AWUS01 KWNH 031025
FFGMPD
TNZ000-KYZ000-INZ000-ILZ000-MOZ000-031500-

Mesoscale Precipitation Discussion 0846
NWS Weather Prediction Center College Park MD
624 AM EDT Thu Aug 03 2023

Areas affected...central and southeastern MO into central KY/TN

Concerning...Heavy rainfall...Flash flooding likely

Valid 031023Z - 031500Z

Summary...Areas of heavy rain and flash flooding are likely to
continue from portions of central and southeastern MO into western
KY through 15Z. Farther east, possible flash flooding will exist
for portions of central KY/TN. Additional totals of 2-4 inches are
expected.

Discussion...10Z regional radar imagery continued to show an axis
of training heavy rain over central and southeastern MO, although
the axis is no longer contiguous. Rainfall rates have ranged from
1-3 in/hr across this region of MO since 06Z and portions of the
region have seen 3 to 8 inches of rain over the past 24 hours
(MRMS estimates). Farther east, a well-defined MCV was located in
southern IN, tracking toward the southeast, associated with a
small region of 1-2 in/hr rainfall rates ~30 miles south of
Louisville, KY along I-65. VAD wind plots at 850 mb from KSGF and
KPAH showed 35-40 kt from the west and tied with some of the
coldest cloud tops on IR imagery. However, overrunning low level
flow and areas of confluence were still producing thunderstorms
upstream across central MO where some of the heaviest rain has
fallen over the past 6-12 hours. Precipitable water values were
estimated to be between 2 and 2.4 inches and instability ranged
from a few hundred J/kg in central KY to 1000 to 2000+ J/kg near
the confluence of the OH and MO rivers.

The focus for the heaviest rain over the next 3-5 hours is
expected to set up from southeastern MO into far southern IL and
western KY, in line with the strongest isentropic lift atop a
surface front draped across the central MO/AR border. Areas of NW
to SE training with 1-2 in/hr rates (perhaps locally higher) are
expected to continue areas of flash flooding. Farther upstream,
ascent is expected to diminish over the next few hours, however, a
localized flash flood threat will remain across central MO where
ground conditions are hyper sensitive due to recent heavy rainfall.

Locations farther east from KY into TN, ahead of the MCV, will see
a localized flash flood threat where lift ahead of the MCV will
continue areas of heavy rain with brief training just downstream
of the MCV center. The greatest limiting factor for excessive
rainfall across central KY/TN will be weak instability. However,
peak rainfall rates of 1-2 in/hr may still be enough to support
localized rainfall totals of 2-3 inches through 15Z.

Otto

ATTN...WFO...EAX...JKL...LMK...LSX...MEG...MRX...OHX...PAH...
SGF...

ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...NWC...

LAT...LON 38809182 38199048 37758952 37478873 37348821
37348770 37498725 38138612 38128551 37818483
37348425 36908404 36388417 36108477 35828556
35528656 35448764 35608834 36088934 36949067
37859232 38349296 38789291

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AWUS01 KWNH 061300
FFGMPD
MOZ000-MNZ000-IAZ000-SDZ000-061900-

Mesoscale Precipitation Discussion 0876
NWS Weather Prediction Center College Park MD
859 AM EDT Sun Aug 06 2023

Areas affected...Iowa and southern Minnesota

Concerning...Heavy rainfall...Flash flooding possible

Valid 061300Z - 061900Z

Summary...Showers and thunderstorms will increase in coverage this
morning and then drift slowly to the northwest across Iowa into
Minnesota. Rainfall rates of 2"/hr or greater at times are likely,
which through slow motions could produce 2-4" of rain. Flash
flooding is possible.

Discussion...The regional radar mosaic this morning shows
expanding coverage of showers and isolated thunderstorms across
central Iowa. This convection is blossoming downstream of a
stacked low pressure moving eastward out of SD, with downstream
enhanced ascent driven by height falls, impressive PVA, and
modestly coupled upper jet streaks. This ascent will continue to
impinge into favorable thermodynamics characterized by PWs of 1.5
to 1.7 inches measured by morning UA soundings, around the 90th
percentile for the date, collocated with MUCAPE above 1000 J/kg
analyzed by the SPC RAP. Within this environment, rainfall rates
have been estimated via KDMX and KFSD to exceed 2"/hr, and while
this may be a bit overdone, it is reflective of the possible
intensity developing through this aftn.

The stacked low will shift slowly eastward through the day,
maintaining robust deep layer ascent across the area. At the same
time, S/SE flow downstream of the wave should drive PWs to above
1.75" this aftn, coincident with MUCAPE remaining 1000-1500 J/kg.
Despite significant cloud cover which may temper surface-based
instability except in clearings, impressive theta-e advection
lifting cyclonically into a TROWAL should supply ample elevated
instability to persist heavy rain rates. This is likely
manifesting as the high MUCAPE in model output, and when combined
with a well-collocated overlap of the highest PW pool and warm
cloud depths surging above 11,000 ft, will drive extremely
efficient warm rain processes. This will result in rainfall rates
which the HREF indicates could exceed 2"/hr, with the HRRR
suggesting brief 3+"/hr rates noted via the 15-min rainfall
accumulation product. Storms that develop will generally move
slowly NW on 10-15 kt 0-6km mean winds, but increasingly
anti-parallel and collapsing Corfidi vectors suggest considerable
backbuilding potential to result in training and at times storm
motions of just 0-5 kts. Where the most persistent training can
occur, rainfall of 2-4" is possible as shown by the HREF and
experimental RRFS TL ensemble probabilities.

Although 7-day rainfall across northern IA and southern MN has
been well below normal according to AHPS, heavy rain did impact
parts of this area in the past 24-hours. This has resulted in
nearly saturated top-soils according to the HRRR, and locally
compromised FFG as low as 0.75-1.5"/3hrs. While the slow motions
of any intense rainfall rates could result in instances of flash
flooding through the aftn, the greatest risk will be where
training can occur atop these most vulnerable soils.


Weiss

ATTN...WFO...ARX...DMX...DVN...EAX...FSD...MPX...OAX...

ATTN...RFC...MBRFC...NCRFC...NWC...

LAT...LON 44479441 44219309 43479205 42409142 41139128
40439170 40349241 40859342 41439461 41799562
42379619 42889648 43299648 44069639 44379578


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AWUS01 KWNH 300932
FFGMPD
FLZ000-301530-

Mesoscale Precipitation Discussion 1117
NWS Weather Prediction Center College Park MD
530 AM EDT Sat Sep 30 2023

Areas affected...Portions of the FL Atlantic Coast

Concerning...Heavy rainfall...Flash flooding possible

Valid 300930Z - 301530Z

SUMMARY...Slow-moving showers and thunderstorms this morning with
locally extreme rainfall rates may produce some areas of flash
flooding.

DISCUSSION...The latest radar imagery has been showing an uptick
in very heavy shower and thunderstorm activity around the Daytona
Beach, FL area and extending offshore with some linear bands
becoming aligned with a convergent low-level flow regime just
north of a quasi-stationary frontal zone.

A very moist and unstable airmass is pooled across the region with
PWs that are running over 2 standard deviations above normal with
values of 2.25 to 2.5 inches. The 00Z RA0B sounding from KXMR
(Cape Canaveral) was reflective of a very deep and warm tropical
column with WBZ heights well over 15,000 feet and a PW of 2.31
inches. The latest RAP analysis shows MLCAPE values of 1500+ J/kg
along the coast and already indicative of a moderately unstable
airmass.

The combination of convergent low-level easterly flow, westerly
shear aloft, and this very moist and unstable airmass will support
slow-moving and locally anchored convective cells focusing along
and adjacent to the coast that will be capable of extreme rainfall
rates.

Some rainfall rates with the more organized convective cells this
morning will be capable of reaching 2 to 4 inches/hour and this
will also be connected to the fact there that is such a deep and
moist warm cloud layer.

The 06Z HREF guidance suggests a threat for localized storm totals
reaching or exceeding 5 inches where the storms become more
focused, and at least in the short-term, areas near Daytona Beach
will be most at risk for seeing these heavier totals. Going
through the morning hours, some additional expansion of convection
especially to the north along the coast may be possible.

Very high FFG values will certainly mitigate any flash flood
threat to an extent, but with such high rainfall rate potential
this morning, some flash flooding will be possible and especially
if any urban areas can get into the stronger convective cores.

Orrison

ATTN...WFO...JAX...MLB...

ATTN...RFC...SERFC...NWC...

LAT...LON 29878130 29828118 29598108 29228087 28808077
28598080 28678113 29008136 29428154 29758153


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