Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
1158 PM EST Sun Mar 04 2018


Prelim Day 1 QPF Discussion
Valid Mar 05/1200 UTC through Mar 06/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...Northern Plains...
An eastward moving upper trough has spawned cyclogenesis in the
Plains with the surface system deepening as it moves slowly
northeast on Monday with the development of a closed low aloft. 
Moisture increases with time as precipitable water values rise in
excess to 2.5+ sigmas above the mean for early March near and
ahead of the low.  Precipitation should increasingly
expand/organize within areas of low- to mid-level frontogenesis,
including the cyclone's comma head.  A slight westward trend
continues in the model guidance this system, which led to some
westward shift in the QPF pattern when compared to WPC continuity.
 Slight increases in liquid equivalent were seen in the latest
guidance so made modest increases in amounts as well.  Overall,
the preferred QPF pattern best resembles a compromise of the 04z
National Blend of Models and the 00z UKMET.  See WPC winter
weather desk products for more information on the winter weather
impact from this system. 

...Gulf Coast/Deep South...
A slow-moving frontal zone erodes the cap near the western Gulf
coast, with 700 hPa temperatures falling below the 6C threshold
after sunrise Monday. The combination of high moisture
(precipitable water values of 1.5-1.75"), 0-6 km bulk shear of
30-45 kts, sufficient 850 hPa inflow, MU CAPE values up to 2000
J/kg, and propagation vectors roughly parallel to the boundary
across the upper TX coast and southwest LA led to an increase in
amounts in this area.  The deep layer flow becomes increasingly
west-southwesterly with time.  Hourly rain totals could reach
1.75" were cells train/merge.  The 1000-500 hPa thickness pattern
suggests convection will try to drift east with time, which should
keep rain totals from becoming too high.  The QPF pattern
resembles a compromise of the 00z GFS/12z ECMWF or a southwesterly
shifted version of the 00z HREF mean.  This was based on 00z GFS
mass fields and its expected instability field.  Did not go
towards the high end of the guidance across MS, AL, and GA as
instability/MU CAPE values Monday night looks low north of the
Gulf coast, and 850-650 hPa frontogenesis appears weak across the
Southeast.

Elsewhere, no hydrologically significant precipitation is expected.

Roth