381 FXUS61 KGYX 100800 AFDGYX Area Forecast Discussion National Weather Service Gray ME 400 AM EDT Wed Oct 10 2018 .SYNOPSIS... An unseasonably warm southerly flow will continue across the area today with many locations reaching the 80s. A backdoor cold front will drop south and west across the area late this afternoon and tonight which will usher in much cooler air in a short amount of time. Low pressure approaching from the west will bring a steady rain to the region Thursday. A cold front will sweep through the region Thursday night bringing an end to the rain. Another low pressure system may once again bring our area some rain early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High Impact Weather Potential: Localized dense fog early...with a slight chance of a thunderstorm along the elevated warm front today. Pattern: Early morning water vapor imagery shows impressive ridge centered off the US East Coast dominating the pattern east of the Mississippi /except for Hurricane Michael/ with just as impressive troughing along the west coast with two embedded shortwaves. Between these features...a deep southerly flow exists...with 1.5"+ PWATs /per blended TPW product/ streaming from the Gulf north and then east around the ridge. As the western flank of the ridge in our region builds north...the flow trajectory aloft has veered and is allowing the stationary boundary now across northern Maine to begin shifting south. This will be the feature to watch today as it separates cool continental polar air from the more maritime tropical airmass to the south. Primary forecast concerns center around temperature evolution as a sharp fall is likely behind this front. Beyond this...watching the potential for any convection to fire along this boundary. Through daybreak: Areas of fog continue...most widespread in southwestern NH...but with a few patches elsewhere. Otherwise... a few showers are impacting far northern parts of western Maine associated with warm front aloft. Very mild and humid out there...with temperatures and dewpoints largely remaining in the 60s through 6am. Today: Boundary over northern Maine will march steadily south and west...but before it arrives...temperatures will quickly move back to around where they were yesterday /upper 70s to lower 80s/ High resolution guidance shows a dramatic temperature drop with the boundary /perhaps 10-15F/ which will reach our Maine zones late this afternoon...and into NH during the evening. While a few warm-front related showers /isolated thunderstorms/ will continue to brush our far northern zones this morning...of potentially more interest is whether the boundary will kick off showers and possible thunderstorms as it moves south and west. Mesoscale guidance /including the HREF mean/ suggests that this with perhaps 500-1000 J/kg of SBCAPE to work with. If a storm or two does develop...gusty winds are certainly possible...with the greatest threat for this occurring over western Maine where the front will arrive while sufficient instability remains. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... High Impact Weather Potential: Locally heavy rainfall possible Thursday. Tonight: Backdoor cold front finishes moving through the region this evening as a cold air damming pattern sets up ahead of cold front approaching from the west. Warm front aloft will actually begin lifting north...so there won/t be a significant amount of forcing for showers...except perhaps over northern Franklin and central Somerset counties. To the south...expect we/ll see a good deal of fog and drizzle given the shallow cool airmass and increasing moisture aloft. Temperatures will fall 10-15 degrees compared to the night previous...with lower 40s over the western Maine mountains...with upper 40s to mid 50s expected elsewhere. Thursday: Low pressure just north of Sault Ste. Marie will track north and east to a position just south of James Bay by evening. Warm front aloft will be north and east of the forecast area with impressive 1.5-2" PWAT air /+4-5 sigma/ pushing into the region from the west ahead of approaching cold front. Forcing associated with the front is not impressive with best mid level QG forcing and upper level jet dynamics still well to our west. Still...with such a moist airmass...even modest lift should have no trouble producing widespread rain through the day with local downpours possible given the deep warm cloud depths and available moisture. With llevel front south and west of the CWA and not really moving too far north before the front arrives...temperatures will be much cooler...with upper 40s to upper 50s from north to south over western Maine and 50s to 60s from north to south over New Hampshire. At this time...while locally heavy rainfall is possible...do not foresee significant hydro issues. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The long term period will start out with a cold front or occlusion moving across the forecast area. A rainy/drizzly and perhaps foggy Thursday evening and early overnight will improve as the front moves through. Thereafter, the 00z deterministic models as well as latest ensemble information are in basic agreement that typical fall weather is in the cards the cool temperatures throughout the period. The next weather maker looks fairly weak as a fairly moisture- starved short wave trough moves through late Friday into Saturday. This is the short wave trough responsible for whisking Michael well south of our region Friday so that we'll have minimal if any effects. The main effect of the trough will be an increase in clouds Friday night and Saturday. However, some ensemble members are more robust than others with showery weather Saturday. Therefore we may have to increase PoPs as time goes on depending on trends. Fair weather is expected to resume Saturday night and Sunday with short wave ridging moving in. The next weather maker potentially comes Monday/Tuesday with fair agreement in the model/ensemble suite that a more moisture-rich low pressure system will pass close or overhead. This could mean another chilly rain event. However, we have plenty of time to watch ensemble trends. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Short Term /through Thursday/... Summary: High pressure will give way to a southwestward dropping back door cold front this afternoon and evening with a vigorous cold front approaching from the west on Thursday bringing widespread rainfall to the region. Restrictions: Some fog impacting LEB /and soon HIE/ will continue through daybreak before burning off with VFR conditions dominating today. Backdoor cold front will march south and west this afternoon and evening...with conditions deteriorating to LIFR/IFR behind it /due to CIGS/ with restrictions likely to continue through the night and Thursday as rain arrives from the west in association with an approaching cold front. Winds: Westerly winds light to around 5kts will continue through daybreak before strengthening to 5-10kts during the morning. By afternoon...back door cold front will quickly shift winds to the northeast as it marches south and west...with winds initially reaching 10g18kts before settling back down to around 10kts by evening. Winds become light/variable through the day Thursday. LLWS: 1-1.5kft westerly winds around 30kts will allow for LLWS through early morning before shear layer mixes out. Next round of LLWS is likely during the day Thursday as winds strengthen aloft. Lightning: Very low chance of an isolated thunderstorm today for AUG/RKD. Long Term...IFR conditions are expected for much of Thursday night as rain/fog/drizzle are expected with a moist northeasterly wind. However, rapid improvement is foreseen late Thu night and Friday as a front sweeps offshore and turns the winds westerly. VFR conditions are therefore expected Friday into early Saturday. MVFR conditions in showers are possible Saturday afternoon in rain showers. && .MARINE... Short Term /through Thursday/...Cancelled ongoing SCA with winds/seas diminishing...but hoisted another one for all but Casco Bay starting late this afternoon as northeasterly winds strengthen behind backdoor cold front. Winds at the time of frontal passage may gust to 25kts with an abrupt shift to northeast. Long Term...Small craft conditions will be possible late in the day Friday and Friday night as Michael moves well to the south of Nantucket and colder air filters in from Canada. The main effect would be northerly gusts around 25 kt and seas possibly reaching 5 ft. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 5 PM this afternoon to 5 PM EDT Thursday for ANZ150>152-154. && $$ NEAR TERM...Arnott SHORT TERM...Arnott LONG TERM...Ekster