Area Forecast Discussion
Issued by NWS Caribou, ME

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326 FXUS61 KCAR 192019 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 419 PM EDT Fri Apr 19 2019 .SYNOPSIS... A cold front will move across northern Maine this evening and will stall out across central Maine late tonight. The front will then lift back northward as a warm front Saturday into Saturday night. The region will remain in a very moist air mass this weekend and into early next week. Low pressure will approach from the southwest on Monday. && .NEAR TERM /THROUGH SATURDAY/... A cold front currently crossing the Caribou area will sink southward tonight, but stall before reaching a Bangor to Calais line later tonight. The front will then slowly lift northward on Saturday. There are sharp temperature and moisture gradients with this frontal boundary that will mark 20F differences in temp and dew point from one side of the boundary tonight and tomorrow. The discontinuity extends up to H925 where a very tight gradient of about 15C exists tonight and tomorrow. Focused along this thermal boundary will be locally heavy precip as deep moisture streams northward from the Gulf of Mexico and is focused along this boundary. PWs will be approaching as much as an inch and a half...very high for this time of year. These PWs will be aided by a deep warm cloud layer for efficient precip processes, a strong LLJ and elevated instability. Furthermore, some training cells may be possible. When these factors are combined with snow melt and flash flood guidance of about one inch in an hour or 1.25 inches for 3 hours, there is the potential for flash flooding later tonight into Saturday morning. The soil is saturated in much of the area with little capability to absorb heavy rainfall rates. The snow melt will be enhanced by fog...which will also cause visibility issues for motorists to see water hazards on roadways tonight. WPC has put the area in a slight risk for excessive rainfall. The heaviest rainfall tonight is expected on the north side of the frontal boundary...north of the Moosehead and Katahdin regions. The heavier precip shifts slightly southward during Saturday but embedded convection will bring locally heavier rainfall. Have not added thunderstorms into the forecast yet, but should be a strong consideration for the next updates. These storms will fire off a very pronounced H925-H850 thermal ridge. Dense fog headlines are also a possibility later tonight into early Saturday morning under the frontal inversion...with the coast being the highest probability. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... A strong southerly flow along the East Coast combined with an upper level trough is expected to move across the northeast over the next several days is expected to bring period of rain from Saturday Night into Monday and Tuesday. The strong southerly flow will also result in high dew points which will produce fog and enhance snow melt. High temperatures through the weekend are expected to be in the 50s and 60s while nighttime lows stay well above freezing. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... The upper level system is expected to move off the East Coast on Tuesday. At the same time low pressure will approach from the Great Lakes and move across the region on Wednesday and early Thursday. Another system is expected to approach from the west on Friday. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... NEAR TERM: The predominant condition into Saturday afternoon will be IFR cigs tempo LIFR cigs near the coast. A cold front will produce some MVFR or even VFR conditions briefly this evening north of PQI, but that window will close quickly later in the night. Heavy rain is possible north of HUL and GNR later tonight into Saturday morning. Isolated embedded thunderstorms are possible late tonight into Saturday. Strong winds above the fog and low clouds will produce LLWS...most prevalent towards BGR and BHB tonight and tomorrow morning. SHORT TERM: Expect MVFR/IFR conditions Sunday into Wednesday. && .MARINE... NEAR TERM: A very moist air mass over the cold waters will generate areas of fog...if not widespread dense fog. In spite of the stability and lack of gusts, the winds will still be strong enough to gusts to 25 kts until decreasing Saturday afternoon. Have adjusted winds...and particularly gusts...downward from model guidance due to stability. SHORT TERM: Have used the Nam to initialize winds however will lower all model winds by 10 percent due to cold sea surface temperature and expected strong warm advection. For Waves: A southerly fetch will persist from the Gulf of Maine Southeastward into the Atlantic through the day Sunday. So expect wave heights to remain around 8 feet/9-10 seconds until Monday then slowly subside. Total Water Level: High tide levels are close to highest levels of the month next few days due to astronomical tide levels however storm surge is expected to remain below 1 foot therefore expect total water level to remain 2 feet below minimum flood level along the coast. In Bangor fresh water run-off continues to increase anomaly at low tide +5 to +6 feet and also produce 2 foot or greater anomaly at high tide Sunday which could bring total water level near or above action level in Bangor. && .HYDROLOGY... This weekend marks one of the most potentially eventful hydro events in many years that covers much of the forecast area. The combination of remaining deep snowpack in northern zones and the clash with a very warm and humid air mass on the backside of a Bermuda High will put a lot of water in the rivers. A stationary front will mark the boundary of the clash across the state tonight into Saturday and bring three separate hydro concerns. First is remaining ice jams on the Aroostook and Saint John Rivers. The second concern is urban and small stream flooding due the combination of heavy rain and snow melt later tonight into Saturday. The last concern will be the response of main stem rivers Sunday into Monday. In terms of the ice jams, a Flood Warning remains in effect today along a portion of the Aroostook River. The gauge at Washburn is reading nearly 17 feet as of this afternoon, which is moderate flood stage. The gauge will continue to show fluctuations tonight and Aroostook Emergency Management reported that Gardner Creek Road near Washburn remain closed due to an ice jam that extends from upstream of the Washburn bridge towards Crouseville. Emergency Management is also watching the Parsons Road between Washburn and Presque Isle. We are watching ice jams on the Saint John near Saint Francis, Frenchville and Van Buren, but have no need to issue warnings at this time. Most or all ice jam issues should be resolved by later this weekend as rivers continue to rise. A point Flood Warning also remains in effect for the Mattawamkeag above Mattawamkeag until further notice. The river is near 14 feet this afternoon and is expected to slowly rise to 15.1 feet by Sunday afternoon, with additional rises into early next week. At 14 feet, flooding begins along the Bancroft Road between Wytopitlock and Danforth. Snow melt is already causing issues on Route 1A in Easton and Route 2 in Island Falls. These types of issues will be exacerbated by locally heavy rainfall tonight into Saturday morning for small streams. The Flood Watch is now in effect for tonight through Monday evening. The combination of rainfall of 1.5 to 3 inches of rain along with significant snowmelt in areas that still have snow on the ground will lead to significant rises on streams tonight and Saturday...and on main stem rivers Sunday into early next week. There is high confidence that smaller streams will flood. There is also high confidence that some areas will experience minor to moderate flooding. Confidence is not as high as to whether any areas will experience major flooding, but it is a possibility. There are uncertainties in terms of the exact remaining SWE that will empty into rivers. According to dam operators, storage capacity in the Penobscot watershed is favorable and that will help mitigate potential main stem issues. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch from 2 AM EDT Saturday through Monday evening for MEZ001>006-010-011-015-031-032. MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ050>052. && $$ Near Term...MCW Short Term...Mignone Long Term...Mignone Aviation...MCW/Mignone Marine...MCW/Mignone Hydrology...MCW/Dumont is the U.S. government's official web portal to all federal, state and local government web resources and services.