Area Forecast Discussion
Issued by NWS Caribou, ME
Issued by NWS Caribou, ME
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907 FXUS61 KCAR 042327 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 727 PM EDT Thu Jul 4 2024 .SYNOPSIS... A weak cold front will stall in the area tonight. The front then slowly lifts back north Friday into Saturday as a warm front. Another weak cold front will begin to cross the region Sunday and move east of the region Monday. A surface trough is expected to cross the area Tuesday. && .NEAR TERM /THROUGH FRIDAY/... 7:27 PM Update: Update to the aviation section below for the issuance of the 00z Tafs. Otherwise, no changes at this time. 6:01 PM Update: Seasonably warm and humid early evening across the FA. Satellite pictures show cumulus fields across the north and mainly cirrus across the Downeast Region. Area radars show a few isolated showers in parts of the Saint Lawrence River Valley, but nothing of note on our FA. The chance of any showers this evening is very low with just the outside chance of an isolated shower moving across the far northwest corner of the FA. Low clouds and fog are expected to develop later this evening and overnight Downeast with fairly high confidence. Patchy lower clouds and fog will form across the north very late tonight, but confidence is lower across the north than it is Downeast. Previous discussion: A low pressure system to the north in Canada will swing a cold front through the region tonight and Friday. For tonight, the cold front will begin a slow transition from NW to SE. High-res models show the blocking tropical high pressure over the waters, which will keep the weak cold front from progressing much further south of the Central Highlands. Thus, isolated to scattered showers will stick to the far north through the early part of the night and clear out by midnight. Afterwards, the marine layer will progress north into interior Downeast bringing areas of fog while patchy fog will develop in the north. By Friday, a low pressure system intensifying over the Great Lakes will start to lift a warm front across the region. During the morning, the warm front will be over the Gulf of Maine, with showers and patchy fog over coastal Downeast. By the afternoon, CAMS models show the warm front moving into the Central Highlands. Some guidance shows the warm front progressing slightly faster with showers reaching into the North Woods by the afternoon. Nevertheless, rain showers will cover the majority of the center of the region. In addition, afternoon heating and frontal lift will produce convection along the line of instability. High res models show an unorganized area of 900-1200 J/kg of CAPE stretching from Greenville to Houlton, which is to be expected along the higher terrain. Weaker, but still high, CAPE north of this line will also produce thunderstorms as well. Recent upper air model soundings show a more impressive directional bulk shear, though the speed at the surface and mixing layer are lower than previous events. Cannot rule out possible strong pulse thunderstorms with the instability. However, as the storms cross over the higher terrain, they will be entering a more stable environment with the S flow marine layer, weaken the storms. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... The warm front will continue to progress slowly northward Friday night. Afternoon convection along the boundary will gradually diminish in the evening. Otherwise, fog and low clouds will spread northward under a frontal inversion. That will help limit lows to the mid 60s for most of the area. The cool spot will be the Downeast coast with an onshore flow producing lows in the 50s. The warm front continues to slowly push northward on Saturday with rain likely. The low level frontal inversion is expected to hold on much of the day, keeping highs in the low to mid 70s...even as 850mb temps surge towards 18C in the afternoon. Surface-based instability is most likely to stay west of the area due to the inversion. The exception might be the far western portions of the North Woods. Given PWs around 2 inches and strong deep layer shear, any surface-based convection could be troublesome. In spite of the impressive precipitable water, forcing looks weak and not expecting widespread QPF much above a half inch. Locally higher amounts are possible with thunderstorms. Did add mention of thunderstorms Saturday afternoon and evening due to elevated CAPE and the chance that the inversion breaks inland. Weak low pressure slowly tracks across the area Saturday night. Low level moisture advection along the low track increases the risk of another round of fog and low clouds. Elevated instability maintains a risk of thunderstorms through the evening. Once again, lows will only drop to the mid 60s for much of the CWA. For Sunday, the low exits the area and ridging builds. In the absence of any cold advection in the wake of the low, temperatures will climb well into the 80s across much of northern and eastern Maine. Humid conditions continue with dew points in the mid to upper 60s. In terms of thunderstorms, rising heights and warming aloft seem likely to overcome the surface-based heating. Kept a slight chance of thunderstorms in the forecast for the afternoon. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... The powerful subtropical ridge in the Atlantic will continue to dominate early next week, keeping fronts from crossing the area with cooler Canadian air masses. This mean temps and humidity well above normal, but falling short of records. Both Monday and Tuesday will bring highs in the mid to upper 80s. Onshore winds will keep it a bit cooler along the coast. The risk of afternoon thunderstorms increases Tuesday per the 04/12Z GFS while the 04/12Z ECMWF suggests a higher risk on Wednesday. While operational models show strong dynamics for Wednesday, the case for severe storms remains in doubt due both to timing and potential for low level clouds limiting heating. Did drop off Wednesday high temps back into the 70s based on more cloud cover. The cold front Wednesday night offers a good chance to bring temporary relief to the heat and humidity for late next week. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... NEAR TERM: VFR this evening. Moderate to high forecast confidence on IFR conditions developing after midnight at KBHB and KBGR in low clouds and fog. Low to moderate confidence on a period of IFR ceilings and visibility at the Aroostook terminals late tonight. Conditions at the Aroostook terminals are expected to improve to VFR Friday morning (if lower conditions develop late tonight), but only slowly lift to MVFR at KBGR and KBHB. A return to VFR likely at KBGR during the afternoon. S/SW wind 5 to 10 knots becoming light and variable later this evening. Light wind on Friday, mainly W at the northern terminals and S/SW at KBGR and KBHB. SHORT TERM: Friday night...Thunderstorms are possible in the evening...mostly north of GNR and HUL. Otherwise, fog is likely to set in for all sites later in the night with IFR to LIFR vis. Saturday...Fog and IFR cigs may be persistent into the afternoon for coastal sites and as far north as Bangor. Other sites will be VFR by afternoon. Afternoon thunderstorms are possible for all sites. Saturday night...Fog and IFR cigs will most likely move north from the coast to affect all sites again. Thunderstorms are possible in the evening. Sunday...IFR cigs will gradually lift to MVFR in the morning and all sites will gradually become VFR in the afternoon. There is a slight chance of thunderstorms in the afternoon for inland locations. Sunday night...Expect generally VFR except possibly on the coast to include BHB. Monday into Tuesday...Mostly VFR except the threat of nighttime fog and low clouds for coastal sites such as BHB. && .MARINE... NEAR TERM: Winds and seas will remain below SCA conditions tonight and Friday. Reduced visibilities in areas of fog. SHORT TERM: Stable conditions persist through the period with little chance of any advisories. Adjusted winds downward this weekend due to stability. Fog is a more likely threat in this warm and humid regime. Everyday well into next week should feature some degree of fog or haze. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...CB/LaFlash Short Term...MCW Long Term...MCW Aviation...CB/LaFlash/MCW Marine...CB/LaFlash/MCW