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. --357FXUS61 KGYX 292342AFDGYXArea Forecast DiscussionNational Weather Service Gray ME742 PM EDT Sat Jun 29 2024.SYNOPSIS...A warm front will bring a period of rain with a few embeddedthunderstorms to the region tonight before a potent cold frontarrives Sunday afternoon bringing the potential for strong tosevere thunderstorms. High pressure arrives early next weekwith dry weather and seasonable temperatures expected for thefirst half of next week.&&.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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730 PM Update...Little change to the going forecast for theevening as as back edge to steadiest rainfall moving out.However, convective showers and islolated thunderstormnscurrently over Upstate NY will likely move ino western zones ina few hours. Otherwise, cloudy and breezy.High Impact Weather Potential: A few downpours are possibleovernight as well as an isolated thunderstorm though the threatfor widespread flooding and severe weather is low.Pattern: Early afternoon water vapor imagery shows a potentshortwave dropping through the western Great Lakes with a plumeof mid level moisture pushing into the northeastern UnitedStates. Beneath this plume...a warm front is slowly advancingthrough NY/PA with a broad region of light to moderate rain fueledby increasing moisture and a 50kt southwesterly LLJ. Forecastconcerns for tonight center on rainfall potential as the surfacewarm front lifts through the region.Through this evening: Rain is overspreading the region from west toeast and this will continue through the evening hours with cloudslowering. SE NH may escape meaningful rainfall through 8pm...butelsewhere conditions will turn wet. Temperatures won/t really movemuch...largely sitting in the 60s across the area.Tonight: Warm front lifts north and east through the region tonightwith 2" PWAT plume overhead this evening gradually shifting east ofthe area by daybreak Sunday. While isentropic ascent up the frontalsurface in the presence of some weak elevated instability will besufficient to support rainfall...broader scale forcing appearsrather lackluster through the overnight with +DPVA mostlybrushing the international boarder with some weak height fallsoverhead and some jet entrance support. Overall this suggestsoccasional showers through the overnight...with the greatestthreat for a few downpours being over the mountains where thesynoptic scale forcing is best. From a hazard perspective...thethreat for flooding appears rather low...but nonzero given thedeep moisture/warm cloud depths. A mild night is in store givencontinued warm air advection with lows falling into the mid 50sin the mountains with 60s to the south.
-- End Changed Discussion --&&.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...High Impact Weather Potential: * Slight Risk of Severe Thunderstorms * Primary threat: Damaging Wind * Secondary threats: Localized flooding...hail and an isolated tornado * Timing: 12pm-7pmPattern: Low pressure north of northern New England will movenorth and east during the day with a cold front over western NewYork as a positively-tilted shortwave and region of mid levelheight falls pushes just north of the region through the day.Our forecast focus will be on severe convective potential as thesurface cold front crosses the area Sunday afternoon. Alsowatching heat indices across southern NH which may make a run atadvisory thresholds ahead of the front.Sunday: Shortwave rotating through the positively-tilted longwavetrough races just north of the region through the day with 70kt H5speed max moving overhead in tandem with right entrance region to120kt upper level jet. Should see some sun in the morning as wemove into the warm sector ahead of the cold front butconvection may already be ongoing across western NewYork...strengthening as downstream instability strengthens. Byearly afternoon convection will likely reach the mountains of NHas well as the CT Valley with the mesoscale guidance favoringthe potential for one line of storms closer to the beset midlevel forcing moving from northern NH ESE through the Capitolregion of ME with another line moving across southern NH wherethe best instability will be located and will be downstream ofthe most likely location for morning convection.Here/s a run through the convective parameters....Instability: Sizable disparity in the guidance here with theNAM nest and the HRRR in their typical wetter/driercamps...respectively. Looking at upstream llevel moisture...acompromise is likely best which favors 1500 J/kg of MLCAPE insoutheast of the mountains as surface dewpoints push just above70.Shear: 40kts in the 0-3km layer with 60kts in the 0-6km layer.Hodographs are fairly straight and parallel to the approachingfrontal boundary. Expect initial cells to grow into lines withbowing segments likely given ample 0-3km shear. Within these bowswould be the best potential for a spin up.Lapse rates: Decent in the H8-7 layer, but weaker /around 6C/ in theH7-5 layer. Sufficient to support deep convection through theafternoon.Overall...this lines up well with the SPC outlook for damaging windsposing our greatest severe weather risk with hail and an isolatedtornado lesser...but non-zero threats.T8s pushing to +18C should allow highs to reach near the 90F markgiven sufficient sun. This...in addition to dewpoints moving above70 will allow a few spots in southern NH/SW ME to approach heatadvisory levels...but not high enough or long enough to warrant anyheadline issuance today.Sunday Night: With the surface cold front near the coast to beginthe period...expect any convection to quickly be exiting the regionwith mesoscale guidance suggesting a few showers along a secondarytrough/cold front that crosses the region overnight. Best potentialfor these overnight will be in the mountains with at least partialclearing elsewhere. Cold air advection will push T8s back into theupper single digits by daybreak Monday with lows to fall into the50s in the mountains and lower 60s elsewhere.&&.LONG TERM /MONDAY THROUGH SATURDAY/...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 jeststream to our N, so we can expect some rounds of SHRA/TSRA, butno significant widespread events.However, on Monday we will start off less warm, but still notout of ordinary summer temp ranges. There is a littleconvergence in central and S NH as NE flow runs into a bot ofdead flow over S New England, so will see more clouds here, andmaybe a couple showers Monday afternoon, but I think this areaIs still partly sunny, with mostly sunny skies to the N and E.Highs will mostly be in the 70s.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 Tue night into early Thursday, but expect clearingskies 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 /00Z SUNDAY THROUGH THURSDAY/...Short Term...Summary: Deteriorating conditions expected through tonight as a warmfront crosses the region with showers and a few embeddedthunderstorms. Showers end Sunday morning...with another round ofshowers and strong to severe thunderstorms in the afternoon beforepartial clearing Sunday night.Restrictions: MVFR CIGS are building across the terminals thisafternoon as showers arrive from the west. Expect deterioration toIFR or low MVFR this evening and overnight with low CIGS andsome fog development. Improvement to VFR is expected on Sundaymorning with showers/thunderstorms bringing additionalrestrictions in the afternoon. Some fog development is possibleHIE/LEB Sunday night with restrictions possible here.Winds: Southerly winds 10kts will continue through tonight beforeshifting southwest and increasing to 12g18kts for the day Sunday.Winds turn northwest less than 10kts behind the cold front Sundaynight.LLWS: Southwesterly winds in the 1.5-2kft layer strengthen to 40-50kts with LLWS expected overnight tonight. This will end Sundaymorning with no additional LLWS through Sunday night.Lightning: Very isolated thunderstorms are possible for theovernight. On Sunday...chances for thunderstorms increase for theafternoon with the potential for thunder throughout the terminals inthe 18Z-00Z timeframe. Some of these storms could be strong tosevere with damaging winds. No lightning is expected Sundaynight.Long Term...VFR expected Monday through Wed, with possiblevalley fog Monday night. Then more widespread flightrestrictions possible Wed night into early Thu in SHRA/TSRA andsome fog.&&.MARINE...Short Term...SCA conditions due to both winds and waves areexpected to continue through Sunday 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.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 Sunday for ANZ150>154.&&$$SYNOPSIS...NEAR TERM...Arnott/EksterSHORT TERM...CempaLONG TERM...CempaAVIATION...MARINE...