Air Resources Laboratory banner image
Air Resources Laboratory web site National Oceanic and Atmospheric Administration (NOAA)

al discuss

Office: BMX

FXUS64 KBMX 190453

Area Forecast Discussion
National Weather Service Birmingham AL
1053 PM CST Sun Feb 18 2018

For 06Z Aviation.



Ridging aloft has migrated further east and is now centered to the
east of the Bahamas today. Global numerical models are in general
agreement in depicting the higher height region in an elongated
form extending from the western Atlantic Basin into the center of
the Gulf of Mexico. GOES-R low-level water vapor imagery along
with global modeling depicts a shortwave trough in the
southwesterly flow aloft over eastern Texas this afternoon. This
disturbance will continue to move northeast toward the state

At the surface, the cold front that moved south overnight
maintained momentum to reach the northern Gulf Coast early this
morning. A relatively quick-moving surface high pressure area
built into the Tennessee Valley region overnight and helped
discourage the surface front to the south from making much
northward progress. The surface high has quickly moved northeast
today and is now analyzed along the border between Ohio and West
Virginia. The position of the surface high this afternoon and its
low-level advection pattern has helped to reinforce and increase
the wedging effects experienced across portions of Georgia and our
eastern and northeast counties yesterday. A generally light
easterly flow is prevalent across many of our eastern and central
counties this afternoon and is helping to maintain cooler
temperatures and lower dew points compared to yesterday.

The 18/12Z BMX sounding contained a notable frontal inversion this
morning with last night's cold front stalled along the northern
Gulf Coast. A fairly saturated layer was present from the surface
to the top of the inversion around 830 mb. A moist layer existed
above this point up to a subsidence inversion that was sampled
around 700 mb. A light northeast flow from 5-10 kts was observed
within the frontal inversion followed by a general unidirectional
zonal flow aloft. Speeds generally increased with height above the
inversion from around 25 kts around 850 mb to near 95 kts around
120 mb.


Today and Tonight.

Isentropic upglide from the stalled front along the northern Gulf
of Mexico is aiding in the developing of generally light showers
across much of our northern and central counties this afternoon.
This activity will continue to develop and move northeast,
providing the highest rain chances across our northern and central
counties this afternoon will become maximized across our far
northern and northeast counties later tonight as a shortwave
trough over eastern Texas approaches from the southwest.

Conditions closer to the surface this afternoon are cooler and
more stable compared to yesterday due to the weak wedging
influence from easterly flow. Temperatures are fairly uniform
generally north of the U.S. Highway 80 corridor with readings
ranging from the mid 60's to low 60's. With the frontal inversion
maintained, vertical mixing has been fairly minimal across much of
our forecast area except across our far southern and southeast
counties where cloud cover as been reduced, allowing for
temperatures to rise into the low to mid 70s at this hour.

Temperatures will remain the warmest across our far southern
counties through sunset as the stalled front gradually returns
northward as a warm front late this afternoon and tonight. With
vertical mixing maximized, some breezy conditions will be possible
across our southern counties until this evening when the boundary
layer will decouple. Some patchy fog will be possible across our
southern counties as early as this evening as dew points rise as the
warm front passes northward. The fog potential will expand northward
with the northward advance of the warm front tonight. Have adjusted
onset of fog formation south in the grids and will mention fog in
the updated HWO product forthcoming. Lows tonight will range from
the lower 50's north to the lower 60's far south and southeast.


Monday through Sunday.

There are two main stories weather-wise for the extended - the above
normal temperatures and the rainfall. Synoptically, the warm front
has lifted north of the area by Monday morning, putting us well into
the warm sector ahead of the deepening trough and cold front. The
cold front is off to the northwest into Missouri, so any dynamic
forcing is limited for rain chances. This should leave Monday
mostly rain-free for Central AL, with only a slight chance in the
morning to give time for that warm front to lift out of here.
Strong ridging is in place to our south and east, leading to
deep/moist southerly flow.

First, the rain - we remain in the warm sector with really only the
possibility of isentropic lift to spark afternoon showers Tuesday
and Tuesday night. As we get into Wednesday, models are in good
agreement that the cold front has pushed into North MS and Western
TN. Lift along and ahead of this front will increase rain chances
across all of Central AL, with the rain likely north of the I-20
corridor Wednesday afternoon and night. The biggest question, and
the focus on all forecast uncertainty from Wednesday night through
Thursday is just how far that cold front gets. The GFS pushes it
through AL on Thursday before stalling it and lifting it northward
as another effective warm front. However, the ECMWF never really
brings it very far into Central AL (maybe to I-59 corridor) before
lifting it north Thursday morning (at least 24 hours sooner than
the GFS). I've been hedging my forecast closer to the ECMWF as it
has more support from the ensembles and the Canadian. This puts me
at around a 45-55% chance of rain for most areas north of the
I-85 corridor on Thursday for my forecast, but this still factors
in the GFS possibility. If the GFS trends closer to the EC in
coming days, I can decrease those PoPs more. Thunderstorms are
possible with this system as surface instability will be more than
enough to support thunderstorm development. However, shear values
are expected to remain too low to support any organize severe
threat. The warm front should be lifted north of our area by
Friday, regardless of which model verifies, so decreasing rain
chances overall for Friday and Saturday. I have kept some mention
for chance or rain in due to isentropic lift ahead of yet another
shortwave trough. That trough will push into Saturday night into
Sunday morning, increasing rain chances again for the weekend.
Have limited the PoPs to 45-50% on this trough due to the
possibility of fluctuations in timing.

Now, for the above normal temperatures - As most have noticed, it
has been unusually warm across Central AL the past few days. I
expect that to continue with the anomalous ridge off to our south
and east advecting warm/moist air into the area. Tuesday through
Thursday, the NAEFs percentiles are highlighting 99.5th to Max
climatological values for geopotential heights, temperatures,
specific humidity, and PWATS at around 3 standard deviations above
the mean(translation -it's going to be warm and humid compared to
a typical mid to late February). Therefore, I have edged the high
temperatures up a few degrees, which will continue to put us in
potential record high territory Monday, Tuesday, and Wednesday. I
have included the records for our climate sites below this
discussion. Thursday's high temps are somewhat uncertain and
dependent on how the GFS trends with that frontal passage. If it
trends more with the EC and keeps the front north of us, then we
could see more near-record highs again on Thursday. If the front
pushes through Central AL, we could see a temporary cool down on
the backside of the front. For locations along and south of the
I-85 corridor, there's good chances the cold front never makes it
that far south, leading to continued above normal high temperatures
Thursday and Friday.



06Z TAF Discussion.

It looks like restrictions will remain in the forecast this
period. Have a combination of vis/ceilings into IFR by 10-11z and
lasting until 14-15z. Thereafter, ceilings should improve into MVFR
and then VFR by 18z.

A surface warm front was meandering across southern Alabama and
may inch northward overnight. Although slightly drier conditions
exist aloft. The cooler near surface conditions and warmer air
riding over the boundary will produce some fog and low clouds.
Models certainly do not have a consensus again with this forecast,
but will lean pessimistic. The warm front moves north of the area
Monday and rain chances will be much less than the previous few
days. We will actually not have to deal with this front again for
a few days. Surface winds will mainly be light and variable
overnight, but some places may experience light drainage northeast
winds briefly. Winds on Monday swing around to the southeast and
south at 8 to 18kts.




Rain showers are expected this evening and into the overnight period
with the higher chances across our northern counties as a warm front
returns northward. Above normal humidity is expected to continue
through most of next week, limiting any fire weather concerns.



Unseasonably warm temperatures are expected to continue for the next
week or so. With forecast highs in the upper 70s and low 80s Monday
through Wednesday, several record highs will be in jeopardy. Here's
a look at the current daily record highs for February 19th
through 21st.

Location            2/19        2/20        2/21
------------       ------      ------      ------
Birmingham        76(2011)*   78(1986)    78(1922)
Montgomery        83(1891)    80(2011)*   81(2011)
Tuscaloosa        77(2011)*   81(2014)    79(2005)
Anniston          76(2011)*   78(1986)*   75(2011)*
Calera            75(2017)*   76(2017)    75(2011)*
Troy              79(2014)    81(2014)    80(2005)

*Record was set in multiple years, but only the most recent is


Gadsden     54  75  57  79  61 /  20  10  10  20  40
Anniston    57  76  58  81  62 /  20  10  10  20  30
Birmingham  57  77  61  81  65 /  10  10  10  20  40
Tuscaloosa  55  78  61  81  64 /  10  10  10  20  30
Calera      56  78  61  81  64 /  10  10  10  20  30
Auburn      60  77  61  79  64 /  10  10  10  20  30
Montgomery  59  81  60  82  64 /  10  10  10  20  30
Troy        60  80  60  81  63 /  10  10  10  30  30





Office: MOB FXUS64 KMOB 190523 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 1123 PM CST Sun Feb 18 2018 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION... 06Z issuance...Challenging aviation forecast for the overnight hours. IFR ceilings and occasional LIFR visibilities will be an issue through the night and into the hours around sunrise. Opted to handle the intermittent nature of the advection fog via TEMPO groups. Things should begin to improve by 19.15Z. Area remains under southeasterly surface flow though the period, which could become gusty around max heating hours on Monday. 05/RR && .PREV DISCUSSION... /issued 947 PM CST Sun Feb 18 2018/ DISCUSSION...Updated for latest marine discussion below. MARINE...Visibility is slowly being reduced by fog over parts of the marine area this evening. The dense fog appears to still be somewhat patchy and variable in nature, but went ahead and issued a Marine Dense Fog Advisory for Mobile Bay, Mississippi Sound, Perdido Bay and the adjacent near shore Gulf waters, valid until 9 AM Monday morning. Visibility at both Pinto Island and Middle Bay Port have both recently dropped to well below one nautical mile, with some locations less than one quarter of a mile. These conditions will likely persist across portions of the Alabama coastal waters through the night and into the early morning hours Monday, and may need to be expanded further east across the Florida near shore marine zones later tonight. 12/DS PREV DISCUSSION... /issued 400 PM CST Sun Feb 18 2018/ NEAR TERM /Now Through Monday/...A southwesterly mid level flow pattern continues across the central Gulf Coast region today between a trough of low pressure over the western CONUS and a ridge that extends from the western Atlantic through the eastern Gulf of Mexico. The surface boundary that was located just south of the coast early this morning has retreated northward as a warm front through all but far northwestern portions of our forecast area this afternoon. Low clouds have dispersed over much of the region to the south of the boundary, with the exception of scattered afternoon cumulus, and temperatures have warmed well into the 70s, with even a few locations peaking in the lower 80s. We have so far reached 80 degrees at Mobile Regional Airport, which ties the previous record of 80 set back in 1887, 1976, and 2000. Weak ascent associated with a shortwave impulse has lifted well north of our area this afternoon, and have removed the slight chance of rain from the forecast over far northern sections of the CWA through the rest of the afternoon. Southwesterly mid level flow will continue over our area tonight through Monday on the western fringe of the upper ridge that will strengthen over the western Atlantic and build slightly westward across the Florida peninsula and eastern Gulf of Mexico. An increasingly dry and subsident airmass under this building feature should keep the weather dry over the eastern 2/3rds of the area through Monday afternoon. The exception may be over portions of southeast MS and far southwest AL, where there is some agreement between the WRF-ARW, GFS, and ECMWF of weak isentropic ascent resulting in the development of a few showers late Monday morning into Monday afternoon. Will have a slight chance of POPs over these locations. Otherwise, conditions will once again favor the development of areas of fog near the coast this evening, before gradually spreading north across the rest of the forecast area overnight into early Monday morning. Fog may be locally dense and have mentioned in the Hazardous Weather Outlook. Will let later shifts monitor its development and assess any potential advisories. Fog should mostly lift after 9 A.M. Monday morning. The unseasonably warm and humid conditions will continue into Monday afternoon. /21 SHORT TERM /Monday night Through Wednesday night/...No real change from yesterday's forecast scenario in the synoptic pattern. A digging upper trough over the western Conus works with a building upper high off the Carolina coast to create a highly amplified upper pattern. Into Wednesday, the eastern upper high helps to prevent the shortwave energy streaming through the upper trough from pushing it significantly eastward and helps to build and maintain a surface ridge stretching southwest over the Southeast from a surface low located off the coast of the Mid- Atlantic region. With southerly flow off the Gulf continuing through the SHORT TERM, moisture levels climb to above season levels (GFS is advertising precip h20 levels above 1.7" by Wednesday). Question is will subsidence from the upper ridge over- rule the thermodynamic instability from the moist airmass. A shortwave rotating around the upper high will bring that needed oomph Tuesday night into Wednesday will provide this first help to increase the rain chances. Shortwave energy moving through the upper trough pushes a front towards, but not quite to the forecast area Wednesday, helping to increase any rain chances Wednesday through Wednesday night, especially over northwestern portions of the area. Any precip that does break the subsidence inversion will likely see thunder mixed in. Again, best chance will be over northwestern portions of the area, with this area seeing a weaker cap. Temps, well, with subsidence from the upper high remaining in control, highs well above seasonal continue, with daytime highs flirting with records through mid week. Another item to deal with is the fog chances. With the organized southerly flow pushing warmer Gulf waters towards the coast, the chance of dense fog will decrease. Also, with the moderate onshore flow, the chance of rip currents will be on the increase. With a neap tidal cycle becoming more amplified through the week, am expecting the risk of dangerous rip currents to increase as the week progresses, LONG TERM /Thursday Through Sunday/...Through the extended, the shortwave energy streaming through the western upper trough begins to win out, shifting the upper high southward until it becomes centered over the easter-central Gulf of Mexico. This will allow pieces of energy to pass closer to the forecast area and keep the rain chances above seasonal. The shifting of the upper high still keeps the forecast area under its influence, with subsidence continuing to bring above seasonal temperatures, just not quite as warm. MARINE...A light to moderate southeasterly flow becomes established over the marine area this evening and persists into the latter part of the week as our area remains between a ridge of high pressure over the western Atlantic and southeastern states, and lower pressure over the Plains states. Areas of marine fog will likely develop again this evening through late tonight near bays, sounds, and near shore coastal waters. Visibility could become reduced to less than one nautical mile and we will monitor trends closely for potential advisories. At least patchy fog development will be possible for the next few days, mainly during the evening through early morning hours. /21 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...None. FL...None. MS...None. GM...Dense Fog Advisory until 9 AM CST Monday for GMZ630>633-650. && $$ This product is also available on the web at: