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Day 2 Outlook >
 
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
 
Updated: 1425 UTC Sun Oct 21, 2018
Valid: 15 UTC Oct 21, 2018 - 12 UTC Oct 22, 2018
 
Day 1 Excessive Rainfall Forecast
 
Forecast Discussion
 
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
654 AM EDT Sun Oct 21 2018
 
Day 1
Valid 1051Z Sun Oct 21 2018 - 12Z Mon Oct 22 2018 

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER FAR SOUTH 
TEXAS...

...Far South Coastal Texas...
The low level flow off the western Gulf is expected to veer with 
time this period from northeasterly early day 1...to a more 
easterly to east southeasterly toward the end of the period.  This 
onshore flow will help focus a boundary layer convergence maxima 
along the far south Texas coast into coastal northeast Mexico in 
the vicinity of a southeast to northwest oriented inverted trof 
across this area.  With pw values expected to remain 2.0 to 2.5+ 
standard deviations above the mean through the period...heavy 
rains are possible along the immediate far south Texas coast. The 
previous marginal and slight risk areas for this period over far 
south Texas were suppressed farther to the south by approximately 
30-50 nm to match the model consensus for the area of heavy rain 
potential.


...Portions of Nevada/California/Arizona/Utah...
Showers and thunderstorms in and near southern NV are thriving to 
the northeast of an upper level low located over southern CA. 
Precipitable water values are 0.5-1" per recent GPS data (2-4 
sigmas above the mean for late October), with surface dew points 
currently into the low to mid 50s.  MU CAPE values are 500-1500 
J/kg have been pushing northward from western AZ and southeast CA 
near and south of a 700 hPa trough moving northward into the area. 
 Effective bulk shear of 20-45 kts lies across the area per SPC 
mesoanalyses. With the expansion of showers and thunderstorms, 
expect precipitable water values to rise another 0.25" and for 
rainfall efficiency to slightly increase into the morning hours, 
with another round of activity expected this afternoon and evening 
as the system moves northward.  Radar estimates have advertised 
localized areas of 0.5"+ so far, which could enhance further, 
particularly if any mesocyclones form within this environment 
(supported by the available bulk shear).  Short periods of 
training with an environment with brisk low-level inflow could 
also lead to these rain rates/totals.  Hourly rain totals of 0.5"+ 
appear probable, with local amounts of 1-2" expected as activity 
spreads northward ahead of the upper low and 700 hPa trough.  A 
marginal risk of excessive rainfall exists across an arid region 
which is sensitive to heavy rainfall.

Roth/Oravec
 
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
 

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