Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Tue May 30 2023
 
Day 2
Valid 12Z Wed May 31 2023 - 12Z Thu Jun 01 2023 

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE 
SOUTHERN HIGH PLAINS...

...West into the Northern Rockies and Plains...
The localized risk for excessive rainfall looks to continue across 
portions of northern CA into northwest NV into Day 2 (beginning 
12Z Weds), also extending farther northeastward across ID/MT and 
into ND as well. This is primarily due to the aforementioned 
mid-upper low over SoCal beginning to lift northeastward through 
the Four Corners region (with another shortwave trough in the 
northern stream digging on its approach into the PacNW). Axis of 
sufficient instability, above normal PWs (as high as ~0.9" and 
around the 90th percentile per the NAEFS) and generally weak flow 
aloft will combine with afternoon heating to support another day 
of isolated to scattered showers and storms. 12Z CAM guidance 
shows the focus a bit farther northeast from CA/NV where they have 
seen some locally higher QPE, where a targeted Slight Risk may be 
warranted (contingent upon rainfall D1). Lower FFG values over ID 
could support such an upgrade as well, but scattered/random nature 
of post-initiated convection has been a hindrance to outlining a 
higher threat.


...Central and Southern High Plains...
In coordination with ABQ, upgraded an area of northeastern NM into 
the western TX/OK Panhandles to a Slight Risk for Wednesday. Upper 
low moving through the Desert Southwest and a ~100kt subtropical 
jet across northern Mexico will aide in providing lift to areas 
just east of the Rockies. Initiation and focus of convection will 
likely be a bit southwest of the D1 area with a moist 
south-southeasterly flow promoting PWs near and over 1.25" (about 
the 95th percentile) with CAPE to 1000-2500 J/kg. Organized 
thunderstorms will slip eastward across northeastern NM into the 
TX/OK Panhandle during the afternoon per the 12Z model consensus, 
and although it is not universal, the multi-cycle trends support 
the upgrade over this area as they have been relatively wet as 
well in the past week (QPE 500-600%+ of normal). This generally 
aligns with the SPC Slight Risk for severe (southern half) and the 
CSU machine-learning first guess fields. Farther north, FFG values 
are lower over northeastern CO into NE/KS, but sufficient QPF may 
be focused farther south closer to the better inflow/moisture flux 
and forcing. 


Fracasso/Churchill
 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt