


Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --374 FXUS61 KGYX 250235 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1035 PM EDT Tue Jun 24 2025 .SYNOPSIS...-- Changed Discussion --It will be 5 to 10 degrees cooler Wednesday, but that will still be hot in places. The relief finally arrives Thursday in the form of a backdoor cold front. The cooler air will move in on northeast winds and bring temperatures back down into the 70s. However with the cooler weather will come higher chances for showers into the weekend.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...-- Changed Discussion --1025 PM Update...Cold front will sag southward into the forecast area tonight but for the most part it will remain dry and very warm/humid. We cannot rule out an isolated shower or thunderstorm but any would be few are far between. Also, some fog will be possible tonight, especially where it rained earlier in the day with storms. 630 PM Update...Have expanded the forecast for thunderstorms into southernmost ME and southeastern NH based on latest trends. However, these should not be long-lived as we lose heating. Previously... Impacts and Key Messages: * A few strong to severe storms capable of producing damaging winds may pop-up, mainly north of the mountains, in the wake of today`s very hot weather. An extremely hot day is well underway with heat indices in many locations south of the mountains reported at 105F to 108F. North of the mountains and the immediate midcoast and islands are reporting heat indices in the range of 90F to 100F. These will begin to come down as we head into the evening, especially in the northern zones as they will be the first to see influence from the approaching frontal boundary. With this being said, we have a robust cumulus field over the area and as forcing for ascent increases ahead of the front late afternoon/early evening, northern areas may see some of these become thunderstorms. Current SPC mesoanalysis is plotting 2500-3000 J/kg of CAPE with around 30 kts of Bulk Effective Shear which would suggest some organized convection. However, what is also present is plenty of very dry air which works in two ways with one of those being the potential to stunt convective development. This is present in the mixed layer mesoanalysis that is plotting 25 J/kg of CIN in most areas south of the mountains. For this reason I have maintained the bulk of PoPs and thunder chances confined to northern zones, with isolated coverage wording. The second way the dry air influences the convective threat is that this increases downburst wind potential with lapse rates over the area currently analyzed at 7-7.5 C/km. So, anything that does overcome the dry air could become strong to severe with the potential to produce damaging winds. Again, this seems like an isolated threat but it is worth watching and SPC has maintained a Marginal Severe Risk for our area. Tonight will feel sticky again south of the mountains with low temperatures and dew points expected to be in the 70s once again. North of the mountains should begin to see the influence of the front in the form of dewpoints dropping into the upper 50 and low 60s, and with low temperatures in the mid to upper 60s it should be a bit more bearable. Patchy valley fog is possible again tonight as well.-- End Changed Discussion --&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... Impacts and Key Messages: * No significant impacts expected Wednesday should feel more comfortable as drier air begins to work into the area from the north behind the front, dropping dewpoints into the 50s and 60s south of the mountains, and into the 40s to the north, before the day is out. It will still be hot tomorrow with temperatures in the upper 80s south of the mountains to low 90s in southern New Hampshire, but with the lower dewpoints it shouldn`t be as sticky and heat indices will remain close to the actual temperature. The only exception may be far southern New Hampshire where they will be the last to see the drier air resulting in dewpoints in the upper 60s into the afternoon. This may get those locations close to heat indices of 95F, but confidence is not high enough it would last the 2 hours that would necessitate a heat advisory as dewpoints will be dropping, so I will hold off. The falling 500 mb heights and forcing of the front in the area may also give far southern New Hampshire a brief shower and even a rumble of thunder before the drier air gets there. Overnight dewpoints drop into the 40s and low 50s, with temperatures in the mid to upper 50s south of the mountains and low 60s in far southern New Hampshire. North of the mountains will bottom out in the upper 40s, so overall a much more comfortable night area wide. && .LONG TERM /FRIDAY THROUGH TUESDAY/...-- Changed Discussion --Evening long term update...01z NBM has been incorporated into the latest forecast and yielded little change to the overall idea that cooler and wetter conditions will be the norm Friday and Saturday. However, locations of heavier precipitation are hard to pin down at this time as convection will likely be involved. Previously... Overview: High pressure resides to the north as moisture makes its way into the Great Lakes. Along with it, a reprieve from hot temperatures. As these features push east, the chance for showers increases across the southern forecast area into Friday. The highest rain chances look to fall Friday night into Saturday as low pressure pushes into Quebec. As this system exits, warming temperatures but drier conditions look to return. Details: The chance for showers pushes into the southern forecast area Thursday as high pressure approaches from the west. Deeper moisture, mostly residing through southern New England, will be producing showers near the MA/NH border Thursday. Of more confidence is greater cloud cover in vicinity of this moisture. While PoPs remain low with showers in a isolated to scattered nature during the day, the cloud cover should limit daytime highs to the 70s. Friday, low pressure rounds the Great Lakes and pushes into southern Ontario. Greater moisture advection will be ahead of this low, and thus increasing rain chances Friday into Saturday. What begins as showers Friday, will eventually become a steadier rain for Saturday morning. Greater IVT values push across the southern Great Lakes and into New England during this period, and increases the confidence of this steadier rainfall. This could last through Saturday morning before becoming more showery for the early afternoon. Daytime highs for Friday and Saturday may be some 30 degrees cooler than early week. Drier air behind the low pushes in for late weekend, allowing both lower rain chances but also increasing temperatures into early next week.-- End Changed Discussion --&& .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Short Term...VFR continues through Wednesday night for most terminals. Similar to last night the exceptions may be LEB and HIE where patchy valley fog could develop near the airport. I went with a persistence forecast that brings near IFR conditions to LEB and 6SM visibility to HIE. There is also a chance for a thunderstorm in the vicinity of HIE this evening, but confidence is not high enough to include in the TAF at this time. Long Term...VFR expected Thursday and Friday. SHRA begin across far southern terminals Thursday, with more coverage in the west expected through the day Friday. A period of lower ceilings will become more probable Friday night into Saturday as low pressure brings more widespread RA into the region. Improvement is expected by late Sat, but uncertainty in exact ceiling and restrictions. && .MARINE... Short Term...SCA conditions are not expected through Wednesday night. A cold front will cross the waters Wednesday morning which will briefly bring about northwesterly winds, before a seabreeze develops in the afternoon. Long Term...Conditions will largely fall below SCA for the period. High pressure to the north and east will keep much of the incoming moisture to the south Thursday, but succumb to westerly flow Friday through Saturday. This will bring low pressure into Quebec along with a period of rain. NE flow Sunday may result in increasing wave heights and therefore SCA conditions towards the end of the period. && .GYX WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --ME...None. NH...None. MARINE...None.-- End Changed Discussion --&& $$ SYNOPSIS... NEAR TERM...Baron/Ekster SHORT TERM...Baron LONG TERM...Cornwell/Ekster AVIATION... MARINE...