textproduct: Gray - Portland

SYNOPSIS

A strong cold front pushes toward the region early today, with rain chances increasing. Southerly wind gusts in the 50 to 60 mph range will be possible by this afternoon, especially near the coast. This will also send temperatures climbing into the 40s and 50s in places ahead of the front. After maybe a brief start as snow in the highest elevations, all rain is expected across the area. Snow melt is unlikely to cause flooding, but some areas may lose all the current snowpack. As the front crosses the area, temperatures will begin a steady decline into the 20s by Saturday morning. A weak system will cross north of the area Saturday night, but only light snow or snow showers are expected. Another clipper is then possible by Tuesday.

NEAR TERM /UNTIL 6 PM THIS EVENING/

530 AM Update...Just a couple of updates. Interior Waldo county has been added to the High Wind Warning, and an SPS has been issued for locally dense fog this morning.

Previously...

Key Messages:

*Impacts from the incoming wind and rain gradually increase this morning and peak in the late morning west and mid afternoon east.

*Damaging south-southeast winds are likely along the coast from Cape Elizabeth to points northward on and near the coast.

*Bouts of moderate to heavy rain are expected. Flood risk is low due to ongoing drought conditions with further details in the Hydrology section below.

*Temperatures drop quickly tonight and any standing water will likely freeze by midnight.

Overall little change to the going forecast for today as the latest guidance has generally settled into a reasonable steady solution. The main story continue to be the winds today. S-SE winds will increase this morning and peak this afternoon. Forecast soundings continue to confirm the presence of a 90-100KT LLJ between 3 and 6 KFT. This along with a tight pressure gradient will supply plenty of strong S-SE wind gusts between 40 and 55 knots depending on location (strongest coast). This would cause tree damage and thus power outages.

Rain will be heavy at times as well, as there should be embedded convection with heavy downpours. Didn't mention thunder in the forecast at this time, but a few rumbles here and there can't be ruled out.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/

Key Messages:

*Temperatures drop quickly tonight and any standing water will likely freeze by midnight.

Colder air quickly overspreads the area early tonight bringing the threat for icing. However, if the winds pick up quickly, the threat for widespread black ice drops significantly. There will also be period of gusty west winds behind the front with gusts to 55 mph within mountain zones and around 40 mph south of the mountains.

A secondary cold front should be located somewhere near the Maine coast Saturday morning, which will move well out to sea through the day. A few upslope snow showers will be possible over the mountains and vicinity, but Saturday should see mainly dry conditions across the forecast area as high pressure moves in. Pressure rises and cold air advection should lead to some good mixing on Saturday afternoon, but soundings suggest we will only see winds up to 20 knots or so at the top of the mixed layer. Thus, it will be cooler on Saturday than it was on Friday but winds should be much less (but still a bit breezy). Highs Saturday afternoon should generally be around average for this time of year, mainly in the mid to upper 20s across the north, to the mid to upper 30s south and along the coast. A few lower 40s will be possible along the coast.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Evening Update...

No major updates to the long term as a cooler pattern returns with multiple chances for light precip. A weak Alberta clipper brings some light snow showers to northern areas Saturday night into Sunday, while highs warm into the 40s along the coast Sunday. A cold front moves through with the clipper, bringing a cold shot of air for Monday with highs in the teens and 20s.

A clipper with some more moisture arrives late Tuesday into Wednesday, bringing the best chance for a white Christmas snowfall. At this point snowfall amounts would most likely be light, but a few inches are possible. Seasonable conditions most likely follow into Christmas Day, with another system then possible late next week.

Full Discussion...

An upper ridge axis moves east Saturday evening as we transition back into southwest flow aloft. The next shortwave then starts to nudge in late Saturday evening, quickly moving through the region on Sunday. For now, the best light snow chances (30 to 60 percent) are favored over the central and north along/behind the next cold front, with the highest chances near the International border. Most of the snow should mainly move out on Sunday morning, but we will likely see some upslope snow showers in the mountains through at least the afternoon, potentially lingering into Sunday night and maybe even into Monday. Highs on Sunday should be above normal (but it will be breezy) with highs in the upper 20s and lower 30s north, to the low to mid 40s south. It will be colder Monday behind the front with the NBM suggesting highs only ranging from the low to mid teens north, to the mid to upper teens south. Northwest winds will once again be fairly breezy so Monday will be blustery.

Ridging crosses the forecast area again Monday night in advance of the next shortwave trough that will impact the region mainly on Tuesday. Widespread low to medium light snow chances will be possible through the day on Tuesday with what looks to be minimal impact at this time. Wednesday may see some lingering upslope snow showers in the mountains but Thursday should mainly be dry as the next ridge moves in. Highs Tuesday through Thursday will mainly range from the low to mid 20s north, to the low to mid 30s south.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Short Term...IFR/LIFR develop by dawn. A strong southerly low level jet ahead of a cold front will bring LLWS from 04Z through 18Z today. Surface winds will gust up to 50 kts near the coast and 40 kts across the interior. Periods of moderate to heavy rain and low cigs continue IFR/LIFR through 18Z to 00Z with drier air improving conditions Friday night. A period gusty west winds to 35 kts is likely Friday night behind a cold front. Saturday should mainly see VFR conditions, except at HIE and LEB where MVFR ceilings are more likely in upslope flow.

Long Term...A period of MVFR conditions are possible late Sunday across northern terminals as a period of light snow is possible. VFR conditions return on Monday, with another system possibly bringing more restrictions late Tuesday.

MARINE

Short Term...Southerly winds increase early today ahead of a cold front with Storm Warnings now in effect for all waters today and this evening. Gales likely needed tonight into Saturday morning in the wake of the cold front.

Long Term... SCA conditions in southwesterly flow are possible Sunday as an Alberta clipper tracks north of the waters. Northwesterly gales are then possible behind the front on Monday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Wind Advisory until 8 AM EST Saturday for MEZ007>009. Wind Advisory until 7 PM EST this evening for MEZ012>014- 018>021-023-033. High Wind Warning from 10 AM this morning to 7 PM EST this evening for MEZ022-024>028. NH...Wind Advisory until 8 AM EST Saturday for NHZ001>005. Wind Advisory until 7 PM EST this evening for NHZ006>015. MARINE...Storm Warning until 7 PM EST this evening for ANZ150>154.