Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun May 28 2023 03:33:40

AWUS01 KWNH 280333
FFGMPD
CAZ000-280735-

Mesoscale Precipitation Discussion 0365
NWS Weather Prediction Center College Park MD
1133 PM EDT Sat May 27 2023

Areas affected...northern CA

Concerning...Heavy rainfall...Flash flooding possible

Valid 280331Z - 280735Z

SUMMARY...Isolated flash flood potential will remain across
portions of northern CA, including the northern Sacramento Valley
with rainfall rate potential of 1 to 1.5 in/hr over the next few
hours. The threat is likely to dissipate after 07Z with the loss
of instability.

DISCUSSION...GOES West water vapor imagery showed a closed upper
level low along the southern coast of OR at 03Z, with a
well-defined vorticity center to its northwest and a
lesser-defined vorticity max to its southwest. Thunderstorms were
ongoing along portions of the Cascades and surrounding mountainous
terrain as well as the northern Sacramento Valley with recent
development in Glenn and Tehama counties, although trends on
infrared satellite imagery have shown warming cloud tops,
indicating a weakening trend. Weak instability remained owing
partially to 700-500 mb lapse rates that ranged between 6 and 7
C/km with estimated MLCAPE of ~500 J/kg or less but higher MUCAPE
available up to 1000 J/kg (SPC mesoanalysis data).

As the upper low continues to track southward tonight, some
increase in moisture will be possible into the northern Sacramento
Valley given transport ahead of the upper low in the low to
mid-levels. Precipitable water values of 1.0 to 1.1 inches in the
Valley (GPS and TPW imagery) are weakly anomalous and relatively
weak deeper-layer mean westerly flow and similarly oriented 700 mb
winds has and will continue to allow for short term training of
cells. A modest increase in upper level diffluence ahead of the
upper low may also help to sustain cells a bit longer prior to the
waning of remaining instability through 07Z. Until then, however,
localized rainfall rates of 1 to 1.5 in/hr will be possible,
posing an isolated flash flood threat given coverage of these
higher rates is expected to fairly limited.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!9wmnzBvByBEfMPNRVNcnf_zPS_2KzmA02bYu-TIQZ3CBmxFhNvZDNUXfIwMrqoFgwNM6=
q-V2k_Cy3BHFxUuVtE4T8-I$  for graphic product...

ATTN...WFO...EKA...MFR...REV...STO...

ATTN...RFC...CNRFC...NWC...

LAT...LON   41622171 41282105 40632090 39982109 39402144=20
            39222220 39522271 40192304 40912289 41502262=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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