Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jan 07 2023 16:01:14 FOUS30 KWBC 071601 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1100 AM EST Sat Jan 07 2023 Day 1 Valid 16Z Sat Jan 07 2023 - 12Z Sun Jan 08 2023 ....THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ACROSS PARTS OF NORTHERN AND CENTRAL CALIFORNIA, INCLUDING NAPA VALLEY AND NORTHERN PORTIONS OF THE BAY AREA... ....Southwest Oregon into Northern and Central California... The models continue to depict robust QPF totals with this latest AR, especially within the Moderate Risk area, where most CAMs have an additional 3-6". The activity has begun to wane a bit in the Moderate Risk area as one embedded vort center comes ashore...but the latest HRRR maintains its idea of rainfall coverage and rates ramping back up later this afternoon and tonight. Morning satellite imagery supports the idea showing additional development where models showed renewed robust low-mid layer moisture transport that should soon be directed toward the Central CA Coast. The latest current high-res CAM guidance still show hourly rainfall rates peaking between 0.50-0.75+ inch after 00Z Sunday, aided by some elevated instability (MUCAPEs 400-600 J/kg), which would pose a flash flood threat over several 2020-2022 burn scars west of the Sierra and south of the Shasta/Siskiyous mountains. Earlier adjustments to the Moderate Risk still look good and were maintained without additional adjustments at this point. Recent excessive rains along with several additional inches forecast, there will likely be widespread areas of flooding and if in proximity of recent burn scars, the threat for landslides, debris flows and road damage will elevate. ....Western Gulf Coast into portions of the Lower Mississippi and Tennessee Valleys... Continued with the Marginal Risk of excessive rainfall over this region. Strengthening right-entrance region upper forcing along with a slow moving front has started to draw moisture northward.=20 There may be enough moisture flux to support a small area of training thunderstorms across this region later today and this evening with enough rainfall to produce isolated run off problems. Considering the spread in the guidance, will loosely organized convection implied in the splotchy QPF pattern, along with the relatively dry conditions over the past few days, have continued with the Marginal Risk with the expectation that any flash flooding will be isolated/localized. Instability is meager as well, at least outside of the Middle and Upper TX Coast, which will tend to impede convective upscale growth. Bann Day 2 Valid 12Z Sun Jan 08 2023 - 12Z Mon Jan 09 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF NORTHERN AND CENTRAL CALIFORNIA... ....Southwest Oregon into Northern and Central California... Compared with yesterday's Day 2 ERO, no significant changes were noted with the overall environment and synoptic pattern during this period. Although there will be a relative "lull" for a few hours as one AR wanes and the next approaches, the additional rainfall over saturated soils will keep the threat for excessive rainfall and flash flooding elevated. The Slight and Marginal Risks that were already in effect remain in good order so no adjustments were needed at this time. At the start of the Day 2 period (12Z Sun), one shortwave trough will have pushed through (pcpn on the wane Sunday morning), while another, more elongated AR approaches Sunday night. Guidance shows PWs ~1.25" approaching the Central CA Coast Sunday night, along with even more anomalous low-mid layer moisture transport compared to the previous AR event(s). The 00Z SREF and GEFS in fact indicates 850-700 mb moisture flux standardized anomalies climbing to near +4 along the coast by 12Z Monday. While the bulk of this particular event will be during the day Monday (current Day 3), deterministic and probabilistic QPF fields, along with analogs and ERO first guess fields using 24 hr ARI exceedance, would support continuing with the Slight Risk that was inherited from yesterday's Day 3 ERO. This especially taking into account the anomalously wet soils (above the 90th percentile in the top 1 meter layer per the latest NASA SPoRT), owing to the onslaught of recent AR events. Hurley/Campbell Day 3 Valid 12Z Mon Jan 09 2023 - 12Z Tue Jan 10 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS A LARGE PORTION OF CALIFORNIA, INCLUDING THE BAY AREA AND MUCH OF THE CENTRAL VALLEY... ....California... The more significant Atmospheric River or AR event is still expect to impact much of CA ahead of a more amplified upper trough, where a more elongated AR is expected to tap into the subtropical regions of the south Pacific. Guidance continues to show PWs climbing between 1-1.5" (highest along the coast), with southwesterly 850 mb flow peaking between 60-70 kts. Low-mid layer moisture transport will be quite robust, as the 850-700 mb moisture flux peaks around 4 standard deviations above normal per the GEFS. Meanwhile, some elevated instability (at least 200-400 J/kg per the ECMWF and GFS), along with the degree of deep-layer forcing and moisture, would support hourly rainfall rates of 0.50-0.75+ inch, especially within the Moderate Risk area. Overall, guidance consensus is quite good with the QPF, with 24 hour totals between 2-4+ inches over most areas, with pockets of 5-8+ inches noted along the coast and coastal ranges and across the western slopes of the Sierra. This is a fairly significant event as far as ARs go, with the latest deterministic QPF indicating the potential for a 5 to 10 year average recurrence interval or ARI within portions of the Moderate Risk area. Considering how wet the soils will be ahead of this event (over the 90th percentile within the top 100 cm across the majority of the outlook areas per the latest NASA SPoRT), impacts from flash flooding or more rapid inundation will become more likely, again especially within the Moderate Risk area. Upon evaluation of the guidance trends over the next couple of days, especially as the event gets within the high-res model windows, a High Risk may become necessary in subsequent ERO issuances. Hurley Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9cZ13cNDTxDb_NpgSkWISYyO5NO-kd9KbRrQLbkOisxC= X5o2dPc6_7BTaWuXNLu9m_Xx4280JqRENSEhPMkHJiSGm6E$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9cZ13cNDTxDb_NpgSkWISYyO5NO-kd9KbRrQLbkOisxC= X5o2dPc6_7BTaWuXNLu9m_Xx4280JqRENSEhPMkHH_ew3No$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9cZ13cNDTxDb_NpgSkWISYyO5NO-kd9KbRrQLbkOisxC= X5o2dPc6_7BTaWuXNLu9m_Xx4280JqRENSEhPMkHa2glnsw$=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) .