Scientific Forecaster Discussion
Area forecast discussion...updated aviation
National Weather Service St Louis MO
657 am CDT Sat Mar 15 2014
Short term: (through late this afternoon)
issued at 328 am CDT Sat Mar 15 2014
Expecting wind to swing back around to the south-southeast today as
low pressure develops over the central and southern Great Plains.
Short range guidance shows deep mixing up to at least 900mb and in
some cases 850mb or a bit higher. 850mb temps range from around +4
to +8 c across the area this afternoon which should be good enough
for low to mid 60s in west central and south central Illinois,
increasing to mid and upper 60s and perhaps topping 70 in central,
east central and southeast Missouri. Should see plenty of sunshine
through most of the day to help these temperatures climb; but there
will be increasing high clouds by late afternoon as upper level
moisture overspreads the Mississippi Valley ahead of tonight's storm
Long term: (tonight through friday)
issued at 328 am CDT Sat Mar 15 2014
(tonight - Sunday night)
Becoming increasingly likely that a late winter storm will affect portions of
the region beginning late tonight. Will certainly be one heck of a 24-hr change
as we go from highs in the 60s today to accumulating frozen precipitation...
temperatures in the 20s/30s...and a very strong/gusty northeast wind
producing wind chills in the teens.
Numerical model guidance has shifted a bit southward will placement of heavier
precipitation axis along with a quicker drop in surface temperatures. Boundary
layer is progged to cool off quicker than warm nose aloft near 850 hpa so
introduced a brief period of freezing rain after temperatures dip below freezing
and then a sleet/snow mix as cold layer deepens/intensifies. Precipitation
should turn over to all snow before ending. Still a lot of uncertainty
on precipitation amounts...especially on northern edge of gradient on Sunday.
Very cold/dry air advection will be persistent and will likely yield a very
sharp cutoff to northern edge of precipitation shield Sunday near/just north
of Interstate 70. Followed GFS for precipitation type/amounts after analyzing
BUFKIT soundings and this model was a good compromise between further north
and wetter NAM and further south and drier European model (ecmwf). Heaviest snow/sleet totals
will likely be in a region along or just to the south of the Interstate 44
corridor in Missouri where thermal profile will be cold enough to support
snow and far enough south to avoid being overwhelmed by the strong dry air
advection/closer to stronger upper-air forcing for ascent. In this
aforementioned area across the Eastern Ozarks...2-3 inches of total snow/sleet
is likely with a light glazing of ice expected before the changeover to snow
and sleet. Further to the north along the Interstate 70 corridor including the
northern half of the St. Louis metropolitan area...1-2 inches of snow/sleet is
likely also with a light glazing of ice expected. Over far southern sections
of the area...thermal profile will be a bit warmer longer and will therefore
cut down on totals a bit but still around one inch of snow/sleet is expected
with 0.05-0.10" of freezing rain accretion possible.
Even though the antecedant conditions will cause warm ground temperatures...
feel that combination of sharply falling temperatures into the 20s and expected
intensity of precipitation (especially for southern third of area) will fairly
easily overcome the warm ground. In addition...a period of sleet or at least
a sleet/snow mixture is forecast...which will also help cool the ground
Will hold off on any headlines attm after coordinating with neighbors.
Certainly appears likely that an advisory will be needed for a portion of the
area...just a matter of where and how much of each precipitation type will fall
from the sky. Did not go with a watch as it did not appear that warning
criteria (6" of snow...0.5" of sleet...0.25" freezing rain) would not be met...
though if sleet does fall a bit longer it is possible that a half of an inch
of sleet could fall in some isolated areas.
System will head out of the region by early Sunday evening with decreasing
cloudiness and lightening winds expected. This will allow temperatures to drop
quickly into the teens for most areas...especially in any regions which do end
up with at least some snow cover.
(Monday - friday)
Fairly quiet weather is expected over the mid-Mississippi Valley region for the
next work week. A surface low will pass just to the northwest of the area late
Tuesday but with little moisture to work with so just have low end chances of
rain. Otherwise...dry weather is expected with seasonable temperatures...highs
in the 50s and 60s and lows in the 30s for the most part.
Aviation: (for the 12z tafs through 12z Sunday morning)
issued at 634 am CDT Sat Mar 15 2014
VFR flight conditions and light south-southeast flow is expected
today. Mid and high level clouds will be increasing late this
afternoon into the evening as a storm system builds strength over
the plains. Wind will shift to the east-northeast during the
evening and ceilings will fall into MVFR range from south to north
through late evening. Rain will overspread areas along and south
of I-70 from the late evening into the pre-dawn hours of Sunday.
The wind will continue to back to the northeast and increase which
will bring much colder air to the region. Expect that flight
conditions will fall as well, though am not very confident how
fast or how low conditions will get before 12z Sunday.
Specifics for kstl:
Expect VFR flight conditions and light southeast flow to prevail
at Lambert today. Should see mid-high level clouds increase this
evening and the wind will shift to the the east-northeast. Think
precip will begin at Lambert around 05-07z, and flight conditions
will likely fall to MVFR sometime before 12z. Have low confidence
in the timing and height of the lower ceilings, as well as the
eventual switch over from rain to freezing rain, then sleet and
snow Sunday morning. To add insult to injury, the wind will
continue to strengthen from the northeast, causing strong a strong
crosswind on the main runways.
Preliminary point temperatures/pops:
Saint Louis 66 30 31 19 / 10 90 80 20
Quincy 61 27 33 17 / 5 30 30 5
Columbia 68 29 31 18 / 10 90 80 5
Jefferson City 69 31 33 18 / 10 100 90 10
Salem 62 31 32 21 / 10 60 80 30
Farmington 66 35 37 19 / 10 100 100 30
Weather forecast office lsx