Lightning Jump and Drop

Severe Thunderstorm along NC/VA border was potent with high cloud flash rates in the 30s and 40s per minute then dropped into the teens.  This produced a negative lightning jump (or lightning drop/ease) of -8 sigma. Lightning then increased and there were 1 and 2 sigma jumps.

 

BAJ

NUCAPS Shows Increasing Instability Across RAH CWA

The mid-day NUCAPS (top below) profile shows an unstable atmosphere across the RAH CWA with MUCAPE around 2500 j/kg. This is especially helpful as the latest LAPS data to come in is over 3 hours old.

The upper levels in the NUCAPS sounding appears to show a much drier profile than the observed sounding from GSO this morning (bottom above). In the upper levels, this seems reasonable, especially after looking at the latest upper level LAP layer PW (below). A substantial dry layer is clearly moving into the region, so this upper level drying is believable. I'm not sold on the much drier lower levels of the NUCAPS sounding because; a) NUCAPS does poorly in the lower levels, b) the LAP layer PW shows moistening in the lower levels, and c) were it not for a few very moist obs around 550mb in the observed sounding, the lower portions of the two soundings would look very similar. Perhaps the moist layer around 550mb in the observed sounding contained bad data?

-Toki Wartooth

Satellite influence on ProbSevere

As storms fired in the Blacksburg CWA, the particular influence of the satellite fields on a developing storm was noted. The storm of interrogation devleoped along the VA/NC border, and was first tracked by ProbSevere at 1750 UTC, with a probability of 3%, no MESH, lightning or satellite growth.

At 1844 UTC, MESH was up to .22 in, lightning to 27 fl/min, and weak satellite growth had been sensed, all bringing the probability up to 20%.

Six minutes later at 1850 UTC, the probability had jumped to 51% as MESH increased to .37 in and lightning to 42 fl/min.

By the next scan (1852 UTC), new values for the satellite fields were ingested into ProbSevere, with strong growth and moderate glaciation rates being measured. This had the effect of bumping up the probabilities to 76%, which really attracted the attention of the forecasters.

 A warning was issued on the storm at 1908 UTC as probabilities continued to rise to 88%.

This case shows the significant impact of the satellite fields have on the probabilties.

Altrenate Color Table For CI Probability

The default CI probability color map creates a very cluttered looking image, hides many interesting features in the satellite imagery with inconsequential, low probability clusters, and the gray-blue color (second lowest) blends in with the gray scale color map used in satellite imagery.

I created an alternate color table to mitigate the issues outlined above. In the new color table (below) All clusters with a probability less than 30 are transparent, and the gray-blue color has been replaced with a darker blue that does not blend in the the gray scale satellite imagery.

-Toki Wartooth

Fast 1-minute Data Loop Proves to be a Good Aviation Forecast Tool

The HWT monitoring the Raleigh forecast area, while waiting on storms to develop noticed a good signal for clearing and improving conditions over Southern Virginia.  Elevated convection moving over the area brought downdraft air which led to a drastic clearing over a small portion of the thick low cloud and fog bank.  This could be a useful tool in Aviation forecasting.

Forecaster: Manbearpig

Good Performance from the CI Program

As Convective Initiation predictors reached values over 50 percent, cells began to form in this low shear, moderate cape environment.

Forecaster: Manbearpig

Raleigh Pre-Storm Analysis

In terms of moisture and instability, the Raleigh CWA appears to be primed for convection this afternoon. Surface dewpoints are well into the 60s, while LAP data shows PWs around 1.3. CAPE in the 1000-2000 j/kg range on the latest LAP analysis, which is over two hours old. Of note are significant differences in the LAP CAPE field which are dependant on the retrieval method. In cloudy areas where the GFS was used, CAPE is largely less than 1000 j/kg, but where the clear sky retrievals can be used, CAPE values are easily double what the GFS is showing, pushing 2000 j/kg in some areas. These higher CAPE values are consistent with the mesoanalysis, so this leads me to believe that the GFS instability is significantly underdone. Largely clear skies over the area should allow the atmosphere to continue to destabilize thought the afternoon.

Lift in this region is not terribly strong, but there does appear to be a subtle shortwave pushing into the region and a weak surface low north of the region. This apparently is enough, as convective initiation is already underway near the surface low.

Shear is modest thanks to fairly weak flow through the atmosphere. There does appear to be some very weak turning in the satellite derived atmospheric motion vectors, especially from the surface to about 925mb. This turning is confirmed on the 12z sounding out of GSO.

Given the convective initiation ongoing to the west and the continued destabilization across the area, I'm expecting at least scattered severe activity across the area.

-Toki Wartooth

LAP PW analysis early

The GFS influence fared much better on LAP PWATs in the same region where LAP CAPE estimates fared poorly.  The selected location sampled on AWIPS is almost a perfect match.

Forecaster: Manbearpig

HWT Acknowledges CAPE Weakness Over the Operational Area of WFO Raleigh

A large area of CAPE went well underforecast over much of the eastern half of the Raleigh CWA by the LAP Thermodynamic  Product due to the dependence on the GFS based capes.  The SPC Mesoanalysis at 16Z shows 1000 to 1500 J/kg Capes, with only a small area of CAPE values over 1000 J/kg denoted by the LAP (clear sky sampling).

Note: these values were 2 hours old compared to updated sources (e.g. RAP).

Forecaster: Manbearpig

Early Afternoon Analysis - Blacksburg (RNK) - Virginia/West Virginia - Thursday Afternoon

As the latest feature has continued to shift Eastward, we are focusing on West Virginia and Virginia this afternoon where the Storm Prediction Center has focused a SLGT Risk for Blacksburg as well as part of Charleston (RLX)'s County Warning Areas.

Already this afternoon the Convective Initiation (CI) Model is forecasting high values for part of our County Warning Area, as we are breaking out into a little but of sunshine with a CU field moving into the area. Severe Convective Initiation (Severe CI) Values are all on the low side, will be keeping an eye on them this afternoon to see if they increase. Wind barbs are indicating that most of the winds coming into the region are westerly, which would go along with expected storm motion this afternoon.

Current 0.5Z Reflectivity from Blacksburg (RNK) is showing that thunderstorms are ongoing over parts of the County Warning Area, with more thunderstorm development expected into the afternoon.

Looking at different indicators this afternoon with the LAP Analysis, CAPE is extremely low, less than 1000 J/kg, would want to increase this, and Lifted Index (LI's) are 0 to -1. I do think these are a little underdone as when compared to objective analysis. Precipitatble Water Values are AOA 1.00", which I would believe for thunderstorm development, and lead to the potential of heavy rainfall.

Widening the view this afternoon, expansive CU field is noted on the satellite imagery from Virginia back through West Virginia, and into Ohio, Kentucky and Tennessee.

Will keep an eye on values to see if they increase as we work into the afternoon.

Moisture values we're increasing in the lower levels of the atmosphere, but it was noted that some drier air was working into the upper levels of the atmosphere (Upper Right Screen) and that would help with the instability factor as we go through the afternoon for thunderstorm development.

Forecaster: Schuerman