Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Birmingham Alabama
551 PM CST Sat Feb 25 2017
for 00z aviation.
tonight and Sunday.
Post-frontal surface high pressure will continue its eastward jog
today through tonight. The pressure center was located over
Oklahoma as of 17z, and will be nudging into the Carolinas by
this time tomorrow. Breezy, gusty northwesterly winds will exist
through the afternoon thanks to mixing of low-level winds as
observed on the 12z weather balloon. Boundary-layer cooling/inversion
development will aid in weaker winds Post-sunset.
The only pressing grid changes have been with trying to parallel
observed vs. Forecast dew points, as the slump has been a bit
steeper in areas. Temperatures are in-check. A clear sky is
forecast today through Sunday, with an increasing presence of
clouds as we step through Sunday evening (a lead-up to rain/storms
Sunday night through Friday.
By Sunday evening, we should see the upper zonal flow turn
southwest with weak disturbances moving through the flow Sunday
night into Monday across eastern conus. At the same time,
onshore/low level flow increase. Isentropic lift precipitation
could begin before sunrise on Monday across the west and spread
across central Alabama during the day. This will be enhanced by a
low level jet of around 40-50 kt. Elevated instability is expected
along with some thunder at times.
As we move into Monday night and Tuesday, our departing ridge is
completely gone allowing low level southerly flow to take over and
for the warm front to push northward allowing dew points to surge
upward from the upper 30s to near 50 Monday afternoon to the mid
50s to the lower 60s by Tuesday morning. Shower and thunderstorm
chances will remain high on Tuesday with the best chances north
along with a noted increase in temperatures. A few unorganized
strong storms will be possible late Monday into Tuesday with
increasing instability but limited overall focus.
Models are coming more into consensus for the timing of the mid
week frontal system for late Wednesday. With increasing moisture
and instability in place, the front will give a good focus for a
few strong to severe storms. The GFS has slowed to come more into
alignment with the Euro solution and thus yields a greater overall
confidence. Will be adding a 1 confidence for tornadoes/severe
threat for Wednesday in the severe weather potential statement along the front. Guidance is
showing elevated sheer and a decent low level jet to accompany the
front as it comes through central Alabama.
Behind the front for Thursday, strong ridging builds over the
central U.S. With decent cold air advection into Alabama. Much
colder temperatures are expected for Thursday and Friday. The
ridge is expected to spread further to the east into the eastern
half of conus on Friday.
00z taf discussion.
Very dry conditions will remain over central Alabama this period
and VFR conditions are expected. Surface high pressure will move
rather quickly from Arkansas to the Carolinas this period. So, the
terminals have a few lines in them for wind direction change only.
The gusty winds should subside quickly after sunset but held some
winds in overnight. Winds should generally be 4-7kts but will
veer from around 300 to 110-150 by Sunday afternoon.
Drier air will move in behind the front today for the weekend.
Relative humidity values will fall to around 30 percent this
afternoon with 20 ft winds around 10-12 mph, and to near 25
percent Sunday afternoon with lighter winds. Critical fire weather
conditions are not expected.
Preliminary point temps/pops...
Gadsden 29 60 41 60 55 / 0 0 10 80 70
Anniston 31 62 42 62 56 / 0 0 10 70 70
Birmingham 32 62 45 63 59 / 0 0 10 80 70
Tuscaloosa 31 63 45 66 59 / 0 0 20 80 60
Calera 33 63 45 64 59 / 0 0 10 80 60
Auburn 34 63 44 65 58 / 0 0 0 60 50
Montgomery 35 66 45 70 61 / 0 0 10 60 40
Troy 34 65 45 70 60 / 0 0 0 60 30