Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220856

Area Forecast Discussion
National Weather Service Saint Louis MO
356 AM CDT SUN MAY 22 2016

.SHORT TERM... (Today and Tonight)
Issued at 330AM CDT Sun May 22 2016

Dry and tranquil weather will dominate the area as surface high
pressure strongly influences the sensible weather. This high
pressure system will slowly retreat to the east over the next 24
hours while a high amplitude upper ridge shifts westward into the
MS Valley. Warming aloft attendant with the upper level ridge
will translate to continued moderation of temperatures with highs
today finally rising to above average levels for late May.


.LONG TERM... (Monday through Saturday)
Issued at 330 AM CDT Sun May 22 2016

An active and warm week ahead with continuous thunderstorm chances
and potential for at least several severe weather episodes. The
upper ridge axis will shift to the east of the area on Monday with
flow aloft becoming southwesterly. Improving southerly low level
flow will result in gradual northeastward moisture return and
increasing warm advection on Monday and support low pops into
central MO during the afternoon. However, the greatest advection
and convergence will be focused further west across the Plains
into western MO in association with a 35-40 kt southerly LLJ and
this is where the highest probability of deep convection will
reside. A veering and strengthening southwesterly LLJ on Monday
night will promote greater eastward moisture transport and warm
advection and the resultant instability, and hence the potential
for advancement of convection into central and northeast MO.

Deepening of the positively tilted long wave trof centered near
the west coast on Tuesday, and the departure of the east coast
upper trof, will allow for gradual strengthening of the flow
aloft. Strengthening of the southwest flow aloft will continue
Tuesday night into Wednesday and this will result in strengthening
deep layer shear favorable for organized convection, as well as
the eastward transport of steep mid level lapse rates atop the
deepening and moistening boundary layer promoting the development
of strong instability.

The pattern pretty much remains unabated through the end of the
week with a steady stream of weak disturbances traversing the
area, relatively undisturbed steep mid level lapse rates promoting
strong instability within a broad warm sector, and favorable deep
layer shear for organized convection. The migratory disturbances
aloft, modulating/veering LLJ, and mesoscale features will largely
drive the thunderstorm risk. Present indications are the most
active periods will be late Monday night-Tuesday morning as previously
stated, Wednesday, and Thursday. The greatest severe weather threat
will be centered on the later two of the aforementioned periods
with potential for several severe MCSs.



.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1117 PM CDT Sat May 21 2016

VFR and dry thru the period. Winds will be light and difficult to
pin down to a direction. However, tonight thru mid morning Sun,
winds will generally be nwly and slowly become sely Sun afternoon
thru the evening.





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