Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 222007
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
307 PM CDT Fri Aug 22 2014
.SHORT TERM: (Through Late Tonight)
Issued at 303 PM CDT Fri Aug 22 2014
Similar to the past few days, isolated thunderstorms are expected
across the southern CWA due to terrain influences in the eastern
Ozarks. These storms will dissipate with the loss of daytime
Isolated to scattered thunderstorms are also possible across
northeast MO/west central IL tonight in the vicinity of a warm
front or outflow boundary. Favorable parameters overnight include
PW values near 2", H7-H5 lapse rates of 6 to 6.5 deg C/km,
sufficient MUCAPE for elevated thunderstorms, and a strengthening
LLJ. At this time, it looks like the best coverage should remain
to the north of the CWA.
.LONG TERM: (Saturday through Next Friday)
Issued at 303 PM CDT Fri Aug 22 2014
Dangerous levels of heat and humidity will remain across the
region through the weekend and into early next week. These
conditions are due to an upper level ridge of high pressure across
the central CONUS along with favorable surface winds that will
maintain high dew points. The Heat Advisory has been spatially
extended to cover additional counties in the eastern Ozarks where
dew points are no longer expected to mix out each afternoon. The
lack of substantial mixing will likely result in at least 4
consecutive days where heat index values exceed 100 degrees F.
This is supported by the Missouri Mesonet site in Crawford County
near Cook Station, which was already reporting heat index values
between 100-104 degrees F this afternoon. The Heat Advisory and
the Excessive Heat Warning have also been temporally extended
through Monday evening now that models have reached improved
agreement on the large scale upper air pattern through Tuesday.
Some portions of the Heat Advisory, especially across northern MO
and west central IL, might be canceled early if convective debris
cloudiness interferes with heating.
A cold front is forecast to end the stretch of hot/humid weather
during the middle of the upcoming week. The best opportunity for
widespread precipitation appears to be on Wed/Wed night with the
cold front and passage of the upper trough, but the details are
still uncertain this far in advance.
.AVIATION: (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1223 PM CDT Fri Aug 22 2014
Main forecast issue is the probability for any showers and thunderstorms
and the need for inclusion in any of the TAFS. An old thunderstorm
boundary has sunk to around I-70 and this has caused some havoc in
the wind direction although they are light. Indications the
boundary will retreat northward and could result in scattered
showers and thunderstorms this afternoon across northern Missouri
into central IL which might impact KUIN. Confidence is below
average and thus have just mentioned a VCTS for this afternoon. A
higher probability of showers and thunderstorms will exist at KUIN
during the overnight hours. Elsewhere can`t rule out isolated
shower or thunderstorms with afternoon heating but the coverage and
probability are too low to mention. Largely outside of any thunderstorms,
VFR conditions will dominate with surface winds at or below 8 kts
through the period.
Specifics for KSTL:
VFR conditions are expected to dominate much of the forecast period
with surface winds at or below 8 kts. Will have to keep an eye out
for any isolated showers or thunderstorms this afternoon, and then
overnight tonight will need to monitor any showers and thunderstorms
across northern MO sagging southeastward. Confidence and probabilities
at this time are too low to mention in the TAF.
MO...HEAT ADVISORY until 7 PM CDT Monday FOR Audrain MO-Boone MO-
Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
MO-Ralls MO-Reynolds MO-Shelby MO-St. Charles MO-St.
Francois MO-Ste. Genevieve MO-Warren MO-Washington MO.
EXCESSIVE HEAT WARNING until 7 PM CDT Monday FOR St. Louis City
MO-St. Louis MO.
IL...HEAT ADVISORY until 7 PM CDT Monday FOR Adams IL-Bond IL-Brown
IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
Macoupin IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-
Randolph IL-Washington IL.
EXCESSIVE HEAT WARNING until 7 PM CDT Monday FOR Madison IL-St.