Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Birmingham Alabama
659 PM CDT Sat Oct 21 2017
this afternoon through tonight.
The low levels of the atmosphere continue to moisten up with
surface dewpoints in the upper 50s to lower 60s. The total column
of the atmosphere is still very dry with precipitable water
values below 1 inch. Cloud cover overnight will mostly be high
clouds with a few cumulus. No rain expected overnight due to dry
air mass in place, but moisture will increase rapidly after
sunrise Sunday as strong upper trof approaches the Mississippi
River. Temperatures overnight will be rather mild overnight due to
warm air advection, with lows in the upper 50s to lower 60s.
Sunday through Friday.
Our dry weather will come to an end on Sunday afternoon into the
evening as a potent upper-level trough approaches from the
Southern Plains. A mass of rain and embedded thunderstorms or
perhaps a qlcs will arrive from Mississippi in the late afternoon.
Aside from a few stray showers, areas east of I-65 should stay
mostly dry through sunset, but West Alabama should see increasing rain
chances after 3 PM. An area of meager instability will become
pinched off near the MS/Alabama due to drier southeasterly low-level
flow over Alabama. Therefore, severe weather is not expected as
the area of moderate to heavy rain with embedded thunder moves
eastward into the nighttime ours. This forecast heavily leans
toward the open wave or more progressive scenario shown by the
European model (ecmwf). The GFS appears to be be way too amplified and closed off
with the 500mb trough. I have sped up the departure of high rain
chances through the day on Monday into Monday night, and a further
increase in forward speed is possible. In fact, Monday afternoon
could end up dry for most of the forecast area.
A very strong upstream shortwave will reinforce the cold advection
regime on Tuesday into Wednesday with afternoon temperatures
barely reaching 60f in the north on Wednesday. A transition to
warmer conditions is expected on Thursday and Friday as southerly
flow develops in response to a developing large trough in the
western Continental U.S..
00z taf discussion.
Winds remain at 4-7kts from the southeast to east overnight. Low
level moisture slowly increases ahead of an approaching storm
system. Coupled with isentropic lift, sct to bkn MVFR cigs will
spread from south to north early Sunday morning. Cig heights improve
through the morning with winds increasing from the southeast, at 10-
10kts with gusts to 18kts.
A line of rain and embedded thunder will approach the area late in
this taf period. Have added rain thunderstorms in the vicinity at tcl at 22/20z and at bhm and
eet at 22/22z. This timing will likely need adjusting with future
Mild and dry weather will continue through Saturday and early
Sunday. Widespread soaking rainfall is expected Sunday night into
Monday. Relative humidity values should remain above critical
thresholds. There are no fire weather concerns.
Preliminary point temps/pops...
Gadsden 57 79 66 72 52 / 0 10 90 100 30
Anniston 59 80 67 72 53 / 0 10 90 100 30
Birmingham 63 81 68 72 54 / 0 30 90 80 20
Tuscaloosa 64 82 68 74 54 / 0 70 100 60 20
Calera 63 80 67 72 54 / 0 40 90 80 20
Auburn 62 78 69 73 55 / 0 20 80 100 30
Montgomery 64 84 70 75 56 / 0 30 100 80 20
Troy 63 83 70 75 56 / 0 30 100 90 20