textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast package this Sunday evening.

KEY MESSAGES

1. A strong cold front crosses the area on Monday bringing gusty winds and a few showers. Colder and breezy conditions continue into Tuesday with the coldest night of the season so far possible Tuesday night. Many locations south of the mountains could see frost and possibly their first freeze of the season.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... A few showers are possible at the immediate coast this evening and tonight as a weak wave of low pressure meanders through the Gulf of Maine. Otherwise, the next best chance of showers for the rest of the area comes during the day Monday as a strong cold sweeps through. The latest probabilities from the HREF and NBM continue to suggest this is going to be a mostly dry passage for areas south of the mountains. At best areas south of the mountains can expect a few hundredths of an inch, with northern zones more likely to end up with around a tenth. Cold air moving in behind the front will transition any lingering showers in the north to light snow Monday night, but this is likely only going to occur at higher elevations with the sustained upslope flow. Wind gusts out of the northwest as the front passes are going to be around 25-35 mph, higher at higher elevations which should be a caution to hikers to prepare for windchills potentially below freezing above treeline. Breezy winds continue through the night which will keep radiational cooling form kicking in, but expect temperatures to still fall into the low 30s in the north and mid to upper 30s in the south. With windchills this could feel more like the 20s across much of the area.

850 mb temperatures in the -4 to -1 C range during the day Tuesday is only going to allow for surface temperatures to mix into the upper 40s and low 50s in the north, and into the mid to upper 50s in the south with continued breezy winds that will diminish as the day goes on. The coldest night of the season is likely to follow as winds calm and radiational cooling kicks in. I have gone ahead ahead and blended some of the cooler MOS guidance into the forecast to account for this which brings near freezing temperatures into the coastal plain. This area has not seen its first frost yet and this looks like the best chance. Many areas in the foothills have yet to see a hard freeze and this is likely going to be that for them, but on paper the growing season has ended in these areas.

Beyond midweek ensemble guidance is hinting at a chance of showers across the area with the next frontal passage. However it does not look quite as strong nor does it looks like significant rainfall is a threat for most areas. Precip will be most likely in the mtns with decreasing chances to the south and downstream of the higher terrain. Overall westerly flow will keep any significant warmth at bay, and seasonable temps are expected. While beyond the forecast period, there is already a fairly strong ensemble signal for more widespread precip threat around the first half of next week. This will be as a deep trof draws tropical moisture northward from the Gulf of Mexico near the Yucatan. It is a long way out but certainly looking like our best chance at widespread beneficial rainfall.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Through 18Z Monday...VFR prevails through this evening, but ceilings will lower and thicken ahead of a cold front tonight. PSM, PWM, and RKD terminals have a chance at seeing IFR ceilings as a wave of low pressure passes near the coast, but everyone else should bottom out around MVFR. LEB may also see IFR if valley fog develops. Ceilings should lift rather quickly on Monday back to VFR as the front sweeps through. Northwesterly winds behind the front gust 20- 30 kts.

Outlook:

Monday Night: VFR prevails with continued breezy northwest winds.

Tuesday: VFR conditions expected with gusty west-northwest winds continuing, but weakening as the day goes on.

Wednesday: VFR conditions expected.

Thursday: Local MVFR conditions possible in showers, especially north, otherwise VFR conditions expected.

Friday: Local MVFR conditions possible in showers, especially north, otherwise VFR conditions expected.

MARINE

Onshore winds swing around northwesterly Monday morning as a front crosses the waters. Behind the front frequent wind gusts of 25-30 knots are expected with wave heights building to around 5 ft. Both diminish by the end of the day Tuesday, followed by high pressure settling over the waters.

Winds and seas generally expected to remain below SCA thresholds thru the extended. There may be a brief period of SCA conditions ahead of the next cold front Wed, but this is low confidence given the southwest wind direction.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory from 2 PM Monday to 5 PM EDT Tuesday for ANZ150>154.