Excessive rainfall forecast issued on Mon, Aug 5, 2019

Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point

Updated: 2020 UTC Mon Aug 5, 2019
Valid: 12 UTC Aug 06, 2019 - 12 UTC Aug 07, 2019

Day 2 Excessive Rainfall Forecast

Forecast Discussion

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 PM EDT Mon Aug 05 2019

Day 2
Valid 12Z Tue Aug 06 2019 - 12Z Wed Aug 07 2019


...Arizona to Colorado and New Mexico...
Monsoonal moisture with precipitable water values 1 to 1.5
standard deviations above normal will remain in place across
portions of the Southwest states, circulating around a sprawling
upper high anchored over New Mexico. Another push of deeper
moisture is slated to arrive across southern Arizona Tuesday
night, maintaining moisture 1.5 standard deviations above normal.
CAM and global guidance favor convective QPF over western NM to
southern CO where instability is greatest, so the Marginal was
maintained there. Little QPF is in AZ where instability is
suppressed. Left the Marginal Risk for AZ for now given the light
southerly mean flow which may trigger isolated thunderstorms/flash

...Central Plains...
Weak mid-level energy in northwest flow will allow surface low
pressure to develop on an existing front in south-central NE
Tuesday night. Convergence of 1.75 inch PW air (about one standard
deviation above normal) on southwest 850mb flow of 15 to 20 kt
with around 1500 J/Kg MLCAPE will promote thunderstorms to develop
and potentially move along the axis of the new front. This
potential for repeating cells warrants introduction of a Marginal
Risk for excessive rain.

...Ohio Valley to Lake Erie...
Expanded the Marginal Risk area over much of the Ohio Valley ahead
of an approaching cold front. Precipitable water values of 1.5 to
1.75 inches are expected which is up to one standard deviation
above normal. Warm cloud depths of 3 to 3.5 km are still expected
during the afternoon/evening hours. With sufficient instability
and lift in place, efficient rain producing thunderstorms are
likely with some probabilities of exceeding 1 inch in 1 hour in
places. Despite drier than normal conditions over the last 7-14
days for much of this area a localized flash flood threat is

...Northern Mid-Atlantic...