SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1159 PM CDT Thu Sep 12 2019
Valid 141200Z - 151200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY INTO
SATURDAY NIGHT ACROSS PARTS OF THE MID MISSOURI INTO UPPER
MISSISSIPPI VALLEY...AND ACROSS PARTS OF THE EAST CENTRAL FLORIDA
PENINSULA...
...SUMMARY...
Strong storms may impact parts of the mid Missouri and upper
Mississippi Valleys Saturday afternoon and evening, accompanied by
at least some risk for severe weather. Showers and perhaps a few
thunderstorms associated with a tropical system may also pose a risk
for strong wind gusts and isolated tornadoes across parts of the
east central Florida peninsula.
...Synopsis...
Models suggest that the westerlies may begin to undergo
amplification during this period, with a large and seasonably cold
mid-level trough forecast to dig from south of the Gulf of Alaska
toward the northern Pacific coast. Downstream, ridging appears
likely to begin to build across the northern U.S. Rockies into the
Canadian Prairies, while troughing, associated with the remnants of
a mid-level closed low now progressing toward the upper Great Lakes
region, shifts east of Ontario through Quebec and parts of northern
New England.
A surface cyclone associated with the lead troughing is forecast to
weaken while migrating east of James Bay toward Newfoundland and
Labrador, but a trailing cold front appears likely to advance
through much of the upper Ohio Valley, Northeast and northern Mid
Atlantic Coast by 12Z Sunday. In its wake, a warm front is expected
to develop and advance from the northern Plains into the Upper
Midwest, with some further deepening of lee surface troughing across
much of the northern and central Plains.
In lower latitudes, a developing tropical system, within troughing
developing northwestward around the southwestern periphery of a
western Atlantic subtropical high, may migrate into east central
Florida Atlantic coastal areas.
...Mid Missouri into upper Mississippi Valley...
It appears that seasonably moist boundary layer air (characterized
by upper 60s to near 70f dew points) may advect into the region by
late Saturday afternoon, associated with modest southerly return
flow, east of the surface troughing, and south of the warm front.
Beneath modestly steep mid-level lapse rates this may contribute to
CAPE near or in excess of 2000 J/kg, in the presence of moderate to
strong deep-layer shear associated with the westerlies.
Mid/upper forcing to support initiation of thunderstorms remains a
bit unclear, but could be provided by a low-amplitude impulse
digging in the wake of the departing larger-scale troughing, before
it becomes absorbed within larger-scale anticyclonic mid-level flow
developing across the Upper Midwest/Great Lakes region by late
Saturday night. It appears at least possible that this could be
favorably timed to support the development of organized convection
near the warm front/surface trough intersection, which at this time
appears most probable across central Minnesota by late Saturday
afternoon. This could include isolated supercell development
initially, then a small southeastward advancing upscale growing
convective system, before boundary layer instability wanes Saturday
evening.
...Florida...
Although uncertainty remains sizable, based on the current forecast
track of the developing tropical system, convection posing a least
some risk for severe wind and isolated tornadoes may impact east
central Florida peninsula coastal areas by Saturday afternoon.
...MAXIMUM RISK BY HAZARD...
Tornado: 2% - Marginal
Wind: 5% - Marginal
Hail: 5% - Marginal
..Kerr.. 09/13/2019
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