A cluster of storms continues ahead of a diffuse surface boundary located across west-central North Carolina into southwest Virginia. Convergence continues to be the primary convective driver in association with an upper-level low continuing to rotate across eastern Tennessee.

Cold temperatures aloft, as shown by H50 temperatures near -20C, and moderately steep lapse rates will continue to support a marginal threat for large hail through 01Z. Near-surface instability will decrease in the next couple of hours as diurnal heating comes to an end and low-level theta-e values decrease as depicted by the CIMSS Nearcast tool. Tend to side with simulated satellite imagery showing storms coming to an end by 03Z across the Blacksburg County Warning Area as

Hampshire/Guseman

Convection is ongoing across North-Central North Carolina westward into the Appalachians. The upper low is currently centered in eastern Tennessee. The most robust thunderstorms of the afternoon have developed across northwest Carolina along a a boundary extending from NW North Carolina into eastern Kentucky.

The environment is not overly robust to sustain severe convection. Surface-based CAPE values across Northern North Carolina  are roughly around 1000 J/Kg with 0-6 km shear 40-50 knots. Low-level lapse rates will be approaching 6-7.5 C/Km by 21z with mid-level lapse rates around 6-7 C/km. The main threat will be marginally severe hail, but 0-3 km helicity values between 150-200 m2/s2 could support a low-end tornado threat. However, as storms move away from the boundary, this threat will decrease.

The EFP has placed a 5% probability of severe storms for the previously mentioned area, while a slight risk of severe storms is forecasted by SPC in small area shown in the image below.

As a lobe of energy wraps around the upper-low and moves northward into northern NC, the storms which have already initiated should be able to continue northward into the Blacksburg, VA CWA while some continuing activity is possible across the northwestern extent of the Raleigh, NC CWA.

Hampshire/Guseman

Today, were are focused on the Upper Mississippi Valley for severe convective development.  A potent, negatively-tilted shortwave trough is moving quickly across the north-central U.S.   Strong deep-layer shear associated with the trough should combine with moderate (to strong) instability and deep moisture to produce severe convection, including supercells.  It is uncertain, however, whether sufficient heating can occur in the wake of a late-morning mesoscale convective system across eastern Minnesota and western Wisconsin.  If destabilization can occur in the vicinity of the residual outflow boundary, tornadoes will be possible.

A secondary area of interest is in south-central Nebraska, where the surface front curves to the southwest.  In this area, the moisture is both deep and quality; the instability , strong to extreme; and the winds at the surface should back, augmenting — to some extent — the marginal wind shear.  That said, severe hail and winds should be the primary threats.

We will start operations in the Minneapolis (MN), Sioux Falls (SD), and Hastings (NE) county warning areas, with an eye toward the  Duluth (MN) CWA — should destabilization occur.

-G. Garfield, Week 5 Coordinator

Today, we are focused on two areas for severe convective development.  The first is in the southern High Plains, where rich, deep moisture resides beneath a very potent elevated mixed later.  As surface temperatures warm, strong to extreme instability is expected to develop over west Texas into eastern New Mexico.  However, kinematic profiles are marginally favorable for the development of organized convection.  Nevertheless, the degree of available potential energy suggests that this area should be watched for severe weather.

The second area is located in the central and northern Plains.  An upper-tropospheric trough is emerging onto the Plains this afternoon, and resultant pressure falls will create a kinematic environment favorable for the development of organized storms.  However, the moisture is limited and the lapse rates are only moderate where moisture quality is the greatest.  Nevertheless, we will monitor this area for convective development.

-G. Garfield, Week 5 Coordinator

Today, we are focusing on the southern High Plains, where a shortwave trough will impinge upon a moist and unstable airmass.  Deep-layer shear favors supercells in initial development, and a tornado threat may emerge, given the presence of adequate low-level shear/CAPE from west Texas to southeast Colorado.  Later this evening, the threat should transition toward damaging winds, as cold pools merge to form an organized linear convective system.

Three county warning areas were selected for product evaluation: Albuquerque, Midland, and Lubbock.   It appears that this will be another opportunity to evaluate the OUN WRF and the Lightning Mapping Array network (Lubbock CWA).

-G. Garfield, Week 5 Coordinator

For the week of 11 June – 15 June, our distinguished NWS guests are Tim Tinsley (NWS WFO Brownsville, TX), Michael Dutter (NWS WFO Marquette, MI), Ty Judd (NWS WFO Norman, OK), Steve Nelson (NWS WFO Peachtree City, GA), Randy Skov (NWS CWSU Atlanta, GA), and Jeff Garmon (NWS WFO Mobile, AL).

Today, we are focusing on two areas: one is associated with the ongoing mesoscale convective system in the lower-middle Mississippi Valley; the other is in the Southern Plains, where strong heating may be able to overcome a substantial cap.  The former environment is characterized by strong instability, weak low and deep-layer shear, and a weak cap.  The latter environment is characterized by strong to extreme instability, weak deep-layer shear, and a formidable capping inversion.  The plan is to start two groups of forecasters (2 in each group) in the eastern target, and one group in the western target.  The initial CWAs will be Memphis (for strongest convection), Huntsville (for LMA considerations), and Tulsa (for convective initiation considerations).

-G. Garfield, Week 5 Coordinator

For the week of 4-8 June, our distinguished NWS guests will be Marc Austin (NWS WFO Norman, OK), Rich Grumm (NWS WFO State College, PA), Chris Leonardi (NWS WFO Charleston, WV), Jennifer Palucki (NWS WFO Albuquerque, NM), Kristen Schuler (NWS CWSU Kansas City, MO), and Gary Skwira (NWS WFO Lubbock, TX),  Other visiting participants this week will include Kathrin Waplir (Deutscher Wetterdienst, Germany), and Wayne Feltz (CIMSS/UW-Madison).

Wapler, Kathrin           DWD, Germany

We’re operating today during the first mod risk of the experiment, however, that is not where we are focusing today… at least not initially.

In order to try and get lightning data into the experiment this week, we’ve initialized in the Sterling, VA and Melbourne, FL domains.

For the FL domain, we’re hopeful that storms will get going as the sea breeze front sets up across the state.  Already, the UAH-CI product is flagging cumulus for development (consistently 50-60%) along the line from Sanderson to -Orlando to just northwest of Okeechobee.

For the DC domain, the CI alg is also flagging development generally a bit lower on the probability though. A region of SBCAPE of >1500-2000 J/kg extends from eastern NC to over much of the LWX CWA, so it appears possible that we could at least see some convective development across some of the DC LMA though likely only marginally severe.

Our observers and some PIs are keeping an eye over central WI and the associated moderate risk region for development of surface based storms (as of now all development across Minnesota appears to be elevated).  Currently instability is limited across much of the region, but we do expect additional destablization with daytime heating and enhanced lift as the cold front moves in.

-Kristin Calhoun, Week 3 Coordinator

Forecasters are beginning the day in NC/SC region, specifically starting in the Raleigh and Wilmington CWA’s. Storms were already going as we initialized in the area, but are expected to grow in strength and coverage over the next couple of hours.   All the products and algorithms seem to working well over the region (only lacking total lightning coverage by an LMA, though this region may have coverage in future years!).  Multiple storms have already been flagged by the UW-CIMSS Cloud-top-cooling product with min values as low as -26 to -27C and warnings may be issued shortly by the forecasters as they get settled in the new operations/CWAs.

We’re still watching the other SPC slight risk area for later this afternoon and early evening.  It is likely we will make a switch (for at least one of the teams) to the central plains (likely Hastings/Omaha CWAs) if we start to see a CI signal.  Like yesterday the high-res models seem to want to initiate convection along the front by 2100 UTC, though moisture continues to be an issue over the region with dewpoints in NE CO in the upper 30s to mid 40’s increasing to only the mid 50’s over central KS/NE.   Unlike yesterday over the Dakotas where a thick cirrus shield covered the region, skies are pretty clear over KS with a bit more cloud coverage behind the front in central NE.  If and when storms develop, steep lapse rates and deep layer shear point to the likelihood of supercells with large hail and damaging wind (especially with the large dewpt depressions).

-Kristin Calhoun, Week 3 Coordinator

Focus for operations is over the Dakotas for today.  Initially, forecast teams were separated into the Bismark and Grand Forks CWA’s, but with delay of any CI, we quickly decided to re-localize the FGF team to Aberdeen, SD.

The HRRR remains quite aggressive at initiating convection across both ND & SD as well as Montana by 2030-2100 UTC, though lessening in strength and coverage with each run (earlier runs developed a strong line of storms and it has moved to smaller, more isolated, cells in recent runs). Almost all the high-res models had similar solutions thought, and initially working off of the NSSL-WRF from last night convection was first expected by 2100 UTC.

The low pressure in ND with corresponding warm front extending across the ND / Canada border still holds promise.  Steep lapse rates, combined with low-level curvature in the hodograph point to supercells with large hail (and isolated tornadoes) if and when storms finally develop…

In the meantime, thick cirrus coverage is preventing the UW-CIMSS Cloud-top-cooling and UAH-Convective Initiation algorithms from flagging any development across the majority of ND.  But the CTC does seem to be flagging development in Montana…

-K. Calhoun, Week 3 Coordinator