Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jan 06 2023 19:44:27

AWUS01 KWNH 061944
FFGMPD
CAZ000-ORZ000-070500-

Mesoscale Precipitation Discussion 0024
NWS Weather Prediction Center College Park MD
243 PM EST Fri Jan 06 2023

Areas affected...Coastal Nortwest California & Southwest Oregon...

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

Valid 061945Z - 070500Z

SUMMARY...Increasing moisture surge to be persistently directed to
a narrowly focused area of NW CA/SW OR over the next 12+ hours.=20
Localized totals of 3-4" probable in SSW facing fairly saturated
orography should result in increased water runoff.

DISCUSSION...GOES-W WV suite has depicted the deepening of a large
scale northeast Pacific gyre centered about 46N135W which has
supported the next northward pull of subtropical moisture plume
ahead of the cold front generally between 127-128W.  CIRA LPW
denotes this plume is not particularly anomalous given total PWAT
values of .7-.8" and is generally narrow in 100-150km wide.=20
Currently, a short 90kt 3H jet-streak and associated shortwave is
analyzed just west of the central and southwestern OR coast and
has accelerated low level flow out of the narrow warm sector with
60-75kts of 850mb flow paralleling the OR coast.  This has
tightened the level pressure gradient and increased sfc to
boundary layer confluence of about 35-45 degrees with 25-35kts
nearing Cape Mendocino resulting in a fairly strong AR signal with
IVT values of 500-600 kg/m/s at the tail end of the exiting
shortwave.   KBHX RADAR reflectivity is starting to detect the
enhanced moisture flux band along the coast which should near the
coast.=20

The concern is the well upstream shortwave is starting to amplify
slightly with a weak sfc to boundary layer inflection expected
just south-southeast of the 40N130W benchmark.  This will keep
strong southerly flow directed toward the Cape and the NW CA/SW OR
coast focused but strong supporting moisture flux into
south-southwest facing orography likely to support .3 to .5"/hr
rates in the best orographic lift while broader .15-.25"/hr rates
will soak the coast through the late afternoon and well into the
overnight period.  So while the rates are not likely to induce
rapid inundation or 'flash' flooding, the persistence and narrow
focus will concentrate totals of 3-4" through 06z locally should
have increased runoff than a typical/similar AR events as soil
saturation ratio are near 90-95% already.  This discussion is more
of a set-up scenario for a further uptick expected later into
tomorrow morning and an update will likely follow about to discuss
its evolution=20

Gallina

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_RazgAC0jCvQT-THxZx4a2psc140cfoTuAAiv4ZrrX9CiYcLbmoY2q7gEa5IxQJENgjB=
VZIqUVmhTkvaq6O9kqJGdGA$  for graphic product...

ATTN...WFO...EKA...MFR...

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

LAT...LON   42702402 42412375 41382379 40502370 40122376=20
            39802387 39842409 40072424 40352452 40932432=20
            41402422 41862434 42042441 42382454 42652450=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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