Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 10 2022 15:59:15 FOUS30 KWBC 101559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Sat Dec 10 2022 Day 1 Valid 16Z Sat Dec 10 2022 - 12Z Sun Dec 11 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE COASTAL RANGES OF CENTRAL CALIFORNIA TO THE WESTERN TRANSVERSE RANGE... 1600Z Excessive Rainfall Outlook Discussion... ....Northern to Central California Coast to the western Transverse Range... Except for removing a small portion of the Marginal Risk area in far northern California where satellite imagery showed the deepest moisture being shunted eastward and out of the area...no changes were made to the remainder of the Marginal or Slight Risk areas.=20 The forecast reasoning remains the same as indicated below in terms of the large scale pattern, evolution and ensemble-based probabilities. Considered adding a focused Marginal Risk area in the upslope region on the east side of the Sacramento Valley where several inches of rain are forecast where precipitation-type is not a concern. The hydrologic response from the National Water Model suggests that there is a non-zero chance for flooding but it appears that the threat will remain below 5 percent.=20 Consequently...no area was highlighted at this point but will be watched for later amendments if needed. ....Northeast Texas into Southern Arkansas... Latest HREF guidance suggests that the 70 to 80 mile southward shift made in the 0830Z ERO still looks good. Radar imagery from early morning showed one area of rain pulling away from southern Missouri...but a cold front pushing southward should provide the focus for additional convection capable of producing rainfall rates of 1+ inch per hour which results in isolated runoff problems or ponding in areas of poor drainage. Bann 0830Z Excessive Rainfall Outlook... ....Northern to Central California Coast, western Transverse Range... An atmospheric river event will be sinking southeastward down the northern to central California coast day 1 on the southeast side of the amplifying mid to upper level trof off the Pac NW coast. A well defined band of heavy precip likely to sink southeastward along and ahead of the associated cold front in the region of strong south southwesterly low level flow, followed by more showery conditions post frontal. 850-700 mb moisture flux anomalies in this onshore flow axis expected to remain in the 3 to 4+ standard deviations above the mean level through day 1. While the front and associated strong low level moisture flux axis will be pressing fairly quickly southeastward, there will be a period of heavy rains with model consensus for heavy precip totals along the northern to central California coast to the western portion of the Transverse Range. The slight risk area was drawn where HREF neighborhood probabilities were high...50-90%...for 3"+ totals this period. With respect to changes from the previous issuance, the slight risk was extended about 80 miles farther to the north to include the higher terrain west of San Jose, which is covered by the above mentioned higher HREF probabilities. Model consensus is for 2 to 4" in the slight risk area, with max totals 5 to 7" in the coastal range from Monterey south to near San Luis Obispo.=20 Hourly rainfall rates likely in the .50"+ range with HREF probabilities high in the anomalous moisture flux axis...60-90%...but drop off significantly for 1"+ totals, illustrating the hourly precip limits due to the fairly quick southeastward push.=20 ....Northeast Texas into southern Arkansas... The latest model guidance continues to show potential for a period of training of convection in west southwest to east northeasterly direction along and ahead of a surface cold front pressing southward across North TX/southern AR at the beginning of the day 1 period. There has been a southward push in the model qpf axes from the previous model runs, resulting in the previous marginal risk area centered from southeast OK/far northeast TX into central OK being relocated approximately 70 miles to the south for the upcoming day 1 period. This marginal risk area lines up well with where the latest HREF neighborhood probabilities are high for 1" and 2"+ totals this period, 90%+ and 40-80% respectively. In areas of training, isolated runoff issues are possible. Oravec=20 Day 2 Valid 12Z Sun Dec 11 2022 - 12Z Mon Dec 12 2022 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTHWESTERN CALIFORNIA... The day 1 atmospheric river event affecting northern to central California coastal sections will continue to press southeastward day 2, with the axis of anomalous 850-700 mb moisture flux values pressing into Southern California. 850-700 mb moisture flux anomalies of 4+ standard deviations above the mean will push across Southern California during the first half of the day 2 period, supporting heavy rainfall potential from the Peninsular Range westward to the coast and to the south of the eastern portions of the Transverse Range. Similar to the day 1 period, this anomalous moisture flux axis will be fairly progressive to the southeast, limiting hourly amounts to 50"+. There continues to be good model agreement for heavy rains across these areas, with consensus for areal average 1 to 1.5"+ amounts with max totals of 2-3"+ in the favored terrain regions of the Transverse and Peninsular Ranges. These rains will support localized runoff issues, especially across the numerous burn scar regions of southwestern California. Oravec Day 3 Valid 12Z Mon Dec 12 2022 - 12Z Tue Dec 13 2022 .....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF THE SOUTHERN PLAINS... The strong closed low moving inland into California and the Great Basin on day 2 will push across the Great Basin, Central Rockies and into the Central High Plains by day 3. South southwesterly low level flow expected to strengthen significantly on the southeast side of this closed low through much of the Southern and Central Plains, with 850-700 mb moisture flux anomalies 3 to 5 standard deviations above the mean across these areas. Favorable upper difluence, strong frontal/pre-frontal convergence in this axis of strong moisture flux will support increasing precipitation coverage day 3 across much of the Southern and Central Plains.=20 The marginal risk area was confined to the southern portion of the model qpf consensus region where instability will be the greatest and possibly support an area of convection that could produce isolated short term precip totals of 1"+. At the moment, it appears any convection that does form along and ahead of this front will be fairly quick moving to the east, keeping the risk level at marginal. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_yPJSCqyolTPdzROhgCju9kWqjY3JGJfYSL9AweEPLYL= g-ZYOgvIiqb05AdZTUPCpKC-DyxeGk-d8iPdEGQzPrKm8pE$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_yPJSCqyolTPdzROhgCju9kWqjY3JGJfYSL9AweEPLYL= g-ZYOgvIiqb05AdZTUPCpKC-DyxeGk-d8iPdEGQzjBkCY-E$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_yPJSCqyolTPdzROhgCju9kWqjY3JGJfYSL9AweEPLYL= g-ZYOgvIiqb05AdZTUPCpKC-DyxeGk-d8iPdEGQzg48bZ1A$=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) .