Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 212231 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 631 PM EDT Mon Aug 21 2017 .SYNOPSIS... High pressure will build south of the area this evening. Low pressure will approach from the west on Tuesday. The low will track to our north Tuesday night into Wednesday as it brings a cold front across the area. && .NEAR TERM /THROUGH TUESDAY/... 630 PM Update... Made adjustments to the sky forecast starting out and then showed clouds filling in across the wnw as depicted on the latest satl loop. Radar imagery showed some returns showing up over the St. Lawrence River dropping se. Activity was setting up on rich mid 60 dewpoint air but as they move to the e, activity should weaken running into somewhat drier air(upper 50s). The latest run of the RAP has been consistent w/its previous forecasts of showing some showers and perhaps a tstm sliding across the Crown of Maine this evening. Daycrew appears to have this handled ok. There is a weak frontal boundary as stated by the daycrew that will slide across the region. This boundary is coupled w/an upper disturbance as seen on the latest WV satl imagery. The boundary is shown by the RAP to move across northern areas. CAPE values are forecast to increase into the evening w/0-6km shear hitting 30 kts. Decided to keep a mention of tstms in for the far n and w through late evening. RAP soundings show potential that if any storms fire, strong wind gusts a possibility. The lacking ingredient is depth of the moisture. Therefore, kept enhanced wording out attm. Will re- assess things through the evening. Previous Discussion... A weak sfc front is located acrs cntrl Quebec and wl be dropping south tonight bfr gradually weakening. Showers and an isold tstm wl accompany the bndry into the St. John Vly tonight as instability begins to wane with loss of diurnal htg. Humid airmass rmns ovrngt with dwpts rebounding into the lwr 60s and this wl lkly lead to patchy fog acrs the north as clds dissipate. Late tonight and Tue mrng wl be quiet, other than patchy fog as brief ridging takes hold thru about 15z tomorrow. Wmfnt lifts thru tomorrow aftn with showers and thunder dvlpng acrs the nw aft about 18z. CAPES increase aft this time and 0-6km bulk shear increase to 30-40kts in the aftn bfr increasing substantially drg the evng hrs. PW values begin to rise in the aftn to nr 1.50 inches acrs srn areas, thus hv retained mention of hvy rain and gusty winds to where convection is lkly. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... For Tuesday night, a strong cold front will cross the area later in the night. This front has the potential to produce locally heavy rainfall and will maintain that threat in the forecast. PW values will approach 2 inches with a deep warm cloud layer around 13K ft. A strong LLJ will be in place and Corfidi vectors show the possibility of some back-building cells. The LLJ also heightens the threat of gusty winds mixing down with thunderstorms and will maintain mention of that in Tuesday night`s forecast. It`s still unclear how much of the action will be with a pre-frontal trough or with the front itself later in the night. Otherwise, it will be a warm and humid night ahead of the front with lows in the mid to upper 60s for much of the area. Humidity will be high with dew points also in the mid to upper 60s. Fog is likely along the coast and in high terrain. Elsewhere, marine layer moisture will be streaming northward in the form of stratus and some patchy fog. On Wednesday, clouds with the front will exit the Down East region with a few residual showers...but no thunderstorms can reasonably be expected. Fog and low clouds will linger along the coast during the morning. It will be a rather breezy day with a deep mixing layer and still warm with highs in the mid to upper 70s. The cooler air behind the front arrives gradually during the day and it will be cooler and less humid Wednesday night with lows mostly in the low to mid 50s. The cool Canadian air mass will be fully in place for Thursday with highs in the low to mid 70s and dew points in the upper 40s to lower 50s. Some cu fields will be possible north of Houlton with the NW flow. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... In the longer term starting Thursday night, a quiet and cool pattern appears likely with persistent upper level troughing and surface high pressure. The primary challenges will be identifying cumulus and stratocu fields in the a north to northwest flow...and when minor shortwaves may kick off some light afternoon showers Friday, Saturday and Sunday. In general, little precipitation is expected and will hold off on specifying chance pops for these days. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... NEAR TERM: VFR next 24 hours with potential MVFR vsbys btwn 07z and 12z for northern terminals. SHORT TERM: IFR conditions due to cigs, fog and thunderstorms will affect all terminals Tuesday night. The low clouds will linger into Wednesday morning for BHB and coastal sites, but all of the area will be VFR by Wednesday afternoon and remain so into Saturday. && .MARINE... NEAR TERM: Winds and seas will remain below SCA levels thru Tue aftn bfr beginning to climb to near 5ft at the very end of the period. SHORT TERM: There is a credible threat of SCA conditions Tuesday night into Wednesday in spite of the stable conditions and fog that will be in place. Wind-driven waves could hit up to 6 feet. After Wednesday, no significant weather is forecast through the end of the period. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...Farrar/Hewitt Short Term...MCW Long Term...MCW Aviation...Farrar/Hewitt/MCW Marine...Farrar/Hewitt/MCW

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