Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 140246 AFDGYX Area Forecast Discussion National Weather Service Gray ME 946 PM EST Mon Nov 13 2017 .SYNOPSIS... A weak area of low pressure will continue to focus precipitation across New Hampshire and western Maine through this evening. While the coast and southern New Hampshire are warm enough to see rain...farther inland is looking a lot like winter. That snow will continue into the evening...with very light accumulations...before gradually tapering off from the northwest. Cool high pressure builds in from the northwest Tuesday and Wednesday. A cold front will move into New England from the west on Thursday...bringing a chance of precipitation and a return to cold temperatures. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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940 pm Update: Precipitation has moved offshore except for a small area of very light snow/rain over extreme southeast NH and southwest coastal ME. The last of any low level precipitation should dry up in the next few hours. Input mesonet data. Only minor tweaks needed to POPs based on latest radar amd satellite imagery trends. 715 pm Update: Light snow continues across southern interior areas of Maine while the coastal areas continue as light rain or a mix. Accumulations of 1-2 inches have been observed over interior portions of York...Cumberland...and Sagadahoc counties in Maine, so a minor increase in snow accumulations from 510 pm update were made. Radar shows back edge of precipitation now pulling east and should be exiting the region by later this evening. Have made adjustments to POPs based on radar data and extrapolating the area further east this evening. 510 pm Update: Quick update to increase POPs/QPF and add accumulations of an inch or so of snow over southwest interior portions early this evening. Bands of light to moderate snow over the southwest interior should move east in the next hour or so. Along coastal areas ptype still rain so no accumulations expected. Temps also adjusted down slightly based on current obs. Previous Discussion: S/wv trof is crossing the Northeast at this time...and helping focus an inverted trof at the surface. The low level trof is running more or less N/S from just W of MVY to near IZG. Convergence within the feature will keep precip steady and heaviest along this line...as it pivots slowly NW/SE...before gradually drifting out to sea this evening. Until that time temps hovering in the low to mid 30s...and dewpoints just now creeping up towards 30...will allow for the majority of this precip to be snow. Some light rain will mix in across Srn NH and near the coast...and an occasional burst of sleet is possible when precip intensity lightens up across the interior too. But with sun beginning to get low in the sky...temps will begin to tick down and allow for some minor accumulations. Still not expecting much more than a half inch at most...but very near the trof axis with a little elevation in SErn NH or SWrn ME could make a run at an inch. Precip will gradually erode from the NW as Wly flow and drier air move into the region. I expect precip will end across most of the area between 00z-03z. With the approach of the next trof and plenty of lingering low level moisture...clouds should remain prevalent tonight and low temps on the milder side.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Surface ridging will build into the region...beneath another upper trof approaching from the W. The high pressure will keep the boundary layer cool and dry...while the approaching trof will help to pool upper level moisture and cloud cover. So I do not expect much sun Tue...at least until trof passes late in the day. But dry low levels and limited moisture aloft should keep any precip at bay. If we can clear the clouds out Tue night...we could see temps radiate well with high pressure in the vicinity. So we will have to monitor just how quickly the mid and upper levels dry out late Tue. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... The deterministic models are in decent agreement on the long wave pattern through late in the upcoming weekend. We begin the period with an exiting shortwave impulse and a low amplitude flow with the mean jet position over the northern tier of the CONUS. A shortwave ridge provides a cool but dry day across the area. With an upstream shortwave impulse over the northern plains racing east into New England on Thursday...with an associated cold front to sweep across the forecast area with rain and snow showers. Shortwave ridging follows for Friday along with more cool but dry weather. Digging shortwave energy that enters the Pacific northwest on Thursday will carve out a deep trough over the central CONUS by the start of the upcoming weekend. At the surface...deepening low pressure will cross the Great Lakes and into eastern Canada. The trailing cold front will sweep into New England on Saturday with a secondary low developing Saturday night before the baroclinic zone races offshore early Sunday. We`ll see a strong onshore flow Saturday night ahead of the front with strong gusty winds possible along the coast as well as over the higher terrain. We`re likely to see mainly rain on the front side of this system with some upslope snow showers in the cyclonic flow Sunday and Monday. The mean jet position will be to our south this period which will result in temperatures averaging below normal. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Short Term...Precip is beginning to focus in the inverted trof and will continue to do so thru the evening. Occasional bursts of heavier precip will bring TEMPO IFR...especially across the interior. Drying from the NW will gradually bring an end to precip...though MVFR CIGs may linger...especially across Srn NH tonight. CIGs lift Tue and Tue night...with VFR conditions expected. Long Term... Thu...Areas of MVFR in -shra and MTN -shra/-shsn. Sat...MVFR with lcl IFR in rain and fog. SE sfc wind gusting up to 30 kt psb at coastal TAF sites. && .MARINE... Short Term...NE flow over the waters will bring conditions outside the bays to just below SCA thresholds this evening. However high pressure beginning to nose in is expected to keep winds and seas below 25 kts and 5 ft. Long Term... Thu...Small craft conditions are likely bays with gales possible on the open waters. Fri...Small craft conditions are likely. Sat PM - Sun AM...Gales are possible all waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Marine

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