Heavy Rain in Alabama, January 13, 2020

Area Forecast Discussion
National Weather Service Mobile AL
1149 PM CST Sun Jan 12 2020

.DISCUSSION...Updated for latest aviation discussion below.

&&

.AVIATION...
06Z issuance...Primary aviation concerns will be IFR to LIFR
ceilings and visibility reductions spreading inland overnight into
early Monday morning, along with the development of numerous SHRA
and a few TSRA across the region. The greatest probability of LIFR
ceilings/visibility reductions will be across locations especially
along and southeast of a KMOB to KPRN line. Visibility should
gradually improve through late Monday morning, but IFR ceilings
may continue through the day across southeast MS and much of
southwest AL and the northwest FL panhandle. Periods of SHRA and
a few TSRA will continue through Monday afternoon. /21

&&

.PREV DISCUSSION... /issued 956 PM CST Sun Jan 12 2020/

DISCUSSION...See updated information for land areas below.

UPDATE...Evening surface observations and analysis show a warm
front extending across the western and north central Gulf of
Mexico and then arcing into the northwest FL panhandle. Surface
winds are becoming light southeasterly and dewpoints are rising
into the mid to upper 60s to the south of the warm front, while
very light north to northeast winds and temperatures in the mid
50s to lower 60s are noted to the north of this boundary. Patchy
dense fog is beginning to develop near the northwest FL panhandle
coast around Destin and Eglin AFB as of 9 PM. High resolution
guidance, including the RAP/HRRR, along with SREF probabilities of
visibility < 1 mile are in good agreement that fog will continue
to advance inland and become more widespread in coverage across
locations especially along and southeast of I-65 overnight into
early Monday morning behind the lifting warm front, while lower
fog probabilities/coverage are noted in model trends over interior
southeast MS and southwest AL which should remain to the
northwest of this feature. Showers, along with a few thunderstorms
should continue to increase in coverage across the area overnight
within increasingly moist southwest flow aloft and ahead of the
warm front. We will keep POPs high overnight.

Given that dense fog looks increasingly unlikely over far
northwestern portions of our area, we opted to remove Wayne and
Choctaw counties from the Dense Fog Advisory, but otherwise will
continue the advisory across the rest of the forecast area.
Overnight lows look on track to range in the mid 50s to around 60
degrees roughly along and to the northwest of I-65, with lows in
the lower to mid 60s across the rest of southwest/south central AL
and the northwest FL panhandle. /21

PREV DISCUSSION... /issued 611 PM CST Sun Jan 12 2020/

DISCUSSION...Updated for latest aviation discussion below.

AVIATION...
00Z issuance...Ceilings will generally be starting off at MVFR
thresholds across the region early this evening, but will
eventually lower to IFR to LIFR thresholds after 03-06Z. A few
showers and even an isolated thunderstorm or two will impact
portions of the region this evening. Areas of fog will also
develop late tonight through Monday morning, some of which will
become dense with visibility becoming reduced to less than 1/2
mile at times. Numerous to widespread rain showers and a few
thunderstorms will develop along a warm front from interior
southeast MS through interior portions of southwest AL starting
mainly after 09Z and continuing into the day Monday. /21

PREV DISCUSSION... /issued 329 PM CST Sun Jan 12 2020/

NEAR TERM /Now Through Monday/...Upper air analysis shows a
mid-level ridge of high pressure oriented from the southwest
Atlantic to the southeast Gulf, while high level trof maintains
its hold over the western half of the CONUS. Within the mid to
high layer southwest flow aloft between these two pressure systems,
lies a quasi-stationary frontal boundary draped from the Mid-
Atlantic southwest to the central Gulf. A weak surface pressure
ridge positioned over the Lower MS River Valley has allowed for a
stable air-mass under a light east to northeast flow. Little to no
rain is shown on radar thus far, but this is expected to change.
The Gulf front begins to lift northwestward as a warm front to the
coast by this evening, bringing an enhancement to ascent and a
return to high rain chances over the central Gulf coast.
Initially, the high resolution convective allowing models (CAMs)
shows a gradual increase in the environmental instability by late
afternoon and on into the evening along the southern zones as the
warm front approaches. 12.17Z HRRR MuCAPE values to 800-1200 J/KG
by evening over the southern zones is indicated with a gradual
northward expansion of environmental de-stabilization thru the
night. An increase in southerly 0-1 KM bulk shear to 25 to 30 kts
also supports convection mixed in within a developing larger
coverage of showers. At this time, appears the threat of severe
weather is low. An active high level southwest flow with passage
of series of mid-level impulses supports maintaining periods of
showers and embedded storms into the day Monday as surface
boundary continues to lift northward. A gradual northward shift in
the higher PoPs is advertised for Monday night. Some areas could
see rainfall totals adding up to between a half to perhaps between
1 and 2 inches encompassing the upcoming next three periods.

In addition to increased rain chances will be a return to fog.
Short range ensembles show probabilities of fog increasing
substantially from southeast to northwest. High resolution
and Localized Aviation MOS products (LAMP) guidance also show
dense fog, with visibilities lowering to a half mile or less
forming along area bays and sounds northward over the land zones
through the night. Considering signals in guidance and the favored
synoptic scale set-up we have in place, a dense fog advisory will
be issued on this package beginning at 13.03Z for portions of the
coastal waters including bays and sounds and including all land
zones as well. Visibility is forecast to improve enough by and
after 13.15Z Monday over land zones but remain low over bays and
sounds where the advisory will continue. In fact, marine fog is
expected to carry over into Monday night, while increasing in
coverage again over land.

A high risk of rip currents will remain through at least
tonight. /10

SHORT TERM /Monday night Through Wednesday night/...The surface
warm front should lift north of our forecast area by Tuesday
morning with a warm and humid airmass in place in its wake. Dense
fog is again likely to form over the near shore coastal waters as
well as local bays and Mississippi Sound, as near 70 dewpoint air
overspreads water temperatures in the mid/upper 50s. This setup
favors dense sea fog development. Dense fog advisories may again
be needed later Monday night into Tuesday, especially over the
marine/coastal areas.

Several weak upper level shortwaves will move through
southwesterly flow aloft which should support scattered showers
and isolated thunderstorms through mid week. Despite increased
thermodynamic instability, weak lapse rates and marginal shear
values should limit any severe weather threat. Overall the greater
focus for storms will be north of the area, therefore not
anticipating any excessive rainfall at this time.

As southerly low level flow quickly returns to the area, the
potential for dangerous rip currents may persist into Tuesday.
This threat will be monitored closely over the next couple of
days. /JLH

LONG TERM /Thursday Through Sunday/...Another northern stream
shortwave aloft will eject from the Central Plains across the
Tennessee/Ohio Valleys through Thursday. In response, a cold
front will gradually slip south Thursday afternoon into Thursday
night. There remains some model discrepancies with regard to how
strong the Gulf Coast ridge will be by this time. This will play a
role in how far south the front progresses and whether it will
make it into our forecast area. At this time, have increased pops
across northern sections of the CWA to account for the front being
in the vicinity. This front should stall and lift back north in
response to a stronger digging upper trough over the Plains
States. Temperatures and humidity levels should remain above
seasonal normals through the remainder of this week.

As the upper trough shifts east by next weekend, expect a stronger
cold front to advance across the area. Showers and thunderstorms
should accompany the frontal passage. Colder temperatures and
drier conditions should follow the frontal passage for the second
half of the weekend. /JLH

MARINE...Fog is forecast to re-develop overnight and become
locally dense over bays and sounds as a warm front approaches the
coast. There are indications that fog will linger into the day
Monday carrying over into Monday night through Tuesday morning.
Coverage of showers will increase and be greatest tonight and
Monday. The potential exists for a few storms to be mixed in as
well. A weak cold front makes passage Wednesday night. Onshore
flow increases and seas build Friday ahead of a stronger cold
front moving eastward out of the southern Plains. /10

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Dense Fog Advisory until 9 AM CST Monday for ALZ052>060-261>266.

     High Rip Current Risk until 6 AM CST Monday for ALZ265-266.

FL...Dense Fog Advisory until 9 AM CST Monday for FLZ201>206.

     High Rip Current Risk until 6 AM CST Monday for FLZ202-204-206.

MS...Dense Fog Advisory until 9 AM CST Monday for MSZ075-076-078-079.

GM...Dense Fog Advisory until 9 AM CST Tuesday for GMZ630>636-650-655.

&&

This product is also available on the web at:
http://weather.gov/mob

Hazardous Weather Outlook...UPDATED
National Weather Service Mobile AL
331 PM CST Sun Jan 12 2020

ALZ265-266-FLZ202-204-206-132200-
Mobile Coastal-Baldwin Coastal-Escambia Coastal-Santa Rosa Coastal-
Okaloosa Coastal-
331 PM CST Sun Jan 12 2020

...HIGH RIP CURRENT RISK IN EFFECT THROUGH LATE TONIGHT...
...DENSE FOG ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 9 AM CST
MONDAY...

This Hazardous Weather Outlook is for southwest Alabama and
northwest Florida.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   High Rip Current Risk.
   Dense Fog Advisory.

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

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   Dense Fog Advisory.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

ALZ051>060-261>264-FLZ201-203-205-MSZ067-075-076-078-079-132200-
Choctaw-Washington-Clarke-Wilcox-Monroe-Conecuh-Butler-Crenshaw-
Escambia-Covington-Mobile Inland-Baldwin Inland-Mobile Central-
Baldwin Central-Escambia Inland-Santa Rosa Inland-Okaloosa Inland-
Wayne-Perry-Greene-Stone-George-
331 PM CST Sun Jan 12 2020

...DENSE FOG ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 9 AM CST
MONDAY...

This Hazardous Weather Outlook is for south central Alabama,
southwest Alabama, northwest Florida and southeast Mississippi.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   Dense Fog Advisory.

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

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   Dense Fog Advisory.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

GMZ630>636-650-655-132200-
Northern Mobile Bay-Southern Mobile Bay-Mississippi Sound-
Perdido Bay-Pensacola Bay System-Western Choctawhatchee Bay-
Eastern Choctawhatchee Bay-
Coastal waters from Pensacola FL to Pascagoula MS out 20 NM-
Coastal waters from Okaloosa Walton County Line FL to Pensacola FL
out 20 NM-
331 PM CST Sun Jan 12 2020

...DENSE FOG ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 9 AM CST
TUESDAY...

This Hazardous Weather Outlook is for the coastal waters of Alabama
and northwest Florida.

.DAY ONE...This Afternoon and Tonight.

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   Dense Fog Advisory.

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

Please listen to NOAA Weather Radio or go to weather.gov/mob (see
Fast Access Product Section) for more information about the
following hazards.

   Dense Fog Advisory.

GMZ670-675-132200-
Waters from Pensacola FL to Pascagoula MS from 20 to 60 NM-
Waters from Okaloosa Walton County Line FL to Pensacola FL from
20 to 60 NM-
331 PM CST Sun Jan 12 2020

This Hazardous Weather Outlook is for the coastal waters of Alabama
and northwest Florida.

.DAY ONE...This Afternoon and Tonight.

No hazardous weather is expected at this time.

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

No hazardous weather is expected at this time.