Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Mobile Alabama
934 PM CDT Wednesday Jul 23 2014
Update...upper air analysis this evening shows a weakness in the
high level flow/trough over the central Gulf Coast between upper ridge
off the southeast coast and upper ridge over The Four Corners of the
Desert Southwest. Within the weakness...a frontal zone was analyzed from
the middle Atlantic back into Oklahoma. South of the boundary...an
organized complex of storms was rolling southward around 30 knots
over Arkansas earlier in the evening. However...cloud top warming
noted on infrared satellite imagery and a net general weakening of storms
is occurring from central Mississippi/northern half of Louisiana to
northeast Texas. Very little on the radar scope further to the east
over our area with only a pop-up shower/storm here and there.
With precipitable water values remaining high (~1.9 inches)...will
not take much from any energy in the flow aloft to continue to
kickoff isolated showers/storms through the night. Made a few minor
adjustments to temperatures/dewpoints given latest observations
initially. Overnight lows near 70 interior to the upper half of the
70s close to the beaches. /10
Previous discussion... /issued 646 PM CDT Wednesday Jul 23 2014/
Aviation [24.00z taf issuance]...a large complex of convection was
dropping southward around 30 knots across Arkansas this evening.
These storms remain west of the terminals in the near term.
Overall...very little cloud cover over the area at this time. Could
be some middle/higher level clouds into the middle to late evening
associated with thunderstorms and rain dropping southward across Louisiana. VFR
conditions in the short term with a light wind flow pattern.
Scattered middle morning rain showers/thunderstorms and rain possible forecast on Thursday. /10
Previous discussion... /issued 344 PM CDT Wednesday Jul 23 2014/
Short term [thursday]...surface front linked with a deepening trough
to our north will bring dynamic forcing into play in our northern
zones Thursday afternoon. Forecast soundings in the WRF-arw indicate
it will stay humid through a deep layer ahead of the front.
Precipitable water forecast near or slightly above 1.8 inches
Thursday afternoon...Li around -4...and cape 1600-2800 j/kg is
expected...so we believe a likely category along our northern
boundary is appropriate and will verify well. Over the western
portions of the County Warning Area...the upper low to our west that has been a big
player the last few days will likely become absorbed into that
trough...and we believe the seabreeze should stay in the scene...
bringing a 40% category along the shoreline. Pop about 30 percent
elsewhere. Daytime highs in the lower 90s. 10/77
[thursday night through Friday night]...the surface cold front
should be stalled across the northwest portion of our forecast area
Thursday night...generally along a line from Hattiesburg MS to
Camden Alabama. This front should remain stalled through Friday morning
before retreating northward as a warm front Friday afternoon and
Friday night. Meanwhile...a medium amplified eastern Continental U.S. Upper
trough will move very slowly eastward and weaken through the
remainder of the short term...reaching the Atlantic Seaboard by late
Friday night. Scattered showers and thunderstorms will be ongoing
near the front Thursday evening...with isolated coverage across the
southern half of the forecast area. The convection will dissipate by
midnight across the inland areas...but may persist along the coastal
sections as moisture continues to move in from the Gulf ahead of the
stalled front..and the base of the upper trough passes over.
Isolated to scattered showers and thunderstorms will redevelop on
Friday...with the best coverage along and east of the I-65 corridor.
The convection should dissipate by early Friday evening
across the inland areas...but again may persist along the coastal
sections as moisture continues to move in from the Gulf.
Lows both Thursday and Friday nights will range from 69 to 73
degrees most locations...with middle/upper 70s along the beaches. High
temperatures Friday will range from 88 to 93 degrees inland
areas...with middle 80s at the beaches. /22
Long term [saturday through wednesday]...for Saturday...the upper
trough over the southeastern Continental U.S./Northern Gulf of mex continues to
weaken as the western upper high builds a ridge-line east over the
Southern Plains and lower miss River Valley. Temperatures above seasonal
come with decreased chance of rain for the first part of the weekend
as a result.
Saturday night through Sunday night...another upper system moving
over the US/California builds...first squeezing the ridge over the lower miss
River Valley and southeastern Continental U.S. East a bit before the digging
trough over the eastern Continental U.S. Pushes it back west. The forecast area remains
under the influence of the upper ridge a bit longer...with temperatures
above seasonal and probability of precipitation below.
Monday through Wednesday...a pair of upper system moving through the
eastern trough help to push first push a weak surface front to just
south of the northern Gulf Coast Tuesday. How guidance handles the
second one varies...with the GFS pushing the boundary farther
south...and the European model (ecmwf) using the boundary for precipitation generation over
the Southern Plains and lower miss River Valley. Both are advertising
probability of precipitation around seasonal Sunday into Tuesday. The European model (ecmwf) maintains the
near seasonal chance of rain through middle week...especially over
western sections of the forecast area...whilst the GFS dries things out. With
the better chance of rain plus increased cloud cover from precipitation to
the west of the forecast area...the European model (ecmwf) drops temperatures below seasonal...whilst
the drier GFS maintains temperatures at or a bit above seasonal. The GFS
ensembles are advertising a solution in the middle...so have blended
them for the forecast.
Marine...a high pressure ridge will remain over the eastern Gulf of
Mexico through the weekend. This feature will bring light to
moderate southwesterly winds over the marine area along with
isolated to scattered showers and thunderstorms...generally more
active overnight through mid-morning. Winds of 10 to 15 knots bring
seas 1 to 2 feet as per rendered by Swan output. This verifies
closely with bretschneider methodology. /77
Preliminary point temps/pops...
Mobile 72 92 72 91 73 / 20 40 20 30 20
Pensacola 75 92 75 89 76 / 20 40 20 30 20
Destin 77 90 76 88 77 / 20 40 20 30 20
Evergreen 69 93 70 92 71 / 20 40 20 30 10
Waynesboro 68 92 69 93 70 / 20 30 30 20 10
Camden 69 89 70 93 71 / 20 60 30 20 10
Crestview 70 93 72 92 71 / 20 40 20 30 20