textproduct: Gray - Portland

WHAT HAS CHANGED

Will let the dense fog advisory continue to run until 8am but some places may continue to see visibility restrictions until mid to late morning, especially towards the Midcoast. Otherwise, just tweaked the aviation section for the 12Z TAF package.

KEY MESSAGES

1. Scattered showers and isolated thunderstorms are forecast both this afternoon and again Sunday afternoon. A couple of strong storms cannot be ruled out both days.

2. Heat and humidity will gradually build through the work week. There remains potential for hazardous heat mid to late week next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Today will be warmer with more in the way of sunshine, especially in the morning. Surface heating will lead to building instability through the morning with CAMs suggesting SB CAPE will approach 1000 J/kg by early afternoon. Cyclonic flow aloft will aid in ascent for clouds and eventually showers and few storms. CAMs have been honing in on the higher terrain and the sea breeze front being an area of focus for storms which should set up somewhere west of I-95 and the foothills. Deep layer shear will be around 30 to 40 kts, which could allow for a few robust updrafts so a couple of strong storms cannot be ruled out. Mis-matched flow with low levels winds and cloud layer flow could lead to some slow moving storms while MBE Velocity vectors suggest movement should be enough to preclude any flash flooding threat. Convection will wane with the loss of heating during the evening. Highs today will be in the upper 70s to low 80s.

Sunday will be similar to today only highs will be a few degrees warmer. Surface based CAPE is again forecast to reach 1000 J/kg by early afternoon with deep layer shear approaching 45 kts. So again, a few strong storms would be possible with CAMs focusing storms along an area of convergence across the interior.

KEY MESSAGE 2 DESCRIPTION...

Confidence is increasing for an H5 ridge axis to build across the eastern CONUS for much of next week with New England sitting on the northeastern periphery. This will result in increasing warmth and humidity across the region with 850 hpa temperatures rising to around +20C. This will result in daily high temperatures into the 80s to at least the lower 90s, with some potential for warmer temperatures some days south of the mountains. Increasing moisture will allow dew points to rise into the 60s/lower 70s, which will likely cause heat index values to approach heat headline criteria some days.

It should be noted though that most forecast guidance continues to show multiple waves of energy to cross during the course of the week as they ride along the ridge axis ("ridge rollers"). The timing of each one of these waves is tough to pinpoint at this time range but these will likely result in cooler temperatures at times as they will help to produce additional cloud cover and convection. As a result, believe the current forecast from the National Blend of Models (NBM) is likely too warm for portions of the region next week, especially along the coast. Despite this, the high dew points will result in warm overnight lows, which will offer little heat stress relief. Will have to watch for possible severe storms as well given the added heat and humidity.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Through 12Z Sunday...FG and low stratus will continue to result in IFR- LIFR restrictions through around 12-13Z this morning, especially at KPWM, KCON, KPSM, KAUG, KRKD, KLEB and KHIE. Conditions will then improve to VFR for most terminals by 14Z with light and variable winds. There is a chance for a few afternoon SHRA/-TSRA, which could bring some localized brief restrictions. Additional FG is likely tonight, bringing IFR or worse restrictions to some sites, especially along the coast and valleys.

Outlook:

Sunday: Mainly VFR, but brief restrictions in showers and storms possible across northern and eastern terminals.

Sunday Night - Tuesday: Mainly VFR, but nighttime valley fog possible.

Tuesday night - Thursday: Mainly VFR, but rounds of showers and storms possible at times.

MARINE

Through Saturday night...Generally fair conditions are expected as broad high pressure gradually build across the waters through early to midweek next week.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Dense Fog Advisory until 8 AM EDT this morning for MEZ012>014- 018>028-033. NH...Dense Fog Advisory until 8 AM EDT this morning for NHZ010-014. MARINE...None.