000 
fxus64 kmob 291249 aab 
afdmob 


Area forecast discussion...updated 
National Weather Service Mobile Alabama 
749 am CDT Mon may 29 2017 


Discussion...see updated information for land and marine areas below. 


&& 


Update... 
initial convective complex continues moving east-northeastward 
across parts of south-central Alabama and the Florida Panhandle. 
Mesoanalysis data indicates decreasing amounts of parcel buoyancy 
available, with 1000-1500 j/kg now noted near the coastal counties 
in our forecast area. Precipitation probabilities have been 
increased downstream to account for this initial convective 
complex. 


Area radars show another convective complex moving toward our area 
from southeast Louisiana. Infrared satellite imagery indicates 
warming cloud tops, which suggests a decreasing convective trend. 
Radar trends show this as well. This trend is expected to 
generally continue through mid-morning, although I made no 
adjustments to precipitation probabilities past 10 am at this 
time. 


Updated text products will be issued shortly. /Butts/ 


&& 


Marine... 
scattered showers and thunderstorms continue moving across the 
marine area this morning. The stronger thunderstorms will be 
capable of producing wind gusts around 30 knots along with locally 
choppy seas and torrential rainfall. 


Observational platforms over the northern Gulf indicate 
significant wave heights over the Gulf of Mexico waters are 
running a skosh higher than what's indicated in the current 
forecast products. Current wind speed forecast appears to be in 
decent agreement with data from available observational platforms. 


Updated text product will be issued shortly. /Butts/ 


&& 


Previous discussion... /issued 651 am CDT Mon may 29 2017/ 


Discussion...updated for latest aviation discussion below. 


Aviation... 
12z issuance...MVFR to VFR conditions can be expected through 
much of the day scattered showers and storms near the terminals by 
the afternoon. IFR to MVFR conditions can be expected in and 
around storms. /13 


Previous discussion... /issued 542 am CDT Mon may 29 2017/ 


Near term /now through Monday night/... 
a large upper-level storm system spinning over southern Ontario this 
morning continues to result in broad troughiness over much of the 
eastern U.S. The associated cold front remains analyzed from middle 
Tennessee into the arklatex early this morning. 


Showers and thunderstorms have already been seen this morning close 
to home, initializing along an outflow boundary (or boundaries) from 
previous convection. Mesoscale analysis indicates a very unstable 
airmass in place across the northern Gulf Coast, with MLCAPE values 
between 1500 and 2000 j/kg common. Mid-level lapse rates and 
effective bulk shear values are marginal, however, with values 6.5 
degrees c/km and 25 knots, respectively. Some stabilization is 
expected across the region as this complex of storms traverses the 
region. The big question is to what degree can we recover for the 
afternoon. 


I think convection today will likely be driven by largely mesoscale 
processes. Sure, synoptic scale forcing is enhanced given the 
proximity of the surface front. The upper jet, though, is forecast 
to remain to our north with a minimum of cross isobaric flow between 
the upper trough and the surface front. That said, I think the front 
(and the best source of large scale forcing/shear) will likely 
remain to our north/west tonight. 


What we will have is a "soupy" airmass, with precipitable water 
values between 1.75 and 2 inches over the region. Forecast soundings 
indicate some airmass recovery is possible this afternoon, with 
maximum MLCAPE values between 1500 and 2000 j/kg possible. Short 
version - ample moisture and instability will be present, as will be 
plenty of mesoscale boundaries and disturbances in the upper 
atmosphere moving through the region. 


The ongoing convection should take full advantage of the 
thermodynamic environment through mid-morning, with additional 
development possible across southeast Mississippi and adjacent 
areas of interior southwest Alabama. Expect the areal coverage of 
this convection to diminish by late morning as instability is 
used. There may be a break in the convection late morning through 
early to mid- afternoon, before more showers and thunderstorms 
develop across southeast Mississippi with the approach of the next 
upper atmosphere disturbance. Timing of precipitation 
probabilities have been based on this train of thought. 


There are lots of flies hanging out in the ointment today, so 
updates will likely have to be made as the event evolves. Locally 
heavy downpours will be possible in the stronger thunderstorms. 


Short term /Tuesday through Wednesday night/... 
minimal cross isobaric flow should be provided by the broad upper- 
level trough through Tuesday. This should result in the surface 
front remaining nearly stationary, generally waffling somewhere 
either side of the ih-20 corridor. 


The atmosphere across our region will remain quite moist. 
Precipitable water values should remain between 2 and 3 Standard 
deviations above climatological means, with amounts above 1.75 
inches expected. Instability should not be as great as today, but 
MLCAPE values around 1000 j/kg may be seen. Weaker perturbations 
moving across our area will interact with this airmass to result in 
additional periods of showers and thunderstorms over the region 
through Tuesday. Expect the greatest convective coverage to remain 
generally along and north/west of ih-65, where better moisture 
transport will be seen. 


Additional upper-level energy is expected to rotate southward across 
the upper Midwest Tuesday afternoon and evening, helping to amplify 
the upper-level trough. This should provide enough momentum to help 
push the surface front southward into our area by Wednesday. Despite 
the loss of daytime heating, increased synoptic scale forcing should 
help maintain a scattered coverage of showers and thunderstorms over 
much of the region Tuesday night. 


The front should gradually weaken as it sags toward the coast 
sometime Wednesday night. I've kept convective probabilities above 
seasonal values through mid-week due to the presence of the 
weakening front. We'll likely see a stronger diurnal signal by 
Wednesday as well, although i've refrained from indicating this in 
the forecast at this time. 


Long term /Thursday through Sunday/... 
broad upper trough axis is forecast to shift east across Quebec 
Thursday. In its wake, weak ridging both at the surface and aloft 
will attempt to rebuild across the region as the old surface front 
gradually dissipates. With the loss of significant synoptic scale 
forcing, expect scattered afternoon convection to exhibit a strong 
diurnal signal with the greatest coverage in the afternoon and early 
evening. 


Low-level flow veers to a more southerly direction Friday night- 
Saturday, just in time for another shortwave trough to move through 
the plains. This feature will likely amplify over the eastern U.S. 
By the end of the weekend and aid in bringing another cold front 
toward the mid-south. Boundary layer moisture increases to nearly 3 
Standard deviations above climatological values, and when combined 
with ample instability, will likely result in an increase in 
convective coverage for the upcoming weekend. 


Marine... 
light to moderate onshore flow is expected over the marine area 
through tonight, along with scattered showers and thunderstorms. A 
weakening cold front is forecast to enter the marine area by Tuesday 
night and become stationary through mid-week. As the boundary 
becomes more diffuse, a decreased shower/thunderstorm coverage will 
likely be seen for the end of the week before showers and 
thunderstorms increasing in coverage again next weekend. Winds and 
seas will be higher in vicinity of any convection. 


&& 


Mob watches/warnings/advisories... 
Alabama...none. 
Florida...none. 
MS...none. 
GM...none. 
&& 






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