Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Feb 16 2024 08:00:23 FOUS30 KWBC 160800 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 259 AM EST Fri Feb 16 2024 Day 1 Valid 12Z Fri Feb 16 2024 - 12Z Sat Feb 17 2024 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Chenard Day 2 Valid 12Z Sat Feb 17 2024 - 12Z Sun Feb 18 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE CENTRAL AND NORTHERN CALIFORNIA COAST... No major changes to the previous forecast issuance of the Slight and Marginal risk areas in CA. An atmospheric river is expected to bring moderate to heavy rainfall to portions of central and northern CA on Saturday. The IVT plume should be weakening as it moves ashore, however IVT anomalies off the 12z ECMWF ensemble mean are still approaching the 97th percentile for February along portions of coastal central/northern CA. Strong low level convergence does stall out for a bit early Saturday over northern CA, which should extend the rainfall duration for a bit, before everything becomes more progressive off to the south and east by later in the day. The anomalous IVT, strong low level convergence, and initial slow movement of the rain shield will all combine to produce an area of moderate to heavy QPF values along/near the coast from just north of San Francisco to near Eureka...and thus we will maintain a Slight risk across this corridor. The NBM probabilities of exceeding 2" of rain are as high as 50-80% within this Slight risk area, with probabilities of exceeding 4" around 50% within the King Range south of Eureka. In addition to these totals, we expect at least some weak instability to work into the front Saturday as a strong mid level shortwave moves into northern CA. This increased forcing and associated steepening lapse rates should help drive some hourly totals up over 0.5". This combination of 1-4" of rain and localized rates over 0.5"/hr suggests some flooding is a possibility. Still think we are good without a Marginal risk over FL. A lack of instability suggests rainfall rates will stay below levels needed for flash flooding. Rainfall totals for this 24 hr period have also shown a gradual decline in the model guidance, with most solutions supporting widespread totals around 1", but keeping any 2"+ amounts fairly localized. Chenard Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7wkFK6aO69fGp-h4mfGY5duexlrjGwu_Mt6bv3DwSpul= R3-LJ8wYJP60JOo07Jaj_3hKkfAiSCjO93NYFJAe9BcI55E$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7wkFK6aO69fGp-h4mfGY5duexlrjGwu_Mt6bv3DwSpul= R3-LJ8wYJP60JOo07Jaj_3hKkfAiSCjO93NYFJAeAUPU1RE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7wkFK6aO69fGp-h4mfGY5duexlrjGwu_Mt6bv3DwSpul= R3-LJ8wYJP60JOo07Jaj_3hKkfAiSCjO93NYFJAeDAk07eE$=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) .