Quantitative Precipitation Forecast
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000
FOUS30 KWBC 220109
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
909 PM EDT Sat Apr 21 2018

VALID 01Z Sun Apr 22 2018 - 12Z Sun Apr 22 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 S KXIH 20 SSE LBX 5R5 10 NE 62H 35 ESE ACT 10 NE 3T1
30 NW LRF 15 E M19 15 W UTA 30 NNW TVR 25 NW MCB 10 ESE BTR
15 WSW KVNP 15 N KCRH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSW PBF 15 WNW MLU 10 NE OCH 10 NNW JSO 10 W M89 20 SSW PBF.


0100 UTC Update...

...ARKLATEX Region into the lower Mississippi Valley...

0100 UTC Update...

The compact warm conveyor belt (WCB) and associated multi-linear
showers/tstms continue to pivot across eastern portions of the
southern Plains and into the lower MS Valley this evening.
Sufficient deep-layer shear (especially directional) is allowing
for steady eastward progression of the convection on the eastern
flank of the comma, which along with the limited available
instability (mucapes < 1000 j/kg), are currently maintaining
observed short-term rainfall rates well below FFG. At the same
time, multiple additional bands were forming this evening farther
west, closer to the mid level trough axis and attendant surface
cold front, still within a favorable region dynamically with the
strong upper level difluence and favorable low-level moisture
transport. The uptick and veering of the low level inflow ahead of
the upper trough/surface will further enhance the risk of
repetitive convection overnight, especially over the ARKLATEX,
however again the mitigating factor in terms of the excessive
rainfall threat will be the limited instability along with the
overall forward speed of the system as the negative PW advection
strengthens from w to e after 06Z. The latest (18Z) HREF 40km
neighborhood probabilities in fact show low (<20%) probs of
rainfall rates exceeding 2"/hr and 3"/3 hr. The SLIGHT risk was
adjusted to encompass the multi CAM signal for additional 2-4"
totals between 00-12Z, which given the anticipated multiple
rounds, would more likely lower the FFGs from where they were
prior to 00Z.

Hurley


Previous discussion below...


There is a Slight Risk of excessive rainfall over the ARKLATEX
region, extending a short distance into southeast Oklahoma, and
extending farther down into the Piney Woods of east Texas. All in
all, there are some limiting factors today, including high Flash
Flood Guidance values and a narrow axis of marginally strong
instability. Still, there will be some wetting rain early in the
period during warm advection, followed by a diurnal maximum of
rainfall coverage and intensity this afternoon/evening. It is
during the early onset of the afternoon convection, in particular,
that cell mergers and local bouts of training may contribute to
rain rates nosing toward FFG values.

A Marginal Risk area is drawn back up the Red River to about
Wichita Falls and including southern OK / north TX. There may be a
period of relatively slow cell movement during the morning during
the approach of a jet streak rounding the base of the upper
trough, and this could be followed by other heavy showers in the
afternoon dependent upon destabilization beneath increasingly cold
upper level temperatures. Isolated flash flooding is possible
today.

Burke/Oravec
$$





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