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. --103FXUS61 KGYX 060125 AABAFDGYXArea Forecast Discussion...UPDATEDNational Weather Service Gray ME925 PM EDT Mon Aug 5 2024.SYNOPSIS...A cold front will cross the region tonight, bringing chancesfor showers and thunderstorms, some of which could producelocally heavy rainfall, damaging winds and large hail. A weakarea of low pressure will track off the southern New Englandcoastline on Tuesday and Wednesday, potentially bringingscattered showers to southern Maine and New Hampshire while highpressure allows for dry conditions for northern areas. Anotherfrontal system will bring scattered showers to the region latein the week as tropical activity lingers near the East Coast.&&.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Update...With the loss of surface based instability the threatfor severe weather has decreased as well. Isolated to scatteredthunderstorms will continue as the frontal boundary slowlyshifts south thru the forecast area overnight.Previous discussion...The first round of convection well aheadof a cold front will continue to cross through the forecast areathe rest of this afternoon. For late this afternoon and thisevening, the latest HRRR continues to depict showers andthunderstorms ahead of and associated with the passage of a coldfront. Despite surface dew points and PWATS lower today, someof the storms still have the capability of producing very heavyrainfall and flash flooding. As dynamics increase through thisevening, the threat for damaging winds will also increase. Asheight falls begin, the possibility for large hail exists aswell as an isolated tornado.Latest mesoscale models continues to indicate the precipitationtapering off after midnight and shift off the coastline and intothe Gulf of Maine. Although drier air will be entering theregion, patchy fog will develop once again, especially in areasthat receive heavy rainfall.Overnight lows will be much more comfortable than the lastseveral with readings in the 50s north to the 60s south. Windswill be light but switch to the northwest.
-- End Changed Discussion --&&.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...Clouds will continue Tuesday and moreso Tuesday night as thefrontal system becomes stalled south of our forecast area.Models suggest a weak wave may ride up the front Tuesday nightwhich will increase the chance for showers over southern areasof Maine and New Hampshire. A few of these showers may be heavyas there will be a sharp gradient in moisture from south tonorth.It will be much cooler during this period with slightly belownormal temperatures which has been a rare case this summer. Wethen shift towards the long range portion of the forecast astropical moisture potentially moves towards northern NewEngland.&&.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...-----------------------------------------------------------------Summary:*Generally cooler, more seasonable temperatures are expected duringthe second half of this week.*Remnants of TC Debbie could move into NH and ME towards the end of the week, with flooding and heavy rain possible early on this weekend. For more information, see `HYDROLOGY` section.*Unsettled weather remains in the forecast after the passage of Debby`s remnants.------------------------------------------------------------------Discussion:A brief shortwave trough passes through the region onWednesday, bringing less humid and more seasonable temperatures intothe northeast. Zonal upper-level flow should allow these moreseasonable temperatures to last through the end of the week.Otherwise, Wednesday and Thursday should be tranquil days withpartly cloudy skies.A large plume of moist air from the south arrives on Friday,bringing increasing clouds and humid conditions. A system associatedwith the remnants of Debby may impact the region, bringingnotable rainfall this weekend. Despite the connection to atropical storm, we are not forecasting strong winds or othertropical-related hazards. Flooding is the main concerning factorwith this weekend`s system.For more details, please see the Hydrology Discussion near thebottom of this AFD.&&.AVIATION /01Z TUESDAY THROUGH SATURDAY/...Short Term...A cold front will bring another round of showersand storms through the region for late afternoon and throughportions of the evening hours. Strong to severe storms arepossible, and TEMPO IFR (possibly LIFR) are likely for manyterminals. Most storms should push east of the area by 04Ztonight, but there may be lingering showers across southernareas through the night. Even though some drier air will beworking in behind the front, expect there to be some fog and lowstratus once again, especially in and around areas that receiveheavy rainfall. VFR expected Tuesday with a few showerspossible across, mainly south of a PWM-LEB line. Showers maybecome more widespread with lowered ceilings Tuesday night,especially over southern areas.Long Term...Some MVFR is possible at MHT and PSM Wednesday morning due toscattered showers, otherwise sites should stay VFR through Fridaymorning before restrictions lower as thunderstorms move intonorthern New England.&&.MARINE...Short Term...SCA conditions are not expected, but south to southwestwinds will become northwest behind a cold front. This frontwill also bring increasing potential for strong to potentiallysevere thunderstorms to push offshore this evening. A fewshowers may linger a bit past midnight tonight, but then windswill turn out of the northwest tonight into early Tuesday. Windsthe return to onshore Tuesday afternoon.Long Term...2-3 foot seas with light and variable winds less than 10kts expectedfrom Wednesday morning through early Friday morning. A storm systemmoves in on Friday, with strengthening winds and seas from the eastexpected during the day on Friday. Seas increase to 2-4 feet by theend of the day Friday. Seas are expected to be elevated this weekendand SCA issuance over the weekend is likely.&&.HYDROLOGY...TONIGHT...Scattered showers and thunderstorms later today willgenerate locally heavy rainfall between 1-3, returning anisolated risk for flash flooding. The airmass as a whole haslost some moisture so rainfall rates would be 1-1.5/hr versusthe 2-3/hr from yesterday, however the repeat nature of somestorms could reintroduce some flash flooding. Areas of concerncontinue to be those hit hard in recent days and where soilabsorption will be slower. Drier air will filter into the regionmidweek allowing for a drying out period ahead of heavy rainpotential late week.THIS WEEKEND...WPC has expanded a slight risk for flashflooding in the Day 5 ERO highlighting some tropical moisturefrom Debby lifting into New England late week. A frontalboundary north of the remnant storm will be a focus for heavyrainfall over the northeast, regardless of the ultimate track ofDebby remnant circulation. However, the timing and location ofthis frontal boundary has very low confidence. Precipitationamounts are likewise very low confidence along with any specificimpacts. Nonetheless, a wet pattern is likely to set up Fri-Satwith a ridge offshore and an approaching trough from Canada inan airmass rich with tropical moisture increasing the risk forflash flooding and will be monitored closely.&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...None.NH...None.MARINE...None.&&$$NEAR TERM...Legro