Area Forecast Discussion
Issued by NWS Portland, ME
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084FXUS61 KGYX 070757AFDGYXArea Forecast DiscussionNational Weather Service Gray ME357 AM EDT Wed Aug 7 2024.SYNOPSIS...-- Changed Discussion --
A weak area of low pressure will track off the southernNew England coastline this morning, with showers coming to anend across southern Maine and southern New Hampshire. Highpressure then builds in and brings dry conditions the rest oftoday and through Thursday. Another frontal system and tropicalmoisture will bring a wet pattern Friday into the upcomingweekend.-- End Changed Discussion --
&&.NEAR TERM /TODAY/...-- Changed Discussion --
The 500mb wave responsible for the area of ongoing steady light tooccasionally moderate soaking rain across southern ME and farSW Maine will quickly shift off to the east his morning. Thiswill allow drier air and subsidence to work in from the northand west, which will gradually end precipitation across theseareas. CAMs are in pretty good agreement with most if not allprecip ending by 8-9AM, except maybe holding on a little laterin the morning across far southern NH.Looking at private weather stations across southern NH, lookslike amounts since midnight have been generally in the 0.50" to0.75" range with some closer to the MA border in the 0.75" to1.00" range. Amounts drop off pretty quickly with northwardextent. Combining this with what fell last evening, the totalhigher amounts in southern NH look to end up being mostly inthe 0.75"-1.25" range, which shows the Probability Matched Meanfrom the HREF yesterday was pretty spot on.For the rest of the day, the drier air will steadily decrease cloudcover from north to south with most being partly-mostly sunny thisafternoon. Highs temperatures will be in the lower to mid 70s.-- End Changed Discussion --
&&.SHORT TERM /TONIGHT THROUGH THURSDAY/...-- Changed Discussion --
High pressure settles overhead tonight, providing light windsand mostly clear skies for good radiational cooling. This willprovide the coolest night for many areas in quite some time withmost seeing low-mid 50s south of the mountains and a few upper40s in normally cooler areas. Across the north, low temperaturesare forecast to be in the mid 40s. Patchy fog is likely todevelop tonight across southern areas that see rain today, andthen valley fog is possible elsewhere.On Thursday, the high pressure shifts to the east over Nova Scotiabut the airmass will remain dry enough to keep skies mostly-partlysunny. High temperatures will be mostly in the 70s, and withdewpoints remaining in the 50s, it`ll feel pretty comfortable out.Later in the day, the stationary boundary to our south will startlifting back north, which will gradually increase moisture fromsouth to north to a provide slight increase in clouds by lateafternoon or early evening. There may even be enough for a fewshowers across southern NH toward sunset, but chances only look tobe around 20%.-- End Changed Discussion --
&&.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...-- Changed Discussion --
The extended period starts quiet but turns unsettled for Friday andSaturday as the remnants of Tropical Cyclone Debby movenortheast. Behind this system an overall cyclonic flow willpromote scattered showers into early next week.In the dallies: By Friday morning Debby will still be locatedwell south of the region over the SE US. Tropical moisture willstart to surge to the north along and north of a frontalboundary that extends from Debby to southern New England. Expectthis initial surge of moisture to result in rain developingduring the day on Friday. The initial surge of rain shouldaffect all areas of the region. Once this moves by, anothersurge of rain is expected to develop as the remnants of Debbiemoves to the northeast. There is much uncertainty as to wherethe heaviest axis of rain will setup with the operationalversions of the Canadian Global being the furthest south and theECMWF furthest north. The GFS is in between these two models.This far out is too early to dial in on where this will actuallysetup. Looking at the ensembles of each also reflects the aboveoutlined model differences. The 12z NAM appears to favor atrack closer to the ECMWF.Regardless of what scenario verifies the bulk of the rain will endovernight Saturday leaving Sunday as the drier of the weekend days.Most of the area should be rain free although some upslope scatteredshowers are possible over the mountains. Aloft an upper level lowwill move over the area late Sunday into early next week. This willcontinue the chances of showers, best chances over the mountains andnorth.Bottom line is the biggest potential hazards from the remnants ofDebby will be rainfall and potential flooding. We do notanticipate strong winds with this system at this time.Additionally tides are running near astronomical minimums,therefore the coastal flood potential is low as well.-- End Changed Discussion --
&&.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...-- Changed Discussion --
Short Term...An area of light to occasionally moderate rain willcontinue bring flight restrictions to southern NH and and southwestMaine this morning. MVFR ceilings (possibly IFR occasionally) arepossible at MHT, CON, and PSM, but maybe PWM and RKD as well.Visibility restrictions to MVFR from -RA or -SHRA expected to belimited to MHT at PSM. Other restrictions may occur at HIE and LEBdue to fog. Rain ends this morning, but MVFR ceilings may last forsouthern NH into early afternoon. VFR then expected at all sitestonight and Thursday other than the possibility of late night/earlymorning valley fog.Long Term...VFR conditions Thursday night to give way to areasof IFR in developing rain on Friday. Areas of rain Friday nightand Saturday associated with the remnants of tropical stormDebby will affect the area with IFR conditions possible. Theexact location of the heavier rain is still uncertain althoughit currently looks to favor the northern and western parts ofthe region. Areas of fog may develop Friday Night.-- End Changed Discussion --
&&.MARINE...-- Changed Discussion --
Short Term...Conditions remain below SCA levels. Winds graduallybecome E/SE by this afternoon and then return to N/NE tonight ashigh pressure becomes centered across northern ME. The high shiftsto the east on Thursday with winds again becoming E to SE in theafternoon.Long Term...Wind and waves below SCA levels Thursday night intoFriday. The remnants of tropical storm Debby will result inwaves and swell to increase to SCA levels late Friday Nightthrough Saturday and into Sunday. Winds will increase tomarginal SCA levels during this timeframe as well.-- End Changed Discussion --
&&.HYDROLOGY...-- Changed Discussion --
WPC continues a Slight Risk ERO for flash flooding in the Day 3(Friday into Friday night) and a Marginal Risk Day 4 (Saturdayinto Saturday night) highlighting some tropical moisture fromDebby lifting into New England late week. A frontal boundarynorth of the remnant storm will be a focus for heavy rainfallover the Northeast, regardless of the ultimate track of Debbyremnant circulation. However, the timing and location of thisfrontal boundary has very low confidence. Precipitation amountsare likewise very low confidence along with any specificimpacts. Nonetheless, a wet pattern is likely to set up Fridaythrough Saturday. This will continue to be closely monitored.-- End Changed Discussion --
&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...None.NH...None.MARINE...None.&&$$NEAR TERM...CombsSHORT TERM...CombsLONG TERM...Lulofs
