Thursday, March 1
Hello, the good news… a very quiet first day and evening of March on the way. Then as we push into tomorrow, big changes move into the Ohio Valley. Yet another intense storm system will pass through the Mississippi and Ohio Valleys. As low pressure deepens to our northwest later tonight and tomorrow, a warm frontal boundary will push north through the TN and OH Valleys the next 24 hours. Warm, moist air will return across our region by midday tomorrow as sfc dewpoints climb back into the lower 60s. As the afore mentioned system moves through our area, showers and storms will develop on a scattered basis but are expected to gradually increase in coverage as the afternoon / early evening hours wear on. At the same time, wind fields will dramatically increase over the Ohio Valley creating shear profiles very favorable for severe weather producing thunderstorms.
Intially, there may be a few scattered thunderstorms in the warm advection region of the northward advancing warm front late tonight and early tomorrow. If (IF) these occur, they would be elevated in nature with any of the stronger cells capable of producing hail. As the warm moist air returns at the surface, any storms towards tomorrow afternoon and early evening are expected to become rooted near the surface and this will likely occur as the shear profiles strengthen. Bottom line, scattered storms tomorrow afternoon will likely become supercellular in nature with damaging winds, hail, and tornadoes a distinct possibility. As the late afternoon / early evening hours wear on, the storms are expected to congeal into a more linear mode with wind becoming the main threat – although tornado spin ups still possible with any bowing segments that form.
Still a little unclear on timing, new GFS has the cold front already towards the I-75 corridor by 7pm Friday while the NAM was about 3 to 4 hours slower. last night’s ECMWF was more in line with the GFS. I’ll have an update later to better pin down timing.
Here’s the latest SPC update…
…THERE IS A SLGT RISK OF SVR TSTMS ELSEWHERE FROM ARKLAMISS REGION
ENEWD TO CAROLINAS AND NWD TO SWRN PA…INDIANA AND OZARKS…
UPPER-AIR PATTERN TRANSITION IS UNDERWAY ATTM…WITH HEIGHT FALLS
ACROSS MUCH OF WRN CONUS IN ADVANCE OF SYNOPTIC SCALE TROUGH
DEVELOPMENT. RESULT THROUGH DAY-1 WILL BE BROADLY CYCLONIC FLOW
ACROSS MOST OF WRN CONUS…MOVING EWD TO CENTRAL CONUS DAY-2. BY
START OF PERIOD…EXPECT NRN-STREAM MID-UPPER CYCLONE LOCATED OVER
ND/MB BORDER REGION…AND BASAL 500-MB SHORTWAVE TROUGH OVER
4-CORNERS REGION. DOWNSTREAM FROM THAT PERTURBATION…LOWER-
AMPLITUDE SHORTWAVE SHOULD BE MOVING ENEWD ACROSS KS. VORTICITY
FIELDS WITH LATTER TWO SHORTWAVES SHOULD REMAIN WELL-CONNECTED…
EFFECTIVELY RESULTING IN POSITIVELY TILTED TROUGH FROM ERN IA/NRN IL
REGION TO ERN NM BY 3/00Z. BY 3/12Z…EXPECT MID-UPPER LOW OVER LH
OR ADJOINING PORTIONS ONT…WITH TROUGH SWWD OVER LOWEST SEGMENT OF
OH RIVER…OK…AND SRN NM.
AT SFC…COLD FRONT NOW IMPINGING ON SWRN APPALACHIANS/TN VALLEY/NRN
LA SHOULD MOVE BACK N AS WARM FRONT THIS PERIOD…WRN PORTION OF
WHICH WILL ATTACH WITH SFC FRONTAL-WAVE LOW OVER MO BY 2/12Z. LOW
WILL DEEPEN AND MOVE NEWD TOWARD SRN LOWER MI BY 3/00Z…THEN
OCCLUDE AND BECOME STACKED WITH MIDLEVEL VORTEX BY END OF PERIOD.
WARM FRONT SHOULD MOVE NEWD OVER MID-UPPER OH VALLEY AND CENTRAL
APPALACHIANS THROUGH PERIOD. COLD FRONT TRAILING SFC LOW SHOULD
START PERIOD OVER OZARKS…SERN OK AND W-CENTRAL TX. BY
3/00Z…COLD FRONT SHOULD REACH ERN INDIANA/WRN OH…SERN AR…AND
MIDDLE TX COASTAL PLAIN. BY 3/12Z…COLD FRONT SHOULD REACH
CENTRAL/ERN PA…WRN VA…NRN GA…AND SRN AL.
…OZARKS…LOWER MS/TN VALLEY AND AL TO OH VALLEY STATES…
SCATTERED ELEVATED TSTMS IN CLUSTERS MAY BE CARRY OVER FROM LATE
DAY-1 PERIOD OVER PORTIONS OZARKS…LOWER OH VALLEY AND MID-SOUTH
REGIONS…WITH FAVORABLE CAPE ALOFT AND DEEP-LAYER SHEAR FOR HAIL.
SOME OF THIS ACTIVITY MAY PERSIST LONG ENOUGH TO BECOME SFC-BASED BY
MIDDAY AND EARLY AFTERNOON IN INCREASINGLY FAVORABLE ENVIRONMENT FOR
SVR. OTHER SCATTERED-NUMEROUS TSTMS SHOULD DEVELOP ALONG/AHEAD OF
COLD FRONT. TSTMS SHOULD BE FAST-MOVING…COVERING LONG SWATHS WITH
THEIR SVR THREATS OVER ANY GIVEN PERIOD OF TIME.
AIR MASS AHEAD OF SFC COLD FRONT AND IN WAKE OF MORNING CONVECTION
SHOULD DESTABILIZE FAVORABLY AMIDST STG LOW-LEVEL WAA/MOISTURE
TRANSPORT. INTENSE DEEP-LAYER SHEAR AND LOW-LEVEL HODOGRAPHS WILL
SPREAD OVER MUCH OF WARM SECTOR…ALONG WITH SFC DEW POINTS
INCREASING FROM MID 50S OVER OH TO MID 60S OVER PORTIONS MS/AL. IN
TANDEM WITH DIURNAL SFC HEATING…THIS SHOULD SUPPORT MLCAPE 250-500
J/KG OVER PORTIONS OH/INDIANA…TO 1500-2000 J/KG RANGE OVER
PORTIONS TN/KY…THEN DECREASING SOMEWHAT FARTHER S DUE TO
INFLUENCES OF STABLE LAYERS ALOFT. DESPITE UNCERTAINTIES REGARDING
EXTENT/COVERAGE OF VARIOUS CONVECTIVE MODES THIS FAR OUT…EXPECT
WEAK CINH…BROADLY FAVORABLE CAPE/SHEAR PARAMETER SPACE…AND
RELATIVELY DENSE COVERAGE OF CONVECTION LIKELY TO IMPINGE ON THAT
SETTING. AS SUCH…NUMEROUS SVR WIND EVENTS ARE POSSIBLE ALONG WITH
POTENTIAL FOR STG TORNADOES FROM EITHER SUPERCELLS OR QLCS-VORTEX
MECHANISMS. AT LEAST A FEW WIND EVENTS AOA 65 KT AND
LONG-TRACK/SIGNIFICANT TORNADOES ARE POSSIBLE. THEREFORE…
SIGNIFICANT-SVR AREA IS BEING INTRODUCED…DRIVING CATEGORICAL MDT
RISK WHERE OVERLAID WITH RELATIVELY DENSE 45% TOTAL-SVR PROBABILITY.