Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 032003

Area Forecast Discussion
National Weather Service Birmingham AL
303 PM CDT Wed Jun 3 2020

/Updated at 0252 PM CDT Wed Jun 03 2020/

Through Thursday.

The radar has become active along a moisture gradient over western
AL. PoPs have been raised to account for earlier initiation and
coverage than previously expected with highest rain chances mainly
west of I-65 this afternoon. Thunderstorms are exhibiting a very
slow eastward propagation. This is due to very weak flow aloft,
especially in the sfc-850mb layer. Favorable moisture is slowly
building eastward with the upper-level shortwave currently moving
into the Lower MS Valley, as viewed on water vapor imagery. The
thunderstorm activity is developing and moving into an increasingly
unstable airmass this afternoon. SBCAPE is near 3500 J/kg just ahead
of the mass of rain where temperatures have risen into the upper 80s
with dewpoints in the lower 70s. Additionally, there is still enough
dry air along the moisture gradient which has resulted in DCAPE ~800-
1000 J/kg and a low to moderate microburst risk in our western
counties. We will be monitoring for a few strong storms this
afternoon capable of producing small hail, strong gusty winds,
frequent lightning, and heavy downpours.

Otherwise, the short term forecast remains on track for the rest of
this period. Showers and storms will diminish across the area this
evening while the upper-level trough axis continues eastward and
positions overhead by tomorrow morning. The associated low-level
trough moves into our northwest and weakens the ridging over
Alabama, resulting in another round of afternoon scattered to
numerous showers and thunderstorms. Highest PoPs tomorrow will be
along and north of the I-20 corridor. Look for upper 80s in the
south with slightly lower temperatures in the north due to better
coverage of rainfall.



/Updated at 0328 AM CDT Wed Jun 03 2020/

Thursday night through Tuesday.

The persistent upper level trough remains in place over the region
Thursday night into Friday, leading to scattered showers and
thunderstorms. The trough axis lifts northeastward out of Central AL
later on Friday and a convergent boundary sets up generally along
and south of I-85 during the afternoon. While scattered
thunderstorms are expected across our entire area, I think we might
see a little focus for more numerous thunderstorms along this
boundary in our southernmost counties.

As we go into the weekend, the main story will be Tropical Storm
Cristobal and its precise northward trajectory. We`ll see a gradual
increase in tropical moisture Saturday into Sunday as PWATs begin to
exceed 2.00", which will lead to effective rain-producing storms,
especially across the southern half of Central AL. There will likely
be a north to south gradient in precip coverage, and pinpointing
where that sets up will heavily depend on the track and timing of
Cristobal. Because model guidance is in surprisingly good
agreement with this system right now,I`ve trended PoPs upwards to
60-70% on Monday. However, the there`s still some uncertainty in
the forecast for Cristobal due to its interaction with land along
the Bay of Campeche coast, and its forecast to undergo
reformations over the next 2-3 days. Because of this, I`ll keep
PoPs capped at 50% for Tuesday, but if the track holds steady as
it is now, rain chances for Monday and Tuesday will likely

UPDATE: POPs were indeed bumped upward on Tuesday, as model
confidence increases just a bit more. Even if the tropical system
(or its remnants) passes well to our west, that would still put
us on the side favorable for deep moisture advection off the Gulf,
with a synoptic scale shortwave trough forecast to move through
the Mississippi Valley during that time frame.



18Z TAF Discussion.

Scattered to numerous showers and thunderstorms have developed over
west AL this afternoon. This activity will slowly spread eastward,
affecting primarily TCL to BHM & EET. Added a TEMPO for TSRA at TCL
this afternoon, but opted for VCTS at the other terminals since
the majority of the favorable moisture should be focused primarily
in the west, and weak southeasterly low-level flow will mean slow
eastward propagation of the activity. As a result of the low
confidence, amendments may be needed throughout the afternoon for
the remaining terminals depending on the spatial extent of
development. Otherwise, diminishing showers and storms overnight
will briefly give way to favorable flight conditions, but MVFR
ceilings are expected at our northern terminals tomorrow morning
as a shortwave trough works across the region followed by
additional scattered thunderstorm development late in this cycle.




Deep tropical moisture will continue to provide daily chances for
showers and thunderstorms for the next several days. Storms will
be most numerous during the afternoon hours, and slow movement
could cause some very heavy downpours for a few locations. Outside
of rain areas, conditions will remain seasonably warm with
generally light winds.


Gadsden     67  86  66  87  66 /  20  60  30  50  30
Anniston    68  86  66  87  66 /  20  50  30  50  30
Birmingham  70  87  69  88  69 /  30  50  30  50  20
Tuscaloosa  70  87  69  88  69 /  40  50  30  50  20
Calera      68  86  68  87  68 /  30  40  30  50  20
Auburn      68  86  67  85  68 /  20  40  30  60  40
Montgomery  69  89  68  89  69 /  20  40  30  60  40
Troy        68  88  68  88  69 /  20  50  30  60  40




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