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Office: BMX

FXUS64 KBMX 121225
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
625 AM CST Tue Dec 12 2017

.UPDATE...
For 12Z Aviation.

&&

.SHORT TERM...
Today and Tonight.

This AM, a surface low pressure system is currently over Lake Erie
with a front extending from it southward into Eastern Tennessee
and southwestward into Northern Alabama and westward into Texas.
The front is expected to make progress through Alabama this
morning and clear through much of the Gulf of Mexico tonight as
the main low moves into New York today and Maine tonight spreading
the front through Eastern Conus. For today, we will see some
cloud cover mostly across the northern half of the state. Rainfall
is still not anticipated though as overall moisture is shallow
for both the front and post front with the passage of the upper
trough. We are looking at cooler temperatures returning behind the
front for today and tonight with breezy northwest winds in store
for today with tight surface pressure gradients ushering in cooler
air. Winds slowly taper off overnight as a surface ridge spreads
from Texas into Louisiana and toward the Alabama Gulf Coast.

08

.LONG TERM...
Wednesday through Monday.

Rain-free weather is expected to continue through Saturday due
persistent dry west to northwest flow aloft. A shortwave moving
through the Ohio Valley will push a moisture-starved front through
the region on Thursday. Another shortwave approaching from the
west on Friday will have little moisture to work with, and should
not amplify enough to generate sufficient moisture return for
precipitation. Surface high pressure across the region on Saturday
will quickly shift eastward by Sunday as a trough amplifies
across the Plains. Moisture recovery in advance of this system
appears more robust due to a deep-layer ridge near the Bahamas and
southerly low-level flow across the Gulf States. Increasing rain
chances could arrive on Sunday and continue into Monday with the
potential for a widespread soaking rainfall.

87/Grantham

&&

.AVIATION...
12Z TAF Discussion.

The cold front has made it through most of the TAF sites with only
TOI to go. It should not be too long for TOI. No rain is expected
with or behind the front today with only shallow moisture with
this system. Some VFR cirrus and 4-6 KFT clouds are possible in
the northern 1/2 of the state this morning. Then, we should see
SKC for all. Northwest winds behind the front will be gusty today
with tight surface pressure gradients, but winds should taper off
in the late evening as the surface ridge builds in from the west.

08

&&

.FIRE WEATHER...

No rain is expected through Saturday. Cooler and breezy
conditions are expected today behind a cold front. Another dry
front will move through on Thursday. RH values will remain above
critical values.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     46  25  49  32  53 /   0   0   0   0   0
Anniston    46  25  50  33  55 /   0   0   0   0   0
Birmingham  48  28  52  36  56 /   0   0   0   0   0
Tuscaloosa  51  29  55  35  58 /   0   0   0   0   0
Calera      49  27  52  35  56 /   0   0   0   0   0
Auburn      51  29  50  35  57 /   0   0   0   0   0
Montgomery  54  29  54  35  61 /   0   0   0   0   0
Troy        55  30  54  36  62 /   0   0   0   0   0

&&

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

&&

$$

08/87



Office: MOB FXUS64 KMOB 121121 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 521 AM CST Tue Dec 12 2017 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION... 12Z issuance...VFR conditions prevail through the period, with breezy northwest winds this afternoon becoming light overnight tonight. && .PREV DISCUSSION... /issued 404 AM CST Tue Dec 12 2017/ NEAR TERM /Now Through Tuesday night/...Northwest flow persists aloft as a vigorous shortwave digs into the New England states, ultimately extending south along the eastern seaboard and over the Florida peninsula. With the passing of this shortwave comes a reinforcing shot of dry and cool northwest flow across our local area as a surface ridge of high pressure builds to our west. The result will be cooler temps this afternoon, reaching the low 50's inland and upper 50's to around 60 along the coast. Lows tonight return to being cold due to the drier air, clear skies, and light winds. Expect temps to dip into the upper 20's to around 30 inland, and low to mid 30's along the coast. /49 SHORT TERM /Wednesday Through Thursday night/...The northwest upper level flow over the region will transition to a zonal flow through the short term as the upper level trough moves east over the western Atlantic. Meanwhile, an Alberta Clipper will dive southeast across the midwest states on Wednesday and then turn east. A light southerly surface wind flow will resume by Wednesday afternoon, followed by another dry cold front entering into the forecast area Thursday night. Rain-free conditions will persist through the short term. /22 LONG TERM /Friday Through Monday/...The cold front will move south of the gulf coast early Friday, with a 1024mb surface high pressure building in its wake across the region. A southerly return flow will follow late Saturday and Sunday as the center of high pressure moves east of the area. The dry period will persist throughout the week. A strong upper level shortwave is expected to move from west to east across the southern conus early next week. The 12.00z ECMWF model is faster and more aggressive with this system compared to the GFS, with a 45 to 55 knot low level jet setting up over the forecast area on Sunday. A 120 to 140 upper level jet is expected to develop over the eastern conus, with the forecast area residing in the favorable right entrance region. While adequate wind shear will certainly be in place early next week with this system, along with upper level diffluence and mid level lift, instability in the low to mid levels is still undefined. However, given the strong dynamics advertised by the ECMWF, added a slight of thunderstorms embedded in the scattered showers. Would not be surprised that higher precipitation chances will be needed as this event nears. Also, this system may bring a round of strong to marginal severe weather with damaging winds and possible tornadoes being the main threats if higher MLCape values are realized. /22 MARINE...Moderate to strong offshore flow continues through this afternoon and evening before settling overnight tonight. A Small Craft Advisory remains in effect until 6 pm CST for unprotected Gulf waters out 60 nm. Winds likely remain at exercise caution levels in area bays and sounds through this time as well. After settling overnight tonight into Wednesday morning, winds strengthen again and shift to southwesterly and then westerly late Wednesday through Thursday. Another frontal passage then brings moderate offshore flow Friday into the weekend. Seas around 3 to 5 feet to start the period subside to around 2 to 3 feet through midweek, before building back to around 3 to 5 feet in the wake of the front late this week. /49 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...None. FL...None. MS...None. GM...Small Craft Advisory until 6 PM CST this evening for GMZ650-655- 670-675. && $$ This product is also available on the web at: http://weather.gov/mob