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. --965FXUS61 KGYX 301727AFDGYXArea Forecast DiscussionNational Weather Service Gray ME127 PM EDT Sun Jun 30 2024.SYNOPSIS...A cold front then crosses the area this afternoon bringingscattered strong to severe thunderstorms. Cooler and drier airarrives tonight followed by a short wave crossing southern NewEngland bringing slight chances for showers. High pressurebuilds in Monday night through mid week for fair weather. Thenext frontal system crosses New England sometime Wednesday nightthrough Thursday.&&.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Noon Update...Severe thunderstorm watch in effect through 8 PM. Anactive day is anticipated especially this afternoon and earlythis evening with with concerns for strong to severe storms. Awarm front has brought warm, humid, and unstable airmass (MLCAPEover 2000 j/kg) over the region. Heat inidices in the Merrimackvalley are nearing the low/mid 90s, but increasing showeractivity and clouds should help alleviate the heat later thisafternoon, and could help limit the severe extent. The triggerfor storms will be an upper level trough pushing a cold frontacross the area later this afternoon. The shear is the mostimpressive part of this set-up with 40kt of effective shear,with the most limiting factor being poor midlevel lapse rates.Note:GYX will do a 17Z sounding to try and capture anymodification in the midlevels that could effect our afternoonsvr potential.Looking at mainly discrete cells at the onset in the north along andahead of the cold front. The shear will highest in this region,however lesser instability may inhibit their organization earlythis afternoon. Concerned as they sink southward there will bethe potential a midlevel mesocyclone and for betterorganization and severe potential including the possibility of abowing line segments and strong downbursts. Dew points are highthis afternoon with heavy rainfall in any storms, but theprogressive nature of the storms will limit the risk forflooding.Previously...Latest water vapor imagery shows a positively tilted trough overeaster North America with an embedded short wave crossing intoQuebec and a secondary embedded wave crossing the northern GreatLakes. The leading short wave has spawned a surface low over SECanada that will track towards the Canadian Maritimes with theattendant warm front lifting northeast of Maine this morning. Thesecondary short wave will dive southeastward sending a mid levelspeed max towards the International Border around mid day withmodest height falls occuring later this afternoon and evening. Allthe while, a cold front drops southeastward through the areaproviding a trigger for convection. The severe threat window startsaround 2 PM as storm cross into northern NH and NW Maine andpersists until 7 PM as storms reach the coast.A review of the last three runs of the HREF shows that the projectedconvective parameter space has remained similar over the past24 hours. This has resulted in no significant changes inforecast thinking for the threat of severe storms this afternoonand evening. The HREF mean MU CAPE builds to 1500-2000 J/kgamidst a corridor of deep layer shear of 40-50 kts by earlyafternoon. Hodographs remain fairly straight with little turningof winds in the low levels, while CAMs do highlight an area ofenhanced SRH across central and Downeast Maine. Convective modelooks to be primarily broken line segments making damaging windsthe primary threat. The latest RAP does show 0-3 km shearapproaching 35-40 kts across northern NH into central Maine andwill have to watch the orientation of these shear vectorsagainst line segments for the potential of QLCS spin ups. Midlevel lapse rates remain unimpressive while the magnitude ofdeep layer shear will be sufficient for a supercells that willbe capable of large hail. Another variable to watch will becloud cover as skies will be mostly cloudy to start today. The00Z HREF suggests there will be breaks in the cloud cover overthe interior by mid morning while clouds may persist longeracross southern NH and coastal Maine. Dewpoints are forecast toclimb near 70F so solar heating will play a role in whetherconvective coverage can over/under achieve. SPC maintains aSlight Risk across much of the area driven by 15 percent windprobabilities followed by 5 percent hail, and a 2 percenttornado.Highs today will climb into the mid to upper 80s south of themountains and away from the immediate coast. These temperaturescombined with dewpoints near 70F will bring heat indices into thelow to mid 90s while falling short of Heat Advisory criteria. Highsin the north and along the Mid Coast will be in the 70s.
-- End Changed Discussion --&&.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...Convection will be pushing offshore this evening with the coldfront while the secondary short wave lags over Upstate NY. Thiswave will maintain chances of showers in the mountains throughthe first part of tonight. Drier air working into the regionwill eventually lead to drying trend across the region by daybreak with lows dropping into the 50s north to low 60s acrossthe south.The lagging short wave crosses southern New England Mondaybringing chances for showers across central and southern NewHampshire. Otherwise, there will be a mix of sun and clouds withtemperatures rising into the 70s with comfortable humiditylevels as dewpoints will be in the 50s.&&.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...At 500 MB across NOAM and environs we still a pattern thatgradually favors warmer and more humid conditions, althoughnothing that I would call hot through next week. We will nearthe boundary of the sub-tropical over the Atlantic and the jetstream to our N, so we can expect some rounds of SHRA/TSRA, butno significant widespread events.Monday night will be the coolest of the stretch with clearingskies and light winds. Expect lows in the upper 40s in some mtnspots and generally low to mid 50s elsewhere. Tuesday looksmainly sunny and dry with low humidity, as high pressure crossesthe region, and highs 80-85, but cooler along the mid-coast.Flow shifts SW as the sfc high shifts offshore, and theresultant return flow will bring in more humid conditions.Wednesday looks mainly dry though, but with partly sunny skiesand highs 80-85 once again.A weakening cold front moves in from the NW Wed night, andloses its steam over the CWA, so some SHRA and maybe some TSRAare possible Wednesday night into early Thursday, but expectclearing skies and warm and humid conditions on Thursday.Weak high pressure moves in for Friday, so its be dry, butstill warm and humid. Next weekend remains uncertain as we sitbeneath weakly anticyclonic flow and troughing to our W, whichthe means the potential waves and rounds of convection, but itshould stay on the warm and humid side.&&.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Short Term...A cold front crosses the region this afternoonbringing broken lines of strong to severe thunderstorms.Highest confidence for TS at terminals are MHT, RKD, and AUG.Drier air moving into the region Sunday night favors VFRconditions into Monday.Long Term...VFR expected Monday night through Wed, withpossible valley fog Monday night. Then more widespread flightrestrictions possible Wed night into early Thu in SHRA/TSRA andsome fog.
-- End Changed Discussion --&&.MARINE...Short Term...SCA conditions due to both winds and waves areexpected to continue through today ahead of an approaching coldfront. Winds shift slowly shift northwesterly and diminishSunday night...though residual SCA waves will likely persistthrough the first half of the night. Winds and seas will be SCAthresholds on Monday.Long Term...Generally light flow is expected through the middleof the week with winds and seas staying below SCA levels, but itcould pick up some Wed night or Thu.&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...None.NH...None.MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ150>154.&&$$SYNOPSIS...NEAR TERM...SchroeterSHORT TERM...SchroeterLONG TERM...CempaAVIATION...MARINE...