Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 091123
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
623 AM CDT Sun Mar 9 2014
.SHORT TERM: (Through Late This Afternoon)
Issued at 357 AM CDT Sun Mar 9 2014
A surface high pressure center will settle south of the area today,
causing winds to become southwesterly with time. Wind speeds should
start to increase during the afternoon hours due to the tightening
pressure gradient between the aforementioned ridge axis and a low
pressure system moving along the US/Canada border towards the Great
Lakes. Highs in the 50s look reasonable based on mostly clear skies,
favorable southwest winds during the afternoon, and Bufkit profiles
which depict mixing to 925-900 hPa.
.LONG TERM: (Tonight through Saturday)
Issued at 357 AM CDT Sun Mar 9 2014
All short range models are depicting the central CONUS to come under
the control of a strong westerly/zonal flow during the early part of
the new work week, as upper low cuts off over old Mexico and
meanders east into the Gulf coast region. Fairly potent upper level
trof in the westerly flow regime should then impact the area by
Return flow that develops today will persist and intensify on
Monday, and this should lead to a very mild March day. Going
forecast...which heads towards warmest MOS guidance...still looks
From late Tuesday-Wednesday, forecast concerns become focused on
precipitation potential associated with strong upper level system.
With some dynamics already impacting the area late Tuesday initially
thought about introducing some low PoPs late in the day, but with
forecast soundings indicating very limited low tropospheric moisture
until very late in the day have kept Tuesday`s forecast dry.
However, there should be a big jump in PoPs on Tuesday night as
lower levels moisten and upper dynamics begin to interact with
increasing baroclinicity across the region, and as a result have
gone with likely PoPs over most of the FA.
In advance of this feature, Tuesday should be a very mild day,
especially over the southern half of the FA. I like the look of
the GFS and ECMWF that generates a surface low over e KS on Tuesday
afternoon, with a warm front extending east along the I-70 corridor
which places southern sections of the CWA in the warm sector. Have
tried to depict a fairly large temp gradient to reflect the position
of the warm front, with highs ranging from the upper 50s in our far
north to the lower 70s across the south. These temps in the south
may not be warm enough if the return of the clouds is slower than
That said, all of the 00z guidance looks like it is coming in a bit
colder for Tuesday night...which would suggest a bit more of a snow
threat if low levels can cool fast enough after the extremely mild
afternoon. Have hit the snow wording a bit harder, but at this
early stage still not certain about any accumulation, especially
with the very warm temps of the preceding 3 days.
Wednesday will be a windy and much colder day, with any lingering
precipitation ending or winding down to flurries and/or sprinkles no
later than midday. Have gone with model consensus for temps which
yields highs in the lm40s...which is about a 10 degree climb from
early morning temps.
With dynamics...and most of the cold air...remaining north of the
CWA, the latter half of the week should be relatively dry and mild.
Temperatures should rebound quickly in the wake of Wednesday`s
system, with readings at or above seasonal averages on Friday and
.AVIATION: (For the 12z TAFs through 12z Monday Morning)
Issued at 618 AM CDT Sun Mar 9 2014
Some light fog is possible for the next couple of hours before
T-Td spreads increase and winds start to pick up out of the
southwest. VFR conditions are expected for the majority of the TAF
period after the morning fog mixes out.
Specifics for KSTL, KSUS, KCPS: Light fog will dissipate within
the next few hours due to the arrival of drier air, increasing
winds after sunrise, and increasing temperatures. Lingering
stratus will continue to break up and move away from the metro
area terminals. Winds become southwesterly today around the back
side of a high pressure center and increase to AOA 10 kts.