textproduct: Gray - Portland

WHAT HAS CHANGED

No major changes were needed for this forecast package.

KEY MESSAGES

1. The weather pattern remains active with continued chances for precipitation. A late week coastal storm remains possible with rain and/or snow, but confidence is low.

2. Temperatures will turn colder this weekend into early next week. Temperatures are expected to average below normal.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Cold advection pattern and upslope clouds and showers will continue tonight into early Tue. Eventually the shower activity will dissipate in response to a shortwave trof approaching from north of the Great Lakes. At this time it looks like precip along the warm front will remain north of the forecast area by and large. So I anticipate showers mainly along the cold front and then in its wake in the upslope zones again.

A deep trof axis will move across the Great Lakes on Thursday as a sfc low develops near the OH Valley and then swings offshore of the Mid-Atlantic Thursday night into Friday morning. This low is then progged to move northeastward towards Cape Cod later Friday into Friday night before exiting towards the Canadian Maritimes on Saturday. A fairly large spread in guidance continues this evening in terms of the eventual track of this low and the severity of any possible impacts across the local region.

Latest cluster analysis continues to favor an offshore track, with most members of the EPS and AI guidance keeping the low well to the SE of Cape Cod. That being said, there are some outliers with a more westward track, which would bring more direct impacts to the area. The latest ECMWF EFI for snow does show a shift of tales for portions of ME and NH but with no shading for EFI. This indicates that a few outlier ensemble members show snow for the region but most guidance does not. Latest ensemble and AI based probabilities for QPF of >=0.50" are generally 30% or less, highest south of the mtns. Therefore, the main takeaway is that while this systems bears watching over the next few days, the likelihood for a direct impact with more significant amounts of rain, snow, and wind are lessening. Given these uncertainties, the latest NBM seemed like a reasonable middle ground approach.

KEY MESSAGE 2 DESCRIPTION...

In the wake of the coastal storm deep northerly flow will drag down some colder air for the weekend into early next week. Initially some of the north northeast wind gusts near the coast especially may be 30 to 35 mph depending on the storm track. Otherwise temps will drop back down to near to below normal. Some adjustments may need to be made to overnight temps, as NBM guidance is opting for radiational cooling bias correction in a pattern more conducive for partially mixed boundary layer.

AVIATION /01Z TUESDAY THROUGH SATURDAY/

Through 00Z Wednesday: Upslope flow will keep MVFR CIGs in the vicinity of the mtns. There is a higher confidence in MVFR CIGs than in showers at HIE, so currently there is only VCSH in the TAF thru early morning. Outside of the mtns VFR conditions prevail with winds turning southwesterly.

Outlook:

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

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

Friday/Friday Night: Lingering restrictions possible due to RA and low ceilings. Some SN may mix in at times across inland terminals, mainly at night. Gusty NNE winds possible, especially along the coast. Low forecast confidence.

Saturday/Saturday Night: Some restrictions possible due to lingering RA and low ceilings. Low forecast confidence. Sunday/Sunday Night: Improving flight conditions with NW winds. Moderate forecast confidence.

MARINE

Winds will remain breezy over the coastal waters but generally remain below SCA thresholds until early Wed. A cold front will cross the waters late Tue and behind it winds may gust to 25 kt. Seas will also build but the short fetch should keep the area of seas greater than 5 ft to a minimum. There is moderate confidence for an area of low pressure to move offshore of the Mid-Atlantic coast late week before moving northeastward through this weekend. While there remains considerable uncertainty in the track of this coastal low, increased winds and seas are likely.

GYX WATCHES/WARNINGS/ADVISORIES

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