Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 060507
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1207 AM CDT Sat Jun 6 2020

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...
/Updated at 1256 PM CDT Fri Jun 05 2020/
Today through Saturday.

The forecast area remains positioned between two deep-layer
ridges, one centered over West Texas with the other Centered over
the Southwest Atlantic. A positive-tilted trough extended from
Ohio southwest through the Tennessee River Valley.

Surface analysis shows surface pressures remain the highest to
our southeast with lower pressures to the northwest.

Examining the 12Z RAOB BMX data, the wet microburst risk appears
to be moderate across our northwest counties today as drier air
settles into the area aloft behind the trough axis while a lower
risk for wet microbursts prevails elsewhere. Higher dew points
along with warmer temperatures will support surface-based
convective available potential energy (CAPE) values higher than
yesterday around 2700 J/kg. Forecast lapse rates over 8C/km are
expected with downdraft CAPE values around 700 J/kg. The low-level
continue to be moist with precipitable water values of 1.68" this
morning. The strongest storms will have a risk of producing strong
winds and some hail but no organized severe storms are expected.

Expect ongoing convection across our North-Central and Northeast
counties to continue moving southeast with time. Further south,
isolated showers have developed and potential persists for a few
thunderstorms as well.

Highs today will range from the mid to upper 80s northeast and
east to the low 90s west and south. Winds will remain from the
southwest to the south 6-12 mph except higher in and near
convection.

The shower and storm activity will weaken and decrease in coverage
overnight but may persist, especially South-Central. Areas that
receive rainfall today may experience some reduction in visibility
overnight north and central but this should be patchy/spotty at
best.

Lows will range from the upper 60s northeast and east to the low
70s west and south. Winds will be light from the west to southwest
overnight.

Isolated to scattered showers and storms are forecast to develop
Saturday with highest coverage south. Highs will range from the
upper 80s southeast and east to the low 90s northwest and north.

Winds will become more southerly to southeast with speeds from
6-12 mph outside of convection.

05

.LONG TERM...
/Updated at 334 PM CDT Fri Jun 05 2020/

Only made a few minor tweaks to the long term forecast. Continued to
hold off on rain chances for most areas on Sunday despite Tropical
Storm Cristobal lifting into the northern Gulf of Mexico. 12Z
guidance subdues convection over much of Central AL due to a mid-
level ridge situated over the Central Plains which will build
eastward and produce dry/stable conditions for the Ohio/Tennessee
Valleys. We will likely see highs in the low 90s Sunday afternoon
across our northern counties while areas in the far south may stay
several degrees cooler due to increased cloud cover. Otherwise,
rain chances will be on the rise through midweek as Cristobal
lifts northward into the Midwest, becomes extratropical, and
merges with an approaching upper-level trough. We will continue to
monitor any changes concerning a low confidence risk for tornado
potential on Tuesday, but uncertainties remain including the
eastward spatial extent of favorable dynamics into our northwest
and degree of sufficient destabilization given widespread
rainfall.

86

Previous long-term discussion:
/Updated at 350 AM CDT Fri Jun 05 2020/
Saturday night through Thursday.

Impacts:

Tropical Depression Cristobal is well inland near the
Mexico/Guatemala border this morning. It is expected to emerge out
over the Gulf tonight. NHC forecasts and guidance consensus
indicate that it will make landfall along the south-central
Louisiana coast Sunday night as a sheared/asymmetric system.
However there has been some spread in guidance in landfall
location ranging from southeast Louisiana to southwest Louisiana,
depending on when the ridge to its north causes it to make a
leftward jog. This also impacts when its remnant low makes a
rightward jog by Tuesday. These track details will determine the
exact impacts that Cristobal has on Central Alabama. If the
current forecast holds, then the main 850mb jet core and
associated breezy conditions, heavy rainfall, and tornado
potential will remain over Mississippi. But any eastward
adjustments in the track could cause some of these impacts to move
into West Alabama. The models should begin to have a better
handle on the system once the center is back over water. At the
current time, impacts for Central Alabama look to be relatively
minor and mainly focused on West Alabama where winds gusts of
15-30 mph and rainfall amounts of 1 to 2 inches are expected with
locally higher amounts. These rainfall amounts are not expected to
cause organized flooding issues, but some locally higher amounts
potentially causing localized flooding would still be possible due
to mesoscale to storm scale processes, especially during the
Tuesday/Wednesday timeframe. The potential for a brief tornado
mainly during the Monday/Tuesday timeframe appears low but non-
zero, depending on how far east the area of enhanced low-level
shear makes it. Will note that we did get a couple tornadoes with
Tropical Storm Cindy in 2017 which made landfall in southwest
Louisiana, though it turned more sharply to the northeast after
landfall. Overall, none of these threats appear to warrant
inclusion in the HWO but will continue to monitor.

Forecast:

A couple isolated storms leftover from Saturday afternoon will
probably linger into Saturday evening before dissipating after
sunset. An outer band of showers from Cristobal will move onshore
Saturday night, aided by a mid-level warm front/deformation zone.
This activity will mainly stay closer to the coast Saturday night
due to dry air over Central Alabama, but a few showers could reach
Pike/Barbour Counties before sunrise Sunday morning. Rain chances
associated with Cristobal`s outer bands will be confined to our
far southern counties on Sunday, where some areas may not get out
of the low 80s. A stable/tropical air mass associated with
easterly flow will likely inhibit thunder, and not expecting
anything heavy during this time. Further north, dry mid-level air
associated with a strong ridge over the Midwest should suppress
convection and allow for temperatures around 90. The dry air
mass/ridging will continue to inhibit the northward movement of
precipitation Sunday night.

Moisture will increase Monday/Monday night as Cristobal moves
northward across Louisiana and Arkansas, allowing flow to shift
from easterly to southerly. However, some relatively drier air
aloft will located over a good chunk of Central Alabama between
the tropical moisture over Mississippi and far West Alabama and
another area over east Georgia. This may allow for more
heating/instability but also keep showers/storms more scattered in
nature. Continued warm temperatures aloft will probably keep
thunder isolated. Will have to monitor a band of convection and
enhanced low-level shear/SRH over Mississippi which will be close
to our far western counties Monday/Monday night for any heavy
rainfall/tornado potential, but confidence is low at this time due
to the track uncertainty. Cristobal will continue to lift
north-northeastward across Missouri and Illinois Tuesday/Tuesday
night as it begins to undergo extratropical transition as it
interacts with an approaching mid-latitude trough. Forcing from
the trough axis south of Cristobal and tropical moisture profiles
with PWATs above 2 inches will result in high rain chances
Tuesday/Tuesday night with the potential for locally heavy
rainfall. Will have to monitor continued enhanced low-level
shear/SRH over Mississippi which will be close to our far
northwest counties for any tornado potential but confidence is low
at this time.

Rain chances will remain enhanced Wednesday as tropical moisture
remains in place along with forcing from the mid-latitude trough
and the cold front from what will by then be post-tropical
Cristobal. Some stronger storms may be possible as well. Forecast
for Thursday remains uncertain regarding whether the front and
associated tropical moisture stalls out over or just east of the
forecast area.

32/Davis


&&

.AVIATION...
06Z TAF Discussion.

Convection has deteriorated for the most part for the night except
for a few showers near TOI. This activity should be gone in a
couple of hours at the latest. Some patchy fog and stratus will be
possible thanks to residual moisture from earlier convection. I
have MVFR mention with possibly a few IFR spots. Afternoon
convection is once again possible with diurnal heating. The best
chances will be at EET/MGM/TOI.

08

&&

.FIRE WEATHER...

Summer-like weather will persist into the weekend with warm and
muggy conditions. Scattered showers and thunderstorms will
develop, mainly in the afternoon and evening hours. Rain chances
will be limited to southern portions of the area Sunday. Rain
chances will increase early next week areawide as Tropical Storm
Cristobal moves inland.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     67  92  67  90  70 /  20  20  10  10  10
Anniston    68  90  67  89  70 /  20  20  10  10  10
Birmingham  70  92  70  90  73 /  20  20  10  10  10
Tuscaloosa  69  93  71  90  73 /  30  20  20  10  20
Calera      69  90  69  88  73 /  20  30  20  10  10
Auburn      68  87  68  84  71 /  40  40  20  20  20
Montgomery  70  90  70  85  73 /  50  40  20  30  30
Troy        71  89  69  83  72 /  50  40  20  40  30

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$


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