Word on the SVR threat in the Mid Atlantic Tomorrow.
Posted: Sun May 30, 2004 4:47 pm
Earlier WV loops suggest the 12z GFS initialized 500H trough over the UPR MS valley better than the ETA, which is in relative agreement w/ the earlier 06z ENSEMBLE means as well as the trend in the GGEM and UKMET. The ETA had the most amplified look to the 500H pattern and was also the fastest.
The GFS however was the quickest w/ the eastward progression of the SFC cold front, at least initially (which is probably the result of grid-scale/convective feedback problems), before, for a short time coming in line w/ the ETA and GGEM solutions, until that is of course, SLP develops along the front tomorrow off the mid Atlantic coast tomorrow, when it becomes the slower solution. This once again is likely b/c of convective feedback. Although, at any rate, the GGEM appears to be the mid ground between the ETA and GFS solutions for tomorrow afternoon WRT to the SLP development.
Synoptically, we notice four key features aloft:
1. LARGE 500H low in the 50-50 low position near New Foundland/SE CAN.
2. 500H trough across the Northern Plains
3. Shortwave Ridging in-between the large low over SE CAN and the trough over the upper plains.
4. 60-65 KT mid level jet streak pulling out of North central TX/S central OK.
18z Surface analysis showed 992mb low over ERN SD/WRN Minnesota, w/ associated occluded boundary draped across south central MN, and into central IA, where the triple point is located. Cold front extended South from the triple point through MO/OK/TX, w/ warm front extending EWD over IL/IN/KY.
During the day tomorrow, 500H trof will build an increasingly negative tilt as it becomes elongated eastward through the southern lakes. Associated 500H jet streak will undercut the shortwave ridge between the large low across SE CAN and the aforementioned through, causing block to form along the western shore of Hudson Bay bay by later in the day, meanwhile triple point associated w/ occluded SLP over the upper Midwest will push into the lower lakes, as cold frontal boundary extends southwestward from it through the OH VLY back into NE parts of TX during the morning hours. Warm front will likely be running from the lower lakes to the Delmarva. The northern portion of the front will move FASTER than the southern part as SLP becomes elongated from MN through the central lakes into WRN NY.
Instability wise --- cloud debris from old convection or blow-off from still ongoing thunderstorms may limit instability in the warm sector (E of the cold front and S of the warm front extending outward/away from the triple point). However, latest 18z MesoETA suggests lowest 100mb Mean layer CAPE values increasing to 1000 J/kg over portions of the Mid Atlantic by late in the day...within the warm sector. This given favorable deep layer shear in the lowest 6 KM AGL of generally 40-50 KT, increasing upper level divergence, and forced ascent along the front as it progresses eastward through the day, should lead to the development of a squall line along the cold front, that will traverse the mid Atlantic before moving out to sea during the late evening hours.
The areas included would be much of Central and SRN MD/ all of VA/ central and SRN DE (Delmarva region in general) and perhaps EXTREME SRN NJ. Primary threat will be isolated wind damage and perhaps some marginally severe hail given weak mid level lapse rates. BEST potential for tornadoes (which is already limited given lackluster instability, and poor lapse rates), would up along the warm front, into N MD, N DE, S/SE PA, S NJ, where 18z ETA forecasts best low level shear, w/ lowest 3 KM SR-helicity values above 200 m^/s^2, and low LCL heights. Also, INVOF the warm front is where the best backing of winds from SE at the surface to South at 850H and eventually West at 500H.
Furthermore, going against the tornadic threat would be the relatively stable boundary layer, implying that convection would likely be elevated.
Overall......the severe threat is much LOWER tomorrow than it has been these past two days, w/ the primary severe threat across the region given anticipated convective mode being ISOLATED ---- marginally severe hail and wind damage.
The GFS however was the quickest w/ the eastward progression of the SFC cold front, at least initially (which is probably the result of grid-scale/convective feedback problems), before, for a short time coming in line w/ the ETA and GGEM solutions, until that is of course, SLP develops along the front tomorrow off the mid Atlantic coast tomorrow, when it becomes the slower solution. This once again is likely b/c of convective feedback. Although, at any rate, the GGEM appears to be the mid ground between the ETA and GFS solutions for tomorrow afternoon WRT to the SLP development.
Synoptically, we notice four key features aloft:
1. LARGE 500H low in the 50-50 low position near New Foundland/SE CAN.
2. 500H trough across the Northern Plains
3. Shortwave Ridging in-between the large low over SE CAN and the trough over the upper plains.
4. 60-65 KT mid level jet streak pulling out of North central TX/S central OK.
18z Surface analysis showed 992mb low over ERN SD/WRN Minnesota, w/ associated occluded boundary draped across south central MN, and into central IA, where the triple point is located. Cold front extended South from the triple point through MO/OK/TX, w/ warm front extending EWD over IL/IN/KY.
During the day tomorrow, 500H trof will build an increasingly negative tilt as it becomes elongated eastward through the southern lakes. Associated 500H jet streak will undercut the shortwave ridge between the large low across SE CAN and the aforementioned through, causing block to form along the western shore of Hudson Bay bay by later in the day, meanwhile triple point associated w/ occluded SLP over the upper Midwest will push into the lower lakes, as cold frontal boundary extends southwestward from it through the OH VLY back into NE parts of TX during the morning hours. Warm front will likely be running from the lower lakes to the Delmarva. The northern portion of the front will move FASTER than the southern part as SLP becomes elongated from MN through the central lakes into WRN NY.
Instability wise --- cloud debris from old convection or blow-off from still ongoing thunderstorms may limit instability in the warm sector (E of the cold front and S of the warm front extending outward/away from the triple point). However, latest 18z MesoETA suggests lowest 100mb Mean layer CAPE values increasing to 1000 J/kg over portions of the Mid Atlantic by late in the day...within the warm sector. This given favorable deep layer shear in the lowest 6 KM AGL of generally 40-50 KT, increasing upper level divergence, and forced ascent along the front as it progresses eastward through the day, should lead to the development of a squall line along the cold front, that will traverse the mid Atlantic before moving out to sea during the late evening hours.
The areas included would be much of Central and SRN MD/ all of VA/ central and SRN DE (Delmarva region in general) and perhaps EXTREME SRN NJ. Primary threat will be isolated wind damage and perhaps some marginally severe hail given weak mid level lapse rates. BEST potential for tornadoes (which is already limited given lackluster instability, and poor lapse rates), would up along the warm front, into N MD, N DE, S/SE PA, S NJ, where 18z ETA forecasts best low level shear, w/ lowest 3 KM SR-helicity values above 200 m^/s^2, and low LCL heights. Also, INVOF the warm front is where the best backing of winds from SE at the surface to South at 850H and eventually West at 500H.
Furthermore, going against the tornadic threat would be the relatively stable boundary layer, implying that convection would likely be elevated.
Overall......the severe threat is much LOWER tomorrow than it has been these past two days, w/ the primary severe threat across the region given anticipated convective mode being ISOLATED ---- marginally severe hail and wind damage.
