Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 271112 AFDGYX Area Forecast Discussion National Weather Service Gray ME 712 AM EDT Wed Mar 27 2024 .SYNOPSIS... A front will approach from the west today bringing increasing chances for rain late Wednesday through Thursday before exiting on Friday. Steadiest and heaviest rains are expected on Thursday night, along with significant snowpack ripening or, in the case of the coastal plain and adjacent interior, significant snowpack melt. Precipitation may end as snow Friday before things become drier and gusty over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Update...Showers have largely passed east of the forecast area for the time being. I have added drizzle to the forecast thru mid morning. After that point additional showers will likely move into the forecast area from the west. Otherwise little change to the previous forecast. Previous discussion...S/WV trof is lifting thru the eastern Great Lakes this morning...and is responsible for forcing some showers moving thru parts of NH currently. To the east flow remains onshore and occasional showers or drizzle continues in that flow. To simplify the weather grids I have left wording showery...as it will be damp either way. With the trof driving into Quebec...the cold front will get left behind and stall over the region. That will keep the threat of showers and drizzle going thru the day today. It will also make it difficult to scour out the cooler surface air...and I have kept interior areas closer to a cold air dam for high temps.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Little movement in temps is expected tonight as the pattern remains fairly well entrenched. Lows will be well above normal for this time of year. Similar to today there will be the chance for both showers and drizzle...but I will keep the wording simplified with showers. Very late tonight precip character will start to trend more towards steady rain as WAA increases northeast of a developing low pressure off the Carolinas. That low will track north along the stalled front and cross the Gulf of ME Fri. The best forcing for ascent is still modeled near the coast...and so the highest PoP and QPF remains there in the forecast. With the mild air mass ptype is predominately rain for all except the highest of high peaks. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Overview: A trough digs into the region to start the extended period. It looks to phase with low pressure forming off the coast of the Carolinas and stay overhead through much of the weekend. This will keep the pattern unsettled, but high pressure forming to the north may keep precipitation at bay. Impacts: 1-2 inches of rain combined with snowmelt may lead to flood concerns Thursday night into Friday, particularly in coastal areas. Details: Rainfall continues Thursday night as a front remains stalled over the area. Most all models have recently come on board with a progressive solution, suggesting the front gets moving overnight just in time to push the low pressure system that will be moving up the coast far enough offshore to keep the heaviest rainfall out to sea. However, we will still be dealing with a very moisture rich airmass with PWAT values 0.75 to 1 inch through the event. The latest available GEFS and ECMWF ensembles suggest the coast could see 1-1.5 inches of rainfall and the 00Z NAM likes amounts closer to 2-2.5 inches. Amounts drop as you move inland with less than an inch likely northeast of the mountains. Trends will continue to be closely monitored as these numbers will be highly dependent on this interaction between the front and the low. If the front doesn`t budge and the low is allowed to come further eastward these numbers will increase. It is also worth noting that we are 2 inches and change from having the wettest March on record in Portland. Precipitation will change to snow in the mountains heading into Friday and then comes to an end Friday night. Cold air advection looks to drop areas north of the mountains into the 20s while the foothills and areas south hover around or just above freezing. At the same time high pressure building over the southeastern U.S. looks to tighten the PGF which could lead to strong wind gusts overnight heading into Saturday morning. Saturday looks mostly dry, but low pressure offshore looks to retrograde to some degree which could bring some light precipitation to eastern zones. Otherwise, it looks to be a pleasant but breezy day with highs ranging from the upper 30s north to near 50 south. With mostly clear skies and a shortwave ridge beginning to build in, temperatures likely drop into the 20s just about everywhere. Sunday and Monday look dry as well as a shortwave ridge keeps forcing associated with a wave ejecting off the Mid-Atlantic coast well to our south. High pressure and a much more amplified ridge build into the region Tuesday out ahead of our next potentially significant system Tuesday night into Wedensday. There is much uncertainty in just about every aspect of this system so I won`t stray far from the NBM at this time range, but snow lovers will want to be rooting for the GFS as it has consistently been bringing us another block buster spring snow. Other models favor rain, but either way this time period will continue to be watched closely. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/... Short Term...Fairly widespread IFR and lower conditions across the area this morning...except for the far northern and western zones where low level moisture has struggled to cross the higher terrain. With little change in the overall pattern and flow...I anticipate IFR or lower conditions will continue for much of the area into Thu. TEMPO improvement is possible...mainly where heavier rainfall can mix the atmosphere into Thu...but it is expected to be short lived. Long Term...IFR/MVFR conditions likely hold on through Friday morning in most areas, but gradually improve from west to east through the evening and overnight hours as precipitation comes to an end and ceilings lift heading into Saturday. VFR looks to prevail through Sunday. Gusty northwesterly winds may be upwards of 30-35 kts Friday into Saturday low pressure tracks close to the coast. && .MARINE... Short Term...Large swell continues on the coastal waters with seas around 10 ft every 10 to 11 sec. Wave heights will gradually diminish thru Thu...but are expected to remain at or above 5 ft. I have extended the SCA thru midnight tonight...when it is possible that seas beyond the islands of Casco Bay fall below 5 ft. Long Term...SCA conditions are likely through the extended forecast period as a strong low pressure system tracks close to the coast Friday night and Saturday. Northwesterly winds to gale force are possible along with seas building to 5-7 ft. Conditions begin to diminish on Sunday. && .HYDROLOGY... The snowpack is likely to melt out across the coastal plain this week as periods of light rain and showers fall across the area. River rises are expected, and some minor flood can`t be ruled out by late this week and into the weekend. Areas further inland and across the mountains can likely handle up to about 1.5" of rainfall, with most of this being absorbed by the snowpack. Beyond that amount, runoff will begin to increase and flooding would become a greater concern. The best chance for exceeding this rainfall would come from a system passing offshore on Friday. At this point the heaviest rainfall is forecast to remain offshore, but this will need to be monitored for any trends toward higher amounts, which would increase flood concerns. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ150- 152>154. && $$ NEAR TERM...Legro SHORT TERM...Legro LONG TERM...Baron

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