188 FXUS61 KCAR 290131 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 931 PM EDT Wed Aug 28 2019 .SYNOPSIS... A cold front will approach tonight and cross the region Thursday morning. A secondary cold front will approach from the west Friday and cross the area Friday evening followed by Canadian high pressure over the weekend. && .NEAR TERM /THROUGH THURSDAY/... 930 PM EDT Update...Made some small updates through 2 am to account for timing of precipitation onset and heavy rain shower potential. Current radar trends show a large area of moderate rainfall moving into Central Maine at this time. Overall rainfall rates are not indicating any potential for 1" or greater rainfall in an hour at this time across Southern Maine at this time. Most of the near term CAM models are showing the most intense rainfall rates will occur across the Penobscot Valley/Downeast from 03z-09z as the 2" PWAT axis moves into coastal Maine along with a surface dewpoint surge. Currently the convective parameter aspect isn't that impressive with no organized convection, will see if things improve as MUCAPE increase to 500 J/KG later on tonight for Downeast. Will need greater instability to support rainfall rates of 2" per/hr, to make the Flash Flood threat a reality. 7 PM Update...No large changes to the forecast except for an increase in the sky cover grids. Looking to our south some locally heavy rainfall rates have been observed in Southern New England as the SPC Meso-Analysis has a PWAT plume of 2.3" coming into Massachusetts this evening. Rainfall rates under the heaviest showers have been approaching over an inch per hour but storm motion is enough to limit the threat. We will see how things materialize later tonight but the atmosphere definitely has the potential for rainfall rates to trigger flash flooding, but training will have to develop for this threat to be realized. Still expect the precip shield just to our south to blossom over the next 3 hours as it begins to interact with the synoptic scale lift associated with an equatorial entrance region of a 110kt jet streak. Upper level trough in process of undergoing negative tilt over the Great Lakes will orient a downstream jet north-south over Quebec during next six hours. Meanwhile, ample moisture originating near Tropical Depression Erin will advect northward under area of divergence aloft. The combination of PWATs around 2 inches, approaching 2.25 Downeast, will be the main case for heavy rainfall. When factoring in a developing LLJ of 30-40 kts, warm cloud layer approaching 14kft, and a nose of warm air from southern New England/Mid-Atlantic, the case becomes even stronger. Rain observations in southern New England have already been promising and efficient. Two areas of greatest rainfall stand out: a quick burst along the arriving front and integration of tropical moisture (across the Central Highlands, Bangor Region, and Southern Aroostook), and a more ‘prolonged’ rain across eastern Downeast where front will slower to exit (Downeast and far eastern Washington Co) through Thursday evening. Prolonged is in quotes because the residence of this system is very short, aided by jet swinging across the Midwest. Heaviest rain will occur between midnight to late morning across the region. This brings question to exactly how much rain will fall in that short amount of time. Ultimately, given the anomalous tropical PWAT and support aloft, have confidence that localized flash flooding is possible early Thursday morning through the morning commute Downeast. Additionally, have expanded the Flash Flood Watch to southern Aroostook County, and central Piscatiquis as QPF collaboration between WPC and the NE RFC indicate 6-hour QPF values will be similar to those further Downeast. While 6 hour flash flood guidance is roughly 2.5 inches, have to factor in that urban areas will shed heavy rain differently. Rain will cut off across western and central zones quickly, with some rain continuing over eastern Washington Co into Thursday evening. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... An upper level shortwave and weak surface front will be pushing east of the area Thursday night carrying the moisture associated with the front and the remnants of tropical depression 6 away to the east. Surface ridging pushing into the area will allow clearing overnight. Winds will be light, and the ground moistened by Thursday's rain will likely allow patchy fog to form late at night. A secondary cold front will approach Friday and push across the area Friday afternoon. The front has very little moisture with it, but could produce a spotty shower during the afternoon. High pressure building into the northern Appalachians combined with a surface trough to our northeast will work to funnel in some much cooler and drier air from the northwest Friday night into Saturday. The gradient will maintain a gusty breezy Saturday morning with the wind diminishing late Saturday as high pressure builds in. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... High pressure will crest over the area Saturday night bringing a clear and very cool night. River valley fog will be likely late at night, and a few isolated colder valleys in the northwest may see some patchy frost before dawn. The high will slide east on Sunday as an area of subtropical moisture circulating around the back side of the high, and ahead of a small upper level shortwave lifts into the area. This will bring increasing clouds and a few showers are possible in the west late Sunday and throughout the rest of the area Sunday night. Clouds will linger into Monday, and some spotty showers are possible, mostly Downeast. However, the upper shortwave is very weak and no discernible surface reflection can be seen so showers will likely be limited. Monday into Monday night will otherwise be partly cloudy, to perhaps mostly cloudy Downeast and seasonably warm. A longwave trough across southern Canada is then expected to support a low tracking into Quebec, well to our northwest, on Tuesday. This low, combined with high pressure well to our east, will likely pull moisture northward into Tuesday bringing increasing clouds and increasing humidity on a southerly wind. The cold front trailing this low may reach the area Wednesday with a chance of showers or spotty thunderstorms. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... NEAR TERM: VFR into the evening hours. Downeast TAF sites will see lowering ceilings overnight, with reduced vis in heavy rain after midnight to IFR. IFR will trend north with RA+ through late morning. Sites will trend to VFR quickly Thursday afternoon and evening. SHORT TERM: VFR conditions are expected Thursday night, possibly lowering to MVFR or IFR in fog in some valley sites by morning. Conditions should return to VFR on Friday and remain mostly VFR into Sunday. Winds will be light Thursday night into early Friday. Cooler air pushing into the area behind a cold front late Friday into Friday night may result in some gusty west winds and a bit of turbulance. Saturday will begin with a gusty breeze. High pressure building in will then bring calmer conditions Saturday afternoon into Saturday night. Patchy fog may locally limit visibilities early Sunday morning. && .MARINE... NEAR TERM: Seas and winds will remain below SCA criteria. Patchy fog will develop overnight tonight, with heavy rain and some isolated thunder. Waves 2-4 ft. Some wind gusts up to 20kts. SHORT TERM: Tropical Depression Erin is expected to pass S of the Gulf of Maine midday Thursday. Moisture from the system will bring some rain Thursday morning, but the low center is expected to be too far south to cause any significant wind affects on our waters. Hurricane Dorian is expected to reach Florida as a major hurricane Monday morning and is not expected to affect our weather in the foreseeable future. Winds and seas are expected to be below SCA Thursday night into Sunday. Visibilities should be good. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Flash Flood Watch through Thursday morning for MEZ005-006-010- 011-015>017-029>032. MARINE...None. && $$ Near Term...Cornwell/Dumont Short Term...Bloomer Long Term...Bloomer Aviation...Cornwell/Dumont/Bloomer Marine...Cornwell/Dumont/Bloomer