Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
121 PM EDT Tue May 22 2018


Prelim Day 1 QPF Discussion
Valid May 23/0000 UTC thru May 24/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1...

...SD/MN/IA border junction...
Tonight should be a good setup for an axis of elevated convection
with heavy rains across portions eastern SD into southwest MN and
northwest IA where a broad region of low-level inflow intersects
and overrides a warm front.  Elevation over the surface boundary
might not be by much as MUCAPE values are expected to start in the
1500-2000 J/kg range at 06z and the best 850 hPa wind
convergence/confluence appears to be near the SD/IA border.  The
850 mb moisture transport increases and persists through the night
downwind of the instability pool.  Storm motion vectors are at a
right angle to the low-level inflow expected, suggesting that
storms could regenerate and train for a period from west-northwest
to east-southeast.  Still a good amount of uncertainty with model
placement, though there is a strong enough signal for 3-5" totals.
 Think a solution somewhat south of the 12z ARW is in the ballpark
of what could materialize.


...Northern Rockies/Divide...
Upslope flow northeast of a deep layer cyclone combined with
precipitable water values of 0.75-1" are expected to focus heavy
precipitation near the western WY/MT border into eastern ID.  For
the most part, continuity resembled recent guidance, so let it
ride.  Increased amounts somewhat in the Wind River Range per the
most recent guidance.


...East...
A wet pattern is expected across the Southeast and Mid-Atlantic
States.  The main foci are the low-level circulation which moved
inland from the Gulf yesterday into eastern AL and a frontal
boundary shifting southward through the region.  This afternoon,
heavy rains are expected to start in north-central VA and southern
MD and shift east and southeast this afternoon and evening before
fading overnight near the VA/NC border.  The guidance has trended
in this direction so have followed suit.  The portion of the
pattern which most resembled continuity was with the eastern AL
circulation which is expected to spread heavy rains into GA.  The
flow pattern in FL suggests a west coast sea breeze maximum, which
resembled continuity which was strongly maintained.


...Southwest OR/northern CA...
Diurnal convection each afternoon and evening is expected near and
downwind of the terrain within the western periphery of a deep
layer low.  Increased amounts somewhat across this area to edge
continuity towards the latest model guidance.


...AR/LA/TX....
An upper low near the southern LA/TX border should act to focus
some convection over portions of AR/LA/MS through tomorrow within
a region of relatively weak flow.  Diurnal convection with brief
heavy rainfall is possible here before the storms pulse/become
outflow dominant.  While very localized heavy totals are possible,
areal averaged rainfall should not be all that high.


...NM/TX border...
Followed the guidance trend to shift activity farther southward
within a regime with shortwaves rotating east to northeast around
the southern periphery of a deep layer cyclone across the Great
Basin.

Roth