Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 260241 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1041 PM EDT Thu May 25 2017 .SYNOPSIS... A broad area of low pressure from the Ohio Valley through the mid Atlantic coast will slowly lift northeast tonight...reaching Cape Cod by Friday morning. Low pressure will continue northeast into the maritimes through Friday night. Weak high pressure will build over the area on Saturday and will shift offshore on Sunday. Weak low pressure over the eastern Great Lakes will lift north into western Quebec Sunday night and will drive a cold front toward the region on Monday. The front will slowly cross the area Late Monday night and Tuesday. && .NEAR TERM /TONIGHT/... 1045PM UPDATE... Initial batch of rain has developed and begun pushing onshore over much of Maine this evening, while another more substantial area of rain is finally taking shape to the south of Rhode Island. HRRR model is handling both areas of rain quite well, and based the forecast update largely on this. Precipitation from the heavier band to the south should be arriving in southern New Hampshire around midnight. Thunderstorms are currently noted with this activity as it is forming. As this wraps around the low, expect the thunderstorm activity to decrease a bit, but there could still be some rumbles of thunder across the southern part of our area overnight as this low winds up. Have increased precipitation amounts as well, as even this earlier area of rain forming along the coast of Maine has produced some decent rainfall rates. Area moving in from the south could produce rates up to about an inch per hour, though the heaviest rain should only last an hour or two before becoming light and drizzly. 945PM UPDATE... Getting a few reports of high, gusty winds. Have increased wind forecast for the overnight hours, especially through 06Z where best wind fields will be in place from the northeast. Otherwise, have updated the forecast based on current conditions and latest set of mesoscale models. Rain continues to spread north and east, however it remains fairly light and fragmented in most areas. Heaviest precipitation remains over Upstate New York well to our west. However, satellite imagery continues to show a large plume of moisture forming off the Mid Atlantic coastline and moving quickly to the north. Mesoscale models have this heavier precipitation arriving from south to north within the 06Z and 12Z time frame. Have made minor adjustments to pops and temperatures for the next 6 hours. Areas of light rain will continue with downsloping over the northern Connecticut River Valley. ORIGINAL DISCUSSION... Higher pressure and easterly winds have kept much rain from intruding into northern New England by retarding the advancement of precipitation into Maine and northern and central NH until the last couple of hours. The flow has intensified along the coast as the pressure gradient increases/low pressure nears. Temperatures have been kept down in this marine airmass while northern sections were able to break out into the 60s. CAM models have been correct in showing a weakness this afternoon in precipitation fields over NH and especially Maine as energy diverges both towards northern NY State as well as offshore. We`ll see a break in most shower activity more or less this afternoon and evening...however there will be widely scattered showers still around...mainly over the mountains. Around midnight a stronger short wave associated with this system will pivot into the area and precipitation will increase both in intensity and areal coverage. This is when we will see the bulk of the 1-2 inches with this event. We`ll see some heavy downpours for the overnight period into Friday morning. Winds are picking up as mixing deepens today and expect ESE winds to gust to 25 kt through the night. Continued with drizzle tonight mainly in between the two systems as the onshore flow intensifies. Lows will be in the upper 40s to around 50. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... After the heavier rain expected during the morning hours...precipitation tapers off to showers by Friday afternoon. Again the heavier rain will be along the coast with some enhancement over terrain. The long duration of this event should preclude any flooding issues but poor drainage areas may see some brief issues in heavier rainfall that occurs through tomorrow. Expect temperatures to warm only about 5-10 degrees from overnight lows tonight to highs Friday. Tomorrow night clouds will begin to decrease across the region. The upper low will be engulfed in another circulation south of Greenland while the surface cyclone fills. Overnight lows Friday night will drop farther in a drier airmass with lows in the 40s most locations and perhaps up to 50 degrees in warm spots. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Mean long wave trof position will remain over the Great Lakes, this will mean a general cool wet pattern can be expect for the outlook period with a few dry periods between systems. Starting with Saturday, the system that exits into the maritimes allows weak high pres over the area and a drier north to northwest flow to develop for Saturday into Sunday with cool temps. By late Sunday into Monday, the next short wave that rotates around the base of the Great Lakes trof then moves northeast bringing another period of wet weather with a developing onshore flow that keeps temps cool. With the mean upper trof remaining over the Great Lakes through mid week a continue unstable southwest flow with embedded short waves with keep unsettled conditions through Wednesday. It appears we may finally get rid of the onshore flow by midweek so temps may actually get back to near normal high temps reaching into the 70s. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Short Term...IFR/LIFR ceilings developing today and persisting through tomorrow. ESE winds will gust to 25 kts most terminals through tomorrow. Early on LLWS will affect HIE and LEB tonight. Drizzle and fog will affect most TAF sites outside of HIE and LEB tonight before the moderate to heavy rain arrives. Long Term...Winds and seas generally light. No flags. && .MARINE... Short Term...Continuing SCAs through Friday afternoon. At that point we may need a SCA just for high seas for the outer waters. Long Term...Conditions become VFR Sat into Sun before returning to MVFR conditions for Sun night and Monday and possibly through midweek in scattered showers. && .TIDES/COASTAL FLOODING... Highest astronomical tides of the year on tap for tonight and Friday night. A Coastal Flood Advisory remains in place the Midcoast region of Maine. The astronomical tide in Portland is 11.8 feet near midnight tonight. Expect around a foot of storm surge overnight. Flood stage in Portland is 12 feet and a storm tide will likely be near 13. Areas of flooding are expected with pockets of moderate flooding. Have therefore upgraded the Coastal Flood Advisories from Portland south to warnings. We may need a Coastal Flood Statement for the tide tomorrow night despite the absence of an onshore wind as astronomical tides will be at the flood stage of 12.0 feet in Portland. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Coastal Flood Advisory until 1 AM EDT Friday for MEZ025>028. Coastal Flood Warning until 1 AM EDT Friday for MEZ023-024. NH...Coastal Flood Warning until 1 AM EDT Friday for NHZ014. MARINE...Small Craft Advisory until 8 PM EDT Friday for ANZ150>154. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Hanes LONG TERM...Marine is the U.S. government's official web portal to all federal, state and local government web resources and services.