000 FXUS61 KGYX 280807 AFDGYX Area Forecast Discussion National Weather Service Gray ME 407 AM EDT Thu Mar 28 2024 .SYNOPSIS... A front stalls across New England today, bringing increasing chances for rain. The steadiest and heaviest rains come Thursday night as low pressure tracks northward offshore. This along with significant snowpack ripening or, in the case of the coastal plain and adjacent interior, significant snowpack melt will increase the threat for flooding. Precipitation ends as snow Friday, especially across the higher terrain, before things become drier and gusty over the weekend. A weak system passes through early Sunday, and then a more significant system is possible toward the middle of next week. && .NEAR TERM /TODAY/... Patchy fog continues this morning...mainly thanks to the colder snowpack in place. This is tending to keep the fog coming in waves as the warmer air pushes inland from the Gulf of ME. Fog has been occasionally dense in the Kennebec River Valley...but otherwise visibilities have been bouncing from around 1/2 mile to 4 or 5 miles. At this time dense fog does not appear to be widespread enough for an advisory. Rainfall beginning to move into the forecast area at this hour. A good soaking is expected...with HREF mean QPF around 2 inches for coastal areas thru the event. Today rainfall rates will generally be light to moderate...but consistent thru the afternoon. && .SHORT TERM /TONIGHT THROUGH FRIDAY/... This evening and overnight guidance suggests that rainfall rates will pick up and may become briefly heavy at times. This will be the most likely window for flooding impacts if they were to occur. No change in the flood watch...which covers this time period nicely. After priming much of the snowpack today an additional inch or so of rain overnight combined with the snow melt will start to push small stream water levels up. Hi-res guidance is also coming around to the idea of more robust forcing as low pressure moves into the Gulf of ME...throwing QPF a littler farther west early Fri before coming to an end. Rainfall is expected to quickly end from southwest to northeast however...as the cold front slips thru the forecast area finally. Gusty winds will develop late in the day as colder air moves into the region. This will also cool the column on the back edge of precip and some of that precip is expected to change from rain to snow. This is especially true in the higher elevations...though a period of freezing rain is possible there as well as colder air undercuts the mild air mass currently in place. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Overview: A negatively titled trough and deepening coastal low will sustain snow into Saturday, mainly in our eastern most zones. A weak wave then crosses Sunday with the bulk of the forcing missing us to the south, but New Hampshire may still get clipped with some light rain/snow showers. Some shortwave ridging builds for Monday and most of Tuesday before a potentially significant system approaches in the mid-week time frame. Impacts: *Slick travel is possible Friday night as snow exits the area. *Confidence is increasing, but still low, in a potentially significant system toward the middle of next week that may bring heavy rain or snow (or both). Details: Snow will be coming to an end overnight/early Saturday morning as low pressure continues its northward journey into the Canadian Maritimes. It deepens as it does so, and with high pressure nosing into the region this looks to create a very tight pressure gradient. Widespread wind gusts overnight Friday and Saturday may be in the 30-35 mph range with locally higher gusts in the mountain terrain. Low temperatures Friday night look to be in the 20s north of the mountains and low 30s to the south, but with elevated winds expect it to feel about 10 degrees colder. Abundant sunshine likely helps temperatures warm into the upper 30s and 40s Saturday. Winds will quickly diminish overnight Saturday as the low exits the region and the pressure gradient relaxes. Winds won't exactly be going calm overnight so would expect good mixing to continue and keep lows only a few degrees cooler than the night before. A shortwave trough passes overhead Sunday with a weak area of low pressure exiting off the Mid-Atlantic coast. This should keep the bulk of the forcing to our south, but some light snow and/or rain showers can't be ruled out during the day in New Hampshire. Ridging builds in overnight Sunday setting Monday up to be clear, dry and warm. Tuesday remains mostly dry as well, but the evening begins our window to watch for the possibility of another significant spring storm. The global models tell a similar story with a deep upper trough phasing with a strong coastal low, but unsurprisingly they differ on timing, precip type, and track. And it is not just each other they disagree with, significant run to run waffling amongst themselves has made it difficult to have confidence in anything more than "there looks like there will be some sort of a system in the neighborhood next week". We will continue to monitor trends as hopefully some details become clearer over the next few days. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... Short Term...Widespread IFR or lower conditions this morning. Much like yesterday some improvement in CIGs is possible during the daylight hours...but moreso LIFR to IFR with plenty of rainfall moving into the area. Likely not looking at significant improvement in flight categories until cold front moves thru the local area Fri. South of the mtns rapid improvement to VFR is forecast once winds go northwest...while upslope clouds keep MVFR CIGs to the northwest. Those northwest winds will increase...with surface gusts at or above 25 kt at times. Long Term...VFR should prevail for most areas by Friday night. RKD to AUG and points eastward will likely still see some MVFR/IFR overnight in lingering snow, but improve to VFR by daybreak Saturday. Winds Friday night and Saturday will be gusting from the northwest upwards of 30 kts for most areas. The next chance for any restrictions will come with a weak system passing through Sunday, but this should just be MVFR ceilings and light rain/snow showers mainly confined to southern terminals. Conditions improve back to VFR through Monday. && .MARINE... Short Term...Swell continues to diminish this morning...remaining around 5 ft thru the day. With long period nature I have cancelled the SCA...especially considering that winds are forecast to increase and become gusty behind the cold front Fri. A gale watch has been issued for the waters outside the bays thru the first part of Sat. Long Term...Northwesterly gales continue through the night Friday behind departing low pressure. SCA conditions gradually diminish through Saturday. By daybreak Sunday high pressure will be settling over the waters keeping winds and waves below SCA criteria through Monday. && .HYDROLOGY... A flood watch remains in effect for portions of southern NH and SW Maine. The primary impact will be small stream and river rises, and flooding along low water crossing and urban areas due to rain and snowmelt. A slow moving frontal boundary will sync up with a southern stream low pressure system to bring an extended period of rain to the area through Friday. Moderate rainfall will combine with warmer temperatures and high dewpoints for snowmelt, with losses of 1.25 to 1.75" from the existing snowpack, less in the headwaters. The snow condition will be a player in this event as snow in the mountains has a low density and is expected to hold, while the snowpack in the coastal watersheds are more ice than snow and will release fairly easily. There is a zone between the mountains and the coast where there is a mixed bag of snow conditions that will likely hold in some areas and melt out in others. This complicates the calculations on the cumulative runoff, adding uncertainty to the river forecasts particularly in the Lower Kennebec River. The latest forecasts show river rises across all watersheds, with isolated minor flood levels reached. The strength of the storm as it moves northward will determine the western extent of the heavier rainfall Thursday into Friday. The latest forecast track will keep the heaviest rainfall across central and eastern Maine, with the regional flood risk highest along the MidCoast and lower Kennebec River Valley with 1.5-2.5" of rain and 1.5" of snowmelt. Though there will be less rainfall, the cumulative rain/snow runoff could be sufficient for small stream and urban issues into southern NH and SW ME. A slight wobble in the track or longer duration of rain could easily result in more widespread impacts. Moderate river flooding is not expected at the time of this issuance, with probabilities less than 10%. Note: Many climate sites are in the top 5 wettest on record, with this late month event expected to approach all time records for Augusta and Portland. Portland's record 11.24" in 2010, Augusta's is 9.71" in 1953. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch from 11 AM EDT this morning through Friday evening for MEZ014-019>022-024>028. Flood Watch from 11 AM EDT this morning through Friday afternoon for MEZ018-023. NH...Flood Watch from 11 AM EDT this morning through Friday afternoon for NHZ008-010-012>015. MARINE...Gale Watch from Friday morning through Saturday morning for ANZ150-152-154. && $$ NEAR/SHORT TERM...Legro LONG TERM...Baron