Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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266 FXUS61 KGYX 291908 AFDGYX Area Forecast Discussion National Weather Service Gray ME 308 PM EDT Sat Jun 29 2024 .SYNOPSIS... A warm front will bring a period of rain with a few embedded thunderstorms to the region tonight before a potent cold front arrives Sunday afternoon bringing the potential for strong to severe thunderstorms. High pressure arrives early next week with dry weather and seasonable temperatures expected for the first half of next week. && .NEAR TERM /TONIGHT/... High Impact Weather Potential: A few downpours are possible overnight as well as an isolated thunderstorm though the threat for widespread flooding and severe weather is low. Pattern: Early afternoon water vapor imagery shows a potent shortwave dropping through the western Great Lakes with a plume of mid level moisture pushing into the northeastern United States. Beneath this plume...a warm front is slowly advancing through NY/PA with a broad region of light to moderate rain fueled by increasing moisture and a 50kt southwesterly LLJ. Forecast concerns for tonight center on rainfall potential as the surface warm front lifts through the region. Through this evening: Rain is overspreading the region from west to east and this will continue through the evening hours with clouds lowering. SE NH may escape meaningful rainfall through 8pm...but elsewhere conditions will turn wet. Temperatures won/t really move much...largely sitting in the 60s across the area. Tonight: Warm front lifts north and east through the region tonight with 2" PWAT plume overhead this evening gradually shifting east of the area by daybreak Sunday. While isentropic ascent up the frontal surface in the presence of some weak elevated instability will be sufficient to support rainfall...broader scale forcing appears rather lackluster through the overnight with +DPVA mostly brushing the international boarder with some weak height falls overhead and some jet entrance support. Overall this suggests occasional showers through the overnight...with the greatest threat for a few downpours being over the mountains where the synoptic scale forcing is best. From a hazard perspective...the threat for flooding appears rather low...but nonzero given the deep moisture/warm cloud depths. A mild night is in store given continued warm air advection with lows falling into the mid 50s in the mountains with 60s to the south. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... High Impact Weather Potential: * Slight Risk of Severe Thunderstorms * Primary threat: Damaging Wind * Secondary threats: Localized flooding...hail and an isolated tornado * Timing: 12pm-7pm Pattern: Low pressure north of northern New England will move north and east during the day with a cold front over western New York as a positively-tilted shortwave and region of mid level height falls pushes just north of the region through the day. Our forecast focus will be on severe convective potential as the surface cold front crosses the area Sunday afternoon. Also watching heat indices across southern NH which may make a run at advisory thresholds ahead of the front. Sunday: Shortwave rotating through the positively-tilted longwave trough races just north of the region through the day with 70kt H5 speed max moving overhead in tandem with right entrance region to 120kt upper level jet. Should see some sun in the morning as we move into the warm sector ahead of the cold front but convection may already be ongoing across western New York...strengthening as downstream instability strengthens. By early afternoon convection will likely reach the mountains of NH as well as the CT Valley with the mesoscale guidance favoring the potential for one line of storms closer to the beset mid level forcing moving from northern NH ESE through the Capitol region of ME with another line moving across southern NH where the best instability will be located and will be downstream of the most likely location for morning convection. Here/s a run through the convective parameters.... Instability: Sizable disparity in the guidance here with the NAM nest and the HRRR in their typical wetter/drier camps...respectively. Looking at upstream llevel moisture...a compromise is likely best which favors 1500 J/kg of MLCAPE in southeast of the mountains as surface dewpoints push just above 70. Shear: 40kts in the 0-3km layer with 60kts in the 0-6km layer. Hodographs are fairly straight and parallel to the approaching frontal boundary. Expect initial cells to grow into lines with bowing segments likely given ample 0-3km shear. Within these bows would be the best potential for a spin up. Lapse rates: Decent in the H8-7 layer, but weaker /around 6C/ in the H7-5 layer. Sufficient to support deep convection through the afternoon. Overall...this lines up well with the SPC outlook for damaging winds posing our greatest severe weather risk with hail and an isolated tornado lesser...but non-zero threats. T8s pushing to +18C should allow highs to reach near the 90F mark given sufficient sun. This...in addition to dewpoints moving above 70 will allow a few spots in southern NH/SW ME to approach heat advisory levels...but not high enough or long enough to warrant any headline issuance today. Sunday Night: With the surface cold front near the coast to begin the period...expect any convection to quickly be exiting the region with mesoscale guidance suggesting a few showers along a secondary trough/cold front that crosses the region overnight. Best potential for these overnight will be in the mountains with at least partial clearing elsewhere. Cold air advection will push T8s back into the upper single digits by daybreak Monday with lows to fall into the 50s in the mountains and lower 60s elsewhere. && .LONG TERM /MONDAY THROUGH SATURDAY/... At 500 MB across NOAM and environs we still a pattern that gradually favors warmer and more humid conditions, although nothing that I would call hot through next week. We will near the boundary of the sub-tropical over the Atlantic and the jest stream to our N, so we can expect some rounds of SHRA/TSRA, but no significant widespread events. However, on Monday we will start off less warm, but still not out of ordinary summer temp ranges. There is a little convergence in central and S NH as NE flow runs into a bot of dead flow over S New England, so will see more clouds here, and maybe a couple showers Monday afternoon, but I think this area Is still partly sunny, with mostly sunny skies to the N and E. Highs will mostly be in the 70s. Monday night will be the coolest of the stretch with clearing skies and light winds. Expect lows in the upper 40s in some mtns pots and generally low to mid 50s elsewhere. Tuesday looks mainly sunny and dry with low humidity, as high pressure crosses the region, and highs 80-85, but cooler along the mid-coast. Flow shifts SW as the sfc high shifts offshore, and the resultant return flow will bring in more humid conditions. Wednesday looks mainly dry though, but with partly sunny skies and highs 80-85 once again. A weakening cold front moves in from the NW Wed night, and loses its steam over the CWA, so some SHRA and maybe some TSRA are possible Tue night into early Thursday, but expect clearing skies and warm and humid conditions on Thursday. Weak high pressure moves in for Friday, so its be dry, but still warm and humid. Next weekend remains uncertain as we sit beneath weakly anticyclonic flow and troughing to our W, which the means the potential waves and rounds of convection, but it should stay on the warm and humid side. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Short Term... Summary: Deteriorating conditions expected through tonight as a warm front crosses the region with showers and a few embedded thunderstorms. Showers end Sunday morning...with another round of showers and strong to severe thunderstorms in the afternoon before partial clearing Sunday night. Restrictions: MVFR CIGS are building across the terminals this afternoon as showers arrive from the west. Expect deterioration to IFR or low MVFR this evening and overnight with low CIGS and some fog development. Improvement to VFR is expected on Sunday morning with showers/thunderstorms bringing additional restrictions in the afternoon. Some fog development is possible HIE/LEB Sunday night with restrictions possible here. Winds: Southerly winds 10kts will continue through tonight before shifting southwest and increasing to 12g18kts for the day Sunday. Winds turn northwest less than 10kts behind the cold front Sunday night. LLWS: Southwesterly winds in the 1.5-2kft layer strengthen to 40- 50kts with LLWS expected overnight tonight. This will end Sunday morning with no additional LLWS through Sunday night. Lightning: Very isolated thunderstorms are possible for the overnight. On Sunday...chances for thunderstorms increase for the afternoon with the potential for thunder throughout the terminals in the 18Z-00Z timeframe. Some of these storms could be strong to severe with damaging winds. No lightning is expected Sunday night. Long Term...VFR expected Monday through Wed, with possible valley fog Monday night. Then more widespread flight restrictions possible Wed night into early Thu in SHRA/TSRA and some fog. && .MARINE... Short Term...SCA conditions due to both winds and waves are expected to continue through Sunday ahead of an approaching cold front. Winds shift slowly shift northwesterly and diminish Sunday night...though residual SCA waves will likely persist through the first half of the night. Long Term...Generally light flow is expected through the middle of the week with winds and seas staying below SCA levels, but it could pick up some Wed night or Thu. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 11 PM EDT Sunday for ANZ150>154. && $$ NEAR TERM...Arnott SHORT TERM...Arnott LONG TERM...Cempa