Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 272341
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
641 PM CDT Sat Jun 27 2015
.SHORT TERM: (Through Late Tonight)
Issued at 325 PM CDT Sat Jun 27 2015
Sfc ridge will continue to build into the region this eve. Ridge
axis is progd to move swd thru the after Midnight tonight, bringing
swly winds to nrn and wrn portions of the CWA late tonight. Expect
high to possible mid level clouds to move into nrn portions of the
CWA near sunrise.
With the winds becoming swly late tonight, have trended slightly
warmer for these areas. For other areas, have trended aob the cooler
guidance for tonight, esp for ern Ozarks regions, with winds
becoming light under a clear sky. With much cooler temps expected,
can not rule out FG development overnight. The deep mixing today
will help cool dewpoints which may help prevent FG development.
Otherwise, expect SHRA that develops this afternoon to dissipate
quickly with sunset with the remainder of tonight dry.
.LONG TERM: (Sunday through Next Saturday)
Issued at 325 PM CDT Sat Jun 27 2015
(Sunday through Sunday Night)
Complex of showers and thunderstorms ahead of a potent northwest flow
vort max is expected to be just northwest of the forecast area early
Sunday morning. This area is expected to head into portions of
northeastern Missouri and west-central Illinois around midday.
Not sure whether or not area of showers/storms will sustain itself
through the morning hours but believe the area might as the
low-level moist/warm advection sustains itself. In any
event...strengthening of this complex...if it sustains
itself...would be likely along with new development downstream.
Supercells will be favored convective mode due to favorable
deep-layer shear (35-45 knots) along with a sufficiently unstable
airmass. As SPC noted in their discussion...NAM dewpoints and
therefore progged instability seems highly suspect but GFS MLCAPE
values would still support supercells. All forms of severe weather
will be possible late afternoon/early evening on Sunday though large
hail does seem like the predominate threat due to steep lapse rates
aloft. However...damaging wind gusts and isolated tornadoes also
possible. Highest threat of severe weather will be during the
afternoon hours across central and northeastern Missouri.
Initial supercells may collide/congeal into clusters by early
evening with damaging winds becoming more of a threat. Storms are
expected to gradually weaken as instability wanes by late evening.
By 0600 UTC, front will be nearly bisecting the CWA with chance PoPs
from 6-12 UTC.
Regarding high temperatures for tomorrow...went near or slightly
above warmer MET guidance as NW flow/clipper type disturbances are
notoriously known for yielding highs warmer than guidance south and
west of the track of the surface low.
(Monday through Saturday)
Quieter weather looks to be on tap for early next week with only a
slight chance of showers/storms Monday through Tuesday mainly east
of the Mississippi River. Another active period of weather looks in
store late Tuesday night through Thursday. Best chances of showers
and storms currently look to be on Wednesday and Wednesday night as
another shortwave embedded within northwest flow transverses the
mid-Mississippi Valley. Still some uncertainty of course with
regards to track/timing...but unfortunately this appears to be
another event which may produce some widespread rain amounts of a
couple of inches and exacerbate ongoing river flooding.
Temperatures will start off near seasonal norms Monday and Tuesday
due to deep mixing and westerly surface flow. Leaned above warmest
guidance each day due to these factors. By Wednesday and
Thursday...clouds/precip chances should yield below normal highs and
near normal low temperatures.
NW flow aloft looks to continue heading into the 4th of July weekend
with continued chances of showers/storms along with slightly below
.AVIATION: (For the 00z TAFs through 00z Sunday Evening)
Issued at 619 PM CDT Sat Jun 27 2015
Specifics for KUIN, KCOU: A few rain showers were moving from
north to south outside the 5-10 nmi vicinity of KUIN and KCOU at
TAF issuance, but radar and satellite trends suggest that these
showers should stay east of the terminals. Rain showers are
expected to dissipate after sunset with the loss of daytime
heating. Light fog is possible tonight given the clear skies and
light winds. Initially north to northwest winds will gradually
back overnight and become southwesterly ahead of an approaching
low pressure system. BUFKIT profiles show that 20kt gusts are
possible after 28/16z.
Specifics for KSTL, KCPS: A few rain showers were moving from
north to south towards the St. Louis metro area TAF sites at TAF
issuance, but these showers should quickly dissipate tonight with
the loss of daytime heating. Generally VFR conditions are expected
overnight, although some light fog is possible given the clear
skies and light winds. Winds will gradually back overnight and
become southwesterly tomorrow ahead of an approaching low
pressure system. Additional thunderstorms are expected to develop
tomorrow afternoon and affect the St. Louis metro area terminals
during the afternoon and evening hours.
Specifics for KSUS: The moderate rain shower which passed over
KSUS about an hour ago has added plenty of moisture to the lower
atmosphere. The late-day addition of so much moisture has
increased the odds of radiational fog development overnight given
the expected clear skies and light winds. Otherwise, aviation
concerns at KSUS are the same as for KSTL and KCPS (please see