Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion...updated aviation 
National Weather Service St Louis MO
1142 PM CST Friday Nov 27 2015

issued at 925 PM CST Fri Nov 27 2015

Large area of rain stretching from the arklatex into southern Illinois
continues to drift south. A quick glance at 00z NAM as well as
hi-res hrrr suggest that this southward shift will persist
overnight, with the heaviest rain threat remaining confined to
areas south of i44 in MO and S of i70 in IL, draped along strong
low level baroclinic zone north of slow moving cold front. Flood
Watch for central MO was cancelled earlier this evening, and based
on above trends have also cancelled the Flood Watch over the stl
Metro. Although the heavy rain threat should be confined to the
southern third of the cwa, I have remained fairly generous with
lower pops further north as area is rrq of jet core over the Great
Lakes. Can't totally rule out a threat of frozen precip in our far
northwest counties late tonight, but very much uncertain about how
much...if any...precip will be able to develop in this area of
sub-freezing temps.



Short term: (through saturday)
issued at 333 PM CST Fri Nov 27 2015

A strong wound-up storm system over the Great Basin region of the
western Continental U.S. Is expected to move little during this period,
maintaining an active southwest flow aloft over our region, with
disturbances training along. This will all intersect a pretty moist
airmass in place still over our region and result in high probs for
precipitation, especially for areas near and south of the I-70

First, will keep the flash Flood Advisory going as-is. Despite rain tapering off in
central and now east-central MO, the rain is cycling to an extent
and should try to fill back in further north into central MO this
evening and overnight. Also, flooding effects are typically
delayed from when the rainfall occurs and so the flood threat does
not end right when the rainfall tapers. Will let the evening and
overnight shifts re-evaluate and cancel early as needed once the
effects on the area are better realized.

Second, surface temps will once again approach the freezing mark
across parts of northeast MO and west-central Illinois and with current
and expected vertical temp profiles, would be supportive of a brief
period of light freezing rain or sleet. Fortunately, much of the
threat for measurable pcpn will be south of this area and any
amounts, should they occur, should be very light. Pops here are
below 50%.

Preferred the higher end of MOS temps for mins tonight and lower end
of MOS for maxes Saturday with extensive cloud cover in place.


Long term: (sunday through next friday)
issued at 345 PM CST Fri Nov 27 2015

(sunday - monday)

As the wound-up western Continental U.S. Storm begins to stir eastward, the
pattern over US remains status quo, with an active southwest flow
aloft and additional disturbances tracking thru, overrunning
moisture well to the north of the old surface boundary.

This should result in another widespread rain event, but quantitative precipitation forecast will be
light, with around a tenth of an inch forecast and should have
minimal to no impact on flooding concerns.

Good agrement then continues on what to do with the storm system
center, bringing it out into the plains by Monday and track it to our
north Monday night. During this process, a strong disturbance will
rotate around the southern periphery and impact our area Monday. Quantitative precipitation forecast
looks low, with a tenth of an inch or less forecast for this event,
but probs remain on the high side, with likely pops forecast.

Temps will be at or a tad below average for daytime maxes, but remain
above average for nighttime mins--all because of the extensive cloud
cover that continues to be forecast.

(Tuesday - next friday)

Good model agreement begins to go away by late Wednesday, with a
pair of dry days expected Tuesday and Wednesday.

GFS is showing a stronger storm system trying to take shape on
Thursday than the ec, but this system at first glance looks to be
moisture starved and have kept pops on the dry side for now.
Consensus then re-achieved for Friday with building heights and
ridging overhead.

With cold air forecast to continue to be locked up well north, temps
will begin this period around average but trend warmer by the end of
the week with the building heights aloft and southerly flow at the



Aviation: (for the 06z tafs through 06z Saturday night)
issued at 1132 PM CST Fri Nov 27 2015

IFR flight conditions will continue to prevail across the area
into Saturday morning. Latest guidance is more pessimistic about
the ceilings rising on Saturday, and it may take until late
morning across northeast MO and west central Illinois to go MVFR. IFR
may stick around for most of the day further south, with little
chance for improving to MVFR in southeast MO and southern Illinois.
Lingering light rain and drizzle will continue to keep lowered
visibility across much of the area along and south of the I-70
corridor through at least mid morning...longer further south.
Ceilings will likely improve later in the afternoon and into the
evening, but the improvement may be short lived as stratus tends
to lower during the nighttime hours.

Specifics for kstl:

IFR ceilings will continue to prevail at Lambert at least through
Saturday morning. Lingering light rain/drizzle will also continue
to lower the visibility to 3-5sm...probably at least until 12-15z.
Latest guidance is more pessimistic about the ceilings rising on
Saturday...and there looks to be little if any probability that
ceilings will rise above 1000 feet before 20z, and ceilings
probably won't rise above 2000 feet through the night into Sunday
morning. In fact, clouds may drop back below 1000 feet overnight
Saturday night as stratus tends to lower during the nighttime



Lsx watches/warnings/advisories:
MO...Flood Watch through Saturday morning for Crawford MO-Iron MO-
Madison MO-Reynolds MO-St. Francois MO-Ste. Genevieve MO-
Washington MO.

Illinois...Flood Watch through Saturday morning for Randolph Illinois.



Weather forecast office lsx

National Weather Service Glossary of Abbreviations