Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 232151 AFDGYX Area Forecast Discussion National Weather Service Gray ME 451 PM EST Mon Jan 23 2017 .SYNOPSIS...
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A storm system tracking up the coast will bring wintry precipitation to the area tonight and lasting into Tuesday night. A cold upper trough will remain over the area through the latter part of the week with a return to colder temperatures. Scattered snow showers in the mountains and foothills can be expected through the latter part of the week.
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&& .NEAR TERM /TONIGHT/...
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First...a well developed ocean effect snow band is slowly lifting Nwd across Srn NH and SWrn ME. Reports indicate the center of the band with rates around 1/2 inch per hour...and accumulations up to 2 inches. I have made sure this is taken care of in the forecast thru the early evening. Then all attention is on the low pressure moving up the East Coast. 23.12z raobs showed that H5 heights were higher across Nrn New England than most model forecasts. This is a not surprising that the high pressure has trended stronger with time. I expect that this will have a significant influence on surface temps overnight. A NE breeze has been transporting mid to upper teens dewpoints SWwd all day. With temps at or below freezing already...any precip falling into the column will see evaporational cooling take nearly all locations into the 20s. A very sharp coastal front should develop...as winds drain out of the high and offshore to meet the increasing WAA to our S. Aloft 23.12z raobs and forecast soundings show plenty of room for wet bulb cooling to yield snow this evening. There is a warm nose above H8...so briefly a sleet mix could start with the precip this evening...but I expect a transition to all snow away from the immediate coast. How fast the snow changes over to sleet and freezing rain remains the question. The 23.12z GFS and ECMWF remain quite cold...well into Tue. The 23.12z NAM on the other hand...very warm and significant sleet to freezing rain scenario. The overwhelming bias of model guidance is to rush the warm air at the surface...but delay it too long aloft. So I went colder than the coldest guidance at the surface...and blended the very warm NAM with the GFS/ECMWF to produce mid level temps. This results in a snow to prolonged sleet event...with freezing rain possible at the tail end of the event as warm nose aloft becomes too warm and deep to allow snowflakes to survive partially melted. The lower confidence comes from the fact that forecast soundings are very close to an isothermal snow. If the mid level temps are only around 1C...strong lift could overcome that warmth and change precip back over to snow. Significant upslope flow component may also help to cool the column slightly and keep snow longer. For that reason I have my highest snowfall in the Monadnocks...Whites...and Wrn ME foothills...with a general 4 to 6 inches of snow and some mixed precip. The cold air should survive the longest...deep over central ME...and so central Somerset County does have higher snowfall amounts. I went with winter wx advisories for all zones for a combination of snow...sleet...and freezing rain. More of frozen precip is expected farther from the coast...and away from downslope areas NW of the mtns. A winter storm warning is in effect for central Somerset. The forecast is going to be fairly fluid overnight...with the lowest confidence across Srn NH and coastal ME...where warm air will be lurking closer than the interior. The strong Ely flow will also lead to some gusty winds near the coast this evening and overnight. Forecast soundings do show some potential for this to get into the NH Seacoast...especially if the coastal front can work far enough W. The gusts to 50 mph have been included in the winter wx advisory to avoid too many headlines and confusion.
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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Models have slowed precip down some...and now lingers it across Wrn ME into Tue. Warmth aloft will really flood the area just ahead of the dry slot...and this is probably the most likely time for freezing rain. By then more low level warmth should have advanced Nwd...so Srn NH and coastal Wrn ME will be rain or drizzle. Interior zones may need winter wx advisories into the afternoon for sleet...freezing rain/drizzle. As dry slot moves overhead Tue night...we should see a quick end to steady precip. I have cut model QPF amounts under the dry slot...with very little accumulating snow or ice expected.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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The 500mb hemispheric pattern, continues to trend away from its chaotic split flow to something, eventually, that resembles a +PNA pattern, if not quite getting there. Still, it looks to be more stable, but colder, especially over the weekend into next week. For days 5-7, the trend is more toward normal, which is colder, but beyond that we could see below normal temps sometime next week. For Wed, models suggesting possible lingering inverted trough, mainly in the ern zones Wed morning, with lingering precip, probably in the form of rain showers, but could be snow in the north. Elsewhere, look for some clearing in srn NH and SW ME, but the flow is weak behind the system, so could see lingering m/cloudy skies through most of the day. Highs will be milder ranging from the mid-upper 30s in the mtns, to the mid 40s on the coast and in srn NH. Wed night should remain mainly dry, with weak SW flow and lows in the mid 20s to low 30s. 500 mb closed low moves from S of James Bay to the Gaspe Peninsula Thu and thu night, and then lingers near Labrador through most of the weekend. Will see some weak waves rotate around this low, which will begin to push colder air into the region Fri through Sunday, and will likely produce some waves of upslope SHSN over the mtns, and periods of partly to mostly cloudy skies elsewhere. Highs Fri-Sun will generally be in the mid 20s N to mid 30s S, so closer to normal, with overnight lows mostly in the teens to mid 20s.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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Short Term /Through Tuesday/...Widespread MVFR will continue this evening as flow becomes onshore. PSM and MHT will also continue to see ocean effect SHSN...with PSM seeing TEMPO IFR or LIFR. Between 00z and 06z...precip will move Nwd into the forecast area and widespread IFR or lower conditions will develop. SN...PL...FZRA will all be possible overnight...as I expect all but PSM to remain below freezing. By early Tue PWM and RKD in addition to PSM may change over to RA. The mix will continue for HIE...LEB...MHT...CON...and AUG until late afternoon Tue. PSM may also see surface gusts around 40 kts at times. Conditions will be slow to improve Tue night. Long Term...Wed may start at IFR, but for the most part should MVFR, fluctuating to VFR, and reaching VFR at all but KHIE Wed night. The trend Thu-Sat will be for VFR with occasional bouts of MVFR in SHSN at KHIE.
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&& .MARINE...
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Short Term /through Tuesday/...Storm and gale warnings remain in effect for tonight into Tue. Best window for the strongest winds will be after midnight thru early Tue. Seas will build to over 20 feet by Tue morning. After that winds and seas will slowly diminish into Wed. Long Term...Winds and seas will gradually recede on Wed and Wed night, but will likely bump back up to SCA late thu night and Fri NW flow behind a cold front, which may linger into Saturday.
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&& .TIDES/COASTAL FLOODING...
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Despite being in the low portion of our astronomical tide cycle, large building waves may produce some erosion and splash-over south of Portland near the times of high tide Tuesday. Farther south, the Seacoast of New Hampshire may see water levels rise to near flood stage. Preliminary storm surge values appear to be around 1.5 to 2 feet with a persistent, strong easterly wind developing. A coastal flood advisory and and coastal flood statement have been issued.
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&& .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory from 1 AM to 7 PM EST Tuesday for MEZ007-008-012>014-018>021. Winter Weather Advisory from 10 PM this evening to 1 PM EST Tuesday for MEZ022>028. Winter Storm Warning from 4 AM to 7 PM EST Tuesday for MEZ009. NH...Winter Weather Advisory from 1 AM to 7 PM EST Tuesday for NHZ001>006. Winter Weather Advisory from 7 PM this evening to 10 AM EST Tuesday for NHZ007>009. Winter Weather Advisory until 7 AM EST Tuesday for NHZ010>015. Coastal Flood Advisory from 6 AM to 10 AM EST Tuesday for NHZ014. MARINE...Gale Warning until 11 AM EST Tuesday for ANZ151-153. Storm Warning until 11 AM EST Tuesday for ANZ150-152-154.
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&& $$ NEAR TERM...Legro SHORT TERM...Legro LONG TERM...Cempa

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