WPC Met Watch |
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Mesoscale Precipitation Discussion: #1100 (2021) |
(Issued at 813 PM EDT Sun Oct 24 2021
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MPD Selection |
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Mesoscale Precipitation Discussion 1100
NWS Weather Prediction Center College Park MD
813 PM EDT Sun Oct 24 2021
Areas affected...northern and central California
Concerning...Heavy rainfall...Flash flooding likely
Valid 250012Z - 251212Z
Summary...An intense atmospheric river event will continue across
California through the overnight hours, although a very gradual
weakening of rainfall rates is expected.
Discussion...An intense atmospheric river event continues across
portions of northern and central California currently. Consistent
rainfall rates between 0.5 and 0.8 inch/hr have caused areas of
debris flows near burn scars in northeastern California and
localized flooding impacts near/northeast of San Francisco today.
Widespread areas of 3-7 inch rainfall totals have been observed
today - highest along terrain-favored areas of the Sierra Nevada
and northern coastal ranges where orographic lift has enhanced
rainfall. The powerful jet stream responsible for the atmospheric
river is currently oriented WSW to ENE across the region, exceeds
100 knots at 500mb based on latest objective analyses, and reports
near-record-breaking integrated water vapor transport for this
time of year.
Over the next 12 hours or so, models indicate that the atmospheric
river will shift slowly southward with time. A subtle weakening
trend is also noted, although very strong flow (exceeding 95 kts
at mid-levels) will continue to orient perpendicular to important
terrain features across the region and contribute to heavy rain.
Additional rainfall totals of 3-5 inches are expected and will be
highest along coastal ranges near the Pacific Coast and also in
the Sierras below the freezing level. Local amounts greater than 7
inches cannot be completely ruled out. A number of burn scars
remain from very large fires over the past couple of years, and
enhanced runoff in/near these areas will result in debris flows
and flash flooding. Urban/hydrophobic land areas will also
experience a heightened flash-flood risk.
Cook
ATTN...WFO...EKA...HNX...LOX...MTR...REV...STO...VEF...
ATTN...RFC...CNRFC...NWC...
LAT...LON 40472057 40182003 39861956 39181937 38441894
37821844 37261810 36631831 35881957 35492057
35902142 36842235 37542251 38842367 39212329
39642271 39972210 40402144
Last Updated: 813 PM EDT Sun Oct 24 2021
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