Area Forecast Discussion
Issued by NWS Portland, ME

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740 FXUS61 KGYX 221317 AFDGYX Area Forecast Discussion National Weather Service Gray ME 817 AM EST Thu Feb 22 2018 .SYNOPSIS...
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Canadian high pressure builds south into the region today with cooler air although a weak weather system passing south of the region today may spread some light snow to southern areas before high pressure builds overhead tonight through early Friday. A series of weather systems will move through the region beginning late Friday and continuing through the weekend with mixture of precipitation. Fair weather returns for early next week.
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&& .NEAR TERM /TODAY/...
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815AM UPDATE... Precipitation already seen on regional radar entering southern New Hampshire. Have updated precipitation chances to reflect the increased confidence. Temperatures down there are in the mid to upper 30s, but dewpoints are mostly in the teens. This suggests that precipitation will fall as snow as temperatures cool when precipitation begin. Elsewhere expect daytime highs to be fairly close to current temperatures with temperatures holding steady or falling through the day as cold advection continues. 650AM UPDATE... Just a few tweaks to the forecast based on current obs, mainly to T/Td/Sky. Otherwise should see temps respond a bit to daylight jumping up a few degrees this morning, but the clouds and incoming precip this afternoon, will hold them steady or cause them to drop off some during the afternoon. Latest meso models support current forecast with light amounts of around an inch to an inch and half along the MA border, mainly west of MHT/ASH. And, highest accums will be on grassy and untreated surfaces. ORIGINAL DISCUSSION... Falling temps continue this early AM, and may see a little surge in temps this morning, but that will likely be it as clouds move in across most of the CWA this afternoon. Stalled cold front will sit over srn New England today, which will be spilling clouds northward as a weak wave moves along it this afternoon. This will bring some light precip into southern zones this afternoon as well. Steady precip is expected across the srn tier of NH counties along the MA border. This could start as a rain or a mix of snow and rain midday to early afternoon, but will likely become mainly snow as evap cooling lowers the BL and sfc temps into the low to mid 30s. Further north, into Sullivan/Merrimack/Strafford/York counties, could see some SHRASN as well this afternoon, and even a little north would not be surprised to see a couple SHRASN. Given the warm antecedent conditions, and the dry air in lower levels, any snow will have trouble accumulating, especially at onset. Think the best chance to see around inch or snow will be in Cheshire county and Hillsborough west of the Merrimack valley. Further east around MHT/ASH and eastward toward the coast, may see a coating in some spots.
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&& .SHORT TERM /TONIGHT AND FRIDAY/...
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For the most part, any precip should be ending by 6pm or so, and skies will clear during the evening as sfc high builds in from the west. Should see a period of decent radiational cooling as winds become light, especially in the mtns, where lows will drop into the single digits. Elsewhere, look for lows mostly in the 15-25 range. Friday will start off mainly sunny, but clouds will begin to increase from SW-NE during the midday, with OVC expected in the afternoon. Any precip looks to hold off until the afternoon, as two weak waves try to move thru 500 mb ridging aloft. Although weak sfc low does develop to our N late in the day. Dynamically, these are weak waves, but they do generate a broad area of WAA, so should see some precip moving eventually, but may not be until late. Will also see flow turn onshore out of the SE, so this will warm boundary enough across most of the coast for rain or a rain/snow mix, with temps here generally in the mid to upper 30s, not looking for much in accums, if anything, outside the mountains and foothills late in the day Friday. Could see a coating to half inch in the north. Best chance for wintry precip will be Friday night.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A developing fast moving west to southwest flow aloft Friday night will allow a weak short to move across northern New England with some very light mixed overrunning WAA precipitation. No accumulations of snow are expected with this system with possibly some very light icing in the mountains. The system quickly exits by Saturday morning as a weak short wave ridge builds over the area on downsloping northwest surface winds allowing skies to become mostly sunny over most areas. Temps on Saturday will be rather mild with highs in the 40s most areas and near 50 over southern NH and southwest ME. Sat night Canadian high pressure becomes centered north of Maine in the maritimes and allows cold air to drain south across the region. Models show this cold air damming setting up nicely by Sunday morning in advance of the next rapidly approaching WAA pattern that approaches from the southwest. Sunday will be a mixed PTYPE event with some light accumulations of snow over southern and central areas before a changeover to the mixed precipitation and eventually rain. Over the western mountains and foothills of Maine enough cold air may remain in place for more significant accumulations of snow to occur before any mix occurs. This system will also be a fast mover and will exit the area by later Sunday night. Early to midweek a more westerly drier flow aloft is expected so generally fair weather is forecast for the latter periods. Stayed close to model blend guidance for temps through the outlook period. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... Short Term...Mainly VFR today, with the exception of KMHT/KPSM, and maybe KCON, where will see MVFR or IFR restrictions in SN or a SNRA mix for several hours this afternoon. VFR expected into Friday morning, with some flight restrictions, likely MVFR, possible during the afternoon in SHRASN. Long Term...IFR to LIFR conditions possible Friday night in some mixed light precipitation then improving to VFR Saturday. Snow and mixed precipitation develops from S-N Sunday lowering conditions to IFR/LIFR. Some brief periods of freezing rain is also a possibility on Sunday. Conditions return to VFR by later Sunday night and continue through Monday. && .MARINE...
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Short Term...Northerly flow today decreases in intensity as high pressure moves into northern Maine tonight. Long Term...SCAs likely over the outer waters Friday night and again Sunday through Monday.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Cempa LONG TERM...Marine

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