Severe Thunderstorm Warning 45, NWS Norman, OK

Area Forecast Discussion
National Weather Service Norman OK
1254 PM CDT Fri Mar 27 2020

...New AVIATION...

.PREV UPDATE...
Issued at 1115 AM CDT Fri Mar 27 2020

Added a slight chance of precipitation for western Oklahoma
through midday, and increased to an even broader area through the
afternoon. Midlevel saturation appears to be significant within
RAP forecast soundings with steepening midlevel lapse rates as
deep western trough approaches. You can see a rather dramatic and
textured look to midlevel convective development in a visible
satellite loop late this morning. Convective showers have already
formed and appear to be rooted around 600-mb within this moist
layer. This will yield a few hundred J/kg of CAPE and so some
lightning is likely too. Storm intensity will be restrained by
overall meager CAPE from parcels lifted from that layer. Given the
steepening lapse rates and potential for deep mixing seen in the
soundings, we'll have to watch for the potential of strong wind
gusts with any echos on radar, especially later this afternoon.
In fact, a substantial amount of the echos may be mostly virga
given the deep sub-cloud dry layer and this was the reason for
keeping the probabilities for measurable precipitation low
relative to what it may appear coverage wise on radar.

Further west across the western panhandles, a more consolidated
band of precipitation/virga is present at the leading edge of
stronger DCVA associated with the approaching trough. This will
probably be the impetus for this evenings convection that will
eventually move into a more deeply moist environment this evening,
yielding better chances of measurable rainfall. We'll continue to
watch trends with this potential and refine precipitation
probabilities/timing later today.

Otherwise, made only minor adjustments to other fields, including
tightening up temperature gradients based on current observational
trends.

BRB

&&

.SHORT TERM...
(Today and tonight)
Issued at 222 AM CDT Fri Mar 27 2020

A meandering front over northern Oklahoma will become a warm front
this afternoon, and move north into Kansas, as surface low
pressure strengthens over southeast Colorado. Southwesterly low-
level flow around this surface low will bring somewhat drier air
into most of central/western Oklahoma and western north Texas. In
the southeast, very humid conditions (especially for late March)
will persist.

A warm layer aloft should stifle most convection today, although
most models show some precipitation over central/eastern Oklahoma
this afternoon. Elevated convection, mainly in the form of
showers, are possible, but surface-based convection is very
unlikely.

As the upper-level system and its surface counterpart shift east
overnight, the extra forcing will further increase the chances for
showers and a few isolated thunderstorms. With the amount of
forcing, shear, and (relatively weak) instability, marginally
severe hail will be possible in advance of the cold front that
will travel eastward across the region tonight.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 156 AM CDT Fri Mar 27 2020

By daybreak Saturday an upper level trough from the southwest will
be lifting into eastern OK and a front from a Great Basin air
mass will bring drying west winds across the state. The deepening
surface low moving off to the northeast and vertical mixing from
the west will lead to a windy day Saturday. The record and near-
record heat of the last several days will abate with this air
mass. During Monday south winds will bring gulf moisture into
Oklahoma as another upper trough passes over Oklahoma in fast
southwesterly flow. This will bring showers/thunderstorms Monday
and early Tuesday before exiting to the east. The upper pattern
changes mid-week where Oklahoma is more in the influence of
northwesterly flow with a front and air mass driving south from
the northern plains. This will maintain temperatures close to
normals and dry weather late into the week.

&&

.AVIATION...
(18Z TAFS)
Issued at 1254 PM CDT Fri Mar 27 2020

Midlevel convection could impact some TAF sites this afternoon,
but the probability is fairly low. PNC, OKC, and OUN would be the
most likely sites affected. The stronger convective cores have
contained small hail but the spatial coverage of this is minimal
so impact to either terminal is low probability. We have not
mentioned TS at this point but will monitor and amend as needed.
Same for this evening with a more consolidated band of showers
with isolated embedded storms. We have covered this with a 4 hour
tempo for now but may need to adjust timing and add thunder for
some sites. Otherwise, a few sites have experienced MVFR stratus
but this should trend toward ceilings above 10,000 feet through
the rest of the TAF period. Southwesterly winds will increase
later tonight through tomorrow morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  85  56  69  43 /  20  40   0   0
Hobart OK         84  51  69  41 /  20  40   0   0
Wichita Falls TX  85  57  72  44 /  20  20   0   0
Gage OK           84  45  64  36 /  30  40   0   0
Ponca City OK     82  55  67  42 /  40  40   0   0
Durant OK         80  62  72  46 /  30  20  10   0

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&

SHORT TERM...23
LONG TERM....09
AVIATION...12

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