisture settled across the eastern CONUS, curling moisture transport SW to SE off the New England coast. Low level wind field associated with the low is marginal but broad while the upper level support is lackluster. For moisture, IVT isn't overly impressive (with SE directions not favorable for New England ARs) as likely probabilities for greater than 500 kg/m/s remains offshore and just noses into southern NH/coastal southern ME briefly Wed afternoon.

Continue to not be overly concerned about short-fused flash flooding this week given the antecedent dry conditions. However, will monitor any localized heavy rainfall locations on Tuesday, to possibly be exacerbated Wednesday/Thursday amid the forecast broader stratiform precipitation. While the greatest precipitation is expected Wednesday and Thursday, dreary conditions with showers could persist through Friday, with reinforced forcing arriving for the weekend with continued precip chances.

The rain mid week will tend to bring a period of more mild temperatures to the area given additional cloud cover and cooler airmass. The northern fringe, roughly the northern third of the forecast area, could see warmer temperatures in the mid 70s to around 80 through this period if clouds are thinner.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Through 18Z Monday....VFR conditions prevail through Monday morning at most terminals with the exception of RKD which may see some IFR fog again tonight, but confidence is not high so low ceilings are only suggested in the TAF for now.

Outlook... Monday afternoon/night: VFR conditions expected as thickening ceilings are likely going to prevent fog Monday night.

Tuesday: SHRA develop across NH in the afternoon with MVFR cigs. TS possible.

Tuesday Night: MVFR to IFR cigs possible as clouds thicken and lower. Fog development possible across southern ME with MVFR/IFR vis restrictions.

Wednesday thru Thursday: Some vis recovery towards VFR, but ceilings remain MVFR with IFR possible for much of NH and far southern ME with RA. Heavy rainfall rates may cause lower restrictions.

Friday: Improvement expected, but there is uncertainty on coverage and intensity of restrictions at this time. RA should be decreasing in coverage, meaning greater chances of VFR/MVFR vs. MVFR/IFR.

MARINE

Sub-SCA conditions continue through at least Monday, as high pressure remains over the waters. Light onshore winds will shift back northerly tonight, before another seabreeze is expected tomorrow afternoon. Winds then look to stay onshore overnight as low pressure begins to approach the region.

Broad low pressure should reside in the region mid to late week. This should allow for slowly building wave heights, and wind gusts approaching SCA conditions. These are more likely on the coastal waters vs. the bays/harbors at this time.

GYX WATCHES / WARNINGS / ADVISORIES

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