SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 AM CDT Wed Jun 26 2024
Valid 261300Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
VALLEY INTO NORTHERN MID ATLANTIC...ACROSS PARTS OF THE OZARK
PLATEAU INTO LOWER MISSISSIPPI VALLEY...AND TO THE LEE OF THE FRONT
RANGE AND SANGRE DE CRISTO MOUNTAINS...
...SUMMARY...
Clusters of thunderstorms accompanied by potentially damaging wind
gusts are possible today into tonight from the Ohio Valley into
northern Mid Atlantic, across parts of the Ozark Plateau into lower
Mississippi Valley, and to the lee of the Front Range and Sangre de
Cristo Mountains.
...Synopsis...
A strong mid/upper-level high over NM is expected to weaken somewhat
and get shunted southward by a series of low-amplitude shortwave
troughs/vorticity maxima crossing the Four Corners region and
central Rockies. This will occur as a strong synoptic trough --
apparent in moisture-channel imagery over the northeastern Pacific
between 130W-135W -- approaches the Northwest Coast. The trough
should move ashore WA/BC around 06Z, accompanied by a broad, closed
cyclone centered over or near Vancouver Island. By 12Z, the 500-mb
low should reach south-central BC, with trough southward to northern
CA. In response to these developments, the downstream synoptic ridge
over the northern/central Rockies also will weaken and shift
eastward over the adjacent High Plains.
Farther downstream, northwest flow aloft will prevail over most of
the Plains States and Mississippi Valley. A shortwave trough and
MCV -- related to an ongoing convective complex moving into the
northern Ozarks region -- should pivot southeastward to the southern
Appalachians and Tennessee Valley regions by 12Z tomorrow. A
northern-stream shortwave trough -- initially located over MN --
will cross the Upper Great Lakes today, reaching southern/eastern ON
and Lake Erie by 00Z. This feature may be preceded by an MCV now
evident near the Wabash River Valley and moving northeastward. By
12Z, the combined perturbation should reach ME and coastal southern
New England.
The surface chart at 11Z showed a cold front from southern QC across
Lake Huron, central Lower MI, southern WI, southern IA, northwestern
MO, southwestern KS and southeastern CO. This front is (and will
remain) preceded across much of its length west of the Mississippi
River by convective outflows. By 00Z, the front should reach
northern NY, western PA, parts of OH and western KY, northern AR and
central OK, becoming a quasistationary to warm front from there over
the northern TX Panhandle into southern CO. By 12Z, the front
should extend from coastal MA across NJ, VA, TN, AR, OK, to central
CO.
...Ozarks/Mid-South to lower Mississippi Valley...
An extensive area of convection is apparent over the northern/
western Ozarks region into northeastern OK, with ragged reflectivity
and satellite presentation, but strong surface pressure/theta-e
deficits, and lingering areas of enhanced rear inflow above the
surface. Occasional damaging to severe gusts are possible with this
activity as it proceeds southward through eastern OK and AR into the
afternoon. See SPC Severe Thunderstorm Watch 463 and accompanying
mesoscale discussions for latest near-term guidance.
Some re-intensification or new development associated with this
convectively generated perturbation may occur as associated
low-level forcing impinges on a diurnally heating/destabilizing and
very moist air mass it its path. Any such activity will pose a
threat for strong-severe gusts across at least parts of AR and
eastern OK, and the ArkLaMiss region -- perhaps persisting
southeastward toward the Gulf Coast. Additional development is
possible (but still not certain) from late afternoon into tonight,
near or even just behind the outflow boundary from the morning
activity over AR and eastern OK. A few convection-allowing model
solutions that develop a second MCS out of such a regime move it
southwestward around the ridge toward east or even parts of
north-central TX, which is a reasonable (albeit conditional)
potential, given the ambient flow and high-theta-e potential inflow
airmass along such a track. The marginal unconditional outlook, and
to some extent the slight risk, have been expanded in that direction
on such a convective contingency. Should confidence further
increase in later outlooks, so would unconditional probabilities.
...Upper Ohio Valley to northern Mid-Atlantic...
Scattered thunderstorms are expected by mid/late afternoon over a
broad swath of the Ohio Valley region into the central Appalachians,
shifting/expanding eastward across the northern Mid-Atlantic region
with time this evening. Scattered damaging gusts are expected, some
of which may be severe in magnitude (50+ kt).
Activity is expected to develop amidst weak MLCINH along/ahead of
the surface cold front, as well as near prefrontal surface trough(s)
and outflow/differential-heating boundaries. Development will be
supported by strengthening large-scale ascent ahead of the shortwave
trough and ejecting MCV, which should increase poor antecedent
midlevel lapse rates somewhat. Low-level lapse rates will be
steepened by daytime heating. That, along with favorable moisture
with 60s F surface dewpoints being common, will contribute to a
field of 500-1200 J/kg peak/preconvective MLCAPE across the outlook
area. Though low-level shear will be limited by near unidirectional
deep-layer flow and lack of stronger boundary-layer winds, deep
shear will increase enough ahead of the trough aloft to support
organized convective bands and clusters offering localized
strong-severe wind swaths, as well as pulse severe from
predominantly multicellular structures.
...Central/southern High Plains...
Isolated to scattered thunderstorms are expected to develop by late
this afternoon, and continuing into early evening, along the eastern
rim of the higher terrain from southeastern WY to northeastern NM.
Difluent northwest flow and weak large-scale lift in mid/upper
levels will prevail by the afternoon convective period, ahead of the
central Rockies/Four Corners perturbations. This should help to
maintain steep lapse rates in the overlying EML, while diurnal
heating/mixing strongly destabilize a deepening boundary layer.
Orographic and thermal lift will initiate the convection, which
should move eastward to southeastward over the High Plains, offering
sporadic severe gusts and large hail. Though modest low/middle-
level flow is expected area-wide, considerable veering of winds with
height will yield favorable deep shear for organized multicells,
and, in about the northern half of the area, isolated supercells.
Forecast soundings suggest effective-shear magnitudes varying from
less than 20 kt across the CAO/DHT region (where hot, very deep
subcloud layers are expected) to about 45-50 kt near BFF (still
well-mixed thermally), along with surface dewpoints remaining
generally in the 50s F even through the mixing cycle. This should
support wind/hail potential with the most vigorous cells, until
activity moves into nocturnally cooling lower elevations and weakens
tonight.
...Southern ID to northern Rockies...
Widely scattered thunderstorm development is anticipated this
afternoon, as increasing large-scale ascent and mid/upper flow
preceding the mid/upper-level trough superimpose a well-heated,
deeply mixed boundary layer over and near the Snake River Plain of
southern ID. Some of this activity may carry over from the isolated
dry-thunderstorm areas of southeastern OR forecast in the SPC fire-
weather outlook. Convection will encounter increasing moisture/
buoyancy as it moves northeastward, but should remain over favorably
high-DCAPE, strongly mixed subcloud layers with inverted-v
thermodynamic profiles, beneath around 200-800 J/kg MLCAPE. This
will support localized strong-severe wind potential, until moving
past higher mountains and into evening diabatic
cooling/destabilization.
..Edwards/Mosier.. 06/26/2024
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