Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Oct 25 2023 14:20:39 FOUS30 KWBC 251420 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1019 AM EDT Wed Oct 25 2023 Day 1 Valid 1416Z Wed Oct 25 2023 - 12Z Thu Oct 26 2023 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN PLAINS... ....1430Z Update... Continued heavy rainfall across the areal convergence axis in eastern KS will continue for the next several hrs with a broader precip field as indicated by the latest radar trends. 12z HRRR has a decent handle on the QPF axis and overall spatial depiction of the rainfall occurring. Latest trends have some of the heavier rains protruding into the Kansas City metro by later this afternoon and evening, compiling on top of the recent rains from the past 24 hrs near the urban corridor. In collaboration with the Kansas City WFO, have expanded the SLGT to include east-central MO, extending westward to about 15 miles west of Wichita in KS. Further south, minor adjustments on the flanks of each outlook with a deviation slightly to the east for all the risk areas, including the MOD. The main axis of heaviest precip is still well on track to fall within the forecast Moderate with trends possibly nudging a bit further to the east. Will provide more insight on any future expansion once we get the full suite of 12z CAMs, but wanted to make reference considering this is the highest expected impact area(s) the next 24 hrs. Kleebauer ....Central Texas into south central Oklahoma... The strong height falls moving across northern Mexico Tuesday into early Wednesday will be ejecting northeastward into the Southern Plains day 1, continuing the multi day heavy rain event for portions of the Southern Plains. No significant changes expected to the axis of above average PW values across the Southern to Central Plains into the Lower MO Valley for the upcoming day 1 period with anomalies remaining 2 to 3+ standard deviations above the mean across these regions. This and the overall strong upper dynamics associated with the northeastward ejecting closed low will support the likelihood for additional widespread heavy rains from the Big Bend, northeastward into Northwest TX, much of OK, save for the Panhandle and southeast OK and into southeast Kansas. While the latest hi res guidance is verifying slow with the current area of organized convection pushing into West Texas early this morning, there is good agreement that this area will continue to push eastward and support additional heavy rains. The previous outlook was upgraded, adding a moderate risk across large portions of Central to Northwest TX into far south central OK. The moderate risk corresponds well with where the latest HREF neighborhood probabilities are high for 2 and 3"+ amounts, 40-80%, and 20-50% for 5"+ totals and also high for the HREF EAS probabilities for 1 and 2"+ amounts. Much of the moderate risk area also corresponds to where there is overlap of heavy precip over the past 24 hours and the expected day 1 heavy qpf axis. The day 1 slight area continues to match fairly well with CSU first guess fields, although having a slightly different orientation to the axis to match the latest day 1 qpf. ....Upper Mississippi Valley... Latest surface analysis continues to show a well defined frontal boundary stretching from southeast MN, east northeastward into central WI and the central to eastern U.P. of MI. This boundary has been a focus for active area of heavy rains pushing parallel, along and to the north of the this front. Model consensus is for additional rains to develop along and to the north of this front late Wednesday afternoon/evening as low level west southwesterly to southwesterly flow strengthens again into the front. This will favor the potential for another round of convection to move parallel to the boundary early Thursday and possibly across areas that received heavy amounts over the past 24 hours. There is expected to be some overlap across southern MN to west central WI=20 with past 24 hours heavy rains and additional rains late day 1.=20 At the moment, we kept the risk level at marginal given latest model qpfs and HREF neighborhood probabilities that are less than 20% for 1"+ amounts in an hour across the overlap areas.=20 Oravec Day 2 Valid 12Z Thu Oct 26 2023 - 12Z Fri Oct 27 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE UPPER MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES... ....Upper Mississippi Valley into the Upper Lakes... The well defined front stretching from the Upper Mississippi Valley into the Upper Great Lakes will continue to be the focus for additional heavy rains day 2. The next round of convection moving along and to the north of this front that is expected to begin late day 1, will continue into the day 2 time period as surface low pressure moving along this front helps to maintain strong west southwesterly flow into this front. This will support potential for additional heavy rains from northern IA, across far southeast MN, central to southern WI into the northern L.P. of MI and the southern U.P. of MI. The model consensus for the day 2 qpf axis has shifted southward from previous runs and has resulted in less overlap of areas that have received heavy rains over the past 24 hours and the day 2 qpf axis. The new day 2 outlook has also trended southward with the marginal and slight risk areas by about 40-60 miles. ,...Eastern Texas... Large scale dynamics will be weakening across the Southern Plains day 2 as the closed low ejecting northeastward day 1 continues to weaken as it presses into the Central Plains and Mid Mississippi Valley region. However, an axis of anomalous PW values ..2 to 3+ standard deviations above the mean... will persist across eastern TX. Model consensus is for moderate to heavy amounts in this anomalous PW axis. This expected precip will be mostly to the southeast of the expected day 1 heavy amounts. For this reason,=20 kept any risk at marginal. This marginal agrees well with the latest day 2 CSU first guess fields. Oravec Day 3 Valid 12Z Fri Oct 27 2023 - 12Z Sat Oct 28 2023 ....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF THE SOUTHERN PLAINS INTO THE LOWER ARKANSAS RIVER VALLEY... ....Northeast Texas, southeast Oklahoma into northwest Arkansas... The anomalous PW axis across eastern Texas on day 2 will begin to lift northeastward ahead of the strong cold front sinking southeastward through the Central to Southern Plains during day 3. This front is expected to slow its southeastward push toward the end of the day 3 period becoming nearly stationary from northeast Texas into northwestern Arkansas. Precipitation should become more active along and ahead of this front late Friday afternoon into the early hours of Saturday when well defined frontal convergence and favorable right entrance region jet dynamics enhance uvvs in the anomalous PW axis. The model consensus is for a narrow axis of potentially moderate to heavy totals along this front from northeast Texas into southeast Oklahoma and northwest Arkansas. There may be some overlap of day 1 heavy precip and day 3 amounts across portions of northeast Texas into southeast Oklahoma. The threat level was maintained as marginal from the old day 4, but may need to be upgraded to slight in later issuances depending upon where the observed heavy amounts on day 1 occur. Oravec Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_23J53C7nRcCeu4hp9_fW02wMNvwAxyh1L23OyMDdWtt= pIFMAfBTV6KkfP193oqAhvejHqz9wk-JQkoddLwexzA9N9Q$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_23J53C7nRcCeu4hp9_fW02wMNvwAxyh1L23OyMDdWtt= pIFMAfBTV6KkfP193oqAhvejHqz9wk-JQkoddLwedsKaBE0$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_23J53C7nRcCeu4hp9_fW02wMNvwAxyh1L23OyMDdWtt= pIFMAfBTV6KkfP193oqAhvejHqz9wk-JQkoddLwe2phPZgE$=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. 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