Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jan 10 2024 04:08:39 AWUS01 KWNH 100408 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-NJZ000-101000- Mesoscale Precipitation Discussion 0009 NWS Weather Prediction Center College Park MD 1107 PM EST Tue Jan 09 2024 Areas affected...portions of southern NY...CT...RI...MA...NH...southern VT...far southern ME Concerning...Heavy rainfall...Flash flooding possible Valid 100400Z - 101000Z Summary...Scattered to numerous instances of flash flooding are likely with localized rainfall totals of 1-3" atop potentially rapid snow water equivalent snowmelt of 1-2". Discussion...Strong low to mid-level (925-700 mb) warm air advection (WAA) is ongoing across much of New England as a surface warm front begins to traverse southern portions of the area. This warm front is in association with an anomalously strong low pressure system (surface pressure ~975 mb) and accompanying upper-level low over the Great Lakes region. As precipitable water values continue to increase to 1.1-1.4 inches (near record territory, per ALB/GYX/CHH/OKX sounding climatology), upper-level divergence is also abundant via the right-exit region of a 140+ kt jet streak (at 250 mb). While instability is certainly the primary factor that is lacking for heavy rainfall, the strong dynamics (WAA, frontogenesis, UL divergence) will largely make up for this lack of instability. The new 00z hi-res guidance is in excellent agreement regarding expected rainfall rates and totals in the near term, suggesting that rates of 0.25-0.75"/hr will largely prevail (though may locally approach as high as 1"/hr) with localized totals of 1-3" (through 10z). While totals of 1-2" are most likely for the vast majority of the area, these amounts should mostly fall a bit short of the associated 6-hr flash flood guidance (which largely ranges from 2-3"). Antecedent conditions are also near normal, per NASA SPoRT 0-100 cm soil moisture generally near the 50th percentile (with the exception of southern VT, northern NH, and adjacent portions of ME which are near the 90th percentile). While an event of this magnitude and relatively short duration would typically not be of great concern (despite the impressive dynamics and highly anomalous tropospheric moisture), the factor that tips the scales in this case is the still unaccounted for unmelted snowpack. According to NOHRSC, unmelted snow water equivalent ranges from 1.0-2.0" across the bulk of the region. This is rather significant, given that dew points are already rising into the 40s and will reach the 50s in southern portions of the region. This quickly warming air mass (and falling rainfall) should efficiently melt at least half (if not more) of the snowpack. This will effectively add at least another 0.5-1.0" of melt on top of the expected 1-3". For this reason, at least scattered instances of flash flooding appear to be likely, and should snowpack melt sufficiently instances of flash flooding may become numerous across the region. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8aoZHuSEqfNYAduxi3QaHPqtjGgq0T5g5DFDpydVmLaeFwJZVOXlwuLomjuJ-mZVzpDA= Xz9ZyxYi3HrTqHxsDxvARZE$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...GYX...OKX... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 44807106 44737076 44577054 44297037 43917018=20 43607033 43187064 42227068 41997092 41637076=20 41417121 41307178 41247281 41107336 40957387=20 41147426 41347453 41607465 42157461 42367417=20 42707380 42777322 43247301 43587269 43617234=20 43977211 44237191 44467152 44717135=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) .