Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 240453 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1153 PM EST Thu Feb 23 2017 .SYNOPSIS...
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A weak cold front will push south across the area overnight before returning north as a warm front by late Friday. A strong cold front and more widespread showers will move across the region Saturday night followed by a drier and colder air mass for Sunday into Monday. A disturbance will approach from the west late Monday and Monday night.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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1150 PM...Minor ESTF update to ingest the current mesonet in near term grids. Prev disc... 846 PM Update: Very minor adjustments needed this hour based on temperature and sky trends. Some fog/stratus over downeast Maine attm...but expect it to take a few more hours before we see much in the way of fog development here given current dewpoint depressions...and slower cooling trends than last night. 658 PM Update: Forecast generally evolving as planned this evening...with primary changes being to reduce sky cover through the first half of the overnight based on evening satellite imagery...and increase overnight temperatures somewhat based on evening observations. Expect the overnight to largely remain dry as weak cold front settles into the region despite robust mid level lapse rates. HRRR/RAP suggest that llevel westerly flow may limit fog development initially with a downslope component developing overnight...but with dewpoints above freezing...and well above where they were 24 hours ago...will continue patchy fog mention in the forecast at this time. Previous Discussion below: A weak front will try and move through the area this evening but for the most part it gets washed out. A few light showers with this front may occur in the mountains but no precipitation is expected elsewhere. The light southwest flow will diminish overnight. The problem of the night will be how widespread fog develops. With light winds and another day of melting snow lower levels will become increasingly moist. With shallow inversions setting up overnight due to the warmer air aloft and shallow cold surfaces due to snow cover its a recipe for some areas of dense fog. Temps will be very mild tonight and went above guidance.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... On Friday and strong push of warmer air with high dewpoints pushes north as a warm front...this will allow a band of light stratiform rain or drizzle to spread from south to north. By later in the day most of the overrunning light rain will be north of the forecast area, but low clouds will persist. Temps will be mild once again but not as warm over southern areas due to widespread clouds. Friday night Widespread low clouds and fog is expected as a broad and very warm southerly flow develops with higher dewpoints and overrides the cooler snow covered surface. Supersaturation should occur. Also with higher dewpoints over the cooler ocean waters additional fog/stratus will be advected to inland areas on the increasing south to southeast flow. A very mild night expected and min temps may end up warmer than forecast even though we went above the blended models. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Extended period begins with a rather robust cold front in place over central New York state and very warm air advection occurring over northern New England. Temperatures on Saturday will average around 20F degrees above normal. By 00z Sunday the cold front and associated convection will be on our doorstep. Strong dynamics will likely produce some isolated thunderstorms as it moves through. QPF amounts could be as high as an inch in some isolated locations while the majority of the region should see around a half inch or so. The combination of very warm temperatures followed by rain will likely get rivers moving and we have issued a Flood Watch with this package. Please see the Hydrology segment for more information. Rapidly moving system pulls off the north and east Sunday morning as much colder air streams in from the northwest. Although this will bring temperatures down from Saturday, they will remain 5F to 10F degrees above normal for most of the next week. Another system is expected to move out of the mid Atlantic states Monday night and Tuesday. This system will bring more precipitation to the area, although confidence with amounts right now is not strong. It will be another fast moving system and looks like it will still be developing as it moves across the Gulf of Maine. Best chance for significant precipitation will be over southern New Hampshire and extreme southern Maine. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... Short Term... Summary: A weak cold front will stall as it settles into the region tonight...before returning north as a warm front on Friday... yielding deteriorating flying conditions due to low clouds... fog...and rain showers. Low clouds and some drizzle are likely to continue through Friday night into Saturday ahead of an approaching cold front. Restrictions: VFR attm...but do expect deterioration after midnight as weakening flow aloft...and elevated dew points over a snowpack should yield some fog development although confidence is only moderate. Am also watching stratus over the Gulf of Maine that will make a run at RKD this evening. Otherwise expect MVFR/IFR restrictions in showers as warm front lifts north on Friday with a murky period of MVFR/IFR /and eventually LIFR/ fog- stratus-drizzle for Friday night/Saturday in southerly flow ahead of approaching cold front. Winds: Southwesterly winds less than 10kts will diminish to light and variable tonight and through the first half of the day Friday before returning southwest 5-10kts by Friday afternoon. Flow becomes southeasterly 5-10kts for Friday night and Saturday. LLWS: 30-35kt southwesterly winds near 1kft this evening will produce a period of LLWS through about midnight before diminishing. Strengthening southerly flow Friday night will likely yield another period of LLWS. Long Term...IFR/LIFR conditions Saturday morning should improve quickly to VFR as temperatures begin to soar. Expect conditions to drop once again to IFR/LIFR in the evening as a cold front moves through. The cold front will likely generate some isolated thunderstorms as well as briefly heavy rain. VFR conditions return on Sunday as colder air works into the area behind the cold front. && .MARINE... Short Term...Southwest flow develops over the waters tonight allowing winds to briefly approach SCA conditions and seas to reach 5 feet. Have issued a SCA for these conditions overnight. after With very warm moist air riding over the cool waters should also see some developing fog/stratus thru Fri night. Long Term...Will likely meet SCA conditions Saturday night and Sunday as winds before and after a fast moving cold front pick up. && .HYDROLOGY... A flood watch has been posted for interior portions of Maine and new Hampshire from 00Z Saturday through 00Z Monday. Temperatures are soaring into the 50s and lower 60s today and this trend will likely continue tomorrow and Saturday. Temperatures in the mountains will be more subdued on Friday with highs there in the lower to mid 40s but bounce back on Saturday. Light rain will move in Friday as a warm front moves north producing around 0.25 inches across mostly central and northern locations. Saturday night the cold front moves through with another 0.50 to 0.75 possible. The warmth will ripen and melt the snowpack starting rivers and streams to rise today and and continuing the rise tomorrow. The rainfall will cause additional runoff Friday night and Saturday morning. At the current time the main threat is ice jam flooding. The threat is higher in New Hampshire where temperatures are warmest and precipitation will be higher than in Maine. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch from Friday evening through Sunday evening for MEZ007>009-012>014-020-021. NH...Flood Watch from Friday evening through Sunday evening for NHZ001>009-011-012-015. MARINE...Small Craft Advisory until 5 AM EST Friday for ANZ150-152-154. && $$ ES

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