Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 242257 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 657 PM EDT Mon Jul 24 2017 .SYNOPSIS... Low pressure tracks south of the state late tonight. High pressure then builds in Tue through Wednesday night. A cold front enters the state Thursday and is expected to stall. && .NEAR TERM /THROUGH TUESDAY/...
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650 PM Update: In addition to the update below, we beefed up storm total QPF ovr Downeast areas with latest radar indicating brief mdt to hvy rnfl rates ovr this area at least thru the next hr or two. Rnfl rates should decrease markedly ovr Downeast areas by late eve. 600 PM Update: Despite dry sub cld air earlier, rn has made steady progress Newrd ovr the last few hrs across interior Downeast and even Cntrl ptns of the Rgn. Subsequently, we used the short term PoPs from QPF for stratiform precip tool to increase PoPs ovr these areas this eve, with stratiform designation of rn with PoPs equal/greater than 55 percent and cvrg shwrs for less. Corresponding cld cvr was adjusted upwards to reflect Nwrd extent of thicker stratiform cld cvr ovr the Rgn. Lastly, the typical hrly fcst temp/dwpt update was made into the ovrngt hrs based on latest late aftn/erly eve sfc obs and obsvd hi temps with no chgs to fcst ovrngt lows attm. Orgnl Disc: Not surprisingly, given the very dry 12z KCAR sounding and dry model forecast soundings for KBGR and KBHB, precip has been rather sluggish advancing into our CWA. Precip finally started reaching the ground at BHB in the past hour, but from a high 9000 ft deck. That said, better returns are moving into the SW`rn CWA in earnest now, so am comfortable with an increase to likely pops for Bangor by 21z. The GFS and ECMWF did shift a bit north on the precip shield and surface low position with the 12z runs, so QPF was tweaked up (not by much). Also did increase POPs over the previous forecast, especially for Bangor and Downeast, since Bar Harbor is already reporting rain and Bangor seems likely to get at least an extended period of light rain. QPF ranges from nothing in the Saint John Valley to around a quarter inch or so along the coast. Precip chances drop off after 06z tonight as the Low shifts south of Nova Scotia. It`s likely that the last of any lingering showers will clear out by late morning as the base of the upper trough swings through the CWA and clears away to the east. Expect gradual clearing from the northwest later Tuesday. As for temps, clouds and increased dewpoints will keep tonight warmer than the past few nights, with lows in the low to mid 50s. Highs tomorrow will generally be similar to today, ranging from the upper 60s to low 70s.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Tuesday night will be the last of the cooler nights that started this past weekend. Lows will drop to the mid to upper 40s north and upper 40s to lower 50s in the southern half of the forecast area. A rather steep radiation inversion will generate shallow patchy fog later in the night, but the inversion and fog will quickly be eradicated by dry southwest winds on Wednesday morning. These winds and sunshine under high pressure will propel temperatures back to the lower 80s Wednesday afternoon, but humidity will still be reasonable. Clouds will gradually increase Wednesday night. These clouds and the warm southwest flow means lows will be around 60F...except cooler along the Down East coast due to onshore winds. The increasing clouds will be associated with a weakening cold front that will enter the northwest corner of the area late Wednesday night and slowly creep southward by later Thursday. The expected cloud cover over most of the area led to a decrease in highs to the lower 70s while dew points creep back to the 60s. The lower temps, clouds and weakening front led to a decision to go with just a slight chance of afternoon convection. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A complex situation develops Thursday night into Friday night in which the front stalls and either a wave develops...or in the case of the GEMS and ECMWF...a full-blown coastal low develops that affects the area into Friday night or even Saturday. The 24/12Z operational GFS scenario was not given much credence in this forecast, but the actual forecast currently mirrors the GEFS mean. There`s a lot of uncertainty before fully jumping to GEMS and ECMWF solutions too. These solutions hinge on a more defined shortwave trough in the Great Lakes region on Thursday night and a strong jet on the backside that will eventually generate a cut-off upper low. The ensemble approach taken in this forecast maintains chance pops over large portions of the area through Friday night due to the uncertainty and goes with highs in the 70s on Friday and Saturday...rather than the 60s dictated by GEMS/ECMWF. Higher confidence in dry conditions and seasonable temperatures is warranted Sunday into Monday. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... NEAR TERM: While it is currently raining out of a high VFR deck for KBHB and KBGR, expect gradual lowering of CIGs through the evening and overnight. KBHB is likely to be the first to MVFR conditions in some rain this evening, and may have some IFR vis or CIGs for a time, as well. KBGR is less certain to see MVFR CIGs, but did include a period in the TAFs for Tue AM. Quite possible that northern sites will remain VFR through the period as low pressure remains well to the south. SHORT TERM: Patchy shallow fog may reduce vis near sunrise Wednesday morning. Otherwise, expect VFR conditions from Tuesday evening into late Wednesday night. At that point, some coastal stratus/fog may affect BHB and Machias while MVFR cigs are possible north of HUL and GNR. The fog will burn off, but the lower cigs in the north may persist through Thursday morning due to a slow moving cold front. Isolated thunderstorms will be possible along the cold front on Thursday afternoon. The front will tend to stall Thursday night into Friday with the threat of IFR cigs and vis. Confidence in VFR conditions returns Friday night into Saturday. && .MARINE... NEAR TERM: Winds should remain below SCA criteria through Tue evening. Seas may flirt with SCA criteria late tonight into Tue AM, but for now have opted to not go with an advisory. SHORT TERM: Fog becomes more likely Thursday into Friday. There is a chance of a coastal storm Friday into Friday night which could necessitate a Small Craft Advisory. Mariners should closely monitor forecasts for this period. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...VJN Short Term...MCW Long Term...MCW Aviation...VJN/MCW Marine...VJN/MCW is the U.S. government's official web portal to all federal, state and local government web resources and services.