EWP2013 1930 UTC Mesoscale Discussion

Broad upper ridging resides over the Southern Plains, with cyclonic flow on both the east and west coasts. In the wake of large upper low currently positions over the Mid-Atlantic, robust moisture has struggled to return, yielding less than stellar severe parameters. Still, the presence of low to mid 50s dewpoints combined with favorable wind fields will yield a chance of a few severe storms, mainly in the form of high based multicell and supercell structures.

A subtle surface trough/boundary extended from the higher terrain of eastern Colorado eastward into western Kansas with a pronounced dryline over far western KS extending down into much of western and central TX. In the presence of appreciable daytime heating, these boundaries are expected to serve as a focus for convective development from now through around 22-23z. Greater storm coverage is expected further north, within area of backed surface flow near subtle trough/dryline intersection. This will correspond to the CWAs of DDC and GLD. Further south, increasing mid level heights will tend to limit convection, though isolated to widely scattered thunderstorms may develop by around 23z to 00z. Large hail, some very large, and damaging winds will be the primary hazards, with significant wind gusts possible due to inverted-V type soundings within meager low level moisture and deeply mixed atmosphere. Tornadoes do not appear to be much of a concern, but if one were to occur, it would be most likely nearer the backed winds over northern/western KS in GLDs forecast area, though lacking wind shear, both in the low levels and aloft, may tend to mitigate this potential.

Mesoscale models (WRF-ARW and WRF-NMM) are in good agreement in developing isolated to scattered supercells across much of western KS as can be seen below. Lesser activity can be noted in the TX panhandles and points southward.

Likewise, CIRA NSSL WRF simulated IR satellite (upper left panel below) depicts thunderstorm development by around 21z over much of DDC/GLD/AMA CWAs. One difference it he more widespread nature of thunderstorms further south, which the above high res runs do not support. The OUNWRF simulated reflectivity (lower left panel) also supports this more active solution. Attm, it appears to be over convecting somewhat, especially considering lack of strongly backed sfc flow and increasing heights aloft.

In the next few hours, storms are expected to develop first over west KS, then, in a more isolated nature, over parts of the TX panhandle and southwest TX. The CI product below has already shown areas of moderate to high CI potential within a line of agitated cumulus along the dryline and sfc trough, with a strong CI and instantaneous CTC signal over eastern CO.

Initial thoughts are to set up shop in GLD and adjacent DDC this afternoon, with potential to migrate southward if more discrete activity develops along southern parts of the dryline. This meshes well with the EFP Severe Probabilities outlook shown below.

We will keep a close on LUB late this afternoon and evening, especially in the case that we can sample some of the PGLM capabilities within the LMA there.

Austin/Frank

Using GOES-R CI to Evaluate Developing Cumulus

A line of cumulus clouds developed across western Kansas near/after 18Z. EFP/SPC forecasts indicate this as a favorable area for storm development in the next few hours. For now, the GOES-R CI product is indicating generally low probabilities of convective initiation along this line of towering cumulus (20-60 percent).

One area with a probability of 80 percent developed, at around the same time that a small/weak cell (Z < 35 dbZ) developed in Wichita County. This indicator decreased below 70 percent in the next few products, as the cell generally failed to develop into anything stronger.

So far, the CI product appears to be correctly indicating that large-scale convective development is not imminent quite yet. Also, the CTC product has not shown any indication of rapid cooling, which also matches the current situation.

–Hatzos

EWP daily debriefing 5/7

This afternoon we had our first EWP daily debrief from the previous day's activities. Yesterday the focus was on the mid-Atlantic coast, specifically the Blacksburg, VA CWA, and while forecasters did issue a handful of warnings, it was an overall quiet day. However, the more docile weather allowed them a chance to work through each set of new data, learning which products they have at their disposal and how to use them. Here are a few comments picked up throughout the day:

Simulated Imagery
- 'We used the simulated imagery to forecast the dissipation of storms in the evening.' This along with the Nearcasting indicated the dissipation of storms in the area of interest.
- 'The WRF simulated imagery seems to be more spotty; it doesn't often seem to forecast the broader cloud shields associated with storm systems.'

Nearcasting Model
- 'The theta-e difference showed stable air moving into the area' and along with the simulated imagery, was used in the forecasting of the dissipation of the storms.
- 'I liked the two and three hour forecasting'

GOES-R CI and Cloud Top Cooling
- Because of the more docile weather 'there were no 80/90% CI values so it made the product more difficult to use'

RGB Airmass
- 'It takes some time to intuitively understand exactly what you're looking at with this product and how it can be integrated into your forecasting techniques, but it has potential'

Training
- Forecasters completed a training shift previous to their arrival in Norman. Monday was then used as a low key forecasting day, giving them a chance to get familiar with the products in an operational setting
- 'Having a chance to interact and use the products on a less busy day was very helpful'

Stay tuned to the blog for further feedback and updates on daily activity!

Slow day, but good ending for UWCTC

The first day of the HWT was slow weather-wise for the UWCTC product.  Most of the convection in the area of focus was not producing any captured CTC signal due to the primarily thicker layers of cirrus over the top of the ongoing convection.  However, toward the end of the shift when focus was shifted elsewhere, some promising CTC signal showed itself.  At 2302 UTC, two moderate cooling rates were detected over north central North Carolina (See Figure 1).

Figure 1.  UWCTC overlaid on visible satellite imagery at 2303 UTC, with a max UWCTC value of ~-8K/15 min.

Cooling rate detection was ongoing for these two areas through 2325 UTC (See Figure 2). 

Figure 2. UWCTC overlaid on visible satellite imagery at 2325 UTC, with a max UWCTC value of ~-13K/15 min.

 As seen on the Hi-Res VIL product on radar (Figure 3), the left detection of CTC went on to produce VILs in excess of 40-45 kg/m-2.

Figure 3 - High Resolution VIL valid at 0035 UTC.

The first hail report for this particular storm was received at 0040 UTC, lending a one hour and thirty-eight minute lead time ahead of the observed hail.  See Figure 4 below for the LSR text.

Figure 4.  LSR of estimated 1" hail received at 0040 UTC.

EWP: 00Z outlook and the Nearcasting model

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.

Current radar imagery overlaid with surface analysis

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.

Nearcasting showing decreasing instability this evening

Simulated Imagery at 03Z as storms come to an end

Hampshire/Guseman

EWP underway

This afternoon the EWP has been focused on the ongoing convective activity over the Eastern U.S., specifically in the Blacksburg, VA CWA. Forecasters have been utilizing the convective initiation and cloud top cooling products to identify areas of developing convection within the broader system, a challenge given that conditions aren't very conducive for robust cell development.

EWP: Simulated Imagery capturing convective activity

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.

Current radar imagery overlaid with surface dewpoint

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. This activity is noted in the 22Z simulated satellite imagery as shown below.

22Z WRF simulated IR imagery

Hampshire/Guseman

Week 1: 2013 Spring Experiment

The 2013 Spring Experiment has begun! This year's experiment will run three weeks, ending on May 24th, and though shorter than previous years, we still look forward to a productive demonstration. Participants include 24 NWS forecasters and a variety of visiting scientists, and as with previous years, the experiment contains both Experimental Forecast Program (EFP) and Experimental Warning Program (EWP) activities with a focus on the forecast and warning of convective initiation and severe weather.

The GOES-R portion of this demonstration will for the most part occur within the EWP. Products will include synthetic satellite imagery from the WRF-ARW, 0-6 hour GOES sounder-based 'Nearcasts', sounder-based RGB Airmass, Pseudo Geostationary Lightning Mapper total lightning and other applications, convective initiation nowcasting, and cloud top cooling rates.

Activities will be ongoing from roughly 8am to 10pm, with most emphasis on severe weather warning occurring in the later portion of the day. Feedback will once again be forecaster driven, stemming from real-time interaction and exploration of GOES-R products in this pre-operational environment, and will be visible via this blog. Additionally visiting scientists and PIs will also be asked to share their experiences. Finally, each week will end with the the typical Tales from the Testbed webinar, where forecasters will have a chance to share their overall thoughts from each shift in a summary presentation. The focus of this year's webinar topics have been pre-selected with week 1 concentrated on GOES-R, particularly the uses of the PGLM in severe weather forecasting.

Stay tuned to the blog for real-time updates of our activities and forecaster feedback!

~AMT

Day/Night Band Provides Better Detail of Low Clouds

During the overnight hours of 23-24 November, 2012, persistent stratus and flurries lingered over much of Wisconsin in the wake of a strong cold front which had swept through the previous day.  As indicated by the below Green Bay 00z sounding, the stratus was shallow and only several hundred feet thick.  Cloud bases were 2 to 3 thousand feet. 




















The short-term forecast concern was timing of the cloud erosion.  The below CONUS wide view 11-3.9 micron imagery from 08z 24 Nov indicated widespread clouds blanketing most of Wisconsin and the western Great Lakes. 


0758z 24 NOV 2012 11-3.9 micron imagery

   At about the same time, the below NPP VIIRS Day/Night band CONUS view indicated thin spots and breaks in the cloud cover across Wisconsin and the western Great Lakes. 


0758z 24 Nov 2012 Day/Night Band

Taking a closer view of the 11-3.9 micon imagery below, the clouds appear to shroud all of Wisconsin except for the far northwest corner. 



11-3.9 micron imagery - closeup

But a closer view of the Day/Night band showed more breaks in the cloud cover across Wisconsin as well as thin spots.  The clearing over northern Lake Michigan and Door County was much more discernable using the D/N band. 

Also, the illumination (reflectance) from the metropolitan areas highlighted the thinness of the clouds as well as helped make the breaks more discernable. 

Day/Night Band Closeup

By using the Day/Night band, a clearer picture of the cloud cover covering Wisconsin was determined.  This better understanding would allow the short-term forecaster to make a more reliable forecast of clouds and timing of low cloud erosion. 

The moon was in waxing gibbous and was 85.3% lit on 24 Nov 2012.  

Marc Kavinsky
National Weather Service - Milwaukee/Sullivan

Using GOES-R IFR/LIFR Probabilities for TAFs

Tracking areas of stratus and fog can be somewhat difficult using traditional satellite images along with METAR observations...particularly on a day with a variety of low and high level clouds. Sky conditions across the Great Lakes during the afternoon of November 6th is a good example. Below are infrared and visible GOES images along with plotted METAR ceilings and visibilities:

GOES Infrared

GOES Visible

Note how conditions are evident at point locations, but it is difficult to discriminate areal coverage across the region. For the purpose of issuing and updating TAFs, it would be very useful to better visually display areas of lower ceilings and visibilities, increasing situational  awareness and improving the ability to track and forecast improving or deteriorating conditions. Fortunately, GOES-R fog and low clouds products are proving quite useful in filling this need. Below are images of GOES-R IFR probabilitly and LIFR probability:

GOES-R IFR Probability

GOES-R LIFR Probability

The IFR product does a very good job of showing the area of ceilings that are less than 1000 feet, particularly for values above 60 percent. Though LIFR percentages are not very high, the highest percentages do coincide pretty well with some of the lower ceilings and visibilities in the region. Something that was immediately useful was observing a loop of the IFR image, which showed that the eastern edge of the lower ceilings had temporarily stalled across eastern Wisconsin. This might lead to delaying the arrival of IFR ceilings in eastern TAF sites.

Another likely use of the GOES-R fog and low cloud products would be tracking stratus or fog advecting into Wisconsin off of Lake Michigan. Using an example off the California coast, note that GOES infrared and fog images will give you an idea of where there is cloud cover, but will not give and immediate idea of what type of conditions are moving into the area:

GOES Infrared

GOES IR Fog

While the traditional fog product above does give a clue that you're looking at either fog or stratus...the GOES-R IFR and LIFR products confirm this and also give an indication of how low the ceilings and/or visibilites are:

GOES-R IFR Probability

GOES-R LIFR Probability

It is immediately clear the conditions are at or below IFR for much of the area of fog/stratus...with a pretty good probability of LIFR conditions over a large portion of the area. This is quite useful...as ceiling and visibility observations are very limited over bodies of water. Hopefully the use of this product will help in troublesome situations where poor conditions can sneak onshore... particularly when somewhat obstructed by other cloud decks.

In summary, GOES-R fog and low cloud products can be very useful in tracking areas of fog and stratus. In contrast to using a combination of surface observations and traditional visible/infrared products, the GOES-R products can give a very quick and fairly accurate representation of where IFR or worse conditions are located. Being able to track these areas will hopefully lead to improvements in TAFs.

Denny VanCleve
NWS Milwaukee/Sullivan