Areal Flood Warning 49, NWS Huntsville, AL

Area Forecast Discussion
National Weather Service Huntsville AL
643 PM CDT Sun Sep 19 2021

.UPDATE...
For 00Z TAFS.

&&

.NEAR TERM...(Remainder of today and tonight)
Issued at 349 PM CDT Sun Sep 19 2021

There have been essentially no changes to the near term forecast
reasoning since the update this morning, as deep-layer south-
southeasterly flow and efficient moisture advection will persist to
the east of a mid/upper-level low lifting slowly northward into the
Ozarks region. This will result in periods of moderate-heavy rain
that will lead to an enhanced threat for both flash and areal
flooding for the remainder of the afternoon.

Over the course of the evening and early morning hours, the low to
our west is predicted to open into a trough and accelerate
northeastward into northern IL ahead of a shortwave trough spreading
eastward across the northern Rockies. Gradient flow aloft across the
local area will respond to this by strengthening and veering to the
south-southwest, which should begin to focus the axis of strongest
moisture convergence and widespread moderate-heavy rainfall in a NW-
to-SE band extending from Middle TN southeastward into northwestern
GA. This would likely clip our southern Middle TN and northeast AL
counties, where the highest risk for significant flash flooding will
likely exist overnight. A slightly lower spatial coverage of showers
and embedded thunderstorms is expected to the southwest of this axis,
where a gradual increase in southwesterly steering flow and storm
motion may reduce the overall risk for flooding just a bit. However,
with precipitable water values remaining in the 2-2.25 inch range and
saturated soils, we will maintain the Flash Flood Watch for all
areas. Otherwise, it will be another warm/muggy night, and given the
combination of low stratus clouds and a light southeast breeze,
temperatures should only drop into the u60s-l70s.

.SHORT TERM...(Monday through Wednesday)
Issued at 349 PM CDT Sun Sep 19 2021

Moderate south-southwesterly flow will continue across the region on
Monday, but should gradually subside and veer to the west-southwest
on Monday night/Tuesday morning, as a trailing mid-level trough axis
originating from the disturbance lifting northward into IL overnight
shifts slowly eastward across the TN Valley. Forecast soundings
suggest that some drying will occur in the mid-levels, which will
result in a slow downward trend in PWAT values into the 1.8-2 inch
range by Monday afternoon and into the 1.6-1.8 inch range in the wake
of the mid-level trough axis by Tuesday morning. Nonetheless, we
still expect a fairly widespread coverage of showers and
thunderstorms, at least until the mid-level trough axis crosses the
region late Monday night/early Tuesday morning.

Meanwhile, models are in good agreement that northern stream wave
tracking eastward across the Great Plains will undergo significant
amplification on Tuesday/Tuesday night, as an upper-level speed max
digs southeastward through the base of the trough. Deep-layer flow
will back to the southwest and strengthen once again by Tuesday
afternoon as the trough begins to approach our area, supporting an
increase in atmospheric moisture and shower/thunderstorm coverage. It
appears as if the surface cold front will outpace the mid-level
trough, with the front likely to shift southeastward across the CWFA
late Tuesday night/early Wednesday morning. Although the risk for
thunderstorms will end with the passage of the cold front, strong
postfrontal lift will lead to a brief period of stratiform rain that
will end from W-to-E during the late morning/early afternoon hours on
Wednesday. North-northwest flow around 15 MPH with gusts up to 25
MPH and a fairly widespread coverage of low stratus clouds will make
for a rather cool day on Wednesday, with temps struggling to reach
the u60s-l70s.

.LONG TERM...(Wednesday night through Saturday)
Issued at 349 PM CDT Sun Sep 19 2021

Northwest flow aloft will prevail across the region during the
extended period, as a broad scale longwave trough encompassing much
of eastern North America will be reinforced by another strong upper
low dropping southeastward from the southern Canadian Prairie
provinces. A cool/dry and stable airmass will support strong
radiational cooling on Thursday/Friday mornings, with lows in the
u40s-l50s. Light southwesterly flow and weak moisture advection in
the low-levels will lead to a gradual increase in low temps this
weekend, with highs also expected to warm back into the m-u 70s by
Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 643 PM CDT Sun Sep 19 2021

VFR conditions currently across the terminals. Showers are lifting
out to the north and east with a few isolated to scattered showers
still near KHSV and continued with -SHRA at HSV over the next couple
of hours. MVFR conditions will return overnight and persist
throughout much of the remainder of the TAF cycle. Another round of
showers will arrive around 12-16z. Expect the heavier of the
precipitation will stay to the east of MSL with visibilities dropping
at to MVFR at KHSV. This precipitation may persist until the end of
the TAF cycle. With the lack of thunder today, did not include VCTS
in the TAFs at this time. Southeasterly winds will also increase
after 16z with gusts up to 20-25 kts at times.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch through Monday evening for ALZ001>010-016.

TN...Flash Flood Watch through Monday evening for TNZ076-096-097.

&&

NEAR TERM...70/DD
SHORT TERM...70/DD
LONG TERM...70/DD
AVIATION...MA

For more information please visit our website
at weather.gov/huntsville.

Hazardous Weather Outlook...UPDATED
National Weather Service Huntsville AL
420 PM CDT Sun Sep 19 2021

ALZ001>010-016-TNZ076-096-097-201130-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
420 PM CDT Sun Sep 19 2021

This Hazardous Weather Outlook is for north Alabama and portions of
southern middle Tennessee.

.DAY ONE...Remainder of today and tonight...

Periods of moderate to locally heavy rainfall and a few embedded
thunderstorms will continue across the outlook area through the early
morning hours on Monday. This will result in an enhanced threat for
both flash, areal, and mainstem river flooding, and a Flash Flood
Watch remains in effect for the entire region through 7 PM Monday.

.DAYS TWO THROUGH SEVEN...Monday through Saturday...

Additional rounds of showers and thunderstorms will impact the
Tennessee Valley on Monday and Tuesday, with an attendant threat for
locally heavy rainfall and flooding. The risk for thunderstorms and
flash flooding will end from northwest-to-southeast late Tuesday
night and early Wednesday morning, as a strong cold front shifts
southeastward. However, areal and mainstem river flooding may
continue across portions of the area through the end of the week.

.SPOTTER CALL TO ACTION STATEMENT...

Activation of storm spotters and emergency management personnel in
support of flooding is possible for the remainder of the day and
overnight.

70/DD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
513 PM CDT SUN SEP 19 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0505 PM     FLOOD            6 W HAZEL GREEN         34.92N 86.67W
09/19/2021                   MADISON            AL   FIRE DEPT/RESCUE

            OPP REYNOLDS RD IN THE AREA OF BLUE WATER
            SPRINGS PARK IS CLOSED DUE TO FLOODING.

&&

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