textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast package.

KEY MESSAGES

1. Expect a few hit or miss showers through midweek, mainly in the mountains. Otherwise, temperatures will cool to near normal readings before a colder airmass arrives at the end of the week.

2. There is a growing signal for a system to bring rain and measurable snow to the area late this week, although significant uncertainty in potential impacts remains.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

A mean upper low will continue to spin over northern Quebec near the Labrador border. Periodic ridging and troughing will rotate around this low leading to hit or miss showers through midweek. Any showers this afternoon will diminish tonight into Tuesday as a progressive ridge axis crosses the forecast area. The next shortwave then arrives late Tuesday into Wednesday morning which will bring more chances of showers. The higher peaks will likely see some snow mixing in. More rain and snow showers will be possible over the mountains on Wednesday but broad ridging will be on approach so coverage may be more limited, especially later in the day.

Temperatures will generally be on a gradual cooling trend through the week, trending closer to normal for this time of year. Tuesday's highs are expected to range from the low/mid 40s north to the low/mid 50s south and then by Thursday most will see highs in the 40s (lower 50s confined to southern NH and coastal ME). By Friday, highs will only range from the mid 30s to mid 40s.

KEY MESSAGE 2 DESCRIPTION...

Deterministic global models have further diverged regarding the track of a late week system with the 09.12Z GFS continuing to favor a track swinging inland and the Euro now whiffing on its last four runs (08.18Z to 09.12Z). The 09.12Z Canadian has also interestingly taken a large jump northward and is more in line with the GFS. Ensembles have remained more consistent with GEFS showing the low centers clustered around Cape Cod and the Gulf of Maine, but the clustering in the ECMWF has taken a notable shift eastward out to sea. This does increase confidence in the fact that this system will ultimately take a coastal track so with that in mind lets break down the potential impacts in a probabilistic sense since the envelope of track solutions is a large range. SNOW: The latest NBM probabilities of measurable snow are low with the higher peaks of the white mountains boasting anything over 50%. Outside of the mountains down through the foothills probabilities are in the 40% range. This leaves the coastal plain at less than 30% and near 0% at the immediate coast. So at this point I have confidence in some degree of high elevation snow with less impacts outside of the mountains, but amounts either way are too track dependent to try and pin down this early.

PTYPE: It is either going to be rain or snow and with current trends and aforementioned snow probabilities any snow looks like it would be confined to the mountains, with maybe more wet snowflakes down through the foothills. Lastly, it seems like any precipitation down at the coast would be mainly a cold rain.

WIND: Confidence is moderate that the highest winds are going to be at the coast, but magnitude is much more uncertain due to how much track factors into this. Yesterday long range ensembles had widespread 25 to 30 mph winds, but now with the ECMWF's westward trends global blends are hard pressed to give you 25 mph. Overall, I think it is fair to say unless there is a drastic shift in guidance wind seems low impact.

In the wake of this system mean troughing persists over the Northeast, but the trend is going to be toward a return to more seasonable temperatures and drier weather heading into next week.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Through Tuesday morning: Upslope showers will allow for MVFR CIGs to prevail in the mountains and by HIE. Outside of the mountains, conditions should mainly be VFR with westerly winds during the day. A few gusts could exceed 20kts. Winds calm tonight with VFR continuing through at least Tuesday morning. Upslope flow keeps MVFR in place in HIE tonight.

Outlook:

Tuesday/Tuesday night: MVFR-IFR restrictions are possible at HIE with SHRA/SHSN but otherwise mainly VFR conditions. WSW wind gusts up to 25 kts possible. Moderate forecast confidence.

Wednesday/Wednesday night: Some lingering restrictions possible at HIE with isolated SHRA/SHSN but otherwise mainly VFR conditions. WNW wind gusts up to 20 kts possible. Moderate forecast confidence.

Thursday/Thursday night: VFR conditions likely through the afternoon before developing RA and lowering ceilings bring an increased risk for restrictions late day into Thursday night. Generally N winds of 5-15 kts. Low forecast confidence.

Friday-Saturday: Widespread restrictions are possible as a potential system brings rain and snow to the area. Low forecast confidence.

MARINE

Conditions during the rest of today should remain below SCA thresholds. Tonight, a burst of cold air advection could lead to some wind gusts up to 25 kts for at least a short time, but as of right now we are forecasting the majority of the winds to remain just under. Calmer winds are expected Tuesday and Wednesday.

Low pressure is going to track somewhere in the vicinity of the Gulf of Maine late in the week and with it will come elevated seas and wind gusts. Magnitude is uncertain, but confidence in at least SCA conditions for coastal waters is high.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.