textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes to overall forecast thinking. AFternoon showers were a bit more widespread than earlier anticipated with a few reports of small hail in the more robust showers. Conditions will rapidly deteriorate over the high terrain into the evening with increasing winds/falling temperatures.

KEY MESSAGES

1. Coldest air of the fall season so far arrives through tonight with blustery and chilly conditions expected through Tuesday night. Dangerous conditions are expected over the higher terrain through this period. Frost and freeze conditions will reach close to the coast Tuesday night.

2. A warming trend is expected for Wednesday and Thursday before another Canadian cold front pushes cooler air back into the region for the end of this week and coming weekend with the primary chance for precipitation taking the form of mountain showers.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

Potent cold front has pushed across the area with showers and even a few rumbles of thunder popping up along the international border. Some small hail has accompanied the more robust showers. T8s this morning off the 12Z GYX RAOB were +8C and will likely fall to around -4C by daybreak Tuesday...remaining near the freezing mark through the overnight Tuesday night. This CAA will drive temperatures into the 30s across most areas tonight...though we/ll remain coupled which should prevent frost over areas that still have an active growing season.

Speaking of wind...that will be the primary focus for Tuesday with H9 gradient winds 30-40kts. While mixing will remain strong through Tuesday...CAA will have ceased and there doesn/t look to be much isallobaric assistance to the low level winds. So...expect surface gusts to reach levels a bit under the H9 winds...generally 35-40mph. Therefore...have not added any wind headlines to the forecast this afternoon.

A chilly night will be in store Tuesday night as arriving high pressure ridge axis should allow surface winds to weaken and decouple in most places. All but our most coastal sites look likely to see a frost...with a hard freeze likely further inland where the growing season has already ended. Blended statistical guidance with the NBM which brings lows into the upper 20s in the mountains with lower-middle 30s elsewhere.

KEY MESSAGE 2 DESCRIPTION...

After brief shortwave ridging builds across the region Tuesday night...winds aloft will back to the southwest ahead of the next shortwave and associated cold front Wednesday and Thursday...which should pass through the region Thursday night. Thus...expect temperatures to warm quickly Wednesday and especially Thursday where T8s will push into the upper single digits C which...fully mixed will allow highs into the 70s south and east of the mountains. Shower chances with the cold front look largely confined to the mountains. T8s fall back towards 1-3C by Friday and into the weekend which will result in seasonable highs in the 50s and 60s from north to south. Bottom line...no high impact weather is expected across the forecast area during the Wednesday-this weekend period.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Summary: Strong northwest winds are expected with improving sky conditions as a cold front passes east of the region through tonight. Winds will weaken Tuesday night.

Restrictions: VFR conditions are expected to dominate the forecast through Tuesday night.

Winds: West-northwest winds 15G25KTS will continue through this evening...diminishing to 10G18KTS from the northwest tonight. Northwest winds 20G25-30KTS are expected for the day Tuesday before diminishing to less than 10kts Tuesday night.

LLWS: While northwest winds around 30kts are expected to continue through tonight at 2kft...the lower levels of the atmosphere look to remain well-mixed with no shear layers expected and therefore no LLWS in the TAFs.

Thunder: An isolated thunderstorm near HIE can/t completely be ruled out over the next few hours. No thunder beyond that through Tuesday night.

Outlook: For Wednesday through this weekend...outside some possible showers late Thursday/Thursday night and again Friday night in the mountains/HIE...expect VFR conditions to dominate the period. Expect breezy conditions from the west and southwest Wednesday shifting northwest for Thursday-Friday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...Small Craft Advisory until 8 PM EDT Tuesday for ANZ150>154.