Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
1150 AM EST Mon Feb 26 2018


Preliminary Day 1 QPF Discussion
Valid Feb 27/0000 UTC thru Feb 28/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Southern Plains/Western Gulf coast...
A returning warm front to the east of an upper cyclone closing off
across the Southwest will move northward across Texas and
Louisiana, leading to initially scattered convection across Texas
through tonight.  Amounts and coverage are expected to ramp up as
850 hPa inflow increases to 25-40 kts, 0-6 km bulk shear rises to
~50 kts, precipitable water values rise to at or above 1.75", and
MUCAPE of 500+ J/kg is projected to lie within the system's warm
sector.  A bulk of the heavy precipitation is expected to lie in
the Tuesday afternoon time frame rather closely to the warm front.
 Hourly rain totals up to 2" are possible at that time.  Mass
fields from the 06z GFS and 12z NAM, along with our in-house
bias-corrected QPF and the 12z-13z National Blend of Models
suggest that a solution most like a compromise between a 00z/12z
ARW, 12z Canadian, 12z NSSL WRF, and 06z/12z GFS blend is most
plausible, so adjusted the WPC QPF to match.  While this is
substantially wetter than WPC continuity, it still lags the 12z
in-house experimental bias corrected QPF.

California, Great Basin, Wyoming Rockies...
A closed low over California combined with modest onshore flow and
seasonal precipitable water values should lead to locally moderate
to heavy rain across southern California.  The best chance for any
locally heavy totals over an inch will be in the transverse and
peninsular Ranges.  To the east and northeast of this developing
closed low---broadly upper diffluent flow will support widespread
scattered precip activity through the Great Basin and into Wyoming
Rockies within a region of good low- to mid-level frontogenesis. 
Using 06z GFS mass fields as a guide, WPC QPF was adjusted to
better match the agreeable model consensus.

Northwest...
As a shortwave passes by to the north, modest onshore flow with
precipitable water values of ~0.5" is expected to lead to light to
moderate precipitation tonight within favored terrain into Tuesday
morning.  Used a compromise of the 00z ECMWF and 12z GFS for QPF
in this region. 

Roth