textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast cycle early Sunday morning.

KEY MESSAGES

1. Low pressure passing south of New England will bring rain to mainly areas south of the mountains tonight.

2. An unsettled weather pattern is going to bring additional chances for precipitation during the upcoming week and into next weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

High pressure over the area early this morning will slide east today as low pressure tracks ENE towards the Mid Atlantic. Much of today will remain mostly dry with clouds increasing this morning yielding mostly cloudy skies this afternoon. Latest available guidance is in decent agreement that low pressure over the Mid Atlantic will track ENE south of Cape Cod tonight through Monday morning. Rain will likely overspread southern NH this evening and then northeastward tonight before tapering off NW to SE Monday morning. Models are in decent agreement that measurable rainfall will likely stay confined along and south of the mountains with the latest NBM bringing QPF amounts around 0.65 inches across southern NH decreasing to the north.

As the low exits east Monday morning skies will turn partly to mostly sunny across much of the area. The exception will be clouds across the north that will advance southward late Monday as a front sags south from Canada. It will be warm with highs ranging from the low 60s north to low 70s south of the mountains.

KEY MESSAGE 2 DESCRIPTION... The 500 mb pattern is dominated by unsettled zonal which will promote shortwave energy crossing the area in conjunction with surface features. The first is going to be low pressure riding along a frontal boundary draped over New England. This crosses the area in the Tuesday/Wednesday time frame and looks to be the next best chance for areawide precipitation. The latest long range ensembles still have moderate uncertainty as far as QPF, likely owing to there being disagreement in the track of the low. The ECMWF and Canadian have the low pressure tracking directly overhead, and the GFS keeps the center north of our area and passing over the crown of Maine. The 25th-75th spread is around 0.75" for most of the area, and a little more confident in southern New Hampshire with around 0.30" of spread. Keeping that in mind, current ensemble means suggest northern New Hampshire and much of interior Maine, down to the Midcoast, have the highest probabilities of 0.75" to an inch of rainfall. Central New Hampshire and southwestern Maine are in the 0.5 to 0.75" range, and southern New Hampshire is in the 0.25 to 0.50" range.

Depending on how fast the low exits, rain could continue through the better part of Wednesday, but should be light as it tapers off. Showers are certainly going to continue in the mountains as northwesterly flow prevails aloft, and this could bring snow to higher elevations Wednesday night. The low pressure system deepens as it moves over Atlantic Canada on Thursday which deepens a trough off the East Coast. This keeps Thursday dry as we see the effects of the upper ridging and high pressure beginning to build in, but the continued cold air advection aloft is going to set up several day with highs in the 50s.

Rain chances return for Friday and Saturday as global models are in reasonable good agreement that a sharp upper level trough swings through somewhere in that time frame. It is too early to try and flesh out details, but this is going to be another window to watch for beneficial rainfall.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Through tonight...Mainly VFR through today. Clouds thicken and lower from SW to NE this afternoon with MVFR transitioning to IFR or lower between 00Z to 06Z from LEB to PWM and points south.

Outlook...

Monday-Monday night: Any lingering restrictions in the morning will transition to VFR with VFR likely through Monday. Low cigs and -SHRA likely bring restrictions to HIE and low stratus may impact the coastal plain Monday night.

Tuesday-Tuesday night: IFR restrictions and rain showers are likely.

Wednesday: Restrictions possible early in the day, but most sites should return to VFR by the afternoon. That said, additional rain showers may produce instances of MVFR, especially at HIE. West to northwest winds may gust 25 to 30 kt.

Wednesday night: MVFR ceilings with possible rain and snow showers at HIE. VFR elsewhere.

Thursday: Mainly VFR with breezy northwest winds remaining possible. HIE may continue to see periods of MVFR and rain/snow showers.

MARINE

High pressure shifting east of the waters will freshen SW today while winds and seas remain below SCA thresholds. A weak area of low pressure passes south of Cape Cod will shift winds NE tonight and then offshore Monday while winds and seas remain below SCA thresholds. A front pushing south from Canada could bring NE winds to 25 kts Monday night.

Low pressure moving through the region on Tuesday is likely to bring SCA conditions through Wednesday as a front crosses the waters. SCA conditions are going to be possible again toward the end of the upcoming week as more fronts are progged to cross the waters.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Freeze Warning from 2 AM to 8 AM EDT Sunday for MEZ019-020. Frost Advisory from 2 AM to 8 AM EDT Sunday for MEZ021>028. NH...Frost Advisory from 2 AM to 8 AM EDT Sunday for NHZ010-012-013. MARINE...None.