textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed with this forecast package.

KEY MESSAGES

1. Isolated showers and storms may bring gusty winds through early this evening. A chance of showers continues overnight before the higher chances for showers and strong storms comes Thursday.

2. High pressure will allow for a fair and pleasant weekend. Unsettled weather looks to arrive early next week in the form of a frontal passage Sunday night into Monday. High pressure returns after the aforementioned frontal passage.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

500mb troughing will be in place across eastern Canada and New England through Thursday ahead of a cold front that will cross Thursday afternoon and evening. For the rest of today into tonight, multiple weak waves/vort. maxes will cross overhead, bringing chances for showers as well as a few storms. The airmass is pretty dry this afternoon, so coverage should remain fairly isolated and mostly in NH, but showers/storms will be capable of producing gusty winds given how dry the low levels are (and possibly small hail with cooling temperatures aloft). Chances for showers (30-50%) continue into this evening and through at least part of the overnight hours as additional upper-level energy arrives. Lows will be mostly in the 50s, and valley fog is possible in the normally prone areas.

A cold front approaches and crosses during the day Thursday, and with better forcing, showers are possible in the morning and will be followed by higher coverage of showers and thunderstorms in the afternoon to early evening hours. Ensemble mean of SBCAPE from the 12Z HREF depicts 500-1000 J/kg and 0-6km shear around 30-35 kt to work with, so a couple of strong to marginally severe storms will be possible. However, confidence is fairly low on where the better chances of seeing strong/severe storm will be as CAMs are showing poor run to run continuity. Aside from showers/storms, temperatures will be close to normal, which is mainly in the upper 70s to low 80s.

The front moves offshore Thursday evening, and aside from a couple of lingering upslope showers in the mountains, dry conditions are expected overnight as a push of drier air arrives from the north. Winds behind the front will be pretty light, so patchy fog is a possibility, especially in valleys and in areas that receive rain. Overnight lows will be mostly in the 50s, except upper 40s possible in the north.

KEY MESSAGE 2 DESCRIPTION...

By Friday morning, low pressure departs to the northeast. A light pressure gradient in it's wake could allow for some light northwesterly winds through the day on Friday. Some wraparound moisture from this low may allow for the development of an isolated shower or two over central Maine Friday afternoon.

On Saturday, high pressure moves in from Canada and remains overhead through most of the weekend. This will allow for mostly clear skies and calm winds on Saturday and through most of the day Sunday. Near average mid-level heights will translate to near-average temperatures. High temperatures are forecast to be around 80F in most of the population corridor, though cooler highs in the lower 70s are expected north of the mountains.

On Sunday a mid-level ridge moves eastward, and a frontal passage may cross the northeast Sunday evening. However, it should be pretty late in the evening before the front makes it into NH. The front looks to pass over the region Sunday night and into Monday morning. High pressure is likely to follow the front, with drier and clearer skies in the forecast through much of the remainder of next week.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...MVFR possible to due isolated SHRA/TSRA from this afternoon with higher chances this evening through portions of tonight. IFR or lower is then possible at HIE and LEB tonight with valley fog, especially if these sites see rain and skies are able to clear out. VFR expected Thursday morning, but a couple of SHRA and MVFR ceilings can't be ruled out.

Outlook:

Rest of Thursday: Higher coverage of SHRA/TSRA could bring TEMPO IFR or MVFR restrictions.

Thursday night: Mainly VFR, except valley fog will again be possible at HIE and LEB.

Friday: Patchy LIFR in the morning due to valley fog. VFR through the rest of the day

Saturday-Sunday: VFR expected.

Sunday night-Monday: MVFR due to showers and thunderstorms.

MARINE

Through Thursday night...SCA conditions are not expected. Winds will be mainly out of the southwest through tonight and into Thursday afternoon ahead of a cold front. Winds then turn northwesterly Thursday evening and Thursday night behind the front.

Winds and seas will largely remain below SCA criteria through the week as a series of generally weak cold fronts cross the waters. Conditions may come close to SCA criteria briefly Friday night and into Saturday.

TIDES/COASTAL FLOODING

Astronomical tides continue to run high with storm surge also continuing to run between 0.5 and 1 foot. So water levels may approach flood stage at times with water getting into the most flood prone low spots. By this weekend tides will be peaking under 11 feet.

GYX WATCHES/WARNINGS/ADVISORIES

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