263 
FXUS64 KBMX 122332
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
632 PM CDT Mon Mar 12 2018

.UPDATE...
Aviation Discussion.

&&

.SHORT TERM...

No changes to the current forecast. Surface low pressure moves
away from the area as high pressure builds in. This reduces the 
gradient enough that will will subside. We have already seen the 
winds beginning to decrease somewhat west, but since gust are still 
occurring, will leave advisory for the entire area until sunset.

These same winds will also subside overnight. Some light winds
still expected and the combination of the cold air advection and
lighter winds will allow temperatures to drop to near freezing 
for large part of north central Alabama. Did not change the 
configuration of the Freeze Warning overnight. Outside the warning
area, temperatures still into the 30s with some patchy frost.

Minor tweaks the remainder of the period with same extended issues
on this run. 

75

Previous short-term discussion:Today and Tonight.

As of 3 am the cold front has almost exited the forecast area and 
the best rainfall coverage has ended. We now shift our eyes to the 
upper low that will begin to swing into the area this morning. 
Overall colder and drier air will filter in behind the front. Most 
of the wrap around moisture associated with the upper low, will 
remain north of Central Alabama through the early morning. If a few 
showers do move through the northern portion of the area, profiles 
just off the surface will be cold enough to support a light 
rain/snow shower. Chances are low and uncertainty high, and will 
only carry slight chance to chance wording. Ground temperatures are 
too warm for any accumulation, and no impacts from any light snow 
showers/flurries are expected. 

With the upper low swinging through, winds will pick up quite a bit 
today, so a wind advisory will be issued to account for the winds of 
20 to 30 mph and higher gusts. These winds will calm down quite 
substantially this evening and the colder airmass will begin to 
settle down into the area. At this point took the consensus of the 
short term models and knocked a couple of degrees off of that for 
the lows tonight.  This puts the northern half of the area generally 
at or below freezing, thus a freeze warning will be issued. Further 
south, temperatures will stay above freezing for most of the area 
but will still be in the low to mid 30s. Dewpoints will remain above 
30 in these areas so patchy frost is possible. So a Frost advisory 
will be issued for the south as well. There could be a few spots in 
the south that drop to 32 degrees but those will be more isolated 
than across the north. 

16

.LONG TERM...
Tuesday through Monday.

Seasonably chilly conditions will continue Tuesday and Wednesday 
under deep layer northerly to northwesterly flow. A highly amplified 
pattern will be present over the CONUS with one longwave trough 
moving onshore along the West Coast and another longwave trough over 
the eastern CONUS, with a ridge located over the Rockies/High 
Plains. An upper low will drift eastward from the eastern Great 
Lakes to the Northeast, while a 'nor'easter occludes near the 
Canadian Maritimes and high pressure moves from the northern High 
Plains to the Lower Mississippi Valley. Cold air advection will not 
be quite as strong Tuesday as today, but highs will still remain in 
the 50s. A shortwave moving down the back side of the trough will 
bring a few mid-level clouds during the day on Tuesday and a 
reinforcing shot of cold air for Tuesday night. There will still be 
a bit of a pressure gradient over the area Tuesday night allowing 
for some light northerly winds, but with clear skies and a very dry 
air mass still think temperatures should cool efficiently (as they 
did even with some gradient winds last Thursday morning) with cold 
air advection also assisting. Therefore expect a freeze for all but 
the most unsheltered locations, and the cooler northern and eastern 
locations will have no trouble reaching the 20s. A freeze watch has 
subsequently been issued for Tuesday night for all of Central 
Alabama. 

The brunt of the coldest air at 850mb will be east of the area, but
850 mb temperatures Wednesday morning will still be as cold as -8C
in the northeastern counties. This results in cooler high 
temperatures for Wednesday with some upper 40s in the typically 
cooler northeastern/eastern locations. The surface high will be 
centered near the Alabama Gulf Coast Wednesday night. This along 
with a clipper low over the Great Lakes causes the low-level wind 
direction to become more westerly, but considering the placement 
of the high and associated calmer winds radiational cooling 
conditions will overall be the best on this night. A freeze watch 
will likely be issued for Wednesday night in future updates. 

A return to more typical spring weather will begin to occur on
Thursday. The western CONUS trough will move the central CONUS 
ridge and eastern CONUS trough eastward. Southwest winds and 
rising 500mb heights should allow temperatures to warm up nicely 
into the 60s by Thursday afternoon. Milder conditions are expected
Thursday night with southwest winds and some high clouds, but the
typically cooler eastern locations could still reach the 30s for 
lows with 40s elsewhere. 

Details remain uncertain, but the pattern becomes more unsettled
by Friday. Uncertainty is due to varied handling of shortwaves 
ejecting out of the western CONUS trough. A surface low is 
expected to develop in the lee of the Colorado Front Range on 
Thursday, causing a frontal boundary to sharpen as it extends 
eastward across the Missouri and Ohio Valleys. This low and 
associated shortwave aloft is expected to weaken as it moves 
eastward but the ECMWF is slower to weaken it, which allows the 
front to move closer to the area Friday through the weekend. 
Meanwhile the GFS is weaker with this system and keeps the front 
further north. This will determine rain chances and temperatures 
Friday through the weekend. Starting off on Friday, an axis of 
enhanced 850-700mb mean RH values combined with warm air advection
and increasing dew points should result in at least scattered 
showers developing. The front will then serve as the main focus 
for showers and thunderstorms Friday night through the weekend, 
especially the further north you go. With some instability and 
deep layer shear along with cool temperatures aloft, there may be 
the potential for a few stronger storms over the weekend near the 
front, but fairly weak low-level flow and lack of upper-level 
forcing suggests nothing particularly organized at this time. 

Models have been indicating that a low-amplitude trough and
associated surface low will move through the Central CONUS during
the Monday timeframe, but have shown variability from model-to-
model and run-to-run regarding timing and placement of this
feature, as well as lingering troughing over eastern Canada and a
potentially strengthening subtropical ridge near the Bahamas. This
system looks to potentially have more instability to work with
than previous systems, so we will keep an eye on the severe
potential as it gets closer. But right now it's too early to
speculate on any details based on the uncertainties with the
system itself and the system before it, and it remains just beyond
the 7-day HWO period.

32/Davis

&&

.AVIATION...
00Z TAF Discussion.

Gusty winds will gradually weaken this evening, remaining at 5-8kts 
overnight from the northwest. 

A FEW to SCT deck of VFR cigs are possible this evening, mainly 
north. Will be watching a cloud deck to our northwest across western 
TN as it advances toward the area overnight. Anticipate the clouds 
to diminish as it nears Central Alabama. If not, it would mean an 
increase in VFR cigs. 

VFR conditions expected Tuesday, with winds increasing from the 
northwest by mid day, with sustained winds around 9-10kts and gusts 
up to 18kts.

14

&&

.FIRE WEATHER... 

Rain-free conditions are expected through Thursday. RH values will 
fall each afternoon due to a dry air mass but remain above critical 
levels. 20ft winds will be weaker the remainder of the week, 
generally below 10 mph by Tuesday. No fog is expected for the next 
few days. KBDI values remain very low due to recent rainfall and 
will likely remain that way with the upcoming rains, so there are no 
fire weather concerns. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     31  54  28  53  28 /   0   0   0   0   0 
Anniston    31  55  28  54  28 /   0   0   0   0   0 
Birmingham  33  56  31  55  31 /   0   0   0   0   0 
Tuscaloosa  34  59  30  58  30 /   0   0   0   0   0 
Calera      33  57  31  56  31 /   0   0   0   0   0 
Auburn      33  57  32  55  31 /   0   0   0   0   0 
Montgomery  35  60  33  59  31 /   0   0   0   0   0 
Troy        35  59  33  58  31 /   0   0   0   0   0 

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Frost Advisory from 3 AM to 9 AM CDT Tuesday for the following 
counties: Autauga...Barbour...Bibb...Bullock...Chilton...
Dallas...Elmore...Greene...Hale...Lee...Lowndes...Macon...
Marengo...Montgomery...Perry...Pickens...Pike...Russell...
Sumter...Tuscaloosa.

Wind Advisory until 7 PM CDT this evening for the following 
counties: Autauga...Barbour...Bibb...Blount...Bullock...
Calhoun...Chambers...Cherokee...Chilton...Clay...Cleburne...
Coosa...Dallas...Elmore...Etowah...Fayette...Greene...Hale...
Jefferson...Lamar...Lee...Lowndes...Macon...Marengo...Marion...
Montgomery...Perry...Pickens...Pike...Randolph...Russell...
Shelby...St. Clair...Sumter...Talladega...Tallapoosa...
Tuscaloosa...Walker...Winston.

Freeze Watch from late Tuesday night through Wednesday morning 
for the following counties: Autauga...Barbour...Bibb...Blount...
Bullock...Calhoun...Chambers...Cherokee...Chilton...Clay...
Cleburne...Coosa...Dallas...Elmore...Etowah...Fayette...Greene...
Hale...Jefferson...Lamar...Lee...Lowndes...Macon...Marengo...
Marion...Montgomery...Perry...Pickens...Pike...Randolph...
Russell...Shelby...St. Clair...Sumter...Talladega...Tallapoosa...
Tuscaloosa...Walker...Winston.

Freeze Warning from 3 AM to 9 AM CDT Tuesday for the following 
counties: Blount...Calhoun...Chambers...Cherokee...Clay...
Cleburne...Coosa...Etowah...Fayette...Jefferson...Lamar...
Marion...Randolph...Shelby...St. Clair...Talladega...
Tallapoosa...Walker...Winston.

&&

$$