Subj : HVYRAIN: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 20 2023 07:18:57 FOUS30 KWBC 200718 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 217 AM EST Mon Feb 20 2023 Day 1 Valid 12Z Mon Feb 20 2023 - 12Z Tue Feb 21 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Gallina Day 2 Valid 12Z Mon Feb 20 2023 - 12Z Tue Feb 21 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Gallina Day 3 Valid 12Z Tue Feb 21 2023 - 12Z Wed Feb 22 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEAST MISSOURI TO NORTHERN INDIANA... ....Midwest from Northern Missouri to Southern MI/Northern Ohio.... A strong dampening shortwave races out of the desert southwest accelerating through the Southern Plains into the Ohio Valley/Great Lakes driven by the digging northern stream kicker wave and nose of expected 170kt jet streak across the Central Plains by the end of the period. This will spur very strong cyclogenesis across the Central High Plains into the Missouri Valley accelerating the low level jet with highly anomalous moisture flux across the broad warm sector. At the start of the period (22.12z) the sharpening warm front should extend from near Kansas City across central MO toward the Ohio River, broad 20-25kts of sfc to boundary layer warm advection should drive the warm front northward throughout the day. As the low takes shape by early afternoon, very strong moisture flux convergence near and downstream of the surface cyclone combined with weak available instability should allow for focused convective development across becoming more scattered in nature further downstream across IL/IN/OH given weaker low level flow and instability. Isallobaric wind flow should back the strengthening low level flow while the LLJ strengthens to over 50-60kts advecting deeper moisture with total PWat values over 1.5" perhaps even up to 1.6" as ECENS and GEFS ensemble show 3.5 to 4 standard anomaly values across the Mississippi River valley for the low level moisture flux parameter. Solid northeasterly flow north of the front should sharpen and steepen the warm front and with directional convergence should further expand convection across W IL toward Chicagoland by evening hours. With the backed flow due to the strong pressure falls, the convergence axis will broaden generally parallel with the motion of the cyclone and deeper layer steering flow. This will allow for favorable training profiles. While cell motions will be very fast, limiting rainfall duration...the length of this convergence axis should support and axis of 2-3" with isolated pockets of higher totals possible. Soil conditions are anomalously dry per NASA SPoRT relative soil moisture fields through 40cm depth nearly 30-40% which is in the 1st to 5th percentile. Given the rates and hard, dormant ground conditions much of the rainfall at this intensity is probable to run off there is good confidence that the short duration should result in scattered incidents of excessive rainfall and possible flash flooding and as such, have maintained the Slight Risk of Excessive Rainfall from the Day 4 period into the short range.=20 Global models seem to have honed in on a axis from north to northeast MO across Western IL toward Northwest IND, peak rains/rates and duration should be over north-central IL and may glance the southern portions of Chicagoland, though a trend southward with time could not be ruled out given limited instability would be greater in this direction. Other considerations are proximity to the sharpening cold air, perhaps supporting a broad streak of freezing rain conditions north of the frontal zone across southern WI/northern IL into the Lower Peninsula of MI, as such the bounding Marginal Risk area to the north is a bit tight and more uncertain given ice formation.=20 As the cyclone races into the Great Lakes, the LLJ will veer and become less orthogonal for the ascent pattern across NE IND into Northern Ohio, but should still be high enough to suggest still some isolated flooding concerns to expand the Marginal as far east as the PA/OH border.=20 ....Southern Plains, Ozarks to the Lower Ohio River Valley... Strong height-falls associated with the shortwave will drive the associated cold front quickly through the Central Plains.=20 Greatest potential for intense rainfall rates may occur with quick imitation and slow initial cell motions across northeast TX, eastern OK and southeast KS before the cold front presses too quickly for prolonged duration for extreme rainfall totals. As such a broad Marginal Risk of Excessive Rainfall remains highlighted across Northern Texas through much of central MO including western AR and eastern OK. Orthogonal moisture flux into the Boston and Ouachita ranges of AR may allow for earlier shallow cell development ahead of the main line suggesting a bit higher risk for enhanced rainfall totals, but there is not sufficient evidence consistency to delineate a higher risk category at this time, but will continue to monitor trend especially as the event enters the Hi-Res CAM window.=20 Gallina Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-0XMDVLuHI0BZoeYszWYdglwI3o4clmpZ4SxR2oGIqA4= QNWnTQUnsGWqzptZwu8Rsz40q0JOZEG5V581t224t8gzNlI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-0XMDVLuHI0BZoeYszWYdglwI3o4clmpZ4SxR2oGIqA4= QNWnTQUnsGWqzptZwu8Rsz40q0JOZEG5V581t2245qIKDus$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-0XMDVLuHI0BZoeYszWYdglwI3o4clmpZ4SxR2oGIqA4= QNWnTQUnsGWqzptZwu8Rsz40q0JOZEG5V581t224_YLwAOk$=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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