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FXUS61 KGYX 090401 AFDGYX

Area Forecast Discussion National Weather Service Gray ME 1101 PM EST Fri Dec 8 2023

SYNOPSIS
High pressure gradually moves east of the region through tomorrow, bringing moderating temperatures and increased moisture into New England. A significant storm strengthens as it approaches on Sunday, moving through New England Sunday night and Monday with damaging winds, flooding rainfall, and some snow all possible. Cooler and drier conditions arrive for the middle of next week as high pressure returns.

NEAR TERM /OVERNIGHT/
1100 PM Update... Another round of updates using latest observational trends for skies and temperatures/dew points. A broken mid-level deck is traversing the area along the warm front moving SW to NE, and is complicating overnight temperatures a bit but overall lows will still land in the 20s toward the SW... and the teens to single digits through the north and in Maine.

652 PM Update... Other than re- running the diurnal trend overnight, while keeping the low temperature itself intact, very little to report at this hour with the forecast well on track.
Temperatures are cooling through the 20s with some locations already seeing teens, mostly in the north. High cirrus remains the predominant cloud type however low clouds associated with a warm front are forecast to fill in across the interior through the morning hours.

Previously... High clouds gradually filter into New England tonight and thicken, as lower clouds on the northwest side of the Whites dissipate. A weak warm front moves through during the overnight, with an isolated sprinkle or freezing rain sprinkle possible late tonight across far northeastern areas. Chances for this increase moreso tomorrow. Tonight's lows look to remain warmer than the last couple of night, with lows generally in the teens and 20s.

SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/
Temperatures continue to warm tomorrow on the backside of high pressure moving offshore. Temps generally warm into the 40s across most of the area. WAA continues to bring more moisture into the region, with scattered showers and some spotty mixed precipitation possible through the mountains and foothill late tomorrow and tomorrow night. Some spotty freezing drizzle is possible across northern areas as well late tomorrow and tomorrow night. While not expected to be widespread, with cold ground temperatures a few slick spots are possible by tomorrow night across northern locations and the higher terrain.

Across the forecast area, lows look to dip into the low to mid 30s under mainly cloudy skies. A few showers from the approaching storm system may start to work into far western New Hampshire by daybreak, but the bulk of any meaningful rainfall will hold off until the daytime Sunday.

LONG TERM /SUNDAY THROUGH FRIDAY/
Overview: Significant storm impacts the area to start the period. This will be followed by trofing and westerly flow. This will generally be drier but with upslope snow showers and cooler temps.

Impacts: Three primary hazards are in play with the Sun/Mon storm. Strong winds near the coast may lead to power outages.
Widespread moderate to heavy rainfall may lead to small stream and poor drainage flooding...potentially even mainstem rivers if enough snow melt occurs. Finally rain may change to snow fast enough on the backside of the system for a short duration but heavy/wet snow accumulation. This could also add to power outage concerns.

Forecast Details: Significant cool season storm to affect the forecast area Sun night into Mon. Multiple headlines have been issued to cover various hazards thru the event.

Strong forecasts for low pressure have led to strong forcing for ascent and resulting QPF has gone up today. Mean forecasts are now comfortably around 1
5 inches
with higher totals where the strongest forcing and upslope is located. So a flood watch has been issued. See the Hydrology section below for more details on that threat.

Coincident with the flooding threat is the threat of strong winds. Model guidance has really ramped up LLJ forecasts today and continue to hold serve. NBM mean gusts are quite robust at this range...but entirely supported by deterministic and ensemble guidance. I tried not to go too overboard with this update...and allow some room to adjust up or down as necessary.
However...NAM and GFS forecast winds at 925 mb approaching 80 even 90 or 95 kt is on the extreme end of model climatology.
Taking half of that wind to the surface is easily wind advisory criteria...and I felt there is more than enough reason for a high wind watch given 50 percent confidence level. If models continue to forecast these kinds of low level winds...an increase in forecast gusts is reasonable to expect.

Finally there is the threat from a rapidly cooling column as low pressure deepens. On the northwest side of the system temps will cool enough to flip rain to snow. In fact forecast soundings show potential to flash over to heavy snow at the changeover.
Even if this window only lasts an hour or two...a quickly 2 to 4 inches is possible. North of the notches 6 or more inches remains a possibility
While the column will be cooling
it will also be near isothermal around freezing as snow starts. So a wet sticky snow is possible...and additional power outages that are not wind related could result. There is more time to iron out that snow forecast however...as the change over will not come until mid morning Mon or later.

Focus of the extended was nearly entirely on the storm Sun into Mon...so the longer range portion of the forecast is composed of the national blend
Westerly winds
cooler temps...and mtn snow showers prevail.

AVIATION /04Z SATURDAY THROUGH WEDNESDAY/
Short Term...Mainly VFR conditions continue through tomorrow morning, with MVFR ceilings becoming VFR at HIE this evening.
Ceilings then lower to MVFR tomorrow, and then MVFR to IFR at most terminals tomorrow night.

Long Term
Conditions will deteriorate quickly Sun
with widespread IFR or lower conditions expected by Sun night. Rain may be heavy at times reducing visibility to IFR or lower as well. Sun night into Mon morning will also feature a period of LLWS as the strongest LLJ winds move overhead. This will primarily affect the coast...as over the interior winds will be weaker aloft behind the cold/occluded front. Rain may change to snow on the backside and bring a short window of LIFR conditions to LEB and HIE before drying out. VFR returns quickly behind the cold front...except for HIE where MVFR CIGs are likely and scattered SHSN possible.

MARINE
Short Term...Fair conditions prevail across the waters through tomorrow night as high pressure moves east of the waters.

Long Term...The axis of strongest winds continues to wobble around for coastal areas...but confidence is growing that the core of the LLJ will affect the coastal waters. A storm watch has replaced the gale watch...as forecast winds may be quite strong for a period Mon morning. In addition I opted for the higher WNA wave guidance...with seas building to near 20 ft north of Port Clyde by Mon morning. Winds and seas will gradually diminish thru midweek...as westerly winds behind the system will remain gusty.

HYDROLOGY
Flood watch in effect for Sunday night through Monday evening, with continued river rises thereafter. The warm temperatures and more notably high dewpoints around 50F will combined with blustery/strong winds to decimate the snowpack from the foothills southward. The accompanying heavy rainfall will combine with snowmelt to cause rapid rises on area streams and rivers. Contrarily, the snow in the higher terrain is cold and dry which supports less snowmelt. The headwaters are still likely to experience flooding just from the 1 to 3 inches of rainfall even with less snowmelt. The rainfall efficiency will be anomalous for this time of year, with the potential for an inch to fall in 6 hours early Monday. The ground conditions are in a variable state of frozen/partially frozen/and near- saturated, which in essence means there will be limited percolation and more rapid runoff. Concerns are present for overland flash flooding during this period, which will also support rapid flooding of small streams and rivers. The mainstem rivers will swell with flooding likely into Tuesday for some forecast points. Attention will be focused on where the axis of heaviest rainfall and interior penetration of the warm dewpoints materialize.

GYX WATCHES/WARNINGS/ADVISORIES
ME...Flood Watch from Sunday afternoon through Monday evening for MEZ007>009-012>014-018>028-033.
High Wind Watch from late Sunday night through Monday afternoon for MEZ019>028.
NH...Flood Watch from Sunday afternoon through Monday evening for NHZ001>015.
High Wind Watch from late Sunday night through Monday afternoon for NHZ014.
MARINE...Storm Watch from late Sunday night through Monday evening for ANZ150>154.

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Salmon Falls River entrance
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Fri -- 02:16 AM EST     Moonrise
Fri -- 02:47 AM EST     1.07 feet Low Tide
Fri -- 07:02 AM EST     Sunrise
Fri -- 08:49 AM EST     6.51 feet High Tide
Fri -- 01:29 PM EST     Moonset
Fri -- 03:23 PM EST     0.94 feet Low Tide
Fri -- 04:07 PM EST     Sunset
Fri -- 09:14 PM EST     6.10 feet High Tide
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Salmon Falls River entrance, Piscataqua River, New Hampshire, Tide feet

Squamscott River RR. Bridge
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Fri -- 02:17 AM EST     Moonrise
Fri -- 03:36 AM EST     1.07 feet Low Tide
Fri -- 07:02 AM EST     Sunrise
Fri -- 09:33 AM EST     6.51 feet High Tide
Fri -- 01:29 PM EST     Moonset
Fri -- 04:08 PM EST     Sunset
Fri -- 04:12 PM EST     0.94 feet Low Tide
Fri -- 09:58 PM EST     6.10 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Squamscott River RR. Bridge, New Hampshire, Tide feet

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