National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, ME

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-- Discussion containing changed information from previous version are highlighted. --504FXUS61 KGYX 072254 AAAAFDGYXArea Forecast Discussion...UPDATEDNational Weather Service Gray ME654 PM EDT Wed Aug 7 2024.SYNOPSIS...High pressure builds in tonight and brings dry conditionsthrough Thursday. Another frontal system and tropical moisturewill bring heavy rain and a localized flood threat Friday intoSaturday. An unsettled weather pattern looks to continue throughat least mid-week as upper level troughs swing through theregion.&&.NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
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Update...Minor changes to reflect latest observational trends.Previous discussion...Visible satellite imagery this afternoonshows a diurnally driven cu field over Northern New England withcirrus skirting across extreme southern NH in association witha sfc trough located over southern New England. Currenttemperatures are into the lower to middle 70s with a few spotsnear 80 degrees. Temperatures will remain nearly steady throughthe remainder of the afternoon before cooling this evening. Itwill otherwise continue to be a pleasant late Summer afternoonand evening.Sfc high pressure will build over the region tonight, allowingfor large scale subsidence. This combined with mainly clearskies, light winds, and low dew points will set the stage forgood radiational cooling conditions. As a result, used MOSguidance for overnight lows, which brings the northern valleysinto the lower to middle 40s with upper 40s and lower 50selsewhere. Valley fog is likely to develop overnight as well.
-- End Changed Discussion --&&.SHORT TERM /7 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...Sfc high pressure will crest over the region tomorrow, allowingfor another pleasant day with dry conditions persisting. Hightemperatures will be a little warmer than today across theinterior with widespread readings into the upper 70s to near 80degrees while developing onshore flow keeps the coast a littlecooler. Diurnally driven cu is likely to develop through the daydue to the cool pool aloft but overall partly sunny skies can beexpected.High pressure will begin to exit to our east on Thursday nightahead of a sfc warm front to our south. Increasing WAA aloftwill result in increasing cloudiness through the night alongwith an increasing chance for scattered showers overnight. Theadded cloud cover and moisture will limit low temperatures tothe upper 50s and lower 60s.&&.LONG TERM /FRIDAY THROUGH WEDNESDAY/...Overview: The remnants of Tropical Storm Debby will be ridingan Atlantic ridge into the Northeast where it will interact withan upper low and upper level jet situated over the Great LakesRegion. This setup would bring a threat for heavy rainfall andlocalized flooding to our area. The extended remains active asthe Atlantic ridge breaks down and troughing moves overheadthrough at least mid week.Impacts:* Tropical moisture interacting with a front will bring a risk of heavy rainfall and localized flooding Friday into Saturday.* Strong wind gusts may create hazardous beach and sea conditions Saturday.Details: The focus of the extended forecast period will be theremnants of Tropical Storm Debby and where the greatest risk forimpacts due to heavy rain will be. The trend in the globalmodels has been to keep the ridge Debby is riding, amplifiedenough to where the axis of high rainfall amounts stays to ourwest. However, this does not mean we would be out of the woodsas global models are in good agreement that PWATs will beapproaching 2.25". So expect a widespread soaking rainfallacross the area, and with these storms in an environment primedfor very efficient rainfall, localized centers of higher amountswould not be out of the question. For more details see thehydrology section below. As usual with systems of this naturethere is still plenty of uncertainty even on Day 3 so thesetrends will have to continue to be watched very closely. If weare in fact going to be more on the eastern side of the storm,wind may become more of a focal point as well, but for now itlooks like the strongest winds will remain over the ocean andthe immediate coast. Lastly, the system is looking moreprogressive so the time window of concern has shifted to Fridaynight through Saturday morning, with the bulk of the rainpotentially being done by early Saturday afternoon. With someheight rises behind the system, skies could be trending clearerfor Saturday night with low temperatures in the low 60s south ofthe mountains, and mid to upper 50s to the north.Unsettled weather will continue through the remainder of theextended forecast period as an upper level trough looks toapproach on Sunday night. The global models also hint at asecond trough mid week with variations in timing. Have kept withNBMs low chance PoPs as this messages the uncertainty in showerpotential and coverage well at this time range.&&.AVIATION /00Z THURSDAY THROUGH MONDAY/...Short Term...VFR conditions will dominate tonight throughThursday evening. The exception will be at valley TAF sitesincluding KHIE, KLEB, and KCON where valley fog is likely todevelop after 06Z tonight and persist through around 12ZThursday, resulting in IFR to LIFR restrictions. Winds will belight and variable tonight before becoming southeasterly at10-15 kts on Thursday afternoon. Ceilings will then graduallylower on Thursday night with scattered SHRA possible, especiallyafter 04Z Friday. No LLWS is expected.Long Term...Friday will start VFR, but as the day goes on andceilings lower we will start to see more MVFR. Friday night intoSaturday morning will be a mixed bag of MVFR and lower ceilingsas heavy rain showers traverse the area. Isolated thunderstormsare possible during this time as well. Ceilings return to VFRlater in the day Saturday and prevail through Monday. Southerlywinds could be gusting 20-25 kts Friday night into Saturday.&&.MARINE...Short Term...Winds and seas to remain below thresholds hazardousto small crafts as high pressure settles over the waters.Long Term...Winds and waves will be rising above SCA criteriabeginning Friday night. Sustained winds Friday night intoSaturday look to be 15-20 kts with gusts 25-30kts. Winds will besoutherly through the day Saturday, shifting westerly by Sundaymorning. Winds calm below SCA criteria Saturday night, but seaswon`t come down until Sunday night.&&.HYDROLOGY...WPC continues a slight risk for flash flooding in the Day 3 EROhighlighting some tropical moisture from Debby lifting into NewEngland late week through Saturday morning. A frontal boundarynorth of the remnant storm will be a focus for heavy rainfallover the Northeast, regardless of the ultimate track of Debby`sremnant circulation. However, the timing and location of thisfrontal boundary is still somewhat uncertain. Widespread soakingrainfall is still expected, but with the track shiftingwestward it makes the flash flood threat more localized to areasthat see repeated rounds of heavy showers. This will continueto be closely monitored.&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...None.NH...None.MARINE...None.&&$$NEAR TERM...Legro