Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201740 AAC AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1240 PM EST Tue Feb 20 2018 .SYNOPSIS... A warm front will cross the region from south to north today. A cold front will cross the region late Wednesday, and stall south of the area Thursday. High pressure build in for Friday. A series of waves moves across the area this weekend with light rain or snow possible, although the most significant will move through Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 10am Update: Primary changes this hour are to continue to mention patchy dense fog for most areas outside of southeastern NH that has broken into the warm sector. Issued another SPS to highlight this fog potential. Otherwise...temperatures north of the front are running behind previous forecast and have lowered in line with recent high resolution consensus. 6am update: A few areas of dense fog now being reported as the sun rises. Have issued an SPS and updated to include Patchy dense fog for the next few hours. Overview: High pressure off to our east will continue to generate southwesterly flow pushing unseasonably warm air into the region through the next several days. Today:Band of light showers associated with a warm front will continue to life north through the area this morning. Temperatures have climbed to the freezing point across the entire region and so the remaining Winter Weather Advisory has been dropped with this forecast update. Temperatures will continue to warm throughout the day, reaching the 60s across southern New Hampshire. In Maine it will not warm up quite as much. Along the coast this is due to the flow coming off the cold ocean water. Interior Maine will also remain in the 40s as the current cold air will be slow to make it out of the region. While shower activity will lift northwards some clouds will remain for much of the day, especially along the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Overnight expect just a slight drop in temperatures as the overall warm advection continues. With dewpoints in the 40s moving over the snowpack fog will be widespread across the region, and dense fog is possible. Wednesday will be the warmest day of the week as the bulk of the warm air moves into the region. This anomalous air mass is forecast to reach near record levels. Daily records for our climate sites appear below. Have gone with high temps at daily record levels for all three locations, but stopped short of the all time February high temp records which are just a few degrees higher. These temperatures will certainly be a refreshing break from winter, and most locations have not seen 60F since early November. While confidence is high for these record temperatures across New Hampshire and interior western Maine, the midcoast is not going to be as warm and is a much lower confidence forecast. Our ocean temperatures continue to run near 40 degrees which will limit the high temperatures coastward of Rt 1 from Portland east. Despite the trend through the day towards a more westerly wind a slight sea breeze is likely to take hold keeping the immediate coast in onshore flow. Another consideration is sunshine. Forecast soundings for RKD continue to show a Marine layer remaining through the day. Without a break in the fog these locations may struggle to reach the upper 40s let along 50. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... A quick look at the 500 mb pattern across NOAM and vicinity shows some flattening of the strong wrn Atlantic ridge late this week, moving the more active part of the jet over the CWA late this week into the weekend. Temps will moderate back closer to normal, but should still trend on the warm side of normal. This active flow will also produce several waves, making for an unsettled period, with the chance of some rain or snow. This should mostly be light, but some areas could see several inches in wave that moves through on Sunday. For Wed night, front will be exiting the CWA during the evening, with temps dropping from their near record warm on Wednesday. A few showers may be possible in the evening over the north, but for the most part this front looks dry. Overnight lows will still be mild for late Feb, generally in the low to mid 20s N, to the low to mid 30s S. On Thu, the front briefly stalls to our south, as a weak wave moves along it, this will keep some clouds in the southern half of the CWA /with an outside chance of some showers/, and also prevent the core of colder air from moving south into the CWA. So, with W_NW winds downsloping will allow for highs in the low 40s in southern NH and the ME coast, with generally mid to upper 30s elsewhere. Sfc high builds over the nrn CWA Thu night into Fri, and the 500mb ridge nudges back to the N, so look for partly to mostly sunny skies with highs in the 30s to low 40s. The weekend will see two fast-moving wave move thru, the first will be Fri night, and the second Sunday into Sunday evening. The first wave look like it could bring some SHRA/SHSN to the region, although the best chance will be in the nrn zones, and any snow accums will be light. The second which will move in Sunday, looks a little bit more impressive, although still not strong, but could produce a period of snow to rain near the coast, and a few inches of snow in the north. Saturday will be mild with highs mostly in the 40s, although cooler near the intl border, and Sunday will see highs closer to normal generally in the 30s. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Short Term... Summary: Deep southwesterly flow will continue to transport moist air across the region through tonight and Wednesday before a cold front pushes through the region Wednesday evening. High pressure will build into the region Wednesday night. Restrictions: Highly variable conditions early this afternoon with fog/low clouds scattering out over southern NH...but showers/fog continuing at HIE-AUG. Expect a bit more improvement through mid afternoon...then deterioration this evening with widespread VLIFR/LIFR in fog/low stratus except perhaps at MHT. Expect more rapid improvement to VFR on Wednesday morning with VFR continuing through Wednesday Night. Winds: Light/variable winds /5-10kt southerlies LEB-MHT-CON-PSM/ remaining light overnight before becoming southwesterly around 10kts for the day on Wednesday...shifting northwesterly 5-10kts Wednesday night. LLWS: Southwesterly winds at 1-1.5kft will increase to around 40kts this evening...promoting LLWS through the night. Winds aloft will strengthen through the day Wednesday which may prolong the LLWS threat despite some morning mixing. Any LLWS will come to an end Wednesday night as the cold front pushes through the area. Long Term...Mainly VFR Wed night into Friday. Some MVFR to IFR may be possible Fri night in SHRA/SHSN.
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&& .MARINE... Short Term...A south to southwest flow will continue over the region through Wednesday. While winds have subsided, seas remain near 5ft on the outer waters and SCAs continue for this region. Long Term...A brief period of NW SCA level winds/seas possible Wed night, but otherwise winds and seas should stay below SCA levels into Saturday. && .HYDROLOGY... Have issued a flood watch for the potential for ice jam flooding. While total QPF amounts with these showers remain small the warm temperatures will begin to melt off the snowpack, and snowpack density analysis through the southern portion of the area supports the runoff. While the melt won`t be enough to cause flooding on its own, forecast hydrographs suggest the potential for enough rise to move ice. With several ice jams already in place the concern for ice jam flooding is increased and thus a flood watch has been issued for western New Hampshire where the combination of temperatures, QPF, and existing ice jams coexist. Further south in NH little snowpack and river ice remains while across Maine temperatures remain lower, especially through the headwaters and less runoff is expected so no flood watch is needed. && .CLIMATE... Record high temperatures are expected across the region on Wednesday. *** February 21 Records Temperatures*** Portland Concord Augusta 59F - 1953 64F - 1872 52F - 1981 ***Warmest February Temperatures*** Portland Concord Augusta 64F - Feb 26, 1957 69F - Feb 24, 2017 60F - Feb 18, 1981 && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...Flood Watch through Wednesday evening for NHZ001>003-005-007. MARINE...Small Craft Advisory until 5 PM EST this afternoon for ANZ150- 152-154. && $$ AVIATION...Arnott

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