Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 280427
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1127 PM CDT Wed May 27 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 415 PM CDT Wed May 27 2015

Cold front has now passed through STL metro, and should sink a bit
more south before stalling out over southern sections of the CWA
this evening.  Convergence is quite weak in the vicinity of the
front, but instability has recovered in the wake of the morning
complex, with 19z MLCAPES of up to 1500 J/Kg over the Ozarks.  Have
continued chance/slight chance PoPs over this area for the evening
hours as some development could occur at any time between now and
7-8pm.  Across northern portions of our CWA, the cooler and drier
air north of the front should make for a very comfortable late May
evening, with weak surface ridge pushes from northern MO into
central IL.

While primary threat of convection in our FA tonight (such as it is)
should be tied to the late afternoon/early evening instability
across the south, have maintained slight chance PoPs across the
south throughout the overnight and into the predawn hours as frontal
boundary will remain parked over this area, In addition, have
actually pushed these slight chance PoPs north into mid Missouri by
daybreak as return flow develops in the wake of the aforementioned
surface ridge, producing weak overrunning of the stalled front.
Certainly, greatest lift/moisture return will be west of our CWA,
but if convection does develop over western MO during the predawn
hours some of this may activity may be able to trickle into our
western counties by 12z.


Truett

.LONG TERM:  (Thursday through Next Wednesday)
Issued at 415 PM CDT Wed May 27 2015

(Thursday-Saturday)

12z guidance continues to support earlier forecasts that indicate
increasingly unsettled conditions as we head into the latter part of
the week.  Today`s various 12z NWP outputs are all similar
synoptically, and indicate a broad southerly flow advecting warm and
increasing moist air into the mid-Mississippi Valley on Thu-Thu
night, with several shortwaves ejecting from the upper trof over the
west coast interacting with this increasingly unstable airmass over
the region.  For now have gone with fairly broad brush chance PoPs
during this time range, with the greatest chances over northwest
sections of the CWA where dynamics and moisture should be somewhat
maximized.  However, it`s certainly possible that meso-scale
processes will force some short-range adjustments to this thinking.

Good model consensus continues into the end of the week, with all
solutions progging a strong cold front across the region from late
Friday into Saturday as west coast trof also works into the central
CONUS. With the ample moisture, strong lift, and instability have
gone with likely PoPs as the front traverses the CWA, and its
certainly possible that these will ultimately be too low.  Not
totally clear on severe weather potential on Friday afternoon and
Friday night as large scale shear is fairly weak and progged
soundings look rather soupy, and at this point it appears that
severe thunderstorm potential will likely hinge on how much
instability can be attained in the warm sector.

Temperatures will remain on the warm side through Friday, but are
expected to drop back into the 70s by Saturday as the cold air
begins to exert its influence over the area.

(Sunday-Wednesday)

The cool down that begins on Saturday will intensify on Sunday as
the strong surface ridge building into the upper Great Lakes sends
chilly Canadian air into the region. Latest guidance suggests
clouds along with a few lingering showers/thunderstorms persisting
over about the southeast half of the CWA, and these clouds and
potential precip along with the chilly air should mean highs only
in the 60s for most of the CWA.

While it looks rather odd for late May, all of the medium range
solutions are forecasting a cut- off upper low to develop in the
vicinity of the Bootheel on Monday, with this low then gradually
drifting south with time. Temperature trends during the Mon-Tue
time frame will indicate a gradual return to near average levels,
although am wondering if this moderation may be a bit too fast if
the upper system hangs around.

Don`t see any large precip threat during this time, but did
continue some low PoPs in a few spots Mon and Tue with weak
ripples rotating around the upper low.

Truett

&&

.AVIATION:  (For the 06z TAFs through 06z Thursday Night)
Issued at 1111 PM CDT Wed May 27 2015

Cold front has pushed southeast of CPS this evening with weak
surface ridging behind it over northeast MO and northern IL.
Light surface wind will become sely on Thursday as the surface
ridge shifts well east of the area and as the front lifts back
northward as a warm front. Diurnal cumulus clouds will develop
late Thursday morning and afternoon. There should be isolated to
scattered showers/storms Thursday afternoon into the evening as
an upper level disturbance approaches with the best coverage
likely in the COU area.

Specifics for KSTL: Diurnal cumulus clouds will develop late
Thursday morning and afternoon. There will likely be isolated
showers/storms Thursday afternoon into the evening, but will
leave the STL taf dry for now. Light surface wind late tonight
will strengthen to around 8 kts by Thursday afternoon from a sely
direction.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     66  85  70  86 /  10  30  30  50
Quincy          61  82  66  81 /  10  20  40  60
Columbia        62  82  65  80 /  20  50  40  70
Jefferson City  62  83  65  81 /  20  50  40  60
Salem           65  84  68  85 /  10  20  20  40
Farmington      62  82  65  83 /  20  30  30  50

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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