Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 14 2023 08:08:04 FOUS30 KWBC 140808 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 407 AM EDT Mon Aug 14 2023 Day 1 Valid 12Z Mon Aug 14 2023 - 12Z Tue Aug 15 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE MID WEST AND LOWER MICHIGAN, FROM THE SOUTHERN TO CENTRAL APPALACHIANS, MID ATLANTIC AND SOUTHEAST NEW YORK STATE INCLUDING THE NEW YORK CITY METRO AREA AND LONG ISLAND... ....Mid West into Lower Michigan... A strong, compact upper low will be pressing eastward Monday through portions of the Mid-West and south of the Lower Lakes.=20 Simulated radars from the latest hi res runs all show a well defined comma head deformation band moving across southern Wisconsin, northern Illinois into the southern portions of the L.P. of Michigan. While instability is not expected to be very high, Mu-cape values generally less than 500 j/kg, the slow motion of the upper low in a region of 1.50-1.75" PW values will provide for a 4 to 6 hour period of moderate to heavy rainfall with hourly rates of .50-1" possible. Northeasterly low level flow off of southern portions of Lake Michigan may also maximize boundary layer convergence along the southeast Wisconsin coast into the northeast Illinois coast. HREF neighborhood probabilities are showing this area having the greatest probabilities, 80%+ for 3"+ totals day 1 and a smaller region of 40-60% probabilities for 5"+ totals. Overall, the slight risk area was drawn to encompass where the greatest 2 and 3"+ HREF probabilities are for the upcoming day 1 period, along where the HREF EAS is showing the best agreement for 1 and 2"+ amounts. The latest outlook was narrowed from the previous issuance as per the above mentioned HREF neighborhood and EAS probabilities. ....Southern to Central Appalachians, Mid-Atlantic into southeast New York State... Anomalous PW values, 2 to 2.5+ standard deviations above the mean, expected to surge northeastward day 1 on the southeast side of the strong upper low moving from the Mid-West and just south of the Lower Lakes. Strong uvvs ahead of this closed low will support heavy rain potential in this anomalous PW axis that will push northeastward day 1 from the Southern to Central Appalachians, Mid-Atlantic and into southeast New York State.=20 There is general model consensus for an axis of heavy rains across these areas, with the slight risk area maintained primarily where the highest HREF neighborhood probabilities for 2"+ are depicted along with where the greatest HREF EAS probabilities for 1"+ are depicted. Changes to the previous outlook were to expand the slight risk area northward by approximately 40 to 50 miles along the northeast PA and Southern Tier of NY border area.=20=20 Instability is expected to be limited across this area, but with lower ffg values from recent rains, runoff issues are possible from .50-1"+ totals in an hour or two in the region of max isentropic lift ahead of the surface wave pushing across the northern Mid-Atlantic into southeast NY State. ....Southwest into the Southern Great Basin and northern Sierra... A surface cold front currently sinking southward across the Southern High Plains is expected to become stationary in the vicinity of the AZ/NM border. The simulated hi res radars suggest this boundary will be the focus for convection Monday afternoon in an axis of 500-1000 j/kg along this front and PW values 1 to 2+ standard deviations above the mean. HREF neighborhood probabilities are fairly high in this axis for 1"+ amounts, although the HREF EAS for 1"+ are not as high. Isolated runoff issues are possible, but with low EAS values 5-15% the risk level was maintained at marginal. The previous marginal risk area was expanded westward into the Southern Great Basin and into the Northern Sierra. This was to cover what may be another day of widely scattered convection in a broadly difluent upper flow to the east of the slow moving upper low off the south central California coast. Oravec Day 2 The Day 2 outlook will be updated by 0830Z. 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!-EaP2cy7CrBz9_X6mo5LiNlLkmLGQfVhNJmG6edpmUP0= 8JGhn9Amw4O0nzjySIov0ys0pyfryUdnhC-M4EVm8734GaU$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-EaP2cy7CrBz9_X6mo5LiNlLkmLGQfVhNJmG6edpmUP0= 8JGhn9Amw4O0nzjySIov0ys0pyfryUdnhC-M4EVmSoD0vrw$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-EaP2cy7CrBz9_X6mo5LiNlLkmLGQfVhNJmG6edpmUP0= 8JGhn9Amw4O0nzjySIov0ys0pyfryUdnhC-M4EVma1_qi60$=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) .