A spring like cold front will move through the Mid-West and combine favorable wind shear with strong instability Saturday into Sunday afternoon and will likely produce widespread severe thunderstorms with large hail, damaging winds with the possibility of a few tornadoes.
An unseasonably strong upper level short wave will drop southward into the Ohio-Valley on Sunday and will increase the mid and upper level flow across the region. Favorable instability, bulk shear & moderate helicity will support organized severe thunderstorms beginning on Saturday across IA/MO/IL/IN. The threat shifts eastward on Sunday into IN/OH/KY/TN/WV. A tornado threat exist along the quasi-stationary front across northern IN/OH and a conditional threat also exist within the low level theta-e advection zone across eastern Ohio/Kentucky & West Virgina where 0-1KM EHI’s & 0-1Km bulk shear are highest.
Should be an active 48 hour period. Additional severe storms are likely into Monday across the Northeast and Mid-Atlantic.
Added the ECMWF 500mb winds to the ECMWF regular resolution graphics. These can be useful in projecting the mid-level winds that can aid in organized severe thunderstorm development. These can be found in the drop down menu, as well as, the individual time frames. These are available for the Northern Hemisphere at the moment, but will include all sectors soon.
NCEP has recently upgraded the WRF-ARW/NMM Hires windows for the Eastern U.S. to a CONUS ARW and NMMB ~4km WRF runs. They are run at 00Z and 12z and produce hourly output out to 48 hours at roughly 5km.
We are in the process of making the necessary changes within our software and systems to accommodate the increase in files sizes and processing requirements to handle the larger domains. We should have these new data sets available and finalized later this week. Look for them where the old WRF-ARW/WRF-NMM EAST model pages were located.
Here is the NCEP technical bulletin describing all the changes to the model & physics in the upgrade.
A slow moving cold front across the lower Great Lakes will provide the low level convergence, combined with favorable instability & shear to ignite numerous severe thunderstorms Wednesday afternoon across the Ohio-Valley. Supercells will be a likely storm mode as bulk shear values will be in excess of 45 knots. In addition, 0-3km helicity values will be over 200, so there is a chance for an isolated tornado in the strongest supercells, although conditions are not ideal for tornado development. Large hail and damaging winds are the primary hazards. Supercells may evolve into a linear or bow echo configuration by late afternoon or evening.
Storms will likely diminish and weaken as they move east-southeastward into Central Kentucky Wednesday night where the low-level theta-e values will be significantly less, resulting in much less instability.
An upper level shortwave will move through the Mid-Atlantic region Friday evening. Ahead of this shortwave, conditions will for a short period of time, become favorable for severe weather across Central and Eastern portions of the Carolinas and Virginia.
Thunderstorms will likely develop by mid day across the central portions of the region and move eastward and intensify under a strong mid-level flow. Moderate helicity and bulk-shear values along with surface CAPE in excess of 1500 will support the potential for supercell development. Low LCL levels will also increase the risk of tornadoes in the strongest supercells. Trends in mid-level wind strength and instability should be monitored for an increase in the severe weather risk assessment.
4/24/14 3:00 PM EDT
A zone of of prolonged freezing rain will extended the I-20 corridor from Atlanta to Augusta to Columbia, SC. Model freezing rain liquid equivalent totals in this area exceed 2 inches. While drip loss will be relatively high with accretion efficiencies likely only being in the 30-40% range due to the high precipitation rates and the temperatures likely remaining close to the freezing point, this still yields radial ice accretion amounts of .50-75″ which would cause widespread electrical distribution disruptions and tree damage.
Here are the latest Freezing Rain Graphics.
A strong winter storm will bring a variety of winter weather to the Southeastern U.S. as an upper level low develops across the mid-south, in combination with a cold air damming event. A strong coastal low will strengthen and move up along and just off the Eastern seaboard and bring heavy precipitation to the Mid-Atlantic and into the Northeast
WRF Hourly Winter Radar through Wednesday Evening
NAM 4km 60hr Winter Radar
New Short Range Ensemble Forecast (SREF) Mean Accumulated Winter Precipitation have been added. They are:
Snow change from previous run (dProg/dt)
Ice Pellets (Sleet)
They can be found in the drop down menu on the SREF model page under “Forecast Parameter (Mean)”
Here is an example. Freezing Rain Accumulation across the Southeast.
2/5/14 1:45 Z
Freezing rain will moving into the populated region of New Jersey and New York City around midnight (2/5/14) and will persist until around noon Wednesday. Temperatures in the New York city metro area are expected to remain near or slightly below freezing the duration of the event. Just northwest and west of the downtown area, slightly colder surface temperatures are likely.
Total precipitation amounts of 1.00-1.25″ is expected. A significant amount of drip loss will occur due to the heavy precipitation rate and the small air temperature delta to freezing point. Where temperatures are likely closer to 29 or 30 degrees just west and northwest of the city, ice accretion amounts of 1/4″ to as much as 1/2″ are possible and could lead to a significant amount of power outages, if ice accretion amounts surpass 1/3″.