Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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886 FXUS61 KGYX 110807 AFDGYX Area Forecast Discussion National Weather Service Gray ME 407 AM EDT Sat May 11 2024 .SYNOPSIS... A cool and unsettled pattern is expected through the weekend as a longwave trough gradually crosses the area. There will be chances for afternoon showers this weekend, with some lingering into the evening hours. Below average temperatures are expected, with a trend warmer into early week. A more widespread rain is likely Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The region remains between weather systems as low pressure passes well off the Atlantic coast today. NE flow will keep moist air in the low to mid levels, resulting in another chance for light showers this afternoon. These will build out of diurnal cu filling in across the CWA through the morning hours. Not much change in thinking on location, but did keep isolated PoPs in the area a bit longer into the evening. This is based on observations the past two nights of nocturnal showers continuing in NH, as well as HRRR/ARW depicting these ongoing amid some convergence. Highs today shouldn`t vary much from Friday, climbing into the mid to upper 50s. We are still under a similar airmass, and if it wern`t for the moisture from 800 to 900mb, it would be a very dry day. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Another challenging forecast tonight in regards to sky condition and thus overnight lows. While much of the initial clouds in the evening should fade w/ loss of daytime heating, clouds Fri night remained broken or overcast in many locations. Think tonight will be a similar story with little change in pattern. This means pockets that will remain warmer around 40, and other that may cool 10 degrees further due to radiational cooling. Current sky forecast depicts clouds thinning once again across much of southern ME and this time more of NH. Thus these spots will be scrutinized for their overnight lows. It`s reasonable to say that sheltered areas under these clearing calm skies will likely see patchy frost develop. With the Frost/Freeze program expanding across the interior today, should confidence and areal coverage fit, Frost headlines may be needed tonight. Sunday will offer another chance of diurnal showers spurred on by continued instability in the mid to low levels. Warm level aloft retreats by Sunday, giving a deeper mixing layer as well as the potential for slightly more CAPE. With some added convergence due to a passing wave to the south, this evening`s MPAS run does depict the chance for some showers to develop graupel across northern NH and far western ME. Would still like to see more MUCAPE above 100 j/kg however for this to be more likely. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... An upper level trough crosses New England late this weekend, with a welcome warming trend following its passage albeit with some rain (although not a washout). A more organized system brings better chances for more widespread rainfall around the middle of next week. Shortwave ridging moves in behind the departing upper level low Sunday night, with rain shower chances diminishing and some clearing. Overall it could be a good radiational cooling night depending on the timing and degree of clearing, with lows most likely near 40 but potentially down into the mid-30s in more ideal scenarios. With the growing season active everywhere but the mountain zones, will have to keep an eye on trends in case a frost/freeze headline may be necessary. High pressure slides offshore to the east on Monday with flow turning more zonal aloft. Meanwhile upstream, another upper level trough will be spinning across northern Ontario into Quebec. Ridging should initially suppress precipitation chances, but it is short- lived and transient so by the time we get into peak heating/mixing we`ll start seeing pressure falls and associated warm advection from the west. These will support high temperatures largely in the 60s, along with diurnal rain shower activity. With the offshore high, there ought to be a strong sea breeze that will limit temperatures along the coast. There is good model agreement by now WRT the aforementioned Canadian trough bringing a warm front across New England Monday night through Tuesday, followed by a cold front on Wednesday. This more organized system brings better potential for more widespread rain to the area though there`s still quite a bit of uncertainty WRT to QPF at this range. Though, the majority of ensemble members keep totals around 0.75" or less which doesn`t raise too many alarm bells for hydro, however PWATs will likely rise above 1.0 inch and SW flow parallel to the front gives some pause... so it`ll be another item to watch trends on. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Short Term...VFR. Some SHRA across interior terminals today, but these shouldn`t impact vis. Winds will also be light, with a wind shift possible at coastal terminals amid a afternoon seabreeze. Long Term...VFR prevails into Mon, except brief MVFR in SHRA possible over the interior and west. More widespread SHRA/RA and associated restrictions are likely to develop Tue into Wed, with VFR returning Wed into Thu. && .MARINE... Short Term...Below SCA conditions with winds generally less than 20 kt and waves 1 to 3 ft through Sunday. Lighter winds will tend to be variable, but in general onshore flow expected today before turning north overnight. A return to onshore is expected again Sunday. Long Term...Light flow and quiet seas are expected over the extended forecast period with SCA conditions unlikely to occur. In general, winds will turn out of the SW to start the next week however daily sea breezes and a nebulous pressure gradient will muddy this progression a bit. The best chance for 25+ kt winds, right now, comes around Tue with a more organized system potentially crossing the region which also brings potential for rain and fog. This system likely departs around Wednesday night with drier air filters in by Thursday, however the trough may cut off near the coast which will impact timing a bit. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Cornwell SHORT TERM...Cornwell LONG TERM...Casey