336 FXUS61 KCAR 200441 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 1241 AM EDT Tue Apr 20 2021 .SYNOPSIS... Weak high pressure remains over the region overnight. A cold front will cross the area Tuesday afternoon. Low pressure will approach on Wednesday lifting a warm front into the area followed by a strong cold front on Thursday. An upper level disturbance will remain over the area into Friday. High pressure will build into the region by Saturday. && .NEAR TERM /THROUGH TODAY/... 12:45AM Update: Satellite images show that the majority of the lingering clouds, and thus the isolated showers, have dissipated. Updated sky grids to reflect this for the rest of the night. The rest of the forecast looks good. Updated the temp and dew point obs. Previous discussion: Diurnally driven cumulus and light showers will quickly die off this evening. Clearing this evening will lead to the development of a very shallow radiation inversion and lows in the upper 30s for most of the area. Aloft, warm air advection is expected through the night and the inversion will be quickly wiped out Tuesday morning. There's two main storylines for Tuesday. The first is the fire weather discussed in the fire weather section below. Bumped up wind gusts in southern zones and also reduced dew points with the mixing. The second is the cold front crossing northern zones in the afternoon. In spite of little SBCAPE showing in guidance, numerous factors make a compelling case for convective activity with the front in northern zones. Diffluence aloft, the LFQ of a very strong upper jet, robust bulk shear, strong low level warm advection and very tight thermal packing with the front led to mention of isolated thunderstorms during the afternoon in northern zones. LFQ or RRQ of strong jets are most often associated with thunderstorms in March and April in this area. Although there's good moisture advection with the front, the line of showers will be moving fast with no more than a quarter inch of precipitation in the heaviest showers...most likely towards the Saint John Valley. With the low freezing levels, graupel is a good bet with the front. An inverted V, dry low levels and fairly strong winds aloft creates concerns for very gusty winds with the front. 40mph is easily possible, but impacts will be muted without leaves on trees. Highs on Tuesday will shoot towards the mid to upper 60s towards Bangor and will even see mid 60s ahead of the front in Aroostook County. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... Tue night clouds will clear out some allowing temps to fall back to the lows around 06z as a pocket of cooler air is advected in on west winds with a trough to the north. Near 40F from Bangor to the coast, low to mid 30s from Eastern Aroostook to St. John Valley and the cold spots near 30F across the North Woods. Temps will warm with increasing clouds ahead of our next weather system Wed. A warm front with overrunning precip develops with a Rain/Snow mix becoming mostly rain across the north. Might be able to squeak out a dusting across the North Woods but it is difficult with the higher sun angle. Models continue to disagree on strength due to the state of the upper level troughing. The Euro remains bullish on producing a tight upper level negatively tilted trough but has trended the surface low track closer to the GFS trend. This results in a sfc low pressure tracking northeast into the State of Maine with strong warm air advection ahead of it and some weak cold air damming across the far north. At the same time as the low tracks northeast Wed night into the state colder air with 925mb falling to between -1 and -3C across the North Woods into St. John Valley. This will correlate to rain changing to steady wet snow as the column cools and a decent period of good snow growth occurs. Snowfall in the North Woods looks to be on the order of 2 to 5 inches which may require an advisory for some of those zones Wed Night into Thu PM. As the low tracks northeast eventually into New Brunswick by Thu AM we will see the Rain/Snow line push east to the Route 11 & I-95. Elsewhere precipitation Wed-Wed Night-Thu will be in the form of rain but might see rain/snow mix as precip tapers to showers Thu late morning in Bangor area. The main precipitation shield comes to an end by late afternoon from SW to NE tapering scattered to widespread rain & snow showers. In the locations that stay all rain we will see a much needed 0.5-1 inch of liquid which is great for western zones that are in D0 (Abnormally Dry) conditions. Lastly, winds will increase Thursday afternoon into the evening in the wake of the departing surface low and tightening pressure gradient. West winds will get gusty in the 20-30mph range with strongest at the coast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Thu night by most model accounts show the storm system up over the Gaspe Peninsula with upper level low vertically stacked. This will likely keep shower activity going with pieces of energy rotating around the low pressure. Widespread snow showers will continue through Fri morning which will likely result in some accumulations north of the Central Highlands into northern Aroostook county as temperatures fall below freezing. This may make for some slippery conditions on untreated roadways, sidewalks and other cold surfaces. As the sun comes up Friday we will melt snow really quickly and we will change to rain showers chances through Friday. The driest spots Friday afternoon look to be from the Bangor region to the coast being the furtherest away from the pesky upper level low. Ridging builds in Saturday with generally mostly sunny skies and light breeze sending temps into the upper 50s to low 60s. Sun morning starts off with increasing clouds and moisture by daybreak. Global models disagree on what will happen as a front approaches from the west. The 12z GFS has shown this front with a decent slug of moisture and surface low developing off the Delmarva tracking it well south of the Maine coast. This scenario would send moisture up along an occluded boundary with a period of widespread rain showers or perhaps steady light rain. The Euro on the other hand has a rapidly deepening surface low tracking SE of the benchmark with a negatively tilted trough pivoting over the Gulf of Maine. This would result in shower activity along the Downeast coast, Bangor region into the Highlands but seems to be an outlier compared to the ensemble members. This would be slow moving in either scenario lasting into Monday so given the trend & ensemble members opted to go with chance POPs Sunday into Monday night. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... NEAR TERM: VFR conditions expected through the period. Isolated thunderstorms are possible north of GNR and HUL with a cold front Tuesday afternoon with brief IFR/MVFR. These storms may have small hail and wind gusts over 40kt. Otherwise, expect light and variable wind overnight. SW wind will increase to 10 to 15 knots with a few higher gusts Tue. SHORT TERM: Wed...VFR/MVFR clgs before 12z. MVFR clgs/vsby with light rain with pockets of IFR after 15z. S winds 5-15kts. Wed Night...IFR possible LIFR clgs & vsby with rain. S-SE winds 5-15kts. Thu...IFR/LIFR clgs & vsby with rain at all sites and possible snow at FVE. BGR & BHB improves to MVFR clgs with rain tapering to showers. HUL to FVE IFR with rain & snow throughout the afternoon. Gusty west winds 15-30kts. Thu Night... MVFR clgs/vsby w/ possible IFR vsby at times with snow showers from GNR to HUL points north. MVFR clgs at BGR & BHB. West winds 10-20kts. Fri...MVFR/VFR clgs & vsby with rain & snow showers from HUL to FVE. VFR at BGR and BHB. West winds 15-25kts. Sat...VFR areawide. W-NW winds 5-15kts with a few gusts to 20kts. && .MARINE... NEAR TERM: There's a low level jet over the waters ahead of Tuesday's cold front, but stability is so high that winds shouldn't exceed over 20kt. Fog is possible with the warm air moving over the cold waters. SHORT TERM: Tue Night - Wed we will be below SCA but creep towards low end SCA by Wed evening. SE winds 10-20kts w/ a few gusts to 25kts by Wed eve. Outer waters will begin gusting to SCA levels by 10pm Wed night and remain at SCA levels through the rest of the period. Wind gusts may approach low end Gales by Thu afternoon. Wed expect seas 3 to 4 feet and build to 4 to 7 feet by Thu. && .FIRE WEATHER... Low relative humidity...below 30 percent...and wind gusts near 30 mph create concerns for Tuesday afternoon. This is mostly for the southern half of the forecast area where afternoon showers are not as likely. Temperatures in the low to mid 60s are another favorable factor. Fine fuels have had a few days to dry and that trend continues for tomorrow. Unsettled weather arrives Wednesday through Friday. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...CB/LaFlash/MCW Short Term...Sinko Long Term...Sinko Aviation...CB/LaFlash/MCW/Sinko Marine...CB/LaFlash/MCW/Sinko Fire Weather...