textproduct: Gray - Portland

WHAT HAS CHANGED

Frost/Freeze headlines have been cancelled as daytime temperatures warm. 12z GYX radiosonde noted a lot of dry air in the lower levels yet, but think current PoP forecast has a good handle on progression.

KEY MESSAGES

1. There will be chances for light rain today followed by more widespread beneficial rainfall Thursday into Friday.

2. A generally dry period with only a few conditional chances for precipitation from Saturday onward.

3. A warming trend from this weekend into next week, but specifics remain uncertain.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Latest available deterministic and ensemble guidance remain in decent agreement that an upper trough digging across the Great Lakes this morning will close off into an upper low that slowly crosses southern New England Thursday into Friday. This will place the forecast area in a favorable region for ascent with chances for rain in the forecast today through Friday with the highest chances centered on Thursday afternoon and night.

The initial surface low over the eastern Great Lakes early this morning will lift a warm front into the area today. This front will bring clouds and NW to SE oriented band of light rain that lifts northeastward through the area late morning through the afternoon. Initial rainfall will have to overcome dry low levels so amounts are forecast to be less than a tenth of an inch with portions of the coastal plain experiencing a break in rainfall behind this band late afternoon through the evening. Chances for rain will continue over the mountains this afternoon through tonight while areas south of the mountains may see just low clouds and possible drizzle.

The approaching trough will take on a negative tilt late tonight into Thursday with a secondary low forming near southern New England. A plume of deep moisture will exist well offshore with some of this moisture being drawn into the Gulf of Maine Thursday. PWATs will climb to around 1 inch along and south of the mountains Thursday afternoon as the best dynamics spread overhead. There does not appear to much in the way of instability and warm cloud depths will be shallow limiting the threat for heavy rainfall while bouts of moderate rainfall seem likely Thursday afternoon into Thursday night. As the upper low slowly drifts southeast away from the area Friday, rainfall chances will decrease from NW to SE. Total rainfall amounts from today through Friday remain on track for much of the area to see 1-2 inches, while there will likely be some areas that see less depending on where the bouts of moderate rain set up. Locally higher amounts are possible along coastal Maine and in the mountains.

KEY MESSAGE 2 DESCRIPTION...

The upper-level trough exits the region Friday night, with height rises quickly building in behind it, which should set us up for a very pleasant weekend. A strengthening ridge will be building over New England, peaking early next week. On face value, a much anticipated pattern change to warm and dry is in the cards.

On Saturday, as a stronger low pressure passes well to the north over Hudson Bay, it will drag a weak shortwave through our area aloft. This may be enough of a trigger to spark scattered afternoon/evening showers, especially across the northern half of the forecast area. POPs spike to 50% near the Canadian border, but are less than 20% from Augusta to Lebanon and points south.

Sunday is much more likely to be a fully dry day as subsidence builds in behind the shortwave, combined with synoptic-level height rises in general. The next meaningful chance for precipitation will not be until early next week. Models are suggesting a cold frontal passage sometime in the Tuesday-Wednesday window. Depending on the timing, there may be some t-storms that fire as may get quite warm and juicy out ahead of the front.

KEY MESSAGE 3 DESCRIPTION...

Saturday is looking to be a mild day with 60s and 70s for the entire region. In fact, WSW surface winds with enough flow should suppress seabreezes and cooler onshore flow for much of the coastline, allowing these pleasant temperatures to be widespread. On Sunday the flow becomes a bit "cooler" out of the northwest, so we may see temperatures fall a few degrees but could see another day of 70s in S NH. Then after, models show easterly flow on Monday along/north of a lifting warm front, which may allow for a sharp temperature gradient across the region. Most likely the warm sector stays down in Southern New England. By Tuesday most guidance is in agreement the warm front fully pushes north of the region. Global models have been rather insistent on "summer-like" temperatures arriving by Tuesday, so stay tuned to see if this holds.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Through 12Z Thursday...Clouds increase from the SW and lower into this afternoon and evening. MVFR cig restrictions arrive this afternoon for LEB and progress east through the evening with light rain. Cigs continue to lower into tonight with IFR cigs possible through the mountains and foothills. SE winds are expected at 5-15 kts. LLWS is possible tonight as a warm front lifts northward.

Outlook:

Thursday: Areas of MVFR likely as rain becomes more widespread/steady. Moderate rain Thursday afternoon and evening may bring visibility restrictions.

Thursday Night: Areas of MVFR likely. IFR or lower conditions becoming more likely thru the night.

Friday: IFR conditions gradually improve thru the day.

Friday Night: VFR conditions expected.

Saturday: VFR conditions expected.

Saturday Night: VFR conditions expected.

Sunday: VFR conditions expected.

MARINE

High pressure sinks south of the waters through this morning with a warm front approaching from the SW Wednesday afternoon. Increasing S winds will bring SCA conditions this afternoon through tonight.

A secondary low will form near southern New England Thursday and will slowly track near the Gulf of Maine through Thursday night. SE winds ahead of the low will gust 20-25 kts during the day Thursday with seas building to 5 feet that remain elevated into Friday. Winds turn northeasterly Friday morning and shift northerly Friday afternoon. An approaching cold front over the weekend may allow southwest winds to freshen late Sat. Southwest winds are less likely to fully mix down, but some gusts near 25 kt are possible outside of the bays.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 8 AM EDT Thursday for ANZ150-152-154.