Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 171103
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
603 AM CDT Fri Apr 17 2015
.SHORT TERM: (Through Late This Afternoon)
Issued at 327 AM CDT Fri Apr 17 2015
Deep cutoff low over the Four Corners has amplified the upper level
ridge over the mid-Mississippi Valley. This ridge should hold fast
today as the low moves slowly east into Colorado. The ridge should
provide enough subsidence to keep the area dry today, and with 850mb
temperatures in the 12-14C range the MOS highs in the upper 70s to
low 80s range look good. The low will continue drifting northeast
tonight and should be in eastern Colorado by 12Z Saturday morning.
Have slowed PoPs down marginally with only a slight chance edging
into central Missouri this evening, and then low chance overnight.
With increasing clouds and southerly flow, should see overnight lows
only dip into the upper 50s to low 60s.
.LONG TERM: (Tonight through Thursday)
Issued at 417 AM CDT Fri Apr 17 2015
Should see a general increase in shower and thunderstorm activity
through Saturday afternoon into Saturday evening as the ridge pushes
east into the Ohio Valley and the low opens up and begins moving
more rapidly east-northeast. There is some discrepancy between the
NAM and ECMWF which keep much of the CWFA dry on Saturday vs. the
GFS which spreads a fairly large swath of light QPF across the
entire CWFA. In the end, certainly cannot rule out thunderstorms
over the area, but think the best chances will be over central and
northeast Missouri which will be deeper into the broad ascent ahead
of the low. Saturday looks a bit cooler due to increasing clouds
and rain; but temperatures should still hit the mid to upper 70s,
especially further east where rain is less likely.
Sunday`s weather looks complex as the low finally opens up fully and
the resulting highly amplified wave moves into Missouri. The
surface reflection of the wave with what looks like a fairly
complicated set of low pressure centers moves through
Sunday afternoon/evening with another round of showers and
thunderstorms. DY3 SPC outlooks is still 15%.. GFS forecast is
perhaps a little weaker with the instability than yesterday`s
runs...showing 500-1200 J/kg MLCAPE but still showing 30-40kts of
0-6km shear Sunday afternoon. NAM is showing similar parameters,
with a little more instability especially across southeast Missouri.
Am feeling a little more confident in the possibility of severe
weather given the decent continuity between models and the
run-to-run consistency noted over the past couple of days Will
therefore go ahead and start mentioning the possibility of severe
thunderstorms on Sunday in the hazardous weather outlook.
Still looks like a cool and dry start to next week as another deep
cutoff low moves across the Upper Midwest/south central Canada
allowing cool Canadian air to drop through the northern Plains into
the Midwest. Guidance is still advertising temperatures around 5-10
degrees below normal at least through Tuesday. Some warmer
temperatures and higher moisture filters in Wednesday into Thursday
as low level flow turns back to the south-southwest. Still looks
like a chance for more thunderstorms...most likely Wednesday night
into Thursday as warm advection and lift from a passing shortwave
combine over the area. GFS is much more aggressive than the ECMWF
with this precip, starting it as early as Tuesday evening. ECMWF
holds off until Wednesday afternoon. Have held PoPs to slight
chance/low chance category because of the discrepancies.
.AVIATION: (For the 12z TAFs through 12z Saturday Morning)
Issued at 513 AM CDT Fri Apr 17 2015
Fog in the St Louis metro area will dissipate later this morning.
Scattered diurnal cumulus clouds will develop late this morning
and this afternoon. High level cloudiness can also be expected
through the period. Showers/storms may move into COU late tonight
well ahead of the slow moving upper level low and associated
surface low moving into the Plains. Light surface winds will
become sely later this morning and this afternoon, albeit still
quite weak with surface ridging over the OH and TN Valley regions.
Specifics for KSTL: At least light fog early this morning should
dissipate by 15Z. High level clouds this forecast period as well as
scattered diurnal cumulus clouds late this morning and afternoon.
Low-mid level, VFR clouds will move into the area Saturday morning.
Light or calm surface wind will become sely later this morning and
this afternoon. The sely surface wind will become light again this
evening, then pick up again in strength Saturday morning.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 82 60 77 60 / 10 10 40 80
Quincy 79 58 74 58 / 10 10 40 80
Columbia 80 60 74 59 / 10 30 70 80
Jefferson City 79 60 73 59 / 10 30 70 70
Salem 79 57 75 60 / 10 10 30 80
Farmington 78 59 73 60 / 10 10 50 80