Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jun 15 2023 08:30:48 FOUS30 KWBC 150830 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 429 AM EDT Thu Jun 15 2023 Day 1 Valid 12Z Thu Jun 15 2023 - 12Z Fri Jun 16 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST AND WYOMING... Lower Mississippi Valley through the Southeast... The series of impulses that have ridden the westerly subtropical jet and provided lift a persistent west to east oriented low level frontal zone over the Southeast continues this morning. Brief ridging builds in later today from the west which should provide a short break in activity, though a shortwave trough currently crossing into New Mexico from Arizona is poised to trigger organized activity that progresses over the lower MS Valley late tonight. Regarding morning activity, the western edge to the impulse series looks to be entering southern AR. Training convection extends east from southern AR across north-central MS and over southern AL. Much of this activity should continue a southeast progressive trend through the rest of the morning with the main threat areas after 12Z expected to be in a zone from central MS through the western FL Panhandle. Pooling of 1.75 to 2" PWs persists through this corridor extending north from the eastern Gulf Coast with abundant instability and deep layer shear maintaining organized activity to repeat over this already saturated section of the Southeast (as well as get into newer areas farther south such as around Mobile Bay. The Slight Risk extends from central MS down to the MS/AL Gulf Coast and east across southern AL/GA and far northern FL. Southern Plains... Mid-level ridging this morning primes OK into northeast TX for heavy and progressive convective activity this evening into the overnight. A marginal risk is warranted to be maintained over these areas with expansion farther south over the Red River where several inches have fallen over the past three days. Intermountain West onto the Great Plains... An upper trough digs south over the northern Rockies this morning in the wake of the departing upper low into the Canadian Prairies, connecting a trough axis through southern CA. Lee-side cyclogenesis off the WY Rockies will draw Gulf-sourced moisture up over the High Plains and promote heavy rain (good potential for 1"+ hourly rainfall) over central through southeastern WY where a Slight Risk is maintained. A QPF axis over UT into the CO Rockies, similar to yesterday is expected with maintenance of the marginal risk there. Farther east on the northern Plains, Gulf moisture drawn up around the lee-side low and slowing cold front allows for increased PW around 1.25" (1.5 sigma above normal) and diurnally enhanced development of locally heavy thunderstorms. Slower southwesterly mean flow should allow some cell mergers, continuing to warrant a marginal risk over much of the Dakotas. Southern Sierra Nevada... Weak instability combined with PW of 0.75 to 1" (2 to 3 sigma above normal) will support locally heavy rainfall rates in diurnal convection. Some instances of flash flooding are possible, particularly in areas where soils are overly saturated from multiple recent days of rain and in rugged terrain warranting maintenance of the Marginal Risk. Jackson Day 2 Valid 12Z Fri Jun 16 2023 - 12Z Sat Jun 17 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER THE EASTERN GULF COAST AND FROM EASTERN COLORADO INTO WESTERN KANSAS... Mid-South through eastern Gulf Coast... The shortwave trough currently entering northern NM tracks over the southern Plains through tonight then pivots southeast to the eastern Gulf Coast Friday morning as it tracks below an amplifying trough over the Midwest. A progressive system is likely to be ongoing over the lower MS Valley to the eastern Gulf Coast Friday morning with persistent boundaries left in the wake that aid development of diurnal convection Friday afternoon in continued ample moisture, instability, and shear. This activity would be over rather saturated soils from the multiday deluge over this region. A Slight Risk has been raised from southeast MS over southern AL and the Fl Panhandle with a marginal risk farther north and east for the more isolated heavy rain risk that is over these saturated areas. Colorado Rockies and over the Great Plains... The upper trough axis over the Intermountain West shifts east which takes the QPF focus area farther east compared to today - generally over the CO Rockies, central High Plains then from eastern KS through eastern SD ahead of a slow moving frontal system with a lee-side low mostly likely places over eastern Neb. 1.25" to 1.5" PW over the Plains is generally 1.5 sigma above normal and the slow motion of the frontal zones warrants a Marginal Risk for these eastern sections of the Plains back through CO. The embedded Slight Risk persists over eastern CO into western KS where a heavy rain focus should occur along a stalled frontal boundary between the upper trough and the lee-side low. Here there is a risk for >1+" amounts and rates >0.75"/hr over low FFG values due to recent rainfall (7-day QPE anomalies 400-600%). Jackson Day 3 Valid 12Z Fri Jun 16 2023 - 12Z Sat Jun 17 2023 ....THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS OF THE GREAT PLAINS TO MID-SOUTH AND THE EASTERN GULF COAST... Great Plains... An upper trough axis slowly shifts east from the Rockies Saturday. Abundant Gulf moisture streams up the Plains, potentially reaching 1.5" over east-central portions of the Plains where a lingering frontal zone helps focus convection north from KS to along the Dakota/MN border. More organized activity develops farther south over KS/OK, spreading later over MO/AR. As of now a sizable marginal risk encompasses this area stretching back to eastern CO. Should focused areas of heavy rain be great enough and/or areas with wet antecedent conditions be impacted again, an upgrade to Slight Risks would be warranted. Eastern Gulf Coast... Locally heavy activity looks to linger over the central through eastern Gulf Coast/northern FL Peninsula on Saturday. Ample moisture and instability will be present for this activity that may shift into the Gulf through the day. Given the wet antecedent conditions here, as well as a heavy rain threat for New Orleans, a marginal risk was raised. Jackson Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!5Zqf-Ib948mb_upLulDd5TUVekUeaeVcm4OravAM54Lf= q0HcCefQ7b70rMV7jYwmzLAgMdWWGZmh9V2C2_IVUfbalAo$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!5Zqf-Ib948mb_upLulDd5TUVekUeaeVcm4OravAM54Lf= q0HcCefQ7b70rMV7jYwmzLAgMdWWGZmh9V2C2_IVwaT4x7k$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!5Zqf-Ib948mb_upLulDd5TUVekUeaeVcm4OravAM54Lf= q0HcCefQ7b70rMV7jYwmzLAgMdWWGZmh9V2C2_IV2UwkHYU$=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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