000 
fxus64 kmob 200437 aac 
afdmob 


Area forecast discussion...updated 
National Weather Service Mobile Alabama 
1137 PM CDT Sat may 19 2018 


Discussion...updated for latest aviation discussion below. 


&& 


Aviation... 
06z issuance...isolated convection over the interior is forecast 
to dissipate overnight. Any convective cloud debris from these 
storms look to be at mid to high levels in the near term. Light 
south/southeast winds to variable. Patchy late night fog possible 
with some potential of MVFR vsbys by and after 20.10z. Convection 
redevelops Sunday afternoon bringing brief strong wind gusts and 
potential of lower end IFR vsbys in moderate to locally heavy 
downpours. /10 


&& 


Previous discussion... /issued 848 PM CDT Sat may 19 2018/ 


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


Update...20.00z upper air analysis shows a weakness in the 
geopotential height field aloft over the southeast US, stretching 
down into the eastern Gulf. Within this weakness, a weak mid level shear 
zone is positioned over The Heart of the forecast area this 
evening which has maintained the growth of new convection within 
a deeply moist environment that remains unstable with sb convective available potential energy 
(1500-2500 j/kg). Some of the storms have become strong with 
concentrated lightning. Will be watching for the potential of a 
few potential brief pulse severe storms which may obtain a deep 
enough updraft to produce 1 inch diameter hail. Given radar 
trends and upper air features, have opted to extend the chance 
pops through around mid-night over the interior zones. /10 


Previous discussion... /issued 622 PM CDT Sat may 19 2018/ 


Discussion...updated for latest aviation discussion below. 


Aviation... 
00z issuance...isolated to scattered pop-up convection ongoing 
north of the terminals is forecast to remain away as to not pose 
any impacts. Any convective cloud debris from these storms look 
to be at mid to high levels in the near term. Light south winds. 
Potential of patchy late night fog possible with some potential of 
MVFR vsbys by and after 20.10z. /10 


Previous discussion... /issued 355 PM CDT Sat may 19 2018/ 


Near term /now through Sunday/...the northern tip of an inverted 
weak upper trough over the eastern Gulf of Mexico will nudge 
northward over North Florida, southeast Alabama and south Georgia 
over the next 24 hours, while the remainder of the southeast 
states remains under the influence of a weak upper ridge. The 
surface ridge extending from the western Atlantic across the 
southeast states and northern Gulf will persist, however there 
will be a very weak easterly wave moving slowly over the eastern 
Gulf on Sunday. Overall we should see a continuation of a light 
south to southeast wind flow this evening and again Sunday 
afternoon. 


The ongoing isolated to low-end scattered showers and storms north 
of I-10 will persist through mid evening, and dissipate by 10 PM. 
Some isolated storms this evening could develop moderate convection, 
but at this time we are not expecting any of the storms to have 
winds above 30 mph. Patchy light fog is expected to form late 
tonight across portions of the forecast area. In addition, a 
moderate rip current risk will persist through tonight. 


Showers and thunderstorms are expected to develop a bit earlier in 
the day Sunday across our northeast zones, and expand in coverage as 
they move southwest across the remainder of the forecast area 
throughout the day. Current precipitation chances Sunday afternoon 
range from 50 to 70 percent. Both of the GFS and NAM have MLCAPES 
ranging from 900-1300 j/kg by noon Sunday, so a few of the storms 
could become strong with winds up to 45 mph and small hail. /22 


Short term /Sunday night through Tuesday night/...an active upper 
pattern over the eastern conus pushes an upper high centered off 
the Carolina coast southward to over the Caribbean by Wednesday 
morning. Shortwave energy swings around the west side of this 
high, with the energy streaming north over the eastern Gulf of 
Mexico in the near term through Sunday night the first item to 
deal with. This energy has moved over the southeast as a semi 
organized non-tropical system by Sunday night where it stalls for 
24-36 hours before more energy moving around the now off the 
Florida coast upper high opens the system and it gets drawn into 
the W-E zonal flow over the northeastern conus Monday night into 
Tuesday. Best influence from this energy remains east of the 
forecast area, but is close enough to bring above seasonal rain 
chances, especially eastern portions of the forecast area. This 
increase in rain and cloud cover will temper daytime 
heating/nighttime cooling, with above seasonal lows expected 
Sunday and Monday nights, and around seasonal highs Monday. 


Tuesday through Tuesday night, an upper trough is left over the 
western Gulf as the afore mentioned energy moves off, with a 
moist airmass remaining over the northern Gulf Coast. A weak 
surface trough that has developed inland from the northwestern and 
north-central Gulf Coast helps to disrupt a surface ridge 
stretching west over the eastern Gulf and Florida. This helps to 
keep the chance of rain above seasonal, spawned a daily Gulf/Bay 
breeze developing and moving inland, and a land breeze setting up 
at night. A system that has developed over the western conus in 
concert with a deepening upper trough over southeast Canada/northeastern 
conus has built an upper ridge over the Mississippi River valley. 
Temps, especially daytime highs, rise to a bit above seasonal with 
the added subsidence from the building Mississippi River upper 
ridge. Lows above seasonal Tuesday night. 


/16 


Long term /Wednesday through Saturday/...the extended has been a 
challenge in previous days, though with better consistency in 
todays guidance in the upper synoptics, have better confidence in 
the forecast. Latest 12z runs show the western Gulf upper trough 
getting a northeast nudge from building high pressure over 
Mexico/eastern Pacific Ocean as more shortwave energy moves around 
the Caribbean upper high. This energy gets drawn into the trough, 
ultimately forming a weakly organized upper low over the central 
Gulf. A digging upper trough over the Mississippi River pushes the 
previous ridge east, and also draws the weakly organized upper 
system north over the north-central Gulf Coast. This system begins 
to develop a surface low over the southern Gulf, then takes it 
north. The European model (ecmwf) continues to take the surface low towards 
Louisiana, whilst the GFS takes it towards the Florida penisula. 
Where this surface low GOES ultimately governs where best chance 
of rain is. Have went with an in the middle solution, bringing a 
surface low towards the north-central Gulf Coast and an increasing 
chance of rain the latter half of the week into the weekend. 
Temps correspondingly decrease to around to a bit below seasonal 
due to the increase in rain and cloud cover limiting daytime 
heating/nighttime cooling. 


/16 


Marine...high pressure will slowly build west over the central 
Gulf of Mexico today promoting a light to moderate onshore wind 
flow. These onshore winds will persist into early next week as a 
series of moist inverted troughs move into the northern Gulf. With 
this additional moisture,rain and thunderstorm chances exist 
everyday next week across all marine zones. /22 


&& 


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






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