CI/CI-Severe Probability

At the tail end of the Pennsylvania squall line near the Pennsylvania/Maryland state line (near Gettysburg, PA), little convection had taken place, but was forecast to develop. The Convective Initiation Probability product did a good job in the 30-60 minute period in forecasting where scattered convection would continue to build southward toward Maryland. The areal extent was underforecast a little bit, but it showed where new development would likely take place. This was along an advancing cold front into an unstable environment where the development was expected, although timing would be uncertain because of some capping. This would have been useful in a forecast office.

Further to the south, additional convection developed over northern Virginia that was not forecast at all by the CI product, while it tried to develop convection from near Richmond, VA to the southern DelMarVa peninsula that never developed. The northern Virginia convection might have been origraphically been induced, as it was ahead of the advancing cold front and just to the east of the Blue Ridge Mountains to the west. It also developed cells to the northeast while the line didin't move eastward at all. The predicted convection from Richmond eastward developed with some mid-level cloud development, but didn't appear to be connected with any near-surface convergence, such as a front or a sea breeze. These areas would have made using the product a little more challenging.

Behind the Pennsylvania squall line, low probability CI's popped up almost continuously where sunshine returned and a field of cumulus clouds developed. Since the probabilities remained low in an areas where convection was unlikely (but not zero),


The CI-Severe product didn't seem to perform too well. The probabilities seemed to be overdone in areas where I wasn't even expecting much convection, and seemed to be underdone in areas where areas along and ahead of the squall line where new cells were forming. The first loop is CI with visible satellite and a regional radar loop; the second loop substitues CI-Severe for CI.

Gary Cannalte

Afternoon Convective Trends for LUB

Shifted over to LUB from ALY late this afternoon. Convection has developed over parts of the forecast area, especially along a west/east oriented boundary across the southern portion of the region. AllSky LAP CAPE and NUCAPS soundings show a distinct north to south moisture/instability gradient through the center of the forecast area, with much drier and more stable air in the west compared to many model progs. Not surprisingly the convection in the west is having trouble getting going, but more robust development is occurring with cells that cross the instability gradient.

20Z AllSky LAP CAPE showing strong instability gradient

2002Z NUCAPS Sounding along eastern edge of instability gradient

Alex Brown

Lightning/Reflectivity Trends

It was good to see the lightning trends following those of the reflectivity.  As the storms reach the coast, they began to weaken but the training line over eastern PA southward toward northern MD maintained intensity.

Both the lightning activity and reflectivity were observed to be the most intense due west of Philadelphia.

Fig 1. The strongest storms remained intensive west of Philadelphia.

Fig 2. Both the Flash Event Density (top left) and Total Energy (lower left) were quite high in the vicinity of the strongest updrafts.

Fig 3. The Group Centroid Density (lower right) stood out to me during this time as well. 

NUCAPS Missing Sounding Points

Stripes of NUCAPS sounding data were missing on the 2002Z product. However, the missing data was not the same on the DB Improved Latency and DB Modified products.

Alex Brown

2002Z NUCAPS DB Improved Latency

2002Z NUCAPS DB Modified

NUCAPS/WV 3 Level Data

We were monitoring a squall line that developed rapidly over Pennsylvania and swept eastward across the state. In the pre-thunderstorm environment ahead of the squall line, the water vapor imagery showed some mid-level drying ahead of the line of storms, leading to increased confidence of strong winds being able to be advected down to near the surface. Local storm reports indicated that damaging surface winds of 60 to 70 MPH were observed along the line. NEXRAD velocity data showed winds of 60 to 80 knots at about 6000 to 7000 feet above ground level.

Just as the squall line was beginning to enter our CWA (Mt. Holly), NUCAPS data became available. Just to the northwest of Philadelphia, the NUCAPS sounding data confirmed the dry air aloft and relatively steep lapse rates. This increased the confidence of severe weather in the CWA.

Gary Cannalte

Day 2 operatoins Update

The line is moving through the northeast very quickly and the northern part will be off the coast within the hour. So, the Albany group is moving out to west Texas to work in the Lubbock CWA.

-Michael

Gridded NUCAPS

The image below shows gridded NUCAPS CAPE from an 1800z pass today. Data is rather sparse. Also convection had already started so couldn't really use NUCAPS to assess the pre-storm environment.  A.Cope

Evolution of ProbSevere Contours

During today's QLCS moving across the northeast, the ProbSevere contours behaved erratically. As the convective line filled in, more elongated contours developed as would be expected. However, they frequently jumped back/forth between elongated and more cellular, despite minimal changes in the intensity of the line itself. This made it difficult to gauge trends with a particular cell/core. Some of the contours were quite spread out as well, as much as 60-70 miles wide in some cases.

Alex Brown

Loop of ProbSevere linear/cellular jumps

GLM Delayed

GLM is delayed by 13 minutes as of 2043 UTC on 5/15/18.  Figure 1 shows a GLM time stamp of 2028 UTC with an AWIPS time of 2041 UTC.

Fig 1. GLM delayed in AWIPS by 13 minutes.

wall_cloud

GLM Lightning with Initiating Storms

The loop below shows GLM lightning for two storms that developed earlier over Delaware Co. NY and Susquehanna Co. PA.  In the upper left panel, ENI lightning is overlaid as well, and the GLM Flash Extent Density shows a much larger horizontal extent of lightning vs. the ENI pulses. The GLM average flash and group areas (two lower panels) show average flash area increasing over time as the storm grows, going from light green to medium or dark blue.  The flash extent density and total energy products (two upper panels) both seem to do a pretty good job of highlighting the more active core.
A.Cope