Dual Jet Captured in Upper Level Simulated ABI Water Vapor Imagery

A forecast of SSEC-CIMSS Simulated ABI Band 08 Water Vapor imagery valid at 12z Wed (above) showed two strongly sheared areas, indicative of two upper level jets moving across the upper Midwest. The southern strong water vapor gradient over southern Minnesota is properly positioned when compared to the 12Z TUE GFS 300-200mb wind speed forecast valid at 12Z Wed (below). There is another strong water vapor gradient apparent at the base of the upper level trough, which is also well-placed when comparing it to model data. The simulated water vapor imagery serves as a proxy for identifying and tracking the evolution of upper level jets without having to rely solely on model data.

Submitted by Marcia Cronce (NWS) and Dan Hartung (CIMSS).

Marine Fog Near California

Marine fog was clearly apparent along the California coastline with the GOES-W 11-3.9 micron satellite channel difference imagery (above) on the morning of Tuesday, August 16, 2011. In fact, we could see fog or low clouds that spread inland near Los Angeles and became trapped against the San Gabriel Mountains.

The SSEC CIMSS GOES-W MVFR Probability product (above) showed 70-75% probability of MVFR ceilings occurring in this region, with higher probabilities further north, off the coast of San Francisco . The SSEC CIMSS GOES-W IFR Probability product (below) showed 40 to 50% probability of IFR ceilings near Los Angeles, with up to 75% near San Francisco. These products both captured the fog that was trapped up against the San Gabriel mountains very well.

The surface observations (overlaid on the satellite products) showed dense fog (1/4 statute mile visibility and vertical visibility of 100 feet) at Catalina Airport on the island, and fog (2 1/2 statute mile visibility and vertical visibility of 500 feet) at Los Angeles Airport (KLAX). Other observations just inland of LAX had MVFR visibility and 500 to 1000 foot ceilings. San Francisco had 200 foot ceilings, lower than those at LAX.

The MVFR and IFR Probability products captured the marine fog very well, spatially. Quantitatively, it tended to be underestimated near the Los Angeles area. Due to the lack of observations offshore, it was difficult to discern between low stratus and fog that we could see in the satellite imagery. Therefore, we could not fully evaluate how well the MVFR vs IFR Probability products captured the event, but we could still infer their validity.

From a short-term forecasting standpoint, we already know we have low ceilings, but it would be very useful to know how deep the fog or low cloud area actually is so that we can determine how long it will be before it can burn off/mix out. We can use NWS soundings, data from aircraft, or other data that may be available at various points that are typically far apart. However, the SSEC CIMSS group has this Fog Depth product that can show from a satellite point of view how thick the fog/low stratus is (see image below). In this image, the fog depth was about 1115 to 1175 feet thick near Los Angeles.

This NWS sounding from KNKX San Diego (above) shows the top of the marine layer was at about 1500 feet AGL, very similar to what the Fog Depth product showed.

I know I will use this product when dealing with fog in the Great Lakes Region when I'm on the short-term forecast desk.

Submitted by Marcia Cronce (NWS) and Dan Hartung (SSEC CIMSS)

Notes From 8/9/11 Session

The above image is a visible satellite image from GOES at 2031UTC on 8/9/11. It shows a line of thunderstorms from southern Lake Huron to southeast lower Michigan into far northwest Ohio and far northeast Indiana. This convection was observed along a cold front advancing east through the area. Now, compare the above image to the image below:

The above image is the Theta-E Nearcast product at 2030UTC on 8/9/11. The green areas indicated unstable conditions (low level theta-E minus mid-level theta-E), and the blue areas indicated stable conditions. Note how this product clearly shows the unstable conditions along and ahead of the cold front, and this area corresponds to the convection shown in the 2031UTC visible satellite image. This also showed the stable airmass behind the cold front. Given that this product can be viewed several hours into the future, this product could have given a forecaster more confidence to diagnose the best areas for convection to initiate and grow.

The above image is the visible satellite image from GOES at 1445UTC on 8/9/11. Note the large area of VFR to MVFR ceilings over nothern and central Minnesota into far northwest Wisconsin. Also of note is a smaller area of MVFR to IFR ceilings over southern Wisconsin. Now, compare the visible image above to the image below:

This image is the MODIS Probability of MVFR Ceilings product, at 1445UTC on 8/9/11. Two things of note here are 1) the high probabilities of MVFR ceilings across northern Minnesota into far northwest Wisconsin, and 2) the strip of low probabilities of MVFR ceilings across southern Wisconsin. This product had a very good depiction of the MVFR ceilings over central/northern Minnesota into far northwest Wisconsin. Some VFR ceilings were also mixed in with the MVFR ceilings.

Another interesting note was this product showed low probabilities of MVFR ceilings over southern Wisconsin, where MVFR to IFR ceilings were observed. These low probabilities could have helped give an aviation forecaster some confidence that low ceilings were possible across TAF sites in this area. These clouds formed quickly after sunrise, as a cold front was moving southeast through the area.

J. J. Wood

National Weather Service

Milwaukee/Sullivan, Wisconsin

8/9/11

Waiting for cirrus to dissipate

Considerable overnight and ongoing convection over the upper midwest on August 2nd has left a large cirrus shield over Wisconsin. The UW Convective Initiation (UWCI) product does not detect convective development in regions where significant ice clouds already exist. The 'ice mask' -- where UWCI cannot be computed, can be displayed in AWIPS, and it shows the extent of the ice cloudiness over Wisconsin. A small gap has developed over the extreme southwest part of the state. If this region expands with time, then UWCI might be able to detect incipient convection over the upper midwest later this afternoon.






A MODIS Cirrus Channel image (1.38 micrometers) from 1710 UTC on 2 August shows that cirrus persists over the upper midwest.














Submitted by Scott Lindstrom (UW CIMSS) and Denny VanCleve (NWS-MKX)

Using NearCast vertical theta-e differences on a Warm Humid morning

Note the outflow boundary that is moving southward (in the 1512 UTC radar composite to the left) into the MKX WFO, arcing from northern Sauk County (south of the Dells) through central Columbia County. (The convection that has spawned this outflow is in the northern strip of counties of the WFO to the west of Fond du Lac) What are the chances that convection will fire along this outflow boundary? Are there products that could help you decide if the convection will continue, or will redevelop as the outflow boundary moves south?






The NearCast forecast of Theta-e differences valid at 1530 UTC shows a region of stronger stability over the MKX WFO -- suggesting that any convection that moves into southeast Wisconsin will struggle to develop. Convection might pop -- and it did over northeast Dane County at 1627 UTC (see below) -- but that convection was short-lived.










NearCast output suggests the convection over Dane County will not persist. The highest tops were to 20-25000 feet, and no lightning occurred. (Radar image at left from 1627 UTC)
















Posted by: Scott Lindstrom (CIMSS) and Denny VanCleve (MKX)

Fog/Stratus over Lake Michigan

Above is the 11-3.9 Low Cloud/Fog product from1101Z that shows an extensive area of stratus and fog over portions of Lower Michigan and Southern Lake Michigan.

The GOES R IFR probability from 1115Z shows over 80% probability of IFR ceilings over much of Lower Michigan and parts of Southern Lake Michigan. While surface obs can tell a forecaster the IFR ceilings over land, the GOES R product adds confidence that IFR conditions with stratus and fog were occurring over lake Michigan.

Below the Visible image from 1515Z confirmed the existence of fog and stratus over Southern Lake Michigan. The GOES R IFR probability showed values of IFR ceilings over 40% over much of the Fog/stratus layer over Lake Michigan. There is uncertainty on whether this is fog or stratus, but web cam images showed mainly fog. The GOES R IFR probabilities are lower over Southern Lake Michigan during the daytime.

Steve Hentz
WFO MKX

Using NRCAST Vertical Theta-e Diff

A 5 hour NRCAST vertical theta-e difference is shown to the left. The gradients between unstable values (greens, yellows, and reds) and stable values (blues) are marked by the white lines. The stronger gradient is along the solid line as a weak cold front pushed southward through the area. A weaker gradient extends to the south.

Observed radar is shown to the left along with the 5-hour theta-e gradient forecast. Note that the stronger storms formed generally along the gradient, rather then in the middle of the unstable area. Additionally, showers were generally confined to the unstable areas. If a general convective initiation time is known, this gradient forecast could be useful in locating the areas where storms will fire. With virtually no precip in the stable areas, this product would also be useful in short term precip probability forecasts.

Denny VanCleve NWS/MKX

Robert Aune NOAA/ASPB, Jordan Gerth UW/CIMSS

NSSL 4km WRF Simulated Satellite imagery

Advanced Baseline Imager bands 8 through 16 are available for the NSSL 4km WRF output.

In this example a 16 hour forecast of band 9 (6.95 um, top image) is compared with the current WV imagery (bottom image) depicting an upper low over the Northern Great Lakes. Band 9 correctly depicts the location and orientation of the upper low and the associated dry slot and cloud regions. Farther to the south over AR, TN, and MS, band 9 is slow in the evolution of a MCS. The various bands of the WRF would be beneficial to forecasters to assess the model evolution of the environment and aid the forecaster in the progression as well.

Mark Gehring NWS/MKX

Justin Sieglaff UW/CIMSS

Fog/Stratus California Coast

The GOES-W MVFR Fog Probability 4km does a fairly nice job assigning high MVFR probabilities to stratus and fog off the coast of CA but also depicts the clearer area over Channel Islands National Park. It does assign only low probabilities to the MVFR-IFR conditions along the coastline however. Could this possibly be due to a thinner depth to the stratus field, assuming it is actually thinner? Farther to the west beyond the various islands the Fog Probability shows an area of "no data" due to clear areas that are present and sct-bkn cloud cover versus the bkn-ovc cloud cover to the east.

Mark Gehring NWS/MKX
Justin Sieglaff UW/CIMSS

CIMSS-MKX Local Area Testbed Beginning Soon

This summer the Hazardous Weather Testbed concept will be expanded to the National Weather Service forecast office in Sullivan, Wisconsin (MKX). Cooperating with the Cooperative Institute for Meteorological Satellite Studies (CIMSS) and Advanced Satellite Products Branch (ASPB), this Local Area Testbed will focus on evaluating GOES-R Algorithm Working Group (AWG) cloud type and mask products, fog probabilities, and simulated ABI longwave bands weekly.

Stay tuned to this blog for exciting posts on how NWS forecasters envision these new products will be used in future forecast operations to improve our assessment of the atmosphere.

J. Gerth