Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 271655
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1055 AM CST Fri Feb 27 2015
.SHORT TERM: (Through Late This Afternoon)
Issued at 311 AM CST Fri Feb 27 2015
Primary concern for the short-range today is wind chill values up
across northeast Missouri and west central Illinois. Quincy has
been reporting wind chill readings at or below -15 for the past
couple of hours. Temperatures will continue to drop a few degrees
as well, so even with the wind falling off to around 5 mph we should
continue to see wind chill readings between -15 and -20 through
13-14Z. Have therefore gone ahead and fired off a quick advisory
for this morning.
After the extremely cold start to the day, we`ll have trouble
rebounding much higher than the mid teens to low 20s. Forecast
soundings show decent low level lapserates, reaching near saturation
around 2000 FT. This would indicate scattered to perhaps broken
cumulus. Wouldn`t be surprised to see a few flurries, though
various hi-res models show no indications of precip, so did not
mention in the forecast for today.
.LONG TERM: (Tonight through Thursday)
Issued at 358 AM CST Fri Feb 27 2015
One more really cold night on tap as Arctic hi pressure is slow to
move away. Light winds should prevent any wind chill criteria from
being met, however.
Round one of a prolonged pcpn event begins late Saturday. Some
question still on where main pcpn axis will setup, but the consensus
seems to be growing on somewhere close to I-70. Stratification of
vertical temp profiles also suggests that pcpn should remain all
snow for much of northern MO and central IL, with snow transitioning
to a wintry mix or rain for areas near I-70 and south as some
warming attempts to occur. The mid-level flow will remain W-E
during this phase and so warm air will struggle to push north but
temps are not expected to be too far below freezing at the onset of
the event. This has not really changed much from previous fcsts.
Preliminary totals show snow amounts could reach 4-7" for much of
our CWA north of I-70 with minimal accums in SE MO and far S IL
where what is frozen will be sleet. Some icing also looks likely,
but prelim ice accums do not look to be too much, with less than a
tenth of an inch for areas generally south of I-70.
After a brief break on Sunday night and much of Monday, phase two
begins with a more backed mid-level flow which will enable a much
greater surge of warm air--first aloft on Monday night in advance of
a warm front--and then at the surface as the warm front passes to
the north. The air will be warm enough thru the column for the
dominant form of pcpn to be liquid during this phase, and where
enough cold air hangs on for Monday night, it will fall as FZRA.
Could see more significant icing this period, especially for areas
north of I-70, but still a bit far out and plenty of time to watch.
Enough warm air and moisture to pump north for SHRA/TSRA on Tuesday
with a Spring-like day. Everything comes crashing back to reality
(winter) by Tuesday night and Wednesday with cold air returning and
pcpn briefly changing back to snow before ending. Model diffs exist
on end time and timing of the front but the end result is
essentially the same.
A quiet latter part of the week then on tap with NW upper flow and
hi pres building in.
.AVIATION: (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1050 AM CST Fri Feb 27 2015
VFR forecast for the most part. MVFR ceilings may make their way
into the area depending on the speed of the next system. Looks
like a pretty good warm air advection snow for Saturday night
Specifics for KSTL: VFR through 18z Saturday, then will bring in
some MVFR ceilings late in the period as the weekend system moves
closer. Timing right now is a question, so will mainly introduce
as an "alert"feature.