MCS over far SW Texas: synthetic vs real IR

Forecaster comments from EWP blog...

As described in this blog a few hours ago, storms developed S of Pecos due to ongoing diabatic heating in an environment modestly supportive for strong/isolated severe pulsating storms. Thunderstorms rapidly grouped in a loosley organized convective cluster, which gradually approached the NM boarder during the following hours. At 2300 Z, both IR showed the peak of activity/organization of that cluster with a constant weakening trend thereafter. However, the synthetic one caused a rapid decay of that cluster until 0100Z, whereas real time IR data still indicated a large cluster with cloud top temperatures of below -50 degree celsius at that time. Also, lightning activity was still present at 0100Z with that cluster although a rapid decline was also noticed until 0130 Z. So peak strength was captured well with a too fast decline of the cluster’s strength thereafter.

The synthetic IR did also an outstanding job in highlighting the area of initiation (both timing and the region…not shown).

Airmass composite used over N-Dakota

Forecaster comments on EWP blog...

Broad upper low, situated over the far NW US, pushed eastwards during the afternoon hours and onwards. A sharp 100-120 kt high-level jet also translated to the east over the N-C Rockies with the favorable left exit region approaching our area of interest over NW Dakota at 19Z onwards. The airmass composite image was helpful in pinpointing the position of the jet max as a sharp moisture gradient evolved (roughly extending from Oregon to Wyoming). Initiation over far NW Dakota also awaited the approach of the “ozone-rich” airmass (purple) as it overtook the eastward progressing dryline between 19-22Z, fostered by reports of surface dewpoints in the mid 50s beneath rapidly drying mid/upper levels.

The first image captured at 1900Z:

and the second one at 2200 Z with initiation already underway/building SE-wards:

Differences noted in the Simulated/Real-Time IR

Forecaster comments from EWP blog...

CIRA/CIMMS NSSL-WRF Simulated IR Satellite suggested convection would develop across central portions of ND and further south towards the border of SD.

Actual Real-time IR is below.  Placement of the cells is off somewhat.  Biggest discrepancy is across central portions of ND, where convection still hasn’t initiated.

UW-CTC Hits in Florida Panhandle

UW-CTC captured strong storm development in the Florida panhandle that later produced hail up to an 1 3/4".  The original storm development exhibited strong cooling rates in the neighborhood of -24K/15 min at 1855 UTC (See below).

The first severe hail was reported at 2000 UTC, giving the CTC a leadtime of one hour and five minutes.  The following SPC image shows the collection of hail reports in the panhandle.

Secondary storm development at 1955 UTC, immediately following behind the first storm, was also captured by the UW-CTC product.  Cooling rates near -27K/15 min were observed with this growth (See below).

The first severe hail report from this storm was made at 2110 UTC with a size of 1 3/4", meaning CTC had a leadtime over the severe hail by one hour and 15 minutes.

CI success over Walker County, TX

Forecaster comments from EWP blog...

The UAH-CI algorithm produced a strong CI signal (94) across southern Walker County in southeast Texas at 2215z. Over the next several images the Cu over this area continued to build and radar returns increased on the KHGX radar.

BIS: Another UAH CI Victory

Forecaster comments from EWP blog...

A severe thunderstorm developed over northeast MT and straddled the Canada/ND border.  The cirrus had finally cleared south/southeast of the storm, so we were waiting for one or both of the GOES CI products to kick in.  Sure enough by 22z, the UAH-CI product indicated about 50% strength of signal along developing cumulus to the south of the severe storm.  By 2224z, KMBX radar indicated convection certainly did “zipper down” the cold front/dryline as the UAH-CI product indictated at 22z, giving us a 24 minute lead time for the developing convection.

2202 UTC

2225 UTC

Rapid storm development over far SW Texas

Forecaster comments from EWP blog...

Isolated thunderstorm development was possible over far SW Texas mainly due to intense diabatic heating (with temperature readings in the lower 90s). Roughly 30kt deep layer shear and 1 kJ/kg SBCAPE overlap were supportive for strong to severe pulsating storms. Rapid to explosive development occurred south of Pecos (isolated in nature) with UAH-CI product showing high probabilities for initiation at 1945Z (not shown) with cloud top cooling of -38K/15 min present at 2010Z. Cloud top cooling peaked at -46K/15 min at 2015Z. Would not be surprised to see an isolated large hail report with that storm (up to 60 dBz present).

BIS: UAH CI and UW CTC Victory, 5/22

Forecaster comments from EWP blog...

1745z image indicates developing cumulus over extreme northeast NM.  In the 1830z image, UAH-CI product indicates a cluster of cumulus with a high confidence of convectively initiating.  UW-CTC product also indicates rapid cloud-top cooling with the eastern-most convective element.  Given the deeply mixed airmass with minimal cap, this would lend confidence to convective initiation soon.  Sure enough, by 1915z the 15-minute lightning plot indicates some CG strikes with the eastern-most convective element, with a lead time to convective initiation of over one hour.

1745 UTC

1830 UTC

1910 UTC

Initiation along diffuse outflow boundary (far SW-KS)

Forecaster comments on EWP blog...

We watched a slowly SE-ward progressing outflow boundary with initiation already underway over far W-OK Panhandle. Northward building of deep convection is closely monitored as CI product indicates high potential with cloud top cooling around -11K/15 min present. Deep and well mixed profiles east of that boundary hint at enhanced downburst / isolated large hail potential as storms also enter a favorable air mass with MLCAPE AOA 2000 J/kg. Shear remains too weak but modest veering present, so a few better organized multicells are possible. Capture was done at 2032Z.

First signals seen in reflectivity fields in the area of interest about 20 min later (2052 Z), which gave a good lead time.

Simulated Satellite for Evaluation of CI Timing

The Tuesday 5/22 EWP focus will be over the northern Plains in the Bismarck (BIS) and Grand Forks (FGF) forecast regions.  As of 20 Z storms had yet to form in the region, so the forecasters were looking at the simulated NSSL WRF imagery to get an idea of the timing of convective initiation.  The 4-panel image below shows the simulated IR and WV bands (top) along with the corresponding GOES-13 IR and WV bands (bottom), valid at 20 Z. Cirrus is abundant in the region in both the simulated imagery and from GOES, complicating the forecast.  But a qualitative comparison reveals that the model appears to have the cirrus in roughly the correct locations, and the shortwave trough and associated cold front in Montana seem to be placed properly at 20 Z.  (This is even more evident when viewing the imagery in a loop in AWIPS-II.)  This provides the forecasters with confidence in the subsequent NSSL WRF forecast imagery.

Below shows the simulated imagery valid 2 hours later, at 22 Z.  It shows that the first storm has formed over west-central North Dakota.  We will evaluate whether or not the model CI forecast was accurate a little later today.