Scientific Forecaster Discussion
fxus64 kbmx 152337
Area forecast discussion
National Weather Service Birmingham Alabama
637 PM CDT sun Sep 15 2019
for 00z aviation.
Deep-layer ridging remains entrenched across the deep south
region today. Tropical Storm Humberto remains east of the Florida
Peninsula while a disturbance is positioned over the western Gulf
of Mexico. To our north, a shallow trough was approaching the
western Ohio River valley from the west.
Surface high pressure was analyzed centered over western
Pennsylvania with an extensive footprint extending from southeast
Canada through the mid Atlantic states west to the mid Mississippi
River valley and down south through the Tennessee Valley into
central Alabama and Georgia.
The 15/12z bmx sounding contained meager instability aloft this
morning with several subsidence inversion from off the surface
through 500 mb. Moisture distribution was fairly uniform through
the vertical profile with an overall precipitable water (pw) value
of 1.64 inches. The vertical wind profile was easterly from the
surface to 500 mb with speeds up to 20 kt. Winds became northerly
around 400 mb followed by a shift from the west and southwest
above 300 mb. Speeds were generally up to 30 kt above 500 mb.
/updated at 0134 PM CDT sun Sep 15 2019/
With deep-layer ridging over the area and surface high pressure
to the northeast, an easterly flow will prevail in the lower to
mid levels while a more west to southwest flow is expected aloft.
Low-level instability values from strong solar insolation will be
sufficient for cumulus formation over the area this afternoon
into early evening. Only a few showers may develop with some
becoming thunderstorms through the remainder of the afternoon into
early evening but conditions do not favor the widespread coverage
of precipitation that is needed across much of the forecast area.
Skies will be fair tonight into Monday as higher-level clouds
will move over the area from the southwest from the disturbance
over the western Gulf of Mexico. The combination of overall
subsidence with drier than normal ground conditions is continuing
to support a larger thermal spread between high and low temperatures
along with lower chances for shower and thunderstorm activity
than typically experienced this time of year.
/updated at 0134 PM CDT sun Sep 15 2019/
Monday through Saturday.
Examining the upper level pattern, a zonal flow over much of the
northern half of the country is forecast to amplify over the next
few days as a potent trough swings into the Pacific northwest
tonight and tomorrow. In response downstream, the broad ridging
over our portion of the country will consolidate and amplify from
central Texas through Georgia and northward into the mid
Mississippi River valley region. The result will be much of the
same with mostly dry conditions persisting as highs reach the mid
to upper 90's through midweek while lows will continue to range
from the 60's to the 70's across the forecast area through
Later this week, another trough will dive into the Pacific
northwest and will further amplify the pattern aloft across the
country. Ridging is forecast to elongate further from eastern
Texas northeast into the Great Lakes region. As the deep-layer
ridge becomes centered more to our west along with the surface
pressure gradient gradually increases between Humberto over the
southwest Atlantic Basin and surface high pressure over the
northeast, some heat relief is expected as a northeast flow
develops late Wednesday into Thursday and persists into the next
Shower and thunderstorm chances will remain minimal through the
rest of the work week with a slightly higher chance in the
Wednesday through Thursday time frame as a weak "back door" or
"wedge" front advances southwest through the forecast area with
some cooler/drier air arriving from the northeast. Though
temperatures will gradually moderate with time over the weekend,
expect dry conditions to persist as broad expansive deep-layer
ridging remains over the region.
00z taf discussion.
VFR conditions are forecast through the taf period. Calm to
occasional very light breezes are expected tonight, increasing to
between 5-10 knots from the ~northeast Post sunrise Monday. A few
spells of passing high-level clouds are possible, the result of
blowoff from a disturbance atop the northern Gulf of Mexico.
Other than a few widely isolated showers and some of which may
develop into thunderstorms, hot and dry conditions will persist
across the forecast area. Relative humidity values will fall into
the low 40 percentile this afternoon followed by even lower values
in the 30 percentile range on Monday and Tuesday afternoons as
drier air arrives from the northeast. With very low rain chances
persisting and low afternoon relative humidity values, expect kbdi values to
continue in the elevated range as drought conditions continue.
Preliminary point temps/pops...
Gadsden 66 95 67 96 67 / 0 10 0 10 0
Anniston 68 95 68 97 69 / 0 10 0 10 0
Birmingham 70 97 71 98 71 / 0 10 0 10 0
Tuscaloosa 72 97 70 98 71 / 0 10 0 10 0
Calera 70 96 70 97 70 / 0 10 0 10 0
Auburn 71 93 70 96 70 / 0 10 0 10 0
Montgomery 72 97 70 99 70 / 0 10 0 10 0
Troy 70 95 69 97 69 / 0 10 0 10 0