Mesoscale Precipitation Discussion 1030
NWS Weather Prediction Center College Park MD
655 PM EST Thu Nov 29 2018

Areas affected...Portions of Northern and Central California

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

Valid 292355Z - 300255Z

Summary...Remaining instability and deep synoptic scale lift ahead
of a cold mid level trough will support low topped convection with
hourly rainfall rates near 1/2 inch. This could pose a flash flood
threat, especially near new burn scars.

Discussion...Regional radars showed an area of low topped
convection across the eastern Sacramento and San Joaquin valleys
early this evening. The convection remains close to the RAP
analyzed 250-500 J/KG MUCAPE pool. As eddies traveling through the
mid level trough position, the lift associated with the eddies
allows the convection to produce lightning. Hourly rainfall rates
with the lightning producing convection are near
one-half inch (as seen in surface observations, as well as the
MRMS hourly rainfall product).

Just ahead of the trough position, the steering flow is fairly
weak, which is allowing for localized training of the convection.
Training supports the enhanced hourly rainfall rates, and the most
recent HRRR 12z WRF ARW2 showed hourly rainfall rates in the
0.25/0.50 inch range. This will pose a flash flood threat into the
evening.

As the mid level trough moves eastward, the lift associated with
it weakens, and the steering increases from the northwest,
decreasing the threat for training. However, HRRR and RAP
soundings indicate that MUCAPE values remain in the 250-500 J/KG
range through at least 03/04z, despite the loss of daytime heating
and warming mid level temperatures.

Given the above, flash flooding is possible 30/04z, especially in
areas with new burns scars. Heavy rainfall in these areas could
produce debris flows and mudslides.

Hayes

ATTN...WFO...HNX...STO...

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

LAT...LON   38952082 38412038 37821993 36841902 36571882
            36291858 35961855 36151916 36491955 37322042
            37822093 38042108 38412137 38802142