Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Birmingham Alabama
541 PM CST Thu Feb 23 2017
for 00z aviation.
Central Alabama remains wedged between a surface low off the
Florida East Coast and a stationary front over Missouri. Surface
high pressure was producing a south to southeast flow over the
state. The latest visible satellite imagery has the cloud cover
finally mixing out with most places into the 70s.
The upper ridge axis shifts just east of the area into Friday.
Deep layer south to southwest flow will keep temperatures quite
mild. Friday morning, temperatures only drop into the 50s. These
temperatures stay some 10 to 20 degrees above normal. Low level
thicknesses and 850 temperatures will produce temperatures at or
above what we experienced this afternoon. Therefore, temperatures
at or above 80 in many locations and the records are in jeopardy.
There will also be low level moisture overnight. With overnight
lows near the crossover temperatures, expect some fog development
after midnight. Due to the southerly flow and isentropic lift,
low clouds are also a possibility. Due to the uncertainty of this
mix between fog and clouds, timing, and specific location, will
not introduce any dense fog yet. The fog and clouds should mix a
bit quicker on Friday.
Shower and thunderstorm development along a cold front and
possibly along a pre-frontal trough will hold off until Friday
evening as the southern end of the upper-level forcing reaches the
front. A broken line at most in a very narrow moisture axis is
expected with the best rain chances in the far north. Some thunder
will be possible, especially north if any stronger updrafts can
form given the steep mid-level lapse rates. However, any severe
storms should remain north of the area. This is due to the main
upper level forcing remaining north of the area as well as warm,
dry air aloft which will result in some capping and dry air
entrainment. The 850 mb low level jet will only be around 30 kts with
veering low-level flow as the surface low occludes and continues
to lift into Ontario. Longer range cam guidance keeps any stronger
updrafts well north of the area. The front should quickly exit
the area by Saturday morning. Did increase the rain chances
slightly north into the likely category.
Saturday through Wednesday.
A brief period of more seasonable temperatures and dry conditions
will occur over the weekend behind the front. Lows will be around
freezing Saturday night as a surface high moves through the area.
An unsettled pattern will take hold for the first half of next
week with moist southwest flow in place between an elongated
upper-level ridge from the southern Gulf to the Bahamas and broad
troughing over the western US. In this southwest flow some
shortwaves will move through, predominately just north of the
area, with low predictability. Meanwhile pwats will be increasing
to near 1.5 inches, with the potential for beneficial rainfall in
some areas. An unstable, sheared air mass will develop with steep
mid-level lapse rates, so some stronger storms may be possible in
this period, but with weak upper-level forcing there is nothing
synoptically that warrants inclusion of anything severe in the severe weather potential statement
at this time.
The GFS is stronger than the European model (ecmwf) with an initial shortwave and
associated surface low ejecting from the Southern Plains to the
Ohio Valley Sunday night into Monday. This solution lifts a warm
front quickly northward through the area Monday with a moist and
unstable air mass developing south of the front. The strongest
low level jet and low-level shear parameters remain north of the warm front,
however. The European model (ecmwf) is weaker with these features and slower to
move the warm front northward, but looks wet on Monday as well.
The GFS sends a trailing cold front into the area that stalls
across the area on Tuesday and serves as a focus for continued
showers and thunderstorms while the European model (ecmwf) keeps the forecast area
solidly in the warm sector. Despite these differences, models are
generally in agreement on a warm and wet period.
Models are in good agreement on a stronger shortwave moving across
the northern US on Wednesday and an associated frontal passage for
central Alabama. Both the GFS and European model (ecmwf) indicate plenty of
instability with the frontal passage and strong deep layer shear,
but the low level jet is weak and very veered as the surface low will be
over the northern Great Lakes. This will be monitored as the time
00z taf discussion.
VFR conds thru 09z with mostly clear skies and light winds.
Southerly low level flow will increase overnight with boundary
layer winds at 10-15 knots. This would favor low cloud formation
over fog development. The models are not very robust with low
level moisture due to weaker isentropic lift, and confidence in
widespread cloud cover is low, as cloud bases may be sct-bkn.
Better convergence and moisture should be from I-65 and eastward,
and held off cigs at ktcl until after sunrise. Good mixing during
the day on Friday should cause cigs to become scattered by 18z.
Dry and warm conditions are expected through Friday. The next
chance of light rain should come Friday night into early Saturday with
a front, followed by low relative humidity values over the
weekend. There are no fire weather concerns at this time.
Record high temperatures for Friday, February 24:
Birmingham: 78 (1930)
montgomery: 80 (1890)
tuscaloosa: 78 (2011)
anniston: 78 (1982)
Preliminary point temps/pops...
Gadsden 53 78 50 58 31 / 0 10 60 0 0
Anniston 55 79 52 59 32 / 0 10 50 0 0
Birmingham 58 79 48 58 33 / 0 10 50 0 0
Tuscaloosa 57 81 48 60 33 / 0 10 40 0 0
Calera 57 79 51 60 34 / 0 10 50 0 0
Auburn 56 78 55 63 36 / 0 10 30 10 0
Montgomery 57 82 56 65 37 / 0 10 30 0 0
Troy 56 81 56 65 37 / 0 10 30 10 0