textproduct: Gray - Portland

WHAT HAS CHANGED

Hot and humid weather settles in for the next couple days, and the primary change was to issue a Heat Advisory for interior southern NH.

KEY MESSAGES

1. High moisture content is going to pose at least a moderate heat risk in most locations through Friday.

2. Thunderstorms early this morning will pose a low threat for isolated flash flooding before dissipating. Showers and thunderstorms should be more isolated today, with an increased threat on Friday.

3. A cold front moves through the area Sunday night, bringing storms to the region. High temperatures will run much closer to normal for early next week.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Dewpoints are going to remain elevated through Friday which will cause a heat risk as temperatures peak in the upper 80s and low 90s Thursday and Friday. Any major heat risk (apparent temperatures >= 95F) continues to look like it would be isolated to the southern tier of counties in New Hampshire, especially the Merrimack Valley and interior Rockingham County. Much of the rest of the area should expect at least a moderate risk as apparent temperatures near 90F. Southeasterly low level flow is going to increase on Friday which should allow for somewhat cooler temperatures on the coastal plain. The remainder of the area will have to wait for the cold frontal passage for relief Friday night.

KEY MESSAGE 2 DESCRIPTION... Scattered showers and thunderstorms early this morning will eventually dissipate well before sunrise as forcing for ascent will wane. Until then a localized flash flood risk due to excessive rainfall will continue. In addition, patchy dense fog may affect the morning commute today.

Another weak short wave trough will approach the forecast area in the midst of the hot and humid air mass. This will aid in triggering isolated thunderstorms during the afternoon. Not everyone will see one. However, locations that do see one may be at risk for localized heavy rain and minor flooding as well as gusty winds. Most CAMs are in agreement that coverage will be limited.

On Friday the Storm Prediction Center has our western zones in a slight risk for severe thunderstorms as a cold front approaches from the west. The extent of the threat will depend on frontal timing. If it's too late we may not see much. However, as of right now conditions in various sources of guidance are favorable for a few severe storms with damaging wind potential Friday afternoon and evening, especially across New Hampshire. Will continue to monitor.

KEY MESSAGE 3 DESCRIPTION... Low pressure over Quebec will allow for the passage of a cold front Sunday evening. PWATs near 1.5" suggest a fairly humid environment in the area. The moist environment in addition to some modest instability will allow for the development of thunderstorms along the cold front. A few may be strong. Behind the aforementioned front, temperatures will run much cooler with high temperatures in the 70s and lower 80s early next week.

AVIATION /06Z THURSDAY THROUGH MONDAY/

Through Friday...IFR looks to become likely at most terminals early this morning as showers come to an end and a very moist air mass remains in place. Fog and low clouds will both be present. Conditions look to begin to improve back to VFR by 12Z this morning, except restrictions may last longer at AUG and RKD.

This afternoon, Generally VFR conditions are expected to continue, but there remains a chance for isolated showers and thunderstorms that could bring about TEMPO MVFR conditions.

Tonight and Friday, Patchy fog tonight will bring potential for restrictions along with low cigs near the coast. Generally VFR Friday with TEMPO restrictions Friday afternoon and evening in showers and thunderstorms, mainly across NH.

Friday night, Restrictions are more likely in showers, low cigs, and patchy fog.

Outlook...

Saturday: Conditions improve to VFR.

Saturday Night: VFR likely, but valley fog possible late.

Sunday-Monday: VFR to start Sunday. A front brings showers and storms late Sunday and potential for restrictions with improving conditions Monday.

MARINE

Generally quiet conditions are expected on the waters through Friday with afternoon seabreezes as high pressure remains in the vicinity of the Gulf of Maine. Increasing moisture will likely lead to fog development.

A cold front crosses the waters Friday night while winds and seas remain below SCA thresholds ahead and behind the front into Sunday. A stronger cold front crosses late Sunday with winds approaching 20 kts and seas approaching 4 feet around this frontal passage.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...Heat Advisory from noon today to 8 PM EDT this evening for NHZ005-007>013-015. MARINE...None.