Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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977 FXUS61 KGYX 082311 AFDGYX Area Forecast Discussion National Weather Service Gray ME 711 PM EDT Mon Jul 8 2024 .SYNOPSIS... High pressure offshore will maintain very warm and humid conditions for much of the week. A stationary front wavering over the Northeast will provide a focus for showers and storms Tuesday afternoon into Wednesday. A trough will approach from the west Wednesday transporting remnant moisture from Beryl into the region Wednesday into Thursday. Thunderstorms are again possible Friday as a stalled remains over the region. A few more scattered showers and storms are expected over the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 7:10pm Update... Just minor tweaks to POPs based on isolated showers along the seabreeze front, and adjustments to dew points based on obs so far this evening. Otherwise, no notable changes to the forecast for tonight as we work our way through this warm summer evening. Previous... Strong surface heating has allowed for CU fields to blossom across the interior while onshore flow has pushed some stable air into the coastal plain resulting in less clouds just inland from the coast. Latest satellite and area webcams show that onshore flow has allowed marine fog to encroach upon the immediate coast and this fog will push inland tonight. A few isolated showers have also developed over the mountains with hi res guidance suggesting additional isolated showers will be possible along the mountains to the Capital District of Maine through this evening. The loss of surface heating will allow CU and any shower activity to dissipate around sunset. In addition to marine fog pushing inland along the coastal plain there will also likely be valley fog developing later tonight. It will remain warm and humid tonight with lows in the 60 to near 70 degrees. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Another very warm day is expected Tuesday with similar high temperatures to today. What will make it feel even hotter than today resulting in a Heat Advisory being issued for southeastern NH is that deep moisture will be on the increase and dewpoints are forecast to remain elevated into the upper 60s and low 70s south of the mountains. This will bring heat index values above 95 degrees for zones in a Heat Advisory and low 90s elsewhere south of the mountains. A short wave embedded in cyclonic flow over eastern Canada will send a glancing blow of forcing for ascent near the area Tuesday afternoon. Diurnal heating will bring SB CAPE near 2000 J/kg by early afternoon across southern NH into the coastal plain of Maine with little in the way of a capping inversion. The approaching short wave will also increase deep layer to 40-50 kts, which will be enough for organized convection. The 12Z CAM suite shows some variance in storm coverage with the HRRR/FV3 showing more widespread strong storms across the southern two thirds of NH into the coastal plain of Maine while the ARW/NSSL show more isolated storms. Overall timing is consistent with storms initiating over NH between 2-4 PM and tracking eastward into southern Maine. SPC has placed the southern two thirds of NH and the coastal plain of Maine in a Marginal Risk for severe storms with the primary threat being strong winds with inverted V profiles. High freezing levels and marginal CAPE within the hail growth zone will limit the potential for hail while PWATs climbing to around 2 inches will make torrential downpours possible. Storm motion looks swift enough to mitigate the flash flood potential while there could be some training of storms that could lead to isolated instances of flooding. Thunderstorm activity will diminish around sunset while the warm and humid airmass will remain in place Tuesday night. Lows will likely struggle to drop below 70 degrees for much of the area south of the mountains. Ample low level moisture will also likely lead to fog across much of the area. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... A deep moisture supply in and around the remains of Beryl will continue to stream east, northeast on Wednesday. Showers will enter the region during the day. Very high PWATs can be expected over the region as values rise to over two inches by late in the day across much of the region. This moisture, the remnants of Beryl and some jet dynamics interplay will allow for locally heavy showers during the day. As the atmosphere destabilizes Wednesday afternoon with temperatures climbing into the 80s some sunshine and surface dew points in the lower 70s, expect a few thunderstorms as well. These conditions will continue Wednesday night as the complex systems continue to approach from the west. Currently, latest 12Z models and ensemble solutions continue to focus on a stripe of high QPFS, mainly across northern and perhaps central areas. In this region, two to four inches of rain are certainly a possibility where localized flooding or flash flooding remains possible. Less precipitation can be expected at this time further to the south, however this will need to be monitored with time as small shifts the rainfall axis can be expected as the atmosphere remains loaded with moisture. Thursday`s forecast will be changeable. Somewhat of a dry slot crosses through the region during the day as evident by lowering of PWATs with time after some early morning rains. However, models soundings keep surface dew points on the high side once again. Therefore, scattered thunderstorms can be expected once again, but not nearly as widespread as Wednesday and Wednesday night. Very warm and muggy conditions will continue during the period Friday through the weekend as a large ridge of high pressure off the Eastern Seaboard continues to pump moisture in the region. Weak short waves crossing through the forecast area will allow for more scattered showers and thunderstorms in the region. Fog...fog may be persistent during the nighttime periods especially Thursday night onwards. Fog will occur both over the interior valleys as well as the coastline. && .AVIATION /23Z MONDAY THROUGH SATURDAY/... Short Term...Marine fog encroaching upon the coast will likely bring IFR/LIFR conditions to KRKD, KPWM and KAUG tonight through day break Monday. Valley fog will also likely bring IFR/LIFR conditions to KLEB and KHIE for a few hours later tonight while remaining terminals likely see prevailing VFR. Conditions improve to VFR for most sites Tuesday morning while fog may linger at KRKD. Scattered showers and thunderstorms will develop across NH around 18Z and track into southern Maine around 20Z and most TAF sites stand a chance of seeing a passing TSRA before activity diminishes around 00Z Wednesday. Fog and low cigs will likely bring periods of IFR/LIFR to most TAF sites Tuesday night. Long Term...LIFR and IFR conditions expected in widespread showers and thunderstorms Wednesday and Wednesday night along with patchy fog. Conditions improve to just IFR at times in scattered showers and storms Thursday and through the weekend. Patchy fog will continue especially at night. && .MARINE... Short Term...Southerly flow will prevail over the waters tonight through Tuesday night while winds and seas remain below SCA thresholds. The humid airmass in place will likely continue areas of marine fog that could become locally dense tonight through Tuesday night. Thunderstorms developing over land Tuesday afternoon will also have the potential to track into the waters with storm diminishing around sunset. Long Term...Winds will generally remain out of the south during the long range portion of the forecast but stay below SCA thresholds. Patchy to areas of fog may become persistent over the coastal waters, especially during the nighttime hours. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...Heat Advisory from noon to 8 PM EDT Tuesday for NHZ010-012-013. MARINE...None. && $$ NEAR TERM...Clair SHORT TERM...Schroeter LONG TERM...Cannon