Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 10 2023 18:03:10 AWUS01 KWNH 101803 FFGMPD MEZ000-MAZ000-NHZ000-110000- Mesoscale Precipitation Discussion 0691 NWS Weather Prediction Center College Park MD 201 PM EDT Mon Jul 10 2023 Areas affected...Eastern NH...Northern ME...Eastern MA Concerning...Heavy rainfall...Flash flooding possible Valid 101800Z - 110000Z SUMMARY...Highly anomalous moisture content in areas sporting overly saturated soils may lead to flash flooding this afternoon. DISCUSSION...New England is sandwiched between the deepening upper low over Upstate NY and a large dome of high pressure northeast of Newfoundland. This synoptic-scale setup is responsible for a deep layer S-SE flow within the 1000-500mb layer this afternoon. The atmosphere remains primed to support efficient warm rainfall processes, evident by the 12Z GYX sounding that depicted a 95% low-mid layer averaged RH value and a warm cloud layer close to 12,000ft in depth. The biggest factor holding back rainfall rates from becoming more intense (at or above 2"/hr) is the lack of instability. With such thick cloud cover encompassing the region, it will be difficult for convection to tap into those highly excessive rainfall rates. However, what this setup does have going for it is highly anomalous moisture content. PWATs from the Boston metro to the Portland metro will likely top 2" while eastern NH and northern ME top 1.75". According to NAEFS, these values are above the 97.5 climatological percentile throughout the region and even portions of northern ME are above the 99.5 climatological percentile. The other favorable factor is upslope enhancement in White Mnts and Great North Woods of NH, and into the Central Highlands of ME. The SE flow is positioned orthogonally to these higher ranges, favoring strong upslope ascent as a result. Lastly, the region lies beneath the left-exit region of a 250mb jet streak that will be located along the Jersey Shore by 22Z. So between orographically-favored ascent and strong synoptic-scale divergence, enough vertical motion will be present to still support as high as 1"/hr rainfall rates. The lone exception is in eastern MA where as storms form off over CT this afternoon, the available PWs and MLCAPE up to 500 J/kg could still support as high as 2"/hr rainfall rates. The past 14 days have been rather west in eastern NH, western ME, and northern MA. AHPS 14-day rainfall totals have ranged between 200-400% of normal, causing soils to be more sensitive to heavier rainfall rates. Flash flooding will have the best odds of occurring in the areas with the most saturated antecedent soil conditions, as well as in more urbanized locations and poor drainage areas. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5AusRbPKaI1LblOIGuhzT3X-PBlU5q3HVdLrjYXgR_hfmI-SuNbGfOSmwrVsr3odC219= UOOyzmtEwvNldsbpTdEqSl4$ for graphic product... ATTN...WFO...BOX...CAR...GYX... ATTN...RFC...NERFC...NWC... LAT...LON 47546935 47336857 46176911 45036953 43907062=20 43277092 42717095 42177119 42227235 42947200=20 44417132 45257138 45577076 46127034 46777003=20 =20=20=20=20=20=20=20=20=20=20=20=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .