Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
153 AM EST Sun Mar 11 2018


Prelim Day 1 QPF Discussion
Valid Mar 11/1200 UTC thru Mar 12/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...Lower MS Valley into the Southeast ...

As of 06z this morning convection stretches across portions of
AR/MS/AL forming within an environment of low level moisture
convergence and steep mid level lapse rates. May continue to see
some training of this convection through 12z across portions of
MS/AL. Thereafter most indications amongst the CAM guidance is for
convection to become more progressive in nature off to the
southeast. This seems reasonable...as by this time we begin to see
the stronger wave currently over the central plains move east and
begin to interact with the lead wave...resulting in a more
progressive push and more of a southwest to northeast orientation
of the 850 mb moisture convergence axis (less conducive to
training than the west to east axis we are seeing early this
morning). Convection is however expected to maintain its intensity
a bit more than previously forecast as it moves south towards the
Gulf Coast...and expect the convection currently initiating over
northeast TX to expand in coverage into the early morning
hours...resulting in a nearly continuous southeast to northeast
axis of convection stretching from LA into southern GA.

None of the 0z high res CAMs were doing a particularly great
job...however thought the more progressive ARW and ARW2 were
handling the ongoing activity better than the others. The 0z UKMET
was also not all that bad. Thus the WPC QPF follows closest to
these models...with extrapolation of the current activity also
used at the beginning of the period. This results in an increase
in amounts over our previous forecast...with an axis of 0.75"-1.5"
across a good portion of the lower MS Valley into the southeast.


...Mid MS Valley into the OH/TN Valley and western Mid Atlantic...

The well defined shortwave over the central plains will move into
the MS Valley today. Models are trending towards a more well
defined wave and area of forcing with this feature as it moves
from the mid MS Valley into the Oh/TN Valley and the western Mid
Atlantic through the day 1 period. This combined with some dual
left exit and right entrance upper jet dynamics...should support a
more focused area of lift and even a surface low reflection ahead
of the wave. Given this trend, it is not surprising that model
QPFs are also trending wetter across this area into tonight.
Eventually the better energy will shift offshore to the developing
coastal low...but at least through 12z Monday should see some good
QPF ahead of this mid level wave. WPC increased QPF over our
previous forecast...using a consensus of the 0z GFS/UKMET and the
0z high res CAM guidance.

Portions of SC/NC will generally be in between the convective
precip over the south and the precip associated with the mid level
wave to the northwest. Thus QPF amounts here were lowered from our
previous forecast. Again WPC utilized a blend of the GFS/UKMET and
the 0z high res models.


...Southwest...

precipitation associated with the southwest wave will continue
moving east today into AZ/NM. The 0z models were in very good
agreement with this feature and resultant QPF...thus WPC utilized
a multi model blend. There was a unanimous slowing trend
noted...which lowers QPF amounts central and eastern NM.

Chenard