Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211157
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
657 AM CDT Thu May 21 2015

.SHORT TERM:  (Through This Afternoon)
Issued at 340 AM CDT Thu May 21 2015

Widespread low cloudiness in the wake of yesterday`s system
continues to blanket much of the region early today.  Although some
holes have developed in the cloud deck over western IL and central
MO, the true back edge of the cloud deck is currently hugging the
MO-IA border and dropping southeast at ~15 kts.

With the surface ridge working southeast and re-exerting its
influence over the area today, see no reason that the above clearing
trend won`t work across the entire FA during the morning.  Should be
quite a bit of sunshine this afternooon, but also anticipate some
CU/SC to reform in the wake of the clearing due to diurnal heating
of the saturated ground.

Temperatures will remain below average today as the chilly Canadian
airmass continues to exert it`s influence...with highs in the 60s.

Truett

.LONG TERM:  (Tonight through Wednesday)
Issued at 340 AM CDT Thu May 21 2015

Not many changes to the prev forecast thru day 3. Large sfc ridge
remains in control of the wx pattern thru Fri. Mdls prog the sfc
ridge moving ewd out of the region on Fri with upper level ridging
occurring over the area. Differences among guidance begin early with
the ECMWF focusing the LLJ much further E than the other guidance.
All other mdls suggest the LLJ will remain focused on the wrn
fringes of the upper ridge. This soln seems more plausible, outside
from any MCS activity. While the ECMWF soln is possible, have
continued drier trend twd other solns. Regardless, mdls come into
better agreement Sat night as the upper ridge moves slightly E and
the LLJ becomes more focused over the region. This trend continues
thru at least Mon, perhaps longer if mdl trends continue. Confidence
quickly drops for Tues and beyond with differences among guidance
and due to the general flow across the region. Have kept chance PoPs
continuing thru the period.

As for temps, have continued cool temps thru Sat due to the sfc
ridge in place and then, precip/cloud cover expected on Sat. That
said, am somewhat concerned that mdls, esp the GFS, are overdoing
cloud cover. Will monitor trends, but going forecast may be too cool
this weekend if clouds do not materialize. Have temps moderating
thru the remainder of the forecast due to mdls suggesting heights
gradually rising. However, temps will be modified somewhat on any
given day due to cloud cover and precip.

Tilly

&&

.AVIATION:  (For the 12z TAFs through 12z Friday Morning)
Issued at 643 AM CDT Thu May 21 2015

Rather chaotic cloud pattern over the region early today, with
clearing working its way south on the IL side of the Mississippi
River, while a 90mi wide band of cigs around 3kft are lingering
on the Missouri side...roughly centered from KMBY to KFAM.
Advection trends over the last few hours suggest that band of
clouds west of the Mississippi River will be dropping south of the
Missouri River by mid morning, but by that time expect some
diurnally driven CU/SC to begin to develop. Have mentioned
occasional VFR cigs around 4kft in the STL area until midday with
these redeveloping clouds as models are suggesting slightly better
moisture in this part of the FA, but feel that these clouds should
tend to dissipate heading into the afternoon as the drier air
scours out the available moisture. VFR conditions are then
forecast overnight as surface high gradually builds into the mid-
Mississippi and lower Ohio River Valleys.

Specifics for KSTL: Clearing wedge dropping south through western
IL shot through KSTL around 11z. However, cigs around 3kft are
lurking just west of the Mississippi River, and with a slight westerly
component to some of the lower level streamlines believe some of
these clouds may tend to work back into the KSTL TAF area over the
next few hours. In addition to the advection of these clouds back
into the area, we should also see diurnally driven scattered to
occasionally broken clouds with bases around 4kft begin to
develop by mid morning. Any clouds that do make it into the area
later this morning should tend to dissipate during the afternoon,
leaving clear skies for the overnight hours.

Truett

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     65  50  76  57 /   5   0   0  10
Quincy          66  47  74  53 /   5   0   0  10
Columbia        65  47  72  51 /   5   0  10  10
Jefferson City  65  46  73  51 /   5   0  10  10
Salem           63  46  74  54 /   5   0   0   5
Farmington      62  42  72  49 /   5   0   5  10

&&

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

$$

WFO LSX





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