Wednesday, May 23, 2012
Simulated Split Window Difference
On Wednesday 5/23, the NSSL-WRF simulated 10.35-12.3 micrometer product showed a local maximum across central Kansas at 21 UTC (see below; the maximum is oriented southwest to northeast and has values approaching +8 K). This maximum is due to water vapor pooling along the surface cold front in the area, and it preceded convective cloud development along that line. When real GOES-R data is available, this product will be very useful for forecasters who are interested in the regions where convective clouds, and eventually storms, are likely to form.
Fire in Catron county, New Mexico
Forecaster comments from EWP blog...
Between 2130 and 2145 Z another burst of the extensive smoke plume occurred, which was also captured by the CIMMS Cld Top Cooling product with values mainly below -5K/15 min.
Between 2130 and 2145 Z another burst of the extensive smoke plume occurred, which was also captured by the CIMMS Cld Top Cooling product with values mainly below -5K/15 min.
DDC: Initiation in C-Kansas imminent?
Forecasters comments from EWP blog...
Latest VIS imagery indicates a rapid increase in convection along slowly SE-ward progressing cold front, namely over Hodgeman, Ness and Rush counties. UAH-CI product already showed modest probabilities (50-60 %) for CI with no reflectivity yet present in local radar data.
Latest HRRR is a bit more optimistic with SW-ward zipping convection compared to OUN WRF. Still unsure if storms can initiate in that area with warm mid-level tongue partly covering the cold front/dry line. Strong shear now gradually moving in from the west, so increasing storm organization is likely in case of initiation.
Latest VIS imagery indicates a rapid increase in convection along slowly SE-ward progressing cold front, namely over Hodgeman, Ness and Rush counties. UAH-CI product already showed modest probabilities (50-60 %) for CI with no reflectivity yet present in local radar data.
UAH-CI product placed in the upper left corner at 2130 Z
Latest HRRR is a bit more optimistic with SW-ward zipping convection compared to OUN WRF. Still unsure if storms can initiate in that area with warm mid-level tongue partly covering the cold front/dry line. Strong shear now gradually moving in from the west, so increasing storm organization is likely in case of initiation.
WFO ILM-Another Cloud Top Cooling Success!
Forecaster comments from EWP blog...
Here in WFO ILM, we have had some great success with the CIMSS Cloud Top Cooling (CTC) product this afternoon (see our previous post). Here is another success story from Horry County, SC. First we will look at the Cloud Top Cooling product at 1845Z (Top Right panel):
Here in WFO ILM, we have had some great success with the CIMSS Cloud Top Cooling (CTC) product this afternoon (see our previous post). Here is another success story from Horry County, SC. First we will look at the Cloud Top Cooling product at 1845Z (Top Right panel):
1845Z Cloud Top Cooling (CTC) image from WFO ILM (Top Right Panel).
There are two “bull’s eye’s” over SC. Our storm is the northern “bull’s eye”. The CTC showed cooling rates of -21C/15minutes AT 1845Z, which typically correlates to strong convection with significant lead times averaging 45 minutes before Maximum Expected Size of Hail (MESH) exceeds 1″. Now let’s look at some verification. First is the MESH image from 1936Z (lower left panel). This is the first time the MESH exceeded 1″ for a lead time of 51 minutes!
1936Z MESH product for WFO ILM (Lower Left panel).
And now for a conventional radar image from 1947Z from the KLTX Radar:
1947Z KTLX Radar image.
The cursor readout shows this storm has 60dbz echos up over 28,000ft…which is above even the -30C level from the 12Z CHS sounding (~25,000ft). We finally got verification of quarter size hail in NW Horry County by around 20Z, though the reports seem to have not come from directly beneath the core of the storm so some larger hail was possibly produced. Now let’s examine some NSSL 3DVAR Imagery:
KTLX Base Reflectivity (top left), NSSL 3DVAR Max Divergence (Top
Right), NSSL 3DVAR Max Updraft Composite (Lower Left) and NSSL 3DVAR Max
Vorticity (Lower Right) at 2005Z.
You can easily identify this storm based on the Max Divergence above 8km, Updraft Composite, and Max Vorticity Images as all show local, significant maxima. Today, the CTC product has shown significant value in lead time for severe hail beneath the Southeastern CONUS upper low.
ILM: CTC Lends to Good MESH Lead Time?
Forecaster comments from EWP blog...
In the 1815 UTC vis satellite image (upper right of top 3-panel), cloud-top cooling was on the order of -17C/15min with a developing thunderstorm. By 1858 UTC, MRMS MESH product reached 1″ hail size (middle image), and just over 2″ hail size by 1906 UTC. The UW-CTC product lead to 45-50 minute lead time for 1-2″ hail (as estimated by MRMS MESH). This is one of many instances we’ve noticed the CTC give decent lead time for 1″ or larger hail.
In the 1815 UTC vis satellite image (upper right of top 3-panel), cloud-top cooling was on the order of -17C/15min with a developing thunderstorm. By 1858 UTC, MRMS MESH product reached 1″ hail size (middle image), and just over 2″ hail size by 1906 UTC. The UW-CTC product lead to 45-50 minute lead time for 1-2″ hail (as estimated by MRMS MESH). This is one of many instances we’ve noticed the CTC give decent lead time for 1″ or larger hail.
1815 UTC. Rapid convective development as indicated by -17C/15min cloud-top-cooling rates.
1858 UTC. MRMS (multi-radar, multi-sensor) MESH (max estimated hail
size) is estimating 1.02" hail, about 45 minutes after rapid CTC.
1906 UTC. MRMS MESH now estimating 2.13" hail, about 50 minutes after initial rapid CTC.
Awaiting initiation over NE Colorado
Forecaster comments from EWP blog...
Conditions gradually improve for thunderstorm development over NE Colorado although initiation may be delayed until the 23-00 Z time frame. Surface boundary pushed through as lee depression slowly consolidated over W-Kansas. 12Z Denver soundings showed steep lapse rates with a deepening and well mixed boundary layer. Numerous weak caps present (roughly at 700, 600 and 500 hPa). CIMSS Cld top cooling product revealed numerous spots with moderately cooling tops in the order of -10 to -15 K/15 min with UAHCI CI product showing low to non existent probabilities. This may be the reason for growing updrafts before reaching one of those aforementioned caps, which suppressed further development. For the forecaster however this is already helpful to pinpoint the area, where enhanced cumulus growth occurs and where initiation may be the most likely.
Question now arises if moisture recovered since 12 Z. Surface dewpoints struggle to exceed mid to upper 30s with lower 40s now entering far NE Colorado as winds backs more to NE-erly directions in response to the consolidating lee cyclogenesis. However, products like the 780mb equiv pot temp and the theta-e diff show robust signals for available potential instability over far NE Colorado with an increasing trend during the following hours. In fact, latest HRRR forecast and the tongue of pot. instability seem to overlap nicely. Hence initiation seems possible around and south of a line Steamboat Springs-Denver-Deer Trail during aforementioned time frame. Incoming mid-level speed max pushes DLS aoa 80 kt, which is more than adequate for well organized storms.
Conditions gradually improve for thunderstorm development over NE Colorado although initiation may be delayed until the 23-00 Z time frame. Surface boundary pushed through as lee depression slowly consolidated over W-Kansas. 12Z Denver soundings showed steep lapse rates with a deepening and well mixed boundary layer. Numerous weak caps present (roughly at 700, 600 and 500 hPa). CIMSS Cld top cooling product revealed numerous spots with moderately cooling tops in the order of -10 to -15 K/15 min with UAHCI CI product showing low to non existent probabilities. This may be the reason for growing updrafts before reaching one of those aforementioned caps, which suppressed further development. For the forecaster however this is already helpful to pinpoint the area, where enhanced cumulus growth occurs and where initiation may be the most likely.
Question now arises if moisture recovered since 12 Z. Surface dewpoints struggle to exceed mid to upper 30s with lower 40s now entering far NE Colorado as winds backs more to NE-erly directions in response to the consolidating lee cyclogenesis. However, products like the 780mb equiv pot temp and the theta-e diff show robust signals for available potential instability over far NE Colorado with an increasing trend during the following hours. In fact, latest HRRR forecast and the tongue of pot. instability seem to overlap nicely. Hence initiation seems possible around and south of a line Steamboat Springs-Denver-Deer Trail during aforementioned time frame. Incoming mid-level speed max pushes DLS aoa 80 kt, which is more than adequate for well organized storms.
CTC provides >1 hr lead time on severe hail report
Forecaster comments from EWP blog...
The CIMSS cloud top cooling algorithm first detected cooling rates of approximately -10 C/15 min with a thunderstorm developing across eastern Hoke and western Cumberland counties on the 1815z image. The algorithm continued to show strong cooling rates on the next two images with accumulated CTC values of approximately -30 to -35 C/15 min before the cell was dropped from the display after 1845z. A report of quarter sized hail was received in far southwestern Harnett county with this thunderstorm at 1937z, almost an hour and a half after the algorithm first detected stronger cooling with this storm.
The CIMSS cloud top cooling algorithm first detected cooling rates of approximately -10 C/15 min with a thunderstorm developing across eastern Hoke and western Cumberland counties on the 1815z image. The algorithm continued to show strong cooling rates on the next two images with accumulated CTC values of approximately -30 to -35 C/15 min before the cell was dropped from the display after 1845z. A report of quarter sized hail was received in far southwestern Harnett county with this thunderstorm at 1937z, almost an hour and a half after the algorithm first detected stronger cooling with this storm.
Accumulated CTC values for a cell that produced severe hail.
CTC success in Raleigh, NC WFO CWA
The UW-CTC product is showing good success with convective development in the Raleigh, NC with the storms being flagged exhibiting severe MESH values, and producing supportive hail reports. At 1715 UTC, the CTC product showed near strong cooling rates of approximately -16.5K/15 min for the initial development of storms along a boundary in eastern NC (see Fig. 1).
This particular storm had a severe MESH of 1.25" by 1832 UTC (see Fig. 2) [lead time of 1 hour and 17 mintues], and subsequently 1.5" by 1845 UTC (see Fig. 3) [lead time of 1 hour and 30 minutes].
The CTC product also picked up the storm following directly to the west of the above first storm, with a cooling rate of ~-18.5K/15 min at 1832 UTC (see Fig. 4).
This storm would also later product a large MESH (not shown). Additionally, further south and west in the other domain of interest today (Wilmington, SC), another storm started to grow first exhibiting an large intermediate cooling value of ~14K/15 min at 1732 UTC (Fig. 5), and attained a severe MESH value of ~1" at 1832 UTC, meaning a lead time of one hour (Fig. 6).
Fig. 1
This particular storm had a severe MESH of 1.25" by 1832 UTC (see Fig. 2) [lead time of 1 hour and 17 mintues], and subsequently 1.5" by 1845 UTC (see Fig. 3) [lead time of 1 hour and 30 minutes].
Fig. 2
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| Fig. 3 |
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| Fig. 4 |
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| Fig. 5 |
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| Fig. 6 |
UAHCI Strength of Signal trends
The weak upper level low over the Southeast United States has proven to produce instances of convective initiation that the UAHCI algorithm has captured. Depending on the individual cell, cells rapidly grew which only provided one forecast of CI before initiation. However, for the slower growing storms, multiple forecasts for an object can be produced. In this example, a storm began to grow in Scotland County, NC at 1702 UTC wtih a CI strength of signal forecast of 41.
At 1715 UTC, the UAH CI Strength of Signal grew to 52 as a line of cumulus continued to develop.
At 1732 UTC, the UAH CI Strength of Signal rose to 61 within the cumulus line.
At 1745 UTC, the UAH CI Strength of Signal produced a forecast of 75.
The UAHCI forecast did not produce a forecast at 1802 UTC as the line matured into cumulonimbus. But this is an example of following a slow growing storm can lead to increased confidence in convective initiation.
At 1732 UTC, the UAH CI Strength of Signal rose to 61 within the cumulus line.
At 1745 UTC, the UAH CI Strength of Signal produced a forecast of 75.
The UAHCI forecast did not produce a forecast at 1802 UTC as the line matured into cumulonimbus. But this is an example of following a slow growing storm can lead to increased confidence in convective initiation.
CI algorithm successes over North Carolina
Forecaster comments from the EWP...
The UAH-CI algorithm displayed two areas with high strength of signal values (64 and 92) across southern Cumberland and western Sampson counties on the 1702z image. These cells intensified quickly into two thunderstorms and a report of penny sized hail was received from the eastern storm at 1823z, more than an hour after the algorithm first detected these thunderstorms.
The CIMSS-CTC algorithm showed cloud top cooling rates of between -10 to
-15 C/15min on several images with a thunderstorm developing across
Sampson county in North Carolina. The CTC first appeared on the 1715z
image and continued to highlight this cell through the 1815z image. As
the algorithm continued to show moderate cooling rates with the cell the
radar presentation became more impressive and a three body scatter
spike developed with the cell. A report of penny sized hail was received
with this cell 1823z 5 miles WSW of Newton Grove, NC.
The UAH-CI algorithm displayed two areas with high strength of signal values (64 and 92) across southern Cumberland and western Sampson counties on the 1702z image. These cells intensified quickly into two thunderstorms and a report of penny sized hail was received from the eastern storm at 1823z, more than an hour after the algorithm first detected these thunderstorms.
The CIMSS-CTC algorithm showed cloud top cooling rates of between -10 to
-15 C/15min on several images with a thunderstorm developing across
Sampson county in North Carolina. The CTC first appeared on the 1715z
image and continued to highlight this cell through the 1815z image. As
the algorithm continued to show moderate cooling rates with the cell the
radar presentation became more impressive and a three body scatter
spike developed with the cell. A report of penny sized hail was received
with this cell 1823z 5 miles WSW of Newton Grove, NC.
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