Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 150022 AFDGYX Area Forecast Discussion National Weather Service Gray ME 822 PM EDT Sat Apr 14 2018 .SYNOPSIS... A back door cold front will push south to the southern New England overnight. Areas of light wintry precipitation will persist through the weekend along the boundary. Low pressure will develop to our SW and track across New England Monday into Monday night, bring warmer air,m but also heavy rain. Unsettled weather continues into the mid to late week, as upper level low pressure remains nearby. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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8pm update...Have expanded the winter weather advisories. Radar CC, KGYX sounding, and vertically pointing radar all show a temperature profile supporting freezing rain, and icy roads have been reported through portions of NH. As the depth of the cold layer increases, it`s still possible to see a switch back over to sleet and precipitation amounts are expected to be light. However with temperatures supporting freezing rain have opted to play it conservative as even a small amount of QPF falling as freezing rain will create dangerous travel conditions. For the expansion will just run through 9am to highlight the threat for morning travel. 6pm update... Have expanded the region of higher Pops right up through our eastern border for the next few hours. Current radar trends suggest a fairly robust precip band along the edge of the front as it begins to sag south and expect a bit of accumulation as far east as Kennebec county in the next hour or so. Have gotten a few reports of IP from HIE area, and CC on radar would also confirm the upper CT river valley seeing some mixing while Maine and northern/eastern NH will rapidly go over to all snow. Prev disc... Cold air continues to surge SWwd behind backdoor cold front...and that downward temp tend is maintained thru the overnight period. Already starting to see some light/showery...WAA precip working into Nrn zones. With surface temps below freezing for much of those zones...freezing rain and sleet are dominating ptype. That will continue N of the mtns tonight...with rain S until temps can tick down below freezing. Overall though I am not expecting significant QPF overnight...as the strongest forcing for ascent remains well to our W. With general light WAA precip expected...any snow or ice amounts will also be light. As front continues to sag SWwd and focus of precip moves in that direction too...wintry precip will move into SWrn NH as well. Despite light precip amounts...the very late nature of this wintry storm and some forecast ice has prompted me to issue a winter wx advisory for overnight and into Sun. This may need to be expanded based on precip coverage and surface temps.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... A very anomalous cold air mass will remain in place Sun. Model guidance continues to indicate low level standardized anomalies around -2 to -3...with mid level temps also hedging on the below normal side. By the time you reach H7 temps actually are forecast to be near to slightly above normal. As mentioned in previous discussions...this sets up nicely for a sleet sounding...with deep low level cold beneath the warmth well aloft. It will be interesting to see what develops...as the forecast soundings aloft argue for widespread sleet. However low level cold is quite impressive for this time of year...with forecast readings around -10 C for the lowest temp in the cold layer. This could support some snowfall is the lift is generate from those low levels...like orographic lift. Something to keep an eye on. Precip should be focused along the mid level front across Srn zones...with the far NErn zones possibly even seeing some sunshine thru the clouds Sun afternoon. Temps will be coldest where there are clouds and precip...and warmer as you head NE and clouds thin. With high temps threatening to stay below freezing during the day...some records may also be broken at out climate locations. Sun night as low pressure approaches from the W...LLJ will begin to help force an expanding precip shield over the area. Precip intensity will increase and if temps can remain below freezing wintry precip types will begin to accumulate at greater rates. This is the most likely period when winter wx advisories may need to be expanded. && .LONG TERM /MONDAY THROUGH SATURDAY/... The 500 MB pattern continues to moderately amplified pattern across NOAM, with several waves or closed lows moving through during the next week. Given the more detailed nature of the systems, have not tried to get too fancy with timing, and there are a lot of periods with chc pops in the extended. Probably not all will see precip. Still no signs of warming, either, other than what a higher sun angle and longer days can do. Monday will see the a triple point sfc low developing into our west, which track NE across New England late Monday into Mon night. This produce some moderate to heavy rainfall across the CWA. Monday, especially the morning, remains questionable as to how quickly the cold air will be displaced by the warmer with increasing E-SE flow. Probably areas of SE NH and the ME coast will be warm enough that the day starts as rain, but most other inland areas could see a period of FZRA/PL. This will probably not last long in srn NH, but will probably affect the morning commute. Further inland and to the N and E, the warm will gradually move in but may take much of the morning in interior central ME, and the freezing precip could last into afternoon in parts of the ME mtns. QPF is mostly in the 1-2" rain for Mon into Mon night, which could cause some river problems /see below/. Winds will be gusty, but not extremely so, generally gusting to 25-30 kts at times during the day Monday. Highs Monday will like be late in the day or even Monday evening, and temps should warm into the 40s across all but the far NE zones, where they may stuck in the upper 30s. Temps will fall off a little Mon night, but should stay above freezing almost everywhere. The 500 mb low will slowly cross the region Tue and Wed, and this will keep lots of clouds and the threat of showers in the forecast. Highs will be in the 40s again on Tue, but warm up a few degrees for Wed, reaching into the low to 50s on the ME coastal plain and in srn NH. Another closed low shifts in from the west Thu, and could bring another round of precip, mostly rain late in the week, but timing right now is difficult as it interacts with the departing closed and may wobble around a bit. Highs will likely remain about 5 F below normal, generally in the mid 40s to mid 50s. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Short Term...Areas of MVFR beginning to develop as warm front aloft remains draped over the area. A fairly deep...well-mixed boundary layer should limit the widespread IFR or lower...but I do expect there will be some pockets in the heaviest precip. N of the front VFR conditions are possible. Will also have to watch mixed precip. PL is most likely given the deep low level cold...but FZRA is possible across Srn NH terminals especially. Confidence is very low in ptype...so no AWW for MHT has not been issued yet. Stronger WAA develops later Sun into Sun night...more widespread IFR is likely to develop then. Also late Sun developing LLJ may bring some LLWS to much of the area. Long Term...Will likely see persistent IFR or lower Monday into Monday night at all terminals, with some PL/FZRA at inland terminals Mon morning. Also could see some E-SE winds gusting to around 25 kt during the day on Monday. Will see some improvement on Tues, but may just MVFR, with SHRA possible as well. Should see some VFR by Wed, but some tempo restrictions in SHRA are possible. && .MARINE... Short Term...SCA conditions will continue behind the backdoor cold front thru Sun. As low pressure approaches from the W...strong ESE flow will develop aloft and some gale force gusts are possible late Sun night. Long Term...Gale watch issued for Monday into Mon evening. Pretty strong E-SE flow develops as low pressure track to the west of the waters. SCA will probably needed Tue into Tue into Tue night. && .HYDROLOGY... Locally heavy rainfall is expected Monday afternoon and Monday night, with many areas seeing 1-2 inches. Southeast facing higher terrain could see up to 3 inches. This, combined with snow melt, will enhance the flooding potential. SWE values are currently in the 8 to 9 inch range over our northern mountains. && .TIDES/COASTAL FLOODING... NWS, NERACOOS, and USGS Wave Runup Models indicating the possibility of beach erosion and splash-over for both Monday and Monday night`s high tides. Nearshore wave heights will top out around 15 feet on Monday with wave periods of around 9 seconds. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory until 9 AM EDT Sunday for MEZ018-023. NH...Winter Weather Advisory until 9 AM EDT Sunday for NHZ004-006- 009-010-012>014. Winter Weather Advisory until 8 PM EDT Sunday for NHZ003-005- 007-008-011-015. MARINE...Gale Watch from Monday morning through Monday evening for ANZ150>154. Small Craft Advisory until 6 AM EDT Sunday for ANZ151-153. Small Craft Advisory until 6 PM EDT Sunday for ANZ150-152-154.
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&& $$ SYNOPSIS... NEAR TERM...Curtis SHORT TERM...Legro LONG TERM...Cempa AVIATION...Cempa/Legro MARINE...Cempa/Legro HYDROLOGY... TIDES/COASTAL FLOODING...

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