Graphic for MPD #0014

Mesoscale Precipitation Discussion 0014
NWS Weather Prediction Center College Park MD
420 AM EST Sat Jan 13 2024

Areas affected...Far Southwest OR...Northwest CA

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

Valid 130920Z - 132120Z

SUMMARY...Heavy rains to overspread the coastal ranges of far
southwest OR and northwest CA going through the day on Saturday as
a quick-hitting and relatively modest atmospheric river moves
ashore. Some flooding concerns may materialize at least locally
given the expectation of locally several inches of rain.

DISCUSSION...The latest GOES-West satellite imagery shows a
shortwave trough amplifying gradually down to the southeast in the
vicinity of 44N and 140W along with a surface low and attendant
frontal zone. This energy over the eastern Pacific Ocean is seen
tapping into a pool of subtropical moisture that is advancing
northeast up around a deep layer cyclone/gale center near 27.5N
and 150.5W to the northeast of Hawaii. The latest NESDIS Blended
TPW and CIRA-ALPW products show an axis of higher PWs/deeper
moisture focused near this low and northeast up along the cold
front that is connected into the low center offshore of the
Pacific Northwest.

Over the next several hours, this low center will be losing
latitude and gradually approaching areas of far southwest OR and
northwest CA which will begin to strengthen the warm air advection
and moisture transport into the coastal ranges. The latest
GOES-West IR satellite imagery shows cooling cloud tops offshore
of western OR and suggestive of stronger forcing/divergent flow
aloft associated with the digging shortwave and related DPVA
parameters. This will begin to overspread the coastal ranges early
this morning and continue through the midday time frame while
coinciding with strengthening Pacific moisture flux. The result
will be the arrival of moderate to heavy rain with rates
increasing with time.

The low-level jet ahead of the low center is forecast by the
latest hires model consensus to increase to as much as 50 kts by
18Z today with IVT magnitudes increasing to as much as 500 to 750+
kg/m/s. The overall deep layer moisture axis/atmospheric river
should become aligned generally orthogonal to the terrain between
15Z and 21Z today which will favor greater orographic ascent and
heavier rainfall rates for the coastal ranges. A cold front will
then arrive after 21Z and advance inland.

Generally the 00Z HREF models support rainfall rates increasing to
around a 0.50"/hour by 15Z across Curry County in far southwest
OR, and into Del Norte and Humboldt County of northwest CA. The
rainfall rates are forecast to peak locally as high as 0.75" to
1"/hour in the 18Z to 21Z time frame as the peak IVT values arrive
just ahead of the cold front. Some convective elements associated
with instability pooling up along the cold front will help
facilitate these heavier rainfall rates.

12-hour rainfall totals going through 21Z today are forecast to be
as much as 3 to 6 inches, with the heaviest amounts over the
northwest CA coastal ranges. This is consistent with the 00Z HREF
consensus. Given the higher rainfall rate potential for at least a
few hours today, and the overall storm totals, some areas of
flooding will be possible and this may include not only the more
sensitive urban areas, but also a couple of the burn scar
locations which will need to be closely monitored.

Orrison

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

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

LAT...LON   42852419 42602373 42042348 40902341 40352339
            39842324 39342305 39052327 39052383 39592408
            40192456 41442440 42472463
Download in GIS format:    Shapefile  | KML



Last Updated: 420 AM EST Sat Jan 13 2024