Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 261050
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
450 AM CST Mon Jan 26 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 318 AM CST Mon Jan 26 2015

Radar and satellite data at 08z indicate another clipper system over
northern MN and producing a swath of pcpn out ahead of it on its
eastern flank but also with good pcpn coverage on its southern
periphery as well.  Mostly cloudy skies extend from this clipper
well to the southeast where they run up against the system that just
moved thru our region on Sunday.  Some breaks in the clouds were
over the STL metro area.  Temps for most areas are in the 25-30F
range.

Model data is in good agreement on phasing of strong WAA,
frontogenesis and broadscale lift from shortwave TROF pushing thru
IA and into west-central IL this morning and working its way thru
southern IL this afternoon with its backedge near the MS river.
This should be enough for isolated to widely scattered showers and
have added 20-30 percent PoPs to the forecast.  The atmosphere also
looks to support varied pcpn-types, with snow initially supported
thru midday and then the western edge of the pcpn near the MS river
transitioning to rain during the afternoon with snow likely
maintaining some presence thru the day in the far eastern CWA around
Vandalia and Salem, IL.

Most QPF amounts will struggle to measure by the very definition of
the low PoPs in the forecast, but some isolated areas in IL may be
able to accumulate a light dusting of snow.

Otherwise, temps will vary widely across the forecast area today
with readings remaining in the 30s for the Salem/Vandalia, IL areas,
but rising into the low 50s for central MO.

TES

.LONG TERM:  (Tonight through Sunday)
Issued at 318 AM CST Mon Jan 26 2015

(Tonight through Wednesday)

Mdls are in relatively good agreement thru the period. Surface fnt
associated with the approaching clipper shud be E of the CWA by 00z
this evening. Precip shud have exited the region by this eve as
well. Clouds are expected to linger thru the night as the low pulls
sewd out of the region. Expect clouds to be slow to clear out on
Tues as well. Have trended cooler thru Tues due to the clouds.
Thermal ridge extends over the region by mid-day Wed. Have raised
temps on Wed and kept temps aoa the warmer guidance. Some
uncertainty exists regarding temps thru this period as mdl solns
begin to diverge with respect to temps and sfc low placement.

(Thursday through Sunday)

Mdl solns continue to diverge thru the period. Mdls differ in timing
of the system to impact the area thru the weekend. Have kept slight
chance PoPs to account for this system. Will keep PoPs low until
solns come into better agreement.

Mdls do agree with temps being much cooler late this week behind the
system on Wed, then cooler still with the reinforcing trof late this
week. Attm, mdls agree that temps will be cold enuf so that any
precip that does occur late this week and into this weekend shud be
SN. Will continue to monitor as the system approaches.

Tilly

&&

.AVIATION:  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 450 AM CST Mon Jan 26 2015

A region of MVFR CIGs will prevail for all TAF sites for early in
the TAF period, but a steady push to the east should end it during
the late morning and early afternoon hours, albeit temporarily for
most sites. At about this time, an upper level disturbance will
race down from the northwest and push isolated to scattered rain
and snow showers for areas generally near and east of the MS
river. For now will list VCSH for these TAF sites and amend to
TEMPOs as needed. By 21z, the pcpn threat is expected to have
ended for all TAF sites with what should also be a break in the
MVFR CIGs. Surface winds during this time will back from the S-SW
but with a TROF passing thru in the afternoon and early evening,
will then veer the winds back from the NW. With the renewed NW
winds, MVFR CIGs are then expected to expand back into TAF sites
near the MS river and to the east.

Specifics for KSTL: MVFR CIGs will expand back into the airport
shortly after the valid time, with isolated showers expected
during the midday and early afternoon hours. Pcpn-types are
expected to be liquid by this time. Have handled as a VCSH for now
and will upgrade to TEMPO as needed. W-NW surface winds will back
from the S-SW today and should get the MVFR CIGs out of the area
temporarily but with a TROF then sliding thru and veering winds
from the NW this evening, the MVFR CIGs are expected to make a
return.

TES

&&

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

$$

WFO LSX



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