Area Forecast Discussion
Issued by NWS Portland, ME

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197 FXUS61 KGYX 220303 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1103 PM EDT SUN AUG 21 2016 .SYNOPSIS... Welcome rains will arrive tonight ahead of a strong cold front. Much cooler and drier air will move into the region on Monday upon gusty northwest winds. Dry weather and moderating temperatures are expected for the middle of the week before a weakening cold front brings another chance for some showers and thunderstorms to the region by the end of the week. && .NEAR TERM /THROUGH MONDAY/...
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Update...Forecast looks on track. Only addition was to add a little drizzle ahead of the front in the coastal stratus. 00z GYX sounding was supportive of drizzle...and that should continue in the WAA flow ahead of the front before rnfl arrives. Previous discussion...A cold front will be moving across NEW Hampshire and Maine tonight. This system will allow showers to develop first across western NH early this evening spreading east into Maine by later in the evening and toward midnight. Used the HRRR for timing of showers west to east tonight. Some of the showers will be heavy with total QPF amounts of 1/2 to 1 1/2 inches of rain expected as per the RFCQPF suggests. Not expecting any thunderstorm activity with this front as atmospheric conditions are simply not favorable. Also this evening, ahead of the front the midcoast of Maine will be encountering ocean stratus and some fog tonight due to the moist southeast flow. Currently this area of low clouds and fog over the midcoast and extending well offshore shows up well on visible satellite imagery and may push inland after sunset. Temperatures will be mild with humid conditions tonight as dewpoints continue to rise in the moist southerly flow ahead of the cold front.
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&& .SHORT TERM /MONDAY NIGHT THROUGH 6 PM MONDAY/... The cold front moves rapidly offshore early Monday morning. Any showers over eastern areas of Maine will be over by early morning as much drier Canadian air with downsloping northwest winds develop behind the front. Skies will become mostly sunny over all southern and central downsloping areas of Maine while some clouds may linger in the mountains. The northwest winds behind the cold front will become gusty at times due the combination of a rather strong pressure gradient and cold air advection aloft. Some winds may gust into the 30 mph range for a while during the afternoon. High temperatures will be cooler reaching only into the 70s, and with much lower dewpoints and gusty winds it may actually feel cool. By early evening the winds will become light as the Canadian high pressure system settles over the area with its cool dry air mass Monday night. It will be the coolest night we have seen in a while with lows dipping into the upper 40s in the mountains to mid 50s elsewhere with very low dewpoints. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... High Impact Weather Potential: Minimal. Pattern: Robust trough progressively heading east as of this writing will already be exiting the region as we reach the start of this forecast period Tuesday. The next feature in the westerlies of note is a shortwave trough dropping south and east along the west coast of Canada. This feature will turn east and move steadily along the US/Canadian border through midweek. Beyond this...impressive ridge amplification takes place across the eastern Pacific /PNA shifting sharply positive with the EPO turning negative/. Downstream of this ridge...troughing will take along the western coast of North America...helping to broaden the troughing associated with the mobile shortwave to the east. The placement of this trough in the west...however...will act to reinforce ridging in the southeastern United States...with the result being a weakening trend of the mobile trough /and associated cold front/ as it reaches our region late in the week. Thus...expect a warming trend as initial troughing departs and ridging builds ahead of approaching shortwave trough. Precipitation potential continues to be confined to the late week cold front...with temperatures likely falling a bit behind it/s passage. Model Trends/Confidence: Unfortunately for those seeking rain...the primary forecast trend has been to weaken further the frontal passage late in the week...which is very reasonable given the larger scale pattern favoring more persistent ridging in the east. Forecast confidence is at or above average through Friday with average confidence for the coming weekend resulting from differences in handling the details of troughing east of the eastern Pacific ridge. The Details.... Tuesday-Tuesday Night: The forecast starts off on a very quiet note with core of dry airmass directly overhead Tuesday morning and high pressure cresting just south of the region. We/ll be too dry to pop nearly any Cu during the day...but a few mid level clouds may reach northern areas in the afternoon associated with mid level warm front just to our north. Warm advection aloft will bring temperatures at H8 back to around +10 C during the afternoon...with highs very close to seasonal norms...in the 70s to around 80. We/ll cool off again Tuesday night with good radiational cooling setup...but warmer airmass aloft will keep temps roughly 5F warmer than the night previous. In collaboration with our neighbors...did undercut consensus guidance for overnight lows...following closer to MOS values. Wednesday-Thursday: The quiet weather theme continues for this period under broad low to mid level southwesterly flow as surface high pressure pushes southeast of the New England coast. Sunny/Mostly sunny skies on Wednesday turn partly cloudy Thursday with some moisture associated with upstream shortwave likely to bring a few clouds to the region. T8s +1-2 sigma...around +16C Wednesday and +17C Thursday. These temperatures suggest upper 80s to around 90 in southeastern NH/southern Maine with lower/middle 80s elsewhere. With deeper moisture plume still to the west of the region... humidity will not be oppressive...with dewpoints likely in the 50s on Wednesday and around 60 Thursday. Friday: As mentioned above...frontal passage on Friday appears weaker in the guidance compared to 24 hours ago...and as mentioned by previous forecaster...front will only have a thin and thinning plume of moisture to work with given limited Gulf of Mexico connection. Synoptic setup favors a weak system dynamically...so slight chance/chance PoPs remain in order with a widespread significant rainfall not expected. Given a lack of confidence in just how widespread any clouds/ precipitation will be...and temperatures aloft still +15-16C...expect another very mild day...especially away from the coast over southeastern NH and southwestern Maine where mid/upper 80s again look possible. Saturday-Sunday: At this early vantage point...the weather for the last weekend of August looks quiet with Friday/s front washing out just south of the region and high pressure /and associated midlevel dry wedge/ building overhead. Given the continued synoptic scale ridging over the eastern half of the country...expect temperatures to remain above seasonal norms despite being a few degrees cooler than ahead of the front. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... Short Term...A band of RA will move across the forecast area from W to E tonight. Just entering the CT River Valley at this hour...the RA should end 3 to 4 hours after it begins...while moving E around 30 mph. RA should bring areas of MVFR conditions to all terminals thru the night...and local IFR cannot be ruled out in a heavier embedded SHRA. Meanwhile coastal stratus continues to develop with areas of IFR CIGs. PSM and RKD are already IFR...and I expect PWM and AUG to follow within the next couple of hours. Approaching front should keep stratus from making it to MHT and CON. I have also removed LLWS from most of the TAFs. Model forecasts are pretty marginal and the 00z GYX sounding is showing winds below model forecasts. However...stronger winds to the N will mean LLWS remains possible for LEB and HIE. Mixing behind the front should help IFR and MVFR conditions improve to VFR more quickly than usual. Gusty W winds are expected Mon...nearing 25 kts at times. Long Term...VFR conditions expected through Thursday under the influence of high pressure with valley fog possible each morning HIE/LEB. Showers/thunderstorms possible Friday with an approaching cold front will bring the potential for restrictions. Widespread MVFR/IFR restrictions not expected through the long term forecast period. && .MARINE... Short Term...An increasing southeast flow ahead of the cold front tonight will build seas to 3-5 ft over the outer waters thus a SCA has been issued for later tonight into Mon morning. The cold front moves off the coast toward morning with a pronounced wind shift to the northwest Monday morning accompanied by gusty winds through the afternoon to near 25 knots. Mon night winds and seas diminish as high pressure settles over the area. Long Term...Southwesterly winds continue through the long term forecast period...with the strongest winds arriving Thursday Night/Friday ahead of an approaching cold front. This will bring the greatest threat of SCA conditions...and likely only to the outer waters. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Small Craft Advisory until 11 AM EDT Monday for ANZ150-152-154.
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&& $$ NEAR TERM...Legro

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