####018003194#### AWUS01 KWNH 161752 FFGMPD MEZ000-NHZ000-170000- Mesoscale Precipitation Discussion 0278 NWS Weather Prediction Center College Park MD 152 PM EDT Fri May 16 2025 Areas affected...Northern NH...North & Northwest ME... Concerning...Heavy rainfall...Flash flooding possible Valid 161800Z - 170000Z SUMMARY...Widely scattered but very slow moving thunderstorms with capability of 1.5"/hr and focused spots of 2-3" are possible, resulting in possible localized flash flooding. DISCUSSION...Well before arrival of eastern edge of very broad/deep layered cyclone across the Great Lakes, a surge of enhanced moisture sourced from the tropics/sub-tropics a week or so ago lifted northward across northern New England and has lingered in place. Total moisture values of 1.25-1.3", mainly loaded from the surface to 700mb as noted by upper 50s low 60s Tds, and 850-700mb CIRA LPW within the 95th-99th percentile (for the running mean over the last 20 years). Combined with solid clear skies and ample insolation throughout the day ahead of forcing/approaching cirrus deck, CAPEs have risen to 1000-1500 J/kg across the area of concern. VWP and RAP analysis shows recent switch of boundary layer (850mb winds) to the south with values increasing to 15kts. Given weak capping, this has been sufficient convergence in proximity to higher terrain/upslope to break out isolated to widely scattered convection over the last few hours from the Presidental Range through the northern deep woods of Maine with a few cells reaching -45 to -50C. GOES-E WV suite shows vorticity center at mid-level intersection of weak warm conveyor belt lifting northeast but will be also peeling more northward over the next few hours this will bring some weak favorable upper-level divergence ascent pattern to help maintain convection but also result in further expansion of the 500-1000mb thickness ridge. With mean steering flow being weak at 5-10kts, this further helps to reduce forward propagation vectors, with some hints in Hi-Res CAMs that retrograding cells may occur toward the north and northwest with the approaching height-falls. This should support longer localized duration and with increasing convective coverage, higher potential for cell interaction and mergers. Given mild moisture flux and instability rates of 1.25-1.5" are possible. As such, localized widely scattered incidents of 2-3"+ may occur especially with any mergers/repeating through the late afternoon. While the area is remote/low population, it is fairly rugged and FFG values (minus the localized maxima near/north of Laconia, NH) of 1-1.5"/hr & 1.5-2" are well within range of being exceeded within/near the cores of these cells, and as such an incident or two of localized flash flooding is considered possible through 00z. Gallina ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...CAR...GYX... ATTN...RFC...NERFC...NWC... LAT...LON 47496897 47196785 46306773 45596830 44856964 43667092 43857186 44997123 45997052 47216964 ####018001009#### PENA01 KWNH 161200 @UHPISF000CNé MPDSUM@V2.0@0101700060@12160525@@0NMCGPHMPD t0@!' `' ` @ ęž& ęBń7)p&ŹPNAM02@@,ŕ4ü{ů~űţ˙˙˙˙˙€˙˙€˙˙˙˙˙€ ‚ƒƒ…†„„~„|„{‚|‚{|€u˙|ţzţ{˙zţz€d˙|˙|@@ŕ4€@@ŕ4€@@A98‚ƒ„„„„…„……………„„††…„………„}„}„|ƒ|ƒ{{‚{|{ýz÷yý~ü~ü~ű}ú}ű}ú}ů}ú}ů}ú~ů}ú}ů}ú~ű~ú~üű~ýýúý€‚ƒƒ‚@@98€@@98€@@  ˇ‚„………†††…‡†…„~‚|‚y€t˙zü}üüúőúęůű˙@@ ˇ€@@ ˇ€@@Źɀ0276 @@xl€0277 @@Ç‘€0278 @@d&€MESOSCALE DISCUSSION SUMMARY GRAPHIC @@d&ţ€ OF ALL VALID MESOSCALE DISCUSSIONS AT @@d&ü€ TIME OF PRODUCT CREATION:@@d&ú€ ISSUED 05/16/2025 1752Z @@ d™€NOAA/NWS/NCEP@@d™ţ€ WEATHER PREDICTION CENTER @@d™ü€ FOR COLOR VERSION SEE: @@d™ú€ WWW.WPC.NCEP.NOAA.GOV @