Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Norman OK
646 am CDT Sat Apr 18 2015
aviation discussion for the 12z tafs is below.
have low confidence of VFR to LIFR conditions in western Oklahoma
through 21z as well as low confidence with thunderstorms and rain timing/coverage
Conditions will bounce between VFR and LIFR with br/fog across
western Oklahoma through 21z. The worst conditions may be near
kcsm and khbr through 15z. IFR conditions may affect ksps and klaw
as well through 15z...but did not mention thinking these lower
conditions will stay west of these sites.
Have high confidence all sites will be VFR by 21z.
Isolated-num thunderstorms and rain will form and affect many taf sites after 19z. Used
thunderstorms in the vicinity/tempos at most sites except kcsm and khbr where confidence of
storms is too low to mention. Brief variable gusty winds...
hail...and MVFR or lower conditions are possible with the
strongest storms. Most storms will be east of all taf sites by
Additional MVFR/IFR conditions may develop after 06z but did not
mention due to low confidence of occurrence.
Previous discussion... /issued 419 am CDT Sat Apr 18 2015/
severe thunderstorm potential this afternoon and evening is the
Rain chances this morning look to be mainly confined to locations
east of I-35 where most latest radar echoes were occurring from a
weak impulse rotating around a middle/upper low in southern
Colorado. No severe storms are expected with this activity...just
some localized heavy rain. Most of this activity may end by 8 am
if the latest hrrr runs are correct. Most locations will remain
dry this morning.
Added patchy fog mention through 11 am this morning across parts
of western Oklahoma and western North Texas where some partial
clearing...abundant low level moisture...and latest hrrr runs
favor some development. Doubt it will get too widespread or dense.
This afternoon and evening...isolated to numerous showers and
thunderstorms will develop across the area. Capping will be rather
weak. With more sun compared to yesterday...think convective
temperatures will be reached rather easily in the 2 to 5 PM time
frame. First development may be focused in western Oklahoma and
western North Texas near a developing dryline. Went near guidance
rain chances. Exactly where and when storms occur remains tricky
today and tonight.
In regards to severe potential this afternoon and evening...
believe there will be some severe storms with large hail as the
main concern. The air will be moderately unstable with MLCAPE
1500-2500 j/kg. Strong 0-6 km shear 30-50 knots supports supercells
and multicells. Strong 0-3 km shear values 25-45 knots and very cold
middle levels with 500 mb temperatures around -18c could support very
large hail in some cells as long as convection is not too
widespread. Some damaging winds may occur as well if storms can
organize into clusters and lines. Tornado potential appears to be
limited due to weak low level shear...though noticed the latest
rap13 indicated stronger low level winds possibly developing in
southwestern Oklahoma in the 5 to 9 PM time frame which may
increase this potential. Will closely monitor.
Locally heavy rainfall may again occur late this afternoon and
tonight...though storm motions will be faster which may limit the
duration of heavy rainfall in one given location.
Most storms will move into eastern Oklahoma after midnight
tonight...allowing for moist and cool conditions. Would not be
surprised if some fog formed...but did not mention due to low
On Sunday...a few showers and storms may linger mainly over
northern Oklahoma...though appears the severe potential will shift
in far eastern Oklahoma and points east. With lingering weak
instability and cold middle/upper levels...a few storms with small
hail could occur. Breezy conditions will develop. There is an
outside chance winds could approach advisory criteria with gusts
over 40 miles per hour in northwest Oklahoma. Went with the warmer side of
guidance temperatures thinking some sun will occur...especially
early in the day.
Sunday night through Friday...a wet pattern may continue with
rain chances remaining in the forecast most days. There are some
model discrepancies with weather features...thus forecast
confidence remains low. Some strong to severe storms may occur
Tuesday through Friday with nearby moisture and instability.