textproduct: Gray - Portland

WHAT HAS CHANGED

A River Flood Warning has been issued for the Pemigewasset River at Woodstock as the River is forecast to climb just above minor flood stage tonight. Overall forecast remains on track with the axis of moderate to heavy rain lifting north of southern NH and now extends from the White Mountains through coastal SW Maine. Otherwise, minor update to the Aviation section for the 00Z TAFs.

KEY MESSAGES

1. Rain continues, heavy at times, overnight. Some minor flooding of flashy rivers and urban areas/small streams is possible where rainfall totals approach 3 inches.

2. Warmer than normal temperatures arrive beginning this weekend, and may be much above normal parts of next week. Warmer temperatures on Tuesday and Wednesday will allow for some scattered thunderstorms in the evenings of both days.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Upper low pressure is beginning move south of Long Island at this hour. As it does so a strengthening warm conveyor belt will remain focused over NH and slowly lift north and pivot thru the night into a more east/west orientation. Where the pivot ultimately occurs will determine who gets the highest totals and where flooding may potentially be an issue. There has been a gradual increase in QPF across model guidance into this morning. I have noted the 14.00z HREF to 14.12z HREF mean and max 24 hour QPF both increasing slightly. Mean QPF amounts are now 2 to 2.5 inches across both the Upper Valley of NH and parts of southwestern Maine. Max amounts are approaching 5 inches. Local research has suggested that while location tends to be harder to pinpoint, the max QPF amounts tend to occur more often than not somewhere in the local forecast area. While rainfall rates have not been extreme so far today, another 6 to 8 hours of 0.25"/hr will result in 3 to 4 inch totals given what has already fallen. Generally speaking we need those totals in 6 hours in order to really be worried about flash flooding. Considering the forecast I anticipate that the flashier rivers may approach minor flooding, more likely rising to action stage, though we will have to watch the upper Pemi basin. Otherwise some small stream and urban flooding is possible where the heaviest rain occurs. It is possible some areal flood warning may be necessary, potentially transitioning to advisories near the morning commute time to highlight any lingering water on roadways. Rain will continue to taper to showers overnight and by midday Fri should be largely done.

KEY MESSAGE 2 DESCRIPTION...

High pressure builds in from the southwest Saturday and settles southeast of New England Sunday setting up mostly fair weather with highs in the 70s Saturday pushing into the low 80s Sunday. Water temperatures remain cold with inland lakes around 50 degrees and ocean temperatures in the 40s. The combination of warm and fair weather may lure people to the water and will likely need cold water safety messaging.

A back door front brings a bit of a cool down Monday with sea breeze keeping coastal areas and parts of central Maine below 70F on Monday, with lower 70s mainly confined to areas west of I-95.

Monday night, winds calm and shift to southwesterlies. This will allow for warm air and moisture advection, with temperatures and dewpoints running at least 10F warmer on Tuesday. High temperatures near 90F can not be ruled out over southern New Hampshire, with below 70F high temperatures staying confined to the Midcoast. The daytime heating and extra moisture looks to collide with a cold front moving southward Tuesday afternoon. Soundings are already showing an unstable environment across northern New England with 500- 1000J of CAPE and around 30kts of wind shear. Within this environment, storms may contain at least small hail and gusty winds. Another hotter day is forecast on Wednesday as well, with high temperatures maybe only a couple degrees cooler from Tuesday. Another cold front looks to move southeastward Wednesday afternoon, arriving into another unstable environment Wednesday evening, with at least 1000J of CAPE and 35kts of shear. So between Tuesday and Wednesday night, it seems likely that Wednesday night's storms could pose more of a severe threat than Tuesdays. With both days, a small marine layer along the coast is likely to keep stronger storms confined to the interior. Temperatures start cooling off further for the end of next week.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Through Friday evening: IFR to LIFR conditions are now present along coastal terminals due to low cigs and visibility restrictions in RA/BR. Conditions trend towards MVFR inland while cigs will lower here overnight with a trend towards IFR. All sites will likely be near IFR into Friday morning except HIE where conditions stay MVFR. Rain will continue to spread north and eventually stall and drift back south while scattering out to more showery conditions by morning. It may take until the second half of Fri until widespread VFR conditions return.

Outlook:

Friday Night: VFR conditions expected.

Saturday: VFR conditions expected.

Saturday Night: VFR conditions expected.

Sunday: VFR conditions expected.

Sunday Night: VFR conditions expected.

Monday: VFR conditions expected.

Monday Night: VFR conditions expected.

MARINE

Onshore winds will gradually turn more northeasterly tonight. There may be occasional 25 kt gusts on the coastal waters overnight. SCA remains in effect but this is mainly for building seas, which will climb above 5 feet this evening and may linger there thru Sat morning. Areas of fog may be possible tonight into Fri as warm advection continues across the Gulf of Maine.

Winds pick up to SCA levels from the southwest Saturday night, with 4-6ft seas expected. Winds become light and variable Sunday night and Monday with seas of 2-3ft expected early next week.

HYDROLOGY

Around 1 to 1.5 inches of rain has fallen across parts of southwestern NH so far today and additional rainfall of up to 3 or 4 inches remains possible overnight. While this amount of rainfall is not expected to cause flash flooding concerns, it may lead to urban or poor drainage flooding. Also depending on where the rainfall maximum sets up, some of the flashier rivers may approach minor flood stage.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 AM EDT Saturday for ANZ150-152- 154.